Abstract
A porous semi-interpenetrating network (semi-IPN) hydrogel adsorbent with excellent adsorption properties and removal efficiency towards Pb(II) was prepared by a facile grafting polymerization reaction in aqueous medium using natural biopolymer sodium alginate (SA) as the main chains, sodium acrylate (NaA) as the monomers, and poly(vinyl alcohol) (PVA) as the semi-IPN component. FTIR, TGA and SEM analyses confirm that NaA monomers were grafted onto the macromolecular chains of SA, and PVA chains were interpenetrated and entangled with the crosslinked network. The incorporation of PVA facilitates to form pores on the surface of hydrogel adsorbent. The semi-IPN hydrogel containing 2 wt% of PVA exhibits high adsorption capacity and fast adsorption rate for Pb(II). The best adsorption capacity reaches 784.97 mg/g, and the optimal removal rate reaches 98.39% (adsorbent dosage, 2 g/L). In addition, the incorporation of PVA improved the gel strength of hydrogel, and the storage modulus of hydrogel increased by 19.4% after incorporating 2 wt% of PVA. The increase of gel strength facilitates to improve the reusability of hydrogel. After 5 times of regeneration, the adsorption capacity of SA-g-PNaA decreased by 23.2%, while the adsorption capacity of semi-IPN hydrogel only decreased by 10.8%. The adsorption kinetics of the hydrogel in the initial stage (the moment when the adsorbent contacts solution) and the second stage are fitted by segmentation. It is intriguing that the adsorption kinetics fits well with both pseudo-second-order kinetic model and pseudo-first-order model before 60 s, while only fits well with pseudo-second-order adsorption model in the whole adsorption process. The chemical complexing adsorption mainly contribute to the efficient capturing of Pb(II).
Highlights
In recent years, the rapid development of lead-zinc metallurgy, electroplating, batteries and other industries has discharged a large amount of toxic Pb(II)-containing wastewater, and the resulting water pollution problems become more and more serious, threatening people’s health, survival and development
The new absorption peak at 1,707 cm−1 were observed in the Fourier transform infrared spectra (FTIR) spectra of the SAg-PNaA/poly(vinyl alcohol) (PVA) hydrogel adsorbent (Figures 1C–F), and the C-OH stretching vibration peak of Sodium alginate (SA) at 1,031 cm−1 significantly weakened and shifted to 1,035–1,037 cm−1, indicating the C-OH groups of SA participate in grafting polymerization reaction, and the PNaA chains were grafted onto the SA molecular chains (Wang et al, 2013a)
The pseudo-second-order kinetic constant of SA-g-PNaA is 3.953 mg/g·s, but increased to 5.947 mg/g·s for Semi-IPN2. These results indicate that the introduction of PVA may clearly increase the adsorption rate of the hydrogel, which is favorable to the practical application of hydrogel
Summary
The rapid development of lead-zinc metallurgy, electroplating, batteries and other industries has discharged a large amount of toxic Pb(II)-containing wastewater, and the resulting water pollution problems become more and more serious, threatening people’s health, survival and development. Due to the superior performance and eco-friendly advantages of SA, it has been widely used to prepare various polymer packing films (Saravanakumar et al, 2020; Zhang et al, 2020), drug-delivery vehicles (Mishra et al, 2021), antibacterial materials (Dwivedi et al, 2020), carrier of catalyst (Khan et al, 2020), superabsorbent hydrogel (Kassem et al, 2020), coatings (Fang et al, 2021) and adsorbent (Wang et al, 2013a; Gao et al, 2020). In light of the excellent advantages of SA and PVA, the semi-IPN hydrogel with improved gel strength and adsorption performance will be formed by combination of SA-g-PNaA and PVA via grafting polymerization reaction in water medium. The averages of three test results were reported in this paper
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