Optimization and modeling of simultaneous ultrasound-assisted adsorption of binary dyes using activated carbon from tobacco residues: Response surface methodology

Abstract

Abstract In this research, Response Surface Methodology (RSM) was applied by utilizing Central Composite Design (CCD) in order to optimize the ultrasound-assisted adsorption of methylene blue (MB) (which is a cationic dye) and Acid Blue 25 (AB 25) (which is an anionic dye), and their binary dye solutions onto tobacco residues activated carbon (TRAC) from water. In order to know the characteristics of the adsorbent, UV–visible spectrophotometry, FTIR, SEM, XRD and BET were applied. The effect of various parameters such as initial concentrations of AB25 and MB, adsorbent mass, pH, sonication time and adsorbent regeneration were studied on the adsorption. In order to make a quadratic model, the experiments needed to be performed 32 times. The adsorption efficiency was measured after all the above parameters were set on their optimized values. The optimized values of initial concentration were achieved 200 and 100 mg/l for MB and AB 25, respectively. For adsorption mass, it was 0.6 g/l, for sonication time it was 8 min and the pH was 10. Under these conditions, the highest efficiency in adsorption belonged to TRAC with the value of 98.94% for MB and 98.65% for AB 25. The responses which were selected showed that one of the parameters which had an outstanding impact statistically, was the Sonication time. The Amount of R2 for the Temkin model is 0.955 and 0.879 mg/g for MB and AB 25 in a single system. This value is equal to 0.978 and 0.996 mg/g in systems that are binary and they all show that the model is applicable. Pseudo-first order, pseudo-second order, Weber–Morris intraparticle diffusion rate and Elovich kinetic models were applied and analyzed for their quality to fit the data. Elovich kinetic model was the best in fitting the adsorption data. Thermodynamics studies affirmed the nature of adsorption is spontaneous and the process is endothermic. The endothermic nature of the processes was determined because of the positive amounts of both enthalpy (ΔH) and entropy (ΔS).