Modification engineering over single-atom catalysts for efficient heterogeneous photocatalysis

Arguably, single-atom catalysts (SACs) have become the most active research direction and a new promising catalytic material in heterogeneous catalysis. Among them, each catalytic unit consists of single metal atom and its surrounding coordination atoms. The alteration of these components will regulate and control the geometrical and electronic structures of SACs, which in turn determine its catalytic activity, selectivity and stability during catalytic processes. In this review, the recently developed modification strategies for SACs are first introduced and classified, with great attention given to how the performance can be further improved by controllably tuning the electronic configuration of the metal centers. The state-of-the-art characterization techniques of experimental (in situ/operando) and computational techniques are discussed, advances in which have made it possible to determine dynamic structural evolution and activation mechanism of SACs. A wide range of applications based on modified SACs in photocatalysis are then elaborately discussed, with attention on the sources of enhanced photocatalytic activity (light-harvesting ability, charge transfer/separation dynamics and surface catalytic reaction kinetics) and reaction mechanisms. Finally, perspectives on the development of modified SACs are provided and prospected, which is hoped to shed some light on the further development of SACs in energy and environmental applications.