Advances in Polyoxometalates as Electron Mediators for Photocatalytic Dye Degradation

The increasing concerns over the environment and the growing demand for sustainable water treatment technologies have sparked substantial interest in the field of photocatalytic dye removal. Polyoxometalates (POMs), known for their intricate metal-oxygen anion clusters, have received considerable attention due to their versatile structures, compositions, and efficient facilitation of photo-induced electron transfers. This paper provides an overview of the ongoing research progress in the realm of photocatalytic dye degradation utilizing POMs and their derivatives. The details encompass the compositions of catalysts, catalytic efficacy, and light absorption propensities, and the photocatalytic mechanisms inherent to POM-based materials for dye degradation are exhaustively expounded upon. This review not only contributes to a better understanding of the potential of POM-based materials in photocatalytic dye degradation, but also presents the advancements and future prospects in this domain of environmental remediation.

Boosted Photocatalytic Performance for Antibiotics Removal with Ag/PW12/TiO2 Composite: Degradation Pathways and Toxicity Assessment

Photocatalyst is the core of photocatalysis and directly determines photocatalytic performance. However, low quantum efficiency and low utilization of solar energy are important technical problems in the application of photocatalysis. In this work, a series of polyoxometalates (POMs) [H3PW12O40] (PW12)-doped titanium dioxide (TiO2) nanofibers modified with various amount of silver (Ag) nanoparticles (NPs) were prepared by utilizing electrospinning/photoreduction strategy, and were labelled as x wt% Ag/PW12/TiO2 (abbr. x% Ag/PT, x = 5, 10, and 15, respectively). The as-prepared materials were characterized with a series of techniques and exhibited remarkable catalytic activities for visible-light degradation tetracycline (TC), enrofloxacin (ENR), and methyl orange (MO). Particularly, the 10% Ag/PT catalyst with a specific surface area of 155.09 m2/g and an average aperture of 4.61 nm possessed the optimal photodegradation performance, with efficiencies reaching 78.19% for TC, 93.65% for ENR, and 99.29% for MO, which were significantly higher than those of PW12-free Ag/TiO2 and PT nanofibers. Additionally, various parameters (the pH of the solution, catalyst usage, and TC concentration) influencing the degradation process were investigated in detail. The optimal conditions are as follows: catalyst usage: 20 mg; TC: 20 mL of 20 ppm; pH = 7. Furthermore, the photodegradation intermediates and pathways were demonstrated by HPLC-MS measurement. We also investigated the toxicity of products generated during TC removal by employing quantitative structure-activity relationship (QSAR) prediction through a toxicity estimation software tool (T.E.S.T. Version 5.1.2.). The mechanism study showed that the doping of PW12 and the modification of Ag NPs on TiO2 broadened the visible-light absorption, accelerating the effective separation of photogenerated carriers, therefore resulting in an enhanced photocatalytic performance. The research provided some new thoughts for exploiting efficient and durable photocatalysts for environmental remediation.

Efficient visible-light-driven reduction of hexavalent chromium catalyzed by conjugated organic species modified hourglass-type phosphomolybdate hybrids

Four conjugated-organic-species modified hourglass-type phosphomolybdate hybrids with a 0-D + 1-D → 3-D supramolecular structure exhibited favorable photocatalytic activity and stability towards Cr(vi) reduction.

Fabrication of novel Cu2WS4/NiTiO3 heterostructures for efficient visible-light photocatalytichydrogen evolution and pollutant degradation

