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Heterogeneous Photocatalysis: A Solution for a Greener Earth
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Heterogeneous Photocatalysis: A Solution for a Greener Earth

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

Deadline for manuscript submissions: closed (10 April 2022) | Viewed by 46448

Printed Edition Available!
A printed edition of this Special Issue is available here.

Special Issue Editors

Prof. Dr. Stéphanie Lambert

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Guest Editor
Department of Chemical Engineering–Nanomaterials, Catalysis and Electrochemistry, B6a, University of Liege, 4000 Liege, Belgium
Interests: heterogeneous (photo)catalysis; sol-gel process; environmental engineering; inorganic biomaterials
Special Issues, Collections and Topics in MDPI journals
Dr. Julien Mahy

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Co-Guest Editor
Institute of Condensed Matter and Nanosciences (IMCN), Université catholique de Louvain, Place Louis Pasteur 1, 1348 Louvain-la-Neuve, Belgium
Interests: Heterogeneous photocatalysis, sol-gel process, thin inorganic films, SiO2, TiO2, water and air treatment
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Since the beginning of the industrial era, various human activities have steadily increased, leading to rapid technological developments and a high population growth. As consequence, the expanding industry has heavily polluted the atmosphere, soil, and water, with negative consequences for humans and environment. Indeed, major pollution can cause human diseases like breath problems, cardiovascular problems, cancer, neurobehavioral disorders. It can also affect global warming and the associated climate change and sea level rise and seriously damage animals and flora. The main pollutants are aromatic compounds, pesticides, chlorinated compounds, SOx, NOx, heavy metals, and petroleum hydrocarbons.

In order to decrease pollution emissions, various chemical, physical, and biological treatment methods have been developed. The major technics for treating wastewater are based on wastewater treatment plants using dry cleaning, decantation, and biological treatments. Sometimes, pollutant molecules are not eliminated by these processes, therefore other technics can be used as secondary treatments to remove these small residual fractions of pollution. Among these methods, photocatalysis is a technic well developed in the past years. Through a photocatalyst and light, photocatalysis allows the production of highly reactive species that can react and decompose organic molecules, yielding, in the best case, the final decomposition products CO2 and H2O. The most commonly used photocatalysts are titanium dioxide (TiO2), zinc oxide (ZnO), tin oxide (SnO2).

In this Special Issue entitled "Heterogeneous photocatalysis: a solution for a greener Earth?", we welcome all kind of papers (research papers, reviews, or communications) dealing with innovative photocatalytic processes for environmental applications. The papers can concern the photocatalytic degradation of pollutants in water, air, or soil, using the photocatalytic process for the valorization of wastes or the production of green energy.

Prof. Dr. Stéphanie Lambert
Dr. Julien Mahy
Guest Editors

Manuscript Submission Information

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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

  • Photocatalysis
  • environmental catalysis
  • micropollutants
  • waste waters
  • polluted gaseous emissions
  • sol-gel process
  • doped photocatalysts
  • UV light
  • visible light

Published Papers (18 papers)

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Editorial

Jump to: Research, Review

6 pages, 222 KiB  
Editorial
Heterogeneous Photocatalysis: A Solution for a Greener Earth
by Julien G. Mahy and Stéphanie D. Lambert
Catalysts 2022, 12(7), 686; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12070686 - 23 Jun 2022
Cited by 1 | Viewed by 1155
Abstract
Since the beginning of the industrial era, various human activities have steadily increased, leading to rapid technological developments and high population growth [...] Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)

