Thermal plasma-synthesized gray-black TiO2 with abundant oxygen vacancies for high-efficiency solar desalination†

Abstract

The growing scarcity of freshwater resources has increased interest in sustainable seawater desalination methods utilizing solar radiation. Titanium dioxide (TiO₂), known for its corrosion resistance and low cost, is an ideal material for photothermal applications. However, its wide bandgap limits the optimal utilization of visible and infrared light. To address this, a grey-black TiO₂ material rich in oxygen vacancies was synthesized using high-frequency low-temperature plasma. This material was integrated into a three-dimensional seawater evaporator with modified polyvinylidene fluoride (PVDF) sponge and polystyrene foam. The resulting structure exhibited a broad spectral absorption profile, low thermal conductivity, and enhanced evaporation efficiency. Experimental results confirmed the effectiveness of oxygen vacancies in narrowing the TiO₂ bandgap, improving light absorption and photothermal properties. In seawater desalination tests, the system achieved an impressive evaporation rate of 2.91 kg m⁻² h⁻¹ and a light-to-water evaporation efficiency of 75.52% under one sun irradiation, outperforming natural evaporation under sunlight conditions by a factor of 7.7. At the same time, the salinity of desalinated seawater significantly falls below the standard set by the World Health Organization (WHO) and even reaches levels comparable to soft water. This research offers insights for developing high-performance TiO₂ photothermal materials and seawater evaporators, contributing to discussions on sustainable and efficient desalination technologies.