Construction of novel Sr0.4H1.2Nb2O6·H2O/g-C3N4 heterojunction with enhanced visible light photocatalytic activity for hydrogen evolution

Enhanced Photocatalytic Properties of All-Organic IDT-COOH/O-CN S-Scheme Heterojunctions Through π-π Interaction and Internal Electric Field

Herein, we present a distinct methodology for the in situ electrostatic assembly method for synthesizing a conjugated (IDT-COOH)/oxygen-doped g-C3N4 (O-CN) S-scheme heterojunction. The electron delocalization effect due to π-π interactions between O-CN and self-assembled IDT-COOH favors interfacial charge separation. The self-assembled IDT-COOH/O-CN exhibits a broadened visible absorption to generate more charge carriers. The internal electric field between the IDT-COOH and the O-CN interface provides a directional charge-transfer channel to increase the utilization of photoinduced charge carriers. Moreover, the active species (•O2-, h+, and 1O2) produced by IDT-COOH/O-CN under visible light play important roles in photocatalytic disinfection. The optimum 40% IDT-COOH/O-CN can kill 7-log of methicillin-resistant Staphylococcus aureus (MRSA) cells in 2 h and remove 88% tetracycline (TC) in 5 h, while O-CN only inactivates 1-log of MRSA cells and degrades 40% TC. This work contributes to a promising method to fabricate all-organic g-C3N4-based S-scheme heterojunction photocatalysts with a wide range of optical responses and enhanced exciton dissociation.

Synergistic Integration of AuCu Co-Catalyst with Oxygen Vacancies on TiO2 for Efficient Photocatalytic Conversion of CO2 to CH4

Photocatalytic reduction of CO₂ toward eight-electron CH₄ product with simultaneously high conversion efficiency and selectivity remains great challenging owing to the sluggish charge separation and transfer kinetics and lack of active sites for the adsorption and activation of reactants. Herein, a defective TiO₂ nanosheet photocatalyst simultaneously equipped with AuCu alloy co-catalyst and oxygen vacancies (AuCu-TiO_2-x NSs) was rationally designed and fabricated for the selective conversion of CO₂ into CH₄. The experimental results demonstrated that the AuCu alloy co-catalyst not only effectively promotes the separation of photogenerated electron-hole pairs but also acts as synergistic active sites for the reduction of CO₂. The oxygen vacancies in TiO₂ contribute to the separation of charge carriers and, more importantly, promote the oxidation of H₂O, thus providing rich protons to promote the deep reduction of CO₂ to CH₄. Consequently, the optimal AuCu-TiO_2-x nanosheets (NSs) photocatalyst achieves a CO₂ reduction selectivity toward CH₄ up to 90.55%, significantly higher than those of TiO_2-x NSs (31.82%), Au-TiO_2-x NSs (38.74%), and Cu-TiO_2-x NSs (66.11%). Furthermore, the CH₄ evolution rate over the AuCu-TiO_2-x NSs reaches 22.47 μmol·g^-1·h^-1, which is nearly twice that of AuCu-TiO₂ NSs (12.10 μmol·g^-1·h^-1). This research presents a unique insight into the design and synthesis of photocatalyst with oxygen vacancies and alloy metals as the co-catalyst for the highly selective deep reduction of CO₂.

Co(OH)2 water oxidation cocatalyst-decorated CdS nanowires for enhanced photocatalytic CO2 reduction performance

Photocatalytic CO2 reduction is a promising technology to resolve the greenhouse effect and energy crisis. In this work, a Co(OH)2 nanoparticle decorated CdS nanowire (Co(OH)2/CdS) based heterostructured photocatalyst was prepared via a solvothermal and subsequent co-precipitation method, and it was used for photocatalytic CO2 reduction. The optimal Co(OH)2/CdS photocatalyst achieves a CO production rate of 8.11 μmol g-1 h-1 under visible light irradiation (λ > 420 nm), which is about 2 times higher than that of bare CdS. The experimental results show that a Co(OH)2 cocatalyst possesses a great capability of consuming holes, which promotes the oxygen-producing half-reaction and accelerates charge separation, thus enhancing the CO2 photoreduction performance of CdS. Notably, without using complex synthesis processes, hazardous substances or expensive ingredients, Co(OH)2/CdS shows high light absorption, efficient charge separation and complete CO product selectivity. This work offers a new pathway for the construction of cost-effective photocatalytic materials to achieve highly efficient CO2 reduction activity by the integration of a Co(OH)2 cocatalyst.

