Enhanced photoactivity of stable colloidal TiO2 nanoparticles prepared in water by nanosecond infrared laser pulses

A simple laser ablation technique was used to prepare a stable colloidal TiO 2 suspension in pure water. A transparent TiO 2 aqueous solution was obtained within a few minutes and its photoactivity for the degradation of methylene blue was measured to be higher than that of commercial TiO 2 nanoparticles. SEM analysis revealed that the average size of the nanoparticles increased from 20 to 40 nm as the laser power was raised from 0.5 to 2 W. The variation in size, however, had little influence on the resulting photodegradation rate under the given condition. Instead, the photodegradation rate is related to the number of colloidal TiO 2 particles in the aqueous solution, which increases proportionally to the ablation time. As the TiO 2 particle density increases, however, the photoactivity is measured to be gradually reduced due to the formation of TiO 2 aggregates. Thus, the optimum ablation time is 10-30 min under our ablation condition. Our results show that well-dispersed small TiO 2 nanoparticles of about a few tens nm can be readily formed by laser ablation within only a few minutes and can be used as highly efficient photocatalysts for photocatalytic remediation of water.