Advances in the Synthesis and Applications of Transition/Noble Metal Oxide Photocatalysts

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

Deadline for manuscript submissions: closed (23 April 2023) | Viewed by 18259

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Laboratory of Science and Technology of Nanoparticles, Faculty of Chemistry and Pharmacy, University of Sofia, J. Bourchier 1, 1164 Sofia, Bulgaria
Interests: heterogeneous photocatalysis; pharmaceutical drug; organic dyes; semiconductor nanomatirials
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Dear Colleagues,

In recent years, photocatalysis, due to its high efficiency, safety and profitability, has become an effective technology for solving environmental problems, for example, in wastewater treatment for the removal of organic pollutants. Despite all the positives of semiconductor photocatalysts, they have disadvantages such as the fast recombination rate of photogenerated electron–hole pairs, low quantum yield and high band gap value. The rapid recombination of the photogenerated pairs (e−/h+), following energy activation of the catalyst, inhibits the redox process and thus results in reduced photocatalytic activity. It is necessary to study a method for optimizing the semiconductor structure in order to improve separation efficiency and to inhibit recombination efficiency toward enhancing the photocatalytic properties of the semiconductor. The recombination process decreases when the surface of the semiconductor is modified by transition/noble metals. Therefore, photocatalysts modified with transition/noble metal oxides can enhance the photocatalytic decomposition of organic pollutants in wastewater.

The aim of the Special Issue “Advances in the Synthesis and Applications of Transition/Noble Metal Oxides Photocatalysts” is to serve scientists through prompt publication of significant advances in solving environmental problems via photocatalysts. In this context, we request you submit your articles to our Special Issue on or before April 23, 2023, so that it may be included article in the upcoming issue.

Dr. Nina Kaneva
Guest Editor

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Keywords

  • transition/noble metal oxides 
  • photocatalysts 
  • organic pollutants 
  • water purification

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Published Papers (11 papers)

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Editorial

Jump to: Research, Review

3 pages, 187 KiB  
Editorial
Editorial Catalysts: Special Issue on “Advances in the Synthesis and Applications of Transition/Noble Metal Oxide Photocatalysts”
by Nina Kaneva
Catalysts 2023, 13(4), 774; https://doi.org/10.3390/catal13040774 - 20 Apr 2023
Viewed by 769
Abstract
Heterogeneous photocatalysis, due to its high efficiency, safety and profitability, has become an effective technology for solving environmental problems, for example, in wastewater treatment, for the removal of organic pollutants [...] Full article

