Solution combustion synthesis of calcium aluminate nanocomposite using coffee husk extract as green fuel and its application in adsorptive amputation of anionic dyes

Abstract

Solution combustion synthesis of calcium aluminate (CaAl _2 O _4 ) nanocomposite using coffee husk extract and its adsorption capacity for removal of Congo red (CR) and Indigo carmine (IC) are reported. Physiochemical properties of adsorbent were studied by PXRD, SEM, TEM and point of zero charge. Batch adsorption studies were conducted to study the effect of adsorbent dosage, pH, contact time, initial dye concentration and temperature on adsorption efficiency of coffee husk derived calcium aluminate nanocomposite (CHCA). Among the isotherms used, Langmuir model explained best the equilibrium data and the maximum monolayer adsorption capacity was found to be 377 and 135 mg/g for CR and IC, respectively. Mass transfer analysis indicated adsorptive removal of dyes was controlled by both external and internal diffusion. Pseudo-first-order model fitted best with experimental kinetic data and adsorption efficiency increased with an increase in the initial bulk concentration of CR and IC. Thermodynamic analysis indicated that adsorption of CR and IC on CHCA is feasible, spontaneous and exothermic in nature. The magnitude of enthalpy and heat of adsorption suggested that the adsorption is physical in nature. The present study explores the potential of coffee husk extract, an agro-based bio-waste, as a novel and eco-friendly fuel in the synthesis of CHCA and the synthesised nanocomposite as a potential adsorbent for the removal of synthetic dyes.

Keywords

• calcium aluminate
• anionic dyes
• coffee husk
• adsorption
• mathematical modelling