Advances in Hybrid Photo-Fenton Processes for Treating Pharmaceutical Contaminants in Water and Wastewater Systems

Brillas, Enric; Peralta-Hernández, Juan M.

doi:10.3390/w18080920

Open AccessReview

Advances in Hybrid Photo-Fenton Processes for Treating Pharmaceutical Contaminants in Water and Wastewater Systems

by

Enric Brillas

^1,*

and

Juan M. Peralta-Hernández

^2,*

¹

Department of Material Science and Physical Chemistry, Faculty of Chemistry, University of Barcelona, Martí i Franquès 1-11, CP 08028 Barcelona, Spain

²

Laboratory of Environment and Electrochemistry (LMAE), Department of Chemistry-DCNE, University of Guanajuato, Cerro de la Venada s/n, Pueblito de Rocha 36040, Guanajuato, Mexico

^*

Authors to whom correspondence should be addressed.

Water 2026, 18(8), 920; https://doi.org/10.3390/w18080920

Submission received: 27 February 2026 / Revised: 18 March 2026 / Accepted: 20 March 2026 / Published: 13 April 2026

(This article belongs to the Special Issue Advances and Innovations in Technologies for Treatment and Toxicity Assessment of Conventional and Emerging Contaminant in Industrial Wastewater)

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Abstract

Advanced oxidation processes based on photo-Fenton chemistry have gained increasing attention as effective treatment alternatives for the removal of pharmaceutical contaminants from water and wastewater systems. However, large-scale implementation remains constrained by operational requirements, limited mineralization efficiency, and challenges associated with process stability and selectivity. This review provides a critical assessment of recent advances (2022–2025) in conventional photo-Fenton and hybrid systems, including photocatalysis/photo-Fenton and sono-photo-Fenton processes, with emphasis on their performance in water and wastewater treatment applications. The removal of non-steroidal anti-inflammatory drugs, antibiotics, pharmaceutical mixtures, and real wastewater matrices is analyzed considering catalyst configuration, irradiation sources, oxidant utilization, and operating conditions relevant to practical treatment scenarios. Conventional homogeneous Fe²⁺/H₂O₂ systems enable rapid contaminant degradation but typically require acidic conditions and show limited mineralization efficiency. In contrast, iron-complexed and heterogeneous catalysts allow operation under near-neutral pH and visible-light irradiation, improving applicability in realistic water treatment systems. Hybrid photocatalysis/photo-Fenton processes enhance treatment efficiency through synergistic generation of reactive oxygen species, while ultrasound-assisted systems further intensify oxidation rates and contaminant removal. Special attention is given to oxidation mechanisms, catalyst stability, transformation products, and toxicity evolution to identify the key factors controlling treatment performance. Finally, current technological limitations, operational challenges, and design considerations for process integration, scale-up, and sustainable implementation in water and wastewater treatment are discussed.

Keywords:

photo-Fenton; hybrid advanced oxidation processes; emerging contaminants; wastewater treatment; pharmaceutical removal; process intensification; catalytic oxidation

1. Introduction

Conventional biological and physicochemical treatments in wastewater treatment plants are largely ineffective for the removal of pharmaceutical contaminants due to their chemical stability, low biodegradability, and continuous input into water systems. As a result, these micropollutants persist in treated effluents and natural waters, highlighting the need for oxidation technologies capable of transforming recalcitrant organic molecules rather than simply transferring them between phases.

Advanced oxidation processes based on photo-Fenton chemistry have emerged as promising alternatives because they generate highly reactive species able to degrade complex pharmaceutical structures. However, practical application remains limited by operational constraints such as acidic working conditions, incomplete mineralization, and reduced efficiency in real wastewater matrices. To overcome these limitations, hybrid systems combining photo-Fenton with photocatalysis or ultrasound irradiation have been increasingly investigated to enhance oxidant utilization and reaction pathways. Despite the rapid growth of these studies, the relationship between oxidation mechanisms, catalyst configuration, and treatment performance has not been critically unified. Therefore, a systematic evaluation of recent developments is required to identify the governing factors controlling efficiency and applicability in water and wastewater treatment.

Advanced oxidation processes (AOPs), based on the in situ production of reactive oxygen species (ROS), which are preeminently hydroxyl radical (^●OH), are the most powerful treatments for pharmaceutical remediation. Among them, simple Fenton (a mixture of H₂O₂ and Fe²⁺) and related processes have experienced a large development in recent years due to their high oxidation effectiveness on drug destruction. Photo-Fenton (PF) is a variety of the Fenton process in which light irradiation is used to enhance its oxidation process. Despite the advantages of this method, only a recent review from 2023 [1] has described its application to hospital wastewater remediation, without any mention of the removal of drugs in water and other wastewater. Several specific reviews have reported the destruction of acetaminophen [2], tetracycline [3,4], and diclofenac [5] by different AOPs, including PF. However, there has not been any review that has considered the general behavior of all drugs under PF treatment and their degradation/mineralization performance. Taking this into mind, an exhaustive search of the Web of Science database was made with the keywords: “Pharmaceutical” and “Photo-Fenton”. The retrieved scientific papers were then analyzed from their title and abstracts, only considering those written in English and excluding books, book chapters, and proceedings from conferences. A total of 127 articles related to the recent period 2022–2025 were selected for the present review. In each year from 2022–2024, about 30 scientific articles were published, and a greater number of 47 articles were found in 2025, demonstrating the increasing recent interest in this technology. Based on their methodology, the scientific papers were grouped according to single PF (66 articles, 52.0%), hybrid photocatalysis (PC)/PF (54 articles, 42.5%), and sono-PF (SPF) (seven articles, 5.5%) processes. In each case, single NSDAIs, antibiotics, and other drugs, as well as a mixture of drugs and real wastewater, were distinguished.

This article presents a comprehensive and critical review dealing with the fundamentals of PF, PC/PF, and SPF and their applications to the removal of pharmaceuticals from different aqueous matrices. The degradation and/or mineralization performance of each process, the system used, the role of generated oxidants, the reuse of catalysts or photocatalysts, and the by-products produced are noted. The change in toxicity of treated drug solutions is analyzed. A final section details the challenges and future perspectives of these technologies.

2. Photo-Fenton Treatment of Pharmaceuticals in Water and Wastewater

This section describes the homogeneous PF, homogeneous PF-like, heterogeneous PF, and heterogeneous PF-like methods developed for drug removal in water and wastewater. Each method considers aqueous solutions with NAIDs, antibiotics, and other drugs, a mixture of drugs, and/or real wastewaters for their degradation/mineralization. Table 1 summarizes the main results obtained for these studies, noting the drug tested, the system used, and the experimental conditions checked.

Figure 1 shows the schemes of several PF photoreactors, including stirred-tanks with external UV light [33], with inner UV light [30], and with inner UV light and thermostatic bath [34]. A flow system with external UVC light is presented in Figure 1b [27] and a recirculation system with inner UV-Vis light in Figure 1e [19].

2.1. Homogeneous Photo-Fenton

The conventional homogeneous Fenton consists of the use of the so-called Fenton reagent, a mixture of H₂O₂ and Fe²⁺ catalyst, to produce the strong oxidant ^●OH by homogeneous Fenton reaction (1) in an acid medium with optimum pH close to 3.0 [5]. Its low absolute second rate constant k₂ of 55 M⁻¹ s⁻¹ indicates a slow reaction between both species for ^●OH generation, which possesses a high standard reduction potential (E°(^●OH/H₂O)) of 2.80 V vs. SHE. The attack of ^●OH on drugs gives hydroxylated derivatives that evolve to final short, linear aliphatic carboxylic acids, originating from Fe(III)-carboxylate complexes, which are highly resistant to oxidation by (^●OH) [2]. The homogeneous Fenton-like reaction (2) allows the Fe²⁺ regeneration with formation of hydroperoxyl radical (HO₂^●) that possesses such a low E°(HO₂^●/H₂O) = 1.65 V vs. SHE that it is unable to function for drug oxidation. HO₂^● can also regenerate Fe²⁺ by reaction (3) or is deprotonated to the superoxide radical anion (O₂^●−) by reaction (4). The very small k₂ value of 2 × 10⁻³ M⁻¹ s⁻¹ for reaction (2) in comparison to that of reaction (1) means that the Fenton reagent acts up to the consumption of one component. So, stoichiometric amounts of both components, related to the theoretical overall mineralization of drug pollutants, are added for Fenton treatment:

Fe²⁺ + H₂O₂ + H⁺ → Fe³⁺ + ^●OH + H₂O k₂ = 55 M⁻¹ s⁻¹

(1)

Fe³⁺ + H₂O₂ → Fe²⁺ + HO₂^● + H⁺ k₂ = 2 × 10⁻³ M⁻¹ s⁻¹

(2)

Fe³⁺ + HO₂^● → Fe²⁺ + O₂ + H⁺

(3)

HO₂^● → O₂^●− + H⁺

(4)

Low solubility product constants (K_sp) of 4.8 × 10⁻¹⁷ and 2.79 × 10⁻³⁹ have been determined for Fe(OH)₂ and Fe(OH)₃, respectively [35]. This means that homogeneous Fenton can only operate at pH < 4.0, because at higher pH values, hydroxides of Fe²⁺ and, mainly, Fe³⁺ precipitate, forming undesired iron sludge. The stringent acidic pH window is then the main drawback for the practical implementation of this method, which is very far from the pH values of 6.5–8.5 of WWTP effluents and natural waters. For Fenton reagent application, these matrices need to be acidified to pH ~ 3. At the end of the process, they must be neutralized, requiring the removal of iron sludge, which results in a consequent rise in operating costs [5].

An alternative process to enhance the oxidation power of homogeneous Fenton is homogeneous PF that involves simultaneous light irradiation of the effluent [36]. Different lamps are used depending on the wavelength (λ) applied. They can provide vacuum UV (VUV) (<190 nm), UVC (190–280 nm, λ_max = 254 nm), UVB (280–315 nm), UVA (315–400 nm, λ_max = 360 nm), and visible (Vis) (400–800 nm) lights. In some cases, direct sunlight (λ > 300 nm) is applied, and the process is called solar PF. This process can be mimicked with a Xe lamp, which can also be filtered to obtain Vis or UV irradiation. Under homogeneous conditions, the rate of homogeneous ^●OH production by the Fenton reaction (1) is enhanced by the homogeneous photo-Fenton reaction (5), in which a soluble Fe(III) hydroxide species, such as Fe(OH)²⁺, is photolyzed [5,36]. This reaction also occurs at an optimum pH near 3.0, with Fe²⁺ regeneration to accelerate the homogeneous Fenton reaction (1). When a UVC light is applied, more ^●OH is produced by the homolysis of H₂O₂ by reaction (6). Additionally, the mineralization process is enhanced by reaction (7), in which the final Fe(III)-carboxylate species, denoted as Fe(OOCR)²⁺, is readily photodecomposed by UV light, regenerating Fe²⁺:

Fe(OH)²⁺ + hν → Fe²⁺ + ^●OH

(5)

H₂O₂ + hν → 2^●OH

(6)

Fe(OOCR)²⁺ + hν → Fe²⁺ + CO₂ + R^●

(7)

Homogeneous PF exhibits the same pH drawbacks as homogeneous Fenton, which can be mitigated by alternative treatments with homogeneous PF-like, heterogeneous PF, and heterogeneous PF-like, as described in the next subsections. This subsection analyzes the oxidative behavior of drugs with homogeneous PF.

2.1.1. NSAIDs

NSAIDs are drugs used to reduce inflammation, fever, and pain, Lopez-Timomer et al. [6] described an excellent degradation of 1 mg L⁻¹ acetaminophen in WWTP effluent at pH = 7.2 by homogeneous PF using a stirred-tank photoreactor under 15 W UVC. A fast and total drug removal was achieved in only 8 min operating with 21 mM H₂O₂ and 2.4 μM Fe²⁺ (see Table 1), demonstrating the high oxidation power of this method. For diclofenac [7,37,38,39], worse results have been reported in pure water at pH 6.2, which is far from the optimal pH 3.0 for this process [7], as shown in Table 1.

2.1.2. Antibiotics

Antibiotics are powerful drugs designed to fight bacterial infections. Due to their relevance and the influence of their residues and metabolites on the health of living beings, their removal from water and wastewater has been widely studied by PF and related processes. For homogeneous PF, the treatments of dicloxacillin [40], doxycycline [8], carbamazepine [9], chlortetracycline [41], indomethacin [42], nitazoxanide [10], sulfamethoxazole [11,34], oxytetracycline [12,43], and tylosin [44] have been assessed.

Figure 2a shows a sketch of a pilot flow plant with a solar compound parabolic collector (CPC) photoreactor for homogeneous PF [8]. This system was used for treating 4 L of 0.6 mM doxycycline in pure water with 4 mM H₂O₂ and 0.1 mM Fe²⁺ at pH = 3.0 and liquid flow rate = 30.6 L min⁻¹. A slow 95% decay with a pseudo-first-rate constant for drug removal (k₁) of 0.0142 min⁻¹ in 180 min was found (see Table 1). Good chemical oxygen demand (COD) and total organic carbon (TOC) reductions for the solution of 81% and 73%, respectively, were obtained. The effects of operating variables are depicted in Figure 2b–d. Figure 2b highlights the progressive decrease in the normalized drug concentration by raising Fe²⁺ content from 0.1 to 0.3 mM. This loss of oxidation power can be ascribed to the gradual loss of generated ^●OH by reaction (8) with the excess of Fe²⁺ added. Figure 2c shows that in all cases, a good linear ln (c₀/c)-time plot was obtained, according to pseudo-first-order kinetics, whose slope corresponded to the k₁-value. Figure 2d makes evident that 4 mM H₂O₂ yielded the best degradation rate. The increase in rate from 3 to 4 mM H₂O₂ can be ascribed to an acceleration of the homogeneous Fenton reaction (1) to form more ^●OH, whereas the subsequent decay for 5 mM H₂O₂ can be related to the large enhancement of reaction (9) by inhibition of the produced ^●OH with the excess of H₂O₂ added. Figure 2e illustrates the quicker degradation achieved for 0.6 mM of drug because the system produced sufficient ^●OH content to remove more drug than 0.2 mM. In contrast, greater concentrations, like 1 mM, inhibited its removal because of the too great organic load, which also involves more ^●OH attack over higher amounts of by-products formed. Note that all these effects are verified for all Fenton treatments due to the inherent characteristics of the oxidant ^●OH:

Fe²⁺ + ^●OH → Fe³⁺ + OH⁻

(8)

H₂O₂ + ^●OH → HO₂^● + H₂O

(9)

The relative degradation rate of drugs depends on their chemical structure. This is shown in Figure 3, where the normalized drug concentration increased in the following order: carbamazepine [38] < oxytetracycline [12] < sulfamethoxazole [11]. For carbamazepine, 200 mL of 1 mg L⁻¹ drug in pure water was treated with 0.75 mg L⁻¹ H₂O₂ and 0.15 mg L⁻¹ Fe²⁺ at pH = 3.0 using a stirred-tank photoreactor under 1500 W Xe light to yield 93% decay with k₁ = 0.0422 min⁻¹ and 14% TOC removal in 30 min (see Table 1).

The treatment of oxytetracycline was performed with 250 mL of 0.1 mM drug in pure water with 100 mg L⁻¹ H₂O₂ and 3 mg L⁻¹ Fe²⁺ at pH = 3.0, filling a stirred-tank photoreactor under 18 W UVA light, giving 97% abatement with k₁ = 0.81 min⁻¹ and 68% TOC removal in 10 min. The same conditions were used with a WWTP effluent, achieving 85% decay with k₁ = 0.59 min⁻¹ and 75% TOC reduction over 15 min, due to competitive oxidation with the organic and inorganic components of the real wastewater (see Table 1). The fastest removal with sulfamethoxazole was obtained with 1 L of 50 mg L⁻¹ drug in pure water with 2 mM H₂O₂ and 5 mg L⁻¹ Fe²⁺ at pH = 3.0 using a stirred-tank photoreactor under a 150 W UV-Vis lamp λ = 350–570 nm, and complete removal with k₁ = 1.0379 min⁻¹ was obtained in only 8 min. In all these treatments, UV light was applied as an effective energy source for homogeneous PF. In the case of carbamazepine, LC-MS analysis of treated solutions revealed the formation of five primary by-products, from which the reaction degradation sequence of Figure 3b was proposed. The initial hydroxylation of this drug (1) with loss of an acetamide group led to 2, which was subsequently oxidized and broken down to three benzene carboxylic acids 3–5 and 3-aminophenol (6).

