Pt nanoparticles embedded spine-like g-C3N4 nanostructures with superior photocatalytic activity for H2 generation and CO2 reduction

Tungsten Oxide/g-C3N4 Heterostructures: Composition, Structure, and Photocatalytic Applications

The construction of heterostructures promotes extending the light adsorption range of graphitic carbon nitride (g-C3N4) materials, improving the photogenerated charge carrier separation/transfer efficiency for attaining much enhanced performances. Because defective tungsten oxide (WOx) materials possess rich composition/morphology and an extended light response in the near-infrared region, WOx is a quite popular nanocomponent for modifying g-C3N4, forming heterostructures that can be used for various photocatalytic applications involving water splitting, CO2 reduction, NOx removal, H2O2 generation, and related chemical to fuel conversion reactions. In this review, important aspects of WOx/g-C3N4 heterostructure photocatalysts are reviewed to provide paradigms for composition adjustment, structural design, and photocatalytic applications of these materials. The WOx growth control in amorphous and crystalline g-C3N4, adjustment on heterostructure types (e.g., type II and Z-scheme), and the catalytic performances of the composite system are also discussed in detail. Moreover, the effects of synthetic methodologies and preparation parameters on the formation of two-dimensional layered heterostructures are discussed to provide inspiration for the construction of state-of-the-art WOx/g-C3N4 heterostructures that can be utilized for photoredox reactions. The challenges and prospects of the heterostructure formation and the photocatalytic applications of the heterostructures in future research are also summarized.

Recent progress of cocatalysts loaded on carbon nitride for selective photoreduction of CO2 to CH4

A photocatalytic system driven by solar light is one of the promising strategies for converting CO₂ into valuable energy. The reduction of CO₂ to CH₄ is widely studied since CH₄ has a high energy density as the main component of nonrenewable natural gas. Therefore, it is necessary to develop semiconductor materials with high photocatalytic activity and CH₄ selectivity. Graphitic carbon nitride (g-C₃N₄/CN) has attracted widespread attention for photocatalytic CO₂ reduction due to its excellent redox ability and visible light response. A hybrid system constructed by loading cocatalysts on g-C₃N₄ can significantly improve the yield of target products, and serve as a general platform to explore the mechanism of the CO₂ reduction reaction. Herein, we briefly introduce the theory of selective CO₂ photoreduction and the basic properties of cocatalysts. Then, several typical configurations and modification strategies of cocatalyst/CN systems for promoting CH₄ selective production are presented in detail. In particular, we systematically summarize the application of cocatalyst/CN composite photocatalysts in the selective reduction of CO₂ to methane, according to the classification of cocatalysts (monometal, bimetal, metal-based compound, and nanocarbon materials). Finally, the challenges and perspectives for developing cocatalyst/g-C₃N₄ systems with high CH₄ selectivity are presented to guide the rational design of catalysts with high performance in the future.

Plasmonic Ag Nanoparticle-Loaded n-p Bi2O2CO3/α-Bi2O3 Heterojunction Microtubes with Enhanced Visible-Light-Driven Photocatalytic Activity

In this study, n-p Bi2O2CO3/α-Bi2O3 heterojunction microtubes were prepared via a one-step solvothermal route in an H2O-ethylenediamine mixed solvent for the first time. Then, Ag nanoparticles were loaded onto the microtubes using a photo-deposition process. It was found that a Bi2O2CO3/α-Bi2O3 heterostructure was formed as a result of the in situ carbonatization of α-Bi2O3microtubes on the surface. The photocatalytic activities of α-Bi2O3 microtubes, Bi2O2CO3/α-Bi2O3 microtubes, and Ag nanoparticle-loaded Bi2O2CO3/α-Bi2O3 microtubes were evaluated based on their degradation of methyl orange under visible-light irradiation (λ > 420 nm). The results indicated that Bi2O2CO3/α-Bi2O3 with a Bi2O2CO3 mass fraction of 6.1% exhibited higher photocatalytic activity than α-Bi2O3. Loading the microtubes with Ag nanoparticles significantly improved the photocatalytic activity of Bi2O2CO3/α-Bi2O3. This should be ascribed to the internal static electric field built at the heterojunction interface of Bi2O2CO3 and α-Bi2O3 resulting in superior electron conductivity due to the Ag nanoparticles; additionally, the heterojunction at the interfaces between two semiconductors and Ag nanoparticles and the local electromagnetic field induced by the surface plasmon resonance effect of Ag nanoparticles effectively facilitate the photoinduced charge carrier transfer and separation of α-Bi2O3. Furthermore, loading of Ag nanoparticles leads to the formation of new reactive sites, and a new reactive species ·O2− for photocatalysis, compared with Bi2O2CO3/α-Bi2O3.

