Air–water interface solar heating using titanium gauze coated with reduced TiO2 nanotubes

Abstract

Using method of electrochemical anodization and subsequent reduction, titanium gauze with reduced TiO2 nanotubes on the surface (reduced TiO2 nanotubes/Ti gauze) was prepared and used for air–water interface solar heating. The electrochemical reduction method can generate Ti3+ and causes the narrowing of optical band gap of TiO2 (ca. 2.91 eV). Combining with the nanotubular structure, reduced TiO2 nanotubes/Ti gauze demonstrated higher absorption ability of visible light than other types of titanium gauzes (reduced P25 TiO2 nanoparticles/Ti gauze, TiO2 nanotubes/Ti gauze and P25 TiO2 nanoparticles/Ti gauze). For evaluating the property of air–water interface solar heating, solar water evaporation test was conducted. The results demonstrated that the reduced TiO2 nanotubes/Ti gauze can efficiently accelerate water evaporation. The water evaporation rate and solar thermal conversion efficiency were 1.41 kg m−2 h−1 and 44.2%, respectively, under solar light irradiation with intensity of 2 kW m−2, which are higher than that of reduced P25 TiO2 nanoparticles/Ti gauze, TiO2 nanotubes/Ti gauze, P25 TiO2 nanoparticles/Ti gauze and pristine Ti gauze. It was further found that the solar thermal conversion efficiency of reduced TiO2 nanotubes/Ti gauze attained 84.2% when solar light intensity increased to 5.6 kW m−2. This work may provide a new route to design more advanced photothermal materials for industrial applications such as waste water treatment, salt production and solar desalination.