Preparation and characterization of sodium lignosulfonate-chitosan hydrochloride composite materials for dye adsorption

With the rapid development of industry, dye wastewater increasingly damaged the ecological environment and human health. Therefore, the treatment of wastewater became an urgent environmental issue. In this paper, sodium lignosulfonate was modified with the Reimer-Tiemann reaction and then cross-linked with chitosan hydrochloride to prepare modified sodium lignosulfonate-chitosan hydrochloride (MSL-CHC) composite materials, which were characterized by infrared spectra (FT-IR), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) surface area, and X-ray photoelectron spectroscopy (XPS). Then, the adsorption performance of MSL-CHC for Congo red (CR) was investigated under different conditions, including adsorbent dosage, adsorption time, inorganic salt ion species, ionic strength and adsorption temperature. The results showed that the adsorption was consistent with the pseudo-second-order kinetic model, indicating that chemical adsorption was dominant. The adsorption isotherm could be fitted as the Langmuir model, indicating monolayer chemical adsorption. Thermodynamics studies showed that the adsorption of CR was a spontaneous endothermic process. The maximum adsorption capacity for CR was 804.32 mg·g⁻¹. Furthermore, the adsorption capacity of different dyes, as well as the adsorption process in various inorganic salt solution, indicated that MSL-CHC composites had good universality, anti-interference ability and recyclability. The composite materials were environmentally friendly, pollution-free, and easy to obtain, which were ideal bio-based adsorption materials for removing dyes from water.