Radiation grafting of DMAEMA and DMAEMA-based adsorbents for thorium adsorption

Abstract

Radiation grafting of two tertiary amine methacrylates; 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 2-(diethylamino)ethyl methacrylate (DEAEMA) onto polyolefin non-woven fabric (PE/PP-NWF) was comparatively investigated in this study. In addition, the absorbent preparation process, grafting kinetics, and mechanism were investigated. The thermal properties were investigated by thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). Fourier transform infrared (FTIR) spectroscopy was performed to confirm the successful grafting and incorporation of the two monomers functional groups onto PE/PP-NWF. X-ray diffraction (XRD) analysis was used to examine the differences between the crystal sizes and structures. Lastly, the adsorption of Th(IV) ion was investigated in batch mode. The results indicate that the radiation grafting of both DMAEMA and DEAEMA onto PE/PP-NWF required high activation energies with increasing temperatures from 313 to 333 K. Furthermore, P-DMAEMA and P-DEAEMA demonstrated different adsorption behaviours towards Th(IV). Results showed that P-DEAEMA exhibited lower Th(IV) adsorption capacity compared to P-DMAEMA, although both contain similar carbonyl and tertiary amino functional groups. These findings indicate that the molecular structure of the adsorbent was responsible. The molecular sizes increased with increasing branched carbon chains from the methyl to ethyl groups. Density functional theory (DFT) analysis indicated that induced steric effect eventually increases the inter-molecular repulsions caused by the additional CH2-groups in the structure, which reduces adsorption capacity.