Synergy of nitrogen dopants and cobalt single atoms in calcium niobate nanosheets for photocatalytic oxygen evolution

The successful separation of photoexcited charge carriers and their effective utilization are crucial for overcoming the slow kinetics of the four-electron process for photocatalytic oxygen evolution. Herein, a novel strategy utilizing urea as a source of N-doping on Ca₂Nb₃O₁₀ nanosheets is adopted, followed by the successful deposition of Co single atoms (Co-SAs) to achieve a synergistic effect. The presence of N-dopants and Co-SAs is validated via various experimental techniques. It is also observed that the presence of N-doping contributed towards the deposition of higher content of Co-SAs (0.21 wt%) in Ca₂Nb₃O_10−xN_x-Co_SA nanosheets compared to 0.15 wt% for non-doped Ca₂Nb₃O₁₀-Co_SA. The optimized Ca₂Nb₃O_10−xN_x-Co_SA nanosheets exhibited an impressive photocatalytic O₂ evolution of ∼727.22 µmol g⁻¹ h⁻¹ via the synergy of N-dopants and Co-SAs. As a result, the O₂ evolution response of Ca₂Nb₃O_10−xN_x-Co_SA is 3.6 times higher than that of pristine Ca₂Nb₃O₁₀ nanosheets (201.26 µmol g⁻¹ h⁻¹), 2.24 times better than Ca₂Nb₃O_10−xN_x nanosheets (323.42 µmol g⁻¹ h⁻¹), and 1.77 times higher compared to Ca₂Nb₃O₁₀-Co_SA, (409.33 µmol g⁻¹ h⁻¹), which clearly demonstrated the synergistic effect of N-dopants and Co-SAs in Ca₂Nb₃O_10−xN_x-Co_SA nanosheets. Based on the findings of various characterization techniques, the co-presence of N-dopants and Co-SAs is observed to contribute towards better charge carrier separation, and utilization to achieve superior photocatalytic response. Thus, this study presents a novel approach for incorporating N-dopants and Co-SAs on Ca₂Nb₃O₁₀ nanosheets, which can be extended to a wide range of nanosheets produced by the soft chemical exfoliation method.