Table 1 shows interesting results for the homogeneous PF behavior of nitazoxanide [10]. It was degraded at 1.5 mg L⁻¹ in pure water and hospital wastewater, with 55 mg L⁻¹ H₂O₂ and 10 mg L⁻¹ Fe²⁺, at pH 2.8 in a stirred-tank photoreactor under sunlight. Total abatement was achieved in 40 min for pure water, with 15 by-products detected by LC-QTOF-MS, and extended to 105 min for hospital wastewater via parallel oxidation of its contaminants.

2.1.3. Other Drugs

Homogeneous PF treatment with diuretic hydrochlorothiazide [45] and HMG-CoA reductase inhibitor (statin) rosuvastatin [13] has been reported. Sharif et al. [13] centered the rosuvastatin study in a stirred-tank photoreactor under 35 W of UVC irradiation, using 20 mg L⁻¹ drug in pure water, with 0.3 mM H₂O₂ and 0.1 mg L⁻¹ Fe²⁺, at pH 3.0. A fast, complete degradation with k₁ = 0.1764 min⁻¹ was observed in 15 min, whereas 79% TOC removal was attained in 120 min (see Table 1). Interestingly, they determined a total cost of 13.0678 US$ m⁻³ for this process.

2.1.4. Mixture of Drugs

The degradation of effluents containing several drug mixtures by homogeneous PF has been investigated to clarify the interference between them [14,15,16,17,46,47,48]. A mixture containing 15 mg L⁻¹ of the antiretroviral lamivudine and zidovudine in 50 mL of pure water was treated in a stirred-tank photoreactor with 600 mg L⁻¹ H₂O₂ and 0.5 mg L⁻¹ Fe²⁺ at pH 2.0–3.0 under 96 W of UVC light [14]. This light yielded better results than operating with 20 W UVA and 300 W Xe lights. After 60 min of treatment, the mixture was degraded by 82% with k₁ = 0.035 min⁻¹, superior to 65% with k₁ = 0.016 min⁻¹ determined for single photolysis, where drugs were removed by UVC light and ^●OH formed from reaction (6) (see Table 1). Cavalheri et al. [15] investigated the removal of a mixture of the NSAID diclofenac and the antibiotic ketoprofen in a stirred-tank photoreactor under 81 W of UVA light. The trials were carried out with 600 mL of 12.5 mg L⁻¹ of each drug in domestic sewage, containing 10–30 mg L⁻¹ H₂O₂ and 3–15 mg L⁻¹ Fe²⁺, at pH 3.0, for 150 min. Good COD and biological oxygen demand (BOD) reductions of 78% and 62%, respectively, were obtained at the optimal concentrations of 10 mg L⁻¹ H₂O₂ and 15 mg L⁻¹ Fe²⁺, determined by response surface methodology (see Table 1). The authors also demonstrated the positive effect of UVA light on producing more OH (from reaction (5)) by determining lower decay rates of 65% COD and 60% BOD with homogeneous Fenton.

Figure 4 highlights a similar removal of the drugs of a mixture of carbamazepine, diclofenac, ibuprofen, and sulfamethoxazole under homogeneous PF in a stirred-tank photoreactor illuminated with 15 W UVC light [16].

More than 90% degradation of all drugs can be observed after 60 min of treatment of 500 mL of 25 mg L⁻¹ of each drug in pure water containing 0.24 mL L⁻¹ of concentrated H₂O₂ and 20 times lower of Fe²⁺ at pH = 3.0 (see also Table 1). Another study on a mixture of diclofenac, ranitidine, and simvastatin reported rapid abatement of these drugs within 10 min in a stirred-tank photoreactor under 56 W of UVA light [17]. A total of 92% simvastatin degradation and 100% destruction of the other two drugs, with 72% mineralization, was found for 1.654 L of 50 μg L⁻¹ of each drug in domestic sewage of initial TOC of 21 mg C L⁻¹ with 40 mg L⁻¹ H₂O₂ and 3 mg L⁻¹ Fe³⁺ at pH = 7.2 (see Table 1).

2.1.5. Real Wastewaters

The efficient homogeneous PF process has been checked directly on several real wastewaters [18,33]. For instance, the COD of 1 L of pharmaceutical wastewater with an initial COD of 4000 mg O₂ L⁻¹ was reduced by 88% by adding a Fe²⁺/H₂O₂ ratio of 1:10 at pH = 4.0 during 60 min in a stirred-tank photoreactor under 80 W Xe light (see Table 1) [18].

2.2. Homogeneous Photo-Fenton-like

Homogeneous PF-like processes have been proposed using other soluble reagents as oxidants, aiming to operate at less acidic and even neutral pH values. This method has been tested for single drugs, mixtures of drugs, and real wastewaters, as described in this subsection.

2.2.1. Single Drugs

The removal of the NSAID acetaminophen [49,50] and antibiotics amoxicillin [19] and sulfamethoxazole [51] was assessed. It is noticeable that the work of de Oliveira et al. [19] involved mineralizing amoxicillin with the recirculation system of Figure 1e using an inner UV-Vis light of λ = 200–500 nm. The trials were performed with 3.6 L of 100 mg L⁻¹ drug in pure water, adding 1.470 mM min⁻¹ of H₂O₂ and 1.560 mM Fe³⁺ at pH 3.0 for 120 min. These conditions were obtained by optimization using response surface methodology, yielding an excellent 90% reduction in TOC (see Table 1). The H₂O₂ content was continuously added from the decomposition of sodium percarbonate via reaction (10):

4Na₂CO₃·3H₂O₂ + 4H₂O → 3H₂O₂ + 4HCO₃⁻ + 8Na⁺ + 4OH⁻

(10)

For sulfamethoxazole, ethylenediaminetetraacetate (EDTA) was used as a soluble iron chelate to operate at pH = 7.5 using a tubular flow photoreactor introduced in a solar box with a 1500 W Xe lamp [51]. Total antibiotic removal was obtained for 1 L of 1 mg L⁻¹ sulfamethoxazole in pure water with 50 mg L⁻¹ H₂O₂ and a 1:1 EDTA/Fe²⁺ molar ratio with 5 mg L⁻¹ Fe²⁺ upon an energy accumulation of 1.2 kJ L⁻¹. The Fe²⁺-EDTA complex formed ^●OH by reactions similar to (1) and (5), but maintaining the iron complexed and soluble in the solution.

2.2.2. Mixture of Drugs

The homogeneous PF-like of mixtures of drugs was developed with complexes of Fe(III) with soluble ligands (L) such as ethylenediamine-N, N-disuccinate (EDDS) [20,21,52,53], nitriloacetate (NTA) [21,53], copoazu extract [54], iminodisuccinate [55,56], citrate [22,57], and humic acid [58]. These complexes stabilize Fe³⁺ in contaminated solutions, which can be treated at circumneutral and neutral pH by reaction (11), which generates Fe²⁺ and produces further ^●OH from the homogeneous Fenton reaction (1) [59]. Moreover, the ligand radical L^● that is formed evolves up to total mineralization:

Fe(III)-L + hν → Fe²⁺ + L^●

(11)

Raceway pond photoreactors illuminated with sunlight were constructed with volumes of 16 and 90 L with different depths of the recirculation effluent for light absorption [22]. Using the 16 L photoreactor, Manikova et al. [20] treated a mixture of caffeine, carbamazepine, diclofenac, sulfamethoxazole, and trimethoprim at 100 μg L⁻¹ of each drug in WWTP effluent with an initial TOC of 15.5 mg C L⁻¹ with 50 mg L⁻¹ H₂O₂, 0.1 mM Fe³⁺, and 0.1 mM EDDS at circumneutral pH = 7.6. Figure 5a shows the effectiveness of the homogeneous PF-like process applied, and in 60 min, 87% degradation for caffeine, 92% for sulfamethoxazole and carbamazepine, and 97% for trimethoprim was found, whereas total removal of diclofenac was more quickly achieved in 45 min. This behavior clearly indicates the different reactivities of the drugs during their oxidation by ^●OH. On the other hand, Nunez et al. [22] compared the oxidation in photoreactors for a mixture of benzotriazole, carbamazepine, and diclofenac at 100 μg L⁻¹ each in natural water with an initial TOC of 3.1 mg C L⁻¹ and WWTP effluent of initial TOC of 25 mg C L⁻¹ containing 40 mg L⁻¹ H₂O², 6 mg L⁻¹ Fe³⁺, and 12 mg L⁻¹ citric acid at pH = 6.3 under 30 W cm⁻² Xe light. For 90 L with the WWTP effluent, low drug removals were achieved by competitive oxidation with its constituents, and so, after 45 min, only about 25% removal for benzotriazole and carbamazepine and 60% for diclofenac were determined (see Table 1). Figure 5b highlights that benzotriazole was more rapidly degraded in pure water with lower organic load, even faster for the 90 than the 16 L photoreactor.

The degradative influence of ligands EDDS and NTA for Fe(III) complexation was studied by Aliste et al. [21] with a mixture of diclofenac and ibuprofen in WWTP effluent with a low initial TOC of 2.5 mg C L⁻¹. Experiments were made with 500 mL of 200 μg L⁻¹ of each drug, 1.47 mM H₂O₂, 0.1 mM Fe³⁺, and 0.1 mM EDDS or 0.1 mM NTA at pH = 6.3 in a stirred-tank photoreactor under a 32 W fluorescent bulb for 360 min. A clear superiority of EDDS was found, as its Fe(III) complex degraded 90% of diclofenac and 95% of ibuprofen, compared with 48% and 47% for Fe(III)-NTA (see Table 1).

Peracetic acid (CH₃COOOH) was used as an alternative reagent to H₂O₂, generating ^●OH and Fe^IVO²⁻ as oxidants from reactions (12) and (13) [23,60]:

CH₃COOOH + Fe²⁺ → Fe³⁺ + CH₃COO⁻ + ^●OH

(12)

CH₃COOOH + Fe²⁺ → Fe^IVO²⁻ + CH₃COOH

(13)

The formation of these oxidants has been confirmed by Li et al. [23], when treating a mixture of carbamazepine, diclofenac, naproxen, sulfamethoxazole, and trimethoprim at 1 μM each in pure water by adding 25 μM peracetic acid and 2.5 μM Fe³⁺ at pH = 4.0 in a stirred-tank photoreactor under 9 W UVA light. The process was very effective, and in only 15 min, the most easily oxidizable naproxen and diclofenac were completely removed, with high k1 values of 0.30 and 0.36 min⁻¹, respectively (see Table 1).

2.2.3. Real Wastewaters

Only a real WWTP effluent with an initial TOC of 82.1 mg C L⁻¹ with 13 drugs at 0.05–0.82 μg L⁻¹ of each content and pH = 7.4 was treated by homogeneous PF-like with Fe(III) complexed with humic acid [24]. The treatment was performed with 250 mL of the wastewater filling a stirred-tank photoreactor submitted to a 32 W fluorescent bulb, and removal of only from 8.5% to 56% was found for all drugs with 31% TOC reduction after 30 min of adding 100 mg L⁻¹ H₂O₂ and 1:6.8 Fe³⁺/humic acid (see Table 1).

2.3. Heterogeneous Photo-Fenton

Heterogeneous PF involves the use of solid iron catalysts to form ^●OH from H₂O₂ via heterogeneous Fenton reaction (14), in which the surface Fe²⁺, denoted as ≡Fe²⁺, is transformed into surface ≡Fe³⁺ [5,36]. Moreover, heterogeneous photo-Fenton (15) with hydrolyzed surface ≡Fe³⁺ can regenerate ≡Fe²⁺ and produce more ^●OH. These reactions present a suitable rate at neutral pH, improving the treatment of homogeneous PF with acidic requirements. The catalysts can be easily extracted from treated solutions and reused for a long duration:

≡Fe²⁺ + H₂O₂ → ≡Fe³⁺ + ^●OH + OH⁻

(14)

≡Fe³⁺-OH+ hν → ≡Fe²⁺ + ^●OH

(15)

However, the process can be complicated by partial solubilization of the catalyst, which can also produce homogeneous Fenton reactions (1) and (5). The formation of O₂^●−, usually from O₂ reduction, and the subsequent production of the non-radical singlet oxygen (¹O₂) is also possible through reaction (16) [5]:

O₂^●− + ^●OH → ¹O₂ + OH⁻

(16)

2.3.1. NSAIDs

The degradation of acetaminophen by FeS₂ and citric acid [25], chitosan/Fe₃O₄ [26], and FeOCl [61] catalysts and diclofenac by CoFe₂O₄ [62], polydopamine-chitosan/Fe₃O₄ [63], and bentonite/Fe/Ag [64] catalysts has been checked. Figure 6a schematizes the proposed mechanism for pyrite activated by citric acid (CA) as a catalyst [25]. As can be seen, CA attacks the pyrite surface to originate the soluble Fe(III)-CA complex that can be photolyzed to Fe²⁺ and the radical anion CA^●− by a ligand-to-metal charge transfer (LMCT) from reaction (17), followed by its attack on O₂ to form O₂^●− from reaction (18). Further reaction (19) between O₂^●− and Fe²⁺ originates H₂O₂ that can react with Fe²⁺ to produce ^●OH from the homogeneous Fenton reaction (1). Additionally, ¹O₂ can be formed from reaction (16). Total acetaminophen degradation was obtained with this system after 30 min of treating 250 mL of 30 μM drug in pure water with 1 g L⁻¹ pyrite and 0.6 mM CA at pH = 6.0, filling a stirred-tank reactor under 70 W Xe light (see Table 1). However, pyrite showed moderate reusability, with 18% degradation after four consecutive cycles, probably due to the inactivation of the surface (Fe³⁺ active centers) by the deposition of by-products:

Fe(III)-CA + hν → Fe²⁺ + CA^●−

(17)

CA^●−+ O₂ → CA_ox + O₂^●−

(18)

O₂^●−+ Fe²⁺ + 2H⁺ → Fe³⁺+ H₂O₂

(19)

A good acetaminophen abatement of 95% has been reported after 60 min of the homogeneous PF process of 100 mL of 10 mg L⁻¹ drug in pure water with 200 mg L⁻¹ H₂O₂ and 20 mg L⁻¹ chitosan/Fe₃O₄ catalyst at pH = 2.0 and 26 °C using a stirred-tank photoreactor submitted to 15 W UVC light [26] (see Table 1). The activation energy (E_a) for the process was found to be 36.3 kJ mol⁻¹. Nevertheless, the system showed moderate reusability, with a 20% loss of activity after four successive steps.

Several authors have reported ROS generation in heterogeneous PF. For instance, Feng et al. [61] determined the effect of specific scavengers on the treatment of 150 mL of 100 mg L⁻¹ acetaminophen in pure water with 2.40 mM H₂O₂ and 100 mg L⁻¹ FeOCl catalyst at pH = 7.0 in a stirred-tank photoreactor with 18 W VUV light. Figure 6b shows a clear inhibition of the degradation rate by adding NaN₃ (scavenger of ¹O₂), NaNO₃ (scavenger of hydrolyzed electrons), and tert-butyl alcohol (TBA, scavenger of ^●OH). Hydrogen atoms can react with O₂ to produce O₂^●. They were also detected by EPR using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and 2,2,6,6-tetramethylpiperidine (TEMP) as trapping agents. Figure 6c,d present the typical 1:2:2:1 quadruplet obtained for DMPO-^●OH and DMPO-O₂^●− adducts, whereas Figure 6e shows the 1:1:1 triplet for the TEMP-¹O₂ adduct.

