Plasmonic semiconductor photocatalyst: Non-stoichiometric tungsten oxide

Surface Plasmon Resonance-Mediated Photocatalytic H2 Generation

The limited yield of H2 production has posed a significant challenge in contemporary research. To address this issue, researchers have turned to the application of surface plasmon resonance (SPR) materials in photocatalytic H2 generation. SPR, arising from collective electron oscillations, enhances light absorption and facilitates efficient separation and transfer of electron-hole pairs in semiconductor systems, thereby boosting photocatalytic H2 production efficiency. However, existing reviews predominantly focus on SPR noble metals, neglecting non-noble metals and SPR semiconductors. In this review, we begin by elucidating five different SPR mechanisms, covering hot electron injection, electric field enhancement, light scattering, plasmon-induced resonant energy transfer, and photo-thermionic effect, by which SPR enhances photocatalytic activity. Subsequently, a comprehensive overview follows, detailing the application of SPR materials-metals, non-noble metals, and SPR semiconductors-in photocatalytic H2 production. Additionally, a personal perspective is offered on developing highly efficient SPR-based photocatalysis systems for solar-to-H2 conversion in the future. This review aims to guide the development of next-gen SPR-based materials for advancing solar-to-fuel conversion.

A novel TiO2-x/TiN@ACB composite for synchronous photocatalytic Cr(VI) reduction and water photothermal evaporation under visible/infrared light illumination

Relatively large band-gap, fast charge carriers recombination, and mono-functionality of photocatalytic materials are still representing stumbling hurdles against their optimal usage for water cleaning. Herein, a novel black titanium oxide/plasmonic titanium nitride@activated coconut biochar (TiO2-x/TiN@ACB) composite was designed to have both photocatalytic and photothermal functions. Intermediate states of black TiO2-x, plasmonic effect of TiN, and high electrons (e-) capacity of biochar enhanced band-gap narrowing, light absorbance extension, and charge carriers separation respectively. Black TiO2-x and plasmonic TiN sensitization via visible/infrared (Vis/IR) portion of photonic spectrum in addition to the confirmed close contact of composite constituents explained the demonstrated major role of e- in photocatalytic mechanism through efficient excitation and facile transfer. Thanks to black photocatalytic semiconductor and carbonic materials for their ultimate photons harnessing and efficient photothermal conversion where the composite exhibited a remarkable photothermal water evaporation upon Vis/IR illumination as well. TiO2-x/TiN@ACB composite revealed 92.8 and 89.7% photocatalytic reduction of hexavalent chromium (Cr(VI)) and water evaporation efficiencies up to 92.9 and 51.1% upon IR and Vis light illumination respectively. This study proposes a new approach for efficient water cleaning by coupling of oxygen deficient and plasmonic semiconductors supported on naturally derived carbonic material as a broad spectrum harvester and bi-functional photocatalytic and photothermal material.

Research progress in metal sulfides for photocatalysis: From activity to stability

Metal sulfides are a type of reduction semiconductor photocatalysts with narrow bandgap and negative conduction band potential, which make them have unique photocatalytic performance in solar-to-fuel conversion and environmental purification. However, metal sulfides also suffer from low quantum efficiency and photocorrosion. In this review, the strategies to improve the photocatalytic activity of metal sulfide photocatalysts by stimulating the charge separation and improving light-harvesting ability are introduced, including morphology control, semiconductor coupling and surface modification. In addition, the recent research progress aiming at improving their photostability is also illustrated, such as, construction of hole transfer heterojunctions and deposition of hole transfer cocatalysts. Based on the electronic band structures, the applications of metal sulfides in photocatalysis, namely, hydrogen production, degradation of organic pollutants and reduction of CO₂, are summarized. Finally, the perspectives of the promising future of metal-sulfide based photocatalysts and the challenges remaining to overcome are also presented.

2D WO3-x Nanosheet with Rich Oxygen Vacancies for Efficient Visible-Light-Driven Photocatalytic Nitrogen Fixation

Oxygen vacancy modulation holds great promise for enhancing the photocatalytic activity for efficient nitrogen fixation under mild conditions. In this work, the two-dimensional WO_3-x nanosheets with rich oxygen vacancies were prepared using solvothermal synthesis. The WO_3-x nanosheets (rich oxygen vacancies) display nice photocatalytic activity for N₂ reduction to ammonia with a high yield rate of 82.41 μmol·g_cat^-1·h^-1 under irradiation of visible light (420 nm), which is 3.59 times higher than that of the WO_3-x nanoparticles (poor oxygen vacancies). Electron spin resonance (ESR), N₂ adsorption-desorption isotherms, and transient photocurrent responses in the N₂ or Ar atmosphere experiments proved that the rich oxygen vacancies, which are induced by the nanosheet structure, could serve as active sites for the chemisorption of N₂ and facilitate the electron transfer from unsaturated sites to activated N₂. Moreover, based on the analysis of banding energy, the oxygen vacancies not only boosted the ability of visible light harvesting but also elevated the defect energy level to the Fermi level, further inhibiting the defect relaxation effect. The findings offer an insight into the design of the efficient photocatalysts via structure engineering and defect engineering for photocatalytic N₂ fixation.

Pyrochlore oxides as visible light-responsive photocatalysts

This perspective describes the use of pyrochlore oxides in photocatalysis with focus on the strategies to enhance their activity.