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A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Environmental Catalysis".

Deadline for manuscript submissions: closed (5 April 2025) | Viewed by 8399

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Special Issue Editors

Prof. Dr. José Ignacio Lombraña

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Guest Editor

Department of Chemical Engineering, Faculty of Science and Technology, University of the Basque Country (UPV/EHU), P.O. Box 644, 48080 Bilbao, Spain
Interests: water processing; catalytic ozonation; activated carbon adsorption; membrane technologies
Special Issues, Collections and Topics in MDPI journals

Dr. Hugo Olvera Vargas

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Guest Editor

Institute of Renewable Energies, National Autonomous University of Mexico (IRE-NAUM), Priv. Xochicalco S/n, Col. Centro, Temixco, Morelos, CP 62580, Mexico
Interests: wastewater treatment and valorization; environmental electrochemistry; advanced oxidation processes; emerging pollutants

Dr. Sandra Yazmin Arzate Salgado

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Guest Editor Assistant

Departament of Earth Resources, Division of Basic Sciences and Engineering, Universidad Autonoma Metropolitana-Lerma, Av. de las Garzas 10, Lerma C.P. 52005, State of Mexico, Mexico
Interests: water treatment; advanced oxidation process; photo-Fenton; micropollutants; recalcitrant organic matter

Special Issue Information

Dear Colleagues,

After the first successful Special Issue focused on energy and pollution control applications as catalysts, available here, we propose a second edition in the same line, now focused on water with regard to the environment, under the title: “Environmentally Friendly Catalysts for Energy and Water Treatment Applications”.

Catalysts are extensively used in different technologies and play a fundamental role in the efficient generation of energy and industrial emission control. Despite the fact that catalysts have remarkable performance, they pose, in some cases, a negative environmental impact due to their massive use, which is imposed by intensive production strategies. Therefore, a reorientation in the search for new materials such as environmental friendly catalysts (EFCs) is urgently needed. Hence, the development of novel EFCs to face sustainable energy production, climate change problems, water resources conditioning and to abate industrial effluents has become a challenge in the current research fields.

A great variety of catalytic materials, which include single metals as well as mixed metals (and their oxides), are currently being used, either supported over alumina, silica, titania, ceria, zirconia, activated carbons, and zeolites or directly attached to the reactor itself, allowing their continuous use and avoiding waste emissions. Similar cases are found in Fenton catalysis, converted into EFCs through heterogeneous Fenton-like variants. Moreover, the combined use of catalysts with UV/solar irradiation or in combination with O₃ and H₂O₂ will always be preferable to that of other oxidant agents (persulfates). Heterogeneous catalysts are also used as electrodes for energy and environmental applications. Indeed, electrochemical processes are key technologies for sustainable development. This Special Issue addresses the aforementioned topics.

Prof. Dr. José Ignacio Lombraña
Dr. Hugo Olvera Vargas
Guest Editors

Dr. Sandra Yazmin Arzate Salgado
Guest Editor Assistant

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Catalysts is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

sustainable advanced oxidation processes (AOPs)
green electrocatalytic processes
sustainable catalytic processes
water resources conditioning
wastewater remediation
green energy production
environmentally friendly catalysts
multiple reused catalysts

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Published Papers (9 papers)

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Research

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17 pages, 2950 KiB

Open AccessArticle

β-Cyclodextrin Functionalization of Nitrogen-Doped Graphene to Enhance Dispersibility and Activate Persulfate for Trace Antibiotic Degradation in Water

