Mechanism study of a novel modified mesoporous silicon-based NiT50/MCM-41 adsorbent for the selective adsorption of methylene blue from water†

Abstract

In this study, a new silica-based adsorbent strategy was developed to achieve a high adsorption capacity and high MB adsorption selectivity by impregnating a cationic [Ni(tepa)]²⁺ complex on a negatively charged silicon carrier, MCM-41. When the [Ni(tepa)]²⁺ loading was 50%, the MB adsorption capacity of the silicon-based adsorbent (NiT₅₀/MCM-41) could reach 130 mg g⁻¹, which was much higher than that of the original silicon-based MCM-41 adsorbent (23 mg g⁻¹). Interestingly, NiT₅₀/MCM-41 exhibited excellent MB adsorption selectivity in binary mixed dye solutions (MB/R6G, MB/RhB, and MB/MO). The adsorption kinetics and adsorption isotherm followed a second-order kinetic model and the Langmuir adsorption model, respectively. Experimental results showed that the aqueous solution of [Ni(tepa)]²⁺ can provide an alkaline environment to promote the deprotonation of Si–OH on the surface of silicon dioxide to form SiO⁻, which makes the surface negatively charged, and [Ni(tepa)]²⁺ effectively occupies these negatively charged sites through Coulomb interactions to better accommodate the cationic complex [Ni(tepa)]²⁺. Structural characterization and analysis confirmed that the NiO_x and NiC_x components were successfully introduced in the mesoporous channels of the silicon-based adsorbent through heat treatment, enabling the cationic dye to be immobilized on the silicon-based adsorbent through Lewis acid–base interaction, which effectively improved the adsorption capacity and adsorption selectivity towards MB.