Wool keratin as a novel, alternative, low-cost adsorbent rich in various –N and –S proteins for eliminating methylene blue from water

Natural polymers exhibit unique chemical and physical characteristics, which make them suitable for various industrial applications, including in the food, pharmaceutical, medical, environmental, and cosmetic industries. Sheep wool fibers, which consist mainly of keratin material, have been used as textile yarn for many years due to their interesting properties. In this study, we extracted keratin from sheep wool through alkaline hydrolysis and explored its potential applications, such as adsorption for water treatment. This method can transform waste wool into wealth, mitigating environmental pressure. To evaluate the effectiveness of wool keratin in eliminating methylene blue (MB) from water through adsorption, we optimized adsorption parameters, such as initial concentration (mg/L), t (min), and sorbent dosage (g/L). We also conducted Fourier transform-infrared spectroscopy and scanning electron microscopy analyses, as well as a pH_pzc analysis. The extraction of keratin from wool required a chemical transformation based on alkaline hydrolysis, which modified the wool structure by breaking the disulfide bridges and lower energy bonds without affecting the peptide bonds. The resulting keratin was rich in protein, particularly L-cysteine. Our research showed that the adsorption mechanisms of keratin are diverse and include hydrogen bonding and physical adsorption on the external surface of the adsorbent, as well as inner adsorption and adsorption in irregular and defective edges. The modeling of the kinetics and adsorption isotherms showed that we achieved specific, multilayer physicochemical adsorption. We successfully modeled the kinetics of MB adsorption using the pseudo-first-order rate equation (PFORE) and pseudo-second-order rate equation and obtained acceptable results with PFORE. This confirmed the mechanism of mixed adsorption (physical and chemical). In the concentration range of 0.5–250 mg/L, we found an adsorption capacity of 794.78 mg/g.