by Min Yao and Nan Wu

Catalysts 2025, 15(6), 541; https://doi.org/10.3390/catal15060541 - 29 May 2025

Viewed by 398

Abstract

The functionalization of nitrogen-doped graphene with β-Cyclodextrin (designated β/N-rGO) was employed to enhance the dispersibility of graphene materials and to establish an adsorption-catalytic oxidation system using peroxymonosulfate (PMS) for the removal of trace antibiotics from water. The experimental results indicated that β-Cyclodextrin was effectively dispersed on the support structure of nitrogen-doped graphene, which enhanced the specific surface area and dispersibility of the material. The adsorption-catalytic oxidation system comprising β/N-rGO and PMS degraded 92.35% of sulfamethoxazole within 12 min and exhibited significant removal efficiency for sulfonamides, quinolones, macrolides, tetracyclines, β-lactams, and chloramphenicol antibiotics across a pH range of 3–12. The reaction time was reduced by over 10% compared to the unmodified material, with a more pronounced improvement in treatment efficiency, particularly under low-pH conditions. The activation energy of β/N-rGO was estimated to be approximately 4.5 kJ/mol, and elevated temperatures accelerated the reaction, with the removal rate remaining above 85% after five regeneration cycles. Quenching experiments and EPR spectra confirmed that the primary pathway for PMS activation by β/N-rGO was a non-radical process dominated by singlet oxygen. These findings broaden the research and application scope of cyclodextrin–graphene interactions and provide a feasible approach for the removal of trace antibiotics from water. Full article

(This article belongs to the Special Issue Environmentally Friendly Catalysts for Energy and Water Treatment Applications)

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18 pages, 1751 KiB

Open AccessArticle

Natural Pyrolusite-Catalyzed Ozonation for Nanoplastics Degradation

by Victor Mello, Julia Nieto-Sandoval, Márcia Dezotti and Carmen Sans

Catalysts 2025, 15(5), 502; https://doi.org/10.3390/catal15050502 - 21 May 2025

Viewed by 426

Abstract

The increasing prevalence of polystyrene nanoplastics (PSNPs) in aquatic environments poses significant risks due to their persistence and potential toxicity. Conventional water treatment methods have proven ineffective in removing these emerging pollutants, highlighting the urgent need for sustainable and efficient treatment. This study investigates the application of catalytic ozonation using natural pyrolusite (n-MnO₂) and oxalic acid (OA) as a co-catalyst for the environmentally friendly degradation of PSNPs. Key operational parameters, including pH, applied ozone dose, pyrolusite dosage, and OA concentration, were systematically evaluated. Results demonstrate that the MnO₂ + OA + O₃ system enhances the generation of reactive oxygen species (ROS), leading to improved PSNP removal while maintaining the applied ozone dose compared to the single ozonation reaction. The highest TOC removal of 75% was achieved within 30 min of treatment under optimal conditions (pH = 4, [MnO₂] = 0.5 g L⁻¹, [OA] = 10 mg L⁻¹, and ozone dose of 37.5 mg min⁻¹), with significant turbidity reduction, indicating both chemical and physical degradation of PSNPs. Catalyst reusability after three consecutive cycles confirmed minimal loss in activity, reinforcing its potential as a sustainable catalytic system. These findings highlight natural MnO₂-driven catalytic ozonation as a green and effective strategy for nanoplastic removal in water treatment applications. Full article

(This article belongs to the Special Issue Environmentally Friendly Catalysts for Energy and Water Treatment Applications)

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20 pages, 34413 KiB

Open AccessArticle

Fabrication of a Novel Silica–Alumina-Based Photocatalyst Incorporating Carbon Nanotubes and Nanofiber Nanostructures Using an Unconventional Technique for Light-Driven Water Purification

by Osama Saber, Abdullah Alshehab, Nagih M. Shaalan, Asmaa M. Hegazy, Fatimah K. Aljasem and Aya Osama