Research

Jump to: Editorial, Review

19 pages, 4714 KiB  
Article
Undoped and Fe-Doped Anatase/Brookite TiO2 Mixed Phases, Obtained by a Simple Template-Free Synthesis Method: Physico-Chemical Characterization and Photocatalytic Activity towards Simazine Degradation
by Stefano Gervasi, Nicola Blangetti, Francesca S. Freyria, Salvatore Guastella and Barbara Bonelli
Catalysts 2023, 13(4), 667; https://doi.org/10.3390/catal13040667 - 29 Mar 2023
Cited by 5 | Viewed by 1304
Abstract
For the first time, Fe-doping (0.05, 1.0, and 2.5 wt.% Fe) was performed on a high-surface-area anatase/brookite TiO2 by adopting a simple template-free sol-gel synthesis followed by calcination at a mild temperature. The powders’ textural and surface properties were characterized by following [...] Read more.
For the first time, Fe-doping (0.05, 1.0, and 2.5 wt.% Fe) was performed on a high-surface-area anatase/brookite TiO2 by adopting a simple template-free sol-gel synthesis followed by calcination at a mild temperature. The powders’ textural and surface properties were characterized by following a multi-technique approach. XRD analysis showed that the anatase/brookite ratio slightly varied in the Fe-doped TiO2 (from 76.9/23.1 to 79.3/22.7); Fe doping noticeably affected the cell volume of the brookite phase, which decreased, likely due to Fe3+ ions occupying interstitial positions, and retarded the crystallite growth. N2 sorption at −196 °C showed the occurrence of samples with disordered interparticle mesopores, with an increase in the specific surface area from 236 m2 g−1 (undoped TiO2) to 263 m2 g−1 (2.5 wt.% Fe). Diffuse Reflectance UV-Vis spectroscopy showed a progressive decrease in the bandgap energy from 3.10 eV (undoped TiO2) to 2.85 eV (2.5 wt.% Fe). XPS analysis showed the presence of some surface Fe species only at 2.5 wt.% Fe, and accordingly, the ζ-potential measurements showed small changes in the pH at the isoelectric point. The photocatalytic degradation of simazine (a persistent water contaminant) both under UV and simulated solar light was performed as a probe reaction. Under UV light, Fe-doping improved simazine degradation in the sample at 0.05 wt.% Fe, capable of degrading ca. 77% simazine. Interestingly, the undoped TiO2 was also active both under UV and 1 SUN. This is likely due to the occurrence of anatase/brookite heterojunctions, which help stabilize the photogenerated electrons/holes. Full article
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18 pages, 3743 KiB  
Article
Application of BiOX Photocatalyst to Activate Peroxydisulfate Ion-Investigation of a Combined Process for the Removal of Organic Pollutants from Water
by Tünde Alapi, Bence Veres, Máté Náfrádi, Luca Farkas, Zsolt Pap and Anett Covic
Catalysts 2023, 13(3), 513; https://doi.org/10.3390/catal13030513 - 02 Mar 2023
Cited by 5 | Viewed by 1659
Abstract
The persulfate-based advanced oxidation processes employing heterogeneous photocatalysts to generate sulfate radicals (SO4•−) from peroxydisulfate ion (PDS, S2O82−) have been extensively investigated to remove organic pollutants. In this work, BiOX (X = Cl, Br, and [...] Read more.
The persulfate-based advanced oxidation processes employing heterogeneous photocatalysts to generate sulfate radicals (SO4•−) from peroxydisulfate ion (PDS, S2O82−) have been extensively investigated to remove organic pollutants. In this work, BiOX (X = Cl, Br, and I) photocatalysts were investigated to activate PDS and enhance the transformation rate of various organic substances under UV (398 nm) and Vis (400–700 nm) radiation. For BiOCl and BiOBr, in addition to excitability, the light-induced oxygen vacancies are decisive in the activity. Although without organic substances, the BiOI efficiency highly exceeds that of BiOBr and BiOCl for PDS activation (for BiOI, 15–20%, while for BiOBr and BiOCl, only 3–4% of the PDS transformed); each BiOX catalyst showed enhanced activity for 1,4-hydroquinone (HQ) transformation due to the semiquinone radical-initiated PDS activation. For sulfamethoxypyridazine (SMP), the transformation is driven by direct charge transfer, and the effect of PDS was less manifested. BiOI proved efficient for transforming various organic substances even under Vis radiation. The efficiency was enhanced by PDS addition (HQ is wholly transformed within 20 min, and SMP conversion increased from 40% to 90%) without damaging the catalyst; its activity did change over three consecutive cycles. Results related to the well-adsorbed trimethoprim (TRIM) and application of biologically treated domestic wastewater as a matrix highlighted the limiting factors of the method and visible light active photocatalyst, BiOI. Full article
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14 pages, 2939 KiB  
Article
Preparation of S-Scheme g-C3N4/ZnO Heterojunction Composite for Highly Efficient Photocatalytic Destruction of Refractory Organic Pollutant
