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Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Photochemistry".

Deadline for manuscript submissions: 31 January 2025 | Viewed by 10233

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Dr. Ruowen Liang

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Guest Editor

Fujian Province University Key Laboratory of Green Energy and Environment Catalysis, Ningde Normal University, Ningde, China
Interests: metal–organic frameworks; environmental catalysis; chemical conversion of solar energy; dynamics of photogenerated carriers; interface engineering
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Following the success of the first Special Issue, "Advanced Photocatalysts for Energy Conversion and Environmental Applications”, we are launching a second edition titled “Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition” and invite submissions from selected experts in this field.

Photocatalysis is an advanced technique that transforms solar energy into sustainable fuels and oxidizes pollutants via the aid of semiconductor photocatalysts. The main scientific and technological challenges for effective photocatalysis are the stability, robustness, and efficiency of semiconductor photocatalysts. For practical applications, developments in energy conversion (i.e., hydrogen evolution, CO₂ reduction, and oriented synthesis) and environmental remediation (i.e., air purification, antibacteria and wastewater treatment) for highly efficient and stable photocatalysts are needed. This Special Issue plans to offer an opportunity for the publication of original research regarding the synthesis of novel photocatalytic materials and their application in energy conversion and environmental remediation.

Potential topics include, but are not limited to, the following:

Photocatalytic performance;
Photocatalytic semiconductor materials;
Metal-organic frameworks;
Mechanisms of photocatalytic process;
Role of photocatalysts in environment;
Role of photocatalysts in energy.

Dr. Ruowen Liang
Guest Editor

Manuscript Submission Information

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Keywords

photocatalyst
nano materials
metal–organic frameworks
environment
energy

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Published Papers (9 papers)

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Research

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14 pages, 3432 KiB

Open AccessArticle

Extended Interfacial Charge Transference in CoFe₂O₄/WO₃ Nanocomposites for the Photocatalytic Degradation of Tetracycline Antibiotics

by Suiying Dong, Jiafu Dai, Ying Yang, Amir Zada and Kezhen Qi

Molecules 2024, 29(19), 4561; https://doi.org/10.3390/molecules29194561 - 25 Sep 2024

Viewed by 569

Abstract

The large-scale utilization of antibiotics has opened a separate chapter of pollution with the generation of reactive drug-resistant bacteria. To deal with this, in this work, different mass ratios of CoFe₂O₄/WO₃ nanocomposites were prepared following an in situ growth method using the precursors of WO₃ and CoFe₂O₄. The structure, morphology, and optical properties of the nanocomposite photocatalysts were scrutinized by X-ray diffraction (XRD), UV-visible diffuse reflectance spectra (UV-Vis DRS), photoluminescence spectrum (PL), etc. The experimental data signified that the loading of CoFe₂O₄ obviously changed the optical properties of WO₃. The photocatalytic performance of CoFe₂O₄/WO₃ composites was investigated by considering tetracycline as a potential pollutant. The outcome of the analyzed data exposed that the CoFe₂O₄/WO₃ composite with a mass ratio of 5% had the best degradation performance for tetracycline eradication under the solar light, and a degradation efficiency of 77% was achieved in 20 min. The monitored degradation efficiency of the optimized photocatalyst was 45% higher compared with the degradation efficiency of 32% for pure WO₃. Capturing experiments and tests revealed that hydroxyl radical (·OH) and hole (h⁺) were the primary eradicators of the target pollutant. This study demonstrates that a proper mass of CoFe₂O₄ can significantly push WO₃ for enhanced eradication of waterborne pollutants. Full article

(This article belongs to the Special Issue Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition)

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11 pages, 3367 KiB

Open AccessArticle

Thermal Exfoliation and Phosphorus Doping in Graphitic Carbon Nitride for Efficient Photocatalytic Hydrogen Production

by Lu Chen, Linzhu Zhang, Yuzhou Xia, Renkun Huang, Ruowen Liang, Guiyang Yan and Xuxu Wang

Molecules 2024, 29(15), 3666; https://doi.org/10.3390/molecules29153666 - 2 Aug 2024