2.3.2. Antibiotics

Heterogeneous PF treatments have been reported for carbamazepine by FeOCl-coated ceramic membrane [27], laccase/Fe₃O₄ [65], and Fe/Fe₂O₃ [66], imidacloprid with zero-valent iron (ZVI) [28], metronidazole with activated carbon/CuCOFe₂O₄ [67], sulfamethazine with perylene diimide/Fe [29], and tetracycline with biochar/iron oxides [68]. The degradation of antimalarial chloroquine phosphate was investigated using a biochar/Fe-Co Prussian blue analog [69].

Yao et al. [27] used the system of Figure 1b upon 1.6 mW cm⁻² UVC to comparatively degrade 10 μM carbamazepine in fresh synthetic urine of pH = 6 and hydrolyzed urine of pH = 9 containing 8 mM H₂O₂ and 0.2 cm of membrane/FeOCl catalyst at liquid flow rate = 2 mL min⁻¹. Blank experiments with phosphate-buffered saline (PBS) of the same pH were also performed, and the solutions were previously maintained in the dark for 60 min to stabilize drug adsorption. Figure 7 highlights the similarity and overall destruction of the drug within 40 min in both PBS at pH 6 and 9. It can also be observed that efficient drug removal occurs at a slower but analogous rate in both urine effluents, reaching total drug removal in about 360 min (see Table 1). This deceleration is mainly due to the oxidation of their organic constituents (urea, uric acid, and creatinine).

Other work treated 2 L of 1 mg L⁻¹ imidacloprid in natural water with 3 mM H₂O₂ and 55.8 mg L⁻¹ ZVI catalyst at pH 7.4 in a stirred-tank photoreactor under sunlight [28]. After 180 min, 86% degradation was achieved with k₁ = 0.0110 min⁻¹ (see Table 1). Yildiz et al. [29] explored the process of 200 mL of 10 mg L⁻¹ sulfamethazine in pure water with 5–10 mM H₂O₂ and 0.1–1 mg L⁻¹ perylene diimide/Fe catalyst at pH = 3.0–7.0 using a stirred-tank photoreactor under a 100 W halogen lamp and lasing for 120 min. Using response surface methodology, 92% of drug abatement was optimized at 6.46 mM H₂O₂ and 0.45 mg L⁻¹ catalyst at pH 3.0 (see Table 1). The authors detected ^●OH as oxidant using specific scavengers and showed the instability of the catalyst due to the leaching of 1.344 mg L⁻¹ Fe.

2.3.3. Mixture of Drugs

Mixtures of drugs have been treated with ZVI [30], sludge from wastewater [70], ferroalloy/Ta [71], and sand/iron oxides [72]. Li et al. [30] studied the heterogeneous PF process of a mixture of acetaminophen, caffeine, diethyltoluamide, and triclosan at 2 μg L⁻¹ of each drug in natural water with the best conditions at 0.2 mM H₂O₂ and 0.4 mM ZVI catalyst at pH = 3.0 in a stirred-tank photoreactor submitted to 11 W UVC light over 30 min. Figure 8a shows that the percent of removal varied with drugs due to their different reactivity depending on their chemical structure.

The removal of all of them increased up to 0.4 mM H₂O₂ at 0.2 mM ZVI (2:1 ratio) and pH = 3.0 due to the gradual rise in the rate of heterogeneous Fenton reaction (14) and photo-Fenton reaction (15) to generate oxidant ^●OH. The steady degradation observed at higher H₂O₂ content suggests saturation of the ZVI catalyst’s active centers. The same behavior can be observed in Figure 8b, where a steady concentration was achieved for a higher ZVI content of 22.4 mg L⁻¹ (0.4 mM) at 0.2 mM H₂O₂ and pH 3.0. The effect of pH in the interval 2.0–7.0, presented in Figure 8b, under the best reagent contents, indicated a maximum degradation of all drugs at pH = 3.0, when the maximum amount of ^●OH was produced. Drug removal decreased in the following order: 98% for acetaminophen >86% for triclosan >70% for diethyltoluamide >65% for caffeine (see Table 1). However, only a 19% TOC reduction was observed, indicating a hard oxidation of the by-products formed by (^●OH).

2.4. Heterogeneous Photo-Fenton-like

In heterogeneous PF-like non-ferrous solid catalysts, peracetic acid is used. It has been tested for the antibiotic tetracycline with MgO/Cu [31], Cu/MoS₂/polyacrylamide/copper alginate hydrogel [73], and biochar/Fe₂O₃ [74], as well as for caffeine with peracetic acid and MnFe₂O₄ [32]. Figure 9a shows a scheme of the proposed mechanism for tetracycline removal with H₂O₂ and the best MgO/5%Cu catalyst [31] under 350 W Xe light. As can be seen, the surface ≡Mg(OH)⁺ is hydrolyzed to Mg²⁺ and OH⁻, whereas surface ≡Cu⁺ yielded ^●OH and O₂^●− being oxidized to surface ≡Cu²⁺, which was again reduced to surface ≡Cu⁺ by light irradiation. The treatment of 100 mL of 25 mg L⁻¹ tetracycline in pure water containing 60 mM H₂O₂ and 500 mg L⁻¹ catalyst at natural pH was highly successful, with total removal achieved in 5 min (see Table 1). The release of 40.7 mg L⁻¹ of Mg²⁺ was determined after 125 min of treatment, and the production of the above oxidants was confirmed by means of specific scavengers. From the 16 primary by-products identified by LC-MS, the reaction sequence for tetracycline (1) mineralization in Figure 9b was proposed. The hydroxylation of 1 led to 2–7 with four condensed rings, which, upon cleavage of one ring, evolved to 8 and 9, and, upon cleavage of two rings, to 10. Further cleavage of these derivatives produced the benzene carbonyl 11 and benzene carboxylic acids 12–14, which are subsequently transformed into final short, linear carboxylic acids, such as malic, fumaric, and succinic. These compounds are finally mineralized to CO₂ and H₂O, along with NH₄⁺ formed from previous nitrogenated intermediates.

It is remarkable that the work of Yu et al. [32] was devoted to degrading 0.5 mg L⁻¹ of caffeine, a psychoactive stimulant drug, in pure water through 2 mM peracetic acid and 250 mg L⁻¹ MnFe₂O₄ catalyst at pH = 7.0 in a stirred-tank photoreactor under 4 W VUV light of λ = 185 nm. A rapid drug removal was obtained with 88% abatement with a high k₁ = 0.243 min⁻¹ in only 8 min (see Table 1). However, moderate reusability of the catalyst was observed after five consecutive runs, with a 10% loss in activity, probably due to adsorption of by-products. The great efficiency of this process was ascribed to the production of ^●OH from CH₃COOOH with ≡Fe²⁺ at the catalyst’s surface by a reaction similar to (12) and heterogeneous photo-Fenton reaction (15). Further oxidation of CH₃COOOH to CH₃COOO^● from ^●OH was also proposed, as well as the positive role of the surface ≡Mn³⁺/≡Mn²⁺ pair over the stability of the ≡Fe³⁺/≡Fe²⁺ one. Specific scavengers and EPR analysis confirmed the generation of these oxidants.

Figure 10a shows the loss of 70% of drug degradation in the above process by adding TBA (scavenger of ^●OH) in front of only 3% with methanol (scavenger of CH₃COOO^●), demonstrating the high ^●OH production. Figure 10b presents the three pathways proposed for caffeine (1) degradation from the by-products detected by LC-MS. In the pathway I, 1 was dihydroxylated to 2, which was subsequently broken to the imidazole 4 and the linear derivative 5. These compounds were also directly produced in pathway II, and 4 was further dihydroxylated to 6. Pathway III was initiated by the three demethylations of 1 to 3, followed by cleavage to 7 and 8.

3. Photocatalysis/Photo-Fenton Treatment of Pharmaceuticals in Waters and Wastewaters

Photocatalysis (PC) is a conventional water treatment in which a semiconductor material submerged in a contaminated solution is irradiated with light. The semiconductor possesses a filled valence band (VB) and an empty conduction band (CB) separated by a band gap energy (E_bg). The photons of the light irradiation with energy >E_bg photoexcite one electron of the CB to the VB, originating an electron in the VB (e_CB⁻) and a positively charged hole in the CB (h_VB⁺) from reaction (20) [75,76,77,78]. The E_bg-value of the photocatalyst is thus determinant for the light irradiation required in PC, namely UVC, UVB, UVA, Vis, or sunlight. Although the photogenerated e_CB/h_VB+ pair rapidly recombines according to reaction (21), the remaining separated charges can produce ROS for the removal of organic pollutants. So, the h_VB⁺ can generate ^●OH by oxidation of H₂O or OH⁻ from reaction (22) or (23), although it can directly oxidize the organic R by reaction (24). For his part, the promoted e_CB⁻ can yield O₂^●− from the dissolved O₂ in the medium by reaction (25), and this radical can consecutively produce HO₂^●, H₂O₂, and ^●OH by reactions (26)–(28). For an incident UVC light, the homolytic photolysis of H₂O₂ by reaction (6) can also produce (^●OH):

Semiconductor + hν (>E_bg) → h_VB⁺ + e_CB⁻

(20)

h_VB⁺ + e_CB⁻ → semiconductor + heat

(21)

h_VB⁺ + H₂O → ^●OH + H⁺

(22)

h_VB⁺ + OH⁻ → ^●OH

(23)

h_VB⁺ + R → R⁺

(24)

e_CB⁻ + O₂ → O₂^●−

(25)

O₂^●− + H⁺ → HO₂^●

(26)

HO₂^● + H⁺ → H₂O₂

(27)

H₂O₂ + e_CB⁻ → ^●OH + OH⁻

(28)

In the hybrid PC/PF process, the photocatalyst with surface iron and/or other metals is immersed in the contaminated solution, even at neutral pH, with H₂O₂ added under appropriate illumination. This excess of H₂O₂ can generate ^●OH not only from reaction (28), but also from surface reactions, e.g., heterogeneous Fenton reaction (14) and photo-Fenton reaction (15) in photocatalysts with iron. An advantage of the hybrid process is the regeneration of the surface ≡Fe²⁺ via reaction (29), which enhances the rate of the heterogeneous Fenton reaction (14) and, hence, the oxidation of organics:

≡Fe³⁺ + e_CB⁻ → ≡Fe²⁺

(29)

This subsection details the advances made in applying the hybrid PC/PF process to the remediation of drugs in water and wastewater. Table 2 collects the main results reported for these assays.

3.1. NSAIDs

The PC/PF treatment of NSAIDs has been mainly applied to acetaminophen using iron photocatalysts, such as metal–organic frameworks (MOFs) like MIL-53(Fe) [79] and CuS₂/MIL-101(Fe) [80], and composites of 3D hollow microarchitectures/α-Fe₂O₃ [106], Fe-BiOBr [81], and Cu-Fe/pillared clay [107], along with non-ferrous photocatalysts such as Ti₃C₂TX (MXene) [108] and carbon/Zr-WO₃ [109]. Ibuprofen with Fe-TUD-1 [110], naproxen with Ag/SnO₂ [111], and phenazopyridine with g-C₃N₄/MIL-101(Fe) [82] have also been checked.

Figure 11a schematizes the proposed mechanism for the removal of acetaminophen (APAP) with the MIL-53(Fe) photocatalyst using PC/PF under Vis light from a 300 W Xe lamp (>400 nm [79]). It can be observed that the photoexcitation of the photocatalyst and the attack of the drug by O₂^●− formed from reaction (25), h_VB⁺ from reaction (24), and ^●OH from heterogeneous Fenton reaction (14), whereas surface ≡Fe²⁺ was regenerated from reaction (29). Specific scavengers and EPR detected these ROS. The trials performed with 100 mL of 20 mg L⁻¹ drug in pure water, with 7 mM H₂O₂ and 100 mg L⁻¹ photocatalyst at pH 7.0, resulted in 96% removal, with k₁ = 0.085 min⁻¹ over 60 min. The leaching of 1.3 mg L⁻¹ Fe during this process demonstrated a certain degree of photocatalyst instability, although good reusability was observed, with 4% degradation after four consecutive steps.

A more complex behavior can be observed with a photocatalyst containing two coupled Fe and Cu metals, as shown in Figure 11b for CuS/MIL-101(Fe) under 300 W Xe light [80]. The two materials were joined by a heterojunction type II, in which the more energetically e_CB⁻ of CuS passed to MIL-101(Fe), whereas the h_vb⁺ circulated in the opposite direction. Thus, the ROS generation (O₂^●−, H₂O₂, ^●OH, and ¹O₂) from e_CB⁻ occurred at the MIL-101(Fe) surface and the oxidative action of h_vb⁺ at the CuS surface. Moreover, the surface ≡Fe²⁺ and ≡Cu⁺ can react to form ≡Fe³⁺ and ≡Cu²⁺ by reaction (30), which can be further reduced by e_CB⁻ to the former species. ^●OH is then formed from a heterogeneous Fenton reaction (14) with surface ≡Fe²⁺ and a heterogeneous Fenton-like reaction (31) with surface ≡Cu⁺. The degradation of 100 mL of 5 mg L⁻¹ drug in pure water containing 10 mM H₂O₂ and 100 mg L⁻¹ photocatalyst at pH = 5.0 yielded overall abatement with k₁ = 0.2099 min⁻¹ in 30 min (see Table 2). A moderate reusability of the photocatalyst, with a 10% degradation loss, was observed after five successive cycles:

≡Fe²⁺ + ≡Cu⁺ → ≡Fe³⁺ + ≡Cu²⁺

(30)

≡Cu⁺ + H₂O₂ → ≡Cu²⁺ + ^●OH + OH⁻

(31)

Much slower oxidation was found in the other photocatalysts. For instance, 240 min were needed to completely degrade APAP, with 58% TOC removal, at 15 mg L⁻¹ drug in pure water containing 10 mM H₂O and 250 mg L⁻¹ Fe-BiOBr photocatalyst, pH 3.0, in a stirred-tank photoreactor illuminated by sunlight [81] (see Table 2). Better performance has been reported for the g-C₃N₄/MIL-101(Fe) membrane photocatalyst under 100 W Vis-LED light for the treatment of phenazopyridine [82]. The proposed mechanism of Figure 11c highlights the Z-scheme heterojunction between the two materials, with the passage of e_CB from the CB of MIL-101(Fe) to the VB of g-C₃N₄, making the e_CB of g-C₃N₄ photoactive and the h_VB⁺ of MIL-101(Fe) photoactive. The reduction in surface ≡Fe³⁺ to ≡Fe²⁺ from reaction (29) and ^●OH formation from H₂O₂ reduction by reaction (28) and heterogeneous Fenton reaction (14) can also be observed. This system was applied to the treatment of 60 mL of 15 mg L⁻¹ drug in pure water with 60 μM of concentrated H₂O₂ and 250 mg L⁻¹ photocatalyst at pH = 6.5, and 97% degradation was attained in 70 min (see Table 2). LC-MS identified 10 by-products, and the photocatalyst showed good reusability, with 8% degradation loss after five successive runs.

3.2. Antibiotics

The PC/PF process of antibiotics has been studied for several iron oxides, such as chloramphenicol with zeolite/Fe⁰/Fe₃O₄ [112], levofloxacin with poly(2-vinylpyridine-b-polystyrene)/iron oxides [113], norfloxacin with Pt/TiO₂/Fe₂O₃ [83], sulfachloropyridazine with α-Fe₂O₃ [114], and tetracycline with ceramic membrane/α-Fe₂O₃ [115] and reduced graphene oxide (rGO)/FeTiO₃ [116]. The treatment of 20 mL of 4 mg L⁻¹ norfloxacin in pure water was studied using 50 mM H₂O₂ and 50 mM Na₂SO₄ in the presence of a 1 cm² Pt/TiO₂/Fe₂O₃ photocatalyst at pH 6.7 in a stirred-tank photoreactor under a 300 W fluorescent lamp [83]. After 30 min of previous dark and 120 min of illumination, the drug was slowly reduced by 88%, with formation of ^●OH and O₂^●− as oxidants (see Table 2). There was moderate photocatalyst reusability, losing 10% degradation after five successive steps, probably due to the adsorption of by-products generated.

