Study On In-Situ Growth Of Nanocrystal ZnO On Cotton Fabric And Its Influence Factors

ZnO, a wide-band-gap semiconductor, is one of the most important candidate material for optoelectronic applications due to its wide band-gap 3.37eV at room temperature and large exciton binding energy 60 meV. Compared with normal size ones, nanocrystal ZnO with small dimension and large specific surface area shows special effect in superficial, volume and quanta tube, which make Nano ZnO obtain many superior properties such as fluorescence, piezoelectricity, photocatalysis, light-absorption, ultraviolet scattering, UV luminescence and so on. Nanometer ZnO has versatile applications in the fields of piezoelectric sensors, transducers, fluorescent material, UV-screening and photocatalyzer.As metal oxide, ZnO can shield ultraviolet through its reflection and refraction to the light. Meanwhile, for the sake of its quantum dimension effect, nanometer ZnO exhibits effective attenuation to ultraviolet especially in the wavelength of 280-320nm. Furthermore, with the existing of air and water, nanometer ZnO automatically produces electronegative electron (e) that can move freely, and cavity (H⁺) with positive electricity, which will activate oxygen in the air to form active oxygen that could react with many organic compounds to obtain the function of the sterilization and deodorization under the irradiation of ultraviolet radiation. So, if nanometer ZnO is treated on textile, the fabric can obtain some special functions, such as UV-screening, antibacterial and deodorizing.Nowadays, nanocrystal ZnO is treated on the fiber and fabric mainly through the filature process or coating method with binder. But there are many defects existing in these two methods above-mentioned. For one thing, nanometer ZnO powder should be firstly prepared for both methods with the complex procedure, high consumed energy and cost. Meanwhile, most of zinc oxide particles are firmly embedded in the fiber during filature process or enwrapped by binder in coating method, both of which make ZnO hardly expose on the surface and cannot fully contact with the oxygen and water. For this reason, the photocatalysis of nanocrystal ZnO is reduced and the antibacterial and deodorizing activities of zinc oxide fine particles could not effectively bring into play. To eliminate the problems, it becomes hotspot for in-situ growth of nano ZnO on the surface of the fabric and providing the fabric with special function.There are many reports about zinc oxide oriented film formed on the substrate of ceramic, glass and steel. But there are few reports about ZnO in-situ growing on fiber materials. John.H.Xin et al from the Hong Kong Polytechnic University firstly prepared zinc oxide seed on cotton fiber, then actualized the in-situ growth of hexagonally oriented ZnO nanorod through hydrothermal method without detailed discussion the influences of the hydrothermal conditions on the growing rule of crystal on fibrous substrate.According to the references [57～59], in-situ growing method for ZnO with SiO₂ sol and hydrothermal method was firstly introduced in this paper. The cotton fabric was firstly coated by SiO₂ sol. Then it accomplished nanometer ZnO crystal in-situ growing on cotton fabric through hydrothermal method at low temperature with the reaction between Zn(NO₃)₂ and C₆H₁₂N₄ and the re-crystallization treatment. The influence of SiO₂ sol, hydrothermal conditions and re-crystallization treating conditions on the in-situ growth rule and properties of zinc oxide crystal including its structure and morphology were discussed by many characteristic methods, such as ultraviolet protective factors analyzer (UPF), X-ray diffraction (XRD), inductively coupled plasma atomic absorption (ICP) , scanning electron microscopy (SEM) and field-emission-gun environment scanning electron microscopy (FE-SEM). The better conditions of ZnO in-situ growing on the surface of fabric were finally confirmed as follow.There was high content and crystalline perfection of nanocrystal ZnO in-situ growing on the cotton fabric when the fabrics coated by SiO₂ sol were put into the solution of Zn(NO₃)₂ (0.02mol/L) and C₆H₁₂N₄ whose molar ratio to Zn(NO₃)₂ was 0.5:1 at the temperature of 80℃for 2.5h. The content of nanometer ZnO linearly increased with the concentration of silicon sol on the fabric accompanied by the gradually improved crystalline perfection. The content and crystalline perfection of nanocrystal ZnO on the cotton fabric was also greatly influenced by different diameter of SiO₂ sol. There was highest content of ZnO on the cotton fabric coated by SiO₂ sol with the diameter of 4.84nm and best crystalline perfection with that of 9.11nm. But there was no change in the content of the zinc oxide during the process of the increase of re-crystallization temperature and the prolonging of the time. And the morphology of ZnO was gradually changed from sphericity and rod to needle-like accompanied by the smaller size and improvement of the crystalline perfection. The performance of UV-screening on cotton fabric treated by the better condition described above was greatly improved even with the value of UPF more than 100 as well as good handle. However, the breaking strength and extension of the treated fabric went down a little. And the performance of UV-screening on cotton fabric was reduced to a certain extent during the washing process, which needed our further study.