Nanoparticle Synthesis by Pulsed Laser Ablation: From H2O to pressurized CO2: Possibilities for supercritical fluid as reactive environment

Abstract

The demand of nanoparticles has been increasing tremendously. However, the traditional methods of synthesis are mostly based on wet-chemical synthesis, that generally need chemical precursors that may not be environment friendly. Due to this, new greener techniques need to be designed and tested. PLAL technique has been demonstrated as a promising method that can be used to synthesize nanoparticles from almost the entire periodic table and requires much cheaper precursors than chemical synthesis techniques. The nanoparticles produced can have clean ligand-free surfaces, due to which they are ready for functionalization and act as better catalysts.

In this work, a single step method, PLA in H2O and supercritical CO2, was used to produce TiO2 nanoparticles and TiO2-carbon core-shell nanoparticles, by utilizing CO2 in the process. Pressurized CO2, in the form of gaseous, liquid, and supercritical CO2 was demonstrated as a promising solvent for producing well-dispersed agglomerate free nanoparticles and core-shell nanoparticles using PLA technique. With the proposed techniques, it is possible to produce stable rutile-TiO2 as nanoparticle suspension by PLA in H2O, while PLA in scCO2 can be used to produce well dispersed non-agglomerate anatase-TiO2 nanoparticles directly as a dry nanoparticle powder. Further, core-shell nanoparticles of anatase-TiO2 as core and carbon as shell can be prepared by PLA in pressurized CO2 and their size can be controlled by simply controlling the CO2 pressure and temperature.