Synthesis of Poly(Acrylic Acid-co-Acrylamide) Hydrogel for Adsorptive Removal of Crystal Violet Dye from Aqueous Solution: Experimental Investigation Combined with a DFT/TD-DFT and Molecular Dynamics Study
DOI:
https://doi.org/10.64354/2kd8dd21Keywords:
Poly(acrylic acid-co-acrylamide); Hydrogel; Crystal violet; Adsorption; Langmuir isotherm; DFT calculations; TD-DFT; Molecular dynamics; NBO analysis; MEP.Abstract
The discharge of synthetic dyes from textile, paper and printing effluents continues to be one of the more troubling sources of water pollution, and finding affordable, easy-to-prepare adsorbents to deal with these contaminants remains a pressing problem. In the present study, a poly(acrylic acid-co-acrylamide) [P(AAc-co-AAm)] hydrogel was prepared by free-radical copolymerization using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as a thermal initiator. The resulting network was characterized using FT-IR and field-emission scanning electron microscopy, both of which confirmed the successful crosslinking and revealed a fairly open, sponge-like internal architecture. The hydrogel was then evaluated for its ability to remove crystal violet (CV) from aqueous media. The maximum adsorption capacity reached 312.5 mg g⁻¹ at pH 7 and 25 °C. The kinetic data were best described by the pseudo-second-order model (R² = 0.998), while the equilibrium data fit the Langmuir isotherm well. Thermodynamic parameters confirmed that the adsorption was spontaneous and mildly endothermic. DFT and TD-DFT calculations were performed at the B3LYP/6-311++G(d,p) level in the PCM water medium, including geometry optimization, frontier-orbital analysis, MEP mapping, theoretical UV-Vis and IR spectra, and Mulliken/NBO charge analysis. Classical MD simulations of the CV–polymer complex in explicit water were also carried out over 50 ns. The simulated UV-Vis spectrum (λmax ≈ 588 nm) reproduces the experimental absorption maximum very closely, and the MD-derived interaction energy (−38.2 kcal mol⁻¹) is in good agreement with the BSSE-corrected DFT value.
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