Studies On PDA Sensitized TiO₂ And Ferroelectric Material For The CO₂ Photoreduction

In the past decades,the increasing fossil fuel consumption aggravates global warming and energy crisis.Among many solutions,the photocatalytic reduction of CO2 into fuels via solar light is believed to be one of the most ideal methods and received much attention.However,the efficiency of commonly used semiconductor photocatalyst is rather low,mainly due to the weak visible light absorption and fast charge recombination.In this thesis,we attempted to address these two problems of semiconductor photocatalyst through two different strategies.Firstly,we used polydopamine as a photosensitizer and obtained the composite of-TiO2@PDA by the method of in-situ oxidation polymerization.The photocatalytic activity for CO2 reduction has been tested under a series of conditions.It was found that PDA could enhance the visible light absorption of TiO2 obviously and it could also extend the life-time of excited electrons by UV-vis and PL.We found the polymorphs of TiO2have a strong effect on the performance:PDA can improve the CO yield of anatase TiO2 under visible light,but it inhibits the activities of brookite and rutile TiO2-Although a thicker PDA-coating could increase the CO yield,we found that the thicker PDA might not be enough stable under light irradiation.The photo-degradation of PDA has been confirmed by N2 control experiments,SSNMR and TGA measurements.Secondly,we used single-crystal and single-domain PbTiO3(PTO)nanoplates as the photocatalyst for the reduction of CO2.The CO yield of PTO nanoplates is 21 times higher than that of P25 TiO2 after the normalization of their specific surface areas in the photoreduction of Cv2 with H2O5 while the CO yield of PTO nanoplates in the photoreduction of CO2 without H2O is 1.65 times higher than that of PTO nanoplates in the photoreduction of CO2 with H2O.PTO nanoplates were able to maintain the photocatalytic activity after multiple recycles.Color change of PTO nanoplates was observed after photoreaction which may be related to the formation of surface oxygen vacancies as confirmed by UV-vis,PL,XPS and spherical-abbreation-corrected HADDF-STEM.Finally,we discussed the possible reaction mechanisms involving roles of surface adsorbed water and surface hydroxyl groups as revealed by SSNMR and FTIR.