In this study, KMnO4 modification was proved to effectively increase the Ni2+ adsorption capacity of biomass. In order to clarify the KMnO4 modification mechanism, the Ni2+ adsorption characteristics of KMnO4 modified corncob (PPCB) under adsorption time, pH and Ni2+ concentration were studied. The results showed that the adsorption was the pseudo second-order kinetic process, indicating that chemisorption was the dominated process, which followed the Langmuir isotherm model and the highest Ni2+ adsorption capacity of PPCB reached 35.6 mg/g. By KMnO4 modification, the corncob was oxidized to generate carboxylates, and the MnO2 (reduction product) was loaded on the modified corncob, both carboxylates and MnO2 increased the Ni2+ adsorption capacity of PPCB. The molecular dynamic results indicated the carboxylate structures had the strongest adsorption capacity. Moreover, the Ni2+ removal efficiency of KMnO4 modified biomass decreased linearly with the increase of lignin content in biomass, while KMnO4 modified lignin showed a good adsorption performance, indicating that the cross-linked structures between lignin and other components in the biomass could inhibit the adsorption capacity of PPCB.
Cd 2+ pollution in aquatic environments can pose a serious threat to human health. Biochar can remove Cd 2+ from aquatic environments, but the Cd 2+ adsorption capacity of conventional biochar is low, therefore, we focused on exploring the Cd 2+ adsorption capacity of modified biochar. In this study, KMnO 4 was used to modify vermicompost biochar (VBC), and static adsorption tests for Cd 2+ were carried out. The biochar properties and its adsorption efficiency toward Cd 2+ before and after modification were studied by kinetics and isotherm model fitting, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Additionally, an adsorption mechanism was discussed. The results showed that the KMnO 4 -modification resulted in a successful loading of the vermicompost biochar with MnO 2 , which greatly improved its adsorption capacity for Cd 2+ . The adsorption of Cd 2+ by VBC and MVBC was a spontaneous, endothermic, and monolayer chemical adsorption process . Mineral precipitation mechanism accounted for the largest proportion, and CdCO 3 was the main precipitate. After modification the proportion of surface precipitation and other mechanisms (π-electron coordination and the inner/outer sphere surface coordination) increased，while adsorption via cation exchange, oxygen-containing functional groups, physical adsorption and electrostatic attraction reduced. Hence, KMnO 4 modification has a significant effect on the Cd 2+ adsorption behavior of vermicompost biochar.
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