Several iron-MOFs have been assessed for antibiotic removal in water and wastewaters by the hybrid PC/PF. Carbamazepine with 2D Fe²⁺/MOFs [117], ciprofloxacin with MIL-100(Fe) [84], sulfadimethoxine with MIL-53(Fe) [85], sulfamethoxazole with MIL-53(Fe) [118], and sulfamethylthiazole with MIL-100(Sc 0.58, Fe 0.42) [86] have been checked. Zheng et al. [84] found 94% degradation and 68% TOC reduction when 20 mg L⁻¹ ciprofloxacin in pure water was degraded by 4 mg L⁻¹ H₂O₂ and 100 mg L⁻¹ MIL-100(Fe) photocatalyst at pH = 6.4 in a stirred-tank photoreactor illuminated with Vis light of λ > 420 nm from 300 W Xe after 120 min with 30 min of previous dark (see Table 2). Figure 12a reveals the degradation achieved by adding 0.1 mM of specific scavengers that decayed in the following order: p-benzoquinone (p-BQ, scavenger of O₂^●−) < L-histidine (scavenger of ¹O₂) < EDTA-2Na (scavenger of holes) < TBA (scavenger of ^●OH). The formation of ^●OH as the main oxidant was confirmed by EPR analysis. Nevertheless, the photocatalyst exhibited moderate reusability, with a 10% decrease in degradation efficiency after five consecutive cycles.

For sulfadimethoxine, a fast removal of 20 mg L⁻¹ drug in pure water with total degradation in 50 min has been reported in the presence of 20 μL of concentrated H₂O₂ and 165 mg L⁻¹ MIL-Fe(53) photocatalyst at pH = 7.0 in a stirred-tank photoreactor under Vis light from 300 W Xe light [85] (see Table 2). The authors identified seven by-products by LC-QTOF-MS and confirmed a moderate photocatalyst reusability, losing 10% degradation after four successive cycles. A slower rate of degradation has been reported for sulfamethylthiazole, as shown in Figure 12b [86]. A 98% decay with k₁ = 0.0315 min⁻¹ can be observed in 100 min for 10 mg L⁻¹ drug in pure water containing 38.8 mM H₂O₂ and 5 g L⁻¹ MIL-100(Sc 0.58, Fe 0.42) photocatalyst at pH = 6.8 in a stirred-tank photoreactor under 300 W Xe light (see also Table 2). Specific scavengers and EPR indicated the production of oxidants ^●OH, O₂^●−, and ¹O₂, whereas good photocatalyst reusability was observed after three consecutive runs, with an 8% loss in degradation.

Various g-C₃N₄ composites have been synthesized for the PC/PF treatment of antibiotics. They include ciprofloxacin with g-C₃N₄/MXene/CuO [87], furazolidone with g-C₃N₄/MnFe₂O₄-S,N-CQDs [119], sulfadimethoxine with g-C₃N₄/Cu [88], sulfamethoxazole with g-C₃N₄/CoFe₂O₄/CDs [120], and tetracycline with g-C₃N₄/Fe₃O₄ [89], g-C₃N₄/CuFe₂O₄ [121], g-C₃N₄/CuO [90], g-C₃N₄/Fe₂TiC₅ [122], and g-C₃N₄/FeMoO₄ [91]. Figure 13a shows the effect of pH on the percentage of ciprofloxacin removal vs. time for 10 mg L⁻¹ drug in pure water with 20 μL of concentrated H₂O₂ and 10 mg L⁻¹ g-C₃N₄/MXene/CuO photocatalyst using a stirred-tank photoreactor under a 400 W Vis-sodium lamp [87]. The best degradation was at pH = 9.0 with 87% abatement and k₁ = 0.0178 min⁻¹ at 90 min, and good photocatalyst reusability had 7% degradation after four successive cycles (see Table 2). From the detection of ^●OH, O₂^●−, and mainly holes by specific scavengers, the mechanism of Figure 13b was proposed.

The photoexcitation occurs for CuO and g-C₃N₄ with a Z-scheme heterojunction that involves the pass of the e_CB⁻ of the former semiconductor to the second one, whereas the e_CB⁻ of (g-C₃N₄) passes directly to MXene by a Schottky heterojunction due to its high electric conductivity. So, ciprofloxacin was destroyed by O₂^●− originated at the MXene surface, and ^●OH formed at the CuO surface. A similar rapid degradation has been reported for sulfadimethoxine with g-C₃N₄/Cu, featuring a Schottky heterojunction between the two materials [88]. Overall abatement was observed after 50 min of treatment with 20 mg L⁻¹ of the drug in pure water, using 1.65 mM H₂O₂ and 1 g L⁻¹ photocatalyst, again at alkaline pH = 10.0 under 300 W Xe light (see Table 2). In both cases, ^●OH production from surface ≡Cu⁺ via reaction (31) is expected.

Cui et al. [89] applied the PC/PF process to remove tetracycline in pure water using the g-C₃N₄/Fe₃O₄ photocatalyst at pH 3.0 and 18 °C in a multi-test tube photoreactor under 500 W Xe light (<420 nm) for 100 min. Figure 14a shows that total degradation with k₁ = 0.03907 min⁻¹ and 67% TOC reduction was achieved in a first cycle with 25 mg L⁻¹ drug, 5 mM H₂O₂, and 1 g L⁻¹ photocatalyst (see also Table 2). A good level of photocatalyst reusability is observed, with a 7% loss in degradation after five successive cycles. Figure 14b highlights the large inhibition of the degradation process when isopropyl alcohol (IPA, scavenger of ^●OH) and p-BQ (scavenger of O₂^●−) were added to the medium. Figure 14c presents the expected EPR spectra of the DMPO adducts of both radicals, confirming their formation in this system.

Based on these findings, the mechanism shown in Figure 15a was proposed. While H₂O₂ was oxidized to O₂^●− by h_VB⁺ formed in the photoexcitation of g-C₃N₄, the corresponding e_CB⁻ charges reduced dissolved O₂ to O₂^●− and were transferred to Fe₃O₄ to reduce the surface ≡Fe³⁺ to ≡Fe²⁺, thus enhancing its reaction with H₂O₂ for the formation of ^●OH from heterogeneous Fenton reaction (14). Note that the H₂O oxidation to ^●OH by h_VB⁺ via reaction (22) is more probable, along with the photoreduction of ≡Fe³⁺-OH to ^●OH from reaction (15), as stated above.

The excellent photocatalytic performance of the g-C₃N₄/CuO photocatalyst for tetracycline removal has been reported by Imran et al. [90]. In only 15 min, 10 mg L⁻¹ drug in pure water was completely abated with k₁ = 0.1242 min⁻¹ in the presence of 0.3 mL L⁻¹ H₂O₂ and 200 mg L⁻¹ photocatalyst at alkaline pH = 9.0 using a stirred-tank photoreactor illuminated with Vis light provided by a 400 W Na lamp (see Table 2). LC-MS identified 11 by-products, and excellent photocatalyst reusability was observed after four consecutive steps. The mechanism of Figure 15b was proposed for the oxidants ^●OH, O₂^●−, and holes detected by specific scavengers. The Z-scheme heterojunction between g-C₃N₄ and CuO can be observed, along with the separated formation of oxidants. However, the possible generation of ^●OH by surface ≡Cu⁺ oxidation from reaction (31) is not mentioned. Note that this tetracycline process with g-C₃N₄/CuO was much faster than previously reported for ciprofloxacin with g-C₃N₄/MXene/CuO, suggesting that g-C₃N₄/CuO is the best option for practical application.

Another interesting study has focused on the degradation of tetracycline in pure water using the g-C₃N₄/FeMoO₄ photocatalyst under 500 W Xe Vis light [91]. The process was slower, and response surface methodology showed that it was optimized at 31.2 mg L⁻¹ drug, 1.31 mM H₂O₂, and 0.24 g L⁻¹ photocatalyst at pH 7.0, yielding 98% degradation in 120 min. Nevertheless, after 11 consecutive runs, the photocatalyst showed moderate reusability, with a 10% loss in degradation. Oxidants ^●OH, O₂^●−, and ¹O₂ were detected by specific scavengers and EPR, and their generation was proposed by the scheme presented in Figure 15c. The Z-scheme heterojunction favored the pass of e_CB⁻ from FeMoO₄ to g-C₃N₄, and these electrons also caused a reduction in the surface ≡Fe³⁺ and ≡Mn⁶⁺ of the former material to surface ≡Fe²⁺ and ≡Mn⁴⁺. The ^●OH formation from heterogeneous Fenton reaction (14) with surface ≡Fe²⁺ was also enhanced by the reduction in surface ≡Fe³⁺ with surface ≡Mn⁴⁺ via reaction (32):

≡Fe³⁺ + ≡Mn⁴⁺ → ≡Fe²⁺ + ≡Mn⁶⁺

(32)

Composites of iron compounds with those of other metals have been considered. So, carbamazepine was with BiVO₄/FeO_x [92] and with BiOCl with Fe²⁺ [123], and ciprofloxacin with TiO₂/Zn-ferrite [124]. It is also included FeVO₄/MoS₂ [125], NiCo₂S₄/CuFe LDH [126], and Fe-UiO-66-NH₂(Zr, Fe)/CuO [127], levofloxacin with Cu/CuFe₂O₄ [93], sulfamethazine with CdS/Fe²⁺ [128], and tetracycline with Fe₃S₄/MoS₂ [129]. Fe₃O₄-FeWO₄ [130], FeWO₄/WO₃/FeOOH [94], and zeolite/LaFeO₃ [131] have been explored. In these cases, the regeneration of surface ≡Fe²⁺ was accelerated by the photogenerated e_CB⁻, and the reduction in surface ≡Fe³⁺ by other surface metallic cations to form ^●OH from the heterogeneous Fenton reaction (14). Moreover, ROS were produced by photoexcitation of the photocatalysts.

The study of carbamazepine with the BiVO₄/FeOx photocatalyst was performed in a stirred-tank photoreactor illuminated with Vis light from a 300 W Xe lamp [92]. The process was very rapid, with total abatement (k₁ = 0.317 min⁻¹) attained in only 20 min for 10 mg L⁻¹ drug in pure water with 0.6 mM H₂O and 500 mg L⁻¹ photocatalyst at natural pH (see Table 2). A moderate photocatalyst reusability, with a 15% loss in degradation, was observed after three consecutive cycles. A slower degradation of levofloxacin has been reported for the Cu0/CuFe₂O₄ photocatalyst in pure water, under the same Vis light [93]. A 92% abatement with k₁ = 0.033 min⁻¹ was found in 90 min for 10 mg L⁻¹ drug. This included 30 mM H₂O₂ and 200 mg L⁻¹ photocatalyst at pH = 6.7, with excellent reusability after four consecutive cycles (see Table 2). The good ability of oxalic acid to regenerate surface ≡Fe²⁺ from photodecarboxylation of surface ≡Fe(III)-oxalate species from a reaction similar to (15) was assessed by Chai et al. [94] using FeWO₄/WO₃/FeOOH photocatalyst under a 100 W LED of λ = 400 nm. So, total drug removal with k₁ = 0.117 min⁻¹ and 72% oxalic acid decay was found in 30 min for the treatment of 50 mg L⁻¹ drug in pure water, 1 mM oxalic acid, and 400 mg L⁻¹ photocatalyst at pH = 3.0, with excellent photocatalyst reusability after six consecutive runs (see Table 2). In all these studies, the oxidative action of ^●OH, O₂^●−, ¹O₂, electrons, and/or holes was confirmed by specific scavengers and EPR, and LC-MS identified the main by-products.

The use of non-ferrous photocatalysts has also been explored. The treatment of chloramphenicol with Zn_1-x-yCo_xNi_yO nanorods [95], rifampicin with biochar/Co₂VO₄ [132], and tetracycline Ce-LaCoO₃ [96] was studied. The generation of ROS occurs via photoexcitation and heterogeneous Fenton-like reactions similar to (14), producing (^●OH) at the surface of ≡Co²⁺, ≡Ni²⁺, and/or ≡Ce³⁺.

For chloramphenicol, there was only an 88% removal of 20 mg L⁻¹ drug in pure water containing 0.1 mL of concentrated H₂O₂ and 50 mg L⁻¹ Zn_1-x-yCo_xNi_yO photocatalyst at pH = 7.0 in a stirred-tank photoreactor under a 500 W halogen lamp in 450 min [95] (see Table 2). The photocatalyst demonstrated excellent reusability after six consecutive cycles. Zhu et al. [96] reported faster degradation up to 92% after 120 min of treating 10 mg L⁻¹ tetracycline in pure water with 100 mM H₂O₂ and 400 mg L⁻¹ Ce-LaCoO₃ photocatalyst at pH = 7.0 under 500 W Xe light, with excellent reusability after five consecutive runs (see Table 2). These works detected oxidants using specific scavengers and/or EPR and used LC-MS to identify the main by-products.

3.3. Mixture of Drugs

A few mixtures of drugs have been degraded by PC/PF [97,98,99,100,133,134,135]. Figure 16a shows the excellent maintenance of 95% degradation for ciprofloxacin >86% for ibuprofen and acetaminophen during five consecutive cycles after 30 min of treatment of a mixture of 20 mg L⁻¹ of each drug in pure water with 1 mM H₂O₂ and 330 mg L⁻¹ SBA-15/Fe photocatalyst at pH = 7.0 using a stirred-tank photoreactor under Vis light from 400 W Xe light [97]. The corresponding k₁-values for these drugs were 0.0633, 0.0431, and 0.0194 min⁻¹, respectively (see Table 2). From the ROS detected by specific scavengers, the authors proposed the mechanism of Figure 16b, where the photogenerated e_CB⁻ in the CB of SBA-15 produced O₂^●− as well as ^●OH from the regenerated surface ≡Fe²⁺ with H₂O₂ via heterogeneous Fenton reaction (14). Moreover, ^●OH was also formed at the VB of the semiconductor from generated ≡Fe²⁺ and h_VB⁺.

Ahmed et al. [97] reported a fast total removal of a mixture of carbamazepine, diclofenac, mecoprop, and sulfamethoxazole of 50 mL of 10 μg L⁻¹ of each drug in pure water after 10 min of treatment with 1 mM H₂O₂ and 250 mg L⁻¹ rGO/FeS₂ photocatalyst at pH = 7.4 filling a stirred-tank photoreactor submitted to 300 W Xe light (see Table 2). ^●OH, O₂^●−, ¹O₂, electrons, and holes were identified as oxidants by EPR analysis. In contrast, He et al. [99] found a much slower degradation of a more concentrated mixture of 10 mg L⁻¹ of acetaminophen, atenolol, and levofloxacin, and 5 mg L⁻¹ sulfamethoxazole in pure water with 50 mM H₂O₂ and 1 g L⁻¹ g-C₃N₄/Fe photocatalyst at pH = 7.46 in a stirred-tank photoreactor with Vis light from 300 W Xe light. After 60 min of previous dark, levofloxacin was completely abated in 20 min of illumination. In contrast, at 60 min of irradiation, removals of 92% for atenolol, 74% for sulfamethoxazole, and 63% for acetaminophen were achieved (see Table 2). It is remarkable that the TOC of the mixture was completely removed within 12 h and that the formation of oxidants ^●OH, O₂^●−, ¹O₂, and holes was confirmed by specific scavengers and EPR.

Good results have been described for a non-ferrous photocatalyst such as MOF-Cu [100]. The trials were conducted in a mixture containing 50 mg L⁻¹ of chlortetracycline, tetracycline, and oxytetracycline in pure water, with 40 mM H₂O₂ and 500 mg L⁻¹ photocatalyst at natural pH, using a stirred-tank photoreactor illuminated with Vis light from a 300 W Xe lamp. Figure 17a depicts the normalized concentration of each drug over time after 30 min of prior dark incubation to stabilize their adsorption onto the photocatalyst. Removal of 84% for chlortetracycline, 82% for oxytetracycline, and 79% for tetracycline can be observed after 120 min of illumination (see also Table 2).

