Synthesizing of MnO2-modified snail shell adsorbent and its application for Cr(VI) removal

Abstract

In this study, a novel adsorbent material, VO-MnO₂, was synthesized via a hydrothermal method using calcined freshwater snail shells (Pila polita) as a biogenic support. Potassium permanganate (KMnO₄) and hydrochloric acid (HCl) were employed as oxidizing and acidifying agents to facilitate the in-situ formation of MnO₂ on the CaCO₃-based substrate. The obtained material exhibited a porous structure, high specific surface area, and was characterized by SEM, EDS, FTIR, XRD, and BET analyses. The Cr(VI) adsorption performance was evaluated under various conditions including solution pH, contact time, initial Cr(VI) concentration, and adsorbent dosage. Optimal adsorption was achieved at pH 3, 90 minutes, 50 mg/L Cr(VI), and 0.5 g/L adsorbent dosage. The adsorption followed the Langmuir isotherm model with a maximum capacity of 47.39 mg/g, and the kinetics were well described by a pseudo-second-order model, indicating chemisorption. With its high efficiency, low cost, and eco-friendly source, VO-MnO₂ is a promising adsorbent for the removal of Cr(VI) from wastewater.