Viewed by 781

Abstract

Photocatalytic H₂ evolution has been regarded as a promising technology to alleviate the energy crisis. Designing graphitic carbon nitride materials with a large surface area, short diffusion paths for electrons, and more exposed reactive sites are beneficial for hydrogen evolution. In this study, a facile method was proposed to dope P into a graphitic carbon nitride framework by calcining melamine with 2-aminoethylphosphonic acid. Meanwhile, PCN nanosheets (PCNSs) were obtained through a thermal exfoliation strategy. Under visible light, the PCNS sample displayed a hydrogen evolution rate of 700 μmol·g⁻¹·h⁻¹, which was 43.8-fold higher than that of pure g-C₃N₄. In addition, the PCNS photocatalyst also displayed good photostability for four consecutive cycles, with a total reaction time of 12 h. Its outstanding photocatalytic performance was attributed to the higher surface area exposing more reactive sites and the enlarged band edge for photoreduction potentials. This work provides a facile strategy to regulate catalytic structures, which may attract great research interest in the field of catalysis. Full article

(This article belongs to the Special Issue Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition)

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17 pages, 4560 KiB

Open AccessArticle

Enhanced Visible-Light Photocatalytic Activity of Bismuth Ferrite Hollow Spheres Synthesized via Evaporation-Induced Self-Assembly

by Thomas Cadenbach, Valeria Sanchez, Karla Vizuete, Alexis Debut, Carlos Reinoso and Maria J. Benitez

Molecules 2024, 29(15), 3592; https://doi.org/10.3390/molecules29153592 - 30 Jul 2024

Viewed by 945

Abstract

Semiconductor hollow spheres have garnered significant attention in recent years due to their unique structural properties and enhanced surface area, which are advantageous for various applications in catalysis, energy storage, and sensing. The present study explores the surfactant-assisted synthesis of bismuth ferrite (BiFeO₃) hollow spheres, emphasizing their enhanced visible-light photocatalytic activity. Utilizing a novel, facile, two-step evaporation-induced self-assembly (EISA) approach, monodisperse BiFeO₃ hollow spheres were synthesized with a narrow particle size distribution. The synthesis involved Bi/Fe citrate complexes as precursors and the triblock copolymer Pluronic P123 as a soft template. The BiFeO₃ hollow spheres demonstrated outstanding photocatalytic performance in degrading the emerging pollutants Rhodamine B and metronidazole under visible-light irradiation (100% degradation of Rhodamine B in <140 min and of metronidazole in 240 min). The active species in the photocatalytic process were identified through trapping experiments, providing crucial insights into the mechanisms and efficiency of semiconductor hollow spheres. The findings suggest that the unique structural features of BiFeO₃ hollow spheres, combined with their excellent optical properties, make them promising candidates for photocatalytic applications. Full article

(This article belongs to the Special Issue Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition)

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17 pages, 4097 KiB

Open AccessArticle

Boosting Visible-Light Photocatalytic Activity of BiOCl Nanosheets via Synergetic Effect of Oxygen Vacancy Engineering and Graphene Quantum Dots-Sensitization

by Zisheng Shi, Wei Chen, Yin Hu, Fen Zhang, Lingling Wang, Dan Zhou, Xuanye Chen and Sugang Meng

Molecules 2024, 29(6), 1362; https://doi.org/10.3390/molecules29061362 - 19 Mar 2024

Cited by 3 | Viewed by 1279

Abstract

In recent years, oxygen vacancy (V_O) engineering has become a research hotspot in the field of photocatalysis. Herein, an efficient GQDs/BiOCl-V_O heterojunction photocatalyst was fabricated by loading graphene quantum dots (GQDs) onto BiOCl nanosheets containing oxygen vacancies. ESR and XPS characterizations confirmed the formation of oxygen vacancy. Combining experimental analysis and DFT calculations, it was found that oxygen vacancy promoted the chemical adsorption of O₂, while GQDs accelerated electron transfer. Benefiting from the synergistic effect of oxygen vacancy, GQDs, and dye sensitization, the as-prepared GQDs/BiOCl-V_O sample exhibited improved efficiency for RhB degradation under visible-light irradiation. A 2 wt% GQDs/BiOCl-V_O composite effectively degraded 98% of RhB within 20 min. The main active species were proven to be hole (h⁺) and superoxide radical (·O₂⁻) via ESR analysis and radical trapping experiments. This study provided new insights into the effective removal of organic pollutants from water by combining defect engineering and quantum dot doping techniques in heterojunction catalysts. Full article

(This article belongs to the Special Issue Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition)

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21 pages, 12034 KiB

Open AccessArticle

Broad Spectral Response FeOOH/BiO_2−x Photocatalyst with Efficient Charge Transfer for Enhanced Photo-Fenton Synergistic Catalytic Activity

by Pengfei Wu, Yufei Qin, Mengyuan Gao, Rui Zheng, Yixin Zhang, Xinli Li, Zhaolong Liu, Yingkun Zhang, Zhen Cao and Qingling Liu

