Pyrolysis mechanism of aliphatic amines bound to titania nanoparticles after H2O2 oxidation

Abstract

Organic compounds bound to peroxotitanates can influence the photocatalytic activity of TiO2 nanoparticles (NPs) obtained by subsequent annealing. Knowledge of how this influence plays out is fundamental for the development of NPs with desirable catalytic behavior, which can be used for several applications. Thermoanalytical techniques can be used to simulate the annealing process on a small scale, but there is a lack of literature on this topic. This is especially true for nitrogen-containing organic compounds, which are not often used as organic modifiers in NP synthesis. Here, we present a multianalytical study of the pyrolytic behavior of the organic fraction of amine-functionalized titania NPs after peroxide treatment (namely peroxotitanate nanoparticles modified with aliphatic amines). The study was carried out by TGA-MS, evolved gas analysis-mass spectrometry (EGA-MS) and double-shot analytical pyrolysis-GC-MS. The most abundant peaks in the GC-MS profiles obtained after thermal desorption were ascribed to nitriles, unsaturated hydrocarbons, and oxygenated compounds, whose total relative areas accounted for almost 100% for DPA and up to 70% for the other amines. This indicated that the presence of an N-Ti bond modulated the oxidating effect of hydrogen peroxide. Pyrolysis of the residual organic fraction on oxidized NPs underwent coupling reactions that led to the formation of aromatic species and, most interestingly, heteroaromatic compounds.