| Silkworm Silk, known as "queen of textile" in the history, is a natural protein fiber. Silk has light, smooth, soft texture, and the beautiful luster that other fibers can not be reach. For its comfortable hand-feel, moisture permeability and health care effect to human body, silk also has the reputation as "second skin of body".With the development of awareness of enhancement on the environment protection of modern society, the environment pollution in the production process of synthetic fibers has aroused great attention. Furthermore, as the crude oil, one of the most important raw materials of synthetic fibres, is running out in years to come, industry and consumer market prefer multifunctional natural, comfortable and healthy textile product to synthetic fibers. From mulberry planting and silkworm culture to filamentation, silk is not contaminated, that enables its increasing interest from consumers. Furthermore, more than 1.2 M tons of silkworm silks are produced around the world annually and the high production makes it a vital raw material in the textiles market.However, compared to other synthetic fabrics, silk fibroin fabric (SFF) still has its inherent disadvantages, such as wrinkle, deformation and even degradation caused by Microorganism, photo-induced aging and yellowish, that has been the main restrictions of market competitive activity. Without damaging the excellent properties of silk, combining silk with functional nano materials is an effective way to overcome its shortcomings and endow it completely new properties.Nano-scale TiO2, as a novel photocatalyst, and an anti-UV and photoelectric effect agent, has broad application in air purification, antibacterial, mold prevention, anti-fouling, sewage treatment, sunscreen lotion and other fields. With the industrialized production and maturation of application developing, nano-TiO2 plays a hardly underestimated role in the environment, information, materials, energy, medical and health fields. TiO2@Ag nano composite materials, not only effectively improve the photo-catalytic activity of TiO2, but also solve the key problems of noble metal Ag catalyst in the application process, such as aggregation, inactivation, loss, etc.According to references investigation, there is no report on combination of silk and nano-TiO2 through chemical bonds, or "implanting" nanoparticles (NPs) inside the bulk of silk.In order to build a complete system for combining silk and functional NPs (TiO2 and TiO2@Ag) strongly, for the first time, three methods are developed, endowing silk completely new and permanent superior performance to produce multi-functional silk composite materials.The main works are as follows:1?Synthesis of TiO2@Ag NPs and surface modification of NPsTiO2@Ag hetero-structured nano composite material was prepared by photocatalytic reduction method. The prepared TiO2@Ag was characterized by TEM, SEM, XPS, etc. The results show that the silvers ions were reduced to elemental Ag NPs. Ag NPs, with the grain size of about 5nm, deposited on the surface of TiO2 NPs with well dispersivity. The preparation process is simple, without template and surfactant as additives. So the as-made product has clean and pollution-free surface.3-(3,4-dihydroxyphenyl) propionic acid (DHBPA) was used to modify the surface of TiO2 and TiO2@Ag Nps. The hydroxyl groups -OH on TiO2 and TiO2@Ag NPs surface are replaced by the two bidentate OH groups of DHBPA. DHBPA is adsorbed on the NPs surface and modifies the surface of TiO2 and TiO2@Ag NPs.2. TiO2 and TiO2@Ag Nanoparticles-Chitosan functionalized silk Silk is pre-modified with chitosan, using 1,2,3,4- Butanetetracarboxylic acid as crosslinker. The carboxyl group -COOH of DHBPA that attached to TiO2 and TiO2@Ag NPs surface reacted with the amino groups of chitosan by ionic bonding. Owing to the strong chemical bonds, TiO2 and TiO2@Ag NPs strongly attched onto the silk surface, even after ultrasonic washing process. Owing to the protection effects of NPs, the NPs functionalized silk have excelent UV protection ability, and anti-bacterial ability against gram-negative bacteria E. coli and gram-positive bacteria S. aureus. Under ultraviolet irradiation test, the functionalized silk were able to degrade more than 90% methyl orange, proving that the silk functionalized by TiO2 and TiO2@Ag NPs have photocatalytic and self-cleaning abilities.This method adopt the traditional finishing process in textile industry and use natural products-chitosan and TiO2 as raw materials, producing high-quality and multi-functional silk products with low cost.3?TiO2 and TiO2@Ag Nanoparticles-2D resin functionalized silk2D resin is widely used in textile industry as a finishing agent.2D resin finishing technology is the mature, effective and a representative technology for natural fibers finishing. The silk was pre-modified by 2D resin finishing technology. The carboxyl group -COOH of DHBPA that attached to the NPs surface reacted with the hydroxyl groups of 2D resin through condensation reaction, and the Nps strongly linked to the silk surface, even after ultrasonic washing process. After functionalization, silk gains excellent UV protection ability, anti-bacterial ability, photo-catalytic and self-cleaning ability. At the same time, the functionalized silk overcomes its easy-wrinkle defect.4. "Implanting" TiO2 nanoparticles inside the bulk of silk fibers.Silk fibroin fiber is not completely solid, but is constituted by numbers of filaments about 1um in diameter with micropores between them. At the same time, a filament is constituted by?10nm fibrils with micropores between them. The constructional features of silk contribute to its 38% porosity, making it poddible to "implant" NPs inside the bulk of silk. So when we soak the silk in the liquid itanium precursor-tetrabutyl titanate (TBOT), the solvent molecules not only adsorbed onto the fibers surface, but also penetrated into the bulk of silk fibers. The following neutral hydrothermal process hydrolyzed TBOT and promoted anatase TiO2 NPs formation not only on the fibers'surface, but also inside the bulk of silk fibers. Silk and TiO2 NPs formed a complete system. TiO2 functionalized silk overcomes its light-induce yellowing and aging defects, and gains excellent anti-aging ability. At the same time, silk changes from hydrophobic to super-hydrophilic. The enhancement of water absorption capacity and permeability will improve the comfortability of wearing.Through photocatalytic reduction method, silver nanoparticles deposited on the TiO2 functionalized silk and then TiO2@Ag functionalized silk were prepared. TiO2@Ag functionalized silk are endowed with excellent UV blocking, antibacterial and self-cleaning ability.We adopt low temperature hydrothermal method and photo-catalytic reduction method, without sintering process which destroys silk, or adding any surfactants or templaes to control the particles size and shape. So the NPs functionalized silk have clean surface without any pollution.In summary, for the first time, the study realized the tightly chemical bonding between silk and TiO2 and TiO2 @ Ag nanoparticles; for the first time, TiO2 NPs are "implanted" inside the bulk of silk fibers, forming a whole system. The TiO2 and TiO2@ Ag NPs functionalized silk are endowed with permanent UV proection, anti-bacterial, self-cleaning abilities, producing high-quality and multi-functional silk composite materials. |
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