Ultrafast Synthesis of Defective Black TiO2 via One-Step NaN3 Deflagration for High-efficiency Solar Water Evaporation

Abstract Titanium dioxide, especially for black-colored TiO2, has aroused increasing attention in the field of solar energy storage and conversion in recent years. Nevertheless, it is reported the fabrication of black TiO2 normally requires a long reaction time and high temperatures, such complexity of method largely limits the fundamental understanding of black TiO2 and development of application for solar energy conversion. In this study, black TiO2 with tunable defects of Ti3+/Ov were successfully prepared from a facile method of NaN3 deflagration, which allows an ultrafast and productive formation of defective TiO2 at 450 o C. EPR spectra proved the substantial presence of Ti3+/Ov species in the obtained black products, which were produced during the ultrafast decomposition of NaN3, with oxygen atoms from TiO2 crystal seized by thermal and reductive Na clusters. Benefited from the introduction of defective Ti3+/Ov sites, the black sample DP-3 with modified energy band achieved an enlarged light absorption across the full solar spectrum. DP-3 demonstrated an impressive water evaporation rate of 1.624 kg m−2 h−1 and conversion efficiency of 85% under one-sun irradiation. To the best of our knowledge, the black TiO2 act as an effective solar-thermal system was firstly reported in our work. By applying the energy-releasing effect of NaN3, this study proposed a simple and fast way for the synthesis and modulation of TiO2 and providing a valuable application in photothermal evaporation.