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Special Issue "10th Anniversary of Catalysts—Feature Papers in Photocatalysis"

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

Deadline for manuscript submissions: 31 August 2022 | Viewed by 22169

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Special Issue Editors

Prof. Dr. Detlef W. Bahnemann
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Guest Editor

Institutfür Technische Chemie, Leibniz Universität Hannover Callinstrasse 3, D-30167 Hannover, Germany
Interests: photocatalysis; self-cleaning; superhydrophilic; antibacterial surfaces; metal and semiconductor particles; nanocristalyne transparent coatings; functional test according to DIN; CEN and ISO
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Prof. Dr. Ewa Kowalska
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Institute for Catalysis (ICAT), Hokkaido University, N21, W10, 001-0026 Sapporo, Japan
Interests: heterogeneous photocatalysis; advanced oxidation processes (AOPs); environmental purification; plasmonic nanoparticles; antimicrobial properties; visible-light-responsive materials
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Ioannis Konstantinou
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Laboratory of Industrial Chemistry, Department of Chemistry, University of Ioannina, 45500 Ioannina, Greece
Interests: photocatalysis; photolytic processes in the environment; photodegradation pathways; identification of phototransformation products
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Prof. Dr. Magdalena Janus
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Engineering Department of Environmental Engineering Piastów 45, Szczecin Faculty of Civil and Environmental, West Pomeranian University of Technology, 70-311 Szczecin, Poland
Interests: photocatalysis; photoactive building materials; titanium dioxide; water and air purification
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Dr. Vincenzo Vaiano
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Department of Industrial Engineering, University Salerno, Via Giovanni Paolo 2 132, I-84084 Fisciano, Salerno, Italy
Interests: photocatalysis for sustainable chemistry; photocatalytic and photo-Fenton processes for pollutants removal in wastewater; catalytic combustion of sewage sludge; decomposition and oxidative decomposition of H₂S; hydrolysis of COS in the liquid phase
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Prof. Dr. Wonyong Choi
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Division of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang 37673, Korea
Interests: semiconductor photocatalysis for environmental and energy applications; solar fuel production, artificial photosynthesis; development of visible light active photocatalysts; photochemical purification of water and air; photochemical purification of water and air; environmental (photo)chemistry; ice (photo)chemistry; redox processes of environmental significance

Prof. Dr. Zhi Jiang
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Institute of Advanced Energy and Powertrain Technology, Shanghai Jiao Tong University, Shanghai, China
Interests: heterogeneous catalysis; catalysis for energy and environment; in situ and operando spectroscopy

Special Issue Information

Dear Colleagues,

It is our pleasure to welcome you to our Special Issue “Photocatalysis”, celebrating the 10th Anniversary of Catalysts. As you all know, photocatalysis has become one of the key areas within the catalysis field. Since it adds just another feature to the already rather complex mechanism of heterogeneous catalysis, that is, the interaction with photons required to initiate the overall process, there is still a large number of unknowns regarding details of the underlying reaction mechanism(s). Therefore, contributions highlighting such mechanistic details are highly welcome in this Special Issue. Moreover, a photocatalyst often requires the presence of one or even several so-called co-catalysts to enable the desired chemical conversions. Therefore, we would like to invite you to submit to this Special Issue your explanations regarding the role of catalysis in a photocatalytic process. Other areas for which high-level contributions are needed—but are by no means limited to—plasmonic photocatalysis, nanocomposite materials, doped and co-doped semiconductor materials, photocatalytic synthesis, solar fuels, theoretical modeling of photocatalytic processes, photoreactor and reaction engineering, non-linear optical effects, decontamination and disinfection, and pilot and full-scale applications, to name but a few. We look forward to receiving your contribution(s) as soon as possible. In addition to original research articles, we welcome review and feature articles.

Prof. Dr. Detlef W. Bahnemann
Prof. Dr. Ewa Kowalska
Prof. Dr. Ioannis Konstantinou
Prof. Dr. Magdalena Janus
Prof. Dr. Vincenzo Vaiano
Prof. Dr. Wonyong Choi
Prof. Dr. Zhi Jiang
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 2200 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

Mechanisms of photocatalysis
(co)-catalysts
Plasmonic photocatalysis
Nanocomposite materials
Doped and co-doped semiconductor materials
Photocatalytic synthesis
Solar fuels and artificial photosynthesis
Water splitting, CO₂ and N₂ conversion
Environmental photocatalysis
Selective synthesis of organic compounds
Theoretical modeling of photocatalytic processes
Photoreactor and reaction engineering
Non-linear optical effects
Photonic crystals
Antimicrobial properties
Degradation mechanisms and pathways
Pilot and full-scale photocatalytic applications

Published Papers (29 papers)

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Research

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Open AccessArticle

Photocatalytic Remediation of Harmful Alexandrium minutum Bloom Using Hybrid Chitosan-Modified TiO₂ Films in Seawater: A Lab-Based Study

Nur Hanisah Ibrahim

Anwar Iqbal

Normawaty Mohammad-Noor

Roziawati Mohd Razali

and

Catalysts 2022, 12(7), 707; https://doi.org/10.3390/catal12070707 - 27 Jun 2022

Viewed by 126

Abstract

The uncontrolled growth of harmful algal blooms (HABs) can negatively impact the environment and pose threats to human health and aquatic ecosystems. Titanium dioxide (TiO₂) is known to be effective in killing harmful algae through flocculation and sedimentation. However, TiO₂ in a dispersed form can harm other non-target marine organisms, which has raised concerns by environmentalists and scientists. This research seeks to explore the utility of immobilized titanium oxide as a photocatalyst for mitigation of HABs, where the Alexandrium minutum bloom was used as a model system herein. Chitosan was modified with 0.2 wt.% TiO₂ (Chi/TiO₂ (x mL; x = 1, 3 and 5 mL) and the corresponding films were prepared via solvent casting method. Scanning electron microscope (SEM) images of the films reveal a highly uneven surface. X-ray diffraction (XRD) analysis indicates the reduction in chitosan crystallinity, where the presence of TiO₂ was negligible, in accordance with its dispersion within the chitosan matrix. The photocatalytic mitigation of A.minutum was carried out via a physical approach in a laboratory-scale setting. The negative surface charge of the films was observed to repel the negatively charged A.minutum causing fluctuation in the removal efficiency (RE). The highest RE (76.1 ± 13.8%) was obtained when Chi/TiO₂ (1 mL) was used at 72 h, where the hydroxyl radicals generated were inferred to contribute to the deactivation of the algae cells by causing oxidative stress. An outcome of this study indicates that such hybrid films have the potential to replace the non-immobilized (dispersed) TiO₂for HAB mitigation. However, further investigation is required to deploy these films for field applications at a larger scale. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

