Preparation of microbeads grafted with poly(2-(acryloyloxy)ethyl]trimethylammonium chloride) cationic polyelectrolyte as recyclable and effective adsorbents for organic dyes

Abstract

Brush polymers have been widely used as a suitable replacement for many adsorbents due to their economical cost, reusability, and mechanical strength. Here, cationic polyelectrolyte microbeads poly(2-hydroxyethyl methacrylate/ethylene dimethacrylate)-g-poly(2-(acryloyloxy)ethyl]trimethylammonium chloride) marked as p(HEMA/EDMA)-g-p(AEtMAC) were prepared by a combination of suspension and controlled radical polymerization methods. Microbeads displayed nonporous, spherical, and uniform morphology with a size of about 250 μm. Thermal stability decreased after grafting of p(AEtMAC) onto the surface of p(HEMA/EDMA)-Br and the final microbeads p(HEMA/EDMA)-g-p(AEtMAC) exhibited the onset degradation temperature of 200 °C. The adsorption of Coomassie Brilliant Blue G250 (CBB) and methyl orange (MO) anionic dyes at different adsorbent dosages (0.5–3 g L−1) and constant concentration of dye (50 mg L−1) was investigated. The adsorbent at the optimum dosage of 2 g L−1 was selected. More than 90% of the mentioned dyes were removed in the optimum pH range of 5–6. The maximum adsorption capacities 145 and 135 mg dye g−1 adsorbent were obtained for MO and CBB dyes, respectively, at ambient temperature and 300 mg L−1 dye concentration. Adsorptions of the MO and CBB on the adsorbent were well fitted to Temkin and Langmuir isotherm models, respectively, which obeyed the quasi-second-order kinetic model. Adsorption enthalpy change values for MO and CBB were found to be 32.17 and 17.59 KJ mol−1, correspondingly, which indicated the exothermic property and the physical nature of the adsorption. Furthermore, the entropy change values of 130 and 70 J mol−1 were determined for MO and CBB, respectively. Positive values of entropy changes are related to the increase in irregularity during dye adsorption on the cationic adsorbent.