Electrocatalytic Degradation Of Acetaminophen By Sulfur And Nitrogen Doped Graphene Electrodes

In this paper,graphene electrode materials doped with different sulfur and nitrogen were prepared.The catalytic activity of graphene electrode materials doped with different heteroatoms was studied by electrocatalytic degradation of paracetamol（APAP）,one of pharmaceuticals and personal care products（PPCPs）.The optimum reaction conditions of graphene electrode materials doped with different heteroatoms were studyed.The degradation pathway and activation mechanism of APAP were concluded.The graphene oxide was prepared by improved Hummer method and S-GN/Pt/TiO₂ was prepared by hydrothermal method.The efficiency of electrocatalytic oxidative degradation of APAP by S-GN/Pt/TiO₂ system was investigated.Under the conditions of initial pH7,current at 20 mA and electrolyte was NaCl,the removal rate of 10 mg L^-1APAP could reach 98%in 90 minutes.In addition,methanol was used to quench active radicals in S-GN/Pt/TiO₂electrocatalytic system,and hydroxyl radicals were identified as the main active radicals in the system.The intermediate products of APAP in S-GN/Pt/TiO₂electrocatalytic system were evaluated by GC-MS analysis,and the degradation pathways were proposed afterwards.In order to improve the activity of graphene,N atoms were added into the carbon skeleton of graphene to improve the electrocatalytic efficiency of graphene as anodic material.The degradation efficiency of APAP by N-GN/Pt/TiO₂ electrocatalytic system was investigated.The results show that optimal APAP degradation efficiency(20mA,1g L^-1 NaCl and initial pH 4.0)could be achieved at 100%by using N-GN/Pt/TiO₂（mainly pyridine N and pyrrolic N doping）.With increased hydrothermal reaction time,the degradation of APAP was decreased.According to XPS results,the doped form of N atoms gradually transfers from pyridinic N and pyrrolic N to graphite N,reducing the degree of defects and redox activity of the material,thus reducing the degradation rate.Through GC-MS analysis,a plausible mechauism of degradationwas proposed.To elucidate the effect of S and N heteroatoms on graphene electrode,N and S co-doped graphene were prepared by hydrothermal method.The characteristics of SNGN/Pt/TiO₂ materials were analyzed via TEM,XPS and CV technologies.The study showed that the introduction of nitrogen atoms into S-GN/Pt/TiO₂ reduces the electrocatalytic efficiency of S-GN/Pt/TiO₂.According to density functional theory（DFT）calculations,the findings indicated that S-doped graphene had better electrocatalytic activity than N-doped,and the co-existence of S and N converted the N species from pyrrolic N（the N species with the highest activity）into graphitic N（the N species with the least activity）.The activity of S was also inhibited.With S and N co-doping,the active sites for direct electrocatalytic oxidation was positioned at the carbon atoms beside S,carbon atoms beside pyrrolic N,and pyridinic N.Moreover,the S species became more favorable for indirect electrocatalytic oxidation than any other kind of N species.