Open AccessArticle

Retention and Inactivation of Quality Indicator Bacteria Using a Photocatalytic Membrane Reactor

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Vanessa Jorge Pereira

Catalysts 2022, 12(7), 680; https://doi.org/10.3390/catal12070680 - 22 Jun 2022

Viewed by 188

Abstract

The development of effective disinfection treatment processes is crucial to help the water industry cope with the inevitable challenges resulting from the increase in human population and climate change. Climate change leads to heavy rainfall, flooding and hot weather events that are associated with waterborne diseases. Developing effective treatment technologies will improve our resilience to cope with these events and our capacity to safeguard public health. A submerged hybrid reactor was used to test the efficiency of membrane filtration, direct photolysis (using ultraviolet-C low-pressure mercury lamps, as well as ultraviolet-C and ultraviolet-A light-emitting diodes panels) and the combination of both treatment processes (membrane filtration and photolysis) to retain and inactivate water quality indicator bacteria. The developed photocatalytic membranes effectively retained the target microorganisms that were then successfully inactivated by photolysis and advanced oxidation processes. The new hybrid reactor could be a promising approach to treat drinking water, recreational water and wastewater produced by different industries in small-scale systems. Furthermore, the results obtained with membranes coated with titanium dioxide and copper combined with ultraviolet-A light sources show that the process may be a promising approach to guarantee water disinfection using natural sunlight. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessFeature PaperArticle

Photocatalytic Reduction of Nitrates and Combined Photodegradation with Ammonium

Francesco Conte

Veronica Pellegatta

Alessandro Di Michele

Gianguido Ramis

and

Ilenia Rossetti

Catalysts 2022, 12(3), 321; https://doi.org/10.3390/catal12030321 - 11 Mar 2022

Viewed by 551

Abstract

Bare titania and metal-promoted TiO₂ catalysts were employed in the treatment of nitrates, which are ubiquitous pollutants of wastewater. The results show that the process can be carried out under visible light (from a white light LED lamp) and, in the best case, 23.5% conversion of nitrate was obtained over 4 h with full selectivity towards N₂ by employing 0.1 mol% Ag/TiO₂ prepared by flame spray pyrolysis. Moreover, the performance was worse when testing the same catalysts with tap water (11.3% conversion), due to the more complex composition of the matrix. Finally, it was found that photoreduction of nitrate can be effectively performed in combination with photo-oxidation of ammonium without loss in the activity, opening up the possibility of treating highly polluted wastewater with a single process. The latter treatment employs the two contaminants simultaneously as electron and holes scavengers, with very good selectivity, in a completely new process that we may call Photo-Selective Catalytic Reduction (Photo-SCR). Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Decomposition of Gaseous Styrene Using Photocatalyst and Ozone Treatment

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Catalysts 2022, 12(3), 316; https://doi.org/10.3390/catal12030316 - 10 Mar 2022

Viewed by 959

Abstract

Because photocatalysis has strong oxidation abilities in redox systems, it has been applied to indoor air purification. However, intermediate products are produced during the photocatalytic oxidative decomposition of aromatic compounds with benzene rings. Therefore, it is essential to improve decomposition performance and evaluate the intermediate products produced for practical applications. Herein, we describe the decomposition performance of ozone, photocatalyst, and their combination, under the target gas of styrene. Using a one-pass mini reactor, decomposition performance was evaluated by analyzing the output gas in the reactor and observing the styrene removal, the amount of carbon dioxide produced, and the composition of a small amount of intermediate products. The combination of ozone and photocatalyst showed the most significant performance, completely decomposing in the photocatalyst and removing odor components in ozone. Moreover, we demonstrated that decomposition performance could be evaluated by observing slight amounts of intermediate products in the exhaust gas. We believe that this research provides insights into the practical application of photocatalysis and ozone oxidation technologies in air purifiers and their performance management, with particular emphasis on the decomposition of odor compounds. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Synthesis and Photoelectrocatalytic Applications of TiO₂/ZnO/Diatomite Composites

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Catalysts 2022, 12(3), 268; https://doi.org/10.3390/catal12030268 - 28 Feb 2022

Viewed by 655

Abstract

ZnO and TiO₂ are semiconductor nanomaterials that are widely used in photocatalysis. However, the relatively high recombination rate and low quantum yield of photogenerated electron–hole pairs limit their practical applications. In this study, a series of TiO₂/ZnO/diatomite composites with various compositions were successfully prepared via a two-step precipitation method. They exhibited stronger UV–visible absorption properties and substantially lower fluorescence intensities than those of ZnO and ZnO/diatomite, which was mainly due to the low recombination rate of the photogenerated electron–hole pairs in the composite system. The reaction intermediates of methylene blue were detected by liquid chromatography–mass spectrometry, and the degradation process was determined. The best composite catalyst was used for the degradation of gaseous methylbenzene and gaseous acetone. The gaseous acetone degradation product was determined to be acetaldehyde via gas chromatography–mass spectrometry. The results show that the composite catalyst exhibited a good photocatalytic degradation of both liquid pollutants and harmful volatile gases. When applied to the hydrogen and oxygen evolution reactions, the composite catalyst retained a good photoresponsivity and electrolytic efficiency. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Effect of Heating Rate on the Photocatalytic Activity of Ag–TiO₂ Nanocomposites by One-Step Process via Aerosol Routes

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Catalysts 2022, 12(1), 17; https://doi.org/10.3390/catal12010017 - 24 Dec 2021

Viewed by 941

Abstract

Ag–TiO₂ nanocomposite films, based of Ag and TiO₂ nanoparticles, were fabricated in a one-step aerosol route employing the simultaneous plasma-enhanced chemical vapor deposition and physical vapor deposition systems. The as-fabricated films were subjected to different heating rates (3 to 60 °C/min) with a constant annealing temperature of 600 °C to observe the significant changes in the properties (e.g., nanoparticle size, crystalline size, crystallite phase, surface area) toward the photocatalytic performance. The photocatalytic activity was evaluated by the measurement of the degradation of a methylene blue aqueous solution under UV light irradiation, and the results revealed that it gradually increased with the increase in the heating rate, caused by the increased Brunauer–Emmett–Teller (BET) specific surface area and total pore volume. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessFeature PaperArticle

Effect of Calcination Conditions on the Properties and Photoactivity of TiO₂ Modified with Biuret

Aleksandra Piątkowska

and

Sylwia Mozia

Catalysts 2021, 11(12), 1546; https://doi.org/10.3390/catal11121546 - 18 Dec 2021