Silver nanoparticles embedded 2D g-C3N4nanosheets toward excellent photocatalytic hydrogen evolution under visible light

Photocatalytic water splitting is considered to be a feasible method to replace traditional energy. However, most of the catalysts have unsatisfactory performance. In this work, we used a hydrothermal process to grow Ag nanoparticlesin situon g-C₃N₄nanosheets, and then a high performance catalyst (Ag-g-C₃N₄) under visible light was obtained. The Ag nanoparticles obtained by this process are amorphous and exhibit excellent catalytic activity. At the same time, the local plasmon resonance effect of Ag can effectively enhance the absorption intensity of visible light by the catalyst. The hydrogen production rate promote to 1035μmol g^-1h^-1after loaded 0.6 wt% of Ag under the visible light, which was 313 times higher than that of pure g-C₃N₄(3.3μmol g^-1h^-1). This hydrogen production rate is higher than most previously reported catalysts which loaded with Ag or Pt. The excellent activity of Ag-g-C₃N₄is benefited from the Ag nanoparticles and special interaction in each other. Through various analysis and characterization methods, it is shown that the synergy between Ag and g-C₃N₄can effectively promote the separation of carriers and the transfer of electrons. Our work proves that Ag-g-C₃N₄is a promising catalyst to make full use of solar energy.

Photothermal methane coupling into liquid fuels with hydrogen evolution over nanocatalysts based on layered double hydroxide (LDH)

The increasing energy and environmental problems have made clean energy-driven catalysis a hot research topic. Methane is an earth-abundant raw material but difficult to be converted by thermochemical processes. It is of great significance to seek novel strategies to convert methane into high-value chemicals. Herein, we synthesize a series of transition metal catalysts based on layered double hydroxide precursors which were used for photothermal methane nonoxidative coupling reactions. The strong photothermal and chemisorption effects of the derived transition metal nanostructures allow the efficient activation of methane molecules. Among them, alumina-supported metallic Ni and NiCo-alloy catalysts show excellent methane nonoxidative coupling activities, achieved hydrogen production rates of 4816.53μmol g^-1h^-1and 5130.9μmol g^-1h^-1, accompanied by liquid fuels production rates of 59.2 mg g^-1h^-1and 63 mg g^-1h^-1, respectively. The findings, therefore, provide a new strategy for methane nonoxidative coupling driven by light energy at mild conditions.

Ultrathin structure of oxygen doped carbon nitride for efficient CO2photocatalytic reduction

Photocatalytic conversion of carbon dioxide into fuels and valuable chemicals is a promising method for carbon neutralization and solving environmental problems. Through a simple thermal-oxidative exfoliation method, the O element was doped while exfoliated bulk g-C₃N₄into ultrathin structure g-C₃N₄. Benefitting from the ultrathin structure of g-C₃N₄, the larger surface area and shorter electrons migration distance effectively improve the CO₂reduction efficiency. In addition, density functional thory computation proves that O element doping introduces new impurity energy levels, which making electrons easier to be excited. The prepared photocatalyst reduction of CO₂to CO (116μmol g^-1h^-1) and CH₄(47μmol g^-1h^-1).

DFT Study on Regulating the Electronic Structure and CO2 Reduction Reaction in BiOBr/Sulphur-Doped G-C3N4 S-Scheme Heterojunctions

Photocatalytic CO2 reduction is a promising method to mitigate the greenhouse effect and energy shortage problem. Development of effective photocatalysts is vital in achieving high photocatalytic activity. Herein, the S-scheme heterojunctions composed by BiOBr and g-C3N4 with or without S doping are thoroughly investigated for CO2 reduction by density functional theory (DFT) calculation. Work function and charge density difference demonstrate the existence of a built-in electric field in the system, which contributes to the separation of photogenerated electron-hole pairs. Enhanced strength of a built-in electric field is revealed by analysis of Bader charge and electric field intensity. The results indicate that S doping can tailor the electronic structures and thus improve the photocatalytic activity. According to the change in absorption coefficient, system doping can also endow the heterojunction with increased visible light absorption. The in-depth investigation indicates that the superior CO2 reduction activity is ascribed to low rate-determining energy. And both of the heterojunctions are inclined to generate CH3OH rather than CH4. Furthermore, S doping can further reduce the energy from 1.23 to 0.44 eV, indicating S doping is predicted to be an efficient photocatalyst for reducing CO2 into CH3OH. Therefore, this paper provides a theoretical basis for designing appropriate catalysts through element doping and heterojunction construction.