Visible light-driven C–C bond formation has attracted increasing attention recently, thanks to the advance in molecular photosensitizers and organometallic catalysts. Nevertheless, these homogeneous methodologies typically necessitate the utilization of noble metal-based (e.g., Ir, Ru, etc.) photosensitizers. In contrast, solid-state semiconductors represent an attractive alternative but remain less explored for C–C bond-forming reactions driven by visible-light irradiation. Herein, we report that photocatalytic pinacol C–C coupling of benzaldehyde to hydrobenzoin can be achieved on two-dimensional ZnIn2S4 nanosheets upon visible-light irradiation in the presence of a sacrificial electron donor (e.g., triethylamine). We further demonstrate that it is feasible to take advantage of both excited electrons and holes in irradiated ZnIn2S4 for C–C coupling reactions in the absence of any sacrificial reagent if benzyl alcohol is utilized as the starting substrate, maximizing the energy efficiency of photocatalysis and circumventing any byproducts. In this case, industrially important benzoin and deoxybenzoin are formed as the final products. More importantly, by judiciously tuning the photocatalytic conditions, we are able to produce either benzoin or deoxybenzoin with unprecedented high selectivity. The critical species during the photocatalytic process were systematically investigated with various scavengers. Finally, such a heterogeneous photocatalytic pinacol C–C coupling strategy was applied to produce a jet fuel precursor (e.g., hydrofuroin) from biomass-derived furanics (e.g., furfural and furfural alcohol), highlighting the promise of our approach in practical applications.

Three density functional approximations (DFAs), PBE, PBE+U, and Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE), were employed to investigate the geometric, electronic, magnetic, and thermodynamic properties of four iron oxides, namely, α-FeOOH, α-FeO, FeO, and FeO. Comparing our calculated results with available experimental data, we found that HSE (a = 0.15) (containing 15% "screened" Hartree-Fock exchange) can provide reliable values of lattice constants, Fe magnetic moments, band gaps, and formation energies of all four iron oxides, while standard HSE (a = 0.25) seriously overestimates the band gaps and formation energies. For PBE+U, a suitable U value can give quite good results for the electronic properties of each iron oxide, but it is challenging to accurately get other properties of the four iron oxides using the same U value. Subsequently, we calculated the Gibbs free energies of transformation reactions among iron oxides using the HSE (a = 0.15) functional and plotted the equilibrium phase diagrams of the iron oxide system under various conditions, which provide reliable theoretical insight into the phase transformations of iron oxides.

As active phases in low-temperature Fischer−Tropsch synthesis for liquid fuel production, epsilon iron carbides are critically important industrial materials. However, the precise atomic structure of epsilon iron carbides remains unclear, leading to a half-century of debate on the phase assignment of the ε-Fe 2 C and ε′-Fe 2.2 C. Here, we resolve this decades-long question by a combined theoretical and experimental investigation to assign the phases unambiguously. First, we have investigated the equilibrium structures and thermal stabilities of ε-Fe x C (x = 1, 2, 2.2, 3, 4, 6, 8) by first-principles calculations. We have also acquired X-ray diffraction patterns and Mossbauer spectra for these epsilon iron carbides and compared them with the simulated results. These analyses indicate that the unit cell of ε-Fe 2 C contains only one type of chemical environment for Fe atoms, while ε′-Fe 2.2 C has six sets of chemically distinct Fe atoms.

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