Viewed by 664

Abstract

A simple wet impregnation-calcination method was used to obtain a series of novel non-metal doped TiO₂ photocatalysts. Biuret was applied as C and N source, while raw titanium dioxide derived from sulfate technology process was used as TiO₂ and S source. The influence of the modification with biuret and the effect of the atmosphere (air or argon) and temperature (500–800 °C) of calcination on the physicochemical properties and photocatalytic activity of the photocatalysts towards ketoprofen decomposition under simulated solar light was investigated. Moreover, selected photocatalysts were applied for ketoprofen photodecomposition under visible and UV irradiation. Crucial features affecting the photocatalytic activity were the anatase to rutile phase ratio, anatase crystallites size and non-metals content. The obtained photocatalysts revealed improved activity in the photocatalytic ketoprofen decomposition compared to the crude TiO₂. The best photoactivity under all irradiation types exhibited the photocatalyst calcined in the air atmosphere at 600 °C, composed of 96.4% of anatase with 23 nm crystallites, and containing 0.11 wt% of C, 0.05 wt% of N and 0.77 wt% of S. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Effects of Preparation Conditions on the Efficiency of Visible-Light-Driven Hydrogen Generation Based on Cd_0.25Zn_0.75S Photocatalysts

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Catalysts 2021, 11(12), 1534; https://doi.org/10.3390/catal11121534 - 16 Dec 2021

Cited by 1 | Viewed by 677

Abstract

Photocatalytic H₂ production utilizing H₂S, an industrial side-product, is regarded as an environmentally friendly process to produce clean energy through direct solar energy conversion. For this purpose, sulfide-based materials, such as photocatalysts, have been widely used due to their good solar response and high photocatalytic activity. In this work, a ZnS–CdS composite was studied, and special attention was dedicated to the influence of the preparation parameters on its H₂ production activity. The ZnS–CdS composite, with an enhanced photoactivity for H₂ production, was synthesized both from ammine complexes and, in a conventional way, directly from acetates at various pH values. Deviating from the traditional method, the photoactivity of ZnS–CdS prepared from ammine complexes was not affected by the pH. Besides, the hydrothermal treatment and the ammonia content strongly influenced the rate of H₂ production in this system. DRS, TEM, SEM, XRD, and quantum yield measurements prove the dependence of the photoactivity of these catalysts on the structural and morphological properties determined by the preparation conditions. The promising photocatalytic efficiency achieved with the application of these ZnS–CdS catalysts, prepared without any metal deposition, encourages further investigations to enhance the rate of hydrogen generation by optimization of the reaction conditions for practical utilization. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

[email protected]₂ Nanoparticles for Photocatalytic Reduction Reactions: Nitrogen Fixation and Hydrogen Evolution

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Catalysts 2021, 11(12), 1443; https://doi.org/10.3390/catal11121443 - 26 Nov 2021

Cited by 2 | Viewed by 487

Abstract

Solar-driven photocatalysis has been known as one of the most potential technologies to tackle the energy shortage and environmental pollution issues. Utilizing bio-pollutants to prepare functional materials has been considered as a green option. Herein, we used Microcystis aeruginosa as a bio-template to fabricate a Microcystis@TiO₂ photocatalyst using a calcination method. The as-prepared Microcystis@TiO₂ showed prominent ability as well as favorable stability for photocatalytic reduction reactions including hydrogen evolution and nitrogen fixation. Under light illumination, Microcystis@TiO₂ calcined at 550 °C exhibited optimal photo-reduced activity among all samples, with the highest hydrogen evolution (1.36 mmol·g⁻¹·h⁻¹) and ammonia generation rates (0.97 mmol·g⁻¹·h⁻¹). This work provides a feasible approach to prepare functional materials from disposed pollutants. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessFeature PaperArticle

Effect of the Type of Heterostructures on Photostimulated Alteration of the Surface Hydrophilicity: TiO₂/BiVO₄ vs. ZnO/BiVO₄ Planar Heterostructured Coatings

Maria V. Maevskaya

Aida V. Rudakova

Alexandra V. Koroleva

Aleksandr S. Sakhatskii

Alexei V. Emeline

and

Detlef W. Bahnemann

Catalysts 2021, 11(12), 1424; https://doi.org/10.3390/catal11121424 - 23 Nov 2021

Cited by 1 | Viewed by 533

Abstract

Here, we report the results of comparative studies of the photostimulated hydrophilic behavior of heterostructured TiO₂/BiVO₄ and ZnO/BiVO₄, and monocomponent TiO₂ and ZnO nanocoating surfaces. The chemical composition and morphology of the synthesized nanocoatings were characterized by XPS, SEM, and AFM methods. The electronic energy structure of the heterostructure components (band gap, top of the valence band, bottom of the conduction band, and Fermi level position) was determined on the basis of experimental results obtained by XPS, UV-V absorption spectroscopy and Kelvin probe methods. According to their electronic energy structure, the ZnO/BiVO₄ and TiO₂/BiVO₄ heterostructures correspond to type I and type II heterostructures, respectively. The difference in the type of heterostructures causes the difference in the charge transfer behavior at heterojunctions: the type II TiO₂/BiVO₄ heterostructure favors and the type I ZnO/BiVO₄ heterostructure prevents the photogenerated hole transfer from BiVO₄ to the outer layer of the corresponding metal oxide. The results of the comparative studies show that the interaction of the photogenerated holes with surface hydroxy-hydrated multilayers is responsible for the superhydrophilic surface conversion accompanying the increase of the surface free energy and work function. The formation of the type II heterostructure leads to the spectral sensitization of the photostimulated surface superhydrophilic conversion. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Figures of Merit for Photocatalysis: Comparison of NiO/La-NaTaO₃ and Synechocystis sp. PCC 6803 as a Semiconductor and a Bio-Photocatalyst for Water Splitting

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Catalysts 2021, 11(11), 1415; https://doi.org/10.3390/catal11111415 - 22 Nov 2021

Cited by 1 | Viewed by 551

Abstract

While photocatalysis is considered a promising sustainable technology in the field of heterogeneous catalysis as well as biocatalysis, figures of merit (FOM) for comparing catalytic performance, especially between disciplines, are not well established. Here, photocatalytic water splitting was conducted using a semiconductor (NiO/La-NaTaO₃) and a bio-photocatalyst (Synechocystis sp. PCC 6803) in the same setup under similar reaction conditions, eliminating the often ill-defined influence of the setup on the FOMs obtained. Comparing the results enables the critical evaluation of existing FOMs and a quantitative comparison of both photocatalytic systems. A single FOM is insufficient to compare the photocatalysts, instead a combination of multiple FOMs (reaction rate, photocatalytic space time yield and a redefined apparent quantum yield) is superior for assessing a variety of photocatalytic systems. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Au-Ag/TiO₂ Thin Films Preparation by Laser Ablation and Sputtering Plasmas for Its Potential Use as Photoanodes in Electrochemical Advanced Oxidation Processes (EAOP)

