Non-derivatizing solvent assisted waste-derived cellulose/ MOF composite porous matrix for efficient metal ion removal: comprehensive analysis of batch and continuous packed-bed column sorption studies

Abstract

The use of metal–organic frameworks (MOFs) for wastewater treatment in continuous operation is a major challenge. To address this, the present study demonstrates the eco-friendly and economic synthesis of Ca-MOF immobilized cellulose beads (Ca-MOF-CB) derived from paper waste. The synthesized Ca-MOF-CB were characterized using standard analytical techniques. Batch sorption studies were performed to check the effect of cellulose composition (wt%), Ca-MOF loading, contact time, and initial metal ion (Pb²⁺, Cd²⁺, and Cu²⁺) concentration. Ca-MOF-CB beads exhibited outstanding equilibrium sorption capacities for Pb²⁺, Cd²⁺, and Cu²⁺, with estimated values of 281.22 ± 7.8, 104.01 ± 10.58, and 114.21 ± 9.68 mg g⁻¹, respectively. Different non-linear isotherms and kinetic models were applied which confirmed the spontaneous, endothermic reactions for the physisorption of Pb²⁺, Cd²⁺, and Cu²⁺. Based on the highest equilibrium sorption capacity for Pb²⁺ ion, in-depth parametric column studies were conducted in an indigenously developed packed-bed column set-up. The effect of packed-bed height (10 and 20 cm), inlet flow rate (5 and 10 mL min⁻¹), and inlet Pb²⁺ ion concentration (200, 300, and 500 mg L⁻¹) were studied. The breakthrough curves obtained at different operating conditions were fitted with the empirical models viz. the bed depth service time (BDST), Yoon–Nelson, Thomas, and Yan to estimate the column design parameters. In order to determine the financial implications at large-scale industrial operations, an affordable synthesis cost of 1 kg of Ca-MOF-CB was estimated. Conclusively, the present study showed the feasibility of the developed Ca-MOF-CB for the continuous removal of metal ions at an industrial scale.