Graphene quantum dot surface ligand and Co and Pt double-doping-engineered Co/Co3O4 nanozyme displaying superior performance to horseradish peroxidase and choline oxidase for the efficient degradation of rhodamine B without an activator

Abstract

Nanozymes show great potential in organic degradation because of their good stability and low cost. However, their poor catalytic activity and functional diversity restrict their practical applications. The present study reports the synthesis of a Pt/Co/Co₃O₄/EW-GQD nanozyme via the coordination of Co²⁺ and Pt⁴⁺ with a glutamate and tryptophan-functionalized graphene quantum dot (EW-GQD) and subsequent thermal reduction and part oxidation. The graphene surface ligand engineering creates a reactive microenvironment similar to natural enzymes, facilitating a high-speed electron-transfer process from Co₃O₄ to graphene and strong adsorption capacity toward rhodamine B. The Co and Pt double doping narrows the bandgap and leads to an improved electronic conductivity. The Pt/Co/Co₃O₄/EW-GQD nanozyme exhibited a peroxidase-like specific activity of 1662.67 U mg⁻¹ and oxidase-like specific activity of 293.45 U mg⁻¹, which exceed by 3.2-fold that of horseradish peroxidase and by 15.6-fold that of choline oxidase. This enabled a 3.6-fold increase in the degradation efficiency of rhodamine B without the need for an activator. The high catalytic activity was mainly attributed to the perfect combination of the graphene surface ligand and Co and Pt double engineering, which produced multiple active sites such as Co³⁺/Co²⁺, Pt⁴⁺/Pt²⁺, and pyrrolic N/pyridinic N and multiple active species such as ¹O₂, ˙O₂⁻, and ˙OH. This work introduces a novel way for the design and synthesis of nanozymes with excellent catalytic activity and multifunctional performance.