Photocatalytic hydrogen peroxide (H2O2) production from O-2 and H2O is an ideal process for solar-to-chemical energy conversion. Herein, ZnO nanorods are prepared via a simple hydrothermal method for photocatalytic H2O2 production. The ZnO nanorods exhibit varied performance with different calcination temperatures. Benefiting from calcination, the separation efficiency of photo-induced carriers is significantly improved, leading to the superior photocatalytic activity for H2O2 production. The H2O2 produced by ZnO calcined at 300 degrees C is 285 umol L-1, which is over 5 times larger than that produced by untreated ZnO. This work provides an insight into photocatalytic H2O2 production mechanism by ZnO nanorods, and presents a promising strategy to H2O2 production. (C) 2022, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Constructing step-scheme (S-scheme) heterojunctions has been confirmed as a promising strategy for enhancing the photocatalytic activity of composite materials. In this work, a series of sulfur-doped g-C3N4 (SCN)/TiO2 S-scheme photocatalysts were synthesized using electrospinning and calcination methods. The as-prepared SCN/TiO2 composites showed superior photocatalytic performance than pure TiO2 and SCN in the photocatalytic degradation of Congo Red (CR) aqueous solution. The significant enhancement in photocatalytic activity benefited not only from the 1D well-distributed nanostructure, but also from the S-scheme heterojunction. Furthermore, the XPS analyses and DFT calculations demonstrated that electrons were transferred from SCN to TiO2 across the interface of the SCN/TiO2 composites. The built-in electric field, band edge bending, and Coulomb interaction synergistically facilitated the recombination of relatively useless electrons and holes in hybrid when the interface was irradiated by simulated solar light. Therefore, the remaining electrons and holes with higher reducibility and oxidizability endowed the composite with supreme redox ability. These results were adequately verified by radical trapping experiments, ESR tests, and in situ XPS analyses, suggesting that the electron immigration in the photocatalyst followed the S-scheme heterojunction mechanism. This work can enrich our knowledge of the design and fabrication of novel S-scheme heterojunction photocatalysts and provide a promising strategy for solving environmental pollution in the future. (C) 2021, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

H-2 is an important energy carrier for replacing fossil fuel in the future due to its high energy density and environmental friendliness. As a sustainable H-2-generation method, photocatalytic H-2 production by water splitting has attracted much interest. Here, oil-soluble ZnxCd1-xS quantum dot (ZCS QD) with a uniform particle size distribution were prepared by a hot-injection method. However, no photocatalytic H-2-production activity was observed for the oil-soluble ZCS QD due to its hydrophobicity. Thus, the oil-soluble ZCS QD was converted into a water-soluble ZCS QD by a ligand-exchange method. The water-soluble ZCS QD exhibited excellent photocatalytic H-2-production performance in the presence of glycerin and Ni2+, with an apparent quantum efficiency of 15.9% under irradiation of 420 nm light. Further, the photocatalytic H-2-generation activity of the ZCS QD was similar to 10.7 times higher than that of the ZnxCd1-xS relative samples prepared by the conventional co-precipitation method. This work will inspire the design and fabrication of other semiconductor QD photocatalysts because QD exhibits excellent separation efficiency for photogenerated electron-hole pairs due to its small crystallite size. (C) 2021, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Constructing step-scheme (S-scheme) heterojunctions has been confirmed as a promising strategy for enhancing the photocatalytic activity of composite materials. In this work, a series of sulfur-doped g-C3N4 (SCN)/TiO2 S-scheme photocatalysts were synthesized using electrospinning and calcination methods. The as-prepared SCN/TiO2 composites showed superior photocatalytic performance than pure TiO2 and SCN in the photocatalytic degradation of Congo Red (CR) aqueous solution. The significant enhancement in photocatalytic activity benefited not only from the 1D well-distributed nanostructure, but also from the S-scheme heterojunction. Furthermore, the XPS analyses and DFT calculations demonstrated that electrons were transferred from SCN to TiO2 across the interface of the SCN/TiO2 composites. The built-in electric field, band edge bending, and Coulomb interaction synergistically facilitated the recombination of relatively useless electrons and holes in hybrid when the interface was irradiated by simulated solar light. Therefore, the remaining electrons and holes with higher reducibility and oxidizability endowed the composite with supreme redox ability. These results were adequately verified by radical trapping experiments, ESR tests, and in situ XPS analyses, suggesting that the electron immigration in the photocatalyst followed the S-scheme heterojunction mechanism. This work can enrich our knowledge of the design and fabrication of novel S-scheme heterojunction photocatalysts and provide a promising strategy for solving environmental pollution in the future. (C) 2021, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

