Plasma-photocatalytic conversion of CO2 at low temperatures: Understanding the synergistic effect of plasma-catalysis

A coaxial dielectric barrier discharge (DBD) reactor has been developed for plasma-catalytic conversion of pure CO2 into CO and O2 at low temperatures (<150°C) and atmospheric pressure. The effect of specific energy density (SED) on the performance of the plasma process has been investigated. In the absence of a catalyst in the plasma, the maximum conversion of CO2 reaches 21.7% at a SED of 80kJ/L. The combination of plasma with BaTiO3 and TiO2 photocatalysts in the CO2 DBD slightly increases the gas temperature of the plasma by 6-11°C compared to the CO2 discharge in the absence of a catalyst at a SED of 28kJ/L. The synergistic effect from the combination of plasma with photocatalysts (BaTiO3 and TiO2) at low temperatures contributes to a significant enhancement of both CO2 conversion and energy efficiency by up to 250%. The UV intensity generated by the CO2 discharge is significantly lower than that emitted from UV lamps that are used to activate photocatalysts in conventional photocatalytic reactions, which suggests that the UV emissions generated by the CO2 DBD only play a very minor role in the activation of the BaTiO3 and TiO2 catalysts in the plasma-photocatalytic conversion of CO2. The synergy of plasma-catalysis for CO2 conversion can be mainly attributed to the physical effect induced by the presence of catalyst pellets in the discharge and the dominant photocatalytic surface reaction driven by the plasma

Proton Transfers at a Dopamine-Functionalized TiO₂ Interface

Despite the many successful syntheses and applications of dopamine-functionalized TiO₂ nanohybrids, there has not yet been an atomistic understanding of the interaction of this 1,2-dihydroxybenzene derivative ligand with the titanium dioxide surfaces. In this work, on the basis of a wide set of dispersion-corrected hybrid density functional theory (DFT) calculations and density functional tight binding (DFTB) molecular dynamics simulations, we present a detailed study of the adsorption modes, patterns of growth, and configurations of dopamine on the anatase (101) TiO₂ surface, with reference to the archetype of 1,2-dihydroxybenzene ligands, i.e., catechol. At low coverage, the isolated dopamine molecule prefers to bend toward the surface, coordinating the NH₂ group to a Ti_5c ion. At high coverage, the packed molecules succeed in bending toward the surface only in some monolayer configurations. When they do, we observe a proton transfer from the surface to the ethyl-amino group, forming terminal NH₃⁺ species, which highly interact with the O atoms of a neighboring dopamine molecule. This strong Coulombic interaction largely stabilizes the self-assembled monolayer. On the basis of these results, we predict that improving the probability of dopamine molecules being free to bend toward the surface through thermodynamic versus kinetic growth conditions will lead to a monolayer of fully protonated dopamine molecules