Synthetic versatility of nanoparticles: A new, rapid, one-pot, single-step synthetic approach to spherical mesoporous (metal) oxide nanoparticles using supercritical alcohols
A simple, rapid (10 min), one-pot, single-step method for the preparation of solid and hollow spherical porous TiO_2 nanoparticles with large surface areas (100-211 m^2/g) was developed in supercritical alcohols using carboxylic acids as organic additives. The shell thickness of the hollow TiO_2 nanoparticles (20-280 nm) was controlled by adjusting the heating rate (2.0-10.0 °C/min). The preparation of different spherical porous metal oxide nanoparticles, including CeO_2, SiO_2, TiO_2, ZrO_2, and ZnO, demonstrated the versatility of the synthetic approach. In addition, several rare earth-doped spherical mesoporous metal oxide nanoparticles, including CeO_2:Er, CeO_2:Er,Yb, ZrO_2:Er, and TiO_2:Er, which exhibit energy upconversion emission, were successfully prepared using this one-pot, single-step, supercritical methanol method. The obtained spherical mesoporous CeO_2:Er and CeO_2:Er,Yb nanoparticles emit green light upon excitation, even when irradiated with a low-power IR laser (980 nm, 10 mW) without calcination. Several other (metal) elements were also easily doped into spherical, mesoporous TiO_2 nanoparticles, such as Eu, Ce, Yb, Fe, and N, using a similar procedure. Furthermore, the spherical mesoporous TiO_2 nanoparticles were successfully applied as a new material for the transport of DNA via biolistic bombardment
