Band Gap Engineering in an Efficient Solar-Driven Interfacial Evaporation System.

Solar-driven interfacial evaporation system is attracting intensive attention for harvesting clean water in the utilization of solar energy. To improve solar-driven interfacial evaporation performance for better application, structuring a solar absorber with high solar-thermal conversion efficiency is critical. Semiconductor materials with stable and economic properties are good candidates as solar absorbers. Semiconductors with a narrow band gap have been proved to offer a broad solar absorption spectrum in the applications of photoelectricity and photocatalysis. However, the correlation between band gap and solar-driven interfacial evaporation performance has not been systematically studied. Herein, TiO2 is selected as a semiconductive absorber and a reproducible process is developed to fabricate band gap engineered TiO2 to understand the relationship between the "electronic structure" and the "performance" in the field of solar-driven interfacial evaporation. After the band gap engineering from 3.2 to 2.23 eV, correlative tests of solar-driven interfacial evaporation performance as well as first-principles calculations are employed to study the correlation mentioned above. As a result, we find that a narrower band gap contributes to improved solar-thermal conversion efficiency and the Ti3+-doped TiO2 (Ti3+-TiO2) with the narrowest band gap of 2.23 eV outperforms other samples, achieving the highest evaporation rate of 1.20 kg m-2 h-1 (solar-thermal conversion efficiency of 77.1%). Besides, the Ti3+-TiO2 also shows the good ability of photocatalytic degradation. This work may provide a way for semiconductor materials to be designed as solar absorbers with higher solar-thermal conversion efficiency and better solar-driven interfacial evaporation performance for applications in clean water harvesting.