Zeolitic imidazolate framework-8/chitosan composite beads for Cu2+ removal and circular utilization as catalysts for the reduction of nitrophenols and organic dyes

Abstract

Due to their detrimental impacts on human health and the environment, removing heavy ions and organic pollutants from wastewater is a significant concern. This study described the preparation of bio-adsorbents using crosslinked chitosan (CS) and zeolitic imidazolate framework-8 (ZIF-8) for Cu²⁺ adsorption. ZIF-8 addition improved the adsorption capacity of the bare crosslinked CS beads. At the optimal 5 % ZIF-8 concentration, the adsorption capacity increased by 38 %. The 5ZIF-8/CS composite beads had a 94.3 % removal efficiency and a 49.0 mg/g adsorption capacity at a dosage of 2 g/L, an initial Cu²⁺ concentration of 100 mg/L, and a contact time of 4 h. The adsorption kinetics and isotherms followed the pseudo-first-order kinetics and Langmuir models, respectively. The Cu²⁺-adsorbed 5ZIF-8/CS composite beads were pyrolyzed to produce copper nanoparticles (CuNPs) immobilized in carbonaceous beads, namely CuNP/carbon composites. Subsequently, they were circularly utilized as catalysts for reducing 4-nitrophenol (4-NP). The composite catalyst could completely reduce 4-NP within 30 min at a 0.248 min^–1 rate constant using a dosage of 0.6 g/L and a sodium borohydride concentration of 100 mM. The composite catalyst could be utilized for a broad pH range. Moreover, the catalyst was effective when assessed in real water samples and in the presence of common inorganic anions and natural organic matter. The catalyst could be easily recovered through filtration and could completely reduce 4-NP for at least five reuse cycles. Additionally, the catalyst effectively reduced 2-nitrophenol and various organic dyes.