Study On Modification Of TiO₂ Nanosheet Films And Properties Of Photocatalytic CO₂ Reduction

CO₂is considered to be the main greenhouse gas responsible for global warming.One of the best solutions to this problem is to use solar energy to convert carbon dioxide into renewable fuels,which can not only reduce CO₂emissions,but also provide useful energy.As one of the most important n-type semiconductors,TiO₂is widely used in the field of photocatalytic reduction of CO₂due to its good electrochemical stability,non-toxicity and strong redox capacity.Because the anatase TiO₂has a band gap of 3.2 e V,it belongs to a wide band gap semiconductor material and can only be excited by ultraviolet light with a wavelength less than 389 nm.Visible light with the largest specific gravity in sunlight cannot be effectively used.Moreover,the electron-hole pairs generated by TiO₂can be easily recombined to reduce their photoelectric conversion efficiency.In this paper,the modification methods of rare earth La element doping,semiconductor Cu₂O recombination and noble metal Pd particle loading are used to gradually solve the problems in the photocatalytic reduction of CO₂.The final experiments show that under the above modification conditions,the yield and selectivity of TiO₂photocatalytic reduction of CO₂are greatly improved.The research results are as follows:（1）La-doped anatase TiO₂nanosheet arrays with co-exposed（101）and（001）planes were prepared by one-step hydrothermal method.Compared with the pure TiO₂nanosheet array,the morphology of the nanosheets did not change significantly,and the thickness was 200-300 nm.When the doping amount of La is 0.5～1.5%mol,La exists in the form of Ti–O–La bond in TiO₂nanosheets;when the doping amount of La increases to 2.0%mol,La in TiO₂nanosheets in the form of La₂O₃.The photoelectric performance and photocatalytic reduction of CO₂experiments show that when the La-doped TiO₂nanosheet array is 1.0%mol,the photocurrent density is 1.28μA/cm²,which is 32 times that of pure TiO₂nanosheets;the CO yield is 102μmol·g^-1·h^-1.（2）Cu₂O nanoparticles were deposited on TiO₂nanosheet arrays with different amounts of lanthanum by electrochemical deposition method—chronoamperometry（CA）to obtain Cu₂O/TiO₂heterojunction films with different amounts of La.The photoelectric performance and photocatalytic reduction of CO₂experiments show that when the doping amount of Cu₂O/TiO₂heterojunction film is 1.0%mol,the photocurrent density is 7.2μA/cm²,which is twice that of pure Cu₂O/TiO₂heterojunction film;the rate of CO production is160μmol·g^-1·h^-1.In addition,CH₄and C₂H₄were added to the reduction product,and their yields were 76.8 and 44μmol·g^-1·h^-1,respectively.（3）Cu₂O/TiO₂heterojunction thin films with different exposure states of（001）plane of TiO₂nanosheets were prepared by changing the deposition times of Cu₂O.When the Cu₂O deposition frequency is 4 times,the（001）surface of the TiO₂nanosheet is the exposed surface,and when the Cu₂O deposition frequency is 6 times,the（001）surface of the TiO₂nanosheet is the non-exposed surface.The photoreduction deposition method was used to load noble metal Pd particles on the surfaces of Cu₂O/TiO₂heterojunction films,and the amount of Pd loading was 1.0 wt%.The effect of Pd particle loading on the performance of Cu₂O/TiO₂heterojunction film was compared.The photoelectric performance and photocatalytic reduction of CO₂experiments show that when Pd is supported on Cu₂O/TiO₂heterojunction film with Cu₂O deposition times of 4times,the photoelectric performance is best,and the photocurrent density is-9.4μA/cm²;The products of CO₂are CO,CH₄and C₂H₄,and the yields are 153,89.73 and 52.18μmol·g^-1·h^-1,respectively.