by Buse Sert, Zeynep Bilici, Kasim Ocakoglu, Nadir Dizge, Tannaz Sadeghi Rad and Alireza Khataee
Catalysts 2023, 13(3), 485; https://doi.org/10.3390/catal13030485 - 27 Feb 2023
Cited by 8 | Viewed by 2019
Abstract
In this study, graphitic carbon nitride (g-C3N4)-based ZnO heterostructure was synthesized using a facile calcination method with urea and zinc nitrate hexahydrate as the initiators. According to the scanning electron microscopic (SEM) images, spherical ZnO particles can be seen [...] Read more.
In this study, graphitic carbon nitride (g-C3N4)-based ZnO heterostructure was synthesized using a facile calcination method with urea and zinc nitrate hexahydrate as the initiators. According to the scanning electron microscopic (SEM) images, spherical ZnO particles can be seen along the g-C3N4 nanosheets. Additionally, the X-ray diffraction (XRD) analysis reveals the successful synthesis of the g-C3N4/ZnO. The photocatalytic activity of the synthesized catalyst was tested for the decolorization of crystal violet (CV) as an organic refractory contaminant. The impacts of ZnO molar ratio, catalyst amount, CV concentration, and H2O2 concentration on CV degradation efficiency were investigated. The obtained outcomes conveyed that the ZnO molar ratio in the g-C3N4 played a prominent role in the degradation efficiency, in which the degradation efficiency reached 95.9% in the presence of 0.05 mmol of ZnO and 0.10 g/L of the catalyst in 10 mg/L of CV through 120 min under UV irradiation. Bare g-C3N4 was also tested for dye decolorization, and a 76.4% dye removal efficiency was obtained. The g-C3N4/ZnO was also tested for adsorption, and a 32.3% adsorption efficiency was obtained. Photocatalysis, in comparison to adsorption, had a dominant role in the decolorization of CV. Lastly, the results depicted no significant decrement in the CV degradation efficiency in the presence of the g-C3N4/ZnO photocatalyst after five consecutive runs. Full article
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22 pages, 4701 KiB  
Article
Photocatalytic Decomposition of Azo Dyes and Phenols Using Polymer Composites Containing Nanostructured Poly(Titanium Oxide) Doped with Gold or Silver Nanoparticles under Light Irradiation in a Wide Wavelength Range
by Evgeniia Salomatina, Pavel Shelud’ko, Vsevolod Kuz’michev and Larisa Smirnova
Catalysts 2023, 13(2), 423; https://doi.org/10.3390/catal13020423 - 16 Feb 2023
Cited by 2 | Viewed by 1320
Abstract
The photocatalytic properties of poly(titanium oxide) (PTO) dispersed in optically transparent polymeric matrices of different natures under the action of both UV and visible light on aqueous solutions of azo dyes and phenols were investigated. PTO in materials forms clusters of mixed polymorphic [...] Read more.
The photocatalytic properties of poly(titanium oxide) (PTO) dispersed in optically transparent polymeric matrices of different natures under the action of both UV and visible light on aqueous solutions of azo dyes and phenols were investigated. PTO in materials forms clusters of mixed polymorphic modification—anatase and rutile—with an average size ~12 nm. With a one-electron transition Ti4+ + e → Ti3+ accompanied by a reversible break of the Ti-O bond, the formation of electron-hole pairs and, consequently, active oxygen species occurs in PTO under UV irradiation. The PTO band gap in nanocomposites is 3.11–3.35 eV. Its doping with gold and silver nanoparticles with sizes from ~10 to ~30 nm reduces the PTO band gap by up to 2.11 eV, which leads to the operating wavelength range extension of the materials. It provides the enhancement of nanocomposites’ photocatalytic properties under UV irradiation and is the reason for their high activity under visible light action. It was found that azo dyes decompose by ~90% in this case. A phenol and para-nitrophenol conversion of 80–90% was proven at ~60 min upon their aqueous solutions’ visible-light irradiation at the nanocomposite concentration in a solution of 0.5 g/L. Full article
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25 pages, 7178 KiB  
Article
Photodynamic Light-Triggered Release of Curcumin from Hierarchical FAU Zeolite
by Ewelina Musielak, Agnieszka Feliczak-Guzik, Mietek Jaroniec and Izabela Nowak
Catalysts 2023, 13(2), 394; https://doi.org/10.3390/catal13020394 - 11 Feb 2023
Cited by 2 | Viewed by 1460
Abstract
Photodynamic therapy (PDT) is a method used in the treatment of various diseases and represents a promising alternative to classical active substance release methods. According to the United States National Institute of Health, this therapy exploits the health-promoting potential of active substances, referred [...] Read more.
