Synthesis and characterization of organic montmorillonite-polyvinyl alcohol-co-polyacrylic nanocomposite hydrogel for heavy metal uptake in water

In the present work, preparation of organic montmorillonite-polyvinyl alcohol-co-polyacrylic (OMMT-PVA/AAc) nanocomposite hydrogels are performed with different OMMT ratios ranging from 1.3 to 15% using γ irradiation as initiator to induce crosslink network structure. These nanocomposites hydrogels are prepared to use in heavy metals water decontamination. The effect of clay ratio and absorbed dose on gel fraction and swelling% has been investigated. It is found that the gel fraction increases up to 92% with increasing the loaded OMMT to 15%, whereas the swelling% reaches its maximum value at a ratio of nanoscale clay of 6% and at an absorbed dose of 4 kGy. The thermal stability of PVA/AAc hydrogel and OMMT-PVA/AAc nanocomposite hydrogels has been determined by thermogravimetric analysis (TGA), which indicated a higher thermal stability of the nanocomposite hydrogel. The FTIR spectral analysis has identified the bond structure of the PVA/AAc hydrogel and the OMMT-PVA/AAc nanocomposite. The nanostructure of the composite as well as the degree of exfoliation of clay are studied by X-ray diffraction (XRD). Its free volume holes parameters (size and fraction) are investigated by means of positron annihilation lifetime spectroscopy (PALS). After loading the bulk and nanocomposites hydrogels with different heavy metals (Cu 2+ , Co 2+ and Ni 2+ ), UV spectroscopy is applied to determine the metal ion concentration before and after treatment. The distribution of heavy metals on the hydrogels is determined by energy dispersive X-ray (EDX). The factors affecting the heavy metal uptake, such as contact time, pH and metal ion concentration of solutions are studied. The results have shown that, the presence of OMMT increases the thermal stability of PVA/AAc due to the hydrogen bond formed between them which, is confirmed by FTIR. In addition, the resulting gel fraction after irradiation with relatively low gamma absorbed dose increased by 120%, enabling the sample to be reused for several times. In addition, the metal adsorption has increased from 194, 185, 144 mg/g for Cu 2+ , Co 2+ and Ni 2+ respectively in case of previously prepared PVA/AAc hydrogel to 835, 785, 636 mg/g for Cu 2+ , Co 2+ and Ni 2+ respectively for OMMT-PVA/AAc nanocomposite.