Low-temperature Synthesis Of Titania With Controlled Phase Composition And Enhanced Photocatalytic Activity By Surface Modification

Early in the middle of the twentieth century, TiO₂was widely studied as a kindof photocatalytic material. Along with the development of modern science andtechnology, people pay more attention on the TiO₂; and more and more preparationmethods were reported. With the time pass by, people become no longer satisfiedwith the synthesis of pure TiO₂and begin to pay more attention to the modificationof it. In this article, titanium tetra-n-butoxide was used as precursor and absoluteethanol as solvent. The titanium tetra-n-butoxide was hydrolyzed under neutral oralkaline condition. After that the products were treated with different volume ofHNO3and different phase compositions of TiO₂samples were obtained. And then theas-obtained samples were modified by Au nanoparticles or assembled under ethanolatmosphere. The photocatalytic abilities of the samples were changed by differentdegree. At last, all the prepared samples were tested and analyzed. We mainlystudied the experiment conditions that influenced the formation of TiO₂crystal phase,such as the amount of intermediates, the volume of acid, and the reaction time.Moreover, the effect of Au nanoparticles on the UV-induced photoactivities of TiO₂samples with different phase composition was also studied. On the other hand, theTiO₂nanoparticles were assembled by interfacial Ti-Ti bonding under ethanolatmosphere. The influence of treating style of the colloid, amount of ethanol,assembling time on the particle size and photocatalytic activity of products wasstudied. In this experiment, TEM, SEM, XRD, Raman, UV-Vis techniques were usedto characterize the morphology, crystal phase, crystallinity and photocatalyticperformance of TiO₂samples.Titanium tetra-n-butoxide was mixed with25.00ml absolute ethanol under lowtemperature, and the titanium tetra-n-butoxide was hydrolyzed in double-distilledwater to get amorphous TiO₂. Then the amorphous TiO₂was treated with NaOH togenerate protonated titanate intermediates. In the next step, a certain amount ofamorphous TiO₂or protonated titanate intermediates were treated with differentvolume of1M HNO3to get TiO₂products with different phase composition. Finallywe reached the purpose of getting TiO₂with controlled phase composition.The effect of the NaOH treatment and the volume of HNO3on the morphologyand crystal phase were studied. Further, the influence of the specific surface, phasecomposition and morphology on the photocatalytic activities was also discussed.After systematic analysis of the above aspects, the following conclusions were drawn:（1） the phase composition is the most important factor;（2） the sample which contains70%anatase and30%rutile shows the best photocatalytic ability;（3） the samples which consist of one-dimensional （1D） nanostructure show better photocatalyticabilities than the samples which only consist of zero-dimensional （0D） nanostructure.After modifying by Au nanoparticles, the introduction of Au enhanced thephotocatalytic ability of rutile TiO₂and decreased the photocatalytic ability ofanatase TiO₂.In the process of surface modification of TiO₂particles at ethanol atmosphere,the anatase TiO₂nanoparticles were washed with absolute ethanol and stirredtogether under heating in order to make the TiO₂absolutely disperse into absoluteethanol. In the following heating process, the heating temperature and time wereadjusted to assemble the TiO₂particles by interfacial Ti-Ti bonding so that make theproducts possess higher ratio of Ti to O and lower band gap. Then the TiO₂productsshow obvious visible light photoactivity.