Ammonia-assisted hydrothermal carbon material with schiff base structures synthesized from factory waste hemicelluloses for Cr(VI) adsorption

Nitrogen doping hydrothermal carbon material (NHTC) is an important metal ion adsorbent. In this work, NHTC with Schiff base structures (NHTC-SBS) was successfully synthesized via ammonia-assisted hydrothermal treatment of industrial hemicelluloses and used for the adsorption of toxic hexavalent chromium Cr(VI). The formation of Schiff base structures depends on the reaction between ammonia and furfural resulting from hemicelluloses hydrolysis. The morphology and structures of NHTC-SBS were characterized by SEM, XRD, BET, XPS and zeta potential. The results of adsorption experiments suggested that a high adsorption capacity of NHTC-SBS towards Cr(VI) was achieved at 349.6 mg/g according to Langmuir isotherm model under 298 K and pH 2.0. The adsorption of Cr(VI) on NHTC-SBS mainly depended on electrostatic attraction, redox, and chelation between nitrogen-containing groups (amino, Schiff base structures, heterocyclic nitrogen) and Cr(VI). This work provides a facial, green, and economical route to synthesize biochar with great adsorption performance.