Metal-free photocatalysts for various applications in energy conversion and environmental purification

During the past few decades, photocatalysis as a green and sustainable technology has received increasing attention owing to its potential to solve energy and environmental problems. For the purpose of obtaining highly efficient and low-cost photocatalysts, various metal-free photocatalytic materials have been designed and developed in recent years for energy conversion and environmental purification because of their unique properties and characteristics. This critical review presents the recent crucial applications and progress in metal-free photocatalysis, including photocatalytic water reduction for H-2 evolution, photocatalytic CO2 reduction, photoremoval of NOx, photodegradation of pollutants and so on. The review also ends with some study highlights and suggestions for future research topics. We hope this review can facilitate deep-level investigation on the subject and provide new opportunities to develop metal-free photocatalytic materials with other important applications in the future.