Carbon quantum dots (CQDs) and graphitic carbon nitride (g-C 3 N 4 ), as advanced metal-free material catalysts have been the focus of considerable attention because of their superior photocatalytic activities. In this study, we developed a novel approach to obtain CQDs/g-C 3 N 4 nanocomposite with effective interfacial contact by incorporating negatively charged CQDs and tailor-made proton-functionalized g-C 3 N 4 via the electrostatic self-assembly strategy. Then, the morphology and microstructure of the new nanocomposite were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), ultraviolet–visible diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). The CQDs and proton-functionalized g-C 3 N 4 nanocomposite exhibited excellent electron transfer properties though electrochemical impedance spectroscopy (EIS), significantly enhanced photoactivity in the photoelectrochemical i–t curve test and degradation of methylene blue solution under visible light irradiation. These results demonstrated that the electrostatic self-assembly strategy process is a promising method of fabricating uniform metal-free material catalysts for an extensive range of applications. [ABSTRACT FROM AUTHOR]