The photocatalyst showed good reusability, losing up to 8% degradation after five consecutive runs. Figure 17b highlights the mechanism proposed for this process, involving the generation of ^●OH and O₂^●− from photogenerated e_CB⁻ and ^●OH from reaction (31) between surface ≡Cu⁺ and H₂O₂.

3.4. Real Wastewaters

Real wastewater has been remediated using MOF-100(Fe) [101] and zeolite/Fe-Cu [136]. Li et al. [101] treated 40 mL of a WWTP effluent containing 24 pharmaceuticals at μg L⁻¹ content and initial TOC of 7.9 mg C L⁻¹ at pH = 7.2 by adding 20 mM H₂O₂ and 100 mg L⁻¹ MOF-100(Fe) photocatalyst using a stirred-tank photoreactor under Vis light supplied by 300 W Xe. Total degradation of all drugs was obtained in 10 h with some instability of the photocatalyst since 0.3 mg L⁻¹ Fe were leached. It was confirmed that the generation of oxidants ^●OH, O₂^●−, and ¹O₂ was detected by specific scavengers and EPR.

4. Sono-Photo-Fenton Treatment of Pharmaceuticals in Water and Wastewater

The hybrid SPF process is based on the application of ultrasound (US) to a solution treated by PF or PC/PF. The presence of the US not only enhances the mass transport of reactants, but also produces radical oxidants like ^●H and ^●OH from water decomposition by reaction (33) [5]. This occurs due to the high local temperature reached, up to 2000 °C, during the violent collapse of the bubbles that were formed:

H₂O + ))) → ^●H + ^●OH

(33)

This subsection describes the SPF treatments for drugs, with the main results listed in Table 2.

4.1. NSAIDs

Adityosulindro et al. [102] used a stirred-tank photoreactor of 500 mL under 6 W UVC or 150 W Xe lights connected to a sono-reactor of 1 L with 20 kHz US to degrade, upon circulation, 1.5 L of 20 mg L⁻¹ ibuprofen in pure water with 1.6–22.4 mM H₂O₂ and 0.134 mM Fe²⁺ at pH = 2.6. Good results were obtained, with overall degradation (k₁ = 0.0130 min⁻¹) in 60 min and 60% TOC decay in 180 min under the best conditions of 6.4 mM H₂O₂ and 150 W Xe light. Moreover, 12 by-products were detected by LC-MS.

4.2. Antibiotics

US was applied to the homogeneous PF of diclofenac [137] and imipenem [138] with Fe²⁺, homogeneous/heterogeneous PF of oxytetracycline with Fe²⁺/ZVI catalysts [103], heterogeneous PF of dexamethasone with zeolite/Fe catalyst [104], and PC/PF of ofloxacin with LaFeO₃/FeOOH photocatalyst [139]. Figure 18a schematizes a stirred-tank photoreactor for PF equipped with a transducer operating at 40 kHz [103]. Figure 18b depicts the percentage of oxytetracycline removal obtained after 60 min of the PF and SPF processes of 10 mg L⁻¹ drug in pure water with 60 mg L⁻¹ H₂O₂ and 8 mg L⁻¹ Fe²⁺ or ZVI as catalysts at pH = 4.0 using UVA, UVB, and UVC lights. As expected, superior degradation was observed with SPF and PF in all cases, demonstrating the generation of oxidants from reaction (33). Moreover, slightly higher degradation can be observed when operating with ZVI (^●OH generation from heterogeneous reaction (14)) than with Fe²⁺, where the same oxidant was formed from the homogeneous Fenton reaction (1), but at pH 4.0, which is higher than its optimum value of 3.0, it slows down. The best results were obtained with ZVI, with degradations of 87% for UVA, 89% for UVB, and 93% for UVC (see Table 2). Under the last set of optimal conditions, the authors identified 11 by-products by GC-MS.

Castaneda-Juarez et al. [104] constructed the continuous sono-photoreactor of Figure 19a with 5 W UVA light and US of 140 kHz to degrade dexamethasone solutions in pure water of pH = 7.0 with a packed zeolite/Fe catalyst. The optimization by response surface methodology yielded the best 99% drug removal and 74% COD reduction at 5.5 mg L⁻¹ drug, 22.5 mg L⁻¹ H₂O₂, and a hydraulic retention time of 140 min (see Table 2). These excellent results were much better than those obtained for single processes such as H₂O₂, US, or UVA, as can be seen in Figure 19b. This demonstrates the great ROS production by the zeolite/Fe catalyst, particularly ^●OH from heterogeneous Fenton reaction (14) and photo-Fenton (15) with ≡Fe²⁺ at the Fe surface.

4.3. Other Drugs

Eshaq et al. [105] used a stirred-tank sono-photoreactor with 350 W Xe light and a US frequency of 20 kHz to treat 10 mg L⁻¹ metoprolol in pure water with 50 mM H₂O₂ and 300 mg L⁻¹ of a multi-walled carbon nanotube (MWCNTs)/Cr₂O₃-Sm photocatalyst at pH 7.0. Good results were determined in 60 min with overall degradation and 95% TOC reduction (see Table 2). Oxidants ^●OH, O₂^●−, ¹O₂, and holes were detected by specific scavengers and EPR. Apart from reaction (33), the ^●OH generation was ascribed to the heterogeneous Fenton-like reaction (34) of surface ≡Cr³⁺ to ≡Cr⁴⁺ with H₂O₂, whereas that of O₂^●− was related to the surface ≡Sm³⁺/≡Sm²⁺ pair with participation of photogenerated e_CB⁻ and O₂ from reactions (35) and (36). ¹O₂ was then formed from reaction (16). For this SPF process, only three by-products were identified by GC-MS:

≡Cr³⁺ + H₂O₂ → ≡Cr⁴⁺ + ^●OH + OH⁻

(34)

≡Sm³⁺ + e_CB⁻ → ≡Sm²⁺

(35)

≡Sm³⁺ + O₂ → ≡Sm²⁺ + O₂^●−

(36)

5. Assessment of the Change in Toxicity of Treated Pharmaceutical Solutions

The reuse of treated pharmaceutical wastewater is an important challenge, at least for agricultural purposes. Apart from the knowledge of the degradation/mineralization performance of PF, PC/PF, and SPF, the change in toxicity of the resulting treated solutions is another crucial factor to confirm or exclude their reuse.

Several articles have reported the theoretically calculated relative toxicities of the primary by-products of different drugs, detected by LC-MS or GC-MS, as a first step toward predicting the evolution of solution toxicity during treatment. The most used predictive model has been the Ecological Structure Activity Relationship (ECOSAR), which is based on the estimation of the acute and chronic toxicity of each by-product by means of bioindicators such as fish, daphnid, and green algae, and their subsequent classification within four toxic groups, considering that it can be highly toxic, toxic, harmful, or not harmful. This procedure has been applied to the following homogeneous PF of rosuvastatin with UVC light [13]; heterogeneous PF of acetaminophen with FeOCl catalyst and UVC light [61]; heterogeneous PF-like of caffeine with peracetic acid, MnFe₂O₄ catalyst, and VUV light [32]; PC/PF treatment of rifampicin with biochar/Co₂VO₄ photocatalyst and Vis-tungsten lamp [132]; and a mixture of bromoxynil and cefixime with Fe₃O₄/NiCu₂S₄ QDs photocatalyst and Vis-halogen lamp [133]. On the other hand, Wu et al. [74] used the Toxicity Estimation Software Tool (T.E.S.T) through the Quantitative Structure–Activity Relationship (QSAR) method to predict the acute toxicity, developmental toxicity, and mutagenicity of tetracycline and its by-products by heterogeneous PF-like with biochar/Fe₂O₃ catalyst, oxalic acid, and Vis from Xe light. Another study by Alanis et al. [107] focused on assessing the loss of human carcinogenic and non-carcinogenic toxicity and freshwater ecotoxicity using the USEtox model for the PC/PF process of acetaminophen with a Cu/Fe-PILC photocatalyst and UVC.

Other works have determined changes in the toxicity of treated pharmaceutical solutions directly using animal or plant (i.e., phytotoxicity) bioindicators. Conte et al. [7] exposed the planktonic crustacean Daphnia magna individuals during 24 h to 100 mg L⁻¹ diclofenac in pure water at pH = 6.5 treated by homogeneous PF with 1 eq H₂O₂ and 45 mg L⁻¹ Fe²⁺ at pH = 6.5 in a stirred-tank photoreactor under 80 W Vis-LED or 125/250 W UVA light during 330 min that yielded 88% and 74% degradation, respectively (see Table 1). Figure 20a shows 100% survival of the crustacean using PF with UVA light, which is the same value as in pure water, indicating the complete removal of all toxic intermediates. In contrast, only 20% survival was obtained with the initial drug solution, which increased to 68% under UVA light, but decreased to 16% with PF under Vis-LED light. This means a large accumulation of more toxic PF intermediates with Vis-LED, which disappeared in the most favorable PF-UVA treatment, even yielding lower degradation. Noticeably, negative results were also reported by Andrade de Lucena [14] for a mixture of lamivudine and zidovudine at 15 mg L⁻¹ of each drug in pure water at pH = 2.0–3.0 after 60 min of homogeneous PF treatment with 600 mg L⁻¹ H₂O₂ and/or 0.5 mg L⁻¹ Fe²⁺ under 96 W UVC, with 82% degradation (see Table 1). Figure 20b illustrates an 80–89% percent germination index (GI) for seeds of Lactuca sativa (lettuce), Daucus carota (carrot), and Solanum lycopersicum (tomato) when they were fed with the initial drug solution. In contrast, phytotoxicity decreased dramatically under UVC/H₂O₂ and PF-UVA treatments, as expected due to the formation of more toxic by-products. However, in most cases, a reduction in toxicity was observed. As an example, Figure 20c,d depict a very low toxicity unit (TU) for the crustacean Artemia salina and Lactuca sativa, respectively, in a mixture of diclofenac and ketoprofen at 12.5 mg L⁻¹ of each drug in WWTP effluent at pH = 3.0 treated by homogeneous PF with 10 mg L⁻¹ H₂O₂ and 15 mg L⁻¹ Fe²⁺ under 81 W UVA light for 120 min [15]. This procedure demonstrated much greater detoxification power than UVA, UVA/H₂O₂, and Fenton (without light), even from a highly toxic initial wastewater. Similar positive detoxification results have been described for the homogeneous PF of doxycycline with Fe²⁺ and sunlight [8], homogeneous PF-like of caffeine with Fe(III)-EDDS catalyst and sunlight [20], heterogenous PF of metronidazole with activated carbon/CuCOFe₂O₄ and UV-mercury lamp [67], PC/PF of furazolidone with g-C₃N₄/MnFe₂O₄ catalyst and Vis-halogen lamp [119], and ciprofloxacin with TiO₂/Zn-ferrite and sunlight [124].

6. Challenges and Future Perspectives

Homogeneous PF and PF-like processes are well-established methods for drug remediation that can be replaced by heterogeneous processes to operate at neutral pH and to reuse catalysts. While drugs are rapidly oxidized in solution bulk under homogeneous conditions, heterogeneous conditions limit drug destruction to the catalyst surface, resulting in slower degradation/mineralization in most cases. The main drawback of the latter processes is the instability of most catalysts due to leaching of their toxic metallic components and by-product adsorption, which decreases the number of active centers and, hence, their oxidation power. The excellent performance when using non-ferrous catalysts like MgO/5% Cu and MnFe₂O₄ opens the door to more in-depth investigations of this kind of material in the near future. Stable, reusable, and powerful iron and non-ferrous catalysts should therefore be sought to enhance drug degradation/mineralization performance. The same challenges can be envisaged for the photocatalysts used in PC/PF. The best options seem to be the development of stable MOFs and g-C₃N₄ composites, along with non-ferrous photocatalysts, all of which can be photoexcited by sunlight to decrease operating costs and make the process more industrially relevant. Most of the PF and PC/PF studies have been performed at bench scale and should be extended to at least a pilot flow plant to demonstrate their applicability at an industrial scale. This should be tested on real wastewater to clearly demonstrate that the resulting water is low in toxicity and can be reused, at least for agricultural purposes. A recent work over the comparative degradation of the pharmaceutical meloxicam has shown a similar degradation rate for PC with TiO₂/H₂O₂ and homogeneous PF with H₂O₂/Fe²⁺ under UV/Vis LED irradiation, although the former yielded greater mineralization and was more cost-effective [140]. The hybrid PC/PF is then expected to improve the performance of both individual treatments. In contrast, the use of SPC is much more expensive due to the much higher energy cost of the applied US.

Apart from the above innovative recommendations, the following general developments are proposed for the near future:

(i): Techno-economic analysis should be carried out for the heterogeneous PF and PC/PF treatments proposed to demonstrate their practical interest for drug destruction under synthetic and real wastewater conditions, and to benchmark whether their applicability can be feasible with respect to other available methods for industrial application.
(ii): The research should be initially performed at a small bench scale with drugs in synthetic solutions to know the oxidants produced and their oxidation ability, along with the by-products formed. New and efficient catalysts and photocatalysts should be synthesized for further checking of heterogeneous PF and PC/PF processes to ensure their stability and reusability, as key factors affecting the cost and maintenance of such methods. The treatment of real wastewaters, including natural waters and WWTP effluents contaminated with drugs, should also be assessed to determine, as a first approach, the optimal operating variables for industrial-scale applications. The detoxification of the process should be well-identified to design sequential processes, usually with biological post-treatment, for reuse as irrigation water.
(iii): Efficient pilot flow plants need to be constructed to be further scaled at the industrial level. Solar pilot flow plants to apply heterogeneous PF and PC/PF processes for drug remediation are recommended. It is interesting to note the need to illuminate solar pilot flow plants with UV or Xe lamps in the absence of sunlight to keep them working all day. In this way, cost-effective systems can be built by coupling photovoltaic cells to accumulate sufficient electrical energy in batteries to supply power not only to UV or Xe lamps but also to the flow systems. Solar photo-assisted procedures are expected to accelerate the degradation/mineralization of synthetic and real drug effluents by generating higher levels of oxidizing agents through additional photolysis of by-products.

7. Conclusions

The reviewed studies confirm that photo-Fenton and hybrid photo-Fenton processes represent highly promising advanced oxidation technologies for mitigating pharmaceutical contaminants in aquatic environments, contributing to improved water-quality protection and safer wastewater reuse strategies. Their relevance within modern water treatment frameworks lies in their ability to transform persistent micropollutants that are insufficiently removed by conventional biological treatment systems.

Although rapid degradation of pharmaceutical compounds is commonly achieved through hydroxyl radical-driven oxidation, the overall efficiency of these processes in water treatment applications is governed by mineralization performance, transformation product evolution, and process robustness under realistic water matrices. The presence of natural organic matter and inorganic constituents in wastewater effluents remains a critical factor limiting oxidation efficiency and must therefore be considered in process design and optimization.

From a water engineering perspective, conventional homogeneous photo-Fenton systems provide high reaction kinetics but require acidic conditions and generate iron sludge, restricting their direct implementation in full-scale water treatment facilities. In contrast, iron-complexed systems and heterogeneous catalysts enable operation at near-neutral pH, representing a significant step toward integration into existing wastewater treatment plants and decentralized water reclamation schemes.

Hybrid configurations combining photocatalysis/photo-Fenton or sono-photo-Fenton processes enhance oxidant utilization and improve contaminant removal efficiency by synergistically generating reactive oxygen species. However, their practical deployment depends strongly on catalyst stability, resistance to deactivation, and long-term operational performance in continuous-flow systems treating real effluents.

Current evidence indicates that future progress should move beyond laboratory-scale degradation studies toward water-treatment-oriented evaluation, including pilot-scale validation, continuous solar-driven operation, and comprehensive techno-economic and life-cycle assessments. Particular attention should be given to integrating the process with biological post-treatment, enabling reduced toxicity and facilitating the reuse of treated water for agricultural or environmental applications.

