Cost-efficient bentonite-based polyvinyl alcohol hydrogels as an adsorbent of paracetamol, methylene blue, and lead (II)

Hydrogels have emerged as a promising solution for water treatment applications due to their efficient and eco-friendly adsorption properties. This study investigates polyvinyl alcohol (PVA)-based hydrogels modified with various clays, including raw (R) and purified bentonite (CP and UP) and organo-montmorillonite (S), for the removal of methylene blue (MB), lead (II), and paracetamol from water. PVA-based composite hydrogels with 5 wt% PVA and 0.25–3 wt% additive were synthesized via the freeze-thaw method (12-h freezing and 2-h thawing, three cycles). The effects of weight percentage, purity, purification procedures, and surface functional groups of additives were examined by water adsorption, gel density, gel percentage, compressive strength, porosity percentage, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV–Vis), atomic absorption spectrometry (AAS), and scanning electron microscopy (SEM) analysis. The results indicate that the composite hydrogel containing 5 wt% PVA and 1 wt% purified bentonite (CP) exhibited the highest MB adsorption (nearly 100% at 50 ppm and 200 ppm) and enhanced lead (II) adsorption by approximately 6.5 times compared to PVA hydrogel without additives. Furthermore, the composite containing 5 wt% PVA and 1 wt% organo-montmorillonite demonstrated superior adsorption efficiency for paracetamol compared to other composites. In this composite adsorption efficiency is almost 14.5% while the adsorption efficiency of PVA hydrogel without any additives is nearly zero. Isotherm and kinetic analyses indicated that MB and Pb(II) adsorption followed the Freundlich and Langmuir models, respectively, with both fitting the pseudo-second-order kinetic model. Despite reduced efficiency after regeneration, P5CP1 showed promising adsorption performance for dye and heavy metal removal.