Preparation of unsaturated MIL-101(Cr) with Lewis acid sites for the extraordinary adsorption of anionic dyes

Abstract

Anionic dyes contaminate water and severely disrupt aquatic ecosystems, urgently demanding effective treatment solutions for safety. This study explores the synthesis of unsaturated MIL-101(Cr) and its exceptional performance in removing anionic dyes from polluted water systems. The synthesized MIL-101(Cr) exhibits medium Lewis’s acid and strong Brønsted acid sites, a high specific surface area (>3000 m2/g), and a Zeta potential of 30 mV, contributing to its strong adsorption capability. Adsorption studies reveal Langmuir isotherm model fitting, with maximum adsorption capacities of 4231, 1266, and 568 mg/g for Acid Blue 92, Congo Red, and Acid Blue 90, respectively. The chemisorption process follows pseudo-second-order kinetics and is spontaneous and exothermic. MIL-101(Cr) demonstrates chemical and water stability, maintaining over 80% removal efficiency after five recycling cycles. This research provides valuable insights into treating anionic dye-contaminated wastewater using MIL-101(Cr) as an efficient adsorbent.