Overall, hybrid photo-Fenton technologies have strong potential to become sustainable polishing or tertiary treatment solutions for emerging contaminants in water and wastewater systems. Advancing catalyst durability, improving mineralization efficiency, and demonstrating scalable operation under realistic conditions will be decisive steps toward their implementation in sustainable water management and circular water reuse strategies. The homogeneous PF has the advantages of providing fast degradation with slower mineralization of antibiotics and other organics by means of a simple and cheap procedure that can be potentiated with sunlight irradiation. It presents as disadvantages the limitation to pH = 3.0, the precipitation of iron hydroxide sludge, and the inhibition by some electrolytes. The heterogeneous PF and hybrid PC/PF seem more applicable because they can work at neutral pH without soluble iron, yielding good degradation/mineralization performance of pollutants, and thus outperforming the homogeneous PF limitations. The instability of the catalysts in heterogeneous PF and photocatalysts in PC/PF leach their components or adsorb by-products, with a progressive decay in performance due to prolonged treatments, which are their main disadvantages. Although SPF also improves the oxidation performance, it presents great limitations due to its application to small effluent volumes with a very high energy cost, making the process rather non-viable in practice.

Author Contributions

E.B. (writing, data analysis, review, and editing), J.M.P.-H. (writing—review and editing). All authors have read and agreed to the published version of the manuscript.

Funding

This work is supported by the CONAHCYT National Laboratory for Water Science and Technology (LNCyTA), number 101, as the National Laboratory for CONAHCYT, Grant LN-2025-I-16, and CIIC-UG-188/2026.

Data Availability Statement

This article is a review study. No new experimental data were generated or analyzed.

Acknowledgments

The authors would like to thank the University of Guanajuato for funding this research and Laboratorio Nacional UG-UAA-CONHACyT, LABORATORIO NACIONAL CONACYT DE CIENCIA Y TECNOLOGÍA DEL AGUA (LNCyTA), number 101, as Laboratorio Nacional Conahcyt, Grant LN-2025-I-16 and CIIC-UG grant 188/2026.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Sketches of photo-Fenton (PF) photoreactors. (a) Stirred-tank with external UV light (adapted from ref. [33]). (b) Flow system with external UV light (adapted from ref. [27]). (c) Stirred-tank with inner UV light (adapted from ref. [30]). (d) Stirred-tank with inner UV light and thermostatic bath (adapted from ref. [34]). (e) Recirculation system with inner UV-Vis light (adapted from ref. [19]).

Figure 2. (a) Sketch of a 4 L pilot flow plant with a solar compound parabolic collector (CPC) photoreactor for the homogeneous PF process of 0.6 mM doxycycline in pure water with 4 mM H₂O₂ and 0.1 mM Fe²⁺ at pH = 3.0, room temperature, and liquid flow rate = 30.6 L min⁻¹. Effect of (b) Fe²⁺ concentration with (c) pseudo-first-order kinetic analysis, (d) H₂O₂ dosage, and (e) drug content over the normalized drug concentration decay in the above process. Adapted from ref. [8].

Figure 3. (a) Normalized drug concentration vs. time for the homogeneous PF in stirred-tank photoreactors of (◆) 200 mL of 1 mg L⁻¹ carbamazepine in pure water using 0.75 mg L⁻¹ H₂O₂ and 0.15 mg L⁻¹ Fe² at pH = 3.0 and 35 °C using 1500 W Xe light (adapted from ref. [9]). (▼) 250 mL of 0.1 mM oxytetracycline in pure water with 100 mg L⁻¹ H₂O₂ and 3 mg L⁻¹ Fe²⁺ at pH = 3.0 and room temperature under 18 W UVA light (adapted from ref. [12]). (▲) 1 L of 50 mg L⁻¹ sulfamethoxazole in pure water with 2 mM H₂O₂ and 5 mg L⁻¹ Fe²⁺ at pH = 3.0 and 30 °C under a 150 W UV-Vis lamp (adapted from ref. [11]). (b) Proposed reaction sequence for carbamazepine degradation by homogeneous PF, including detected and proposed intermediates (adapted from ref. [6]).

Figure 4. Percentage of drug removal in front of time for the homogeneous PF process of 500 mL of a mixture of 25 mg L⁻¹ of each drug in pure water with 0.24 mL L⁻¹ of concentrated H₂O₂ and 20 times lower for Fe²⁺ at pH = 3.0 and 20 °C using a stirred-tank reactor under 15 W UVC. Adapted from ref. [16].

Figure 5. Degradation using 16 L and 90 L raceway pond photoreactors for homogeneous PF-like treatments. Time course of normalized drug concentrations of (a) 100 μg L⁻¹ of each drug in WWTP effluent with initial TOC of 15.5 mg C L⁻¹ with 50 mg L⁻¹ H₂O₂, 0.1 mM Fe³⁺, and 0.1 mM EDDS at pH = 7.6, room temperature, and irradiated with sunlight (adapted from ref. [20]), and (b) 100 μg L⁻¹ of benzotriazole in natural water with initial TOC of 3.1 mg C L⁻¹ and WWTP effluent of initial TOC of 25 mg C L⁻¹ with 40 mg L⁻¹ H₂O₂, 6 mg L⁻¹ Fe³⁺, and 12 mg L⁻¹ citric acid at pH = 6.3 and room temperature with several photoreactors under a 30 W cm⁻² Xe lamp. Adapted from ref. [22].

Figure 6. (a) Proposed mechanism for the production of oxidants in the heterogeneous PF process of 250 mL of 30 μM acetaminophen in pure water with 1 g L⁻¹ pyrite catalyst and 0.6 mM citric acid at pH = 6.0 and 25 °C under 70 W Xe light (adapted from ref. [25]). (b) Effect of specific scavengers on the normalized acetaminophen decay by heterogeneous PF of 150 mL of 100 mg L⁻¹ drug in pure water with 2.40 mM H₂O₂ and 100 mg L⁻¹ FeOCl catalyst at pH = 7.0 and 25 °C in a stirred-tank photoreactor with 18 W VUV light. EPR spectra recorded for (c) DMPO-^●OH, (d) DMPO-O₂^●−, and (e) TEMP-¹O₂ in the above system without drug (adapted from ref. [62]).

Figure 7. Variation in the normalized carbamazepine content with time for the heterogeneous PF treatment of 10 μM drug with 8 mM H₂O₂ and 0.2 cm of membrane/FeOCl catalyst using the system of Figure 1b at liquid flow rate = 2 mL min⁻¹ under 16 mW cm⁻² UVC light. Phosphate-buffered saline (PBS) at pH 6.0 and 9.0, fresh synthetic urine at pH 6, and hydrolyzed urine at pH 9 were used as reaction media. Adapted from ref. [27].

Figure 8. Effect of (a) H₂O₂/Fe concentration molar ratio, (b) Fe content, and (c) pH over the percentage of drug removal after 30 min of heterogeneous PF process of 500 mL of a mixture with 2 μg L⁻¹ of each drug in natural water with 0.2 mM H₂O₂ and 0.4 mM ZVI (22.4 mg L⁻¹) catalyst at pH = 3.0 and 25 °C using a stirred-tank reactor under 11 W UVC. Adapted from ref. [30].

Figure 9. (a) Proposed mechanism for the production of oxidants by heterogeneous PF-like of tetracycline with H₂O₂ and MgO/5%Cu catalyst under 350 W Xe light. (b) Proposed reaction sequence for tetracycline mineralization in such a process. Adapted from ref. [31].

Figure 10. (a) Effect of 1 mM MeOH and 0.8 mM TBA as specific scavengers on the percent of caffeine removal after 8 min of heterogeneous PF-like of 0.5 mg L⁻¹ drug in pure water with 2 mM peracetic acid and 250 mg L⁻¹ MnFe₂O₄ catalyst at pH = 7.0 and 25 °C using a stirred-tank photoreactor under a 4 W VUV lamp. (b) Proposed reaction sequence for caffeine degradation in the above process. Adapted from ref. [32].

Figure 11. Proposed mechanism for photocatalysis (PC)/PF processes of (a,b) acetaminophen (APAP) and (c) phenazopyridin. (a) MIL-53(Fe) photocatalyst under 300 W Xe light (Vis) (adapted from ref. [79]). (b) CuS/MIL-101(Fe) photocatalyst under 300 W Xe light (adapted from ref. [80]). (c) g-C₃N₄/MIL-101(Fe) membrane photocatalyst under 100 W Vis-LED light (adapted from ref. [82]).

Figure 12. (a) Effect of 0.1 mM of specific scavengers over the percent of ciprofloxacin (CIP) removal after 120 min of PC/PF of 50 mL of 20 mg L⁻¹ drug in pure water with 4 mg L⁻¹ H₂O₂ and 100 mg L⁻¹ MIL-100(Fe) photocatalyst at pH = 6.4 and 25 °C, with 30 min of previous dark, using a stirred-tank photoreactor under 300 W Xe light (Vis) (control) (adapted from ref. [84]). (b) Normalized drug content vs. time for the PC/PF treatment of (◆) 20 mL of 10 mg L⁻¹ sulfamethylthiazole in pure water with 38.8 mM H₂O₂ and 5 g L⁻¹ MIL-100(Sc 0.58, Fe 0.42) photocatalyst at pH = 6.8 and 25 °C using a stirred-tank photoreactor under 300 W Xe light (adapted from ref. [86]), and (▼) 20 mL of 20 mg L⁻¹ sulfadimethoxine in pure water with 1.65 mM H₂O₂ and 1 g L⁻¹ g-C₃N₄/Cu photocatalyst at pH = 10.0 and room temperature using a stirred-tank photoreactor under 300 W Xe light. Adapted from ref. [88].

Figure 13. (a) Effect of pH on the percentage of CIP removal vs time for the PC/PF treatment of 100 mL of 10 mg L⁻¹ drug in pure water with 20 μL concentrated H₂O₂ and 10 mg L⁻¹ g-C₃N₄/MXene/CuO photocatalyst using a stirred-tank photoreactor under 400 W Vis-sodium lamp. (b) Proposed mechanism for this process. Adapted from ref. [87].

Figure 14. (a) Influence of the number of successive cycles on the change in normalized tetracycline (TC) concentration and TOC removal with time after 100 min of the PC/PF process of 50 mL of 25 mg L⁻¹ drug in pure water with 5 mM H₂O₂ and 1 g L⁻¹ g-C₃N₄/Fe₃O₄ photocatalyst at pH = 3.0 and 18 °C using a stirred-tank photoreactor under 500 W Xe light (Vis). (b) Effect of specific scavengers on the above treatment. (c) EPR spectra recorded for the DMPO-^●OH and DMPO-O₂^●− adducts in the above conditions without the drug and 50 mM DMPO. Adapted from ref. [89].

Figure 15. Proposed PC/PF mechanisms for the generation of oxidants for tetracycline (TC) removal. (a) g-C₃N₄/Fe₃O₄ photocatalyst under 500 W Xe light (Vis) (adapted from ref. [89]. (b) g-C₃N₄/CuO photocatalyst under 400 W Vis-Na lamp (adapted from ref. [90]). (c) g-C₃N₄/FeMoO₄ photocatalyst under 500 W Xe light (Vis) (adapted from ref. [91]).

Figure 16. (a) Effect of 5 successive cycles on the percentage of drug removal after 30 min of PC/PF treatment of 450 mL of a mixture of acetaminophen, ibuprofen, and ciprofloxacin at 20 mg L⁻¹ each in pure water with 1 mM H₂O₂ and 330 mg L⁻¹ SBA-15/Fe photocatalyst at pH = 7.0 and room temperature using a stirred-tank photoreactor under 400 W Xe light (Vis). (b) Proposed reaction mechanism for the generation of oxidants in the SBA-15/Fe photocatalyst. Adapted from ref. [97].

Figure 17. (a) Change in normalized drug concentration with time for the PC/PF process of 100 mL of a mixture of tetracycline, oxytetracycline, and chlortetracycline at 50 mg L⁻¹ each in pure water containing 40 mM H₂O₂ and 500 mg L⁻¹ MOF-Cu photocatalyst at natural pH and room temperature, filling a stirred-tank photoreactor under 300 W Xe light (Vis). The solution was maintained in the dark for 30 min before light application. (b) Proposed mechanism for the generation of oxidants in the MOF-Cu photocatalyst. Adapted from ref. [100].

Figure 18. (a) Scheme of the stirred-tank photoreactor used for the PF and SPF processes of 10 mg L⁻¹ oxytetracycline in pure water with 60 mg L⁻¹ H₂O₂ and 8 mg L⁻¹ Fe²⁺ or ZVI catalyst at pH = 4.0 and room temperature under UVA, UVB, or UVC light and 40 kHz US. (b) Percentage of drug removal obtained after 60 min of the above treatments. Adapted from ref. [103].

Figure 19. (a) Scheme of the continuous-flow sono-photoreactor used for the sono-PF (SPF) of 5.5 mg L⁻¹ dexamethasone in pure water with 22.5 mg L⁻¹ H₂O₂ and packed zeolite/Fe catalyst under 5W UVA light and 140 kHz US at hydraulic retention time = 140 min. (b) Percent of drug removal for different processes. Adapted from ref. [104].

Figure 20. (a) Percentage of survival of the planktonic crustacean Daphnia magna individuals after 24 h of exposure to different solutions, including control in pure water. The initial drug solution consisted of 1 L of 100 mg L⁻¹ diclofenac in pure water at pH = 6.5 and was treated during 330 min with 1 eq H₂O₂ and 45 mg L⁻¹ Fe²⁺ in a stirred-tank photoreactor under 80 W Vis-LED or 125/250 W UVA light by homogeneous PF (adapted from ref. [7]). (b) Percentage of germination index (GI) for seeds of Lactuca sativa (lettuce), Daucus carota (carrot), and Solano lycopersicum (tomato) feed with a solution containing a mixture of lamivudine and zidovudine at 15 mg L⁻¹ each in pure water at pH = 2.0–3.0, before and after homogeneous PF treatment with 600 mg L⁻¹ H₂O₂ and/or 0.5 mg L⁻¹ Fe²⁺ under 96 W UVC lasting 60 min (adapted from ref. [14]). Toxicity unit determined for the bioindicators (c) crustacean Artemia salina and (d) Lactuca sativa before and after treatment with homogeneous PF with a mixture of ketoprofen and diclofenac at 12.5 mg L⁻¹ each in WWTP effluent at pH = 3.0 using 10 mg L⁻¹ H₂O₂ and 15 mg L⁻¹ Fe²⁺ under 81 W UVA light for 120 min (adapted from ref. [15]).

Table 1. Relevant results obtained for homogeneous and heterogeneous photo-Fenton (PF) and photo-Fenton-like treatments of pharmaceuticals in waters.