Luis Alejandro Martínez-Chávez

Eric Mauricio Rivera-Muñoz

Rodrigo Rafael Velázquez-Castillo

Luis Escobar-Alarcón

and

Karen Esquivel

Catalysts 2021, 11(11), 1406; https://doi.org/10.3390/catal11111406 - 20 Nov 2021

Cited by 3 | Viewed by 734

Abstract

Titanium dioxide (TiO₂) is widely used, studied, and synthesized using different methodologies. By a modification of the material, it can be applied to wastewater treatment. A combined sputtering-laser ablation setup was used to deposit TiO₂ thin films modified, individually and simultaneously, with gold (Au) and silver (Ag). To investigate the effect of the metal incorporation in titanium and its impact on the photocatalytic activity, with dye discoloration as a pollutant compound model, the deposited films were characterized by UV–Vis, photoluminescence, and Raman spectroscopies, as well as by parallel beam X-ray diffraction. The results showed that films with different Au and Ag loads, and an 18 nm average crystallite size, were obtained. These metals have an essential effect on the deposited film’s compositional, structural, and optical properties, directly reflected in its photocatalytic activity. The photocatalytic test results using UV-Vis showed that, after 1 h of applying a 4.8 V electric voltage, a discoloration of up to 80% of malachite green (MG) was achieved, using ultraviolet (UV) light. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Intra-Molecular Electrical Field Regulated Nonlinear Catalyst Charge Transfer in the Organic Conjugated Molecular System

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Catalysts 2021, 11(11), 1375; https://doi.org/10.3390/catal11111375 - 15 Nov 2021

Viewed by 389

Abstract

The application of organic conjugated molecular systems to photocatalysis is based on the charge transition with different electronegative substituents and the electron–hole separation behavior of charge transfer under light excitation. In this work, the relationship between the intra-molecular electrical field and molecular second-order nonlinear optical properties is investigated theoretically by the sum-of-states (SOS) method. We use substituents with different electron affinity energy to construct internal electric fields with different properties in similar conjugated systems. The studies of these systems reveal the intra-molecular electric field strength and mode regulation of nonlinear optical coefficients and explain its physical mechanism. The intra-molecular charge recombination caused by the electrostatic potential multipole field of different substituents changes the transition behavior of one-photon, resulting in the enhancement of nonlinear optical properties (second-harmonic generation and sum-frequency coefficient) greater than 10⁴. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Development of a Novel Microgap Reactor System for the Photocatalytic Degradation of Micropollutants from Aqueous Solutions with TiO₂-Based Photocatalysts Immobilized by Spray Coating

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Catalysts 2021, 11(11), 1351; https://doi.org/10.3390/catal11111351 - 11 Nov 2021

Cited by 1 | Viewed by 462

Abstract

The presented investigation focuses on the development of a novel microgap reactor concept for the photocatalytic degradation of micropollutants from aqueous solutions with titanium dioxide-based catalysts immobilized by spray coating. Combinatorial experiment designs were utilized in order to study the influence of the microgap width, irradiance and catalyst layer thickness on the conversion of 17 α-ethinyl estradiol. The impact of catalyst-doping is discussed as well. Regarding conversion analyses, LC-MS/MS and GC-MS techniques were deployed, while XRD, ESEM and BET were utilized for catalyst characterization. The results show that the built-up microgap reactor system enables a conversion of 65% within a residence time of 2.7 min with UV-A irradiation and under steady flow conditions. Thus, the presented bench scale photocatalysis reactor provides promising fundamental findings for the future development of pilot scale approaches. With the deployment of industrial catalysts and base materials, microgap reactor photocatalytic degradation represents an attractive technology for large-scale application. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessFeature PaperArticle

Influence of rGO and Preparation Method on the Physicochemical and Photocatalytic Properties of TiO₂/Reduced Graphene Oxide Photocatalysts

Agnieszka Wanag

Ewelina Kusiak-Nejman

Adam Czyżewski

Dariusz Moszyński

and

Antoni W. Morawski

Catalysts 2021, 11(11), 1333; https://doi.org/10.3390/catal11111333 - 02 Nov 2021

Cited by 1 | Viewed by 631

Abstract

In this study, a series of TiO₂/rGO photocatalysts were obtained with a two-step procedure: a solvothermal method and calcination at 300–900 °C in an argon atmosphere. It was noted that the presence of rGO in photocatalysts had an important role in the changes in crystallite size and specific surface area. In TiO₂/rGO samples, different surface functional groups, such as C−C_graph, C−C_aliph, C−OH, C=O, and CO(O), were found. It was observed that rGO modification suppressed the anatase-to-rutile phase transformation. The photocatalytic activity of the obtained nanomaterials was investigated through the decomposition of methylene blue under UV and artificial solar light irradiation. It was found that the adsorption degree played an important role in methylene blue decomposition. The experimental results revealed that TiO₂/rGO samples exhibited superior removal efficiency after calcination for methylene blue compared toTiO₂ without rGO, as well as a commercial photocatalyst KRONOClean 7000. It was noted that photocatalytic activity increased with the increase in the calcination temperature. The highest activity was observed for the sample calcined at 700 °C, which consisted of 76% anatase and 24% rutile. This study clearly demonstrated that TiO₂/rGO samples calcined in argon can be used as efficient photocatalysts for the application of methylene blue decomposition. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Mitigation of Particulate Matter and Airborne Pathogens in Swine Barn Emissions with Filtration and UV-A Photocatalysis

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Catalysts 2021, 11(11), 1302; https://doi.org/10.3390/catal11111302 - 28 Oct 2021

