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Recent Advances in Photocatalysis for Wastewater Treatment: Synthesis of the Materials and Photocatalytic Reactors

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

Deadline for manuscript submissions: closed (31 December 2022) | Viewed by 19618

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Special Issue Editors

Dr. Wan Norharyati Wan Salleh

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Guest Editor

Advanced Membrane Technology Research Centre, School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Jalan Iman, Skudai 81310, Johor, Malaysia
Interests: photocatalyst; nanomaterial and nanocomposite synthesis; polymeric nanocomposite; membranes; wastewater treatment; gas separation

Dr. Farhana Aziz

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Guest Editor

Advanced Membrane Technology Research Centre, School of Chemical and Energy Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, Skudai Johor, Malaysia
Interests: photocatalysis; nanomaterial and nanocomposite synthesis; polymeric nanocomposite; membrane separation processes; wastewater treatment; gas separation
Special Issues, Collections and Topics in MDPI journals

Dr. Mohamad Azuwa Mohamed

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Guest Editor

Department of Chemical Science, Faculty of Science and Technology, Universiti Kebangsaan Malaysia
Interests: photocatalyst; nanomaterial; nanocomposites; membranes; polymeric nanocomposites; wastewater treatment

Special Issue Information

Dear Colleagues,

With the growing awareness of environmental protection, researchers and scientists are paying a great deal of attention to exploiting and utilizing clean energy, particularly solar energy, to resolve issues related to both energy and the environment. In this regard, photocatalysis has been largely considered as one of the most viable technologies, as the process only requires a semiconductor photocatalyst and a light source. Photocatalysis is one of the promising technologies because of its potential application in degrading pollutants, reducing CO₂ levels, and producing sustainable hydrogen (H₂) fuel. Due to the potential of utilizing freely available solar energy for environmental remediation and fuel generation, this topic has been of increasing interest. Auge amount of work has been done in developing a large variety of photocatalyst materials, and advances have been made in understanding the process.

Though inorganic semiconductors have shown tremendous progress in different fields of application, there are some inherent challenges in these photocatalysts. Various types of photocatalytic materials (TiO₂, ZnO, ZnS, perovskites, MoS₂, WO₃, Fe₂O₃, g-C₃N₄ etc.) and reactors have been explored for the degradation of pollutants in wastewater. The photocatalytic efficiency and the reaction rate highly depend on the different operational parameters. Therefore, the aim of this Special Issue is to provide comprehensive coverage on the recent advances in photocatalysis, particularly focusing on the new insights from recent findings and their applications. This includes the recent efforts to tailor the underlying problems in the synthesis of photocatalysts and the latest advancements in the design and development of photocatalytic reactor systems for wastewater treatment. With this new knowledge, technological innovations are expected in the field of photocatalysis.

We encourage the submission of all types of papers, including communications, original research, and review papers, covering all the topics related to innovative photocatalysts and their environmental applications.

Dr. Wan Norharyati Wan Salleh
Dr. Farhana Aziz
Dr. Mohamad Azuwa Mohamed

Guest Editors

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.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Synthesis of photocatalysts
Visible-light-driven photocatalysts
Photocatalysis
Waste treatment
Pharmaceutical waste
Degradation of organic pollutants
Emerging contaminants
Photocatalytic reactor design

Published Papers (7 papers)

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Research

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14 pages, 2790 KiB

Open AccessArticle

UV and Zero-Valent Iron (ZVI) Activated Continuous Flow Persulfate Oxidation of Municipal Wastewater

by Yerkanat N. Kanafin, Perizat Abdirova, Dinara Kanafina, Elizabeth Arkhangelsky, George Z. Kyzas and Stavros G. Poulopoulos

Catalysts 2023, 13(1), 25; https://0-doi-org.brum.beds.ac.uk/10.3390/catal13010025 - 24 Dec 2022

