Modification of chitosan with Kryptofix222 as a novel adsorbent for removing lead and cadmium ions

A novel adsorbent was prepared by modifying chitosan with 5,6-Benzo-4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane-5-one (Kryptofix222). This absorbent was utilized to eliminate cadmium and lead ions from an aqueous mixture. Both chitosan (CS) and Kryptofix222 (K-222) possess individual capabilities for heavy metal adsorption. However, incorporating K-222 into the CS matrix significantly and synergistically led to a marked improvement in adsorption efficiency. The [CS + K-222] composite demonstrated substantially higher removal rates for Cd²⁺ and Pb²⁺ compared to either CS or K-222 used alone. Functionalization of chitosan with Kryptofix222 introduced crown ether groups that enhance its affinity for metal ions. The successful preparation of the adsorbent was confirmed through various characterization techniques, involving FTIR, FESEM, EDX, and BET. Optimal adsorption conditions were established as a contact time of 50 min, pH 6.0-7.0, an adsorbent dosage of 0.01 g, and metal ion concentrations ranging from 5.0 to 80 mg/L for both lead and cadmium. The impact of adsorbent quantity, solution pH, temperature, shaking time, and initial cadmium and lead ion concentration on the elimination efficiency was investigated. The pseudo-second-order model best depicted the sorption kinetics, while the Langmuir isotherm model described the sorption behavior most effectively. The highest sorption capabilities for cadmium and lead were 510 mg/g and 340.3 mg/g, respectively. Additionally, the absorbent could be regenerated using 0.1 M HCl and 0.1 M H₂SO₄ and reused in subsequent adsorption cycles.