Design and DFT-based optimization of a GO-containing guar gum hydrogel for dye removal

Abstract

A superabsorbent hydrogel composed of graphene oxide (GO), guar Gum (GG), and resorcinol (Res), cross-linked by lanthanum nitrate trihydrate (La³⁺) ions, was synthesized through the solvent rotation method. All the components involved in the formation of the hydrogel complex were optimized separately using the Gaussian16W/GaussView6.1 software package and density functional theory (DFT), followed by the optimization of the complex and the target dye crystal violet (CV). The Stuttgart–Dresden (SDD) basis set and the WB97XD functional were used for the GO–GG–Res–La(III) complex, and for the rest of the computations, the combination of B3LYP functional and 6-311G(d,p) basis set was used. To correlate the adsorption of CV with the designed hydrogel, the key electronic structures and the covalent and non-covalent factors responsible for the adsorbent behaviour were examined. Moreover, molecular orbital energies, electronegativity, ionization energy, electron affinity, and other global reactive descriptors were explained in the context of the aim of this study. Experimentally, the prepared hydrogel exhibited significant swelling behaviours in water across solutions of varying ionic strengths and pH environments for both GO and non-GO beads. The equilibrium elimination capacity of the crystal violet (CV) dye increased from 134.88 mg g⁻¹ to 234.32 mg g⁻¹ in deionized water and from 226.66 mg g⁻¹ to 241.09 mg g⁻¹ at pH 9, both with and without graphene oxide (GO), respectively. Various kinetic adsorption isotherms were also applied. The enhanced dye removal efficacy of CV supported by the DFT integrated experimental studies, indicates the potential of these hydrogel beads in wastewater treatment.