N-doped biochar from chitosan gel-like solution: Effect of hydrothermal temperature and superior aqueous Cr (VI) removal performance

N-doped biochar was prepared by gel-like chitosan solution via hydrothermal carbonization followed by low temperature oxidation, where the effect of hydrothermal temperature on the structure of biochar was studied. The removal of Cr (VI) on biochar was studied as a function of pH and contact time via batches of adsorption experiments. Results indicated that the as-made biochar included numbers of N, O-based groups with limited surface areas of similar to 50 m(2)/g and main mesopores, and Cr (VI) removal efficiency was largely affected by hydro thermal temperature. Adsorption kinetics and isotherms of Cr (VI) were well-described by pseudo-second order and Langmuir model, respectively, and an initial pH of two was most favorable for Cr(VI) removal. Significantly, OCS-160 sample had an unexpected maximum Cr (VI) capacity up to 190.48 mg/g at 25 ?degrees C with good recyclability, showing great potential as inexpensive and highly efficient adsorbents for Cr (VI) removal from wastewater.