Efficient Boron Removal from Activated Carbon-Nitrogen-Doped Graphene Oxide

Abstract

Efficient boron removal from seawater remains a significant challenge in environmental remediation. In this study, we synthesized an activated carbon–nitrogen-doped graphene oxide (ACNGO) composite with enhanced pore structure and surface properties. Optimization experiments revealed that factors like immersion time, freeze-drying duration, and polyethyleneimine volume had negligible effects, resulting in a cost-efficient and reproducible synthesis process. ACNGO exhibited efficient boron removal, achieving a maximum capacity of 11 mg/g, while long-term tests confirmed its ability to maintain boron concentrations below 0.5 mg/L across 29 regeneration cycles. Granular and column adsorption experiments further validated ACNGO's potential for industrial applications. Isotherm, kinetic, and thermodynamic analyses revealed that the adsorption behavior of boric acid (B3) and borate ions (B4) on ACNGO is governed by both chemical and physical processes, influenced by internal diffusion and boundary layer effects. Density functional theory calculations confirmed the formation of stable structures with distinct adsorption sites. The primary mechanisms driving boron adsorption involved hydrogen bonding, van der Waals forces, and complexation interactions, with binding energies of -36.53 kJ/mol for ACNGO-B3-o-1 and -23.48 kJ/mol for ACNGO-B4-p-3. These differences in intermolecular forces resulted in distinct adsorption performances for B3 and B4, underscoring ACNGO's potential for scalable industrial applications and its promise in advancing seawater treatment technologies with robust performance and cost-effectiveness.

Keywords: Activated carbon (AC), Nitrogen-doped graphene oxide (NGO), Boron, Adsorption mechanisms, Density functional theory (DFT) calculations