Hole Scavenging by Organic Adsorbates on the TiO2 Surface: A DFT Model Study.

Understanding the interfacial hole transfer between photoirradiated anatase TiO2 nanoparticles and organic adsorbates at the surface is a crucial step toward the full comprehension and control of the photooxidation processes, which are fundamental in photocatalytic applications for energy production, environmental care, and medical cancer phototherapy. In this density functional study, we use the hybrid functional B3LYP in order to investigate how the hole transfer process takes place at the anatase (101) surface when a series of organic alcohols and acids are adsorbed. The results allow us to propose a mechanism of photoinduced proton dissociation and a scale of scavenging power of the different organic adsorbates (glycerol > tert-butanol > iso-propanol > methanol > formic acid). We observe that the surface dipole originated by the molecular adsorption causes a reduction in the cost to form a hole at a surface oxygen. This can then be trapped by the organic adsorbate only if proton dissociation takes place. In the case of glycerol, the hole transfer triggers further photoinduced chemical reactivity than the simple proton dissociation. Only in the case of cathecol, which is an excellent hole scavenger, the proton dissociation is not a required step.