Catalysts 2025, 15(5), 452; https://doi.org/10.3390/catal15050452 - 6 May 2025

Viewed by 425

Abstract

The advancement of optical materials has garnered significant interest from the global scientific community in the pursuit of efficient photocatalysts for the purification of water using light. This challenge, which cannot be addressed using traditional methods, is tackled in the present study utilizing unconventional approaches. This study presents the fabrication of an effective photocatalyst using an unconventional approach that employs explosive reactions. This method successfully produces 3D nanostructures composed of carbon nanotubes (CNTs), carbon nanofibers (CNFs), and silica–alumina nanoparticles at temperatures below 270 °C. Gold-supported silica–alumina–CNT–CNF nanostructures were synthesized and characterized using XRD, TEM, SEM, and EDX, in addition to mapping images. To study and determine the photoactivity of these produced nanostructures, two well-known photocatalysts—titanium dioxide and zinc oxide—were synthesized at the nanoscale for comparison. The results showed that the presence of CNTs and CNFs significantly reduced the band gap energy from 5.5 eV to 1.65 eV and 3.65 eV, respectively, after modifying the silica–alumina structure. In addition, complete degradation of green dye was achieved after 35 min of light exposure using the modified silica–alumina structure. Additionally, the surface properties of the modified silica–alumina had a positive role in accelerating the photocatalytic decomposition of the green dye NGB. A kinetic study confirmed that the modified silica–alumina functions as a promising additive for optical applications, accelerating the photocatalytic degradation of NGB to a rate three times faster than that of the prepared titanium dioxide and six times that of the prepared zinc oxide. Full article

(This article belongs to the Special Issue Environmentally Friendly Catalysts for Energy and Water Treatment Applications)

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18 pages, 6704 KiB

Open AccessFeature PaperArticle

Amorphous MnO₂ Supported on CN@SiO₂ for Levofloxacin Degradation via a Non-Radical Pathway by PMS Activation

by Longfei Xia, Xilin Wang, Jiahui Li and Dongyan Xu

Catalysts 2025, 15(5), 419; https://doi.org/10.3390/catal15050419 - 24 Apr 2025

Viewed by 292

Abstract

Mn-based catalysts have been extensively studied in advanced oxidation processes based on peroxymonosulfate (PMS) oxidants, demonstrating their significant potential for treating antibiotic-contaminated wastewater. In this study, an amorphous MnO₂-based composite catalyst (MnO₂/CN@SiO₂) was prepared and used to activate PMS for degrading levofloxacin (LEV). The effects of reaction conditions, such as reaction temperature, catalyst dosage, PMS concentration, and solution pH, on LEV degradation were comprehensively investigated. The interference of water components, e.g.,

{NO}_{3}^{-}

{SO}_{4}^{2 -}

, Cl⁻,

{CO}_{3}^{2 -}

, and humic acid, on the degradation efficiency of LEV was analyzed, and the stability of the catalysts was explored by cycling experiments. Finally, radical quenching experiments and electron paramagnetic resonance spectroscopy were employed to elucidate the contribution of active species to the degradation reaction process. A non-radical-based pathway for LEV degradation was proposed based on these results. Full article

(This article belongs to the Special Issue Environmentally Friendly Catalysts for Energy and Water Treatment Applications)

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35 pages, 9518 KiB

Open AccessArticle

Green Innovation: Multifunctional Zinc Oxide Nanoparticles Synthesized Using Quercus robur for Photocatalytic Performance, Environmental, and Antimicrobial Applications

by Selma Redjili, Houria Ghodbane, Hichem Tahraoui, Lokmane Abdelouahed, Derradji Chebli, Mohammad Shamsul Ola, Amine Aymen Assadi, Mohammed Kebir, Jie Zhang, Abdeltif Amrane and Sabrina Lekmine

