Nano-TiO₂ Suface Functionalization By Hydroxy Groups

Nano titanium dioxide has been intensively studied for various technological applications in field of antibacterial materials, heterogeneous photocatalysis, biosensors and semiconductor materials due to its excellent electro-optical properties and photochemical characteristics, high biochemical stability, and low cost. Research confirmed that nano-titanium dioxide was a super hydrophilic material with rich hydroxyl radicals in its surface, which was one of the main active matter in photocatalytic reaction system, and played an important role on the photocatalytic properties of titanium dioxide. In addtion, surface hydroxyl group has a far greater impact on protein adsorption characteristic. When nano titanium dioxide suface was functional by hydroxy groups, the amino acid residues with positively charged in the protein amino groups would be attacted in the surface and the amount of protein adsorption would be changed. The species of titanium dioxide surface hydroxyl was greatly affected by the species of crystalline phase, lattice plane and the preparation conditions of the aqueous phase reaction system.This paper utilized inorganic doping method with PO43-, SO42-, Na+ and K+ being used to increase the amout of surface hydroxy density, and the photocatalytic properties and protein adsorption characteristic were studied in the work. The results were as follows:Titanium dioxide was prepared by adding PO43-?SO422- and Na+ in the sol-gel process and acetic acid used as an inducer, which has significantly increased the surface hydroxyl groups of nano-TiO2, mainly consisting of isolated hydroxyl groups. The characterization reasults of FT-IR spectroscopy showed that there were two-OH vibration peaks (3400cm-1 and 1600cm-1) at 500?. Moreover, The redox-inert anions (PO43- and SO42-) also had an affect on crystal structure of titanium dioxide. The process of anatase-rutile phase transition and surface structural change were controllable by them, and until the phase change temperature reached 800? did it have been begun to ransform anatase to rutile.TiO2 nanoparticles, as photocatalytic material degradating methyl orange solution, was synthetised with controllable surface hydroxyl density and crystallinity by altering the added ratio of modifier and calcination temperature. The reasults illustrated that temperature was an important factor affecting the density of surface hydroxyl groups, while calcination temperature was increased, surface hydroxyl density groups being reduced. Generally, the 1600cm-1 O-H will dispear at 600?, and 3400cm-1 O-H will dispear at 700? or higher temperature. In addition, when the anatase crystallinity of samples were roughly the same, increasing the density of surface hydroxyl is conducive to the increase in photocatalytic activity, or even the amount of surface hydroxyl density increased also had little effect on the photocatalytic activity.While the specific surface area and crystallinity of TiO2 was roughly the same, adsorption capacity of bovine serum albumin would be affected by the surface hydroxyl density of spherical nanometer titanium dioxide. The more isolated hydroxyl groups of TiO2 surface, the more adsorption amount of BSA, but the adsorption amount of BSA would be reduced by the increase of weak thermal stability hydroxyl like hydrogen bonding hydroxyl. Meanwhile, interface characteristics of adsorption BSA with spherical titanium dioxide was investigated by SEM, XRD, XPS, TG FT-IR techniques and so on. The SEM images showed that the absorption of BSA had an effect on the crystal morphology changes, and The good dispersed spherical appearance began to reunion, surface becoming rough comparison; The FT-IR and XPS figures illustrated that TiO2 surface elements had changed by adsorbing BSA.