Microwave-assisted synthesis of hybrid materials "Posidonia oceanica-copper nanoparticles" for wastewater purification

Synthetic dyes released by the textile and related industries are a major source of water pollution due to their persistence, toxicity, and resistance to conventional treatment methods The development of sustainable and efficient biosorbents therefore represents a key challenge in wastewater treatment. In this study, dried Posidonia Oceanica (P.O) biomass was used for the first time in the microwave-assisted synthesis of hybrid materials functionalized with copper (1 %, 2 %, and 4 % Cu²⁺), offering a rapid, energy-efficient, and solvent-free alternative to conventional methods. This technique enhances chemical yield and reaction control while minimizing environmental impact. The raw and modified P.O fibers were characterized using zero point of charge (pH_pzc) and Boehm titration to determine surface acidity/basicity. Further structural and morphological analyses were conducted using infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS), confirming the formation of Cu–OH, Cu–O–C, and Cu(COOH)₂ bonds and an increase in basic surface sites. The materials' adsorption performance was assessed by removing methyl orange (MO) from aqueous solutions. Biosorption capacity increased from 0.768 mg g⁻¹ for raw P.O to 0.981 mg g⁻¹ for P.O-4 % Cu²⁺. Important factors influencing adsorption were examined. Prewashing with 0.01 M EDTA reduced NaCl interference, thereby enhancing MO removal. Increasing the adsorbent mass improved dye uptake; while higher temperature slightly improved adsorption, indicating a slightly endothermic process. Kinetic modeling using pseudo-first-order, pseudo-second-order, and Brouers–Sotolongo (n = 2) models indicated that the Brouers–Sotolongo model best described the process, with improved retention rates and homogeneity (α = 1; ζc = 2.51 min). Recyclability tests demonstrated that P.O-4 % Cu²⁺ retained 92 % of its adsorption capacity after three cycles when regenerated with HCl + NaCl, highlighting its potential for reuse. These results demonstrate that microwave-assisted Cu²⁺ modification significantly enhances the biosorption properties of P.O fibers, making them promising, sustainable biosorbents for dye removal in wastewater treatment applications.