Wool keratin fiber, one of the earliest natural fibers used by human beings, is considered an important raw material in the textile industry because of its excellent mechanical and thermal properties. A great quantity of short fibers and crude fibers are discarded during wool weaving every year, and a mass of waste wool keratin textile fibers are abandoned in our daily life; this not only causes a waste of keratin resources but also pollutes the environment. Because about 50 wt % of these waste wool fibers are made of keratin, a usable protein, they have been regarded a renewable resource worthy of a better study of the recycling of waste wool fibers for effective utilization. Keratin molecules, which are not dissolved under normal conditions, are highly crosslinked, three-dimensional stable structures with disulfide bonds, hydrogen bonds, salt bonds, and other bonds. Therefore, the dissolution procedure of keratin is the basis and premise of using these renewable resources. The key step of the preparation of a keratin solution is to make the bonds rupture; this provides crosslink between the keratin macromolecules. At present, there are several methods for obtaining wool keratin solutions, such as the oxidation method, the reduction method, and ionic liquids. Yu and Fan reported that anisotropic cortical cells could be extracted from waste wool fibers by formic acid ultrasonic treatment and could be successively included in different proportions in a chitosan matrix to make film-forming composites suitable for film casting and filament spinning. Among all of the methods listed previously, ionic liquids, which can also be called room temperature molten salts and are typically composed of organic cations and large anions, are quite unique for their low volatility, wide liquid range, good thermal stability, strong solvent power for organic and inorganic compounds, high ionic conductivity, and wide electrochemical window. Because of these special structures compared to the traditional molecular solvents, ionic liquids as solvents for the dissolution of natural polymer materials (e.g., cellulose and silk protein) and the preparation of nanoparticles, have exhibited promising applications in materials science.[6-8] Researchers have used 1-allyl-3-methylimidazolium chloride ([AMIM]+Cl−) and 1-Butyl-3-methylimidazolium Chloride [BMIM]+Cl− as solvents to dissolve wool fabric and have measured the properties of regenerated films.
Indium tin oxide (ITO) is receiving a great deal of attention because of its outstanding optical and electrical properties. ITO is the most widely used transparent conducting oxide material for its excellent characteristics in conductivity and optical transparency and its good surface features.[10, 11] Thus, it has a wide variety of applications, including flat panel displays, functional glass, and solar cells. Several synthesis and processing methods for making ITO nanostructures have been reported. One of the approaches is based on thin-film deposition; another uses solution-based synthesis. ITO can be fabricated in the form of thin films with various techniques, such as physical and chemical vapor deposition, which are quite cost intensive. Solution-based approaches, including solvothermal synthesis and the coprecipitation method, have gained more popularity over the deposition approach. Kanga et al. reported that ITO nanospheres of various sizes can be synthesized by the selective etching of ITO thin films with diluted HCl solution as the etchant. Moreover, the sizes of the ITO nanospheres can be readily controlled by variation of the thicknesses of the ITO films. Ding et al. synthesized nanoscale ITO particles with a distribution of particle size of 30–90 nm by liquid-phase coprecipitation method under given conditions with solutions of indium chloride, tin chloride, ammonia, and two kinds of surfactants as dispersants. In the consideration of a fast and inexpensive fabrication method, the wet-chemical deposition of ITO nanoparticles as an alternating approach should be preferred.
Although many successes have been focused on the optoelectrical properties of ITO fabricated on glass or on plastic foil, little work has been done to discuss the properties of its composite films prepared on other substrates. In this study, a functional composite of wool keratin and nano-ITO was successfully prepared by a new and simple method. The process involved the following steps: (1) dissolving the wool keratin fibers with a new type of green solvent, ionic liquids; (2) adding the ITO powder prepared by the coprecipitation method into wool/ionic liquid solution, and finally (3) obtaining the composite material by its regeneration from a wool/ionic liquid solution. The structures and optoelectrical properties of the functional composite were also studied.