Efficient dye adsorption by water-based magnetic fluid-Spirulina platensis hybrid: synthesis and application

The persistent challenge of treating different kinds of dye wastewaters has driven the development of innovative biosorption technologies. Unlike conventional bio-adsorbents, the novel magnetic functionalization enabled rapid solid-liquid separation under external magnetic fields, overcoming a critical bottleneck in practical applications. This study presented a breakthrough approach by engineering a magnetically responsive hybrid biosorbent through the nanoscale integration of Fe₃O₄ nanoparticles with Spirulina platensis (Sp) microalgae. The synthesized magnetic Spirulina platensis (M-Sp) demonstrated unprecedented dual-affinity, achieving removal of both anionic (congo red; CR) and cationic (methylene blue; MB) dyes. Results showed that M-Sp achieved the highest removal efficiency under the conditions: 4 mL magnetic fluid/2.0 g algae, 0.8 g/L adsorbent dosage, pH 3 for CR (anionic), and pH 9 for MB (cationic). Through advanced characterization and mechanistic studies, the unique binding mechanisms were revealed: CR followed Freundlich multilayer adsorption while MB exhibited Langmuir monolayer behavior, mediated by specific interactions with functional groups on the hybrid matrix. The adsorption capacities could reach 101.78 mg/g (CR) and 218.57 mg/g (MB). This work not only provided a recyclable solution for different kinds of dye pollutants but also opened new avenues for designing smart biosorbents through controlled nanomaterial-biology integration.