•The p-PDA reduced graphene oxide (ArGO) has positive charge on its surface.•Positive surface charge on ArGO is mainly from the protonation of amine groups.•Positive charge enhances the diffusion and adsorption of negative ions onto ArGO.•The maximum MoO42− adsorption capacity of ArGO can reach to 61 mg g−1.To speculate the performance of chemically reduced graphene oxide from different reductants, detailed investigation of chemical structures needs diverse characterizations. Surface charge, mainly resulting from surface functional groups, may provide a facile method to comprehensively predict performance on certain levels. Surface charge of hydrazine-reduced graphene oxide (HrGO) and p-phenylenediamine (p-PDA)-reduced graphene oxide (ArGO) was investigated by cyclic voltammetry. The charge generation mechanism was further analysed by X-ray photoelectron spectroscopy. Electrical impedance spectroscopy was applied to investigate the effect of surface charge on the adsorptive properties. Furthermore, the experiments on MoO42− adsorbed by ArGO were carried out at different pH values. Results indicate that the surface charge on ArGO was more positive than that on HrGO, which is mainly due to protonation of amino group. MoO42− adsorption experiments indicate that relative positive charge made ArGO more efficient than HrGO to adsorb MoO42−.