Cited by 1 | Viewed by 565

Abstract

This study evaluated the use of filtration and UV-A photocatalysis for the reduction of particulate matter (PM) and airborne bacterial pathogens in swine barns. Two MERV filters (8 and 15) were used to mitigate PM concentrations measured at the PM 1, PM 2.5, respirable PM, and PM 10 ranges. Filtration was also used to generate different levels of airborne pathogens to be treated by UV-A. Results show that MERV 8 and 15 filters effectively reduced PM concentrations (96–98%) in air exhausted from a swine barn (p ranged from <0.01 to 0.04). UV-A photocatalysis did not mitigate PM concentrations. UV-A photocatalysis treatment reduced measured colony-forming units (CFUs) by 15–95%. The CFU percent reduction was higher when airborne PM concentration was low. The numeric results suggested a real mitigation effect despite p-values that did not meet the usual statistical cut-off of <0.05 for significance due to the large variability of the CFU control samples. Normalization of measured airborne pathogen concentrations by smaller PM size range concentrations led to emerging significant treatment differences for CFUs. A significant decrease (~51% reduction; p < 0.02) in the concentration of viable airborne bacteria was shown for all PM below the 10 micron range. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Synthesis of Nano-ZnO/Diatomite Composite and Research on Photoelectric Application

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Catalysts 2021, 11(10), 1232; https://doi.org/10.3390/catal11101232 - 13 Oct 2021

Cited by 2 | Viewed by 527

Abstract

The key to the commercialization of sustainable energy conversion technologies is the development of high-performance catalysts. The discovery of a stable, efficient, and low-cost multi-function catalysts is the key. We used a simple green precipitation method to load nanozinc oxide particles onto a diatomite substrate. The ZnO is nano-sized. This precipitation method produces ZnO nanoparticles in situ on diatomite. The catalysts degraded 90% of Methylene blue solution and also degraded gaseous benzene and gaseous acetone. Not only can the catalysts be used for the organic degradation of wastewater, but it also has the potential to degrade volatile organic compounds. Photocatalytic efficiency is closely related to the generation and separation of photogenerated electrons and holes. The effective suppression of the recombination rate of photoliving carriers and thus improvement of the photocatalytic activity, has become a key research area. At present, photocatalysis is an effective technology to inhibit photogenerated carrier recombination, which is often studied in sewage treatment. Photoelectrochemical decomposition of water reduces the recombination of photogenerated electrons and holes by applying an external bias, thus improving the quantum efficiency for the complete mineralization of organic pollutants. The composite catalysts were used for oxygen and hydrogen extraction reactions, and a comparison of the catalysts with various loading ratios showed that the photoelectrochemical decomposition of water activity of the composite catalysts are due to pure ZnO, and the efficiency is highest when the loading ratio is 10%. This work provides new methods for the design and further optimization of the preparation of photoelectrochemical decomposition of water catalysts. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Mesoporous TiO₂ Implanted ZnO QDs for the Photodegradation of Tetracycline: Material Design, Structural Characterization and Photodegradation Mechanism

Anwar Iqbal

Usman Saidu

Srimala Sreekantan

Mohammad Norazmi Ahmad

and

Catalysts 2021, 11(10), 1205; https://doi.org/10.3390/catal11101205 - 08 Oct 2021

Cited by 2 | Viewed by 704

Abstract

A sol-gel method was used to prepare a mesoporous TiO₂ implanted with a ZnO quantum dot photocatalyst (TZQ) for the photodegradation of tetracycline (TC) under fluorescent light irradiation. Scanning electron microscopy (SEM) shows the presence of cavities on the photocatalyst surface due to the use of starch as a synthetic template, where the nitrogen sorption results indicate that TZQ contains mesopores with reduced size (ca. 4.3 nm) versus the pore size of the parent meso-TiO₂ (ca. 7.5 nm). The addition of ZnO quantum dots (QDs) resulted in spherically-shaped binary composite particles in layers onto the surface of TiO₂. The coexistence of the ZnO QDs and TiO₂ phase was observed using high resolution-transmission electron microscopy (HR-TEM). The photodegradation of TC was carried out in a homemade reactor equipped with two fluorescent lights (24 W each) and within 90 min of irradiation, 94.6% of TC (40 mg L⁻¹) was photodegraded using 250 mg L⁻¹ of TZQ at pH 9. The major reactive oxygen species identified from the scavenging tests were O₂^●− followed by HO^●. The deconvolution of the photoluminescence spectrum of TZQ indicates the presence of a strong quantum confinement effect (QCE) of the ZnO QDs, a defect related to Ti-species and oxygen. The analysis of the intermediates detected by LC-time-of-flight/mass spectrometry (LC/TOF-MS) suggest two photodegradation pathways. The pathways were validated using the Fukui function approach and the Wheland localisation approach. This simple and efficient photocatalytic technology is anticipated to benefit small-scale animal husbandries and aquaculture operators that have limited access to sustainable water treatment technology. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Fe-TiO₂/AC and Co-TiO₂/AC Composites: Novel Photocatalysts Prepared from Waste Streams for the Efficient Removal and Photocatalytic Degradation of Cibacron Yellow F-4G Dye

Roberto Machado Garcia

Robert Carleer

Maria Arada Pérez

Jeamichel Puente Torres

Ying Gu

Pieter Samyn

and

Jan Yperman

Catalysts 2021, 11(10), 1137; https://doi.org/10.3390/catal11101137 - 23 Sep 2021

Cited by 2 | Viewed by 789

Abstract

Fe-TiO₂/AC and Co-TiO₂/AC composites were prepared from activated carbon (AC) derived from residues of peanut hulls and TiO₂ photocatalyst, electrochemically prepared from titanium scrap, and doped with Fe and Co, respectively. The adsorption capacity and photocatalytic activity of the Fe-TiO₂/AC and Co-TiO₂/AC composites were studied for removing and degrading Cibacron Yellow F-4G (CYF-4G) from wastewater. Doped ACs were characterized by thermogravimetry (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), a new X-ray absorption technique (XRA), and elemental analysis (EA). Interesting relationships were found between SEM, XRA, and TGA data and the doped amount of catalyst on ACs. Optimal dye adsorption was found at a pH of 2.0. The CYF-4G adsorption kinetics are followed according to the pseudo-second order model. The experimental data revealed that the Langmuir model fits better than the Freundlich and Temkin models. A decrease in adsorption capacity was observed when the catalyst dope percentage increased. A removal and degradation efficiency of the dye close to 100% was achieved around 120 min. A synergistic adsorption and photocatalytic degradation effect of the Fe-TiO₂/AC and Co-TiO₂/AC composites could be observed when adsorption experiments were conducted under simulated visible radiation. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