Photodynamic therapy (PDT) is a method used in the treatment of various diseases and represents a promising alternative to classical active substance release methods. According to the United States National Institute of Health, this therapy exploits the health-promoting potential of active substances, referred to as “photosensitizers”, and radiation of specific energy. Curcumin is a natural “photosensitizer” that exhibits anti-inflammatory, antioxidant, and anti-cancer effects. Despite the novelty and innovation of PDT, the method is limited by the difficulty of using “photosensitizers” such as curcumin because of its low solubility in water, which hinders the clinical application of this technique. The use of a “photosensitizer” along with suitable carriers such as hierarchical zeolites is a potential strategy to offset this difficulty. Therefore, the objective of this study was to develop the photodynamic release of curcumin from hierarchical zeolites using the classical open-circuit release method and a novel closed-circuit release technique involving light of different wavelengths. Based on the obtained data, it was possible to unequivocally state that the speed and efficiency of curcumin release from the zeolite carrier is influenced by light with a wavelength in the range of 430–525 nm (blue-cyan-green). As much as 53.24% of the active substance was released upon light exposure. Full article
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13 pages, 3576 KiB  
Article
Application of BiVO4/TiO2/CNT Composite Photocatalysts for Membrane Fouling Control and Photocatalytic Membrane Regeneration during Dairy Wastewater Treatment
by Elias Jigar Sisay, Szabolcs Kertész, Ákos Fazekas, Zoltán Jákói, Endre Zsolt Kedves, Tamás Gyulavári, Áron Ágoston, Gábor Veréb and Zsuzsanna László
Catalysts 2023, 13(2), 315; https://doi.org/10.3390/catal13020315 - 01 Feb 2023
Cited by 4 | Viewed by 1540
Abstract
This study aimed to investigate the performance of composite photocatalytic membranes fabricated by incorporating multiple nanoparticles (TiO2, carbon nanotubes, BiVO4) into polyvinylidene fluoride membrane material for real dairy wastewater treatment. The composite photocatalytic membranes exhibited superior antifouling behavior, lower [...] Read more.
This study aimed to investigate the performance of composite photocatalytic membranes fabricated by incorporating multiple nanoparticles (TiO2, carbon nanotubes, BiVO4) into polyvinylidene fluoride membrane material for real dairy wastewater treatment. The composite photocatalytic membranes exhibited superior antifouling behavior, lower filtration resistance, better flux, and higher flux recovery ratio than the pristine membrane. Salinity, pH, and lactose concentration are determinant factors that affect filtration resistance and rejection performance during the ultrafiltration of dairy wastewater. Generally, higher irreversible and total resistances and slightly lower chemical oxygen demand (COD) rejections were found at higher salinity (expressed by electric conductivity values of >4 mS/cm) than lower salinity (<4 mS/cm) levels. The presence of lactose in dairy wastewater increased irreversible resistance and severely reduced COD rejection during ultrafiltration due to the ability of lactose to pass through the membranes. It was ascertained that membranes require further treatment after filtrating such wastewater. Lower resistances and slightly better COD rejections were observed at pH 7.5 and pH 9.5 compared to those observed at pH 4. Photocatalytic membranes fouled during the ultrafiltration of real dairy wastewater were regenerated by visible light irradiation. The membrane containing all constituents (i.e., TiO2, carbon nanotubes, and BiVO4) showed the best regeneration performance, exceeding that of the pristine membrane by 30%. Full article
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17 pages, 4126 KiB  
Article
Sol-Gel Obtaining of TiO2/TeO2 Nanopowders with Biocidal and Environmental Applications
by Albena Bachvarova-Nedelcheva, Reni Iordanova, Anton Naydenov, Angelina Stoyanova, Nelly Georgieva, Veronica Nemska and Tsvetelina Foteva
Catalysts 2023, 13(2), 257; https://doi.org/10.3390/catal13020257 - 22 Jan 2023
Cited by 5 | Viewed by 1485
Abstract
TiO2/TeO2 powders were obtained by an aqueous sol-gel method. Telluric acid (H6TeO6) and titanium butoxide were used as precursors. The as-prepared gel was step-wisely heated in the temperature range 200–700 °C and subsequently characterized by XRD, [...] Read more.
