Search Results (45)

In this study, the degradation of Nile Blue dye was investigated using homogeneous and heterogeneous photocatalytic methods based on the photo-Fenton reaction. More specifically, for homogeneous photocatalysis, the classical photo-Fenton (UV/Fe²⁺/H₂O₂) and modified photo-Fenton-like (UV/Fe²⁺/S₂O₈²⁻) systems were studied, while for heterogeneous photocatalysis, a commercial MOF catalyst, Basolite F300, and a natural ferrous mineral, geothite, were employed. Various parameters—including the concentrations of the oxidant and catalyst, UV radiation, and pH—were investigated to determine their influence on the reaction rate. In homogeneous systems, an increase in iron concentration led to an enhanced degradation rate of the target compound. Similarly, increasing the oxidant concentration accelerated the reaction rate up to an optimal level, beyond which radical scavenging effects were observed, reducing the overall efficiency. In contrast, heterogeneous systems exhibited negligible degradation in the absence of an oxidant; however, the addition of oxidants significantly improved the process efficiency. Among the tested processes, homogeneous techniques demonstrated a superior efficiency, with the conventional photo-Fenton process achieving complete mineralization within three hours. Kinetic analysis revealed pseudo-first-order behavior, with rate constants ranging from 0.012 to 0.688 min⁻¹ and correlation coefficients (R²) consistently above 0.90, confirming the reliability of the applied model under various experimental conditions. Nevertheless, heterogeneous techniques, despite their lower degradation rates, also achieved high removal efficiencies while offering the advantage of operating at a neutral pH without the need for acidification. Full article

In this study, chromium ferrite (FeCr; CrFe₂O₄) nanoparticles supported on activated carbon (AC), obtained from agricultural olive mill solid waste, were synthesized via a simple hydrothermal process. The structural, morphological, optical, and chemical properties of the FeCr/AC composite were characterized using XRD, SEM, EDX, DRS, BET, and FTIR techniques. The FeCr/AC composite was applied as a heterogeneous photo-Fenton catalyst for the degradation of methylene blue (MB) dye in an aqueous solution under 25 W visible-light LED irradiation. Critical operational factors, such as FeCr/AC dosage, pH, MB concentration, and H₂O₂ levels, were optimized. Under optimal conditions, 97.56% of MB was removed within 120 min of visible-light exposure, following pseudo-first-order kinetics. The composite also exhibited high efficiency in degrading methyl orange dye (95%) and tetracycline antibiotic (88%) within 180 min, with corresponding first-order rate constants of 0.0225 min⁻¹ and 0.0115 min⁻¹, respectively. This study highlights the potential of FeCr/AC for treating water contaminated with dyes and pharmaceuticals, in line with the Sustainable Development Goals (SDGs) for water purification. Full article

The sludge produced by the Fenton process contains mixed-valence iron particulates (hereafter called Fenton wastes). Using a solvothermal method, we fabricated a new heterogeneous photo-Fenton catalyst using Fenton wastes and metal–organic frameworks (MOFs). Nanoporous metal carboxylate (MIL-88) MOF impregnated with Fenton waste was functionalized using 2,5-dihydroxyterephthalic acid (x-HO-MIL-88-C, x, concentration of the 2,5-dihydroxyterephthalic acid). The efficiency of x-HO-MIL-88-C was examined under visible light radiation using methylene blue (MB) as an index pollutant. We observed the best catalytic performance for MB degradation by 4-HO-MIL-88-C. In the photo-Fenton process, the simultaneous presence of singlet oxygen, superoxide, and hydroxyl radicals is confirmed by free radical quenching and electron spin resonance spectral data. These free radicals associate with holes in the non-selective degradation of MB. The 4-HO-MIL-88-C catalyst shows good stability and reusability, maintaining over 80% efficiency at the end of five consecutive cycles. This work opens up a new path for recycling Fenton wastes into usable products. Full article

