One-pot fabrication of rod-like magnesium silicate and its adsorption for Cd²⁺

Sepiolite is a natural clay mineral with powerful adsorption performance. In this work, rod-like magnesium silicate (RMS) with sepiolite-type structure was fabricated by ingeniously designing the ethanol/water ratio of the solvent. RMS exhibited a hierarchical pore structure from micropores to mesopores. The adsorption behavior of RMS towards Cd2+ was systematically investigated. Adsorption isotherm could be described well by the Langmuir model, and the saturation adsorption capacity of 346 mg/g was higher than other reported clay minerals. Adsorption kinetics followed the pseudo-second-order kinetic model and the adsorption rate controlling step was intra-particle diffusion. Thermodynamic parameters indicated that the adsorption was a spontaneous physicochemical reaction and accompanied by endotherm and increased randomness at the adsorbent-adsorbate interface. RMS exhibited higher adsorption amount in neutral solution than in acidic or alkaline conditions as the physicochemical properties of RMS and Cd2+ were significantly affected by the pH. After five cycles, around 92 % of the adsorption performance still maintained, demonstrating the excellent reusability of RMS. This work demonstrated that the sepiolite-type RMS can be facile synthesized and is appropriate for removing Cd2+ from wastewater.