TiO2/TeO2 powders were obtained by an aqueous sol-gel method. Telluric acid (H6TeO6) and titanium butoxide were used as precursors. The as-prepared gel was step-wisely heated in the temperature range 200–700 °C and subsequently characterized by XRD, IR, and UV-Vis analysis and SEM. Mixtures containing TiO2 (anatase), α-TeO2 (paratellurite), and TiTe3O8 were established by XRD as final products, depending on heating temperature. The thermal stability of the obtained gels in the temperature range 100–400 °C was investigated. It was found by IR spectroscopy that the samples heated up to 300–400 °C consist mainly of an organic–inorganic amorphous phase which is transformed into an inorganic one above these temperatures. The microstructure of the gels was verified by scanning electron microscopy (SEM). The photocatalytic degradation of the synthesized nanopowders toward Malachite green organic dye (MG) was examined in order to evaluate the potential applications for environmental remediation. The prepared TiO2/TeO2 samples showed up to 60% decoloration efficiency after 120 min exposure to UV-light. The composition exhibited good antimicrobial activity against E. coli K12. The properties of the obtained material were investigated by the reactions of complete catalytic oxidation of different alkanes and toluene, and it could be suggested that TiO2/TeO2 powders are promising material for use as an active phase in environmental catalysts. Full article
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16 pages, 5151 KiB  
Article
Enhanced Removal of Organic Dyes Using Co-Catalytic Ag-Modified ZnO and TiO2 Sol-Gel Photocatalysts
by Nina Kaneva, Assya Bojinova and Karolina Papazova
Catalysts 2023, 13(2), 245; https://doi.org/10.3390/catal13020245 - 21 Jan 2023
Cited by 9 | Viewed by 1479
Abstract
Zinc oxide and titanium dioxide semiconductor photocatalysts have been widely utilized in the last few decades for water treatment because of their high photocatalytic efficiency. Recently, a lot of researchers have focused on the improvement of the photocatalytic properties of catalysts through modifying [...] Read more.
Zinc oxide and titanium dioxide semiconductor photocatalysts have been widely utilized in the last few decades for water treatment because of their high photocatalytic efficiency. Recently, a lot of researchers have focused on the improvement of the photocatalytic properties of catalysts through modifying and co-modifying them with different metals and nonmetals. These co-catalytic ions improve the photocatalytic activity of ZnO and TiO2 by reducing its energy band gap. This might be useful in wastewater treatment for the photocatalytic degradation of organic contaminants. In this study, we prepared semiconductor films that were surface-modified with Ag co-catalyst layers via the photo-fixation of Ag (I) ions with varied concentrations (10−2–10−4 M) in the water phase under UV illumination for the first time. The photocatalytic behavior was evaluated by the degradation of malachite green and methylene blue under UV and visible light irradiation. The ZnO/Ag and TiO2/Ag samples showed a faster degradation of malachite green compared to methylene blue due to the formation of stable intermediates by the reaction of OH radicals with the triarylmethane dye (C=C bond) during the photocatalysis. The co-catalytic-silver-modified films had a higher photocatalytic efficiency in comparison with the pure nanostructures. The dye photodegradation rate constants increased in the following order: pure films < films modified with Ag, 10−4 M < films modified with Ag10−3 M < films modified with Ag10−2 M. The Ag modification and the heterojunction of the composites contributed to trapping and transfer of the electrons. Therefore, the photogenerated charges had a longer lifetime, resulting in a strengthened photocatalytic ability of the ZnO/Ag and TiO2/Ag films. Full article
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13 pages, 3396 KiB  
Article
Assembled Porphyrin Nanofiber on the Surface of g-C3N4 Nanomaterials for Enhanced Photocatalytic Degradation of Organic Dyes
by Hoan Thi Lai, Giang Thi Nguyen, Nga Thuy Tran, Thanh Tung Nguyen, Chinh Van Tran, Duy Khiem Nguyen, S. W. Chang, W. Jin Chung, Dinh Duc Nguyen, Hoai Phuong Nguyen Thi and Duong Duc La
Catalysts 2022, 12(12), 1630; https://doi.org/10.3390/catal12121630 - 12 Dec 2022
Cited by 4 | Viewed by 1622
Abstract
In this work, a g-C3N4/porphyrin nanocomposite was fabricated through the self-assembling of monomeric Tetrakis (4-carboxyphenyl) porphyrin (TCPP) molecules with g-C3N4 nanomaterials. The characterizing results showed a good distribution of TCPP nanofibers with a diameter of < [...] Read more.
In this work, a g-C3N4/porphyrin nanocomposite was fabricated through the self-assembling of monomeric Tetrakis (4-carboxyphenyl) porphyrin (TCPP) molecules with g-C3N4 nanomaterials. The characterizing results showed a good distribution of TCPP nanofibers with a diameter of < 100 nm and several micrometers in length on the g-C3N4 nanoflakes’ surfaces. The prepared g-C3N4/porphyrin nanocomposite had two bandgap energies of 2.38 and 2.7 eV, which could harvest a wide range of photon energy in the light spectrum, particularly in visible light. The obtained C3N4/TCPP nanocomposite revealed a remarkable photodegradation efficiency toward rhodamine B dyes, with a RhB removing rate of 3.3 × 10−2 min−1. The plausible mechanism for the photocatalytic performance of the g-C3N4/porphyrin photocatalyst for the RhB dye’s degradation was also studied and discussed. Full article
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Review