Research

Jump to: Editorial, Review

11 pages, 3374 KiB  
Article
Visible Light Induced Nano-Photocatalysis Trimetallic Cu0.5Zn0.5-Fe: Synthesis, Characterization and Application as Alcohols Oxidation Catalyst
by Asma Ghazzy, Lina Yousef and Afnan Al-Hunaiti
Catalysts 2022, 12(6), 611; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12060611 - 02 Jun 2022
Cited by 3 | Viewed by 1516
Abstract
Here, we report a visible light-induced-trimetallic catalyst (Cu0.5Zn0.5Fe2O4) prepared through green synthesis using Tilia plant extract. These nanomaterials were characterized for structural and morphological studies using powder x-ray diffraction (P-XRD), scanning electron microscopy (SEM) and [...] Read more.
Here, we report a visible light-induced-trimetallic catalyst (Cu0.5Zn0.5Fe2O4) prepared through green synthesis using Tilia plant extract. These nanomaterials were characterized for structural and morphological studies using powder x-ray diffraction (P-XRD), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The spinel crystalline material was ~34 nm. In benign reaction conditions, the prepared photocatalyst oxidized various benzylic alcohols with excellent yield and selectivity toward aldehyde with 99% and 98%; respectively. Aromatic and aliphatic alcohols (such as furfuryl alcohol and 1-octanol) were photo-catalytically oxidized using Cu0.5Zn0.5Fe2O4, LED light, H2O2 as oxidant, 2 h reaction time and ambient temperature. The advantages of the catalyst were found in terms of reduced catalyst loading, activating catalyst using visible light in mild conditions, high conversion of the starting material and the recyclability up to 5 times without loss of the selectivity. Thus, our study offers a potential pathway for the photocatalytic nanomaterial, which will contribute to the advancement of photocatalysis studies. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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14 pages, 8124 KiB  
Article
Natural Clay Modified with ZnO/TiO2 to Enhance Pollutant Removal from Water
by Julien G. Mahy, Marlène Huguette Tsaffo Mbognou, Clara Léonard, Nathalie Fagel, Emmanuel Djoufac Woumfo and Stéphanie D. Lambert
Catalysts 2022, 12(2), 148; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12020148 - 25 Jan 2022
Cited by 14 | Viewed by 2760
Abstract
Raw clays, extracted from Bana, west Cameroon, were modified with semiconductors (TiO2 and ZnO) in order to improve their depollution properties with the addition of photocatalytic properties. Cu2+ ions were also added to the clay by ionic exchange to increase the [...] Read more.
Raw clays, extracted from Bana, west Cameroon, were modified with semiconductors (TiO2 and ZnO) in order to improve their depollution properties with the addition of photocatalytic properties. Cu2+ ions were also added to the clay by ionic exchange to increase the specific surface area. This insertion of Cu was confirmed by ICP-AES. The presence of TiO2 and ZnO was confirmed by the detection of anatase and wurzite, respectively, using X-ray diffraction. The composite clays showed increased specific surface areas. The adsorption property of the raw clays was evaluated on two pollutants, i.e., fluorescein (FL) and p-nitrophenol (PNP). The experiments showed that the raw clays can adsorb FL but are not efficient for PNP. To demonstrate the photocatalytic property given by the added semiconductors, photocatalytic experiments were performed under UVA light on PNP. These experiments showed degradation up to 90% after 8 h of exposure with the best ZnO-modified clay. The proposed treatment of raw clays seems promising to treat pollutants, especially in developing countries. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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13 pages, 1985 KiB  
Article
TiO2-Acetylacetone as an Efficient Source of Superoxide Radicals under Reduced Power Visible Light: Photocatalytic Degradation of Chlorophenol and Tetracycline
by Lucas A. Almeida, Anja Dosen, Juliana Viol and Bojan A. Marinkovic
Catalysts 2022, 12(2), 116; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12020116 - 19 Jan 2022
Cited by 8 | Viewed by 2233
Abstract
Visible light-sensitive TiO2-based nanomaterials are widely investigated for photocatalytic applications under high power (≥300 W) UV and visible light. The formation of charge transfer complexes (CTCs) between bidentate ligands and nanocrystalline TiO2 promotes visible light absorption and constitutes a promising [...] Read more.
Visible light-sensitive TiO2-based nanomaterials are widely investigated for photocatalytic applications under high power (≥300 W) UV and visible light. The formation of charge transfer complexes (CTCs) between bidentate ligands and nanocrystalline TiO2 promotes visible light absorption and constitutes a promising alternative for environmental remediation under reduced visible light power. However, the efficiency of photodegradation, the volatilization profile of bidentates, and the role of reactive oxidizing species (ROS) are not fully understood. In this study, thermogravimetric analyses coupled with mass spectroscopy (TGA-MS) were performed on TiO2-Acetylacetone (ACAC) CTC. TiO2-ACAC CTC calcined at 300 °C (TiO2-A300) was applied for the photocatalytic degradation of chlorophenol (4-CP) and tetracycline (TC) under low power visible light (26 W). Furthermore, the ROS scavengers isopropanol and benzoquinone were added for studying the photocatalytic role of •OH and •O2− radicals. The TGA-MS showed the release of ACAC fragments, such as ethyl ions and acetone, in the range between 150 °C and 265 °C, while between 300 °C and 450 °C only CO2 and H2O were released during oxidation of ACAC. The photocatalytic abatement of tetracycline (68.6%), performed by TiO2-A300, was ~two times higher than that observed for chlorophenol (31.3%) after 6 h, indicating a distinct participation of ROS in the degradation of these pollutants. The addition of the ROS scavenger revealed •O2− radicals as primarily responsible for the high efficiency of TiO2-ACAC CTC under reduced visible light. On the other hand, the •OH radicals are not efficiently generated in the CTC. Therefore, the development of heterostructures based on TiO2-ACAC CTC can increase the generation of ROS through coupling with semiconductors capable of generating •OH under visible light. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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14 pages, 3981 KiB  
