S-Scheme Heterojunction Photocatalyst

The appropriate interfacial contact of heterojunction photocatalysts plays a critical role in transfer/separation of interfacial charge carriers. Design of two-dimensional (2D)/2D surface-to-surface heterojunction is an effective method for improving photocatalytic activity since greater contact area can enhance interfacial charge transfer rate. Herein, ultrathin 2D/2D WO3/g-C3N4 step-like composite heterojunction photocatalysts were fabricated by electrostatic self-assembly of ultrathin tungsten trioxide (WO3) and graphitic carbon nitride (g-C3N4) nanosheets. The ultrathin WO3 and g-C3N4 nanosheets were obtained by electrostatic-assisted ultrasonic exfoliation of bulk WO3 and a two-step thermal-etching of bulk g-C3N4, respectively. The thickness of ultrathin WO3 and g-C3N4 nanosheets are 2.5–3.5 nm, which is equivalent to 5–8 atomic or molecular layer thickness. This ultrathin layered heterojunction structure can enhance surface photocatalytic rate because photogenerated electrons and holes at heterogeneous interface more easily transfer to surface of photocatalysts. Therefore, the obtained ultrathin 2D/2D WO3/g-C3N4 step-scheme (S-scheme) heterojunction photocatalysts exhibited better H2-production activity than pure g-C3N4 and WO3 with the same loading amount of Pt as cocatalyst. The mechanism and driving force of charge transfer and separation in S-scheme heterojunction photocatalysts are investigated and discussed. This investigation will provide new insight about designing and constructing novel S-scheme heterojunction photocatalysts.

Ultrathin 2D/2D WO3/g-C3N4 step-scheme H2-production photocatalyst

Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

To solve the problem of the global energy shortage and the pollution of the environment, in recent years, semiconductor photocatalytic technology that converts solar energy into chemical fuel has been widely studied. Regarding semiconductor-based photocatalysts, CdS has attracted extensive attention due to its relatively narrow bandgap for visible-light response and sufficiently negative potential of the conduction band edge for the reduction of protons. Studies have shown that CdS-based photocatalysts possess excellent photocatalytic performance in terms of solar-fuel generation and environmental purification. This critical review presents the recent advances and progress in the design and synthesis of various CdS and CdS-based photocatalysts. The basic physical and chemical properties of CdS and the related growth mechanism have been briefly summarized. Moreover, the applications of CdS-based photocatalysts have been discussed such as in photocatalytic hydrogen production, reduction of CO2 to hydrocarbon fuels and degradation of pollutants. Finally, a brief perspective on the challenges and future directions for the development of CdS and CdS-based photocatalysts are also presented.

CdS-Based photocatalysts

Direct Z-scheme photocatalysts: Principles, synthesis, and applications

Photocatalytic CO2 conversion into solar fuels has an alluring prospect. However, the rapid recombination of photogenerated electron–hole pairs for TiO2-based photocatalyst hinders its wide applica...

TiO2–MnOx–Pt Hybrid Multiheterojunction Film Photocatalyst with Enhanced Photocatalytic CO2-Reduction Activity

Hierarchical porous Ni/Co-LDH hollow dodecahedron with excellent adsorption property for Congo red and Cr(VI) ions

Photocatalytic water splitting is a promising strategy to convert solar energy into chemical energy. Herein, a series of g-C3N4/polydopamine (g-C3N4/PDA) composites were successfully fabricated by in situ polymerization of dopamine on the g-C3N4 surface. Among all the as-prepared composites, the best photocatalytic hydrogen evolution rate of the as-prepared composites was up to 69 μmol h–1 under the irradiation of visible light (λ > 420 nm), which was about 4.5 times than that of pristine g-C3N4 (16 μmol h–1). The enhancement of photocatalytic H2 evolution is reasonably attributed to the markedly enhanced light harvesting, broadened spectral response range and low onset potential of H2 production, as well as effective separation and rapid transportation of photogenerated charge carriers. More importantly, the surface modification of g-C3N4 by a small amount of PDA can effectively inhibit the overgrowth of Pt nanoparticles (NPs) during the photocatalytic reactions, which promotes the photoelectron injectio...

Dopamine Modified g-C3N4 and Its Enhanced Visible-Light Photocatalytic H2-Production Activity

Review on DFT calculation of s‐triazine‐based carbon nitride

Photoelectrochemical (PEC) water splitting is one of the most efficient strategies to meet the challenges of the global energy crisis. Although hematite (α-Fe2O3), is a suitable material for PEC, its performance is limited by passive surface state and slow charge transfer kinetics. Here, a successful design and fabrication of novel ternary Fe2O3/CdS/Co-Pi nanorod arrays (NRAs) photoanode is reported aimed at boosting charge separation and transfer kinetics within the bulk and at the electrode/electrolyte interface. As expected, the results reveal that α-Fe2O3 sluggish reaction kinetics is greatly ameliorated upon depositing CdS and Co-Pi, and surface charge recombination decreases even more, resulting in substantially enhanced photocurrent density. Moreover, noticeable onset potential negative shift evidenced by the I–V curve is found to result from the deposition of CdS and Co-Pi, which allows the ternary composite to generate photocurrent at much lower applied potential. We elaborate the synergistic effect of CdS and Co-Pi in achieving faster charge transfer kinetics and lower onset potential for photocurrent. These results provide new insights into the surface reaction kinetics of Co-Pi/semiconductor photoanode toward PEC application.

Liuyang Zhang

Papers

TiO2–MnOx–Pt Hybrid Multiheterojunction Film Photocatalyst with Enhanced Photocatalytic CO2-Reduction Activity

Hierarchical porous Ni/Co-LDH hollow dodecahedron with excellent adsorption property for Congo red and Cr(VI) ions

Dopamine Modified g-C3N4 and Its Enhanced Visible-Light Photocatalytic H2-Production Activity

Review on DFT calculation of s‐triazine‐based carbon nitride

Enhanced charge transfer kinetics of Fe2O3/CdS composite nanorod arrays using cobalt-phosphate as cocatalyst