Crystal violet removal by sodium alginate-g-polyacrylamide/ hydroxyapatite/ Cu-Fe LDH nanocomposite
Alireza Massrour, Seyed Jamaleddin Peighambardoust, Mahsa Foroughi, Rauf Foroutan, Bahman Ramavandi
Abstract
The removal of dyes from wastewater remains a significant environmental challenge due to their toxicity, persistence, and potential health risks. This study presents the development of a novel sodium alginate-g-poly(acrylamide) (SAl-g-PAA) hydrogel reinforced with hydroxyapatite (HAp) and Cu-Fe layered double hydroxide (LDH) to enhance the adsorption of crystal violet (CV) from aqueous media. BET analysis showed that Hydrogel/HAp/Cu-Fe LDH has a surface area of 134.53 m²/g, confirming its mesoporous structure, while XRD analysis revealed both crystalline and amorphous phases, ensuring effective adsorption performance. The incorporation of HAp and Cu-Fe LDH significantly increased the hydrogel’s surface area and adsorption efficiency, achieving maximum removal rates of 98.51 %, 98.46 %, and 98.72 % for hydrogel, hydrogel/HAp, and hydrogel/HAp/Cu-Fe LDH, respectively, under optimized conditions (pH 8, 10 mg/L CV, 80 min time). Adsorption kinetics followed a pseudo-second-order model, and equilibrium data were best described by the Freundlich isotherm, indicating multilayer adsorption. Thermodynamic analysis confirmed that the process is spontaneous and endothermic (ΔG°: −5.298 to −12.754 kJ/mol), highlighting the composite’s strong affinity for CV adsorption. The hydrogel/HAp/Cu-Fe LDH composite demonstrated exceptional reusability, maintaining 94 % efficiency after eight regeneration cycles. This study demonstrates that CV dye adsorption by Hydrogel/HAp/Cu-Fe LDH and Cu-Al LDH occurs through electrostatic interactions, hydrogen bonding, and π-π interactions, as validated by FTIR and BET analyses. Compared to conventional adsorbents, the newly developed hydrogel system offers superior adsorption capacity, mechanical stability, and practical applicability for wastewater treatment. These findings underscore the potential of hydrogel-based nanocomposites as efficient, sustainable, and cost-effective solutions for dye-contaminated water remediation. • Hydrogel/HAp/Cu-Fe LDH removed 98.7 % crystal violet (CV) at pH 8, 10 mg/L CV, 80 min. • BET analysis showed a 134 m²/g surface area, ensuring high adsorption capacity. • The process followed a pseudo-second-order model with multilayer sorption. • Adsorption was spontaneous, endothermic with ΔG° from −5.29 to −12.75 kJ/mol. • The composite kept 94 % efficiency after 8 cycles, showing high stability.