Molecules 2024, 29(4), 919; https://doi.org/10.3390/molecules29040919 - 19 Feb 2024

Cited by 2 | Viewed by 1389

Abstract

In this work, to promote the separation of photogenerated carriers, prevent the catalyst from photo-corrosion, and improve the photo-Fenton synergistic degradation of organic pollutants, the coating structure of FeOOH/BiO_2−x rich in oxygen vacancies was successfully synthesized by a facile and environmentally friendly two-step process of hydrothermal and chemical deposition. Through a series of degradation activity tests of synthesized materials under different conditions, it was found that FeOOH/BiO_2−x demonstrated outstanding organic pollutant degradation activity under visible and near-infrared light when hydrogen peroxide was added. After 90 min of reaction under photo-Fenton conditions, the degradation rate of Methylene Blue by FeOOH/BiO_2−x was 87.4%, significantly higher than the degradation efficiency under photocatalysis (60.3%) and Fenton (49.0%) conditions. The apparent rate constants of FeOOH/BiO_2−x under photo-Fenton conditions were 2.33 times and 3.32 times higher than photocatalysis and Fenton catalysis, respectively. The amorphous FeOOH was tightly coated on the layered BiO_2−x, which significantly increased the specific surface area and the number of active sites of the composites, and facilitated the improvement of the separation efficiency of the photogenerated carriers and the prevention of photo-corrosion of BiO_2−x. The analysis of the mechanism of photo-Fenton synergistic degradation clarified that ·OH, h⁺, and ·O₂⁻ are the main active substances involved in the degradation of pollutants. The optimal degradation conditions were the addition of the FeOOH/BiO_2−x composite catalyst loaded with 20% Fe at a concentration of 0.5 g/L, the addition of hydrogen peroxide at a concentration of 8 mM, and an initial pH of 4. This outstanding catalytic system offers a fresh approach to the creation and processing of iron-based photo-Fenton catalysts by quickly and efficiently degrading various organic contaminants. Full article

(This article belongs to the Special Issue Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition)

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14 pages, 4579 KiB

Open AccessArticle

Effects of Temperature, Axial Ligand, and Photoexcitation on the Structure and Spin-State of Nickel(II) Complexes with Water-Soluble 5,10,15,20-Tetrakis(1-methylpyridinium-4-yl)porphyrin

by Máté Miklós Major, Zsolt Valicsek and Ottó Horváth

Molecules 2024, 29(2), 310; https://doi.org/10.3390/molecules29020310 - 8 Jan 2024

Cited by 1 | Viewed by 1166

Abstract

Water-soluble metalloporphyrins, depending on the metal center, possess special spectral, coordination, and photochemical features. In nickel(II) porphyrins, the Ni(II) center can occur with low-spin or high-spin electronic configuration. In aqueous solution, the cationic nickel(II) complex (Ni(II)TMPyP⁴⁺, where H₂TMPyP⁴⁺ = 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin), exists in both forms in equilibrium. In this study, an equilibrium system involving the low-spin and high-spin forms of Ni(II)TMPyP⁴⁺ was investigated via application of irradiation, temperature change, and various potential axial ligands. Soret band excitation of this aqueous system, in the absence of additional axial ligands, resulted in a shift in the equilibrium toward the low-spin species due to the removal of axial solvent ligands. The kinetics and the thermodynamics of the processes were also studied via determination of the rate and equilibrium constants, as well as the ΔS, ΔH, and ΔG values. Temperature increase had a similar effect. The equilibrium of the spin isomers was also shifted by decreasing the solvent polarity (using n-propanol) as well as by the addition of a stronger coordinating axial ligand (such as ammonia). Since triethanolamine is an efficient electron donor in Ni(II)TMPyP⁴⁺-based photocatalytic systems, its interaction with this metalloporphyin was also studied. The results promote the development of efficient photocatalytic systems based on this complex. Full article

(This article belongs to the Special Issue Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition)

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13 pages, 1497 KiB

Open AccessArticle

Synergistic Spatial Confining Effect and O Vacancy in WO₃ Hollow Sphere for Enhanced N₂ Reduction

by Yuzhou Xia, Xinghe Xia, Shuying Zhu, Ruowen Liang, Guiyang Yan, Feng Chen and Xuxu Wang

Molecules 2023, 28(24), 8013; https://doi.org/10.3390/molecules28248013 - 8 Dec 2023

