Solution Plasma-Synthesized Black TiO₂ Nanoparticles for Solar–Thermal Water Evaporation

Black TiO2 nanoparticles (b-TiO2) with superior solar–thermal water evaporation performance are prepared using a one-step solution plasma process (SPP) in ambient conditions. It is found that radicals that are generated during SPP play a critical role in b-TiO2 formation by comparing several water–alcohol electrolyte environments for the SPP synthesis. Our results show that the radical-induced formation of a black TiO2–x layer on the Ti electrode is necessary for b-TiO2 formation, which was ignored in previous studies. A two-step mechanism for b-TiO2 formation in SPP synthesis is proposed: (I) preoxidation of a Ti electrode surface; and (II) quenching and aggregation of sputtered molten TiOx clusters to form b-TiO2 particles. The b-TiO2-loaded hydrophobic mesh exhibited high water evaporation rates in the solar–thermal water evaporation experiments, which were 1.2, 1.4, and 2.3 times higher than that of the control group without using mesh at 1000, 2000, and 5000 W·m–2, respectively. The understanding in this study may inspire strategies for the facile synthesis of self-structured modified metal-oxide materials for more efficient solar energy harvesting in solar–thermal conversion applications.