Study On The Growth Of Highly Crystalline TiO₂ Nanofibers On Aerogel Surface And Photocatalytic Reduction Of CO₂

Environmental degradation and energy crisis have become two major problems in the 21 st century.The sustainable development is facing great challenges for human society,because of the increasing CO2 emission in the atmosphere and the increasing shortage of non-renewable fuel resources.Attribute to low cost and high stability,TiO₂ has attracted much attention by photocatalyst researchers.However,TiO₂ can only absorb ultraviolet light,the lifetime of photogenerated electrons is short,and the photoquantum efficiency is low.（1）SiO₂ aerogel and CuO-SiO₂ composite aerogel were prepared by sol-gel method and freeze-drying method.The aerogel was filled with Ti Cl4 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 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 Cu O had a band gap of 3.04 e V.When Cu O was hierarchically loaded on the nanofiber surface and into the aerogel core（SiO₂/Cu O@TiO₂/Cu O）,the absorption edge significantly red shifted,and the band gap was further narrowed to 2.66 e V.Under the irradiation of 300 W xenon lamp and without sacrificial agent,the yield of methanol synthesized by SiO₂/Cu O@TiO₂/Cu O can reach 1901 μmol/g-cat after 4 h.（2）Fe³⁺ was successfully dopped into TiO₂.SiO₂/Cu O@Fe-TiO₂/Cu O was obtained by loading of Cu O onto the SiO₂@Fe-TiO₂.Fe³⁺-doping and Cu O heterojunction both enhanced the stability of photogenerated charge.After photocatalytic reaction for 4 h,the yield of methanol was 2386 μ mol/g-cat,and TOF reached to 0.095 h-1.（3）Fe³⁺ implanted TiO₂ nanofibers on the Cu O-SiO₂ composite aerogels by the same method（Cu O-SiO₂@Fe-TiO₂）,loading of Cu O onto the nanofibers,the fluorescence intensity of the Cu O-SiO₂@Fe-TiO₂/Cu O was further reduced.Both the Cu O loaded on the surface of Fe-TiO₂ and the Cu O in the gel can transfer the excited electrons to the TiO₂ conduction band and increase the number of photogenerated carriers.The photocatalytic reduction of CO2 was carried out in 0.2 mol/L Na OH aqueous solution.The Cu O-SiO₂@FeTiO₂/Cu O were used as photocatalysts,the methanol yield was 2035 μmol/g-cat,which was 12 times higher than P25,and the corresponding TOF was 0.061 h-1.The structure and optoelectronic properties of the materials were characterized by SEM,TEM,XPS,UPS,UV-Vis DRS,PL,I-T,EIS and so on.