Article
Investigation of Photocatalysis by Mesoporous Titanium Dioxide Supported on Glass Fibers as an Integrated Technology for Water Remediation
by Cristina De Ceglie, Sudipto Pal, Sapia Murgolo, Antonio Licciulli and Giuseppe Mascolo
Catalysts 2022, 12(1), 41; https://0-doi-org.brum.beds.ac.uk/10.3390/catal12010041 - 31 Dec 2021
Cited by 10 | Viewed by 1721
Abstract
The photocatalytic efficiency of an innovative UV-light catalyst consisting of a mesoporous TiO2 coating on glass fibers was investigated for the degradation of pharmaceuticals (PhACs) in wastewater effluents. Photocatalytic activity of the synthesized material was tested, for the first time, on a [...] Read more.
The photocatalytic efficiency of an innovative UV-light catalyst consisting of a mesoporous TiO2 coating on glass fibers was investigated for the degradation of pharmaceuticals (PhACs) in wastewater effluents. Photocatalytic activity of the synthesized material was tested, for the first time, on a secondary wastewater effluent spiked with nine PhACs and the results were compared with the photolysis used as a benchmark treatment. Replicate experiments were performed in a flow reactor equipped with a UV radiation source emitting at 254 nm. Interestingly, the novel photocatalyst led to the increase of the degradation of carbamazepine and trimethoprim (about 2.2 times faster than the photolysis). Several transformation products (TPs) resulting from both the spiked PhACs and the compounds naturally occurring in the secondary wastewater effluent were identified through UPLC-QTOF/MS/MS. Some of them, produced mainly from carbamazepine and trimethoprim, were still present at the end of the photolytic treatment, while they were completely or partially removed by the photocatalytic treatment. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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15 pages, 3774 KiB  
Article
Phytochemical-Assisted Green Synthesis of Nickel Oxide Nanoparticles for Application as Electrocatalysts in Oxygen Evolution Reaction
by Vidhya Selvanathan, M. Shahinuzzaman, Shankary Selvanathan, Dilip Kumar Sarkar, Norah Algethami, Hend I. Alkhammash, Farah Hannan Anuar, Zalita Zainuddin, Mohammod Aminuzzaman, Huda Abdullah and Md. Akhtaruzzaman
Catalysts 2021, 11(12), 1523; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11121523 - 15 Dec 2021
Cited by 22 | Viewed by 4648
Abstract
Electrocatalytic water splitting is a promising solution to resolve the global energy crisis. Tuning the morphology and particle size is a crucial aspect in designing a highly efficient nanomaterials-based electrocatalyst for water splitting. Herein, green synthesis of nickel oxide nanoparticles using phytochemicals from [...] Read more.
Electrocatalytic water splitting is a promising solution to resolve the global energy crisis. Tuning the morphology and particle size is a crucial aspect in designing a highly efficient nanomaterials-based electrocatalyst for water splitting. Herein, green synthesis of nickel oxide nanoparticles using phytochemicals from three different sources was employed to synthesize nickel oxide nanoparticles (NiOx NPs). Nickel (II) acetate tetrahydrate was reacted in presence of aloe vera leaves extract, papaya peel extract and dragon fruit peel extract, respectively, and the physicochemical properties of the biosynthesized NPs were compared to sodium hydroxide (NaOH)-mediated NiOx. Based on the average particle size calculation from Scherrer’s equation, using X-ray diffractograms and field-emission scanning electron microscope analysis revealed that all three biosynthesized NiOx NPs have smaller particle size than that synthesized using the base. Aloe-vera-mediated NiOx NPs exhibited the best electrocatalytic performance with an overpotential of 413 mV at 10 mA cm−2 and a Tafel slope of 95 mV dec−1. Electrochemical surface area (ECSA) measurement and electrochemical impedance spectroscopic analysis verified that the high surface area, efficient charge-transfer kinetics and higher conductivity of aloe-vera-mediated NiOx NPs contribute to its low overpotential values. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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12 pages, 3217 KiB  
Article
Ceramized Fabrics and Their Integration in a Semi-Pilot Plant for the Photodegradation of Water Pollutants
by Lara Faccani, Simona Ortelli, Magda Blosi and Anna Luisa Costa
Catalysts 2021, 11(11), 1418; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11111418 - 22 Nov 2021
Cited by 5 | Viewed by 1834
Abstract
The use of nano-photocatalysts for the water/wastewater purifications, particularly in developing regions, offers promising advantages over conventional technologies. TiO2-based photocatalysts deposited on fabrics represent an efficient solution for obtaining heterogeneous photocatalysts, which are easily adaptable in the already installed water treatment [...] Read more.
