Construction of Nitrogen‐rich Graphene Oxide/Chitosan Adsorbent for the Removal of Hexavalent Chromium from Wastewater

ABSTRACT

To overcome the limitations of low hexavalent chromium (Cr(VI)) adsorption capacity and poor acid stability in traditional chitosan (CS)‐based adsorbents, a nitrogen‐rich graphene oxide (N‐GO/CS） adsorbent was prepared. Specifically, GO and polyethyleneimine (PEI) were covalently cross‐linked onto CS using γ‐aminopropyltriethoxysilane and glutaraldehyde. Herein, GO improves the structural stability of CS in acidic solutions, while PEI enhances the adsorption capacity toward Cr(VI). The successful fabrication of N‐GO/CS was confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy‐energy dispersive spectroscopy. The maximum Cr(VI) adsorption capacities of N‐GO/CS, based on the Langmuir model, were 537.6 mg/g at 25°C, 568.2 mg/g at 35°C, and 643.6 mg/g at 45°C, surpassing those of most reported CS‐based adsorbents. Adsorption experiments indicated that the process was dominated by chemisorption and followed a homogeneous monolayer mechanism. Thermodynamic investigation confirmed that the adsorption process was endothermic (Δ H ⁰ = 55.98 kJ/mol) and spontaneous (Δ G ⁰ < 0). Furthermore, interference tests demonstrated that N‐GO/CS selectively adsorbed Cr(VI) in the presence of coexisting metal cations and monovalent ions (e.g., Cl ⁻ and NO ₃ ⁻ ). Cycling experiments indicated that N‐GO/CS maintained 70.6% of its initial adsorption capacity after eight consecutive cycles. The primary adsorption mechanism, including electrostatic interactions, reduction of Cr(VI), and coordination of Cr species, was further elucidated. This work provides valuable technical support for the structural design of adsorbents for the removal of Cr(VI) from wastewater.