Tuning the composition of porous resin-templated TiO2 macrobeads for optimized photocatalytic performance

Abstract

TiO2 in the form of macroscopic beads was prepared by resin templating. Anion-exchange macroporous resin beads were treated with a synthesis gel containing titanium isopropoxide, iso-propanol and diluted (0–5 wt.%) tetrapropylammonium hydroxide (TPAOH) aqueous solutions. The Ti-resin composite obtained was calcined at 600 °C to remove the resin. The presence of TPAOH in the precursor solution was essential for producing intact TiO2 beads. The use of 1–1.5 wt.% TPAOH resulted in anatase beads, whereas further increase in the TPAOH content promoted the anatase to rutile phase transformations. Decreasing the heating rate used during calcination also resulted in changes in the TiO2 composition from pure anatase (16 °C min−1 heating rate) to anatase with rutile impurities (0.5 °C min−1 heating rate). The photocatalytic activity of the TiO2 beads was evaluated for the degradation of acetone under ultraviolet irradiation. A high activity was displayed by the TiO2 samples composed of anatase with rutile impurities, whereas the activity was lower for pure anatase samples or samples containing mainly rutile. The TiO2 beads showed higher rates of charge carrier generation and slower charge trapping/recombination rates compared to a reference Cristal ACTiV™ PC500. In addition, the TiO2 beads could be used in at least five consecutive catalytic cycles without any in-between cycle treatment, without significant changes in their activity. The TiO2 beads prepared in this work are beneficial for photocatalytic applications in the gas-phase compared to powders due to easy handling, reduced pressure drop and attrition resistance.