Adsorptive performance of cottonseed cakes biosorbent and derived activated carbon towards Cu2+ ions removal from aqueous solution: Kinetics modelling, isotherms analysis and thermodynamics

Abstract

Compatible and environmentally clean activated carbon material was prepared via physicochemical method and used for harmful pollutant removal from aqueous solution. The performance of the pristine cottonseed cakes and its activated carbon was examined towards copper ions removal as targeted pollutant through adsorption process. The physicochemical properties of adsorbents were evaluated by numerous experimental techniques such as Fourier transform infra-red spectroscopy, Raman spectroscopy, scanning electron microscopy, the point of zero charge, iodine number and specific surface area. The effect of several key operational parameters such as contact time, adsorbent dose, pH, concentration and temperature were considered. Results of the adsorption tests exhibited significant sensitivity towards copper ions elimination at optimum conditions; the copper uptake capacity was enhanced with time up to equilibrium of 30 min with a minimum adsorbent dose of 0.1 g at alkaline pH of 10 for maximum concentration of 50 mg/L at room temperature (25 °C) and achieved appropriate adsorbed quantities of 51.56 mg/g for cottonseed cakes activated carbon (CCAC) and 48.5 mg/g for cottonseed cakes biosorbent (CCB). The values of point of zero charge are 2.63 and 6.32 for CCB and CCAC respectively which present high electrostatic attraction between positive charge of copper ions and negative charge of the surface at basic medium. Iodine number of 30.35 and 41.92 mg/g indicates random distribution of micropores. The specific surface area of CCAC (30.35 m²/g) is higher than the one of CCB (11.94 m²/g). FTIR shows good surface chemistry with various functional groups while Raman spectroscopy and SEM analyses revealed myriad morphological features and carbon phases (graphite and diamond). The adsorption of copper ions was described by pseudo second order kinetic model and favoured by Redlich Peterson isotherm corresponding to physisorption on CCB while the one CCAC involves chemical bonding and can be qualified as chemisorption mechanism as confirm by ΔH° of both materials.