Dual-Functional Photocatalytic and Photoelectrocatalytic Systems for Energy- and Resource-Recovering Water Treatment

The solar-driven photo(electro)catalytic process is a key technology for utilization of solar energy. It is being intensively investigated for application to environmental remediation and solar fuel production. Although both environmental and energy applications operate on the basis of the same principle of photoinduced interfacial charge transfer, most previous studies have focused on either the environmental or energy process only since these two processes require very different catalyst properties and reaction conditions. This Perspective describes a dual-functional photo(electro)catalytic process that enables water treatment along with the simultaneous recovery of energy (e.g., H2 and H2O2) or resources (e.g., metal ions) and discusses the status and perspectives of this emerging technology. The essential feature of the process is to utilize the hole oxidation power for the degradation of water pollutants and the electron reduction power for the recovery of energy and resources from wastewaters at the same time. Various PC, PEC, and photovoltaic-driven electrochemical (PV-EC) processes with different dual-functional purposes (e.g., pollutant removal combined with H2 or H2O2 production, heavy-metal recovery, denitrification, fuel cell) are introduced and discussed. The reviewed technology should offer chances for the development of next-generation water treatment processes based on the water–solar energy nexus.