Viewed by 1147

Abstract

Visible-light-driven N₂ reduction into NH₃ in pure H₂O provides an energy-saving alternative to the Haber–Bosch process for ammonia synthesizing. However, the thermodynamic stability of N≡N and low water solubility of N₂ remain the key bottlenecks. Here, we propose a solution by developing a WO_3−x hollow sphere with oxygen vacancies. Experimental analysis reveals that the hollow sphere structure greatly promotes the enrichment of N₂ molecules in the inner cavity and facilitates the chemisorption of N₂ onto WO_3−x-HS. The outer layer’s thin shell facilitates the photogenerated charge transfer and the full exposure of O vacancies as active sites. O vacancies exposed on the surface accelerate the activation of N≡N triple bonds. As such, the optimized catalyst shows a NH₃ generation rate of 140.08 μmol g⁻¹ h⁻¹, which is 7.94 times higher than the counterpart WO₃-bulk. Full article

(This article belongs to the Special Issue Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition)

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11 pages, 6451 KiB

Open AccessArticle

Preparation, Characterization, Photochromic Properties, and Mechanism of PMoA/ZnO/PVP Composite Film

by Tiehong Song, Jinyao Li, Qiyuan Deng and Yanjiao Gao

Molecules 2023, 28(22), 7605; https://doi.org/10.3390/molecules28227605 - 15 Nov 2023

Cited by 3 | Viewed by 1267

Abstract

A novel photochromic heteropolyacid-based composite film consisting of phosphomolybdic acid (PMoA), ZnO, and polyvinylpyrrolidone (PVP) was fabricated by a sol–gel process. The microstructure and photochromic properties of the PMoA/ZnO/PVP were characterized via Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible spectroscopy (UV-Vis). The FTIR spectra showed that the basic structures of ZnO and PVP, and the Keggin structure of PMoA in the PMoA/ZnO/PVP composite film, had not been destroyed during the preparation. The TEM images demonstrated that ZnO presented a rod-like structure, while PMoA was spherical, and many PMoA balls adhered to the surface of the ZnO rods. The XPS spectra of Mo 3d indicated that the valency of Mo atoms in the PMoA/ZnO/PVP was changed by visible light exposure. After visible light irradiation, the PMoA/ZnO/PVP varied from slight yellow to blue, while undergoing an opposite color change upon heating. The discoloration mechanism of the PMoA/ZnO/PVP was consistent with the photoelectron transfer mechanism. Full article

(This article belongs to the Special Issue Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition)

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Review

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23 pages, 5192 KiB

Open AccessReview

Design and Preparation of Heterostructured Cu₂O/TiO₂ Materials for Photocatalytic Applications

by Yating Tai, Boxuan Yang, Jing Li, Lingshi Meng, Pengcheng Xing and Shengjie Wang

Molecules 2024, 29(21), 5028; https://doi.org/10.3390/molecules29215028 - 24 Oct 2024

Viewed by 1072

Abstract

The extensive use of fossil fuels has sped up the global development of the world economy and is accompanied by significant problems, such as energy shortages and environmental pollution. Solar energy, an inexhaustible and clean energy resource, has emerged as a promising sustainable alternative. Light irradiation can be transformed into electrical/chemical energy, which can be used to remove pollutants or transform contaminants into high-value-added chemicals through photocatalytic reactions. Therefore, photocatalysis is a promising strategy to overcome the increasing energy and environmental problems. As is well-known, photocatalysts are key components of photocatalytic systems. Among the widely investigated photocatalysts, titanium dioxide (TiO₂) has attracted great attention owing to its excellent light-driven redox capability and photochemical stability. However, its poor solar light response and rapid recombination of electron–hole pairs limit its photocatalytic applications. Therefore, strategies to enhance the photocatalytic activity of TiO₂ by narrowing its bandgap and inhibiting the recombination of charges have been widely accepted. Constructing heterojunctions with other components, including cuprous oxide (Cu₂O), has especially narrowed the bandgap, providing a promising means of solving the present challenges. This paper reviews the advances in research on heterostructured Cu₂O/TiO₂ photocatalysts, such as their synthesis methods, mechanisms for the enhancement of photocatalytic performance, and their applications in hydrogen production, CO₂ reduction, selective synthesis, and the degradation of pollutants. The mechanism of charge separation and transfer through the Cu₂O/TiO₂ heterojunctions and the inherent factors that lead to the enhancement of photocatalytic performance are extensively discussed. Additionally, the current challenges in and future perspectives on the use of heterostructured Cu₂O/TiO₂ photocatalysts are also highlighted. Full article

(This article belongs to the Special Issue Advanced Photocatalysts for Energy Conversion and Environmental Applications, 2nd Edition)

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