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

Direct Z-scheme PDA-modified ZnO hierarchical microspheres with enhanced photocatalytic CO2 reduction performance

Emerging 2D/0D g-C3N4/SnO2 S-scheme photocatalyst: New generation architectural structure of heterojunctions toward visible-light-driven NO degradation

0D/2D (Fe0.5Ni0.5)S2/rGO nanocomposite with enhanced supercapacitor and lithium ion battery performance

0D/2D NiS/CdS nanocomposite heterojunction photocatalyst with enhanced photocatalytic H2 evolution activity

Summary Developing highly efficient photocatalysts with low production costs is critical to practical applications. Single-atom photocatalysts (SAPs), in which isolated atoms are anchored on the semiconductor supports, have attracted considerable attention owing to their preeminent catalytic activity, superior selectivity, impressive stability, and maximum atom utilization efficiency. Moreover, they offer a great opportunity to explore photocatalysis on the atomic level. Single atoms stand out from bulk, nanoparticle, and nanocluster counterparts. Herein, we summarize their recent progress, mainly focusing on their properties, geometric structures, synthetic strategies, characterization techniques, and photocatalytic applications. Also, the functions of isolated metal atoms in photocatalytic reactions are discussed. Finally, the challenges and perspectives of designing and fabricating highly active SAPs are presented.

Liuyang Zhang

Papers

Direct Z-scheme PDA-modified ZnO hierarchical microspheres with enhanced photocatalytic CO2 reduction performance

Emerging 2D/0D g-C3N4/SnO2 S-scheme photocatalyst: New generation architectural structure of heterojunctions toward visible-light-driven NO degradation

0D/2D (Fe0.5Ni0.5)S2/rGO nanocomposite with enhanced supercapacitor and lithium ion battery performance

0D/2D NiS/CdS nanocomposite heterojunction photocatalyst with enhanced photocatalytic H2 evolution activity

Single-atom heterogeneous photocatalysts