Adsorption of cationic dyes onto chemically modified activated carbon: Kinetics and thermodynamic study

In this study, Activated carbon (AC) was successfully modified by carboxylic group (–COOH) via AC mechanical attrition in the presence of NaOH and Chloroacetic acid. Modified activated carbon (AC-COOH) was characterized by XRD, SEM, EDS and FTIR. The effect of modified activated carbon by NaOH and Chloroacetic acid towards the adsorption of methylene blue and crystal violet dyes was demonstrated. Various adsorption parameters were studied as a function of contact time, initial concentration of the dye, adsorbent content, pH, and temperature. The modified AC-COOH can quickly adsorb the two dyes and equilibrium is achieved within 15 min. Moreover, the adsorption performance was enhanced with increasing the pH of the dye solution. The adsorption isotherms of both dyes were significantly described by the Langmuir model with maximum adsorption capacities of 123.75 mg g−1 for MB and 120 mg g−1 for CV. Based on the values of the correlation coefficient and the adsorption capacities, the kinetics of both dyes were pseudo-second-order. Furthermore, the measured thermodynamic parameters indicated that the organic dye adsorption was endothermic and spontaneous. Finally, the AC-COOH demonstrated acceptable removal percentage of the two dyes over five cycles. This study showed that the role of ball milling technique in the modification of activated carbon and showed the effect of functional groups and active sites on the activated carbon adsorbent (phenol, alcohol and carboxylic groups) contributed to its considerable affinity for adsorption in dye removal. As a result, the optimum AC-COOH can serve as efficient and inexpensive adsorbents for removing dyes from industrial wastewater.