Fibrous keratin protein bio micro structure for efficient removal of hazardous dye waste from water: Surface charge mediated interfaces for multiple adsorption desorption cycles

Abstract

For the first time we report fabrication of a keratin protein based bio material for efficient removal of hazardous dye waste from water using merino wool fibers. Surface hydrolysed keratin protein fibers were prepared by subjecting merino wool fibers to controlled hydrolysis. During the hydrolysis the cuticle cells which sheath the hierarchical microstructure of the wool fibers were denatured. This has resulted in exposing ortho cortex of the fibers with comparatively higher degree of free amine and other surface functional groups which were confirmed by the SEM, EDX, AFM, FT-IR, NMR and CHNS analysis. The material showed exceptional adsorption capacities for carcinogenic Rhodamine B dye in the presence of acetic acid. Under optimized conditions, the surface hydrolysed keratin protein fibers showed ~95% of dye adsorption with maximum adsorption capacity of 294 mg/g at 298 K, in the presence of 3.5% acetic acid. This is the highest reported for the Rodhamine dye adsorption at similar conditions using other dye adsorption methods. Adsorption isotherm studies and Scatchard analysis of the isotherms were carried out to understand the binding mechanism of the dye molecules to the keratin protein fiber material. The main chemical attractions were found to be due to the free amine and carboxylic functionalities presence in the hydrolysed wool fiber material. Also it was observed to have charge induced adsorption and desorption which were driven mainly due to the protonation and deprotonation of the amine groups present in the keratin protein fibers. It is also confirmed that keratin protein fiber can be used for multiple times for adsorption of the dye molecules from an aqueous medium. Combining the high adsorption capacity and recyclability, surface hydrolysed keratin protein fibers prepared from merino wool can be a promising bio material to remove Rhodamine B dye from an aqueous medium modulated by acetic acid.