The use of nano-photocatalysts for the water/wastewater purifications, particularly in developing regions, offers promising advantages over conventional technologies. TiO2-based photocatalysts deposited on fabrics represent an efficient solution for obtaining heterogeneous photocatalysts, which are easily adaptable in the already installed water treatment plants or air purification systems. Despite the huge effort spent to develop and characterize novel nano-photocatalysts, which are especially active under solar light, knowledge gaps still persist for their full-scale application, starting from the reactor design and scale-up and the evaluation of the photocatalytic efficiency in pre-pilot scenarios. In this study, we offered easily scalable solutions for adapting TiO2-based photocatalysts, which are deposited on different kinds of fabrics and implemented in a 6 L semi-pilot plant, using the photodegradation of Rhodamine B (RhB) as a model of water pollution. We took advantage of a multi-variable optimization approach to identify the best design options in terms of photodegradation efficiency and turnover frequency (TOF). Surprisingly, in the condition of use, the irradiation with a light-emitting diode (LED) visible lamp appeared as a valid alternative to the use of UV LED. The identification of the best design options in the semi-pilot plant allowed scaling up the technology in a 100 L pilot plant suitable for the treatment of industrial wastewater. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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19 pages, 47335 KiB  
Article
Innovative Ag–TiO2 Nanofibers with Excellent Photocatalytic and Antibacterial Actions
by Petronela Pascariu, Corneliu Cojocaru, Anton Airinei, Niculae Olaru, Irina Rosca, Emmanouel Koudoumas and Mirela Petruta Suchea
Catalysts 2021, 11(10), 1234; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11101234 - 13 Oct 2021
Cited by 21 | Viewed by 2672
Abstract
Ag–TiO2 nanostructures were prepared by electrospinning, followed by calcination at 400 °C, and their photocatalytic and antibacterial actions were studied. Morphological characterization revealed the presence of one-dimensional uniform Ag–TiO2 nanostructured nanofibers, with a diameter from 65 to 100 nm, depending on [...] Read more.
Ag–TiO2 nanostructures were prepared by electrospinning, followed by calcination at 400 °C, and their photocatalytic and antibacterial actions were studied. Morphological characterization revealed the presence of one-dimensional uniform Ag–TiO2 nanostructured nanofibers, with a diameter from 65 to 100 nm, depending on the Ag loading, composed of small crystals interconnected with each other. Structural characterization indicated that Ag was successfully integrated as small nanocrystals without affecting much of the TiO2 crystal lattice. Moreover, the presence of nano Ag was found to contribute to reducing the band gap energy, which enables the activation by the absorption of visible light, while, at the same time, it delays the electron–hole recombination. Tests of their photocatalytic activity in methylene blue, amaranth, Congo red and orange II degradation revealed an increase by more than 20% in color removal efficiency at an almost double rate for the case of 0.1% Ag–TiO2 nanofibers with respect to pure TiO2. Moreover, the minimum inhibitory concentration was found as low as 2.5 mg/mL for E. coli and 5 mg/mL against S. aureus for the 5% Ag–TiO2 nanofibers. In general, the Ag–TiO2 nanostructured nanofibers were found to exhibit excellent structure and physical properties and to be suitable for efficient photocatalytic and antibacterial uses. Therefore, these can be suitable for further integration in various important applications. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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13 pages, 1745 KiB  
Article
Photocatalytic Degradation of Thiacloprid Using Tri-Doped TiO2 Photocatalysts: A Preliminary Comparative Study
by Antonietta Mancuso, Wanda Navarra, Olga Sacco, Stefania Pragliola, Vincenzo Vaiano and Vincenzo Venditto
Catalysts 2021, 11(8), 927; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11080927 - 30 Jul 2021
Cited by 12 | Viewed by 2276
Abstract
Different tri-doped TiO2 photocatalysts (Fe-N-P/TiO2, Fe-N-S/TiO2, Fe-Pr-N/TiO2, Pr-N-S/TiO2, and P-N-S/TiO2) were successfully prepared and tested in the photocatalytic removal of thiacloprid (THI) under UV-A, visible, and direct solar light irradiation. The physical-chemical [...] Read more.
Different tri-doped TiO2 photocatalysts (Fe-N-P/TiO2, Fe-N-S/TiO2, Fe-Pr-N/TiO2, Pr-N-S/TiO2, and P-N-S/TiO2) were successfully prepared and tested in the photocatalytic removal of thiacloprid (THI) under UV-A, visible, and direct solar light irradiation. The physical-chemical properties of the prepared catalysts were analyzed by different characterization techniques, revealing that dopants are effectively incorporated into the anatase TiO2 lattice, resulting in a decrease of the energy band gap. The reduction of photoluminescence intensity indicates a lower combination rate and longer lifespan of photogenerated carriers of all doped samples in comparison with the un-doped TiO2. The doped photocatalysts not only significantly promote the photodegradation under UV-A light irradiation but also extend the optical response of TiO2 to visible light region, and consequently improve the visible light degradation of THI. Fe-N-P tri-doped TiO2 sample exhibits the highest THI photodegradation degree (64% under UV-A light, 29% under visible light and 73% under solar light). Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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13 pages, 2239 KiB  
Article
Cytostatic Drug 6-Mercaptopurine Degradation on Pilot Scale Reactors by Advanced Oxidation Processes: UV-C/H2O2 and UV-C/TiO2/H2O2 Kinetics
by Luis A. González-Burciaga, Juan C. García-Prieto, Manuel García-Roig, Ismael Lares-Asef, Cynthia M. Núñez-Núñez and José B. Proal-Nájera
Catalysts 2021, 11(5), 567; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11050567 - 29 Apr 2021
Cited by 7 | Viewed by 2090
Abstract
6-Mercaptopurine (6-MP) is a commonly used cytostatic agent, which represents a particular hazard for the environment because of its low biodegradability. In order to degrade 6-MP, four processes were applied: Photolysis (UV-C), photocatalysis (UV-C/TiO2), and their combination with H2O [...] Read more.
