| Ethylene is a plant hormone which can ripen the fruit and vegetable in the process of storage and transportation. It will cost huge economic losses. In order to prolong the shelf life, reduce loss rate, adjust market supply and increase economic benefits, it is necessary for people to seek for a new ethylene removal technology that is non-polluting, low energy consumption and good performance. Bismuth Tungstate(Bi2WO6) is a narrow band gap(2.76 e V) semiconductor, which can response to visible light with excellent performance. Moreover, it can degrade organic into small molecule inorganic, such as H2 O, CO2. Therefore, it is significant that using Bi2WO6 for ethylene degradation during storage and transportation of fruits and vegetables. However, in general, a larger crystalline size of Bi2WO6 was obtained owing to its large molecular weight, which resulted in a higher recombination rate of photo-induced charge carriers. Thus, the photocatalytic activity of Bi2WO6 was lower than the theoretical value in practice use. To obtain the highly active Bi2WO6 photocatalyst, in this work, the modification of Bi2WO6 was carried out. In this paper, Bi2WO6 was chosen as the main research object, and was modified by nano Titanium dioxide(Ti O2) and Graphene oxide( GO) with the purpose of obtaining the highly active Bi2WO6 based photocatalyst. The structure and optical properties were investigated by X-ray diffraction(XRD), Raman spectroscopy(Raman), Field emission scanning electron microscopy(FE- SEM) and Transmission electron microscopy(TEM), X-ray photoelectron spectroscopy(XPS) and Ultraviolet-visible diffuse reflection spectrum(UV Vis) and Fluorescence photoluminescence spectroscopy(PL). Meanwhile, Ethylene was set as the target degradation, and the Langmuir-Hinshelwood model was used to fit the procession of ethylene degradation with constant K' represented the degradation of Bi2WO6 based catalyst. All these were to research the catalyst' s structure-function relationship and reaction mechanism, which provided a effective method to remove the ethylene in the environment of fruits and vegetables storage environment. The results were as follows:(1) BiWO nano powders were Synthesized by s(1) Bi2WO6 nano powders were Synthesized by solid-phase method, microemulsion method, hydrethermal method, mixed alcohol water hot method and solvent thermal method respectively. It could be known from the characterization analysis and performance test that solvent thermal method was regarded as the best method to Synthesize Bi2WO6, among all the methods mentioned. Bi2WO6 average lattice size of the solvent thermal was 40.138 nm, flaky powder particles had an average diameter of about relative 60 ~ 80 nm, the band gap was 2.987 e V with a wide range of the visible light response rate, the maximum value of constant K' was 6.045 × 10-4min-1 tested by the photocatalytic degradation reaction. Its visible light degradation rate of ethylene reached to 13.82% within 240 min that was the highest among five methods. However, the sample's dispersion was poor. So, It still needed to optimize the preparation process solvent thermal method.(2) On the basis of the first part, the effect of Bi2WO6 catalytic activity under visible light that about the amount of surfactant PVP K30 and the p H value precursor suspension were investigated. It could be known from the characterization that the visible light response range of Bi2WO6 was both affected by them, when the amount of PVP K30 of 0.75%, p H value precursor suspension of 4, the narrowest band gap of the sample was 2.86 e V, which broadened the range of visible light response effectively. In addition, the microstructure was impacted greatly by the amount of PVP K30, the regular shape, flake diameter of approximately 50-70 nm nanosheet could be obtained in the condition of suitable PVP K30 amount of 0.75%. The crystallinity was affected by them, smaller size Bi2WO6 could be got in condition of suitable amount of PVP K30 and the p H value precursor suspension. The visible light catalytic performance test results that the amount of PVP K30 of 0.75%, the p H value precursor suspension of 4, the maximum value of constant K' was 6.710 ×-4min-1, degradation rate of ethylene reached to 14.03% within 240 min.(3) The flaky Ti O2-Bi2WO6 Nano- powder was successfully synthesized by Ti O2 composite modified through solvent thermal method on the basis of second part. A series of experiments were carried out to diacuss the effect of visible light activity by the hydrothermal reaction temperature, calcination temperature and Ti O2 addition. Ti O2-Bi2WO6 composite photocatalyst appeared in a regular polygon, particle size of about about 30 nm with good dispersion. It was revealed that Ti O2 entered the Bi2WO6 lattice to form Ti O2-Bi2WO6 crystal phase system, which refined the average particle size of Ti O2-Bi2WO6 and equiped it with higher specific surface area. The staggered heterojunction was built as the band of Bi2WO6 match with Ti O2, narrowing compound semiconductor band gap was narrowed, Ti O2-Bi2WO6 response range of visible light was broaden, the recombination rate of photo-induced charge was decreased. The photocatalytic activity of Ti O2-Bi2WO6 was better than pure Bi2WO6 or Ti O2: Hydrothermal reaction temperature of 160?, the calcination temperature of 450?, Ti O2 added in an amount of 35%, the maximum value of constant K' was 9.081×10-4min-1, visible light degradation rate of ethylene reached to 19.01% within 240 min, which was 3.19 times of Ti O2 and 1.35 times of Bi2WO6.(4) In order to improve the photocatalytic properties of TiO2-Bi2WO6, GO-TiO2-Bi2WO6 composite photocatalyst was successfully synthesized by graphene oxide doped modified In order to improve the photocatalytic Ti O2-Bi2WO6 performance, successfully prepared package type GO-Ti O2-Bi2WO6 composite photocatalyst solvent by-step method for Ti O2-Bi2WO6 composite material graphene oxide doped. Nano particle of Ti O2-Bi2WO6 was distributed on the surface of tulle shaped GO. The Ti-C bond was formed by C atom of GO replaced the oxygen atom in the Ti O2 lattice, multiple heterojunction of GO-Ti O2-Bi2WO6 was formed which reduced the band gap of heterojunction. In addition, the the photo-generated carriers separation and migration of GO-Ti O2-Bi2WO6 was promoted effectively by good electrical conductivity of GO, The specific surface of composite photocatalyst was increased which increasing the photocatalytic activity site. composite photocatalyst surface area, increasing the photocatalytic activity sites, significantly improving its visible catalyzed ethylene degradation activity. In short, the degradation activity of GO-Ti O2-Bi2WO6 was significantly improved: amount of GO of 0.75%, the maximum value of constant K' was 1.310×10-3min-1, visible light degradation rate of ethylene reached to 24.04% within 240 min, which was 1.26 times of Ti O2-Bi2WO6. |
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