Batch biosorption experiments were carried out for the removal of malachite green (MG) from its aqueous solution using raw Sargassum swartzii biomass (RSSB) as biosorbent. The effect of various operating parameters was optimized for enhancing biosorption capacity. The biosorption capacity was found to increase with contact time and initial malachite green concentration. The biosorption of the dye was pH dependent and maximum uptake was observed at a pH of 10. The experimental data were analyzed using Langmuir, Freundlich, and Temkin equilibrium isotherm models. Langmuir isotherm (R² = 0.98) was found to fit the experimental data well. The biosorption kinetics of MG was found to follow pseudo-second-order kinetic model (R² = 0.967). The mechanistic study revealed that the biosorption of malachite onto RSSB was controlled by film diffusion. The characteristics of the RSSB biosorbent were studied using Fourier transform-infrared spectroscopy and scanning electron microscopy.

A novel nanoscale zero-valent iron-Sargassum swartzii (nZVI-SS) biocomposite was synthesized and evaluated for its ability to adsorb crystal violet (CV) from aqueous solutions. Involvement of various functional groups of the biosorbent in preferential adsorption of cationic dye was observed using Fourier transform infrared (FTIR) spectroscopy. Morphological changes occurring on the biocomposite materials were characterized using scanning electron microscopy (SEM). Significant increase (∼90%) in the biosorption of cationic dye was observed with gradual increase in pH of the medium from 3 to 12. The effect of biosorbent concentration, initial pH, temperature, agitation rate, adsorption time, and initial dye concentration was studied for the biosorption of CV using nZVI biocomposite. During the optimization study, maximum biosorption capacity was observed at pH of 8. At various initial CV concentrations (20–100 mg/L), attainment of batch sorption equilibrium was observed within 120 min of reaction time. The Langmuir isotherm model expressed high coefficient of determination (R² = 0.999). The maximum dye uptake of 200 mg/g was reported at pH 8. Kinetics and temperature profiles were evaluated and reported. Desorption study was carried out with 0.1 M HCl. Investigations proved that nZVI-SS is an excellent biosorbent for the sequestration of CV in aqueous media.