Development of a nitrogen-functionalized carbon adsorbent derived from biomass waste by diammonium hydrogen phosphate activation for Cr(VI) removal

This work presents a one-step method for preparing a nitrogen-functionalized carbon adsorbent derived from biomass by diammonium hydrogen phosphate (DAP) activation for Cr(VI) removal. The activation mechanisms and nitrogen functionality were measured by thermogravimetric analysis. The effects of the preparation parameters on the properties of the final carbon adsorbent were examined by N2 adsorption/desorption and Boehm's titration. The optimum parameters of preparation are a heating temperature of 700°C and impregnation ratio of 1.5. The produced carbon adsorbent shows an excellent micropore structure and a wealth of nitrogen-containing functional groups. The carbon adsorbent was used for Cr(VI) removal and showed a high adsorption capacity (43.86mg/g). The adsorption kinetics, isotherms, pH effects and adsorption mechanisms were investigated. The results show that the adsorption data are well fitted by a pseudo-second-order model and the Freundlich model. The adsorption capacity of the activated carbon decreased with increasing solution pH. Microporous entrapment, NH3+ adsorption and OH reduction all played key roles in the Cr(VI) removal process. [Display omitted] •DAP was used as a novel, effective, low cost activating agent in activated carbon preparation.•The physical and chemical properties of activated carbons were characterized.•The processes of activation were investigated in this paper.•The Cr(VI) adsorption behaviors and mechanisms onto the activated carbon were studied.