Organic pollutants released into water bodies have posed a serious threat to aquatic ecosystems. The elimination of organic pollutants from water through the photo-Fenton process has attracted extensive attention. Among various photo-Fenton catalysts, iron oxides have been intensively studied due to their environmentally benign characteristics and abundance. However, the rapid recombination of photogenerated charge carriers (e⁻–h⁺) and slow Fe(III)/Fe(II) cycling of iron oxides restrict their catalytic performance. Thus, this state-of-the-art review focuses on the recent research development regarding iron oxide-based heterojunctions with enhanced catalytic performance to eliminate organic pollutants. This review provides a fundamental understanding of the iron-based heterogeneous photo-Fenton reaction. In addition, various heterojunctions for photocatalytic applications are comprehensively summarized. A thorough discussion is held on the material design for iron oxide-based heterojunctions with improved photo-Fenton catalytic performance. Ultimately, the challenges and prospects of iron oxide-based heterojunction catalysts for photo-Fenton water decontamination are outlined. Full article

Textile wastewater containing dyes poses significant environmental hazards. Advanced oxidative processes, especially the heterogeneous photo-Fenton process, are effective in degrading a wide range of contaminants due to high conversion rates and ease of catalyst recovery. This study evaluates the heterogeneous photodegradation of the azo dyes Acid Red 18 (AR18), Acid Red 66 (AR66), and Orange 2 (OR2) using magnetite as a catalyst. The magnetic catalyst was synthesized via a hydrothermal process at 150 °C. Experiments were conducted at room temperature, investigating the effect of catalyst dosage, pH, and initial concentrations of H₂O₂ and AR18 dye. Kinetic and thermodynamic studies were performed at 25, 40, and 60 °C for the three azo dyes (AR18, AR66, and OR2) and the effect of the dye structures on the degradation efficiency was investigated. At 25 °C for 0.33 mmolL⁻¹ of dye at pH 3.0, using 1.4 gL⁻¹ of the catalyst and 60 mgL⁻¹ of H₂O₂ under UV radiation of 16.7 mWcm⁻², the catalyst showed 62.3% degradation for AR18, 79.6% for AR66, and 83.8% for OR2 in 180 min of reaction. The oxidation of azo dyes under these conditions is spontaneous and endothermic. The pseudo-first-order kinetic constants indicated a strong temperature dependence with an order of reactivity of the type OR2 > AR66 > AR18, which is associated with the molecular size, steric hindrance, aromatic conjugation, electrostatic repulsion, and nature of the acid–base interactions on the catalytic surface. Full article

Following the goals of the circular economy, this work demonstrates that an industrial by-product can be used in environmental remediation. Metallurgical slag and citric acid were used to form an Fe:Cit complex by simultaneously carrying out the lixiviation of the iron and the chelating stages with an 87% iron recovery. This complex was evaluated in the photo-Fenton process to produce HO^• through salicylic acid dosimetry or salicylic acid hydroxylation, producing 0.13 ± 0.1 mM HO^• after 30 min of operation; such a value is three orders of magnitude higher than the one reported for the metallurgical slag (as a heterogeneous catalyst, 22 μM) in the photo-Fenton-like process. The system was tested for its ability to degrade a mixture of drugs, including dexamethasone (DEX), naproxen (NAP), and ketorolac (KTR), which are often used to treat the symptoms of COVID-19. The drug degradation tests were performed in two stages. In the first stage, the Fe:Cit complex from the metallurgical slag was compared to the one formed by analytical-grade reactants; the drug degradation was faster for the former, with the major difference being observed at 5 cm and 500 W/m². Here, 85–90% of the drugs was degraded in 5 min using Fe:Cit from slag, while at least 20 min was necessary to achieve such degradation with the analytical reagent, conceivably because of the trace compounds being lixiviated from the slag. Then, the effects of the liquid depth (5, 10, and 15 cm) and irradiance (250, 500, and 750 W/m²) were tested; the pseudo-first-order kinetic degradation constants for the three model pollutants were in the range of 0.009 > k_D > 0.09 min⁻¹, showing that degradation is more feasible for DEX than for NAP and KRT because the radical attack feasibility is related to the molecular structures. Full article

