Simple Crystal Phase Control of TiO2 Nanoparticles via Pulsed Laser Ablation in Nitric Acid

We have selectively synthesized anatase, rutile, and a mixture of these phases as TiO2 nanoparticles via employing pulsed laser ablation in HNO3 solutions of various concentrations. In the absence of HNO3 (i. e. in DI water), only pure anatase TiO2 nanoparticles were formed; however, in 1 M HNO3 solution, only pure rutile TiO2 nanoparticles were obtained. At a midway between these two concentrations, namely for 10-3 M HNO3, a mixture of the both phases was generated. Further increase of the HNO3 concentration gives rise to the enhancement of anatase compared to the rutile phase, which enables to the control of the ratio of anatase/rutile TiO2. We speculate that the TiO2 crystal phases are influenced by the amount of oxygen atom sources in the solvent used in PLAL, but this hypothesis remains to be tested. This procedure can be employed to selectively synthesize individual and mixed TiO2 phases and control the size of the mixed phase nanoparticles by simply varying the concentration of HNO3 under ambient experimental conditions. We propose that this simple method for producing selectively different anatase or rutile phases TiO2 nanoparticles as well as for the control of the anatase/rutile ratio provides a very promising tool for the design and synthesis of highly active TiO2 photocatalysts