Cu²⁺-modified hollow carbon nanospheres: an unusual nanozyme with enhanced peroxidase-like activity

A Cu²⁺-modified carboxylated hollow carbon nanospheres (Cu²⁺-HCNSs-COOH) was designed with enhanced peroxidase-like activity for the detection of hydrogen peroxide (H₂O₂) and degradation of methylene blue (MB). Hollow polymer nanospheres were fabricated from aniline, pyrrole, Triton-100, and ammonium persulfate via confined interfacial copolymerization reaction, which can be pyrolyzed to create HCNSs with the hollow gap diameter of about 20 nm under high temperature. Combining the synergistic effect of coordination and electrostatic interaction, Cu²⁺-HCNSs-COOH was constructed by anchoring Cu²⁺ on the surface of HCNSs-COOH. Furthermore, Cu²⁺-HCNSs-COOH has higher affinity for 3,3',5,5'-tetramethylbenzidine and H₂O₂ of 0.20 mM and 0.88 mM, respectively. Based on the rapid response of Cu²⁺-HCNSs-COOH to H₂O₂, we constructed a colorimetric sensing platform by detecting the absorbance of the 3,3',5,5'-tetramethylbenzidine-H₂O₂ system at 652 nm for quantifying H₂O₂, which holds good linear relationship between 1 and 150 μM and has a detection limit of 0.61 μM. We also investigated the degradation of MB in the presence of Cu²⁺-HCNSs-COOH and H₂O₂, which can degrade 80.7% pollutants within 30 min. This research developed an unusual nanozyme for bioassays and water pollution treatment, which broadened the way for the rapid development of clinical diagnostics and water pollution treatment.