Visible-Light-Activated Black Organotitanias: How Synthetic Conditions Influence Their Structure and Photocatalytic Activity.

A series of low-temperature, visible-light-activated black organotitanias were synthesised through a sol-gel strategy that allowed the in situ incorporation of p-phenylenediamine (PPD) into the framework of anatase nanoparticles. The effect of the synthetic conditions on the crystalline structure and photocatalytic activity of these materials was assessed by several characterisation techniques, which revealed a small crystalline domain size (4.6-5.5 nm), effective incorporation of PPD inside the nanoparticles, and a significant reduction in the band gap of these materials (from 3.2 to 2.7-2.9 eV). A systematic study of the synthetic parameters also allowed a significant reduction of the solvent used for the preparation of these black organotitanias (20-fold), as well as the crystallisation time, without compromising the structural properties and photocatalytic activity of these materials. The organotitanias with the highest PPD content and high crystallinity result in the best performing materials in the photocatalytic degradation of rhodamine 6G under both UV- and visible-light irradiation.