Hierarchical loading of CuO on SiO2 aerogel@high crystalline TiO2 nanofibers for efficiently photocatalytic reduction of CO2 without sacrificial agent

Silica aerogel was prepared by a sol-gel method with combination of freeze drying. The aerogel was filled with TiCl4 in autoclave and used to fabricate a hierarchical structure of TiO2 nanofiber shell and SiO2 aerogel core (SiO2@TiO2). The TiO2 nanofibers with a diameter of 10–15 nm were highly crystalline and mainly grew along the (101) or (001) planes, favoring charge migration along the growth axis of the fibers. The photoluminescence (PL) emission spectra show that the TiO2 nanofibers exhibited much lower PL intensity than P25. The free standing TiO2 nanofibers loaded with CuO had a band gap of 3.04 eV. When CuO was hierarchically loaded on the nanofiber surface and into the aerogel core (SiO2/CuO@TiO2/CuO), the absorption edge significantly red shifted, and the band gap was further narrowed to 2.66 eV. Meanwhile, Fe3+ implanted TiO2 nanofibers on the aerogel surface (SiO2@Fe-TiO2) were also fabricated in the same strategy. The CuO loaded nanofibers (SiO2/CuO@Fe-TiO2/CuO) had a band gap of 2.62 eV. The photocatalytic reduction of CO2 was performed under light irradiation by a 300 W Xe-lamp for 4 h. The methanol yield over the SiO2/CuO@Fe-TiO2/CuO reached ∼ 2,400 µmol·gcat−1 in the absence of sacrificial agent.