Adsorptive removal of chromium (Cr(III)) and lead (Pb(II)) ions from water using crosslinked polyvinyl alcohol-acrylamide P(VA-AAm) hydrogel
Ahmed Neamah Thamer, Alaa S. Alwan, Nawras A. Alwan, Layth S. Jasim, Maryam Batool
Abstract
Herein, a crosslinked hydrogel P(VA-AAm) was prepared using free radical polymerisation method for exploring its efficiency towards removal of Cr(III) and Pb(II) from their solutions. The characterisation analysis of prepared hydrogel was carried out by Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-Ray Analysis (EDX), Fourier Transform Infrared (FTIR) spectroscopy, Transmission Electron Microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis, X-ray Diffraction (XRD), swelling ratio measurement, and point of zero charge (PZC) determination. Experimental parameters affecting adsorption process as pH, contact time, initial ion concentration, and presence of competing ions, were studied. Results showed that nanocomposite exhibited a high swelling ratio of 6190% with a point of zero charge of 5. Optimal adsorption conditions were determined to be as 0.03 g adsorbent weight, pH of 6, and a contact time of 60 min and 120 min (for Cr(III) and Pb(II) ions, respectively) for metal ion concentration of 400 mg/L at 20°C. The adsorption capacities for Cr(III) and Pb(II) were observed to be 475.47 mg/g and 449.08 mg/g, from non-linear Langmuir model, respectively. Furthermore, the adsorption behaviour was well-described by Langmuir, Freundlich, and Temkin isotherm models, with pseudo-second-order kinetic model provided the best fit. The negative values of ΔG confirmed that the adsorption process was spontaneous, while the positive value ΔH confirmed endothermic nature of process. The P(VA-AAm) hydrogel exhibited good reactivation efficiency over 5 cycles for both Pb(II) and Cr(III), with Pb(II) showing better retention (78% adsorption in fifth cycle) compared to Cr(III) (65%). Overall, the study highlights crosslinked hydrogel P(VA-AAm) as an efficient adsorbent for removal of Cr(III) and Pb(II) ions from aqueous solutions.