Sodium alginate-encapsulated nano-iron oxide coupled with copper-based MOFs (Cu-BTC@Alg/Fe 3 O 4 ): Versatile composites for eco-friendly and effective elimination of Rhodamine B dye in wastewater purification.

This study explores the effectiveness of Alginate-coated nano‑iron oxide combined with copper-based MOFs (Cu-BTC@Alg/Fe ₃ O ₄ ) composites for the sustainable and efficient removal of Rhodamine B (RhB) dye from wastewater through adsorption and photocatalysis. Utilizing various characterization techniques such as FTIR, XRD, SEM, and TEM, we confirmed the optimal synthesis of this composite. The composites exhibit a significant surface area of approximately 160 m ² g ^-1 , as revealed by BET analysis, resulting in an impressive adsorption capacity of 200 mg g ^-1 and a removal efficiency of 97 %. Moreover, their photocatalytic activity is highly effective, producing environmentally friendly degradation byproducts, thus underlining the sustainability of Cu-BTC@Alg/Fe ₃ O ₄ composites in dye removal applications. Our investigation delves into kinetics and thermodynamics, revealing a complex adsorption mechanism influenced by both chemisorption and physisorption. Notably, the adsorption kinetics indicate equilibrium attainment within 100 min across all initial concentrations, with the pseudo-second-order kinetic model fitting the data best (R ²  ≈ 0.999). Furthermore, adsorption isotherm models, including Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich, elucidate the adsorption behavior, with the Temkin and Dubinin-Radushkevich models showing superior accuracy compared to the Langmuir model (R ²  ≈ 0.98 and R ²  ≈ 0.96, respectively). Additionally, thermodynamic analysis reveals a negative Gibbs free energy value (-6.40 kJ mol ^-1 ), indicating the spontaneity of the adsorption process, along with positive enthalpy (+24.3 kJ mol ^-1 ) and entropy (+82.06 kJ mol ^-1  K) values, suggesting an endothermic and disorderly process at the interface. Our comprehensive investigation provides insights into the optimal conditions for RhB adsorption onto Cu-BTC@Alg/Fe ₃ O ₄ composites, highlighting their potential in wastewater treatment applications.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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