The Effect of Synthesis Conditions on Mesoporous Structure and the Photocatalytic Activity of TiO2 Nanoparticles

Mesoporous TiO2 nanoparticles have been synthesized by sot gel method in different preparation conditions to investigate the effect of triblock copolymer, acetic acid and water on mesoporous structure and the photocatalytic activity. The synthesized photocatalysts were characterized by means of X-ray powder diffraction, Nitrogen adsorption/desorption studies, High resolution transmission electron microscopy, Scanning electron microscopy, Diffuse reflectance UV-Vis spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and thermogravimetric analysis. Among the various synthesized materials, nnesoporous TiO2 synthesized using triblock copolymer as a structure directing template in acetic acid medium with high water ratio calcined at 400 degrees C was found to have the highest photocatalytic activity due to the enhanced band gap energy, high specific surface area and high average pore size. The large mesopores provide more pathways for the reactants to enter and products to escape and enhances the adsorption of methylene blue. The photocatalytic activity decreases with increase of solution pH. The rate of 'OH formation is high at lower pH, which enhances the photocatalytic activity was revealed by photoluminescence technique. In addition, the adsorbed hydroxyl groups on the surface of nnesoporous TiO2 particles can interact with photogenerated holes to produce more (OH)-O-center dot radicals, which enhances charge transfer efficiency and enhances the rate of 'OH formation.