Charge-selective magnetic bionanosorbents for multi-dye wastewater treatment: performance, regeneration and ecotoxicity assessment
Sofia F. Soares, Bárbara Pereira, Joana Santos, Tito Trindade, Ângela Barreto, Vera L. Maria, Ana L. Daniel‐da‐Silva
Abstract
The discharge of synthetic dyes from industrial activities poses significant environmental and health risks due to their toxicity, persistence, and resistance to conventional wastewater treatments. To address this issue, this study presents a dual nanosorbent strategy employing magnetic bionanosorbents with charge-selective properties, specifically designed for the simultaneous removal of cationic and anionic dyes from aqueous solutions. Core@shell nanostructures were synthesized by coating magnetite (Fe 3 O 4 ) nanoparticles with trimethyl chitosan (Fe 3 O 4 @TMC, cationic) or κ-carrageenan (Fe 3 O 4 @κCRG, anionic). The resulting materials efficiently and selectively adsorbed oppositely charged dyes, achieving maximum adsorption capacities of 605.8 mg/g (methylene blue, MB) and 671.5 mg/g (malachite green, MG) for Fe 3 O 4 @κCRG, and 316.6 mg/g (rose Bengal, RB) and 510.2 mg/g (remazol brilliant blue R, RBBR) for Fe 3 O 4 @TMC. Adsorption kinetics followed pseudo-second-order behavior (MB and MG), indicative of chemisorption, and concentration-dependent transitions from physical to chemical adsorption (RB and RBBR), described by pseudo-first-order and Elovich models. Equilibrium data best fit the Langmuir model for MB, MG, and RB, while RBBR adsorption showed a more complex mechanism described by both Langmuir and Sips models. Both nanosorbents demonstrated excellent reusability over five adsorption–desorption cycles, with removal efficiencies above 95 % for most dyes. Despite a moderate decrease in efficiency in real wastewater matrices, the nanosorbents effectively removed dyes in single- and multi-pollutant scenarios. Preliminary ecotoxicity assessments using zebrafish embryos confirmed their environmental safety at relevant exposure levels. This work highlights the potential of these magnetic bionanosorbents as efficient, reusable, and environmentally friendly alternatives for complex wastewater treatment applications, though further studies addressing regeneration optimization and fate of used adsorbents are recommended before large-scale implementation.