Facile fabrication of a low-cost carboxymethyl cellulose–polyacrylamide composite for the highly efficient removal of cationic dye: optimization, kinetic and reusability

Bio-adsorbents with high adsorption efficiency, sustainability, and reusability are desired in wastewater treatments. Herein, a covalently cross-linked green macroparticle hydrogel biocomposite (AM-AC/CMC-Ca) as a bio-adsorbent was prepared through an acrylamide (AM) reaction with a polysaccharide carboxymethyl cellulose (CMC)-modified activated carbon (AC) and further Ca(II) cross-linking polymerization, with efficient removal of Safranin T (ST) cationic dye. FESFM/EDX, XRD, FTIR, BET, and TGA were used to limit the structure and characteristics of the biocomposite. The effects of the concentration for both AM, CMC, AC, and Ca(II) cross-linked on swelling behavior were studied, which yielded that the maximum swelling ratio (SR%) in distilled water was 3500%. The ST dye adsorption capacity was evaluated, and the results illustrated that (AM-AC/CMC-Ca) biocomposite prepared under the optimized conditions displays a super strong adsorption efficiency of 1558.52 mg/g and almost 100% removal efficiency within 1 h adsorption time at pH 7.6 and 25 °C. They decrease slightly with the decrease in pH 3, and the zero-point charge was determined to be 4.2. The pseudo-first-order, pseudo-second-order, chemisorption, and intra-particle diffusion kinetic models were useful to test the experimental result, the second order exhibited the best fit for the kinetic studies. The equilibrium result was assessed using the Freundlich, Langmuir, and Fritz–Schlender isotherm model, and the Freundlich isotherm best refers to the uptake of ST dye, which suggests that the adsorption of dye in this study onto biocomposite is heterogeneous with multilayers. Thermodynamic parameters indicated that the adsorption of ST dye onto the biocomposite was spontaneous (ΔG < 0), and endothermic (ΔH > 0). Additionally, the biocomposite showed high reusability and regeneration, maintaining an 88.8% removal capacity for ST dye after 6 cycles.