In this study, Fe₃O₄/Ag magnetite-silver (MSx) nanocomposites were investigated as catalysts for advanced oxidation processes by coupling the plasmonic effect of silver nanoparticles and the ferromagnetism of iron oxide species. A surfactant-free co-precipitation synthesis method yielded pure Fe₃O₄ magnetite and four types of MSx nanocomposites. Their characterisation included structural, compositional, morphological and optical analyses, revealing Fe₃O₄ magnetite and Ag silver phases with particle sizes ranging from 15 to 40 nm, increasing with the silver content. The heterostructures with silver reduced magnetite particle aggregation, as confirmed by dynamic light scattering. The UV–Vis spectra showed that the Fe:Ag ratio strongly influenced the absorbance, with a strong absorption band around 400 nm due to the silver phase. The oxidation kinetics of organic pollutants, monitored by in situ luminescence measurements using rhodamine B as a model system, demonstrated the higher performance of the developed catalysts with increasing Ag content. The specific surface area measurements highlighted the importance of active sites in the synergistic catalytic activity of Fe₃O₄/Ag nanocomposites in the photo-Fenton reaction. Finally, the straightforward fabrication of diverse Fe₃O₄/Ag heterostructures combining magnetism and plasmonic effects opens up promising possibilities for heterogeneous catalysis and environmental remediation. Full article

Heterogeneous photocatalysis–self-Fenton technology is a sustainable strategy for treating organic pollutants in actual water bodies with high-fluent degradation and high mineralization capacity, overcoming the limitations of the safety risks caused by adding external iron sources and hazardous chemicals in the homogeneous Fenton reaction and injecting high-intensity energy fields in photo-Fenton reaction. Herein, a photo-self-Fenton system based on resorcinol–formaldehyde (RF) resin and red mud (RM) was established to generate hydrogen peroxide (H₂O₂) in situ and transform into hydroxy radical (^•OH) for efficient degradation of tetracycline (TC) under visible light irradiation. The capturing experiments and electron spin resonance (ESR) confirmed that the hinge for the enhanced performance of this system is the superior H₂O₂ yield (499 μM) through the oxygen reduction process (ORR) of the two-step single-electron over the resin and the high concentration of ^•OH due to activation effect of RM. In addition, the Fe²⁺/Fe³⁺ cycles are accelerated by photoelectrons to effectively initiate the photo-self-Fenton reaction. Finally, the possible degradation pathways were proposed via liquid chromatography-mass spectrometry (LC-MS). This study provides a new idea for environmental recovery in a waste-based heterogeneous photocatalytic self-Fenton system. Full article

A large variety of pharmaceutical compounds have recently been detected in wastewater and natural water systems. This review highlighted the significance of removing pharmaceutical compounds, which are considered indispensable emerging contaminants, from wastewater and natural water systems. Various advanced oxidation processes (AOPs), including UV-H₂O₂, Fenton and photo-Fenton, ozone-based processes, photocatalysis, and physical processes, such as sonolysis, microwave, and electron beam irradiation, which are regarded as the most viable methods to eliminate different categories of pharmaceutical compounds, are discussed. All these AOPs exhibit great promising techniques, and the catalytic degradation process of the emerging contaminants, advantages, and disadvantages of each technique were deliberated. Heterogeneous photocatalysis employing metal oxides, particularly anatase TiO₂ nanoparticles as catalysts activated by UV light irradiation, was reviewed in terms of the electron–hole separation, migration of the charge carriers to the catalyst surfaces, and redox potential of the charge carriers. This brief overview also emphasized that anatase TiO₂ nanoparticles and TiO₂-based nanomaterials are promising photocatalysts, and a combination of photocatalysis and other AOPs enhanced photocatalytic degradation efficiency. Finally, the challenges of applying anatase TiO₂-based photocatalysis in environmental remediation and wastewater treatments to degrade pharmaceutical compounds, including mass spectroscopic analysis and a biological activity test of by-products of the emerging contaminants resulting from photocatalysis, are summarized. Full article

