Type of presentation: Poster

MS-1-P-5885 TiO2 nanoparticles obtained by laser ablation in water: influence of pulse energy and duration on the crystalline phase

Canton P.¹, Giorgetti E.², Marsili P.², Muniz-Miranda M.³, Vergari C.⁴, Giammanco F.⁴

¹Department of Molecular Sciences and Nanosystems, University of Venezia, Mestre, 30170, Italy cantonpa@unive.it, ²Istituto dei Sistemi Complessi - CNR, Via Madonna del Piano 10, Sesto Fiorentino (Firenze), Italy, ³Department of Chemistry “U. Schiff”, University of Firenze, Firenze, Italy , ⁴Department of Physics "E. Fermi", University of Pisa, Pisa, Italy.

cantonpa@unive.it

Pulsed laser ablation (PLAL) can be used for production of stable and unprotected TiO2 nanoparticles (NPs) in pure solvents [1]. In general, rutile or anatase phase are required, depending on the applications, the first one being more attractive in the development of pigments and the second one more appropriate in photocatalysis. However, in spite of the large amount of work described in the literature, the control of the crystalline phase of the obtained samples is still a challenging tasks.
For this purpose, we performed a thorough characterization of the ablation of a Ti target in deionized water, by using the 1064 nm fundamental wavelength of a ns or a ps Nd:YAG laser and by tuning the energy per pulse and the fluence on target. We analyzed the colloids by UV-vis and Raman spectroscopy and by SAED, NBD, HRTEM and found some experimental rules which allow the control of the different phases of the oxide. According to Raman tests, we obtained the characteristic bands at 440 and 605 cm-1 of rutile NPs with ns pulses and prevalently rutile or anatase NPs with ps pulses, being anatase (395, 506 and 625 cm-1) more abundant when ps ablation is carried out with high energy pulses (see Fig. 1, 2 showing BF and NBD of three nanoparticles evidencing crystalline and amorphous structures).
The previous experimental results were compared with a theoretical model, which gives a detailed description of the ablation process during the laser pulse and the subsequent time-space evolution of key parameters of yields, i.e. pressure and temperature, in the surrounding solvent. By using simplified rate equations and phase diagrams of Ti oxides, the model not only allows to explain the observed energy and pulse-width dependence of TiO2 crystalline phase, but also provides a guide to choose the experimental parameters required to isolate the different crystalline species .

References.
[1] J. S. Golightly and A. W. Castleman, Jr.; J. Phys. Chem. B 110 (2006) pp. 19979-19984

Fig. 1: BF of 8mJ ps ablation specimen

Fig. 2: NBD of the three particles shown in figure 1