Preparation Of Ag-TiO₂ Photocatalysis Material Based On Low-temperature Growth Of TiO₂ Nanocrystals

TiO₂ has been the hot research field of photocatalysis for a long time due to the excellent photocatalytic activity,good chemical and thermal stability,and nontoxicity,etc.However,the disadvantages of the single TiO₂ including narrow photoresponse range and low quantum yield have restricted the widely application of TiO₂ photocatalyst.Ag-TiO₂ composite material has received a universal concern of many researchers because it is able to improve the photocatalytic activity of TiO₂ and shows a good antibacterial ability thanks to the synergistic effect of Ag and TiO₂.Herein,anatase titania sol and large size porous TiO₂ materials have synthesized based on the low temperature growth of TiO₂ nanocrystal at first.Then,film- and large size porous particles-type Ag-TiO₂ photocatalytic materials with good photocatalytic and antibacterial properties were also prepared by introducing Ag⁺ to sol and in-situ reduction of silver ions under liquid phase conditions.It shows a good way to overcome the deficiency of easy agglomeration and difficult recovery of nanosized TiO₂ powders.The main parts of thesis are as follows:(1) Study on Preparation and Characterization of Ag-TiO₂ Crystalline Thin FilmsAnatase TiO₂ sol was prepared by controlling the hydrolysis and condensation processes of n-butyl titanate via a sol-gel method.Subsequently,Ag⁺ was added to above sol and the anatase Ag-doped TiO₂ composite films were obtained after thermal treatment.The influence of different heat treatment temperature and amount of Ag on the structure and properties of thin film was investigated.The results show that the crystallinity of TiO₂ is improved with the increase of the heat treatment temperature,and the anatase converted to rutile at 500℃. However,Ag particles would aggregate at higher temperature and existed as elemental silver. The composite film shows a great photocatalytic activity when they were treated under 250℃. In addition,the photocatalytic activity of Ag-TiO₂ films increased at first and then decreased with increasing Ag amount,and its comprehensive properties reached the best when the doping amount of Ag is 5.0 at%.(2) Study on Low-temperature Synthesis of Size-tunable Porous Anatase Titania Spheres The monodisperse titanium glyeolate precursor spheres were prepared by the homogeneous nucleation and growth process of the ethylene glycol chelated n-butyl titanate precursor in an acetone bath containing a small amount of water(0.3～2.0%).Then,the mesoporous anatase spheres were fabricated by the simple hot water treatment at low temperature under atmospheric pressure.The results show that the average size of the titania particles could be tuned in range from 200 nm to 500 nm by changing the precursor concentration.The surface of the precursor particle became rough and the anatase phase began to form at the beginning of hot water treatment.With increasing treatment time,the crystallinity of the particles is improved,and the nanoporous structure further formed in the interior of the spheres.In particular,there was little change in the size of the spheres during hot water treatment,thus the size of the mesoporous anatase titania spheres could be easily tailored by controlling the diameter of precursor spheres. After refluxing the precursor spheres(400 nm) for 6 h,the mesoporous anatase spheres were finally obtained,which were composed of interconnected nanocrystals with the size less than 15 nm and pores with the mean size of 8.31 nm.The as-prepared mesoporous anatase titania spheres exhibited excellent adsorption capacity and better photocatalytic activity compared with the commercial photocatalyst P25 due to the large specific surface area(194.91 m²/g) and fine anatase nanocrystals.Ostwald ripening and surface energy effects accompanied in the crystallization process were presumed to play an important role in the formation of mesoporous structure and anatase nanocrystals.(3) Study on the Fabrication and Characterization of Large-size Ag-deposited TiO₂ Porous SpheresAg nanoparticles were successfully deposited on the large size mesoporous TiO₂ spheres (400 nm) via a photocatalytic and in-situ chemical reduction method.The influence of Ag load on the structure and properties of different TiO₂ powder was investigated.XRD results show that the load of silver is metal Ag⁰ and the crystallinity of TiO₂ is influenced by the deposit amount to a certain extent.As the loading increases,the average size of silver particles gradually increased.Adsorption tests show that all Ag-TiO₂ porous spheres show a good adsorption capacity except the higher deposition rate(5 wt%or 10 wt%) prepared by chemical reduction. Photocatalytic results showed that the Ag-TiO₂ photocatalyst basically exhibits the same properties under the ultraviolet and visible light which is enhanced at first,then decreased with the increase of Ag content.Furthermore,the samples originate from Ag⁺ storage(AgBr) and with a loading of 2.5 wt%have high photocatalytic and antibacterial comprehensive properties.