Developing an effective adsorbent from asphaltene for the efficient removal of dyes in aqueous solution

A novel adsorbent was prepared by the functionalization of asphaltenes, which were isolated from crude oil and used for the removal of organic pollutants in aqueous solution. The functionalized asphaltenes were characterized by Fourier transform infrared, scanning electron microscope and elemental analysis and found to contain higher amounts of oxygen atoms and carbonyl and hydroxyl functional groups. The impact of different variables such as pH, adsorbent dose, dyes concentration, reaction temperature and contact time were studied during the adsorption process. At 5 h contact time, the best pH for the high efficient adsorption of bromophenol blue (BPB) and methyl orange (MO) were found to be 6.30 and 2.75, respectively. The adsorption isotherms fitted well the Langmuir, Freundlich, Temkin as well as Lagergren models. The adsorption isotherm data of BPB and MO were in good conformity with all models studied, however, BPB was more closely fitted with Freundlich and Temkin isotherms while MO was more closely fitted with Langmuir and Lagergren models thereby implying that the adsorption occurred as a monolayer as well as a heterogeneous surface adsorption. The calculated maximum adsorption capacity for Langmuir model was 7.44 and 2.24 mmol/g for BPB and MO, respectively. Several adsorption kinetic models were fit with experimental data and pseudo-second-order kinetic model was found to be best fitting model. The separation factor (R-L) values found between 0 and 1 that indicates the favorability of the adsorption process on adsorbent surface. The thermodynamic parameters were calculated and the respective values for BPB and MO dyes were found to be Delta G degrees (-11.808 and -14.057 kJ/mol),.H (8.509 and 6.460 kJ/mol) and Delta S degrees (65.954 and 66.613 J/K mol), which exhibited that the adsorption of dyes on functionalized asphaltenes was spontaneous, endothermic with increased randomness. The functionalized asphaltene showed high adsorption capacity with highly efficient removal for BPB and MO dyes.