Highly efficient and robust oxygen vacancy-rich molybdenum trioxide aerogel evaporator for Photothermal conversion and clean water generation

Abstract

Interfacial evaporation of seawater and other wastewater is used to produce clean water by the infinite solar energy which attracts an intense interest and displays a great prospect. An efficient and robust photothermal evaporator is a key to solar-driven interfacial evaporation. Herein, the oxygen vacancy-rich MoO₃ aerogel evaporator is designed to purify seawater and wastewater. Hydrogen etching is used to construct oxygen vacancies of MoO₃, which regulate its optical and thermophysical properties. MoO₃* possesses stronger broadband absorption and lower reflectance than MoO₃ across the wavelength ranges of 200 nm–2500 nm, which insures more energy input. Besides, band gap energy of MoO₃* decreases from 2.90 eV of MoO₃ to 1.92 eV, which is more beneficial for the visible light absorption and its degradation of organic pollutant. As a result, the MoO₃*-based evaporator displays a higher evaporation rate of 1.78 kg m⁻² h⁻¹ as well as 92.6 % of efficiency for pure water at 1 sun illumination, in contrast to the MoO₃-based evaporator with an evaporation rate of 1.04 kg m⁻² h⁻¹ and 60.0 % efficiency, suggesting that oxygen vacancies induced by hydrogen etching improve photothermal conversion efficiency. In practical application, the MoO₃*-based evaporator also displays an excellent purification performance for seawater, heavy metal wastewater and tetracycline wastewater, in which the evaporation rates are close to pure water, and the quality of the purified water is better than drinking water specified by WHO standard. In addition, the defected MoO₃*-based aerogel evaporator not only possesses an excellent thermal management, but also offers an excellent salt self-cleaning ability. This work convincingly demonstrates that the “defect chemistry” is perfect for constructing the defected MoO₃* aerogel evaporator for sustainable production of clean water from seawater, heavy metal wastewater and tetracycline wastewater by means of the solar-driven interfacial evaporation.