Mn/Co bimetallic catalyst immobilized on N-doped biochar for enhanced photocatalytic degradation of sulfanilamide in water

Single-atom catalyst has shown promising effect in photocatalysis. In particular, the construction of bimetallic catalytic sites can address the limitations of single-metallic catalysts, such as clustering and slow electron transfer, which enhances electron transfer between active sites and promotes photocatalytic activity. In this paper, Mn and Co bimetallic catalyst (Mn/Co@N-biochar) was developed by using the electronegativity difference of the bimetallic sites on N-doped biochar to construct catalytically active sites to enhance electron transfer. XRD and HR-TEM characterization confirmed that metal atoms were evenly dispersed within the carbon layer without aggregation or clustering of metal particles. The catalytic efficiency of Mn/Co@N-biochar was assessed through sulfanilamide (SNM) degradation experiments, demonstrating a remarkable degradation rate of 99.3% and a mineralization rate of 49.0%. These values were 10.45 times and 13.24 times more than that for biochar, respectively, indicating that the loading of bimetals greatly improved the photocatalytic activity. Furthermore, the doping of N atoms adjusted the electronic structure of adjacent C atoms and activated the free-flowing π electrons on the biochar surface, creating solid anchoring sites that facilitated efficient electron circulation between Mn and Co atomic sites. The higher local electron density at the Co-N4 site compared to the Mn-N4, created electron transfer channels, where Mn atoms (catalytic site) facilitated the flow of electrons to Co atoms (active site). This could rapidly generate the primary active species (‧OH and ‧O2-) to degrade SNM. Additionally, the stability and applicability of bimetallic catalysts in real water systems were also confirmed, providing valuable insights for the construction of bimetallic biochar structures to degrade organic pollutants in water.