Cited by 4 | Viewed by 1447

Abstract

Currently, sulfate-radical-based advanced oxidation processes are promising candidates to become viable post-treatment processes for wastewater purification. In this work, a continuous flow UV light/persulfate (PS)/zero-valent iron (ZVI) system has been applied for wastewater treatment for the first time. The influence of certain photo-Fenton-like process parameters, such as space time, PS concentration, and PS to ZVI molar ratio, on the removal of total organic carbon (TOC), was examined using the Box–Behnken design. First, synthetic municipal wastewater was used for the experiments, and the polynomial regression model was constructed utilizing the real data by using the response surface methodology (RSM). The adequacy of the RSM model was assessed by analysis of variance, which showed that the model was reliable and could be applied to improve the process parameters for TOC removal. Moreover, both synthetic and real municipal wastewater were spiked with carbamazepine (CBZ), which is commonly prescribed as an antiepileptic drug, to investigate its fate in the UV/PS/ZVI system. With a space time of 60 min, PS concentration of 60 mM, and PS to ZVI molar ratio of 15, it was possible to remove 71% of TOC and completely remove CBZ from the synthetic municipal wastewater, whereas a 60% TOC removal and complete removal of CBZ were achieved at a space time of 50 min, PS concentration of 50 mM, and PS/ZVI molar ratio of 15 for the real municipal wastewater. This difference in TOC removal could possibly be linked to the complex matrix of the real wastewater and the presence of radical scavenging agents. Full article

(This article belongs to the Special Issue Recent Advances in Photocatalysis for Wastewater Treatment: Synthesis of the Materials and Photocatalytic Reactors)

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23 pages, 5170 KiB

Open AccessArticle

Photocatalytic Filtration of Zinc Oxide-Based Membrane with Enhanced Visible Light Responsiveness for Ibuprofen Removal

by Nurafiqah Rosman, Wan Norharyati Wan Salleh, Juhana Jaafar, Zawati Harun, Farhana Aziz and Ahmad Fauzi Ismail

Catalysts 2022, 12(2), 209; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12020209 - 10 Feb 2022

Cited by 11 | Viewed by 2229

Abstract

The growing interest in mixed matrix membranes (MMMs) for developing photocatalytic membranes has provided a new direction in the search for efficient methods to concurrently separate and degrade contaminants. In this study, a visible light-responsive photocatalyst was blended into a polyvinylidene fluoride (PVDF) membrane casting solution to prepare PVDF-ZnO/Ag₂CO₃/Ag₂O MMMs using the wet phase inversion method. The potential of ZnO/Ag₂CO₃/Ag₂O as a photocatalytic component that is incorporated into the membrane was explored in detail under various loadings (0.5–2.91 wt%). The membranes were tested under ibuprofen (IBF) aqueous solution to analyze the membrane behavior in the synergistic combination of membrane filtration and photodegradation. The resulting PVDF-ZnO/Ag₂CO₃/Ag₂O membrane with a rougher membrane surface area and excellent light harvesting capability showed higher photocatalytic filtration activity in removing IBF under visible light irradiations. The MMM fluxes demonstrated higher IBF fluxes than their initial fluxes at certain durations. This indicates that the membrane actively responds to light irradiation. The increase in the positive flux could be attributed to the photoinduced hydrophilicity generated by the ZnO/Ag₂CO₃/Ag₂O photocatalyst, resulting in easier water layer formation and rapid transport through membranes. The highest IBF removal was demonstrated by the PVDF-ZAA₂ membrane (1.96 wt% loading), with 49.96% of IBF removal within 180 min upon visible light irradiation. The reason for this lower IBF removal is that the UF membrane pores exceed the size of IBF molecules, thereby preventing the size exclusion mechanism. Thus, charge repulsion, hydrophobic adsorption, and photocatalytic activity were considered along with the IBF removal of the photocatalytic membranes. However, the recyclability of the PVDF-ZAA₂ photocatalytic membrane showed a great improvement, with 99.01% of IBF removal recovery after three cycles. These results highlight the potential of such hybrid membranes in mitigating membrane fouling by providing a platform for photocatalysts to continuously degrade pollutants present in such wastewaters. Therefore, the hybridization of a photocatalyst and membrane provides insight that could be utilized to improve and retrofit current water effluent treatment methods. Full article

(This article belongs to the Special Issue Recent Advances in Photocatalysis for Wastewater Treatment: Synthesis of the Materials and Photocatalytic Reactors)

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16 pages, 4322 KiB

Open AccessArticle

Controlling the Structural Properties and Optical Bandgap of PbO–Al₂O₃ Nanocomposites for Enhanced Photodegradation of Methylene Blue

by Abdelazim M. Mebed, Alaa M. Abd-Elnaiem, Alhulw H. Alshammari, Taha A. Taha, Mohamed Rashad and Dalia Hamad

Catalysts 2022, 12(2), 142; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12020142 - 24 Jan 2022

