Synthesis and effective dispersion of Fe3O4 NPs on alfalfa as a green nanoadsorbent for the removal of cationic dyes from aqueous solutions

Abstract

ABSTRACT In this paper, Fe3O4 magnetic nanoparticles (Fe3O4 NPs) were successfully synthesised and dispersed on alfalfa to prepare Fe3O4/alfalfa nanocomposite for cationic dye removal from aqueous solutions. Characterisation of Fe3O4/alfalfa nanocomposite using FT-IR, FESEM, and EDX analyses showed that the Fe3O4 NPs were excellently dispersed on alfalfa. The results display that the Fe3O4/alfalfa as a green adsorbent have high removal ability for toxic cationic dyes, such as malachite green (MG) and crystal violet (CV). For Fe3O4-alfalfa, the average particle size of nanoparticles on alfalfa (around 20–30 nm) has decreased compared with alone Fe3O4. The experiments showed that the adsorption of dyes onto Fe3O4-alfalfa better described with pseudo-second-order kinetic and Freundlich isotherm models, suggesting the surface heterogeneity of the Fe3O4/alfalfa. Furthermore, Fe3O4-alfalfa with adsorption capacity of 62.68 mgg−1 and 55.12 mgg−1 towards MG and CV, respectively, was comparable with those of the reported adsorbents. The results indicated that the adsorption of both dyes onto Fe3O4-alfalfa was thermodynamically spontaneous and more favourable at lower temperatures. The results also confirmed that the removal of MG and CV by Fe3O4-alfalfa were remarkable after reusing five times. Therefore, the Fe3O4-alfalfa as a green and low-cost nanoadsorbent with an easy synthesis route could be used for purification of water and wastewater contaminated by pollutants.