In-situ immobilization of ZIF-8 on sodium lignosulfonate/chitosan foams for efficiently removal of ciprofloxacin from water

Ciprofloxacin (CIP) contamination poses a great threat to the environment due to it can induce the growth of antibiotic-resistant bacteria. Herein, a composite adsorbent material, sodium lignosulfonate/chitosan @ZIF-8 (SLS/CS@ZIF-8), was synthesized by introducing sodium lignosulfonate into chitosan foams (CS-FM) and then loading ZIF-8 onto the resulting foams (SLS/CS-FM) by in-situ immobilization to effectively remove CIP from water. The introduction of sodium lignosulfonate improved the mechanical strength of chitosan foams and provided more attachment sites for ZIF-8. The effects of pH, contact time, initial concentration and temperature for CIP adsorption were investigated. Overall, the adsorption capacity of SLS/CS@ZIF-8 for CIP was better than chitosan@ZIF-8 (CS@ZIF-8) in the pH range of 4 to 11, and SLS/CS@ZIF-8 kept high adsorption capacities at a wide pH range from 6 to 9. SLS/CS@ZIF-8 maximum adsorption capacity for CIP was 413 mg/g when the CIP concentration of 250 mg/L at 303K, which was better than most previously reported adsorbents. Pseudo-second-order kinetics and Langmuir isothermal model could better describe the adsorption process, indicating that the adsorption of CIP was mainly controlled by chemisorption mechanism and monolayer adsorption. Adsorption thermodynamic showed that the adsorption process of CIP on SLS/CS@ZIF-8 was spontaneous and endothermic. After 6 cycles, SLS/CS@ZIF-8 still had good adsorption capacity for CIP. According to FT-IR and XPS analysis, the adsorption mechanisms of CIP on SLS/CS@ZIF-8 was mainly electrostatic interaction, hydrogen bond interaction and π-π interaction. This work synthesized a potential adsorbent to effectively remove CIP from wastewater, developed a new low-carbon green chemical technology for potential applications of sodium lignosulfonate and chitosan.