Preparation Of The Plasma-photocatalytic Materials And Their Photocatalytic Activity In Degradation Of Pollutant

With the development of the society, energy shortage and environmental pollution have become the hot issues of human concerns. The photocatalytic technology is a green oxidation technology. It has been widely applied in the field of environmental pollution protection and energy conversion. The photocatalyst can convert the low-density solar energy into the easily stored high-density hydrogen, and solve the problem of shortage of energy. It can also reduct the CO2into low-carbon alkane, which can reduce the amount of the greenhouse gas carbon dioxide and turn it into fuel to solve the energy crisis at the same time. Besides, it can degrade toxic and harmful organic pollutants into non-toxic substances. So, photocatalytic technology has great potential for development. However, the wide band gap of the traditional photocatalyst TiO2is large, so it can only use ultraviolet light in sunlight, thus it’s scope of application are greatly limited. This paper is emphasized on the controlled synthesis of the photocatalytic materials as well as its application in environmental purification. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), TEM, UV-vis diffuse reflectance spectroscopy (DRS), photolumin-escence (PL), Electrochemical Impedance Spectroscopy (EIS) were used to test the catalyst structure, morphology, optical performance and photocatalytic properties, and the relationship between the structure and activities were also studied.The main content and conclusions are summarized below:1. In this work, Ag nanowire was firstly synthesized, and then it was etched into core-shell Ag@AgCl by [Bmim]FeCl4ionic liquid. The photocatalyst was characterized by XRD, XPS, SEM-EDS, DRS and other methods. The core-shell Ag@AgCl structure forming process was also proposed. Ag@AgCl exhibited the surface plasmon resonance absorption, which is peculiar to the noble metal. The resonance absorption is closely related with Ag@AgCl morphology and proportions. The DRS result showed that the plasmon resonance absorption increased with the etching time prolonged. The methyl orange was used as the target pollutant to test the photoactivity of the photocatalyst under visible light irradiation. The experiment result showed that the degradation ability of the catalyst with enhanced plasmon resonance absorption enhancement. Among those samples, the Ag@AgCl etched for20h showed the highest photocatalytic ability, which was able to degrade95%methyl orange in40min. In addition, the catalyst could also degrade the highly toxic4-chlorophenol. The relationship between the structure of the photocatalyst and the photocatalytic activities was disscussed, and the result indicated that the high photoactivity of the Ag@AgCl is attributed to the synergetic effect between surface plamon resonance absorption effect of Ag and AgCl.2. A new composite photocatalyst Ag/AgCl/ZnO was fabricated by a two-step synthesis method under the hydrothermal condition. The sample was characterized by XRD, TG-DSC, SEM, TEM, DRS and XPS. Methyl orange (MO) was used as a representative dye pollutant to evaluate the photocatalytic activity of Ag/AgCl/ZnO under ultraviolet light irradiation. The photocatalytic activity of Ag/AgCl/ZnO catalyst was higher than that of the pure ZnO catalyst. Further study found that Ag/AgCl and ZnO were able to form a heterojunction structure and the Ag/AgCl/ZnO structure changed to Ag/ZnO gradually after several repeated experiments. However, the photocatalytic ability of the sample was not reduced. Finally, a possible photocatalytic mechanism was proposed.3. Carbon nanotubes (CNT)-loaded Ag/AgBr was prepared by a facile, one-step hydrothermal method. The purpose of the study was to further enhance the photocatalytic activity of plasma photocatalyst Ag/AgBr by taking advantage of the excellent conductivity of CNT. The structure, morphology and optical properties of the samples were characterized by SEM-EDS、XPS、IR、PL. The CNT/Ag/AgBr composite exhibited much higher photocatalytic activity than the pure Ag/AgBr in degrading Methyl orange (MO) dye pollutant under visible light irradiation. The loading amount of CNT has a significant influence on the photoactivity of the CNT/Ag/AgBr composite. When the CNT loading amount was1.4at%, the hybrid material showed the highest photocatalytic ability. The result showed that a small amount CNT was beneficial to the photo-generate electron transfer, and the photoactivity of the CNT/Ag/AgBr could be enhanced. The degradation process of the dye solution was tested by liquid chromatography mass spectrometry (LC/MS) and total organic carbon (TOC). Based on the results, the possible degradation path of the MO dye was proposed. In addition, a possible visible light photocatalytic degradation mechanism was also discussed.4. A new plasmonic photocatalyst of Ag/AgBr/g-C3N4was prepared by a hydrothermal method. It is expected to enhance the dispersity of the Ag/AgBr on the surface of the g-C3N4, which can further enhance the photoactivity of the hybrid. XRD, TEM, DRS, PL emission spectra and IR spectra were employed to confirm the structure, morphology and optical property of the as-prepared Ag/AgBr/g-C3N4composite. XPS analysis indicated the interaction between Ag/AgBr and g-C3N4. They formed the heterojunction structure, which was facile to the separation of the electron-hole, and hence enhanced the photocatalytic activity of Ag/AgBr/g-C3N4in degrading Rhodamine B under visible light irradiation. Besides, the highly dispersion of Ag/AgBr anchored on the surface of g-C3N4was also assumed to responsible for the enhanced activity and good recycling ability. The17.8at%Ag/AgBr/g-C3N4 showed the highest photoactivity, the degradation rate constant of17.8at%Ag/AgBr/g-C3N4was as high as18.3times to that of the pure g-C3N4. The relationship between the photocatalytic activity and the structure of Ag/AgBr/g-C3N4hybrid materials was discussed.5. The white g-C3N4and CNT combined together and formed the CNT/white g-C3N4composite due to electrostatically-driven self-assem-bly by the hydrothermal method. The structure, morphology and optical properties of the white g-C3N4and CNT/white g-C3N4composite photocatalyst were characterized by TEM, XRD, IR, DRS, XPS and PL The photoactivity of the catalysts was evaluated by degrading methylene blue (MB) dye solution. The results showed that the photoactivity for the degradation of MB solution was in the following order:CNT/white g-C3N4composite> g-C3N4> the white g-C3N4. The photoactivity of the CNT/white g-C3N4composite was66.5%and34.5%higher than that of the white g-C3N4sample and that of the g-C3N4at1.5h, respectively. The degradation rate of the CNT/white g-C3N4photocatalyst was almost8.1times as high as that of the white g-C3N4. The PL result showed that the CNT/white g-C3N4have much lower electron-hole recombination rate, which leads to the enhanced photoactivity. The reason to the photoactivity of the CNT/white g-C3N4was much higher than that of g-C3N4and the white g-C3N4was discussed based on characterize and the photocatalytic experiment.