The winery industry generates large volumes of wastewater which can be toxic if released to the environment without proper treatment. The aim of this work was to treat two winery wastewaters (from red and white wine production) using Fenton-based processes. With the application of the best operational conditions, namely, pH = 3.0, [ferrocene] = [FeSO₄•7H₂O] = 0.50 g/L, [H₂O₂] = 155 mM, temperature = 298 K, and radiation UV (254 nm), to the treatment of a red WW, a chemical oxygen demand (COD) removal of 98.9 and 84.5% for the homogeneous and heterogeneous photo-Fenton processes, respectively, was achieved. The same conditions were applied in the treatment of a white WW and a 98.9 and 84.5% COD removal was achieved. Based on the results, it can be deduced that homogeneous and heterogeneous Fenton-based processes are effective in organic carbon removal, UV-C radiation is essential in hydroxyl radical (${\mathrm{HO}}^{\text{•}}$) generation, and the multiple addition of H₂O₂ reduces ${\mathrm{HO}}^{\text{•}}$ scavenging. Finally, it is concluded that both the homogeneous and heterogeneous photo-Fenton processes are effective for red and white WW treatment. Full article

MoS₂ has garnered considerable attention as an exceptional co-catalyst that is capable of significantly enhancing the efficiency of H₂O₂ decomposition in advanced oxidation processes (AOPs). This improvement allows for a reduction in the required amounts of H₂O₂ and Fe²⁺. In this study, we investigated the cyclic durability of photo-Fenton catalysts, focusing on the degradation of pollutants through the introduction of PPy into heterogeneous 1T-2H MoS₂ units. The resulting photothermal-Fenton catalysts, comprising non-ferrous Fenton catalysts, demonstrated excellent degradation performance for simulated pollutants. In comparison with 1T-2H MoS₂, the PPy@1T-2H MoS₂ composite exhibited remarkable stability and photothermal enhancement in the photo-Fenton degradation of methylene blue (MB) under visible light irradiation. The photo-Fenton reaction efficiently degraded contaminants, achieving 99% removal within 5 min and 99.8% removal within 30 min. Moreover, the co-catalyst complex displayed enhanced cyclic stability during the photo-Fenton reaction, with a contaminant removal efficiency of 92%, even after the 13th cyclic test. The combined effects of PPy and 1T-2H MoS₂ demonstrated improved efficiency in both photocatalytic and photo-Fenton catalytic reactions. Furthermore, PPy@1T-2H MoS₂ exhibited outstanding performance in the photothermal evaporation of water, achieving an efficiency of 86.3% under one solar irradiation. Full article

In line with the development of industrial society, wastewater has caused multiple environmental problems. Contaminants of emerging concern (CECs) in water and wastewater are persistent, and for this reason they can cause serious problems for human health, animal health, and the whole environment. Therefore, it is absolutely necessary to apply efficient methods for the treatment of wastewater that has a high concentration of organic compounds. Over recent years, the prescribed and non-prescribed consumption of antibiotics has increased significantly worldwide. Large quantities of antibiotics are discharged into wastewater because of their incomplete absorption by living organisms. However, even small concentrations present in aquatic environments represent a major risk to human health and environment protection. This paper presents the main advantages and disadvantages of advanced oxidation processes, and the current state and new perspectives in the field of environment protection. This study summarizes data from the most recent specialized scientific literature that focuses on the topic of advanced oxidation processes, thus bringing all these aspects to the attention of researchers in a single work that adds comments and interpretations related to the presented processes. Advanced oxidation processes (AOPs) are often used in the treatment of different types of wastewater. AOPs are based on physicochemical processes that create significant structural changes in chemical species. The majority of antibiotics may be eliminated using physicochemical processes, such as photo-Fenton oxidation, photolysis, ozonation, electrooxidation, heterogeneous catalysis, and other bioprocesses. In comparison to conventional chemical processes, AOPs provide superior oxidation efficiency, ideal operating costs, and zero secondary pollutants. Full article