6-Mercaptopurine (6-MP) is a commonly used cytostatic agent, which represents a particular hazard for the environment because of its low biodegradability. In order to degrade 6-MP, four processes were applied: Photolysis (UV-C), photocatalysis (UV-C/TiO2), and their combination with H2O2, by adding 3 mM H2O2/L (UV-C/H2O2 and UV-C/TiO2/H2O2 processes). Each process was performed with variable initial pH (3.5, 7.0, and 9.5). Pilot scale reactors were used, using UV-C lamps as radiation source. Kinetic calculations for the first 20 min of reaction show that H2O2 addition is of great importance: in UV-C experiments, highest k was reached under pH 3.5, k = 0.0094 min−1, while under UV-C/H2O2, k = 0.1071 min−1 was reached under the same initial pH; similar behavior was observed for photocatalysis, as k values of 0.0335 and 0.1387 min−1 were calculated for UV-C/TiO2 and UV-C/TiO2/H2O2 processes, respectively, also under acidic conditions. Degradation percentages here reported for UV-C/H2O2 and UV-C/TiO2/H2O2 processes are above 90% for all tested pH values. Ecotoxicity analysis of samples taken at 60 min in the photolysis and photocatalysis processes, suggests that contaminant degradation by-products present higher toxicity than the original compound. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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15 pages, 4162 KiB  
Article
Comparison of Advanced Oxidation Processes for the Degradation of Maprotiline in Water—Kinetics, Degradation Products and Potential Ecotoxicity
by Nuno P. F Gonçalves, Zsuzsanna Varga, Edith Nicol, Paola Calza and Stéphane Bouchonnet
Catalysts 2021, 11(2), 240; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11020240 - 11 Feb 2021
Cited by 9 | Viewed by 2141
Abstract
The impact of different oxidation processes on the maprotiline degradation pathways was investigated by liquid chromatography-high resolution mass spectrometry (LC/HRMS) experiments. The in-house SPIX software was used to process HRMS data allowing to ensure the potential singular species formed. Semiconductors photocatalysts, namely Fe-ZnO, [...] Read more.
The impact of different oxidation processes on the maprotiline degradation pathways was investigated by liquid chromatography-high resolution mass spectrometry (LC/HRMS) experiments. The in-house SPIX software was used to process HRMS data allowing to ensure the potential singular species formed. Semiconductors photocatalysts, namely Fe-ZnO, Ce-ZnO and TiO2, proved to be more efficient than heterogeneous photo-Fenton processes in the presence of hydrogen peroxide and persulfate. No significant differences were observed in the degradation pathways in the presence of photocatalysis, while the SO4− mediated process promote the formation of different transformation products (TPs). Species resulting from ring-openings were observed with higher persistence in the presence of SO4−. In-silico tests on mutagenicity, developmental/reproductive toxicity, Fathead minnow LC50, D. magna LC50, fish acute LC50 were carried out to estimate the toxicity of the identified transformation products. Low toxicant properties were estimated for TPs resulting from hydroxylation onto bridge rather than onto aromatic rings, as well as those resulting from the ring-opening. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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21 pages, 5539 KiB  
Article
Green Synthesis of N/Zr Co-Doped TiO2 for Photocatalytic Degradation of p-Nitrophenol in Wastewater
by Hayette Benkhennouche-Bouchene, Julien G. Mahy, Cédric Wolfs, Bénédicte Vertruyen, Dirk Poelman, Pierre Eloy, Sophie Hermans, Mekki Bouhali, Abdelhafid Souici, Saliha Bourouina-Bacha and Stéphanie D. Lambert
Catalysts 2021, 11(2), 235; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11020235 - 10 Feb 2021
Cited by 12 | Viewed by 3001
Abstract
TiO2 prepared by a green aqueous sol–gel peptization process is co-doped with nitrogen and zirconium to improve and extend its photoactivity to the visible region. Two nitrogen precursors are used: urea and triethylamine; zirconium (IV) tert-butoxide is added as a source of [...] Read more.
TiO2 prepared by a green aqueous sol–gel peptization process is co-doped with nitrogen and zirconium to improve and extend its photoactivity to the visible region. Two nitrogen precursors are used: urea and triethylamine; zirconium (IV) tert-butoxide is added as a source of zirconia. The N/Ti molar ratio is fixed regardless of the chosen nitrogen precursor while the quantity of zirconia is set to 0.7, 1.4, 2, or 2.8 mol%. The performance and physico-chemical properties of these materials are compared with the commercial Evonik P25 photocatalyst. For all doped and co-doped samples, TiO2 nanoparticles of 4 to 8 nm of size are formed of anatase-brookite phases, with a specific surface area between 125 and 280 m2 g−1 vs. 50 m2 g−1 for the commercial P25 photocatalyst. X-ray photoelectron (XPS) measurements show that nitrogen is incorporated into the TiO2 materials through Ti-O-N bonds allowing light absorption in the visible region. The XPS spectra of the Zr-(co)doped powders show the presence of TiO2-ZrO2 mixed oxide materials. Under visible light, the best co-doped sample gives a degradation of p-nitrophenol (PNP) equal to 70% instead of 25% with pure TiO2 and 10% with P25 under the same conditions. Similarly, the photocatalytic activity improved under UV/visible reaching 95% with the best sample compared to 50% with pure TiO2. This study suggests that N/Zr co-doped TiO2 nanoparticles can be produced in a safe and energy-efficient way while being markedly more active than state-of-the-art photocatalytic materials under visible light. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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17 pages, 1268 KiB  
Article
Assessing an Integral Treatment for Landfill Leachate Reverse Osmosis Concentrate
by Javier Tejera, Daphne Hermosilla, Ruben Miranda, Antonio Gascó, Víctor Alonso, Carlos Negro and Ángeles Blanco
Catalysts 2020, 10(12), 1389; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10121389 - 28 Nov 2020
