Hydrothermal treatment of colloids induced via liquid-phase laser ablation: a new approach for hierarchical titanate nanostructures with enhanced photodegradation performance

Abstract

The liquid-phase laser ablation of solid targets may create new materials and structures as a result of unique reactions and the rapid quenching of a liquid-confined plasma plume with features of high temperature and pressure. We demonstrated here the formation of novel nanostructures by laser ablation of a Ti plate in de-ionized water. When the pulse laser is focused on a fixed tiny spot on the target surface during ablation, Ti@TiO₂ core-shell nanoparticles (NPs) can be obtained. The crystalline metal core was a metastable faced-centered-cubic (fcc) phase of Ti; while the Ti plate was being rotated, the pulse laser interacted with different spots on the metal surface in one circle and only amorphous TiO₂ species could be found. Toward the synthesis of hierarchical titanate nanostructures, the unique colloidal suspensions obtained by laser ablation were further hydrothermally treated in alkaline solutions. The TiO₂ NPs synthesized from the rotated Ti target could form titanate hierarchical spheres by self-assembly of nanostripes. The core-shell Ti@TiO₂ NPs initially formed titanate nanostripes assembled hierarchical spheres, however, with increasing duration time these spheres with Ti cores would separate and reorganize into fibers, which evolved into single crystalline nanoribbons, and ultimately grew into long rod-like hierarchical nanostructures. Both the titanate hierarchical spheres and the corresponding calcined spheres presented high photocatalytic activity in the degradation of a trace amount of pentachlorophenol.