Cited by 15 | Viewed by 2588

Abstract

In the present work, PbO-x wt% Al₂O₃ nanocomposites (where x = 0, 10, 20, 30, 40, 50, 60, 70, and 100 wt%) were prepared by a microwave irradiation method. Their structural parameters, morphology, and chemical bonds, were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared spectroscopy (FTIR). It was noticed that the produced phases have an orthorhombic crystal structure and the smaller average crystallite sizes were formed when the ratio of Al₂O₃ is 40 wt%. The FTIR analysis reveals the formation of various bonds between Al or Pb and O. The TEM analysis reveals that the PbO-x%Al₂O₃ composites (x = 20, 40, and 60), composed of dense particles, and their size are smaller compared to the pure Al₂O₃ sample. The optical bandgap obeys the direct allowed transition and decreases from 4.83 eV to 4.35 eV as the PbO ratio in the composites increases from 0 to 100%. The intensity of the photoluminescence emission, at the same wavelength, increases as the PbO ratio increases from 0% to 60% implying that increasing the PbO content increases the capacity of free carriers within the trap centers. The prepared composites are used as a catalyst to remove the methylene blue (MB) from the wasted water under UV-visible or visible light irradiations. The photocatalytic degradation of MB was investigated by applying various kinetic models. It was found that the PbO-30% Al₂O₃, and PbO-40% Al₂O₃ composites are the best ones amongst other compositions. Furthermore, the pseudo-second-order model is the best model for describing the deterioration mechanism among the models studied. The formed composites could be suitable for the degradation of organic dyes for water purification as well as applications that required a higher optical bandgap. Full article

(This article belongs to the Special Issue Recent Advances in Photocatalysis for Wastewater Treatment: Synthesis of the Materials and Photocatalytic Reactors)

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20 pages, 6323 KiB

Open AccessArticle

Floating Carbon-Doped TiO₂ Photocatalyst with Metallic Underlayers Investigation for Polluted Water Treatment under Visible-Light Irradiation

by Sarunas Varnagiris, Marius Urbonavičius, Sandra Sakalauskaitė, Emilija Demikyte and Simona Tuckute

Catalysts 2021, 11(12), 1454; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11121454 - 29 Nov 2021

Cited by 11 | Viewed by 1954

Abstract

In the current study, we analysed the influence of metallic underlayers on carbon-doped TiO₂ films for RhB decomposition and Salmonella typhimurium inactivation under visible-light irradiation. All the experiments were divided into two parts. First, layered M/C-doped-TiO₂ film structures (M = Ni, Nb, Cu) were prepared by magnetron sputtering technique on borosilicate glass substrates in the two-step deposition process. The influence of metal underlayer on the formation of the carbon-doped TiO₂ films was characterised by X-ray diffractometer, scanning electron microscope, and atomic force microscope. The comparison between the visible-light assisted photocatalytic activity of M/C-doped TiO₂ structures was performed by the photocatalytic bleaching tests of Rhodamine B dye aqueous solution. The best photocatalytic performance was observed for Ni/C-doped-TiO₂ film combination. During the second part of the study, the Ni/C-doped-TiO₂ film combination was deposited on high-density polyethylene beads which were selected as a floating substrate. The morphology and surface chemical analyses of the floating photocatalyst were performed. The viability and membrane permeability of Salmonella typhimurium were tested in cycling experiments under UV-B and visible-light irradiation. Three consecutive photocatalytic treatments of fresh bacteria suspensions with the same set of floating photocatalyst showed promising results, as after the third 1 h-long treatment bacteria viability was still reduced by 90% and 50% for UV-B and visible-light irradiation, respectively. The membrane permeability and ethidium fluorescence results suggest that Ni underlayer might have direct and indirect effect on the bacteria inactivation process. Additionally, relatively low loss of the photocatalyst efficiency suggests that floating C-doped TiO₂ photocatalyst with the Ni underlayer might be seen as the possible solution for the used photocatalyst recovery issue. Full article

(This article belongs to the Special Issue Recent Advances in Photocatalysis for Wastewater Treatment: Synthesis of the Materials and Photocatalytic Reactors)

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14 pages, 6396 KiB

Open AccessArticle

Rational Design and Synthesis of ZnWO₄ Nanorods Decorated with SnS Nanodots with Enhanced Visible-Light Photocatalytic Performance

by Xiaoyi Shan, Tiekun Jia and Fang Fu

Catalysts 2021, 11(11), 1345; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111345 - 09 Nov 2021

