Solvothermal preparation of metallized titania sols for photocatalytic and antimicrobial coatings

The one-pot preparation of metal doped titania sols for coatings with photocatalytic and antimicrobial properties can be realized by using solvothermal conditions in alcoholic solvents at temperatures of 140 deg C and above. Under these conditions, hydrolysis of Ti(OR)4 results in photoactive anatase modification while simultaneously added silver or palladium salts will be reduced to colloidal metals. The formation of the nanosized anatase particles is confirmed by wide-angle X-ray scattering (WAXS) and Raman measurements, and the formation of nanosized metal particles of silver and palladium is demonstrated by WAXS and high-resolution transmission electron microscopy (HRTEM). Dynamic light scattering investigations into the particle size of solvothermal TiO2 and Ag sols (compared with their mixtures) suggest that common composite agglomerates are formed due to considerable interactions between the sol particles. After being coated onto viscose fabrics the Ag/TiO2 and Pd/TiO2 composite sols show strong photocatalytic properties. These were determined via decomposition of the organic dye Acid Orange 7, and by antimicrobial effects against gram negative bacteria E. coli even in the dark. Therefore, since no annealing is required to form the photoactive anatase modification, solvothermal sols are well suited to functionalizing less thermally-stable materials such as textiles, polymer foils or paper.