Synthesis, characterization, swelling studies and applications of poly (acrylic acid-co-acrylamide) in adsorption: Experimental, COMSOL and Hartree-Fock studies

Paraquat is a widely used herbicide that poses significant environmental and health risks due to its persistence in water. In this study, a bulk hydrogel composed of acrylic acid and acrylamide was synthesized via free radical polymerization to remove paraquat from aqueous solutions. The hydrogel exhibited a swelling ratio of 494.08 % over 3060 min and achieved an 83.17 % water content within 2430 min. One of the main challenges was maintaining the mechanical stability of the hydrogel at high swelling ratios, which was addressed by optimizing the monomer ratio and crosslinking density. Another challenge involved accurately modeling the molecular-level adsorption behavior of paraquat due to its complex electrostatic interactions. Its structural and chemical properties were characterized using ultraviolet–visible spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Adsorption experiments demonstrated that the hydrogel effectively removed 93 % of paraquat within 60 min, achieving a maximum adsorption capacity of 111.69 mg per gram after 150 min. The adsorption data fit well with the Freundlich isotherm model, suggesting multilayer adsorption on a heterogeneous surface, while kinetic analysis indicated pseudo-second-order behavior. To complement the experimental findings, computational modeling using Hartree-Fock methods and Multiphysics simulations provided insight into the molecular interactions, swelling behavior, and diffusion mechanisms. The combined approach demonstrates the hydrogel's potential as an efficient and scalable material for paraquat removal in water treatment applications.