A Review of Direct Z‐Scheme Photocatalysts

Abstract

Recently, great attention has been paid to fabricating direct Z‐scheme photocatalysts for solar‐energy conversion due to their effectiveness for spatially separating photogenerated electron–hole pairs and optimizing the reduction and oxidation ability of the photocatalytic system. Here, the historical development of the Z‐scheme photocatalytic system is summarized, from its first generation (liquid‐phase Z‐scheme photocatalytic system) to its current third generation (direct Z‐scheme photocatalyst). The advantages of direct Z‐scheme photocatalysts are also discussed against their predecessors, including conventional heterojunction, liquid‐phase Z‐scheme, and all‐solid‐state (ASS) Z‐scheme photocatalytic systems. Furthermore, characterization methods and applications of direct Z‐scheme photocatalysts are also summarized. Finally, conclusions and perspectives on the challenges of this emerging research direction are presented. Insights and up‐to‐date information are provided to give the scientific community the ability to fully explore the potential of direct Z‐scheme photocatalysts in renewable energy production and environmental remediation.

Morphology‐controlled Fabrication of SnO2/ZnO Nanocomposites with Enhanced Photocatalytic Performance

“…For example, the reduction and oxidation reactions of photocatalysts in type II mechanism may be weakened simultaneously, because SnO 2 has a lower reduction potential and ZnO has a lower oxidation potential. In addition, it is not an easy transfer process because it could cause electrostatic rejection between e − –e − or h + –h + . In addition, according to the analysis of hydroxyl radical‐trapping experiments, the number of ˙OH radicals on the SnO 2 /ZnO composites is also larger than the pure components as shown in Fig.…”

g‐C3N4‐Based Heterostructured Photocatalysts

“…[67,80,81] Generally, constructing a suitable heterostructure is consid ered as the most feasible strategy to improve the separation efficiency of electron-hole pairs, which greatly enhances the photo catalytic performance. The main design considerations of heterostruc tures are focused on extending light absorption, increasing spe cific surface area, and active site density, introducing cocatalyst to reduce the overpotential of catalytic reaction and enhancing the separation of photogenerated electron-hole pairs.…”

“…In nature, this desirable chargetransfer pattern has been found in the photosynthesis process of green plants. [80,81,168] As shown in Figure 11b, the photogenerated electrons on the lowerlying CB of SI can directly transfer to the VB of SII to recombine with the holes. This type of charge transfer, called Zscheme, can achieve efficient separation of photogenerated charge carriers and maintain their strong redox abilities simul taneously.…”

“…Under light irradiation, the charge transfer in the plant follows a different direction from conventional type II heterojunctions with the help of electron mediators. [80,167] This type of charge transfer is called direct Zscheme transfer mechanism. [167] Learning from nature, constructing gC 3 N 4 based Zscheme heterojunction photocatalysts has been explored as an efficient means of improving the photocatalytic perfor mance of gC 3 N 4 .…”

Photocatalysis: Basic Principles, Diverse Forms of Implementations and Emerging Scientific Opportunities

“…The simplicity, nevertheless, also introduces significant challenges, the most critical of which is the low efficiency. [63] Reasons for the low efficiency include severe recombination. [42b] Because the reduction and oxidation sites at the nanoscale in such an integrated system are often not well defined, the charge separation mechanisms are consequently not optimized, thereby resulting in charge recombination within an individual photocatalyst or on the surface or both.…”