Comparative study on the novel bare and immobilized forms of phyco-synthesized Ag-Fe bimetallic nanoparticles for bioremediation of aquaculture wastewater

Abstract

Abstract Green synthesized Ag-Fe bimetallic nanoparticles (Ag-FeBNPs) offer a promising candidate for heavy metal removal thanks to their exceptional properties, efficiency in adsorption processes, stability, enhanced catalytic activity, and eco-friendliness. The current work uses the red alga; Laurencia Papillosa for a novel synthesis of the Ag-FeBNPs, which has been prepared in two different forms; bare and immobilized to test the efficiency of the Ag-FeBNPs at the first stage and to compare the potentiality of both forms for the bioremediation process. This study introduces a novel bio-inspired synthesis route using L. Papillosa , which has not been previously reported for Ag-FeBNPs, highlighting the distinctive phycochemical reduction mechanism as a key element of novelty. The optimal parameters for this bimetallic synthesis were established via the central composite design (CCD), which set the pH at 10 and employed 10.5 g of algae/100 mL water for 95 min. The alginate beads were used to immobilize the optimized Ag-FeBNPs (Ag-FeBNPs@Alg beads) as a strategy to mitigate the potential toxicity of bare nanoparticles. Bare and immobilized phyco-synthesized Ag-FeBNPs were investigated for Fe and Zn removal from aquaculture wastewater. Results indicated significant removal ratios for Fe and Zn with 94.8% and 76.0% when using the bare Ag-FeBNPs and 78.0% and 45.5% when using Ag-FeBNPs@Alg beads, respectively. Qualitative observations further revealed improved particle dispersion, high adsorption affinity, and enhanced surface functional group interactions in the bare form, whereas the immobilized form showed greater operational handling, safety, and reusability. Various characterization approaches, including Scanning Electron Microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy, were employed to confirm the synthesis of Ag-FeBNPs forms and their role in metal removal. The results proved that Ag-FeBNPs@Alg beads are simply prepared, practically utilized, and relatively low in cost. These characteristics reveal their potential as a promising adsorbent for heavy metals removal from wastewater not only at small or bench-scale but also with potential for large-scale and commercial applications in aquaculture and industrial wastewater treatment systems. Graphical abstract