Fig. 1. Bandgaps and light absorption of photocatalysts. (a) Comparison of the band structures of common wide-bandgap photocatalysts with that of Co3O4, along with the redox potentials of relevant species. All potentials are referenced to the SHE. (b) Plot showing the light intensity by wavelength of the full solar spectrum, with common absorbers indicated for each region. Reprinted with permission from Ref. [6]. Copyright 2026, Springer Nature.

Fig. 2. Investigation of the reaction mechanism. (a-d) EPR spectra of DMPO-O2??, DMPO-?OH, DMPO-?OOH and DMPO-?CH3 produced in aqueous solution over Pd/Co3O4. (e) In-situ DRIFTS spectra of the photocatalytic OCM over the Pd/Co3O4 composite. (f) Schematic illustration of the proposed reaction mechanism for the photocatalytic OCM to C2H6 with O2 over Pd/Co3O4. The asterisks denote active sites where species can be adsorbed to form surface-bound intermediates; the dots represent radicals carrying an unpaired electron. Reprinted with permission from Ref. [6]. Copyright 2026, Springer Nature.