Jump to: Editorial, Research

20 pages, 3179 KiB  
Review
Recent Developments in Photocatalytic Nanotechnology for Purifying Air Polluted with Volatile Organic Compounds: Effect of Operating Parameters and Catalyst Deactivation
by Augustine Jaison, Anandhu Mohan and Young-Chul Lee
Catalysts 2023, 13(2), 407; https://doi.org/10.3390/catal13020407 - 14 Feb 2023
Cited by 16 | Viewed by 2892
Abstract
Photocatalytic oxidation (PCO) is a successful method for indoor air purification, especially for removing low-concentration pollutants. Volatile organic compounds (VOCs) form a class of organic pollutants that are released into the atmosphere by consumer goods or via human activities. Once they enter the [...] Read more.
Photocatalytic oxidation (PCO) is a successful method for indoor air purification, especially for removing low-concentration pollutants. Volatile organic compounds (VOCs) form a class of organic pollutants that are released into the atmosphere by consumer goods or via human activities. Once they enter the atmosphere, some might combine with other gases to create new air pollutants, which can have a detrimental effect on the health of living beings. This review focuses on current developments in the degradation of indoor pollutants, with an emphasis on two aspects of PCO: (i) influence of environmental (external) conditions; and (ii) catalyst deactivation and possible solutions. TiO2 is widely used as a photocatalyst in PCO because of its unique properties. Here, the potential effects of the operating parameters, such as the nature of the reactant, catalyst support, light intensity, and relative humidity, are extensively investigated. Then the developments and limitations of the PCO technique are highlighted, especially photocatalyst deactivation. Furthermore, the nature and deactivation mechanisms of photocatalysts are discussed, with possible solutions for reducing catalyst deactivation. Finally, the challenges and future directions of PCO technology for the elimination of indoor pollutants are compared and summarized. Full article
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