| With the rapid development of China's economy, there is no doubt that agricultural issues such as fruits and vegetables freshing is important pillar industry for economic development.Every year in China, countless fruits and vegetables rot and billions economic losses because of the improper preservation techniques.However, there exists some technical defects in most traditional preservation technologies, which can not fully meet the needs of economic development.It is imperative to seek more efficient, environmental, of energy conservation and sustainable development of the technology for fruits and vegetables freshing. Studies have shown that ethylene as ripening plant hormone is one of the major causes of vegetable and fruit rotting and bastardize, so removal of ethylene on fresh-keeping storage environment is of great significance.Since the 20th century, photocatalytic technology represented by TiO2 nanometer photocatalytic materials have got rapid development, which are widely used in all aspects of life and production. However, only under uv irradiation TiO2 has the strong photocatalytic ability, which limites its application under visible light.A new type of composites nano Bi2WO6-TiO2 photocatalysis has high visible light response value, which can efficiently removal of ethylene in fruit and vegetable storage environments.Due to the smaller volume, nanomaterials is difficult to recycle in the practical application, which often cause the iste of resources. Starch, a macromolecular polysaccharide which widely exists in the nature of natural, has excellent degradability, biocompatibility and film-forming properties. Film products prepared by starch has good light penetration and mechanical properties, thus can be used as an effective carrier of nanometer photocatalytis. Nano Bi2WO6-TiO2/starch composite film, prepared by starch and nanometer photocatalytis, have the dual role of fruit and vegetable packaging and fresh-keeping, which rarely make the news both inside and outside China.In this study, as the ultimate goal, a kind of functional composite film which can automatically remove the ethylene gas under visible light is prepared. LiuYanFa is used to prepare substrate of starch film, and a heterostructure nano Bi2WO6-TiO2 composite photocatalysis is obtained through hot ethylene glycol solvent method.The dispersion stability of nano Bi2WO6-TiO2 in aqueous phase is improved by ultrasonication and dispersant modification. Last but not least, the effect of different load method and mass of nanometer photocatalysis on pervious to light performance, mechanical properties and photocatalytic degradation of ethylene under visible light in gas phase of nano Bi2WO6-TiO2/starch composite film is clearly discussed. Using scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT IR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) to character microstructure and thermal propertiesof the Bi2WO6-TiO2 composite photocatalysis and nano Bi2WO6-TiO2/starch composite film materials. In this paper, the main research contents and conclusions are as follows:Starch film is prepared through casting method, and the optimal film forming technical conditions are starch concentration of 5%, plasticizer glycerol amount of 50% and film-forming temperature of 55?.Under this condition, a soft, dense and thin film material with thickness of 282?m, transparency of 1.65?m-1, tensile strength of 1.32 MPa and elongation at break of 21.51% is successfully obtained. Starch film surface is relatively flat, smooth and dense and cross section in good structural integrity is observed by SEM. XRD shows that starch film with strong B type crystallization, while FTIR shows absorption peak both starch and glycerol.Nanosized Bi2WO6/TiO2 composite photocatalytic materials is prepared through ethylene glycol heat solvent method. A series of characterization prove that nano Bi2WO6/TiO2 generates a unique heterostructure, which can effectively restrain light gave birth to the combination of electrons and holes. The Bi2WO6 is rhombic or rhombic, and its JCPDS number is 39-0256, lattice parameter of a=5.457°a, b=16.435°a,°c= 5.438 a. XRD showed product has very high crystallinity.On the peak shape, FT-IR combine characteristic absorption peak both nano Bi2WO6 and nano TiO2, but change and weakness have taken in the peak position and peak intensity.The research results show that the highest absorbance value of nano Bi2WO6/ TiO2 aqueous suspension is achieved when the conditions are as follows:dispersant of PVP, pH of 7.0, dispersant adding amount of 20%, and ultrasonic environment (ultrasonic temperature 40?, power 400 W, and time of 25 min). Laser scattering particle size distribution analyzer display Bi2WO6/TiO2 nanoparticles on average particle size of 110.3 nm, which matches well with observation of single Bi2WO6/TiO2 nanoparticles size with SEM and TEM, indicating that under the condition, Bi2WO6-TiO2 nanoparticles is in good dispersion and stable effect in water phase.The research showed that nano Bi2WO6-TiO2/starch composite film materials have visible light response value and excellent ethylene-removing ability, within the photocatalytic time of 7 h, the ethylene degradation rate of different composite film obtained through different load method is:the composite method> surface coating method> surface penetrant method> internal dopping method> dipping-pull method. Ethylene degradation rate links closely with the structure of the composite film. The more load and the more homogenerous of Nano Bi2WO6-TiO2 photocatalytic materials on thin film, the higher ethylene degradation rate the composite film. Moreover, the effective contact area with visible light plays a important role on ethylene degradation rate.The composite film prepared through surface preparation method has a dual advantage. With the increase of photocatalytic materials load amount, thickness, transparency and tensile strength of composite film increase, while photocatalytic degradation of ethylene of composite film rise before fall. When the load is 2.0%, the optimal value of ethylene degradation rate of 13.14% is achieved. Due to its good internal and external structure, composite film is good at photocatalytic performance and mechanical properties.By employing internal doping method, nano Bi2WO6-TiO2/starch composite film has good stability, high repeatability and superior light catalytic performance. Different nanomaterials doping ratio have significant impact on composite film performance. As the doping ratio is increasing, thickness, transparency and tensile strength of composite film is increasing, while elongation at break is declining. Nano Bi2WO6-TiO2 can significantly improve the light transmittance of starch film.Compared with starch film, the transparency of composite film increases by 375%.The thickness of composite film vary from 200?m to 340?m. The degradation of ethylene rate of composite film assumes the approximate linear increase while the doping ratio increases. When the doping ratio is 4%, ethylene degradation rate achieves to maximum value of 10.68%.The section of composite film prepared by internal doping method has a dense and smooth structure, and there is no starch grain dissolution, indicating nanomater materials can effectively improve the internal structure of the starch (composite) film. FT-IR shows that nano Bi2WO6/TiO2 can inhibit the action between starch and plasticizer glycerin, and it interact with glycerol. XRD combines characteristic peak of nano Bi2WO6/TiO2 and starch film in common. The diffraction peak intensity of composite film is relatively low than single materials (nano Bi2WO6/TiO2 and starch film). The thermal properties of thin film materials is analysised by using DSC and TG. The results show that nano Bi2WO6-TiO2 can reduce the glass transition temperature (Tg) of starch film, and the influence degree on the composite film is different between different doping ratio. The thermal stability performance of starch based nanocomposite thin film is better than starch film, and nano Bi2WO6-TiO2 has good delay and inhibition effect on the thermal decomposition behavior of composite film.To explore the effect of different nano Bi2WO6-TiO2 load amount under the composite method on composite film performance. After making full advantages of two kinds of load method, composite method have a synergy effect on photocatalytic properties of the composite film. When the load amount is 6.4%, ethylene degradation rate arrives highest value of 19.42%, showing the best synergy effect of two load methods. According to analysis results, the covering of photocatalytic activity sites is the major factor of decreasing of ethylene degradation rate. Composite film's thickness can achieve to 340?m, significantly higher than other preparation methods.With the increase of the load amount, thickness and tensile strength of the composite film increases significantly, while transparency is declining, and there is no significant change in elongation at break. When nano Bi2WO6-TiO2 load arrived at 5.6%, tensile strength of the composite film is 5.54 MPa.Composite film's cross-section is smooth, flattening and consistent, indicating that nanoparticles has a good dispersion in the interior of the composite film and they can form a complete microstructure. |
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