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 N-2 adsorption/desorption and Boehm's titration. The optimum parameters of preparation are a heating temperature of 700 degrees 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 (43.86 mg/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. (C) 2017 Elsevier B.V. All rights reserved.