Adsorption of azo dyes by a novel bio-nanocomposite based on whey protein nanofibrils and nano-clay: Equilibrium isotherm and kinetic modeling

[Display omitted] •We produced an easy-separable bio-nanocomposite using whey nanofibrils and MMT, with high adsorption capacity.•Nanofibrils help disperse MMT particles uniformly in the WP matrix.•The adsorbent’s performance was compared with the adsorbents in absence of MMT and nanofibrils.•This composite adsorbs cationic, anionic, direct and reactive azo dyes with different kinetics.•Adsorption isotherms and kinetics are studied in detail. Excessive discharge of synthetic azo dyes into the aquatic ecosystem is a global concern. Here, we develop a green approach to remediate dye pollutants by fabricating an easily separable bio-nanocomposite, based on nanofibrils from whey protein concentrate together with montmorillonite. The nanocomposite was characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and surface area analysis. Nanofibrils lead to a uniform dispersion of montmorillonite in the matrix and also reinforce the nanocomposite. The adsorption efficacy was monitored using cationic (Chrysoidine-G, Bismarck brown-R), reactive (reactive black-5, reactive orange-16), acidic (acid red-88, acid red-114) and direct (direct violet-51, Congo red) dyes. The nanocomposite adsorbed different dyes with different kinetics, cationic dyes quicker and reactive dyes slower. Greater than 93% of Chrysoidine-G was adsorbed over a wide range of dye concentration and pH. Acidic pH and higher temperature are more favorable for the process. Equilibrium adsorption data were reasonably fitted with a linear (Nernst) isotherm model indicating the existence of an unlimited number of adsorption sites which is consistent with the high experimental uptake of 731 mg/g. Kinetic data were well-described by pseudo-second-order and intra-particle diffusion models. We conclude that this environmentally friendly nanocomposite has good potential for use in wastewater treatment and related purposes.