TiO2 anatase and rutile grains and the effect of particle printing on porphyrin adsorption

Abstract

Nanoparticle formulation and processing represents a pressing challenge in developing efficient and reproducible routes for the generation of functionalized TiO2 particle films. Powders and inkjet printed (IJP) films of TiO2 nanoparticles were evaluated with regard to their interfacial self-metalation activity toward 2H tetraphenylporphyrin (2HTPP). Respective reaction corresponds to the transfer of a titanyl group (Ti-O)2+ from the particle surface to the macrocycle and its incorporation into the center of the macrocycle. Reactive porphyrin adsorption and self-metalation were investigated with Vis diffuse reflectance (DR) and photoluminescence (PL) spectroscopy after porphyrin contact with both dehydroxylated TiO2 anatase and TiO2 rutile grains in vacuum. Additional spectroscopic changes occur upon subsequent contact with water vapor or air and the resulting coincidence of the band positions with those measured for the solution spectra reveal that co-adsorbed water molecules do assist in the reorganization of metalated porphyrins at the grain surfaces. We discuss the impact of TiO2 polymorphism and grain integration into inkjet-printed films on the adsorption and optical properties of the adsorbed porphyrins. Finally, a systematic comparison of gas phase functionalization of particles with porphyrins with corresponding wet-chemical approaches in toluene solution reveal solvent-assisted inhibition effects in the reactive adsorption of free-base porphyrins on TiO2 grains.