Highly effective and reusable cellulose-based amphoteric adsorbent for dye removal from single and binary system

High adsorption efficiency, synchronized removal of anionic and cationic dyes, and adsorbent recyclability are three contemporary challenges in treating wastewater generated during dyeing operations. In this study, citric acid (CA) and polyethylenimine (PEI) co-functionalized cellulose adsorbent (CS-CA/PEI) with an elevated density of amino and carboxyl functional groups were synthesized using two-step simple methods. CS-CA/PEI with double-network exhibited high electrostatic affinity for both anionic (methyl orange, MO, sunset yellow, SY) and cationic (methylene blue, MB and victoria blue B, VB) dyes over a pH range. The fitted adsorption capacities of CS-CA/PEI for MB, MO, VB and SY were 134.58 mg/g (0.42 mmol/g), 3792.59 mg/g (11.58 mmol/g), 124.53 mg/g (0.24 mmol/g) and 215.51 mg/g (0.47 mmol/g), respectively, outperforming the majority of the reported adsorbents. Langmuir isotherm and pseudo-second order kinetic model established better correlation with experimental data, representing single-layered adsorption through strong electrostatic interactions. CS-CA/PEI performed better in binary pollutants system than in single system, with binary adsorption capacity for MB, MO, VB, and SY being 56%, 7%, 128%, and 14% higher, respectively, demonstrating synergism between dyes and adsorbents. After four repeated adsorption-desorption cycles, CS-CA/PEI showed good structural stability and recyclability, with > 90% of the initial adsorption efficiency for MB and VB and > 70% for MO and SY. Therefore, CS-CA/PEI, with excellent adsorption performance in single and binary pollutant systems, high recyclability, and ease of separation, has significant application potential in treating dyeing wastewater.