Integrated Experimental and DFT/MD Investigation of Rhodamine B Adsorption Kinetics onto Pectin/Poly(NIPAm-co-Acrylic Acid) Hydrogel: Mechanism, Diffusion Pathways, and Computational Insights

Abbas, Sajid S.; Sameer, Layth S

doi:10.29350/qjps.2026.171440.1106

Integrated Experimental and DFT/MD Investigation of Rhodamine B Adsorption Kinetics onto Pectin/Poly(NIPAm-co-Acrylic Acid) Hydrogel: Mechanism, Diffusion Pathways, and Computational Insights

10.29350/qjps.2026.171440.1106

Volume 31, Special
Summer 2026

Document Type : IAAQC Conference

Authors

Sajid S. Abbas ¹

Layth S sameer ²

¹ Ministry of Education, General Directorate of Al-Qadisiyah Education, Diwaniyah, Iraq

² Department of Chemistry, College of Education, University of Al-Qadisiyah, Diwaniyah, Iraq

Abstract

This study reports an integrated experimental and computational kinetic investigation of rhodamine B (Rh.B.) adsorption onto a pectin/poly(N-isopropylacrylamide-co-acrylic acid) hydrogel synthesized via free-radical copolymerization. The same hydrogel reported in our companion equilibrium study was used to ensure mechanistic consistency. Adsorption kinetics were probed over 1–240 min at C₀ = 50–500 mg/L (Configuration A: 0.008 g hydrogel in 10 mL, pH 7, 25 °C, 120 rpm; n = 3) and were modeled using pseudo-first-order (PFO), pseudo-second-order (PSO), Elovich, intraparticle (Weber–Morris), and Boyd film/particle diffusion equations. Equilibrium was established within 60–90 min, with PSO providing the best correlation (R² = 0.9988; qe,calc = 478.21 mg/g vs. qe,exp = 466.39 mg/g; k₂ = 3.16 × 10⁻⁴ g·mg⁻¹·min⁻¹; initial sorption rate h = 72.3 mg·g⁻¹·min⁻¹). Weber–Morris analysis revealed two diffusion regimes (kid,1 = 22.4, kid,2 = 1.18 mg·g⁻¹·min⁻⁰·⁵) with non-zero intercepts confirming a mixed boundary-layer/intraparticle mechanism. Boyd plots were linear and offset from the origin, indicating that external film diffusion governs the early stage while particle diffusion dominates the later stage. The Arrhenius activation energy (Ea = 24.7 kJ/mol) and the negative ΔH° (−20.27 kJ/mol) are consistent with a mixed physisorption–chemisorption pathway. =

Keywords

Rhodamine B

Pectin hydrogel

Pseudo-second-order

Boyd diffusion

DFT binding energy