Magnesium-doped lithium manganese oxide composite with mesoporous silica for methylene blue dye and heavy metal removal†

Abstract

In this study, magnesium-doped lithium manganese oxide nanoparticles were prepared through a solid-state reaction technique, and their surface was modified with mesoporous silica. The surface-modified material exhibited a significantly enhanced BET surface area from 5.791 to 66.058 m² g⁻¹, thus enhancing the adsorption property. The prepared material was characterized using advanced analytical techniques such as powder XRD (PXRD), FT-IR, BET surface area analysis, and scanning electron microscopy (SEM). The effect of the adsorbent dosage, contact time, pH, and initial concentration on adsorption characteristics was evaluated for methylene blue (MB) dye. A maximum adsorption capacity of 94.34 mg g⁻¹ was obtained from the Langmuir adsorption isotherm. Kinetic properties were characterized using the pseudo-first-order, pseudo-second-order, and intra-particle diffusion models, and the pseudo-second-order model was found to be the best fit. Effectively, four cycles of adsorption–desorption for the prepared material were demonstrated through thermal desorption technique. To understand the feasibility of adsorption in different matrix conditions, MB dye-spiked samples of well water, lake water, and tap water were treated with the adsorbent material and 64.5%, 62.8%, and 53.5% removal performance, respectively, was observed. In addition, mixed solutions of heavy metals (Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Pb²⁺) were also tested for adsorption performance study of the adsorbent and 65.5–99.7% removal was observed at a sample dose of 25 g L⁻¹.