Sustainable synthesis and dual adsorption of methyl orange and cadmium ions using biogenic silica-based fibrous...

In pursuit of sustainable nanomaterial production, this study presents a novel biogenic fibrous silica sphere functionalized with a crown ether ionic liquid for advanced dual-adsorption of methyl orange and Cd(II) from aqueous solution. Sorghum waste serves as the silica source in the adsorbent preparation process, ensuring an eco-friendly approach. The benzo-15-crown-5 ionic liquid is coupled to thiol-functionalized fibrous silica spheres through an efficient thiol-ene click reaction. Under constant conditions (temperature: 298 K, solution volume = 50 mL, adsorbent dosage = 5 mg, pH = 7, shaking speed = 200 rpm), the synthesized material demonstrates maximum adsorption capacities of 507.1 mg g^-1 and 306.3 mg g^-1 for methyl orange and Cd(II), respectively, according to the Langmuir model. Thermodynamic investigations reveal exothermic adsorption for methyl orange with an enthalpy change of -77.49 KJ mol^-1, while endothermic adsorption is observed for Cd(II) with an enthalpy of +24.10 KJ mol^-1. The entropy change of adsorption is -0.153 KJ mol^-1 K^-1 for methyl orange, indicating a more ordered state, and + 0.192 KJ mol^-1 K^-1 for Cd(II), suggesting increased disorder. The change in Gibbs free energy ranges from -32.66 to -29.60 KJ mol^-1 for methyl orange and -32.29 to -35.99 KJ mol^-1 for Cd(II), demonstrating that both adsorption processes are spontaneous. These results indicate that the adsorbent has potential as a dual-adsorption material for water remediation applications.