Reinforced photocatalytic H2 generation behavior of S-scheme NiO/g-C3N4 heterojunction photocatalysts with enriched nitrogen vacancies

In view of limited light response capacity and fast recombination of photon-excited charge pairs (e−/h+), photocatalytic efficiency of graphite carbon nitride (g-C3N4) is inferior, giving rise to the confined utility of the single g-C3N4 (GCN). In this paper, S-scheme NiO/g-C3N4 (NiO/CN) heterojunction photocatalysts were acquired via a facile impregnating approach and characterized through a sequence of measurements. Based on the characterization results of XPS and ESR, abundant nitrogen defects exist in the prepared NiO/g-C3N4 sample. Nitrogen vacancies (NVs) serve as the electron trapping site, effectively inhibiting the recombination of photo-induced charge pairs, dramatically boosting the photocatalytic hydrogen production efficiency. Under solar light irradiation, 2% NiO/CN composite presents the highest photocatalytic H2 generation performance (169.5 μmol h−1 g−1) without any co-catalyst, realizing 140.3 folds higher than that of GCN (1.2 μmol h−1 g−1). S-scheme NiO/g-C3N4 heterojunctions and the defect level formed by nitrogen vacancies (NVs) accelerate the photo-induced carrier separation and transfer. This approach is demonstrated to be a potential measure to remarkably ameliorate the photocatalytic H2 production behavior of g-C3N4 via utilizing the transition metal oxides to effectively separate and migrate photo-excited charge pairs under solar light irradiation.