Photocatalysis has been regarded as a promising strategy for hydrogen production and highvalue-added chemicals synthesis, in which the activity of photocatalyst depends significantly on their electronic structures, however the effect of electron spin polarization has been rarely considered. Here we report a controllable method to manipulate its electron spin polarization by tuning the concentration of Ti vacancies. The characterizations confirm the emergence of spatial spin polarization among Ti-defected TiO 2 , which promotes the efficiency of charge separation and surface reaction via the parallel alignment of electron spin orientation. Specifically, Ti 0.936 O 2 , possessing intensive spin polarization, performs 20-fold increased photocatalytic hydrogen evolution and 8-fold increased phenol photodegradation rates, compared with stoichiometric TiO 2. Notably, we further observed the positive effect of external magnetic fields on photocatalytic activity of spin-polarized TiO 2 , attributed to the enhanced electron-spin parallel alignment. This work may create the opportunity for tailoring the spin-dependent electronic structures in metal oxides.

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Photocatalysis via direct solar-to-chemical energy conversion is an intriguing approach for alleviating the pressure of high energy consumption caused by social development. However, photocatalytic efficiency is greatly restricted by unsatisfactory light-harvesting capacity, high carrier recombination rates, and sluggish reaction kinetics. Indeed, vacancy engineering is an attractive strategy to regulate photocatalytic reaction performance to maximize the utilization and storage of solar energy. In this review, we summarize recent progress about the important roles of vacancy defects on solar-driven photocatalytic applications. The current advanced characterization techniques, especially for in situ/operando techniques, are first presented for elucidating the structure-performance relationships of defective semiconductors in photocatalysis. Subsequently, the crucial roles of vacancies in enhancing photocatalytic performance are highlighted from three important processes: light absorption, carrier separation and migration, and surface reaction. Finally, based on the above understanding, perspectives and opportunities about defective materials are considered for various photocatalytic applications.

The spin degree of freedom is an important and intrinsic parameter in boosting carrier dynamics and surface reaction kinetics of photocatalysis. Here we show that chiral structure in ZnO can induce spin selectivity effect to promote photocatalytic performance. The ZnO crystals synthesized using chiral methionine molecules as symmetry-breaking agents show hierarchical chirality. Magnetic circular dichroism spectroscopic and magnetic conductive-probe atomic force microscopic measurements demonstrate that chiral structure acts as spin filters and induces spin polarization in photoinduced carriers. The polarized carriers not only possess the prolonged carrier lifetime, but also increase the triplet species instead of singlet byproducts during reaction. Accordingly, the left- and right-hand chiral ZnO exhibit 2.0- and 1.9-times higher activity in photocatalytic O2 production and 2.5- and 2.0-times higher activities in contaminant photodegradation, respectively, compared with achiral ZnO. This work provides a feasible strategy to manipulate the spin properties in metal oxides for electron spin-related redox catalysis.

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The visible-light responsive semiconductor carbon nitride (C 3 N 4 ) exhibits suitable electronic band structure, rich sources of precursors, and high stability, which is exploited to satisfy energy demands. However, the photocatalytic efficiency of C 3 N 4 is limited because of its low surface area and low separation and transfer efficiency of charge carriers. As Z-scheme strategy can effectively help C 3 N 4 overcome its instinct shortage, this review will outline the recent significant progress on the development of C 3 N 4 -based all-solid Z-scheme photocatalysts for energy-conversion applications including water splitting and CO 2 reduction. In the beginning, the fundamental principles of Z-scheme will be introduced, especially for all-solid-state system. Then, the comprehensive account of the development of C 3 N 4 -based Z-scheme photocatalysts are discussed. Finally, perspectives on the challenges and future directions at the forefront of Z-scheme photocatalysts are provided.