The Construction Of Three-dimensionl Tio₂Nanomaterial And Its Catalysis-adsorption Function For Heavy Metal

Prevention and remediation technology of heavy metal pollution, especially thedepth removal technology of heavy metal in water has become one of the key researchcontents. In this paper, in order to remove arsenic and chromium in water, nanometertitanium dioxide materials and three-dimensional rutile phase titanium dioxidematerials were prepared. The characterization of these materials was performed bySEM, TEM, XPS and N2adsorption-desorption methods. As(III) adsorption-oxidation process, Cr(VI) adsorption-reducing property and mechanism in water werestudied. The work was as follows:Titanium dioxide nanoparticles were prepared from tetrabutyl titanate adopted asprecursor.The anatase phase and rutile phase crystals with different particle size wereobtained by sintering method. The effects of TiO2particle size, specific surface areaand the surface hydroxyl content for As(III) adsorption and catalytic oxidation werestudied. The results showed that the rutile phase titanium dioxide had catalyticoxidation ability and the surface hydroxyl was the functional group for adsorption.Three-dimensional rutile TiO2nanostructures were prepared using template-freemethod. The effects of reaction time, temperature, precursor concentration, dryingtemperature and stirring methods on the structure and morphology ofthree-dimensional TiO2structure were discussed. The microstructure and compositionof the materials were performed by SEM, TEM and XPS. The results showed that thediameter of TiO2spheres was in micron level with a core-shell structure. The shellstructure was composed of spiny rutile phase structure with a high degree ofcrystalline; the core structure was composed of rutile with low crystallinity andamorphous TiO2nanoparticles. Using this method, the yield of TiO2wasapproximately97.8%and the surface hydroxyl density was approximately18.9OH/nm2. The formation mechanism of TiO2three-dimensional nanostructures wasfurther studied, which was controlled by particle growth kinetics and crystallizationgrowth kinetics in prophase and by the Ostwald effect in anaphase.In view of the adsorption process of As(III), As(Ⅴ), Cr (VI) and Cr(Ⅲ) in water,thermodynamic and kinetic experiments were carried out. Effect of PH values,coexisting ions and the structure of TiO2on the adsorption behavior was analysed indepth. Experiment results showed that its structure and composition were in favour of the adsorption of arsenic and Cr(VI), the impact of pH value was related to the releaseof H+and OH-in the compound formation process. In the range of pH=2-10, As(III)and As(Ⅴ) adsorption capacity was above17and24mg g-1; The adsorption capacityof As(Ⅴ) was60mg g-1.The adsorption process achieved at least80%within5minand the residual arsenic concentration decreased under detection limit. With theincreasing of pH, the adsorption capacity of Cr(VI) decreased from28mg g-1(pH=2.1)to6mg g-1(pH=10.3) and the adsorption capacity of Cr(Ⅲ) was less than1.5mg g-1.In UV/TiO2system, the As(III) and Cr(VI) adsorption-reduction process werediscussed. Ultraviolet light enhance hydroxyl functional group density of TiO2, butthese hydroxyl was unsteady adsorption sites with high reactivity and lowthermodynamics stability. Ultraviolet light cannot improve the adsorption capacity ofAs(Ⅴ) but the adsorption rate.-H2O/-OH in crystal defects played a direct role incatalytic oxidation process; rutile TiO2could be applied to Cr(VI) reductionapplication.