Catalysts 2025, 15(3), 256; https://doi.org/10.3390/catal15030256 - 7 Mar 2025

Cited by 1 | Viewed by 1304

Abstract

This study investigates the green synthesis of zinc oxide nanoparticles (ZnO NPs) using leaf extract as a natural reducing agent, evaluating their antimicrobial and photocatalytic properties. The nanoparticles were annealed at 320 °C and 500 °C, and the effects of leaf extract concentration and annealing temperature on their structural, morphological, and electronic properties were systematically explored. X-ray diffraction (XRD) analysis confirmed the hexagonal wurtzite structure of ZnO, with crystallite size and defect density being influenced by the concentration of the extract. Scanning electron microscopy (SEM) revealed the formation of smaller, spherical particles, with increased aggregation observed at higher extract concentrations. Fourier-transform infrared spectroscopy (FTIR) identified key functional groups, such as hydroxyl groups, C–O bonds, and metal–oxygen vibrations. UV–Vis spectroscopy showed a reduction in band gap energy and an increase in Urbach energy as the extract concentration and annealing temperature were increased. The antimicrobial activity of the ZnO NPs was evaluated against Gram-positive and Gram-negative bacteria as well as Candida albicans, demonstrating significant antibacterial efficacy. Photocatalytic degradation studies of methylene blue dye revealed a superior efficiency of up to 74% for the annealed samples, particularly at 500 °C. This research highlights the potential of green-synthesized ZnO NPs for a wide range of applications, including antimicrobial agents, water purification, and environmental catalysis. It contributes to the advancement of sustainable nanotechnology, offering promising solutions for both technological and ecological challenges. Full article

(This article belongs to the Special Issue Environmentally Friendly Catalysts for Energy and Water Treatment Applications)

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21 pages, 6099 KiB

Open AccessFeature PaperArticle

Peroxymonosulfate Activation by Fe/C Composites for Paracetamol Degradation: Performance Evaluation and Mechanism Insight

by Yujun Zhuo, Hong Meng, Yongqing Zhang, Yu Chen and Jiaqi Cui

Catalysts 2025, 15(3), 217; https://doi.org/10.3390/catal15030217 - 26 Feb 2025

Viewed by 684

Abstract

Peroxymonosulfate-based advanced oxidation processes (PMS-AOPs) relying on non-radical pathways offer advantages such as resistance to interference, efficient oxidant utilization, and selective degradation of pollutants. In this study, an Fe, N co-doped activator (Fe-N-C_1.5) was synthesized using a simple mixed solvent pyrolysis method. The Fe-N-C_1.5 exhibited excellent PMS activation activity. A total of 100% of paracetamol (PCT, 10 ppm) was degraded in the Fe-N-C_1.5/PMS system in 7 min. Furthermore, this oxidation system maintained effective PCT removal even in the presence of background ions and in real water matrices. In addition, the leached Fe concentration after 60 min was only 0.084 mg/L, and 94% of PCT could still be removed during the fourth cyclic use of the catalyst. Quenching experiments, electron paramagnetic resonance (EPR), and electrochemical analysis revealed that the Fe-N-C_1.5/PMS/PCT system predominantly relies on non-radical pathways, including singlet oxygen (¹O₂) and catalyst-interface-mediated electron transfer process (ETP). X-ray photoelectron spectroscopy (XPS) analysis and KSCN toxicity experiment confirmed that the graphitic N, carbonyl (C=O), and Fe-N_x were the main PMS activation sites. This study provides an understanding of degradation mechanisms of the Fe-N-C_1.5/PMS/PCT system and offers insights into the design of iron–carbon composite catalysts that carry out non-radical PMS activation. Full article

(This article belongs to the Special Issue Environmentally Friendly Catalysts for Energy and Water Treatment Applications)

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13 pages, 2416 KiB

Open AccessFeature PaperArticle

Kinetic Study of the Water Quality Parameters during the Oxidation of Diclofenac by UV Photocatalytic Variants

by Natalia Villota, Begoña Echevarria, Unai Duoandicoechea, Jose Ignacio Lombraña and Ana María De Luis

