Preparation and characterization of sulphonated bio-adsorbent from waste hawthorn kernel for dye (MB) removal

Abstract

In this study, hawthorn kernel (HK), obtained from agricultural waste, which is eco-friendly and low cost material was selected as bio-adsorbent to remove of methylene blue (MB) from aqueous solutions. Since hawthorn kernel has low adsorption capacity, a new hawthorn-based bio-adsorbent having sulphonic acid groups (SHK) was prepared by activation using sulfuric acid with a very simple method. The optimal activation conditions were determined as 6 h, 85 °C, in 18 M sulfuric acid, with a sample/acid ratio of 1/5 (mass/volume). To determine the basic properties such as chemical structure, porosity and surface properties of the HK and SHK, they were characterized by Boehm Titration, BET, FTIR, SEM-EDX, XRD and pHpzc methods. Also, the thermal behavior of both adsorbents was examined by TGA. It was observed that activation has improved the thermal stability and also caused more amorphous structure. Optimum adsorption conditions were determined considering the amount of adsorbent, solution pH, MB initial concentration, and contact time and temperature parameters. Activation significantly changed the surface properties of the HK such as total acidity, functionality, porosity and surface pH. For MB adsorption on both adsorbents, pseudo-second-order kinetic model was found to be appropriate to explain kinetic behavior and equilibrium data fitted better to the Langmuir isotherm model. The maximum MB adsorption capacities of HK and SHK were calculated as 49.5 and 151.5 mg/g, respectively. It was determined from the calculated thermodynamic parameters that the adsorption of MB onto HK is spontaneous at low concentrations and high temperatures, but the adsorption of MB onto SHK is spontaneous at both high concentrations and low temperatures. After reusability studies which were carried out with 100 mg/L MB for five times, the SHK lost about 1% of its removal efficiency. As a result it was observed that SHK could be used as an efficient adsorbent for MB removal from aqueous solutions.