Cited by 13 | Viewed by 2053
Abstract
An integral treatment process for landfill leachate reverse osmosis concentrate (LLROC) is herein designed and assessed aiming to reduce organic matter content and conductivity, as well as to increase its biodegradability. The process consists of three steps. The first one is a coagulation/flocculation [...] Read more.
An integral treatment process for landfill leachate reverse osmosis concentrate (LLROC) is herein designed and assessed aiming to reduce organic matter content and conductivity, as well as to increase its biodegradability. The process consists of three steps. The first one is a coagulation/flocculation treatment, which best results were obtained using a dosage of 5 g L−1 of ferric chloride at an initial pH = 6 (removal of the 76% chemical oxygen demand (COD), 57% specific ultraviolet absorption (SUVA), and 92% color). The second step is a photo-Fenton process, which resulted in an enhanced biodegradability (i.e., the ratio between the biochemical oxygen demand (BOD5) and the COD increased from 0.06 to 0.4), and an extra 43% of the COD was removed at the best trialed reaction conditions of [H2O2]/COD = 1.06, pH = 4 and [H2O2]/[Fe]mol = 45. An ultra violet-A light emitting diode (UVA-LED) lamp was tested and compared to conventional high-pressure mercury vapor lamps, achieving a 16% power consumption reduction. Finally, an optimized 30 g L−1 lime treatment was implemented, which reduced conductivity by a 43%, and the contents of sulfate, total nitrogen, chloride, and metals by 90%. Overall, the integral treatment of LLROC achieved the removal of 99.9% color, 90% COD, 90% sulfate, 90% nitrogen, 86% Al, 77% Zn, 84% Mn, 99% Mg, and 98% Si; and significantly increased biodegradability up to BOD5/COD = 0.4. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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11 pages, 2759 KiB  
Article
Synergistic Effect on Photocatalytic Activity of Co-Doped NiTiO3/g-C3N4 Composites under Visible Light Irradiation
by Duc Quang Dao, Thi Kim Anh Nguyen, Thanh-Truc Pham and Eun Woo Shin
Catalysts 2020, 10(11), 1332; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10111332 - 16 Nov 2020
Cited by 8 | Viewed by 3452
Abstract
Co-doped NiTiO3/g-C3N4 composite photocatalysts were prepared by a modified Pechini method to improve their photocatalytic activity toward methylene blue photodegradation under visible light irradiation. The combination of Co-doped NiTiO3 and g-C3N4 and Co-doping into [...] Read more.
Co-doped NiTiO3/g-C3N4 composite photocatalysts were prepared by a modified Pechini method to improve their photocatalytic activity toward methylene blue photodegradation under visible light irradiation. The combination of Co-doped NiTiO3 and g-C3N4 and Co-doping into the NiTiO3 lattice synergistically enhanced the photocatalytic performance of the composite photocatalysts. X-ray photoelectron spectroscopy results for the Co-doped NiTiO3/g-C3N4 composite photocatalysts confirmed Ti-N linkages between the Co-doped NiTiO3 and g-C3N4. In addition, characteristic X-ray diffraction peaks for the NiTiO3 lattice structure clearly indicated substitution of Co into the NiTiO3 lattice structure. The composite structure and Co-doping of the C-x composite photocatalysts (x wt % Co-doped NiTiO3/g-C3N4) not only decreased the emission intensity of the photoluminescence spectra but also the semicircle radius of the Nyquist plot in electrochemical impedance spectroscopy, giving the highest kapp value (7.15 × 10−3 min−1) for the C-1 composite photocatalyst. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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15 pages, 6345 KiB  
Article
Photocatalytic Reactivity of Carbon–Nitrogen–Sulfur-Doped TiO2 Upconversion Phosphor Composites
by Seong-Rak Eun, Shielah Mavengere, Bumrae Cho and Jung-Sik Kim
Catalysts 2020, 10(10), 1188; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10101188 - 15 Oct 2020
Cited by 5 | Viewed by 2164
Abstract
Sol–gel synthesized N-doped and carbon–nitrogen–sulfur (CNS)-doped TiO2 solutions were deposited on upconversion phosphor using a dip coating method. Scanning electron microscopy (SEM) imaging showed that there was a change in the morphology of TiO2 coated on NaYF4:Yb,Er from spherical [...] Read more.
Sol–gel synthesized N-doped and carbon–nitrogen–sulfur (CNS)-doped TiO2 solutions were deposited on upconversion phosphor using a dip coating method. Scanning electron microscopy (SEM) imaging showed that there was a change in the morphology of TiO2 coated on NaYF4:Yb,Er from spherical to nanorods caused by additional urea and thiourea doping reagents. Fourier transform infrared (FTIR) spectroscopy further verified the existence of nitrate–hyponitrite, carboxylate, and SO42− because of the doping effect. NaYF4:Yb,Er composites coated with N- and CNS-doped TiO2 exhibited a slight shift of UV-Vis spectra towards the visible light region. Photodecomposition of methylene blue (MB) was evaluated under 254 nm germicidal lamps and a 300 W Xe lamp with UV/Vis cut off filters. The photodegradation of toluene was evaluated on TiO2/NaYF4:Yb,Er and CNS-doped TiO2/NaYF4:Yb,Er samples under UV light illumination. The photocatalytic reactivity with CNS-doped TiO2/NaYF4:Yb,Er surpassed that of the undoped TiO2/NaYF4:Yb,Er for the MB solution and toluene. Photocatalytic activity is increased by CNS doping of TiO2, which improves light sensitization as a result of band gap narrowing due to impurity sites. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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15 pages, 3153 KiB  
Article
Activation Treatments and SiO2/Pd Modification of Sol–Gel TiO2 Photocatalysts for Enhanced Photoactivity under UV Radiation
by Julien G. Mahy, Valériane Sotrez, Ludivine Tasseroul, Sophie Hermans and Stéphanie D. Lambert
Catalysts 2020, 10(10), 1184; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10101184 - 14 Oct 2020
