Effect of acid during synthesis on the agglomerated strength of TiO ₂ nanoparticles

Titanium dioxide (TiO₂ or titania) photocatalyst nanopartiele (NPs) powders were prepared. The synthesis steps were performed at room temperature. Based on X-ray diffraction evidence, it was found that only the anatase structure was formed when hydrochloric acid was added during the synthesis. With no acid, both anatase and brookite structures were formed. Transmission electron microscopy (TEM) showed that the primary particles from both the acid and no-acid routes were of approximately the same size. A particle-size analyzer equipped with an ultrasonic generator showed, however, that the aggregates of acid NPs were more difficult to break apart than those of the no-acid NPs. Gel formation was used to explain the difference in strength by which the NPs aggregated.