Synthesis of (NH4)2Ta2O3F6 mesocrystals via a hydrothermal route and their conversion to TaO2F and Ta2O5 mesocrystals for photocatalytic dyes degradation

Abstract

(NH4)2Ta2O3F6 mesocrystals were constructed by oriented self-assembly ultra-fine subunits (nanosheets or nanobelts) via a one-step hydrothermal process. The influence of hydrothermal temperatures and reaction time was also investigated, which (NH4)2Ta2O3F6 mesocrystals were preferred to form under a higher hydrothermal temperature (>180 °C) and a longer reaction time (>6 h), otherwise the occurrence of C7H8N4O2. The addition of acetic acid hindered the hydrolysis process of Ta ions by forming intermediate tantalum acetate complex ions ([(CH3COO)xTaF6-x]-) instead of [TaOF3·2F]2−, and their subsequent hydrolysis-condensation process controlled the morphology evolution of (NH4)2Ta2O3F6 mesocrystals. More importantly, the mesocrystal precursor transformation strategy was employed to synthesize tantalum-based oxides nanomaterials, by calcining the (NH4)2Ta2O3F6 mesocrystals ranging from 400-1200 °C. Mesocrystalline TaO2F nanosheets were formed after heat-treatment at 400 and 500 °C, Ta2O5 nanorods occurred as the annealing temperature is higher than 800 °C. The as-synthesized (NH4)2Ta2O3F6, TaO2F and Ta2O5 mesocrystals were evaluated as photocatalysts on the methylene blue (MB) degradation efficiency, which exhibited enhanced photocatalytic performance except for sample (NH4)2Ta2O3F6-180, in comparison with commercial nanosized Ta2O5 powders. Kinetics analysis indicated that photocatalytic degradation of MB to these samples followed the pseudo-first order model. Particularly, the highest photocatalytic activity was obtained by sample (NH4)2Ta2O3F6-160 with a rate constant of 0.018 min−1, which was nearly 9 times that of commercial Ta2O5 powders.