A Novel Machine Learning Model to Predict the Photo-Degradation Performance of Different Photocatalysts on a Variety of Water Contaminants

and

Catalysts 2021, 11(9), 1107; https://doi.org/10.3390/catal11091107 - 15 Sep 2021

Cited by 1 | Viewed by 1111

Abstract

This paper describes an innovative machine learning (ML) model to predict the performance of different metal oxide photocatalysts on a wide range of contaminants. The molecular structures of metal oxide photocatalysts are encoded with a crystal graph convolution neural network (CGCNN). The structure of organic compounds is encoded via digital molecular fingerprints (MF). The encoded features of the photocatalysts and contaminants are input to an artificial neural network (ANN), named as CGCNN-MF-ANN model. The CGCNN-MF-ANN model has achieved a very good prediction of the photocatalytic degradation rate constants by different photocatalysts over a wide range of organic contaminants. The effects of the data training strategy on the ML model performance are compared. The effects of different factors on photocatalytic degradation performance are further evaluated by feature importance analyses. Examples are illustrated on the use of this novel ML model for optimal photocatalyst selection and for assessing other types of photocatalysts for different environmental applications. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Degradation Efficiency and Kinetics Analysis of an Advanced Oxidation Process Utilizing Ozone, Hydrogen Peroxide and Persulfate to Degrade the Dye Rhodamine B

Piotr Zawadzki

and

Małgorzata Deska

Catalysts 2021, 11(8), 974; https://doi.org/10.3390/catal11080974 - 14 Aug 2021

Viewed by 1037

Abstract

In this study, the effectiveness of a rhodamine B (RhB) dye degradation process at a concentration of 20 mg/L in different advanced oxidation processes—H₂O₂/UV, O₃/UV and PDS/UV—has been studied. The use of UV in a photo-assisted ozonation process (O₃/UV) proved to be the most effective method of RhB decolorization (90% after 30 min at dye concentration of 100 mg/L). The addition of sulfate radical precursors (sodium persulfate, PDS) to the reaction environment did not give satisfactory effects (17% after 30 min), compared to the PDS/UV system (70% after 30 min). No rhodamine B decolorization was observed using hydrogen peroxide as a sole reagent, whereas an effect on the degree of RhB degradation was observed when UV rays strike the sample with H₂O₂ (33% after 30 min). The rhodamine B degradation process followed the pseudo-first-order kinetics model. The combined PDS/O₃/UV process has shown 60% color removal after 30 min of reaction time at an initial dye concentration of 100 mg/L. A similar effectiveness was obtained by only applying ozone or UV-activated persulfate, but at a concentration 2–5 times lower (20 mg/L). The results indicated that the combined PDS/O₃/UV process is a promising method for high RhB concentrations (50–100 mg/L) comparing to other alternative advanced oxidation processes. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Fabrication of Six Manganese Containing Polyoxometalate Modified Graphite C₃N₄ Nanosheets Catalysts Used to Catalyze Water Decomposition

and

Catalysts 2021, 11(7), 856; https://doi.org/10.3390/catal11070856 - 17 Jul 2021

Cited by 2 | Viewed by 679

Abstract

With the increase in gas population, the demand for clean and renewable energy is increasing. Hydrogen energy has a high combustion conversion energy while water is its combustion product. In recent years, a way to convert water into hydrogen and oxygen has been found by human beings inspired by plant photosynthesis. However, water decomposition consumes a significant amount of energy and is expensive. People expect to obtain a water decomposition catalyst with low cost and high efficiency. This work selected a six-manganese containing polyoxometalate with a similar structure characteristic to photosynthesizing PSII to fabricate with graphite C₃N₄ nanosheets for the construction of composite film (Mn₆SiW/g-C₃N₄NSs) electrode via layer by layer self-assembly technology, which was used for the photo-electrochemical decomposition of water under visible light conditions. The binary composite film electrode displayed good catalytic efficiency. The photoelectric density of the composite electrode is 46 μA/cm² (at 1.23 V vs. Ag/AgCl) and 239 μA/cm² (at 1.5 V vs. Ag/AgCl). Compared with the g-C₃N₄NSs electrode alone, the photoelectric density of the composite electrode increased by 1 time. The reason is attributed to the fact that Mn₆SiW has a similar structure characteristic to photosynthesizing PSII and high electron transferability. The construction of the composite film containing low-cost Mn₆SiW to modify g-C₃N₄NSs can effectively improve the photocatalytic decomposition of water, thus this study provides valuable reference information for the development of low-cost and high-performance photo-electrocatalytic materials. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Green Synthesis, Structural Characterization and Photocatalytic Applications of ZnO Nanoconjugates Using Heliotropium indicum

Udari Wijesinghe

Gobika Thiripuranathar

and

Catalysts 2021, 11(7), 831; https://doi.org/10.3390/catal11070831 - 08 Jul 2021

Cited by 5 | Viewed by 1458

Abstract

In recent years, biosynthesized zinc oxide nanoparticles (ZnO NPs) have been gaining importance due to their unique properties and tremendous applications. This study aimed to fabricate ZnO NPs by using extracts from various parts of the traditional medicinal plant Heliotropium indicum (H. indicum) and evaluate their photocatalytic activity. Further, their potential in photoluminescence and fluorescence resonance energy transfer (FRET) was assessed. The Ultraviolet-Visible spectrum exhibited a hypsochromic shifted absorption band between 350–380 nm. Transmission electron microscopy (TEM) analysis revealed spherical NPs, while X-ray diffraction (XRD) data revealed wurtzite, hexagonal and crystalline nature. The TEM and XRD consistently determined an average particle size range from 19 to 53 nm. The photocatalytic degradation reaches a maximum of 95% for biogenic ZnO NPs by monitoring spectrophotometrically the degradation of methylene blue dye (λ_max = 662.8 nm) under solar irradiation. Photoluminescence analysis revealed differentiated spectra with high-intensity emission peaks for biogenic ZnO NPs compared with chemically synthesized ZnO NPs. Eventually, the highest efficiency of FRET (80%) was found in ZnO NPs synthesized from the leaves. This remains the first report highlighting the multifunctional ZnO NPs capabilities mediated by using H. indicum, which could lead to important potential environmental and biomedical applications. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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WO₃ Fibers/g-C₃N₄ Z-Scheme Heterostructure Photocatalysts for Simultaneous Oxidation/Reduction of Phenol/Cr (VI) in Aquatic Media

