Harnessing synchronous photothermal and photocatalytic effects of cryptomelane-type MnO2 nanowires towards clean water production

Abstract

Solar energy is a major source of energy with the potential to solve the water-energy nexus. Driven by the development of photothermal materials and photocatalysts, much effort has been made to harness solar energy for clean water production. To maximize the utilization of solar energy, we herein, fabricated a solar steam generator based on a cryptomelane-type MnO₂ light absorber, which offered synergistic high-efficiency steaming and photocatalytic functions. Instead of integrating two functional components, cryptomelane-type MnO₂ worked as a photothermal–photocatalytic dual-functional light absorber in the device and thus expanded the utilization of solar energy. Remarkably, we achieved a solar thermal efficiency of up to 84% and an evaporation rate of 2.2 kg m⁻² h⁻¹ under one sun illumination. Moreover, MnO₂ exhibits highly efficient catalytic activity during solar-driven water evaporation under irradiation of the full solar spectrum. Both conventional photocatalytic effect and photothermal-induced thermodynamic reaction contribute to the oxidation catalytic process at the MnO₂ surface. These results demonstrate the promising application of this novel solar steam generator for clean water production.