On the Redox Mechanism Operating along C₂H₂ Self-Assembly at the Surface of TiO₂

Abstract

The interaction of acetylene with the TiO2 surface at room temperature entails a complex set of self-assembly reactions with the formation of products having relatively high molecular weight. In a previous paper by some of us (Jain, S. M.; et al. J. Mater. Chem. A 2014, 2, 12247-12254), the C2H2-TiO2 reaction has been monitored, essentially by Fourier transform infrared spectroscopy, at the surface of P25 (a mixture of anatase and rutile, typical benchmark material in the field of photocatalysis) in order to elucidate the nature of the products of this surface reaction. In the present paper, the same process was followed, for the first time, using electron paramagnetic resonance (EPR) and monitoring by the thermogravimetric analysis the weight loss of the material upon heating in order to further investigate the complex mechanism of the surface reaction. This was done using pure anatase and comparing the EPR results with those concerning both rutile and P25. The self-assembly mechanism occurring at the interface is accompanied by the formation of EPR visible Ti(3+) centers due to electrons injection in the TiO2 substrate. This finding clarifies that at least one of the reaction channels of this complex process (namely, the formation of polycyclic aromatic hydrocarbons) is based on the heterolytic dissociative chemisorption of acetylene, followed by a redox interaction between the adsorbate and the solid, which allows the creation of the building blocks necessary to assemble polyaromatic molecules.

Fabrication of Ti substrate grain dependent C/TiO2 composites through carbothermal treatment of anodic TiO2

“…53). 54,55 Anatase TiO 2 was found to be particularly efficient for the decomposition of acetylene, which is in line with our findings.…”

Molecules and heterostructures at TiO2 surface: the cases of H2O, CO2, and organic and inorganic sensitizers

“…[139] The validity of the reaction pathways proposed in Refs. [138,139] and summarized in the above schemes has been recently supported by DFT (density functional theory) simulations of the interaction of acetylene with the (101) and the less stable (001) surfaces of anatase [140]. Both the faces result to be fully inactive when saturated with OH groups, while after dehydroxylation they gain the ability to adsorb the acetylene molecules through dispersive forces (physical adsorption).…”

“…Adapted from Ref. [138] In a subsequent work the interaction of C2H2 with P25, anatase and rutile TiO2 was studied for the first time by EPR spectroscopy [139]. In all cases upon acetylene dosage on highly dehydroxylated samples, the appearance of EPR signals undoubtedly associated with the formation of reduced Ti 3+ species is observed.…”

“…Adapted from Ref. [139] The validity of the reaction pathways proposed in Refs. [138,139] and summarized in the above schemes has been recently supported by DFT (density functional theory) simulations of the interaction of acetylene with the (101) and the less stable (001) surfaces of anatase [140].…”

“…The overall reaction can be summarized as: where the need for the contemporary formation of condensed (conjugated) products, surface hydroxyls and reduced Ti 3+ species well account for the IR, UV-Vis and EPR results in Refs [138,139].…”