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·g_cat⁻¹ in the absence of sacrificial agent.