LAUSR

Abstract Hybrid of metal oxide and graphene quantum dots may pave one way to improve their electronic, chemical and electrochemical properties. The paper reports one new strategy for synthesis of Co 3 O 4 -histidine-functionalized graphene quantum dots (Co 3 O 4 -His-GQD). Here, His-GQDs are combined with Co 2+ ions to rapidly produce Co-His-GQD complex. Followed by the thermal annealing at 350 °C in air to form Co 3 O 4 -His-GQD. The resulting nanohybrid offers a well-defined three-dimensional architecture with the rich of porous structures. The regulation of His-GQDs on the release rate of Co 2+ ions during the oxidation process of Co 2+ make the formed Co 3 O 4 crystals have a small particle size of about 22 nm. The in situ synthesis of Co 3 O 4 on the surface of graphene sheets achieves to the intimate chemical and electrical contacts of Co 3 O 4 with His-GQDs. This creates a fast energy and electron transfer between Co 3 O 4 and His-GQDs in the nanohybrid. The sensor based on the Co 3 O 4 -His-GQD exhibits an ultrahigh electrochemical response towards hydroquinone. Its differential pulse voltammetric peak current linearly increases with increasing hydroquinone in the range of 2 × 10 −9 –8.0 × 10 −4  M with the detection limit 8.2 × 10 −10  M (S/N = 3). The sensitivity is better than that of both His-GQDs sensor and Co 3 O 4 sensor. The analytical method provides the advantage of sensitivity, selectivity and stability, it has been successfully applied in the determination of hydroquinone in environmental water samples. The study also provides a promising approach for fabrication of functional graphene quantum dot-based electrode materials with high-performance for sensing, electrocatalysis, supercapacitors and lithium ion batteries.