Pollutant	System	Experimental Remarks	Best Results	Ref.
Homogeneous PF
NSAIDs
Acetaminophen	Stirred-tank photoreactor, H₂O₂, Fe²⁺, 15 W UVC	100 mL of 1 mg L⁻¹ drug in WWTP effluent, 0–107 mM H₂O₂, 0–29 μM Fe²⁺, pH = 7.2, 25 °C, 20 min	Overall degradation in 8 min with 21 mM H₂O₂ and 2.4 μM Fe²⁺	[6]
Diclofenac	Stirred-tank photoreactor, H₂O₂, Fe²⁺, 80 W Vis-LED or 125/250 W UVA	1 L with Vis-LED and 250 mL with UVA. 100 mg L⁻¹ drug in pure water, 1 eq H₂O₂, 45 mg L⁻¹ Fe²⁺, pH = 6.5. Room temperature for 330 min	88% degradation for Vis-LED at 330 min and 78% degradation for UVA at 220 min	[7]
Antibiotics
Doxycycline	Pilot flow plant with solar CPC ^a photoreactor of Figure 2a, H₂O₂, Fe²⁺, sunlight	4 L of 0.06 mM drug in pure water, 4 mM H₂O₂, 0.1 mM Fe²⁺, pH = 3.0. Room temperature, liquid flow rate = 30.6 L min⁻¹, 180 min	95% removal with k₁ = 0.0142 min⁻¹. 81% and 73% of COD and TOC reductions	[8]
Carbamazepine	Stirred-tank photoreactor, H₂O₂, Fe²⁺, 1500 W Xe	200 mL of 1 mg L⁻¹ drug in pure water, 0.75 mg L⁻¹ H₂O₂, 0.15 mg L⁻¹ Fe²⁺, pH = 3.0. 35 °C, 30 min	93% decay with k₁ = 0.0422 min⁻¹ and 14% TOC removal. Detection of 5 by-products by LC-MS	[9]
Nitazoxanide	Stirred-tank photoreactor, H₂O₂, Fe²⁺, sunlight	1 L of 1.5 mg L⁻¹ drug in pure water and hospital wastewater, 55 mg L⁻¹ H₂O₂, 10 mg L⁻¹ Fe²⁺, pH = 2.8, room temperature, 105 min	Total degradation in 40 min for pure water and 105 min for hospital wastewater. Detection of 15 by-products by LC-QTOF-MS	[10]
Sulfamethoxazole	Stirred-tank photoreactor, H₂O₂, Fe²⁺, 150 W UV-Vis lamp (λ = 350–570 nm)	1 L of 50 mg L⁻¹ drug in pure water, 2 mM H₂O₂, 5 mg L⁻¹ Fe²⁺, pH = 3.0, 30 °C, 30 min	Complete removal with k₁ = 1.0379 min⁻¹ in 8 min. Release of SO₄²⁻ and NO₃⁻	[11]
Oxytetracycline	Stirred-tank photoreactor, H₂O₂, Fe²⁺, 18 W UVA	250 mL of 0.1 mM drug in pure water and WWTP effluent, 100 mg L⁻¹ H₂O₂, 3 mg L⁻¹ Fe²⁺, pH = 3.0, room temperature, 30 min	97% abatement with k₁ = 0.81 min⁻¹ in 10 min for pure water and 95% decay with k₁ = 0.59 min⁻¹ in 15 min for WWTP effluent. 68% and 75% TOC reduction, respectively. Evolution of ^●OH concentration	[12]
Other drugs
Rosuvastatin	Stirred-tank photoreactor, H₂O₂, Fe²⁺, 35 W UVC	20 mg L⁻¹ drug in pure water, 0.3 mM H₂O₂, 0.1 mg L⁻¹ Fe²⁺_, pH = 3.0, room temperature, 120 min	Total degradation with k₁ = 0.1764 min⁻¹ in 15 min and 79% TOC removal in 120 min. Total cost = 13.0678 US$ m⁻³	[13]
Mixture of drugs
Lamivudine, Zidovudine	Stirred-tank photoreactor, H₂O₂, Fe²⁺, 96 W UVC, 20 W UVA, 300 W Xe	50 mL of 15 mg L⁻¹ of each drug in pure water, 600 mg L⁻¹ H₂O₂, 0.5 mg L⁻¹ Fe²⁺, pH = 2.0–3.0, room temperature, 60 min	82% degradation of the mixture with UVC with k₁ = 0.035 min⁻¹ > 65% with k₁ = 0.016 min⁻¹ for photolysis	[14]
Diclofenac, Ketoprofen	Stirred-tank photoreactor, H₂O₂, Fe²⁺, 81 W UVA	600 mL of 12.5 mg L⁻¹ of each drug in domestic sewage, 10–30 mg L⁻¹ H₂O₂, 3–15 mg L⁻¹ Fe²⁺, pH = 3.0, 23 °C, 150 min	Optimization by response surface methodology = 78% COD and 62% BOD removals for 10 mg L⁻¹ H₂O₂, and 15 mg L⁻¹ Fe²⁺, for Fenton, 65% and 60%, respectively	[15]
Carbamazepine, Diclofenac, Ibuprofen, Sulfamethoxazole	Stirred-tank photoreactor, H₂O₂, Fe²⁺, 15 W UVC	500 mL of 25 mg L⁻¹ of each drug in pure water, 0,24 mL L⁻¹ of concentrated H₂O₂, 20 times lower for Fe²⁺, pH = 3.0, 20 °C, 60 min	More than 90% degradation of all drugs	[16]
Diclofenac, Ranitidine, Simvastatin	Stirred-tank photoreactor, H₂O₂, Fe³⁺, 56 W UVA	1.654 L of 50 μg L⁻¹ of each drug in domestic sewage (TOC₀ = 21 mg C L⁻¹), 40 mg L⁻¹ H₂O₂, 3 mg L⁻¹ Fe³⁺, pH = 7.2, room temperature, 10 min	Degradation = 97% simvastatin < 100% for diclofenac and ranitidine. 72% mineralization	[17]
Real wastewaters
Pharmaceutical wastewater	Stirred-tank photoreactor, H₂O₂, Fe²⁺, 80 W Xe	1 L of wastewater (COD₀ = 4000 mg O₂ L⁻¹), 1:10 Fe²⁺/H₂O₂, pH = 4.0, 35 °C, 60 min	88% COD reduction	[18]
Homogeneous PF-like
Antibiotics
Amoxicillin	Figure 1e, sodium percarbonate, Fe³⁺, UV-Vis (λ = 200–500 nm)	3.6 L of 100 mg L⁻¹ drug in pure water, 1.470 mM min⁻¹ H₂O₂, 1.560 mM Fe³⁺, pH = 3.0, 35 °C, 120 min	Optimization by response surface methodology yielding 90% TOC removal	[19]
Mixture of drugs
Caffeine, Carbamazepine, Diclofenac, Sulfamethoxazole, Trimethoprim	Raceway pond photoreactor of Figure 5a, H₂O₂, Fe(III)-EDDS ^b, sunlight	100 μg L⁻¹ of each drug in WWTP effluent (TOC₀ = 15,5 mg C L⁻¹), 50 mg L⁻¹ H₂O₂, 0.1 mM Fe³⁺, 0.1 mM EDDS, pH = 7.6, room temperature, 60 min	Degradation = 87% for caffeine <92% for sulfamethoxazole and carbamazepine <97% for trimethoprim <100% at 45 min for diclofenac	[20]
Diclofenac, Ibuprofen	Stirred-tank photoreactor, H₂O₂, Fe(III)-EDDS, Fe(III)-NTA ^c, 32 W fluorescent bulb	500 mL of 200 μg L⁻¹ of each drug in WWTP effluent (TOC₀ = 2.5 mg C L⁻¹), 1.47 mM H₂O₂, 0.1 mM Fe³⁺, 0.1 mM EDDS, 0.1 mM NTA, pH = 6.3, room temperature, 360 min	Degradation = 90% and 48% for diclofenac, and 95% and 47% for ibuprofen using Fe(III)-EDDS and Fe(III)-NTA. Detection of 2 and 1 by-products for diclofenac and ibuprofen, respectively	[21]
Benzotriazole, Carbamazepine, Diclofenac	Raceway pond photoreactors of Figure 5a,b, H₂O₂, Fe(III)-citrate, 30 W cm⁻² Xe (λ > 290 nm)	100 μg L⁻¹ of each drug in WWTP effluent (TOC₀ = 25 mg C L⁻¹), 40 mg L⁻¹ H₂O₂, 6 mg L⁻¹ Fe³⁺, 12 mg L⁻¹ citric acid, pH = 6.3, room temperature, 45 min	About 25% removal for benzotriazole and carbamazepine <60% for diclofenac with WWTP effluent	[22]
Carbamazepine, Diclofenac, Naproxen, Sulfamethoxazole, Trimethoprim	Stirred-tank photoreactor, peracetic acid, Fe²⁺. 9 W UVA	200 mL of 1 μM of each drug in pure water, 25 μM peracetic acid, 2.5 μM Fe³⁺, pH = 4.0, 25 °C, 15 min	Degradation = 30% for sulfamethoxazole <45% for carbamazepine <62% for trimethoprim, and <100% for naproxen and diclofenac. Corresponding k₁-values = 0.02, 0.04, 0.06, 0.30, and 0.36 min⁻¹. Fe^IVO²⁺ and ^●OH as oxidants detected by specific scavengers	[23]
Real wastewaters
WWTP effluent	Stirred-tank photoreactor, H₂O₂, Fe³⁺. humic acid, 32 W fluorescent bulb	250 mL of WWTP effluent (TOC₀ = 82.1 mg C L⁻¹), 100 mg L⁻¹ H₂O₂, 1:6.8 Fe³⁺/humic acid, pH = 7.4, room temperature, 30 min	Removal of between 8.5% and 56% of all drugs. 31% TOC reduction	[24]
Heterogeneous PF
NSAIDs
Acetaminophen	Stirred-tank photoreactor, H₂O₂ generated, pyrite catalyst, citric acid, 70 W Xe (λ > 350 nm)	250 mL of 30 μM drug in pure water, 1 g L⁻¹ pyrite, 0.6 mM citric acid, pH = 6.0. 25 °C, 30 min	Total drug removal, 27 μM of Fe released and 75% citric acid destroyed. ^●OH as oxidant detected by specific scavengers. Moderate reusability, losing 18% degradation after 4 consecutive cycles	[25]
Acetaminophen	Stirred-tank photoreactor, H₂O₂, chitosan/Fe₃O₄ catalyst, 15 W UVC	100 mL of 5–100 mg L⁻¹ drug in pure water, 50–400 mg L⁻¹ H₂O₂, 5–100 mg L⁻¹ catalyst, pH = 2.0–6.0. 26–60 °C, 60 min	95% abatement for 10 mg L⁻¹ drug, 200 mg L⁻¹ H₂O₂, 20 mg L⁻¹ catalyst, pH = 2.0, and 26 °C. E_a = 36.3 kJ mol⁻¹. Moderate reusability, losing 20% degradation after 4 consecutive cycles	[26]
Antibiotics
Carbamazepine	Figure 1b, H₂O₂. ceramic membrane/FeOCl catalyst, 1.6 mW cm⁻² UVC	10 μM drug in fresh synthetic urine (pH = 6) and hydrolyzed urine (pH = 9), 8 mM H₂O₂, 0.2 cm of membrane, room temperature, liquid flow rate = 2 mL min⁻¹	Total removal after 360 min in both matrices. ^●OH as oxidant	[27]
Imidacloprid	Stirred-tank photoreactor, H₂O₂. ZVI catalyst, sunlight	2 L of 1 mg L⁻¹ drug in natural water, 3 mM H₂O₂, 55.8 mg L⁻¹ catalyst, pH = 7.4, room temperature, 180 min	86% degradation with k₁ = 0.0110 min⁻¹	[28]
Sulfamethazine	Stirred-tank photoreactor, H₂O₂. perylene diimide/Fe catalyst, 100 W halogen lamp	200 mL of 10 mg L⁻¹ drug in pure water, 5–10 mM H₂O₂, 0.1–1 mg L⁻¹ catalyst, pH = 3.0–7.0, 25 °C, 120 min	Optimization by response surface methodology = 92% abatement for 6.46 mM H₂O₂, 0.45 mg L⁻¹ catalyst, and pH = 3.0. 1.344 mg L⁻¹ Fe leached. ^●OH as oxidant detected by specific scavengers	[29]
Mixture of drugs
Acetaminophen, Caffeine, Diethyltoluamide, Triclosan	Stirred-tank photoreactor, H₂O₂, ZVI catalyst, 11 W UVC	500 mL of 2 μg L⁻¹ of each drug in natural water, 0.2 mM H₂O₂, 0.4 mM catalyst, pH = 3.0, 25 °C, 30 min	Removal at pH = 3.0 = 98% for acetaminophen >86% for triclosan >70% for diethyltoluamide, and >65% for caffeine. 19% TOC reduction	[30]
Heterogeneous PF-like
Tetracycline	Stirred-tank photoreactor, H₂O₂, MgO/5% Cu catalyst, 350 W Xe	100 mL of 25 mg L⁻¹ drug in pure water, 60 mM H₂O₂, 500 mg L⁻¹ catalyst, natural pH, 25 °C, 125 min	Total removal in 5 min. Release of 40.7 mg L⁻¹ of Mg²⁺, Detection of oxidants ^●OH and O₂^●− by specific scavengers, Identification of 16 by-products by LC-MS	[31]
Caffeine	Stirred-tank photoreactor, peracetic acid, MnFe₂O₄ catalyst, 4 W VUV lamp (λ = 185 nm)	0.5 mg L⁻¹ drug in pure water, 2 mM peracetic acid, 250 mg L⁻¹ catalyst, pH = 7.0, 25 °C, 20 min	88% abatement with k₁ = 0.243 min⁻¹ in 8 min. Detection of oxidants ^●OH and CH₃CO₃^● by specific scavengers and EPR. 7 by-products identified by LC-MS. Moderate reusability with a loss of 10% degradation after 5 successive runs	[32]

Table 2. Relevant results reported for hybrid photocatalysis/photo-Fenton (PC/PF) and sono-photo-Fenton (SPF) treatments of pharmaceuticals in waters.

