Systematic optimization of alginate gelation parameters in the synthesis of oleaster-based magnetic granules for enhanced binary cationic dye removal

Abstract

In this study, activated carbon (AC) derived from oleaster seeds was modified with iron nanoparticles (Fe-AC) and granulated using sodium alginate (NaAlg) via the wet gelation method to develop efficient granular adsorbents. The effects of various parameters, such as mixture pH, type and concentration of the cross-linking solution, initial mass ratio of NaAlg to Fe-AC, drying method, and final granule size were investigated in terms of both the physical appearance of the granules and their performance in removing crystal violet (CV) and methylene blue (MB) dyes. The selected granules were prepared under optimal conditions: a pH of 7, an iron (III) chloride cross-linking solution with a concentration of 2 % w/v, an initial alginate to Fe-AC ratio of 1:4, airdrying, and an initial granule size of 1 mm. Analytical techniques including FTIR, SEM-EDX, and BET confirmed the successful incorporation of iron nanoparticles within the adsorbent framework and revealed a well-developed porous structure with a specific surface area of 47.306 m2/g. Under these optimal conditions, the highest removal efficiencies achieved were 96.29 % for CV and 94.26 % for MB, with maximum adsorption capacities of 14.2857 mg/g for CV (single system) and 9.7370 mg/g for the binary CV/MB system, according to the Langmuir isotherm. These results demonstrate that the synthesized Fe-AC/NaAlg granules combine high adsorption efficiency with ease of separation, mechanical stability, and reusability, making them a promising and scalable adsorbent for industrial wastewater treatment, particularly in textile and dyeing applications where removal of cationic dyes is critical.