Feidias Bairamis

and

Ioannis Konstantinou

Catalysts 2021, 11(7), 792; https://doi.org/10.3390/catal11070792 - 29 Jun 2021

Cited by 3 | Viewed by 797

Abstract

A sequence of WO₃/g-C₃N₄ composites was synthesized at various % weight ratios (1, 5, 6.5, 8, 10, and 15%) of WO₃ into g-C₃N₄ via electrospinning and wet-mixing method. The prepared photocatalytic materials were characterized by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR) spectroscopy, UV–vis diffuse reflection spectroscopy (DRS), scanning electron microscopy (SEM), N₂ porosimetry and dynamic light scattering (DLS). Electrospun fibers of WO₃ with diameter 250–300 nm was prepared using polyvinylpyrrolidone (PVP) polymer and used for the synthesis of composite WO₃/g-C₃N₄ heterojunction structures. Results showed mesoporous materials with triclinic WO₃ crystal phase, surface areas up to 67.7 m²g⁻¹ and band gaps lower than 2.5 eV confirming the absorption to visible light region. The photocatalytic performance of the prepared photocatalysts were assessed towards the oxidation of phenol and reduction of Cr (VI), in single and binary systems using simulated solar light illumination, that followed first-order kinetics. The WO₃/g-C₃N₄ composites were found to exhibit improved photocatalytic performances compared to the pure WO₃ and g-C₃N₄ with 6.5 wt% WO₃/g-C₃N₄ and 5 wt% WO₃/g-C₃N₄ composites being the most efficient catalysts for the oxidation of phenolics and reduction of Cr (VI), respectively. The improved performance was explained by a Z-scheme photocatalytic mechanism which was proposed based on scavenging experiments and the determination of the corresponding energy levels of valence and conduction bands. The study demonstrated that such composites present interesting photocatalytic properties that can be further expanded to other environmental depollution applications as well as in energy applications. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

Bifunctional Polymeric Carbon Nitride via Tuning Fabrication Conditions for Photocatalysis

Malgorzata Aleksandrzak

and

Catalysts 2021, 11(6), 651; https://doi.org/10.3390/catal11060651 - 21 May 2021

Cited by 1 | Viewed by 830

Abstract

In this contribution, the hydrogen evolution reaction and photodegradation of Rhodamine B (RhB) dye were studied using urea-based polymeric carbon nitride (PCN) as photocatalyst. The effects of calcination temperature and heating rate of the PCN on structural, morphological, optical, photoelectrochemical, and photocatalytic properties were addressed. Different properties were found to be crucial in boosting photocatalytic performance dependending on the reaction type. The highest efficiency in hydrogen evolution was observed in the presence of PCN characterized by the superior charge transport and charge lifetime properties arising from higher degree of structural arrangement and lower defect content in comparison to that of other photocatalysts. However, photocatalytic degradation of RhB was the most powerful when the catalyst exhibited the highest specific surface area as a key parameter determining its efficiency, although it presented lower charge transport and charge carrier properties. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessArticle

ZnO Nanospheres Fabricated by Mechanochemical Method with Photocatalytic Properties

Zhou Zhou

Jing Wang

and

Chul Gyu Jhun

Catalysts 2021, 11(5), 572; https://doi.org/10.3390/catal11050572 - 29 Apr 2021

Cited by 2 | Viewed by 675

Abstract

The preparation of high specific area (86.5 m²/g) ZnO nanospheres with good photocatalytic efficiency via a simple, green and efficient mechanochemical method was reported in this work. The products were characterized by XRD, SEM, TEM, BET and UV–Vis. The ball milling parameters were improved to reduce the agglomeration hazard during the ball milling process, and the specific surface area, band gap and photocatalytic efficiency were investigated in relation to ball milling time. Our study developed the opportunity for the low-cost and facile synthesis of a high specific surface area photocatalyst on a large scale for future industrial applications. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Review

Jump to: Research

Open AccessFeature PaperReview

Engineered Nanostructured Photocatalysts for Cancer Therapy

Javier Bonet-Aleta

Jose I. Garcia-Peiro

and

Jose L. Hueso

Catalysts 2022, 12(2), 167; https://doi.org/10.3390/catal12020167 - 28 Jan 2022

Viewed by 882

Abstract

The present review aims at highlighting recent advances in the development of photocatalysts devoted to cancer therapy applications. We pay especial attention to the engineering aspects of different nanomaterials including inorganic semiconductors, organic-based nanostructures, noble metal-based systems or synergistic hybrid heterostructures. Furthermore, we also explore and correlate structural and optical properties with their photocatalytic capability to successfully performing in cancer-related therapies. We have made an especial emphasis to introduce current alternatives to organic photosensitizers (PSs) in photodynamic therapy (PDT), where the effective generation of reactive oxidative species (ROS) is pivotal to boost the efficacy of the treatment. We also overview current efforts in other photocatalytic strategies to tackle cancer based on photothermal treatment, starvation therapy, oxidative stress unbalance via glutathione (GSH) depletion, biorthogonal catalysis or local relief of hypoxic conditions in tumor microenvironments (TME). Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Sulfide-Based Photocatalysts Using Visible Light, with Special Focus on In₂S₃, SnS₂ and ZnIn₂S₄

José C. Conesa

Catalysts 2022, 12(1), 40; https://doi.org/10.3390/catal12010040 - 30 Dec 2021

Viewed by 565

Abstract

Sulfides are frequently used as photocatalysts, since they absorb visible light better than many oxides. They have the disadvantage of being more easily photocorroded. This occurs mostly in oxidizing conditions; therefore, they are commonly used instead in reduction processes, such as CO₂ reduction to fuels or H₂ production. Here a summary will be presented of a number of sulfides used in several photocatalytic processes; where appropriate, some recent reviews will be presented of their behaviour. Results obtained in recent years by our group using some octahedral sulfides will be shown, showing how to determine their wavelength-dependent photocatalytic activities, checking their mechanisms in some cases, and verifying how they can be modified to extend their wavelength range of activity. It will be shown here as well how using photocatalytic or photoelectrochemical setups, by combining some enzymes with these sulfides, allows achieving the photo-splitting of water into H₂ and O₂, thus constituting a scheme of artificial photosynthesis. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Open AccessFeature PaperReview

The Evolution of Photocatalytic Membrane Reactors over the Last 20 Years: A State of the Art Perspective