Pollutant	System	Experimental Remarks	Best Results	Ref.
PC/PF
NSAIDs
Acetaminophen	Stirred-tank photoreactor, H₂O₂, MIL-53(Fe) photocatalyst, 300 W Xe (λ > 400 nm)	100 mL of 20 mg L⁻¹ drug in pure water, 3–10 mM H₂O₂, 100 mg L⁻¹ photocatalyst, pH = 7.0. 25 °C, 60 min	96% removal with k₁ = 0.085 min⁻¹ for 7 mM H₂O₂. Leaching of 1.3 mg L⁻¹ Fe, and detection of ^●OH and O₂^●− as oxidants by specific scavengers and EPR; 8 by-products identified by GC-MS. Good reusability, losing 4% degradation after four consecutive cycles	[79]
Acetaminophen	Stirred-tank photoreactor, H₂O₂, CuS/MIL-101(Fe) photocatalyst, 300 W Xe	100 mL of 5 mg L⁻¹ drug in pure water, 10 mM H₂O₂, 100 mg L⁻¹ photocatalyst, pH = 3.0–11.0. 25 °C, 30 min	Complete abatement with k₁ = 0.2099 min⁻¹ at pH = 5.0. ^●OH, O₂^●−, and ¹O₂ as oxidants detected by specific scavengers and EPR, with seven by-products identified by LC-MS. Moderate reusability with a loss of 10% degradation after five successive runs	[80]
Acetaminophen	Stirred-tank photoreactor, H₂O₂, Fe-BiOBr photocatalyst, sunlight	100 mL of 15 mg L⁻¹ drug in pure water, 10 mM H₂O₂, 250 mg L⁻¹ photocatalyst, pH = 3.0, room temperature, 240 min	Overall degradation and 58% TOC removal. ^●OH and O₂^●− as oxidants detected by specific scavengers	[81]
Phenazopyridine	Stirred-tank photoreactor, H₂O₂, g-C₃N₄/MIL-101(Fe) membrane photocatalyst, 100 W Vis-LED	60 mL of 15 mg L⁻¹ drug in pure water, 60 μM concentrated H₂O₂, 250 mg L⁻¹ photocatalyst, pH = 6.5, room temperature, 70 min	97% removal. Detection of ^●OH and O₂^●− as oxidants detected by specific scavengers. Identification of 10 by-products by LC-MS. Good reusability with a loss of 8% degradation after five successive steps	[82]
Antibiotics
Norfloxacin	Stirred-tank photoreactor, H₂O₂, Fe₂O₃/Pt/TiO₂ photocatalyst, 300 W fluorescent lamp	20 mL of 4 mg L⁻¹ drug in pure water, 50 mM H₂O₂, 50 mM Na₂SO₄, 1 cm⁻² photocatalyst, pH = 6.7, 25 °C, 30 min of previous dark, 120 min	88% removal. ^●OH and O₂^●− as oxidants. Moderate reusability, losing 10% degradation after five successive steps	[83]
Ciprofloxacin	Stirred-tank photoreactor, H₂O₂, MIL-100(Fe) photocatalyst, 300 W Xe (λ > 420 nm)	50 mL of 20 mg L⁻¹ drug in pure water, 4 mg L⁻¹ H₂O₂, 100 mg L⁻¹ photocatalyst, pH = 6.4, 25 °C, 30 min of previous dark, 120 min	94% degradation and 68% TOC reduction. ^●OH as the main oxidant detected by specific scavengers and EPR. Moderate reusability with a loss of 10% degradation after five consecutive cycles	[84]
Sulfadimethoxine	Stirred-tank photoreactor, H₂O₂, MIL-53(Fe) photocatalyst, 300 W Xe (λ > 400 nm)	30 mL of 20 mg L⁻¹ drug in pure water, 20 μL concentrated H₂O₂, 165 mg L⁻¹ photocatalyst, pH = 7.0, 25 °C, 60 min of previous dark, 50 min	Complete abatement. ^●OH, O₂^●−, ¹O₂, and holes detected as oxidants by specific scavengers and EPR. Identification of 7 by-products by LC-QTOF-MS. Moderate reusability, losing 10% degradation after 4 consecutive runs	[85]
Sulfamethylthiazole	Stirred-tank photoreactor, H₂O₂, MIL-100(Fe) photocatalyst, 300 W Xe	20 mL of 10 mg L⁻¹ drug in pure water, 38.8 mM H₂O₂, 5 g L⁻¹ photocatalyst, pH = 6.8, 25 °C, 100 min	98% decay with k₁ = 0.0315 min⁻¹. ^●OH, O₂^●−, and ¹O₂ detected as oxidants by EPR. Identification of 14 by-products by LC-MS. Good reusability with a loss of 8% degradation after three successive runs	[86]
Ciprofloxacin	Stirred-tank photoreactor, H₂O₂, g-C₃N₄/MXene/CuO photocatalyst, 400 W sodium lamp (λ > 400 nm)	100 mL of 5–30 mg L⁻¹ drug in pure water, 10–40 μL concentrated H₂O₂, 5–30 mg L⁻¹ photocatalyst, pH = 3.0–11.0, room temperature, 90 min	87% abatement with k₁ = 0.0178 min⁻¹ for 10 mg L⁻¹ drug. 20 μL concentrated H₂O₂, 10 mg L⁻¹ photocatalyst, and pH = 9.0. ^●OH, O₂^●−, and mainly holes detected as oxidants by specific scavengers. Good reusability, losing 7% degradation after four successive cycles	[87]
Sulfadimethoxine	Stirred-tank photoreactor, H₂O₂, g-C₃N₄/Cu photocatalyst, 300 W Xe	20 mL of 20 mg L⁻¹ drug in pure water, 1.65 mM H₂O₂, 1 g L⁻¹ photocatalyst, pH = 10.0, room temperature, 50 min	Overall decay. ^●OH, O₂^●−, and ¹O₂ detected as oxidants by specific scavengers and EPR	[88]
Tetracycline	Multi-test tube photoreactor, H₂O₂, g-C₃N₄/Fe₃O₄ photocatalyst, 500 W Xe (λ < 420 nm)	50 mL of 25 mg L⁻¹ drug in pure water, 5 mM H₂O₂, 1 g L⁻¹ photocatalyst, pH = 3.0, 18 °C, 100 min	Total degradation with k₁ = 0.03907 min⁻¹ and 67% TOC reduction. ^●OH and O₂^●− as oxidants detected by specific scavengers and EPR. Eight by-products identified by LC-MS. Good reusability, losing 9% degradation after five successive runs	[89]
Tetracycline	Stirred-tank photoreactor, H₂O₂, g-C₃N₄/CuO photocatalyst, 400 W Na lamp (λ > 400 nm)	100 mL of 5–40 mg L⁻¹ drug in pure water, 0.1–0.4 mL L⁻¹ H₂O₂, 25–300 mg L⁻¹ photocatalyst, pH = 3.0–11.0, room temperature, 15 min of previous dark, 15 min	Complete abatement with k₁ = 0.1242 min⁻¹ for 10 mg L⁻¹ drug, 0.3 mL L⁻¹ H₂O₂, 200 mg L⁻¹ photocatalyst, and pH = 9.0. Detection of oxidants ^●OH, O₂^●−, and holes by specific scavengers, and 11 by-products identified by LC-MS. Excellent reusability after four successive cycles	[90]
Tetracycline	Stirred-tank photoreactor, H₂O₂, g-C₃N₄/FeMoO₄ photocatalyst, 500 W Xe (λ > 420 nm)	100 mL of 31.2 mg L⁻¹ drug in pure water, 1.31 mM H₂O₂, 1.24 g L⁻¹ photocatalyst, pH = 7.0, 25 °C, 60 min of previous dark, 120 min	98% degradation determined by response surface technology. Detection of oxidants ^●OH, O₂^●−, and ¹O₂ by specific scavengers and EPR. Identification of 10 by-products by LC-MS. Moderate reusability with a loss of 10% degradation after 11 successive runs	[91]
Carbamazepine	Stirred-tank photoreactor, H₂O₂, BiVO₄/FeO_x photocatalyst, 300 W Xe (λ > 420 nm)	40 mL of 10 mg L⁻¹ drug in pure water, 0.6 mM H₂O, 500 mg L⁻¹ photocatalyst, natural pH, room temperature, 20 min	Total abatement with k₁ = 0.317 min⁻¹. ^●OH, O₂^●−, and holes detected as oxidants by specific scavengers and EPR. Moderate reusability with a loss of 15% degradation after three successive runs	[92]
Levofloxacin	Stirred-tank photoreactor, H₂O_2, Cu⁰/CuFe₂O₄ photocatalyst, 300 W Xe (λ > 420 nm)	50 mL of 10 mg L⁻¹ drug in pure water, 2–150 mM H₂O₂, 50–600 mg L⁻¹ photocatalyst, pH = 3.0–11.0, room temperature, 90 min	92% abatement with k₁ = 0.033 min⁻¹ for 10 mg L⁻¹ drug. 30 mM H₂O₂, 200 mg L⁻¹ photocatalyst, and pH = 6.7. ^●OH, O₂^●−, electrons, and holes detected as oxidants by specific scavengers and EPR. 10 intermediates identified by LC-MS. Excellent reusability after four consecutive cycles	[93]
Tetracycline	Stirred-tank photoreactor, FeWO₄/WO₃/FeOOH photocatalyst, oxalic acid, 100 W LED (λ = 420 nm)	50 mL of 50 mg L⁻¹ drug in pure water, 1 mM oxalic acid, 400 mg L⁻¹ photocatalyst, pH = 3.0, 25 °C, 30 min	Total drug removal with k₁ = 0.117 min⁻¹ and 72% oxalic acid decay. ^●OH, O₂^●−, ¹O₂, and holes as oxidants detected by specific scavengers and EPR. 17 by-products identified by LC-MS. Excellent reusability after six successive runs	[94]
Chloramphenicol	Stirred-tank photoreactor, H₂O₂, Zn_1-x-yCo_xNi_yO nanorods photocatalyst, 500 W halogen lamp	20 mL of 20 mg L⁻¹ drug in pure water, 0.1 mL concentrated H₂O₂, 50 mg L⁻¹ photocatalyst, pH = 7.0, room temperature, 450 min	88% removal. ^●OH and holes detected as oxidants by specific scavengers. GC-MS analysis revealed the formation of four by-products. Excellent reusability after six successive runs	[95]
Tetracycline	Stirred-tank photoreactor, H₂O₂, Ce-LaCoO₃ photocatalyst, 500 W Xe	100 mL of 10 mg L⁻¹ drug in pure water, 100 mM H₂O₂, 400 mg L⁻¹ photocatalyst, pH = 7.0, room temperature, 120 min	92% decay. ^●OH, O₂^●−, and holes as oxidants detected by specific scavengers and EPR. 13 by-products identified by LC-MS. Excellent reusability after five consecutive steps	[96]
Mixture of drugs
Acetaminophen, Ciprofloxacin, Ibuprofen	Stirred-tank photoreactor, H₂O₂, SBA-15/Fe photocatalyst, 400 W Xe (λ > 390 nm)	450 mL of 20 mg L⁻¹ of all drugs in pure water, 1 mM H₂O₂, 330 mg L⁻¹ photocatalyst, pH = 7.0, room temperature, 30 min	Degradation = 95% for ciprofloxacin, and >86% for ibuprofen and acetaminophen. Respective k₁-values = 0.0633, 0.0431, and 0.0194 min⁻¹. Detection of oxidants ^●OH and O₂^●− by specific scavengers. Excellent reusability after five consecutive runs	[97]
Carbamazepine, Diclofenac, Mecoprop, Sulfamethoxazole	Stirred-tank photoreactor, H₂O₂. rGO/FeS₂ photocatalyst, 300 W Xe	50 mL of 10 μg L⁻¹ of each drug in pure water, 1 mM H₂O₂, 250 mg L⁻¹ photocatalyst, pH = 7.4, room temperature, 10 min	Total degradation of all drugs. ^●OH, O₂^●−, ¹O₂, electrons, and holes identified as oxidants by EPR	[98]
Acetaminophen, Atenolol, Levofloxacin, Sulfamethoxazole	Stirred-tank photoreactor, H₂O₂, g-C₃N₄/Fe photocatalyst, 300 W Xe (λ > 400 nm)	50 mL of 10 mg L⁻¹ of each drug, except 5 mg L⁻¹ sulfamethoxazole, in pure water, 50 mM H₂O₂, 1 g L⁻¹ photocatalyst, pH = 7.46, room temperature, 60 min of previous dark, 60 min	Degradation = 100% at 20 min for levofloxacin, >92% for atenolol, >74% for sulfamethoxazole, and >63% for acetaminophen. Total TOC decay at 12 h. Detection of oxidants ^●OH, O₂^●−, ¹O₂, and holes by specific scavengers and EPR	[99]
Chlortetracycline, Tetracycline, Oxytetracycline	Stirred-tank photoreactor, H₂O₂, MOF-Cu photocatalyst, 300 W Xe (λ > 420 nm)	100 mL of 50 mg L⁻¹ of each drug in pure water, 40 mM H₂O₂, 500 mg L⁻¹ photocatalyst, natural pH, room temperature, 30 min of previous dark, 120 min	Degradation = 84% for chlortetracycline, >82% for oxytetracycline, and >79% for tetracycline. ^●OH, O₂^●−, and holes identified as oxidants by specific scavengers. Good reusability, losing up to 8% degradation after five consecutive runs	[100]
Real wastewaters
WWTP effluent	Stirred-tank photoreactor, H₂O₂, MOF-100(Fe) photocatalyst, 300 W Xe (λ > 420 nm)	40 mL of 24 pharmaceuticals at μg L⁻¹ in WWTP effluent (TOC₀ = 7.9 mg C L⁻¹), 20 mM H₂O₂, 100 mg L⁻¹ photocatalyst, pH = 7.2, 25 °C, 10 h	Complete removal of all drugs. Leaching of 0.3 mg L⁻¹ Fe. Oxidants ^●OH, O₂^●−, and ¹O₂ detected by specific scavengers and EPR	[101]
SPF
NSAIDs
Ibuprofen	Stirred-tank photoreactor/sono-reactor, H₂O₂, Fe²⁺, 6 W UVC or 150 W Xe, 20 kHz US	Circulation at 150 mL min⁻¹ between 500 mL in PF and 1 L in US, 1.5 L of 20 mg L⁻¹ drug in pure water, 1.6–22.4 mM H₂O₂, 0.134 mM Fe²⁺, pH = 2.6, 25 °C, 180 min	Overall degradation with k₁ = 0.0130 min⁻¹ in 60 min and 60% TOC decay in 180 min for 6.4 mM H₂O₂ and 150 W Xe. Detection of 12 by-products by LC-MS	[102]
Antibiotics
Oxytetracycline	Figure 18a, H₂O₂, Fe²⁺ or ZVI catalyst, UVA, UVB, or UVC, 40 kHz US	10 mg L⁻¹ drug in pure water, 60 mg L⁻¹ H₂O₂, 8 mg L⁻¹ Fe²⁺ or ZVI, pH = 4.0, room temperature, 60 min	Degradation with Fe²⁺ or ZVI = 86% or 87% for UVA, 90% or 89% for UVB, and 85% or 93% for UVC. 11 transformation products identified by GC-MS	[103]
Dexamethasone	Continuous-flow sono-photoreactor of Figure 19a, H₂O₂, zeolite/Fe catalyst, 5 W UVA (λ = 380–400 nm), 140 kHz US	1.2–9.7 mg L⁻¹ drug in pure water, 9.8–35.1 mg L⁻¹ H₂O₂, packed catalyst, pH = 7.0, 20 °C, hydraulic retention time = 39.5–140 min	Optimization by response surface methodology = 99% removal and 74% COD reduction for 5.5 mg L⁻¹ drug, 22.5 mg L⁻¹ H₂O₂, and hydraulic retention time = 140 min	[104]
Other drugs
Metoprolol	Stirred-tank sono-photoreactor, H₂O₂, MWCNTs ^a/Cr₂O₃-Sm photocatalyst, 350 W Xe, 20 kHz US	110 mL of 10 mg L⁻¹ drug in pure water, 50 mM H₂O₂, 300 mg L⁻¹ photocatalyst, pH = 7.0, 25 °C, 60 min	Complete degradation and 95% TOC removal. Detection of oxidants ^●OH, O₂^●−, ¹O₂, and holes by specific scavengers and EPR. Three by-products identified by GC-MS	[105]

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Brillas, E.; Peralta-Hernández, J.M. Advances in Hybrid Photo-Fenton Processes for Treating Pharmaceutical Contaminants in Water and Wastewater Systems. Water 2026, 18, 920. https://doi.org/10.3390/w18080920

AMA Style

Brillas E, Peralta-Hernández JM. Advances in Hybrid Photo-Fenton Processes for Treating Pharmaceutical Contaminants in Water and Wastewater Systems. Water. 2026; 18(8):920. https://doi.org/10.3390/w18080920

Chicago/Turabian Style

Brillas, Enric, and Juan M. Peralta-Hernández. 2026. "Advances in Hybrid Photo-Fenton Processes for Treating Pharmaceutical Contaminants in Water and Wastewater Systems" Water 18, no. 8: 920. https://doi.org/10.3390/w18080920

APA Style

Brillas, E., & Peralta-Hernández, J. M. (2026). Advances in Hybrid Photo-Fenton Processes for Treating Pharmaceutical Contaminants in Water and Wastewater Systems. Water, 18(8), 920. https://doi.org/10.3390/w18080920

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Advances in Hybrid Photo-Fenton Processes for Treating Pharmaceutical Contaminants in Water and Wastewater Systems

Abstract

1. Introduction

2. Photo-Fenton Treatment of Pharmaceuticals in Water and Wastewater

2.1. Homogeneous Photo-Fenton

2.1.1. NSAIDs

2.1.2. Antibiotics

2.1.3. Other Drugs

2.1.4. Mixture of Drugs

2.1.5. Real Wastewaters

2.2. Homogeneous Photo-Fenton-like

2.2.1. Single Drugs

2.2.2. Mixture of Drugs

2.2.3. Real Wastewaters

2.3. Heterogeneous Photo-Fenton

2.3.1. NSAIDs

2.3.2. Antibiotics

2.3.3. Mixture of Drugs

2.4. Heterogeneous Photo-Fenton-like

3. Photocatalysis/Photo-Fenton Treatment of Pharmaceuticals in Waters and Wastewaters

3.1. NSAIDs

3.2. Antibiotics

3.3. Mixture of Drugs

3.4. Real Wastewaters

4. Sono-Photo-Fenton Treatment of Pharmaceuticals in Water and Wastewater

4.1. NSAIDs

4.2. Antibiotics

4.3. Other Drugs

5. Assessment of the Change in Toxicity of Treated Pharmaceutical Solutions

6. Challenges and Future Perspectives

7. Conclusions

Author Contributions

Funding

Data Availability Statement

Acknowledgments

Conflicts of Interest

References

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