Understanding hydroxyl radicals addition to CO2 on α-Fe2O3(1 1 0) surface photocatalyst for organic compounds production

In this work, Density Functional Theory (DFT) calculations were performed to assess the photo-catalytic properties of hematite (α-Fe2O3) and the atomistic modeling of the CO2 conversion mechanism to organic molecules on such a surface. The reaction pathways for the CO2 simulated photo-transformation were modeled with the string method. The reaction mechanism obtained by DFT calculations evidenced the H2O2 molecules reduction instead of the CO2 reduction at the first step, inducing •OH radical formation. The following CO2 activation is induced by the addition of the •OH radical through one of the π∗ bonds of CO2 molecule, unlike the commonly reported CO2 reduction, resulting in the bicarbonate anion. The emergence of carbonic acid is followed by carbon reduction reactions up to methanol. According to the adsorption energies and topological analysis of the bond critical points, the intermediates exhibited closed-shell interactions with the hematite surface. Electronic structure properties were evaluated at the DFT+U＋J level. Opto-electronic parameters were also evaluated experimentally; giving validity to the results obtained by the DFT. This work also shows the first theoretical insight into the conversion of CO2 with H2O2 into H2CO3, HCOOH, CH2O and CH3OH on the hematite (1 1 0) surface. Additionally, to support the theoretical elucidation, a mixture of iron oxides (Fe2O3- FeOOH) nanoparticles were prepared in accordance to recent published results suggesting a heterogeneous catalytic process, instead a homogeneous Fenton’s method to evaluate the photocatalytic properties and the redox-potential to degrade CO2. One of the predominant phases observed in the iron oxide mixture corresponds to hematite. Moreover, the photocatalytic process of CO2 conversion with iron oxide nanoparticles was experimentally performed. The formation of methanol was evidenced via FTIR analysis.