In today’s industries, a diversity of processes give rise to increasing numbers of non-biodegradable compounds that need to be degraded totally or transformed to other less toxic and/or more biodegradable compounds, before their discharge into the environment. One such compound chosen for this study is Orange II, a representative azo-dye that is widely used and easy to monitor in its degradation. The photo-Fenton process was used under heterogeneous and homogeneous conditions to study several different variables. At the end of this research, a comparative study was carried out between the two types of catalysis. It was observed that better results in primary degradation and mineralization were provided by homogeneous catalysis. The photo-Fenton process takes place effectively under heterogeneous and homogeneous catalysis conditions. The process is much faster under homogeneous conditions than under heterogeneous conditions (99.9 and 24% after 90 min, respectively, especially when only 2 ppm of iron in solution is required). Mineralization was observed through total organic carbon, through the variable C/Co as a function of time during photo-Fenton and Orange II degradation, and the data obtained for the final oxidation capacity are in agreement with the experimental percentages of mineralization. A linear fit was observed using the Chan–Chu kinetic model for heterogeneous and homogeneous catalysis. For heterogeneous catalysis, 56% mineralization was reached whereas the model predicts 63%. Regarding homogeneous catalysis, according to the model, 100% mineralization is reached because (1/σ) takes a value greater than 1 since the model calculates it on infinite time. Full article

Photocatalytic inactivation of pathogens in aqueous waste is gaining increasing attention. Several homogeneous and heterogeneous photocatalytic protocols exist using the Fenton’s reagent and TiO₂, respectively. A comprehensive study of homogeneous and heterogeneous photocatalysis on a range of microorganisms will significantly establish the most efficient method. Here, we report a comparative study of TiO₂- and Fe⁺³-based photocatalytic inactivation under UV-A of diverse microorganisms, including Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, bacterial spores (Bacillus stearothermophilus spores) and viruses (MS2). We also present data on the optimization of TiO₂ photocatalysis, including optimal catalyst concentration and H₂O₂ supplementation. Our results indicate that both photo-Fenton and TiO₂ could be successfully applied for the management of microbial loads in liquids. Efficient microorganism inactivation is achieved with homogeneous photocatalysis (7 mg/L Fe⁺³, 100 mg/L H₂O₂, UV-A) in a shorter processing time compared to heterogeneous photocatalysis (0.5 g/L TiO₂, UV-A), whereas similar or shorter processing is required when heterogenous photocatalysis is performed using microorganism-specific optimized TiO₂ concentrations and H₂O₂ supplementation (100 mg/L); higher H₂O₂ concentrations further enhance the heterogenous photocatalytic inactivation efficiency. Our study provides a template protocol for the design and further application for large-scale photocatalytic approaches to inactivate pathogens in liquid biomedical waste. Full article

Currently, environmental pollution by various organic pollutants (e.g., organic dyes) is a serious, emerging global issue. The aqueous environment is highly exposed to the harmful effects of these organic compounds. Furthermore, the commonly applied conventional purification techniques are not sufficient enough. Heterogeneous photocatalysis and the photo-Fenton process are effective, low-cost and green alternatives for the removal of organic pollutants. In this study, different iron(III) oxide/titanium(IV) oxide/polyvinyl chloride (Fe₂O₃/TiO₂/PVC) nanocomposites in tablet form were investigated in the photodegradation of methylene blue (MB) under simulated sunlight, and their possible antibacterial effects were examined. The newly synthesized nanocomposites were characterized by scanning electron microscope, X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, and Raman spectroscopy. The results showed a hematite crystal form in the case of Fe₂O₃₍₂₎ and Fe₂O₃ samples, while the Fe₂O₃₍₁₎ sample showed a combination of hematite and synthetic mineral akaganeite. The highest photocatalytic efficiency was achieved in the presence of Fe₂O₃/TiO₂/PVC, when 70.6% of MB was removed. In addition, the possible photo-cleaning and reuse of the mentioned photocatalyst was also examined. Based on the results, it can be seen that the activity did not decrease after five successive runs. Nanocomposites also exhibited mild antibacterial effects against the two tested Gram-positive bacteria (S. aureus and B. cereus). Full article