Cited by 5 | Viewed by 1848
Abstract
The objective of this work is to improve the efficiency of TiO2 photocatalysts by activation treatments and by modification with palladium nanoparticles and doping with SiO2. The influence of the additive loading was explored, and two activation treatments were performed: [...] Read more.
The objective of this work is to improve the efficiency of TiO2 photocatalysts by activation treatments and by modification with palladium nanoparticles and doping with SiO2. The influence of the additive loading was explored, and two activation treatments were performed: UV exposition and H2 reduction. TiO2/SiO2/Pd photocatalysts were synthesized by an original cogelation method: a modified silicon alkoxide, i.e., [3-(2-aminoethyl)aminopropyl]trimethoxysilane (EDAS), was used to complex the palladium ions, thanks to the ethylenediamine group, while the alkoxide groups reacted with TiO2 precursors. Pure TiO2 was also synthesized by the sol–gel process for comparison. X-ray diffraction evidenced that the crystallographic structure of TiO2 was anatase and that Pd was present, either in its oxidized form after calcination, or in its reduced form after reduction. The specific surface area of the samples varied from 5 to 145 m2 g-1. Transmission electron microscopy allowed us to observe the homogeneous dispersion and nanometric size of Pd particles in the reduced samples. The width of the band gap for pure TiO2 sample, measured by UV/Visible diffuse reflectance spectroscopy at approximately 3.2 eV, corresponded to that of anatase. The band gap for the TiO2/SiO2/Pd composite samples could not be calculated, due to their high absorption in visible range. The photocatalytic activity of the various catalysts was evaluated by the degradation of a methylene blue solution under UV radiation. The results showed that the photocatalytic activity of the catalysts was inversely proportional to the content of silica present in the matrix. A small amount of silica improved the photocatalytic activity, as compared to the pure TiO2 sample. By contrast, a high amount of silica delayed the crystallization of TiO2 in its anatase form. The activation treatment under UV had little influence on photocatalytic efficiency. The introduction of Pd species increased the photocatalytic activity of the samples because it allowed for a decrease in the rate of electron–hole recombinations in TiO2. The reduction treatment improved the activity of photocatalysts, whatever the palladium content, thanks to the reduction of Ti4+ into Ti3+, and the formation of defects in the crystallographic structure of anatase. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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19 pages, 20468 KiB  
Article
In-Depth Structural and Optical Analysis of Ce-modified ZnO Nanopowders with Enhanced Photocatalytic Activity Prepared by Microwave-Assisted Hydrothermal Method
by Otman Bazta, Ana Urbieta, Susana Trasobares, Javier Piqueras, Paloma Fernández, Mohammed Addou, Jose Juan Calvino and Ana Belén Hungría
Catalysts 2020, 10(5), 551; https://0-doi-org.brum.beds.ac.uk/10.3390/catal10050551 - 15 May 2020
Cited by 13 | Viewed by 2555
Abstract
Pure and Ce-modified ZnO nanosheet-like polycrystalline samples were successfully synthesized by a simple and fast microwave-based process and tested as photocatalytic materials in environmental remediation processes. In an attempt to clarify the actual relationships between functionality and atomic scale structure, an in-depth characterization [...] Read more.
Pure and Ce-modified ZnO nanosheet-like polycrystalline samples were successfully synthesized by a simple and fast microwave-based process and tested as photocatalytic materials in environmental remediation processes. In an attempt to clarify the actual relationships between functionality and atomic scale structure, an in-depth characterization study of these materials using a battery of complementary techniques was performed. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-Ray spectroscopy-scanning transmission electron microscopy (STEM-XEDS), photoluminescence spectroscopy (PL) and UV–Visible absorption spectroscopy were used to evaluate the effect of Ce ions on the structural, morphological, optical and photocatalytic properties of the prepared ZnO nanostructures. The XRD results showed that the obtained photocatalysts were composed of hexagonal, wurtzite type crystallites in the 34–44 nm size range. The SEM and TEM showed nanosheet-shaped crystallites, a significant fraction of them in contact with bundles of randomly oriented and much smaller nanoparticles of a mixed cerium–zinc phase with a composition close to Ce0.68Zn0.32Ox. Importantly, in clear contrast to the prevailing proposals regarding this type of materials, the STEM-XEDS characterization of the photocatalyst samples revealed that Ce did not incorporate into the ZnO crystal lattice as a dopant but that a heterojunction formed between the ZnO nanosheets and the Ce–Zn mixed oxide phase nanoparticles instead. These two relevant compositional features could in fact be established thanks to the particular morphology obtained by the use of the microwave-assisted hydrothermal synthesis. The optical study revealed that in the ZnO:Ce samples optical band gap was found to decrease to 3.17 eV in the samples with the highest Ce content. It was also found that the ZnO:Ce (2 at.%) sample exhibited the highest photocatalytic activity for the degradation of methylene blue (MB), when compared to both the pure ZnO and commercial TiO2-P25 under simulated sunlight irradiation. The kinetics of MB photodegradation in the presence of the different photocatalysts could be properly described using a Langmuir–Hinshelwood (LH) model, for which the ZnO:Ce (2 at.%) sample exhibited the highest value of effective kinetic constant. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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Review