Catalysts 2024, 14(9), 580; https://doi.org/10.3390/catal14090580 - 31 Aug 2024

Cited by 4 | Viewed by 1575

Abstract

Diclofenac (DCF, C₁₄H₁₁Cl₂NO₂) is a widely used non-steroidal anti-inflammatory drug, with a significant occurrence in waste effluents. DCF is especially persistent and difficult to degrade, with numerous toxic effects on aquatic fauna and humans. In 2015, DCF was identified as a priority pollutant (EU Directives on water policy). In this work, UV irradiation and its combination with hydrogen peroxide only or catalyzed by iron salts (photo-Fenton) are analyzed to find the most efficient alternative. DCF aqueous solutions were treated in a stirred 150 W UV photocatalytic reactor. Depending on the case, 1.0 mM H₂O₂ and 0–5.0 mg/L Fe²⁺ catalyst, such as FeSO₄, was added. During the reaction, DCF, pH, turbidity, UVA at 254 and 455 nm, dissolved oxygen (DO), and TOC were assessed. The degradation of DCF yields a strong increase in aromaticity because of the rise in aromatic intermediates (mono-hydroxylated (4-hydroxy-diclofenac and 5-hydroxy-diclofenac) and di-hydroxylated products (4,5-dihydroxy-diclofenac), which subsequently generate compounds of a quinoid nature), which are very stable and non-degradable by UV light. Thus, only if H₂O₂ is added can UV completely degrade these aromatic colour intermediates. However, adding ferrous ion (photo-Fenton) the aromaticity remains constant due to iron com-plexes, that generates maximum colour and turbidity at an stoichiometric Fe²⁺ : DCF ratio of 3. As a result of the study, it is concluded that, with UV light only, a strong yellow colour is generated and maintained along the reaction, but by adding H₂O₂, a colourless appearance, low turbidity (<1 NTU), and [DO] = 8.1 mg/L are obtained. Surprisingly, photo-Fenton was found to be unsuitable for degrading DCF. Full article

(This article belongs to the Special Issue Environmentally Friendly Catalysts for Energy and Water Treatment Applications)

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15 pages, 3488 KiB

Open AccessArticle

The Direct Formation of an Iron Citrate Complex Using a Metallurgical Slag as an Iron Source for Micropollutant Removal via the Photo-Fenton Process

by Sandra Yazmin Arzate Salgado, Ana Yañez-Aulestia and Rosa-María Ramírez-Zamora

Catalysts 2024, 14(7), 426; https://doi.org/10.3390/catal14070426 - 4 Jul 2024

Cited by 2 | Viewed by 1688

Abstract

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

(This article belongs to the Special Issue Environmentally Friendly Catalysts for Energy and Water Treatment Applications)

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52 pages, 15996 KiB

Open AccessFeature PaperReview

Current Strategies to Improve the Properties of Graphitic Carbon Nitride for Effective and Scalable Wastewater Pollutant Removal: A Critical Review

by Xan Barreiro-Xardon, Emilio Rosales and María Ángeles Sanromán

Catalysts 2025, 15(6), 523; https://doi.org/10.3390/catal15060523 - 26 May 2025

Viewed by 383

Abstract

Heterogeneous photocatalysis has emerged in recent years as a promising and sustainable decontamination method. However, several drawbacks limit the effective usage of this process up to date, such as photocatalysts’ limited properties, difficulty in modifying and improving their properties, as well as the environmental impact and cost associated with the use of the metals on which conventional photocatalysts are based. Graphitic carbon nitride (gCN), a new carbon-based photocatalyst, offers the possibility of easy modification and improvement of their properties. There are several strategies to improve the properties of these derivatives, such as increasing the surface area (modifying morphology into 0D, 1D, 2D, or porous structures), increasing the absorption in the visible (doping), and improving the separation and mobility of photogenerated charges (introducing defects, vacancies, functional groups, and doping). In this review, a compilation of these modifications, the associated improvements in its properties, and its derivatives was carried out with focus on the degradation of emerging pollutants (EPs). The property modifications enhance their behavior and efficiency of degradation, all in a cheaper and more sustainable way. Thus, improved gCN derivatives offer real possibilities for the upscaling of heterogeneous photocatalytic processes as an effective alternative for decontaminating water bodies. Full article

(This article belongs to the Special Issue Environmentally Friendly Catalysts for Energy and Water Treatment Applications)

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