The design and development of efficient and durable catalysts with visible-light response for photocatalytic hydrogen production and pollutants degradation is considered as one of the most challenging tasks. In present work, a novel Cu₂WS₄/NiTiO₃ (abbreviated as × CWS/NTO; x  = 0.25, 0.50, 0.75 and 1.00) composite was prepared via a facile electrospinning/calcination technique along with a convenient hydrothermal method. The as-prepared CWS/NTOcomposite was composed of 2D CWS nanosheets and 1D NTO nanofibers manifested by SEM and TEM images. The results of XPS verified the interfacial interaction between CWS and NTO, confirming the heterojunction formation in CWS/NTOcomposite. Photocatalytic tests demonstrated as-prepared CWS/NTO catalysts exhibited outstanding and stable photocatalytic performances for H₂ production and pollutants degradation under visible light (λ > 420 nm) irradiation. Specially, 0.50 CWS/NTO sample displayed the highest H₂-evolution activity of 810 μmol·g^-1·h^-1 with the apparent quantum efficiency (AQE) value of 1.65 % at 420 nm. Additionally, it also exhibited the optimal photodegradation properties with the rate constants of 0.030, 0.413 and 0.028 min^-1 for TC, RhB and Cr(VI), respectively. The excellent catalytic activities could be attributed to the enhanced visible-light adsorption, high specific surface area and efficient separation of photogenerated charge carriers. The ESR tests and free radicals capturing experiments confirmed that ·O₂^- and h⁺ were primary active species for TC/RhB degradation. Eventually, the probable catalytic mechanism was put forward and detailly analysed. The present work provides perspectives of rational design on NiTiO₃-based catalysts with superior photocatalytic performance for energy regeneration and environmental remediation.

Two-dimensional ultrathin surfactant-encapsulating polyoxometalate assemblies as carriers for monodispersing noble-metal nanoparticles with high catalytic activity and stability

Noble metal nanoparticles (NMNPs) with excellent catalytic activity and stability play an important role in the field of environmental governance. A uniform distribution and a strong binding force with the carriers of the noble metal nanoparticles are important, but avoidance of the use of additional reducing agents is a promising direction of research. Herein, 2D ultrathin surfactant-encapsulating polyoxometalate (SEP) nanosheets constructed by the self-assembly of dodecyldimethylammonium bromide (DODA) and molybdophosphate (H3PMo12O40, PMo12) are designed to be versatile carriers for Ag nanoparticles. Under the synergistic effect of the well-arranged PMo12 units, encapsulating hydrophobic oleic acid (OA) and reductive molybdophosphate under Xe lamp irradiation, the silver oleate (AgOA)-derived Ag nanoparticles (5 ± 2 nm) are monodispersed on the DODA-PMo12 assemblies and form the Agx/DODA-PMo12 composite. The optimized Ag4.89/DODA-PMo12 composite exhibits high catalytic activity and stability in the degradation of 4-nitrophenol (4-NP), which reaches a superior rate constant of 6.49 × 10-3 s-1 and without significant deterioration after three recycles. This technique can be facilely promoted to other noble metal nanoparticles with excellent catalytic activity and stability.

An innovative magnetic Ni0.1Co0.9Fe2O4/g-C3N4 nano-micro-spherical heterojunction composite photocatalyst with an extraordinarily prominent visible-light-irradiation degradation performance toward organic pollutants

Environmental pollution removal is attracting more attention these days because of increasing environmental problems. The use of photodegradation catalysts is a promising avenue in resolving environmental issues and therefore high-performance photocatalysts are urgently needed. Herein, we solvothermally synthesized a micro-spherical g-C3N4 photocatalyst and a nanospherical Ni0.1Co0.9Fe2O4 photocatalyst, and then innovatively employed small amounts of Ni0.1Co0.9Fe2O4 nanospheres coupled with g-C3N4 microspheres to fabricate a novel magnetic Ni0.1Co0.9Fe2O4/g-C3N4 nano-micro-spherical heterojunction photocatalyst through post co-calcination. Various techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform-infrared spectroscopy and UV-vis diffuse reflectance spectroscopy, were employed to analyze the as-synthesized hybrid photocatalyst. The resultant photocatalyst exhibits a record high photocatalytic degradation activity against methylene blue under visible-light irradiation with a 100% degradation rate within only 10 min, corresponding to an extraordinarily prominent degradation reaction rate constant k value of up to 0.586 min-1. Our strategy opens a new effective way for fabricating high-performance photocatalysts and our novel Ni0.1Co0.9Fe2O4/g-C3N4 heterojunction photocatalyst is of great potential for application in environmental treatments.

