A novel alginate/fruit waste/Fe3O4 hydrogel biobeads for highly efficient removal of methylene blue from aqueous solution

Abstract Today, for effective wastewater management, water resources need to be treated in an environmentally friendly, cost-effective and less complex manner. It is very important to develop alternative low-cost, high adsorption capacity adsorbents based on sustainable materials. For this purpose, glutaraldehyde cross-linked alginate-coated magnetic orange peel composite beads (ALG-Op@Fe 3 O 4 ) and nectarine peel composite beads (ALG-Np@Fe 3 O 4 ) were synthesized using fruit waste as an alternative adsorbent and alginate as a biopolymer. The dropping and pH precipitation method was used to alginate containing hydrogel beads n-Fe 3 O 4 , and fruit waste with a well-defined structure. FTIR, SEM, EDX-mapping and XRD analyses of synthesized new biobeads were performed. The adsorption effects of experimental parameters such as pH (3–9), adsorbent dosage (1–8 g/L), time (5–360 min), temperature (25–55 °C) and dye concentration (10–300 ppm) were investigated. Langmuir, Freundlich, Scarthard, D–R and Temkin adsorption isotherm models were applied for the adsorption of methylene blue onto newly synthesized adsorbents through equilibrium studies. Kinetic constants were determined by pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models. The adsorption process was found to fit better with Langmuir isotherm model, and adsorption capacity of 188.7 mgg −1 and 100.0 mgg −1 was obtained for ALG-Op@Fe 3 O 4 and ALG-Np@Fe 3 O 4 , respectively. The adsorption process followed the pseudo-second-order kinetic model, and thermodynamic studies revealed that it was an exothermic and spontaneous process. Waste fruit peels have been shown to be an effective and alternative material when compared to different adsorbents in the removal of methylene blue molecules from aqueous media due to reasons such as high removal capacity, easy availability, low cost, usability, recyclability and the fact that alginate as a biopolymer does not harm the environment. Graphical abstract