Modified Titanium Dioxide Composites And Their Functional Applications In Photoelectrocatalysis

Photo?electro?catalytic water splitting has attracted increasing attentionin recent years because it could convert solar energy to chemical energy.Due to the fact that sunlight and water are abundant and renewable,photocatalytic water splitting represents a promising technology to solve the global energy and environmental challenges.Titanium dioxide?TiO₂?is one of the most important materials in photocatalysis due to its advantages such as high stability,low cost,relatively low toxicity,and excellent photocatalytic performance.To further improve the photocatalytic performance of TiO₂,in this thesis,we modified TiO₂with other novel materials like graphene,ionic liquid and polyaniline.In addition,the photoelectrochemical performance of the modified TiO₂ composites was thoroughly investigated.First,we developed a stepwise synthetic route to prepare TiO₂-deposited graphene sheets using a porous polyurethane sponge as template.Nucleation and growth of TiO₂ on graphene sheets took place within the porous polyurethane.The robust three dimensional structure of polyurethane sponge effectively prevented the restack of graphene sheets and suppressed the agglomeration of TiO₂ nanoparticles on the graphene sheets.The anatase TiO₂ nanoparticles were uniformly grown on graphene sheets.As expected,the obtained sponge-template graphene-TiO₂,with greatly improved TiO₂ dispersion,large surface area,closer graphene–TiO₂ interaction,and improved absorbance of visible light,showed remarkable enhanced photoelectrochemical oxidation for aqueous phase ethanol solution.We also demonstrated an efficient approach to synthesize ionic liquid modified TiO₂ as a novel photocatalyst using for photoelectrochemical water oxidation.A series of measurements confirmed the electronic interaction and chemical bonding between ionic liquid and TiO₂.The resulted ionic liquid-TiO₂ showed prominent photoelectrochemical water oxidation performance,exhibiting ten-fold photocurrent than unmodified TiO₂ under the same conditions and possessing an improved charge transfer efficiency of 37%compared with that of TiO₂?ca.15%?.Such an improved photoelectrochemical activity is believed to ascribe to the synergistic effect between ionic liquid and TiO₂,resulting in a high charge separation rate based on the electron transfer and efficient electron extraction.Finally,we further prepared a ternary polyaniline–graphene–TiO₂ hybrid as a highly efficient photocatalyst by a simple method.The ternary material not only exhibited a remarkably high photocatalytic activity,but also possessed promising photo-stability under continuous working conditions.The improved photoelectrocatalytic performance is attributed to the following crucial factors:?1?extended visible light absorption with enhanced solar energy harvesting by introducing the graphene and polyaniline components;and?2?facilitated charge separation at the surface and improvement of the electron transfer rate with the presence of polyaniline as an electrochemical active component.