Poly(hydroxyethyl methacrylate) nanoparticles for environmental applications

Abstract

The poly(hydroxyethyl methacrylate) (PHEMA) nanoparticles with an average size of 150 nm in diameter and with a polydispersity index of 1.171 were produced by a surfactant free emulsion polymerization. Specific surface area of the PHEMA nanoparticles was found to be 1779 m2/g. 3-(2-Imidazoline-1-yl)propyl(triethoxysilane) (IMEO) was covalently attached to the nanoparticles as a metal-complexing ligand. The PHEMA-IMEO nanoparticles were used for the removal of $Hg^ {2+}$ ions from synthetic solutions. To evaluate the degree of IMEO loading, the PHEMA nanoparticles were subjected to Si analysis by using flame atomizer atomic absorption spectrometer and it was estimated as 280 mg IMEO/g of polymer (1021 µmol/g). The PHEMA nanoparticles were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and fourier transform infrared spectroscopy (FTIR). Adsorption equilibrium was achieved in about 10 min. The adsorption amount of Hg2+ ions onto the PHEMA nanoparticles was negligible (0.14 mg/g). The IMEO attachment significantly increased the $Hg^ {2+}$ adsorption amount (746 mg/g). Adsorption amount of PHEMA-IMEO nanoparticles increased significantly with increasing Hg2+ concentration. The adsorption of $Hg^ {2+}$ ions increased with increasing pH and reached a plateau value at around pH 5.0. Competitive heavy metal adsorption from aqueous solutions containing $Cd^ {2+}, Pb^ {2+} and Hg^ {2+}$ was also investigated. The competitive adsorption capacities are 238.8 mg/g for $Hg^ {2+}$; 45.9 mg/g for $Cd^ {2+}$ and 19.6 mg/g for $Pb^ {2+}$. These results may be considered as an indication of higher specificity of the PHEMA-IMEO nanoparticles for the Hg2+ comparing to other ions. Consecutive adsorption and elution operations showed the feasibility of repeated use for PHEMA-IMEO nanoparticles.