Fuller’s Earth–immobilized FeS nanoparticles for efficient adsorption of crystal violet in aqueous solution

Abstract

FeS@Fuller’s Earth (FeS@FE) was synthesized by borohydride reduction in presence of dithionite with a 10% w/w iron loading. FESEM analysis reveal immobilized FeS NPs (40–100 nm) on the surface of Fuller’s Earth with agglomeration. The presence of sulfur as confirmed from XPS and EDX analysis of FeS@FE. Batch adsorption study of FeS@FE for crystal violet (CV) dye adsorption in aqueous solution yielded an optimized adsorption at pH 8, adsorbent dose 0.1 g/L, with a removal of upto 80% of the dye from a 20 mg/L CV solution. The CV adsorption on FeS@FE followed a good non-linear fit for Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm with R² > 0.95. The maximum monolayer adsorption capacity of FeS@FE was found to be 601.2 mg/g for CV with a D-R Isotherm Free energy of 141.58 kJ/mol at optimum conditions of pH 8, 100 mg/L of CV, and 0.1 g/L of adsorbent dose. The non-linear kinetic fit for CV dye adsorption on FeS@FE fitted to the pseudo-second-order (PSO) and intraparticle diffusion (IPD) models, indicating a strong chemical interaction between CV and FeS@FE. The strong adsorption of CV using FeS@FE is attributed to the Fe-OOH surface formation by FeS immobilized on FE under alkaline conditions, leading to deprotonation and electrostatic adsorption of the dye.