Hydrothermal Synthesis Of TiO₂ Micro/Nanomaterials And Their Related Applications

As one of the most important semiconducting oxide materials,titania(TiO2)has a wide range of applications including paints,cosmetics,biomedicine,energy storage,solar cells,photocatalysis,gas sensors and self-cleaning materials owing to its advantageous characteristics such as non-toxicity,high chemical stability,low-cost,high photocatalytic activity,and strong optical absorption.With the rise of nano science and technology,it has been revealed that the properties of materials not only depend on their chemical compositions and crystalline structures but also on the microstructures such as particle sizes and morphologies.When the particle size decreases to micro/nano scale,the properties of TiO2 will be enhanced to a large extent.In recent years,many studies have been carried out on the synthesis of TiO2 micro/nanomaterials and a great many of methods have been developed,such as hydro/solvothermal method,sol-gel method,micro-emulsion method,electrochemical method,vapor deposition method and so on.TiO2 nanomaterials prepared by hydrothermal method have the advantages of integrated crystal structure,controllable morphology and size and narrow size distribution.Therefore,hydrothermal method has been paid much attention in the preparation of TiO2 nanomaterials.The main purpose of this dissertation is to synthesize micro/nanostructured TiO2 materials with different morphologies and study their potential applications.Ti02 micro/nanomaterials with three different microstructures have been prepared by hydro/solvothermal method.The effects of preparation conditions on their morphologies have been discussed and their applications in dye-sensitized solar cell or self-cleaning have been studied.The detailed information of this dissertation is listed as follows:1.Solvothermal synthesis of hierarchical TiO2 submicron-sized spheres(HSS)for enhanced power conversion efficiency in dye-sensitized solar cellsHerein,TiO2 submicron-sized spheres were solvothermally synthesized using titanium tetraisopropoxide(TTIP)as raw material and the mixture of ethylenediamine(EDA)and ethanol as solvent.The results of SEM,TEM,XRD and BET revealed that the submicron-sized spheres with large surface area and mesoporous structure were made of nanoparticles.When applied as the scattering overlayer in dye-sensitized solar cells(DSCs),such TiO2 HSSs effectively improved light harvesting and led to the increase of photocurrent in DSCs.Furthermore,bilayer-structured photoanode also provided fast electron transportation and long electron lifetime as confirmed by electrochemical impedance spectra.As a result,DSC based on P25 nanoparticle underlayer and HSS overlayer exhibited the highest cell efficiency(6.23%)compared with ones with pure P25(5.50%)or HSS(2.00%)photoanodes.2.Hydrothermal synthesis of TiO2 superhydrophobic material and its self-cleaning propertyHerein,TiO2 nanosheets on Ti plate were prepared by hydrothermal treatment of Ti plate in NaOH aqueous solution.Wettability test demonstrated that the as-prepared Ti plate was superhydrophilic with a water contact angle of nearly 0°.After treating with perfluorosilane,the hydrothermal treated Ti plate shows superhydrophobic with a water contact angle as high as 158°.Moreover,the contact angle of glycerin was also exceeded 150°,exhibiting superamphiphobic properties.Then,the self-cleaning property of the treated Ti plate was studied by sprinkling graphite powder on its surface and dripping water droplets on the graphite.After the sand impacting test,the plate reserved its superhydrophobic property,indicating the good mechanical stability of the self-cleaning plate.3.Hydrothermal synthesis of underwater superoleophobic TiO2 coatings and its self-cleaning propertyHerein,TiO2 coatings on fluorine-doped tin oxide(FTO)substrate with hierarchical rutile TiO2 flowers were fabricated through a simple one-step hydrothermal method with TTIP,water,and concentrated hydrochloric acid as starting materials.The flower-like coatings exhibited superhydrophilicity in air and superoleophobicity underwater with a contact angle as high as 157°,indicating good underwater self-cleaning property.After contamination treatment,the film lost its superwetting state with the WCA increased to 137° and the OCA decreased to 64°.After irradiating by UV light for 2 h,the film recovered its superamphiphilic and underwater superoleophobic property caused by its good photocatalytic ability,indicating that the TiO2 coatings exhibit excellent self-cleaning ability under UV irradiation.Therefore,these coatings with two different self-cleaning properties can provide an insight into fabrication of functional materials for some underwater applications such as anti-bioadhesion and marine anti-pollution in the future.