| Photocatalysis is a promising method to degrade the refractory organic pollutants,and it is also an economic and effective method.Different from traditional methods such as biodegradation or activated carbon adsorption,photocatalysis technology can remove the refractory organic pollutants through the transformation of pollutants into CO2 and H2O,so as not to leave harmful decomposition products.Among all the known photocatalysts,Ti O2 has been widely studied because of its chemical stability,high chemical inertness,nontoxicity,and low cost and the ability of photodegradation of most organic pollutants.However,there are two issues that limit the industrial application of titanium dioxide:(1)slow reaction rate:photocatalysis only occurs when photoinduced electrons and holes transfer to the surface active center of semiconductor.However,photogenerated electrons and photogenerated holes are easy to compound,resulting in low photocatalytic efficiency.(2)Low solar energy utilization:Ti O2 with band gap of 3.2e V can only be excited by photons with wavelength less than 400nm in the range of ultraviolet wavelength,accounting for about 4%of solar radiation energy.As a result,it is necessary and urgent to find a more efficient visible light driven photocatalyst.For this objective,various modified Ti O2 and Ti O2-alternative photocatalysts have been fabricated.Currently,it is still a challenge to design new photocatalysts that are stable abundant and facile in fabrication besides high visible-light performance.In recent years,WO3,as a visible light driven polymer semiconductor material,has attracted wide attention.WO3 possess many advantages such as an appealing electronic structure combined with a medium-band gap(2.5?2.8 e V),as well as good physicochemical stability.WO3 is one of the n-type semiconductors,It belongs to acid oxide,which is stable in acid and neutral aqueous solution and soluble in strong alkaline aqueous solution,resistant to photo corrosion in aqueous solution.These unique properties make WO3 a promising candidate for visible light photocatalytic applications utilizing solar energy,and is considered as a substitute for Ti O2.In order to strengthen the photocatalytic performance of WO3nanomaterials,many strategies have been used to boost the sunlight harvesting and promote the separation and transportation of photo-induced electron-hole pairs.Heterojunction construction is the most common strategy to enhance the photocatalytic performance of a single semiconductor,which can accelerate the separation of photo-induced carriers and broaden the wavelength of photo-response for the system.This thesis focuses on the study of WO3's photocatalytic degradation performance,and modifies it by constructing a heterojunction structure compounded with g-C3N4.The WO3and g-C3N4/WO3 composite photocatalysts were prepared by hydrothermal method,and the morphology,structure,specific surface area and element composition of the samples were measured by XRD,XPS,SEM,TEM,PL spectroscopy,UV-vis and other characterization methods.Analyze the photoelectrochemical performance and so on.Taking oxytetracycline(OTC)as the target pollutant,the degradation performance of the photocatalyst to oxytetracycline under the simulated visible light of xenon lamp was studied,and the mechanism of its photocatalytic reaction was discussed.The main research contents of this paper are as follows:(1)Hexagonal WO3 photocatalyst was synthesized by a simple hydrothermal method,and Na Cl,citric acid,oxalic acid,and PABA(para-aminobenzoic acid)were added as structure directing agents,and characterized by XRD,SEM,TEM,BET,XPS,etc.Methods,the effects of adding different structure directing agents on the growth,morphology,structure and specific surface area of WO3 crystals were studied.The degradation efficiency of each WO3 sample to oxytetracycline(OTC)under the irradiation of visible light was tested,and the synergistic effect of adsorption and catalytic degradation was discussed.The results show that the three-dimensional flower-like microsphere structure of the WO3-Na Cl sample observed by scanning electron microscopy increases its specific surface area and makes it have the largest adsorption performance.In addition,the WO3-Na Cl sample has the best photocatalytic activity.Under visible light irradiation The degradation efficiency of oxytetracycline reached60%in 120 minutes,which can be attributed to the synergistic effect of adsorption and degradation to improve the removal rate of oxytetracycline.(2)A kind of Z-scheme heterojunction with high adsorption and photocatalytic activity was successfully synthesized by in-situ hydrothermal method by loading WO3 nanorods on layered g-C3N4.It was characterized by XRD,XPS,SEM,TEM,PL spectra and UV-Vis.The degradation efficiency of Oxytetracycline(OTC)by g-C3N4/WO3 composite under visible light irradiation was tested.The results showed that 0.6g g g-C3N4/WO3 had the best photocatalytic activity,and the degradation efficiency of oxytetracycline reached 86%in 120minutes under visible light irradiation,which was better than that of single component g-C3N4and WO3.Loading WO3 on g-C3N4 could accelerate the transfer of photogenerated electrons,effectively promote the separation of electrons and holes,and improve the photocatalytic efficiency.The free radical trapping experiments show that the photocatalytic degradation mechanism of g-C3N4/WO3 composite may be due to the formation of Z-scheme heterojunction system. |
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