Poly(sodium methacrylate)/eggshell particles hydrogel composites as dye sorbent.

Eggshell (ES) particles as an available and low-cost waste material were utilized to prepare novel hydrogel composites for dye adsorbing application. For this purpose, solution polymerization of sodium methacrylate was carried out in the presence of ES particles with various size ranges. Results showed that incorporation of ES particles resulted in heterogeneous pores and cavities in the structure of the poly(sodium methacrylate) (PNaMA) matrix. Hydrogel composites with lower content (20 wt%) and smaller size (<75 μm) of ES particles presented higher water absorption capacity. The equilibrium water absorption values in distilled water were higher than phosphate buffered saline medium. ES particles showed low methylene blue (MB) and crystal violet (CV) adsorption capacities due to electrostatic repulsion of the positively charged species on the surface of ES particles and dye molecules. In contrast, hydrogel composites depicted fast and considerable dye adsorbability. The combination of 60 wt% ES particles within PNaMA provided a cost-effective adsorbent with similar CV adsorption capacity compared with the unfilled matrix, while MB removal was slightly decreased. The dye adsorption by either ES particles or hydrogel composites followed the pseudo-second-order kinetics, indicating that chemical sorption is the rate-limiting step for both of them.