Raffaele Molinari

Cristina Lavorato

and

Pietro Argurio

Catalysts 2021, 11(7), 775; https://doi.org/10.3390/catal11070775 - 26 Jun 2021

Cited by 2 | Viewed by 825

Abstract

The research on photocatalytic membrane reactors (PMRs) started around the year 2000 with the study of wastewater treatment by degradation reactions of recalcitrant organic pollutants, and since then the evolution of our scientific knowledge has increased significantly, broadening interest in reactions such as the synthesis of organic chemicals. In this paper, we focus on some initial problems and how they have been solved/reduced over time to improve the performance of processes in PMRs. Some know-how gained during these last two decades of research concerns decreasing/avoiding the degradation of the polymeric membranes, improving photocatalyst reuse, decreasing membrane fouling, enhancing visible light photocatalysts, and improving selectivity towards the reaction product(s) in synthesis reactions (partial oxidation and reduction). All these aspects are discussed in detail in this review. This technology seems quite mature in the case of water and wastewater treatment using submerged photocatalytic membrane reactors (SPMRs), while for applications concerning synthesis reactions, additional knowledge is required. Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Highly Ordered Mesoporous Cobalt Phosphide (CoP) for Efficient Overall Electrochemical and Photoelectrochemical Water Splitting
Authors: Feng Li, Baoshan Liu, Jing Liu, Liping Zhao, Xuefeng Song, Peng Zhang, Lian Gao
Affiliation: Shanghai Jiao Tong University 800 Dongchuan Road Shanghai 200240 China
Abstract: The design and development of high-active non-noble bifunctional catalyst for electrocatalytic and photoelectrocatalytic water splitting with optimized nanostructures is one of the critical tasks for sustainable energy technologies. Herein, we reported a highly ordered mesoporous CoP particles for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1.0 M KOH electrolyte. Benefiting from the ordered mesoporous structure, the as-prepared CoP exhibits low overpotentials for both HER and OER. The voltage needed for overall water splitting is only 1.656 V at 10 mA cm-2, close to the performance of Pt/C and RuO2 group. The catalytic performance of the mesoporous CoP is further demonstrated in silicon (Si) based photoelectrochemical (PEC) cathode and anode consisting of bottom Si photo-absorber, TiO2 protective layer, and the CoP surface cocatalyst. This study provides a commercial non-noble catalyst for overall electrochemical and photoelectrochemical water splitting.

Title: Sulphide-based photocatalysts using visible light
Authors: José C. Conesa
Affiliation: Instituto de Catálisis y Petroleoquímica, CSIC Marie Curie 2, 28049 Madrid, Spain
Abstract: Sulphides are used frequently for photocatalysis, since they are better absorbers of visible light than oxides. Their drawback is however that they are prone to photocorrosion, mainly in oxidizing conditions, so that they are more frequently used in reductive processes, e.g. H2 production or CO2 reduction to fuels. Here an overview will be given of different sulphides used for different photocatalytic processes, giving where appropriate recent reviews on their behaviour. Results obtained in recent years by our group with some octahedral sulphides will be described, showing how to measure their wavelength dependent photocatalytic activities, checking in some cases their mechanisms; how to modify them in order to extend their wavelength range of activity, and how photocatalytic and photoelectrochemical techniques can be used, combining these sulphides with some enzymes, to achieve the photo-splitting of water or the reduction of CO2 in an artificial photosynthesis scheme.

Title: Degradation efficiency and kinetics analysis of an advanced oxidation process utilizing ozone, hydrogen peroxide and persulfate to degrade the rhodamine B dye
Authors: Piotr ZAWADZKIa*, Małgorzata Deskaa
Affiliation: a Department of Water Protection, Central Mining Institute, Plac Gwarków 1, 40-166 Katowice, Poland
Abstract: In this study, the effectiveness of a rhodamine B (RhB) dye degradation process at a concentration of 20 mg/dm3 in advanced oxidation processes: H2O2/UV, O3/UV and PDS/UV has been studied. The dynamics of the RhB decolorization process dynamics was described by the pseudo-first-order and pseudo-second-order reaction kinetics. Independently of the treatment system, the degree of rhodamine B degradation increased simultaneously with the process time. The rhodamine B degradation process followed the pseudo-first-order kinetics model. The use of UV in a photo-assisted ozonation process (O3/UV) proved to be the most effective method of RhB decolorization (up to 90% after 30 min of reaction time). The addition of sulfate radical precursors (sodium persulfate, PDS) to the reaction environment did not give satisfactory effects (17% after 30 min), compared to the PDS/UV system (70% after 30 min). No rhodamine B decolorization was observed using hydrogen peroxide as a sole process, whereas the effect on the degree of RhB degradation was observed when UV rays strike the sample with H2O2 (33% after 30 min). The combined PDS/O3/UV process has shown 60% color removal after 30 min of reaction time at an initial dye concentration of 100 mg/dm3. The results indicated that the AOP combination is a promising method for RhB degradation from aqueous solutions.

Title: Development of A Novel Micro Gap Reactor System for the Photocatalytic Degradation of Micropollutants from Aqueous Solutions with Spray Coat Immobilized TiO2-based Photocatalysts
Authors: Tony B. Engelhardt, Minrui Zhu, Claudia Heilmann, Sabine Schmitz-Stöwe, Thomas Schwarz and Klaus Stöwe*
Affiliation: Institut für Chemie, Fakultät für Naturwissenschaften, Technische Universität Chemnitz, Straße der Nationen 62,09111 Chemnitz, Germany
Abstract: The presented investigation focuses on the development of a novel micro gap reactor concept for the photocatalytic degradation of micropollutants from aqueous solu-tions with spray coat immobilized, titanium dioxide-based catalysts. Combinatorial experiment designs were utilized for studying the influence of the micro gap width, irradiance and catalyst layer thickness on the conversion of 17α-ethinyl estradiol. The impact of catalyst-doping and solution matrix effects are discussed, as well. Regarding conversion analysis, LC-MS/MS and GC-MS techniques were deployed, as PXRD, ESEM and BET were utilized for catalyst characterization. Results show that the build micro gap reactor system enables a conversion of 65 % within a residence time of 2.7 min with UV-A irradiation and under steady flow conditions. Thus, the presented bench scale photocatalysis reactor provides promising fundamental findings for a future development of pilot scale approaches. With the deployment of industrial available catalyst and base materials, the micro gap reactor photocatalytic degradation represents an attractive technology for large-scale application.

Title: Coinage Metal based Photocatalysts, Electrocatalysts, and Photoelectrocatalysts for CO2 conversion
Authors: Nikhil Dhabarde, Prichard M. Tembo, Vaidyanathan Subramanian*
Affiliation: Chemical and Materials Engineering Department University of Nevada, Reno LME 309, MS 388
Abstract: Carbon dioxide (CO2) conversion to value-added products is one of the key pathways to address climate change caused by CO2 emissions. Over the past decades, catalytic (photocatalytic, electrocatalytic, and photoelectrocatalytic) approaches for CO2 conversion have been investigated as an increasingly important and viable solution. Coinage metals, especially those belonging to Group 11 of the periodic table (copper, gold, and silver), have exhibited high catalytic activities for organic chemical reactions. In this review, the key research conducted on coinage metal-based photocatalytic, electrocatalytic, and photoelectrocatalytic CO2 conversion is discussed. This article will also provide insights into the challenges and opportunities to the application of coinage metals for catalytic CO2 conversion.

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