Cited by 2 | Viewed by 1347

Abstract

Aiming to construct a direct Z-scheme binary heterostructure for efficient degradation of the organic dye Rhodamine B (RhB), ZnWO₄ nanorods decorated with SnS nanodots were rationally designed and prepared via a facile two-step route. Morphological observation and structural study showed that ultra-fine SnS nanodots were anchored on the surface of ZnWO₄ nanorods to form an intimate contact between the two components. Such a special structure provided SnS/ZnWO₄ nanocomposites with significantly enhanced light harvesting capacity, revealed by the results of UV-vis diffuse reflection spectroscopy (DRS). Photoluminescence (PL) analysis in combination with electrochemical measurements demonstrated that the recombination of photoactivated charge carriers was efficiently inhibited and the transfer of photoactivated charge carriers was successfully achieved due to the introduction of SnS. The degradation rate over SnS/ZnWO₄ nanocomposites reached a maximum value at SnS content of 9 wt%. The significantly enhanced photoactivity of SnS/ZnWO₄ nanocomposites was imputed to the synergistic effect of the promoted light absorption ability and effective photogenerated charge carriers’ transfer and separation. Full article

(This article belongs to the Special Issue Recent Advances in Photocatalysis for Wastewater Treatment: Synthesis of the Materials and Photocatalytic Reactors)

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Review

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32 pages, 5825 KiB

Open AccessReview

Removal of Organic Dyes from Water and Wastewater Using Magnetic Ferrite-Based Titanium Oxide and Zinc Oxide Nanocomposites: A Review

by António B. Mapossa, Washington Mhike, José L. Adalima and Shepherd Tichapondwa

Catalysts 2021, 11(12), 1543; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11121543 - 18 Dec 2021

Cited by 26 | Viewed by 4441

Abstract

Heterogeneous photocatalysis using titanium dioxide (TiO₂) and zinc oxide (ZnO) has been widely studied in various applications, including organic pollutant remediation in aqueous systems. The popularity of these materials is based on their high photocatalytic activity, strong photosensitivity, and relatively low cost. However, their commercial application has been limited by their wide bandgaps, inability to absorb visible light, fast electron/hole recombination, and limited recyclability since the nanomaterial is difficult to recover. Researchers have developed several strategies to overcome these limitations. Chief amongst these is the coupling of different semi-conductor materials to produce heterojunction nanocomposite materials, which are both visible-light-active and easily recoverable. This review focuses on the advances made in the development of magnetic ferrite-based titanium oxide and zinc oxide nanocomposites. The physical and magnetic properties of the most widely used ferrite compounds are discussed. The spinel structured material had superior catalytic and magnetic performance when coupled to TiO₂ and ZnO. An assessment of the range of synthesis methods is also presented. A comprehensive review of the photocatalytic degradation of various priority organic pollutants using the ferrite-based nanocomposites revealed that degradation efficiency and magnetic recovery potential are dependent on factors such as the chemical composition of the heterojunction material, synthesis method, irradiation source, and structure of pollutant. It should be noted that very few studies have gone beyond the degradation efficiency studies. Very little information is available on the extent of mineralization and the subsequent formation of intermediate compounds when these composite catalysts are used. Additionally, potential degradation mechanisms have not been adequately reported. Full article

(This article belongs to the Special Issue Recent Advances in Photocatalysis for Wastewater Treatment: Synthesis of the Materials and Photocatalytic Reactors)

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31 pages, 2383 KiB

Open AccessFeature PaperReview

Impact of Doping and Additive Applications on Photocatalyst Textural Properties in Removing Organic Pollutants: A Review

by Safia Syazana Mohtar, Farhana Aziz, Ahmad Fauzi Ismail, Nonni Soraya Sambudi, Hamidah Abdullah, Ahmad Nazrul Rosli and Bunsho Ohtani

Catalysts 2021, 11(10), 1160; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11101160 - 26 Sep 2021

Cited by 34 | Viewed by 4407

Abstract

The effect of ion doping and the incorporation of additives on photocatalysts’ textural properties have been reviewed. Generally, it can be summarised that ion doping and additives have beneficial effects on photocatalytic efficiency and not all have an increase in the surface area. The excessive amount of dopants and additives will produce larger aggregated particles and also cover the mesoporous structures, thereby increasing the pore size (P_d) and pore volume (P_v). An excessive amount of dopants also leads to visible light shielding effects, thus influence photocatalytic performance. Ion doping also shows some increment in the surface areas, but it has been identified that synergistic effects of the surface area, porosity, and dopant amount contribute to the photocatalytic performance. It is therefore important to understand the effect of doping and the application of additives on the textural properties of photocatalysts, thus, their performance. This review will provide an insight into the development of photocatalyst with better performance for wastewater treatment applications. Full article

(This article belongs to the Special Issue Recent Advances in Photocatalysis for Wastewater Treatment: Synthesis of the Materials and Photocatalytic Reactors)

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