Preparation of N-doped cellulose-based hydrothermal carbon using a two-step hydrothermal induction assembly method for the efficient removal of Cr(VI) from wastewater

Cr(VI) pollution is a growing problem that causes the deterioration of the environment and human health. We report the development of an effective adsorbent for the removal of Cr(VI) from wastewater. N-doped cellulose-based hydrothermal carbon (N–CHC) was prepared via a two-step hydrothermal method. The morphology and structural properties of N–CHC were investigated by various techniques. N–CHC has many O and N groups, which are suitable for Cr(VI) adsorption and reduction. Intermittent adsorption experiments showed that N–CHC had an adsorption capacity of 151.05 mg/g for Cr(VI) at pH 2, indicating excellent adsorption performance. Kinetic and thermodynamic analyses indicates that the adsorption of Cr(VI) on N–CHC follows a monolayer uniform adsorption process, which is a spontaneous endothermic process dominated by chemical interaction and limited by diffusion within particles. In a multi-ion system (Pb2+, Cd2+, Mn7+, Cl−, and SO42−), the selectivity of N–CHC toward Cr(VI) was 82.62%. In addition, N–CHC demonstrated excellent reuse performance over seven adsorption–desorption cycles; the Cr(VI) removal rate of N–CHC in 5–20 mg/L wastewater was >99.87%, confirming the potential of N–CHC for large-scale applications. CN/C-OR, pyridinic-N, and pyrrolic-N were found to play a critical role in the adsorption process. This study provides a new technology for Cr(VI) pollution control that could be utilized in large-scale production and other environmental applications.