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29 pages, 5906 KiB  
Review
Eco-Friendly Colloidal Aqueous Sol-Gel Process for TiO2 Synthesis: The Peptization Method to Obtain Crystalline and Photoactive Materials at Low Temperature
by Julien G. Mahy, Louise Lejeune, Tommy Haynes, Stéphanie D. Lambert, Raphael Henrique Marques Marcilli, Charles-André Fustin and Sophie Hermans
Catalysts 2021, 11(7), 768; https://0-doi-org.brum.beds.ac.uk/10.3390/catal11070768 - 24 Jun 2021
Cited by 17 | Viewed by 4240
Abstract
This work reviews an eco-friendly process for producing TiO2 via colloidal aqueous sol–gel synthesis, resulting in crystalline materials without a calcination step. Three types of colloidal aqueous TiO2 are reviewed: the as-synthesized type obtained directly after synthesis, without any specific treatment; [...] Read more.
This work reviews an eco-friendly process for producing TiO2 via colloidal aqueous sol–gel synthesis, resulting in crystalline materials without a calcination step. Three types of colloidal aqueous TiO2 are reviewed: the as-synthesized type obtained directly after synthesis, without any specific treatment; the calcined, obtained after a subsequent calcination step; and the hydrothermal, obtained after a specific autoclave treatment. This eco-friendly process is based on the hydrolysis of a Ti precursor in excess of water, followed by the peptization of the precipitated TiO2. Compared to classical TiO2 synthesis, this method results in crystalline TiO2 nanoparticles without any thermal treatment and uses only small amounts of organic chemicals. Depending on the synthesis parameters, the three crystalline phases of TiO2 (anatase, brookite, and rutile) can be obtained. The morphology of the nanoparticles can also be tailored by the synthesis parameters. The most important parameter is the peptizing agent. Indeed, depending on its acidic or basic character and also on its amount, it can modulate the crystallinity and morphology of TiO2. Colloidal aqueous TiO2 photocatalysts are mainly being used in various photocatalytic reactions for organic pollutant degradation. The as-synthesized materials seem to have equivalent photocatalytic efficiency to the photocatalysts post-treated with thermal treatments and the commercial Evonik Aeroxide P25, which is produced by a high-temperature process. Indeed, as-prepared, the TiO2 photocatalysts present a high specific surface area and crystalline phases. Emerging applications are also referenced, such as elaborating catalysts for fuel cells, nanocomposite drug delivery systems, or the inkjet printing of microstructures. Only a few works have explored these new properties, giving a lot of potential avenues for studying this eco-friendly TiO2 synthesis method for innovative implementations. Full article
(This article belongs to the Special Issue Heterogeneous Photocatalysis: A Solution for a Greener Earth)
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