New Precursor Route Using a Compositionally Flexible Layered Oxide and Nanosheets for Improved Nitrogen Doping and Photocatalytic Activity

Nitrogen doping into a metal oxide is a conventional method to prepare a visible-light-responsive photocatalyst. However, the charge imbalance that results from aliovalent anion substitution (i.e., O^2–/N^3– exchange) generally limits the concentration of nitrogen that can be introduced into a metal oxide, which leads to insufficient visible-light absorption capability. Here we report an effective route to synthesize nitrogen-doped metal oxide using KTiNbO₅, which is a compositionally flexible layered oxide and can be exfoliated into nanoscale sheets. KTiNbO₅ has a unique layered structure, in which Ti⁴⁺ and Nb⁵⁺ coexist in the same two-dimensional sheet, and controllable Ti⁴⁺/Nb⁵⁺ ratios while maintaining the original KTiNbO₅-type structure. The use of a Nb-rich oxide precursor could allow for the improvement in the introduction of nitrogen compared with stoichiometric KTiNbO₅ during thermal ammonolysis with ammonia gas. Reassembled KTiNbO₅ nanosheets with a larger surface area were found to be more useful as a precursor than the layered precursor in terms of nitrogen introduction and thus yielded more pronounced visible-light absorption and photocatalytic activity for water oxidation