The interaction between a gas molecule and photocatalyst is vital to trigger photocatalytic reaction. The surface state of photocatalyst affects much in this interaction. Herein, adsorption of H2O molecules on s-triazine-based g-C3N4 was thoroughly studied by first-principle calculation. Although various initial adsorption models with multifarious locations of H2O molecules were built, the optimized models with strong adsorption energy pointed to the same adsorption configuration, in which the H2O molecule hold an upright orientation above the corrugated g-C3N4 monolayer. An intermolecular O-H center dot center dot center dot N hydrogen bond formed via the binding of a polar O-H bond in H2O molecule and a two-coordinated electron-rich nitrogen atom in g-C3N4. Under the bridging effect of this intermolecular hydrogen bond, electrons would transfer from g-C3N4 to the H2O molecule, thereby lowering the Fermi level and enlarging work function of g-C3N4. Interestingly, regardless of the substitute, i.e. g-C3N4 multilayer, large supercell and nanotube, this adsorption system was highly reproducible, as its geometry structure and electronic property remained unchanged. In addition, the effect of nonmetal element doping on adsorption energy was explored. This work not only disclosed a highly preferential H2O adsorbed g-C3N4 architecture established by intermolecular hydrogen bond, but also contributed to the deep understanding and optimized design in water-splitting process on g-C3N4-based photocatalysts. (C) 2021, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

The NiS/CQDs nanocomposite (CQDs represents carbon quantum dots), with a mass ratio of NiS/CQDs to be 1.19:1 based on the ICP result, was obtained via a facile hydrothermal method from a mixture of CQDs, Ni(OAc)(2) and Na2S. The self-assembly of ZnIn2S4 microspheres on the surface of NiS/CQDs was realized under microwave conditions to obtain a ternary NiS/CQDs/ZnIn2S4 nano-composite. The as-obtained NiS/CQDs/ZnIn2S4 nanocomposite was fully characterized, and its photocatalytic hydrogen evolution under visible light irradiation was investigated. The ternary NiS/CQDs/ZnIn2S4 nanocomposite showed superior photocatalytic activity for hydrogen evolution than ternary CQDs/NiS/ZnIn2S4, which was obtained by deposition of NiS in the preformed CQDs/ZnIn2S4. The superior photocatalytic performance of ternary NiS/CQDs/ZnIn2S4 is ascribed to the introduction of CQDs, which act as a bridge to promote the vectorial transfer of photo-generated electrons from ZnIn2S4 to NiS. This result suggests that the rational design and fabrication of ternary CQDs-based systems are important for the efficient photocatalytic hydrogen evolution. This study provides a strategy for developing highly efficient noble-metal-free photocatalysts for hydrogen evolution using CQDs as a bridge to promote the charge transfer in the nanocomposite. (C) 2019, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

Hierarchically nanostructured CdS composed of 4.7 nm-thick self-assembled ultrathin nanosheets was synthesised through a microwave-assisted solvothermal method. Ag2S nanoparticles (NPs) were deposited at the edge of the CdS nanosheets by an in situ ion exchange strategy. The hierarchically CdS-Ag2S nanocomposites exhibited a high visible light photocatalytic H-2 evolution rate of 375.6 mu mol h(-1) g(-1), which was 11.5 times higher than that of pure CdS. Given the difference in work functions between CdS and Ag2S, electrons diffused from the CdS side to the Ag2S side until the Fermi levels align after their contact. When the CdS-Ag2S was illuminated, the photogenerated electrons on the conduction band of the CdS further migrated to Ag2S. Considering the lower overpotential of Ag2S, the electrons more easily participated in the reduction of protons. Meanwhile, the holes on the valence band of CdS reacted with the hole sacrificial agent (triethanolamine). In this process, the photogenerated electron-hole pairs realised effective separation. The introduction of Ag2S also enhanced the utilisation of infrared light and increased the temperature of CdS surface.

The pi-conjugated structure of graphitic carbon nitride (g-C3N4) is particularly vital to many photocatalytic reactions. Herein, the hybrid structure of tri-s-triazine unit in g-C3N4 framework is chemically analyzed and expounded according to the hybrid orbital theory. The localized pi-conjugated structure of g-C3N4 is also monitored by the electron paramagnetic resonance (EPR) or electron spin resonance (ESR) technique. The experimental results indicate that this pi-conjugated structure is attributed to the orbital overlapping of the hybrid carbon and nitride atoms in their 2p(z) orbits. Unlike graphene with the nonlocalized pi-conjugated structure, this orbital overlapping in the whole two-dimensional plane of g-C3N4 is separated by the electrons pairs in 2p(z) orbits of the bridging nitride atoms, leading to the localized pi-conjugated structure. Therefore, the g-C3N4 exhibits the typical features of a semiconductor with band gap and visible-light response. Meanwhile, the EPR or ESR technique can be acted as the ideal tool to indirectly evaluate the yield of photoelectrons by detecting the superoxide radicals (center dot O-2(-)) in g-C3N4-based photocatalytic reactions.