Optimizing Co site electron structure by construction of heterogeneous interface for efficient sulfite activation on paracetamol removal

Sulfite(S(IV))-induced advanced oxidation processes (AOPs) have great prospect in the field of removing organic pollutants , yet developing highly efficient sulfite activation systems and optimizing active sites for favorable catalytic processes are important but still challenging. Herein, we have achieved a composite catalyst with modulated Co electron structure for efficient AOPs by decorating Co(OH) 2 on ultrathin graphitic carbon nitride (g-C 3 N 4 ) nanosheet through an adjustable strategy, which exhibits high catalytic performance in S(IV) activation system. At optimal pH 9, 92% of paracetamol (APAP) (0.005 mM) is removed with the degradation rate constant of k 1 = 0.193 min −1 within 30 min in presence of the composite material. The in-situ synthesis mode introduces strong heterogeneous interface interaction, resulting in directional electron transfer from cobalt hydroxide layer to g-C 3 N 4 sheet revealed by X-ray photoelectron spectroscopy and density functional theory (DFT) calculations. The underlying activity enhanced mechanisms for APAP in S(IV) activation system using Co(OH) 2 /g-C 3 N 4 are proposed: (i) The ultrathin g-C 3 N 4 nanosheets provide more anchoring centers for generating small Co(OH) 2 nanoparticles with abundant active sites which benefit to form metastable intermediates of Co(II)-SO 3 ; (ii) The strong interface interaction induces charge redistribution between Co(OH) 2 and g-C 3 N 4 conformed by DFT calculation, which modulates the d-band center of Co site and strengthens the bind of Co(II)-SO 3 , thereby giving rise to radicals ( • OH, SO 4 • and O 2 • ) and nonradicals ( 1 O 2 and electron transfer) oxidation for highly-efficient removal APAP. Our work will pave the way to build an environmentally friendly strategy for emerging organic pollutant degradation in water through building efficient catalysts in sulfite activation system.