Experimental and modelling study of adsorption and diffusion of hexavalent chromium in zeolitic imidazolate framework-11

Abstract

In this study, Zeolitic Imidazolate Framework-11 (ZIF-11) was successfully synthesised at room temperature and characterised by XRD, SEM/EDAX, TGA/DSC, FTIR, and CO₂ adsorption techniques. The material exhibited high crystallinity, well-defined morphology, a thermal stability up to 350 °C, low synthesis cost, and the possibility of scaling up production. Motivated by these favourable properties, ZIF-11 was investigated as an adsorbent for the removal of (Formula presented.) from aqueous solutions. Optimal adsorption conditions were found to be a pH 2, a stirring speed of 400 rpm, a contact time of 70 min and a 20 mg dose of ZIF-11 for 50 mL of (Formula presented.) solution. Thermodynamic studies indicated that the adsorption process is spontaneous and endothermic. Kinetic analysis showed that the adsorption follows the pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Isotherm modelling using Langmuir and Freundlich equations confirmed a uniform distribution of (Formula presented.) species on the ZIF-11 surface. The maximum adsorption capacity of ZIF-11 was found to be 10.61 mg/g, surpassing many reported adsorbents. These findings demonstrate that ZIF-11 is a highly promising material for the (Formula presented.) removal from water. Its excellent adsorption capacity, thermal stability, and ease of synthesis highlight its potential for practical applications in water treatment and environmental remediation.