CoAl2O4-g-C3N4 Nanocomposite Photocatalysts for Powerful Visible-Light-Driven Hydrogen Production

There is no doubt that the rate of hydrogen production via the water splitting reaction is profoundly affected to a remarkable degree based on the isolation of photogenerated electrons from holes. The precipitation of any cocatalysts on the substrate surfaces (including semiconductor materials) provides significant hindrance to such reincorporation. In this regard, a graphite-like structure in the form of mesoporous g-C₃N₄ formed in the presence of a template of mesoporous silica has been synthesized via the known combustion method. Hence, the resulting g-C₃N₄ nanosheets were decorated with varying amounts of mesoporous CoAl₂O₄ nanoparticles (1.0-4.0%). The efficiencies of the photocatalytic H₂ production by CoAl₂O₄-doped g-C₃N₄ nanocomposites were studied and compared with those of pure CoAl₂O₄ and g-C₃N₄. Visible light irradiation was carried out in the presence of glycerol as a scavenger. The results showed that the noticeable photocatalytic enhancement rate was due to the presence of CoAl₂O₄ nanoparticles distributed on the g-C₃N₄ surface. The 3.0% CoAl₂O₄-g-C₃N₄ nanocomposite had the optimum concentration. This photocatalyst showed extremely high photocatalytic activities that were up to 22 and 45 times greater than those of CoAl₂O₄ and g-C₃N₄, respectively. This photocatalyst also showed 5 times higher photocatalytic stability than that of CoAl₂O₄ or g-C₃N₄. The presence of CoAl₂O₄ nanoparticles as a cocatalyst increased both the efficiency and productivity of the CoAl₂O₄-g-C₃N₄ photocatalyst. This outcome was attributed to the mesostructures being efficient charge separation carriers with narrow band gaps and high surface areas, which were due to the presence of CoAl₂O₄.

Oxygen vacancy engineering of BiOBr/HNb3O8 Z-scheme hybrid photocatalyst for boosting photocatalytic conversion of CO2

Photo-chemical conversion of CO₂ into solar fuels by photocatalysts is a promising and sustainable strategy in response to the ever-increasing environmental problems and imminent energy crisis. However, it is unavoidably impeded by the insufficient active site, undesirable inert charge transfer and fast recombination of photogenerated charge carriers on semiconductor photocatalysts. In this work, all these challenges are overcome by construction of a novel defect-engineered Z-scheme hybrid photocatalyst, which is comprised of three-dimensional (3D) BiOBr nanoflowers assembled by nanosheets with abundant oxygen vacancies (BiOBr-V_O) and two-dimensional (2D) HNb₃O₈ nanosheets (HNb₃O₈ NS). The special 3D-2D architecture structure is beneficial to preventing photocatalyst stacking and providing more active sites, and the introduced oxygen vacancies not only broaden the light absorption range but also enhance the electrical conductivity. More importantly, the constructed Z-scheme photocatalytic system could accelerate the charge carriers transfer and separation. As a result, the optimal BiOBr-V_O/HNb₃O₈ NS (50%-BiOBr-V_O/HNb₃O₈ NS) shows a high CO production yield of 164.6 μmol·g^-1 with the selectivity achieves to 98.7% in a mild gas-solid system using water as electron donors. Moreover, the BiOBr-V_O/HNb₃O₈ NS photocatalyst keeps high photocatalytic activity after five cycles under the identical experimental conditions, demonstrating its excellent long-term durability. This work provided an original strategy to design a new hybrid structure photocatalyst involved V_Os, thus guiding a new way to further enhance CO₂ reduction activity of photocatalyst.

0D ultrafine ruthenium quantum dot decorated 3D porous graphitic carbon nitride with efficient charge separation and appropriate hydrogen adsorption capacity for superior photocatalytic hydrogen evolution

Ultrafine Ru quantum dot decorated 3D porous g-C₃N₄ (U-Ru/3DpCN) photocatalysts were prepared. The optimal photocatalyst U-1Ru/3DpCN achieves an excellent H₂ evolution of 2945.47 μmol g⁻¹ h⁻¹ under visible light with a high AQE of 9.5% at 420 nm.

Soft and hard templates assisted synthesis mesoporous CuO/g-C3N4 heterostructures for highly enhanced and accelerated Hg(II) photoreduction under visible light

Herein, triblock copolymer surfactant (F127) and mesoporous silica (MCM-41) as soft and hard templates were employed to synthesize of mesoporous CuO/g-C₃N₄ heterostructures with large surface areas for Hg(II) photoreduction in existence of formic acid as a holes sacrificial. TEM image for mesoporous CuO/g-C₃N₄ indicated that CuO NPs are homogeneously distributed with spherical shape in particle size ~5 nm onto the surface of g-C₃N₄. Mesoporous 2%CuO/g-C₃N₄ heterostructure was achieved a high Hg(II) photoreduction rate of 628.74 µmolg^-1h^-1 and high photoreduction efficiency of ~100% within 50 min compared with the pure either mesoporous CuO NPs (130.11 µmolg^-1h^-1, 21%) and g-C₃N₄ (88.54 µmolg^-1h^-1, 14%). The highest Hg(II) photoreduction rate achieved was 628.74 µmolg^-1h^-1, which is 4.83 and 7.1 magnitudes stronger than mesoporous CuO NPs and g-C₃N₄. The excellent photocatalytic performance of mesoporous CuO/g-C₃N₄ heterostructures for Hg(II) photoreduction is referred to highly dispersed mesoporous CuO NPs with small particle size onto g-C₃N₄, narrow bandgap, large surface area, a rapid transfer of Hg(II) ions and HCOOH to easily reach the active sites due to the facile penetration through the mesostructure, thus promoting the utilization of porous structure of CuO/g-C₃N₄ heterostructures for efficient diffusion of Hg(II) ions. The intense interaction between mesoporous CuO NPs and porous g-C₃N₄ confirms the durability of the CuO/g-C₃N₄ heterostructures during recyclability for five times.