Hybridized 2D Nanomaterials Toward Highly Efficient Photocatalysis for Degrading Pollutants: Current Status and Future Perspectives

Organic pollutants including industrial dyes and chemicals and agricultural waste have become a major environmental issue in recent years. As an alternative to simple adsorption, photocatalytic decontamination is an efficient and energy-saving technology to eliminate these pollutants from water environment, utilizing the energy of external light, and unique function of photocatalysts. Having a large specific surface area, numerous active sites, and varied band structures, 2D nanosheets have exhibited promising applications as an efficient photocatalyst for degrading organic pollutants, particularly hybridization with other functional components. The novel hybridization of 2D nanomaterials with various functional species is summarized systematically with emphasis on their enhanced photocatalytic activities and outstanding performances in environmental remediation. First, the mechanism of photocatalytic degradation is given for discussing the advantages/shortcomings of regular 2D materials and identifying the importance of constructing hybrid 2D photocatalysts. An overview of several types of intensively investigated 2D nanomaterials (i.e., graphene, g-C₃ N₄ , MoS₂ , WO₃ , Bi₂ O₃ , and BiOX) is then given to indicate their hybridized methodologies, synergistic effect, and improved applications in decontamination of organic dyes and other pollutants. Finally, future research directions are rationally suggested based on the current challenges.

Self-Assembly Hydrothermal Synthesis of Silverton-Type Polyoxometalate-Based Photocatalysts for Enhanced Degradation

The synthesis of some complex polyoxometalates (POMs) is critical to develop potential photocatalysts with high catalytic activity and selectivity. Here, we address this challenge by a hydrothermal self-assembly route to obtain a novel POM-based Co₄W₆O₂₁(OH)₂·4H₂O with a hierarchical microsphere structure. The Co₄W₆O₂₁(OH)₂·4H₂O crystallizes in the cubic space group Im3̅ with cell parameters: a = b = c = 12.878 Å, α = β = γ = 90°, and Z = 4. The structure is further characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis spectroscopy, thermogravimetric analysis, and Fourier transform infrared spectra. After depositing Ag₂O nanoparticles on the 3D Co₄W₆O₂₁(OH)₂·4H₂O microsphere by photochemical synthesis, the Co₄W₆O₂₁(OH)₂·4H₂O/Ag₂O heterojunction presents enhanced photocatalytic activity for RhB compared with P25 and pristine Ag₂O. Moreover, we confirm the key role of holes for the Co₄W₆O₂₁(OH)₂·4H₂O/Ag₂O and put forward a possible mechanism for the photocatalytic degradation reaction.

Preparation and characterization of an Ag3PO4/GaOOH composite with enhanced photocatalytic performance toward rhodamine B

A highly efficient Ag₃PO₄/GaOOH composite was innovatively prepared and its photocatalytic performance was evaluated through degrading rhodamine B (RhB) under illumination, in this paper.

Octamolybdate-based hybrid constructed by flexible bis-triazole ligands: synthesis, photocatalytic and electrochemical properties

A novel polyoxometalate-based organic–inorganic hybrid compound was synthesized via a facile in situ hydrothermal reaction. 1 exhibits selective photocatalytic degradation of dyes and the great property to electrocatalytically reduce H₂O₂ and NaNO₂.

Pt/POMs/TiO2 composite nanofibers with an enhanced visible-light photocatalytic performance for environmental remediation

Pt/PMo₁₂/TiO₂ composite nanofibers have been prepared and exhibit a highly efficient visible-light photocatalytic performance for removing methyl orange, tetracycline, Bisphenol A and Cr(vi).