Preparation And Characterizations Of Completely Disperse A-TiO₂ Nanoparticles

Titanium dioxide?TiO₂?is one of the catalysts that have been widely used to bring pollution under control,duing to its excellent electronic properties and chemical stability,as well as high photocatalytic activity.It is known that TiO₂ is a polymorphic material which may exist in anatase?a-TiO₂?,rutile?r-TiO₂?and brookite?b-TiO₂?phases at different temperatures.Compared to other polymorphs,a-TiO₂ exhibits the highest photocatalytic activity in the degradation of various organic pollutants.In recent years,chemical deposition,doping and coating approaches were applied to improve the catalytic activity instead of controlling the a-TiO₂ structure.However,phase,morphology,dispersity,particle size and size uniformity of TiO₂ nanoparticles are important factors for the performances of the products.There are still many challenges remaining before the preparation of completely disperse pure a-TiO₂ nanoparticles become feasible.With the development of particle dispersion technology,physical and chemical methods as a deagglomeration of the aggregates are used to improve dispersity of particles.Although the aggregates are deagglomerated by mechanical agitation dispersion and maintained in a dispersant dispersion process,the use of the dispersant causes a decrease in product yield while increasing the cost.Therefore,the deagglomeration of the hard or severely hard aggregates is the most simple and low-cost way to improve the catalytic activity of a-TiO₂ nanoparticles.In this work,we innovatively developed a novel top-down method to improve the dispersity of a-TiO₂ nanoparticles,namely hydrothermal corrosion approach.The initial a-TiO₂ powders prepared by hydrothermal crystallizations or calcinations are hard or severely hard aggregates of fine primary nanoparticles.Then a corrosion approach was designed to improve the dispersity of a-TiO₂ nanoparticles.The completely disperse a-TiO₂ nanoparticles with average particle sizes of 4.6 and 7.8 nm,and size distributions of 1-12 and 3-13 nm were obtained by being hydrothermally crystallized at 140°C for 10 h and calcined at 450°C for 2 h and then HCl-corroded at 100°C for 72 h.In addition,to further evaluate the photocatalytic activity of disperse a-TiO₂ nanoparticles,Rhodamine B?RhB?was used as model water pollutants under ultraviolet?UV?light irradiation for 120 min.As a result,the photocatalysis reaction rates of the completely disperse a-TiO₂ nanoparticles with average sizes of 4.6 and 7.8 nm are 18.50×10-3 and 15.65×10-3 min-1,respectively.And different sizes of completely a-TiO₂ nanoparticles have more effective photocatalytic activity under UV light irradiation with RhB degradation percent of 92 and 90% than the hard and severely hard aggregates of primary nanoparticles.