Methylene Blue and Lead(II) Removal via Degradable Interpenetrating Network Hydrogels

A novel degradable interpenetrating network hydrogel based on poly(vinyl alcohol) (PVA), potassium humate (KHA), and guar gum (GG) was successfully prepared via aqueous solution polymerization for the efficient adsorption and removal of methylene blue (MB) dye and Pb(II). The PVA/KHA/GG adsorbent was characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction, thermogravimetric analysis, zeta analysis, and scanning electron microscopy. Adsorption kinetics, pseudo-second-order equations, and activation energy (Ea) calculations illustrated that there was physisorption and chemisorption of both MB and Pb(II). Moreover, batch adsorption results were best suited to the Langmuir model; the maximum adsorption capacity (qm) for MB and Pb(II) at optimum conditions was 1166.73 and 625.21 mg/g, respectively. The results of thermodynamic analysis demonstrated that the adsorption of MB and Pb(II) onto PVA/KHA/GG was an endothermic and spontaneous process, driven by an increase in entropy. Furthermore, both FT-IR and X-ray photoelectron spectroscopy studies confirmed that the possible mechanism by which Pb(II) was removed mainly occurred via chemisorption of the anionic groups, whereas the adsorption of MB took place via physisorption through H-bonding, electrostatic interactions, and π–π stacking. Note that the adsorbent can be readily regenerated and efficiently reused for several cycles.