N doped carbon quantum dots modified defect-rich g-C3N4 for enhanced photocatalytic combined pollutions degradation and hydrogen evolution

Exploiting metal-free cocatalysts is of huge interest for photocatalytic technology in environmental wastewater remediation and water splitting fields. The N doped carbon quantum dots (NCDs) modified defect-rich g-C3N4 (DCN) was prepared through impregnation method. The structural, optical and electronic properties of NCDs/DCN were systematically investigated. The NCDs/DCN with outstanding visible light absorption, narrowed gap and electron transfer ability were conducive to combined pollutions photocatalytic removal and simultaneous H2 production and rhodamine B (RhB) degradation. The resulting NCDs/DCN performed much higher removal efficiency in different combined pollutions systems containing OFL/Cr (VI), BPA/Cr (VI) and CIP/Cr (VI) than in single system owing to the synergistic effect between organic pollution oxidation and Cr (VI) reduction. The free-radical quenching experiments, spectral technology and electron spin resonance (ESR) confirmed that Cr(VI) can be reduced by the conduction band (CB) electrons, and the h+ and O2− radicals dominated OFL degradation. The optimized NCDs/DCN displayed excellent simultaneously photocatalytic H2 production activity and RhB degradation with the H2 evolution rate of 3.68 μmol‧h−1‧g−1 and 100% RhB removal efficiency. The photocatalytic activity of simultaneous combined pollutions removal and synergistic H2 generation and RHB degradation provides a promising strategy for real wastewater remediation applications and energy utilization.