Preparation Of Dual-Effect TiO₂-based Nanomaterials And Study On The Mechanism Of DEHP Photocatalytic Degradation And Resistance To Pst.DC3000

Against the background of rapid economic development and intergenerational changes in policies,the planting industry structure's adjustment is progressing steadily.Heilongjiang locates in the northeastern part of China.Due to the low temperature in winter,long sunshine,and sufficient sunshine,the people's demand for shed planting increases the quality of life.Plastic greenhouses have significantly increased the output of off-season vegetables and fruits to meet public consumption needs.However,due to the excessive use of plastic greenhouse films,PAEs are non-covalently bonded with polymers in plastics and continuously released into the greenhouse environment in molecular form,accumulating leaves and edible parts,causing"three causes"hazards to humans and causing significant risks.Simultaneously,because the shed is in a closed or semi-closed environment all year round,it is beneficial for plant pathogenic microorganisms to cause plant diseases,hinder the average growth and development of plants,affect vegetable yield,production quality,food safety,and cause significant economic losses.Few reports on the research can simultaneously solve the above-mentioned agricultural production problems.Photocatalytic technology has the function of removing environmental pollutants and killing pathogenic bacteria.Therefore,this study prepared a green,multifunctional and efficient TiO₂-based photocatalytic nanomaterial to simultaneously solve the above environmental problems.And its mechanism of photocatalytic degradation of typical phthalate DEHP was deeply explored.At the same time,its antibacterial mechanism against typical plant pathogenic bacteria Pst.DC3000 were explained.The application potential of controlling tomato leaf spot disease had analyzed the interaction between nanomaterials and bacteria and plants.The main results of the study are as follows:(1)Prepare a multifunctional TiO₂-based nanomaterial.In this study,a three-step method(Hummer's method,solution combustion method and hydrothermal synthesis method)was used to prepare nanomaterials with different doping amounts.X-ray diffraction(XRD)observed that the composition of the material contained independent crystals of anatase phase TiO₂,rutile phase TiO₂and?-Bi₂O₃.Fourier transform infrared spectroscopy(FTIR)analysis showed that GO was successfully reduced to reduced graphene oxide(r GO)through the hydrothermal process.The elemental composition of the material was further verified;the formation of Ti³⁺and oxygen vacancies in the sample was determined by X-ray photoelectron spectroscopy(XPS),and the surface chemistry of the material was clarified.Scanning electron microscope(SEM)confirmed that r GO was used as a two-dimensional template with doping of Bi₂O₃.According to UV-vis diffuse reflectance spectroscopy(UV-vis DRS),it was confirmed that the light absorption edge of 4%r GO-(Bi₂O₃-TiO₂)was significantly red-shifted,and the bandgap energy value was 2.89 e V,which enhanced the absorption in the visible light region.(2)TiO₂-based nanomaterials had high degradation activity for DEHP photocatalysis.DEHP was used as the target pollutant to explore the photocatalytic degradation efficiency of nanomaterials under simulated solar radiation.The results showed that 4%r GO-(Bi₂O₃-TiO₂)exhibited the best photocatalytic activity,reaching 89%conversion within 90 min.The photocatalytic degradation of DEHP conformed to zero-order kinetics.The k value of 4%r GO-(Bi₂O₃-TiO₂)was 0.1158 mg·L^-1·min^-1,which was unmodified TiO₂(k=0.0566 mg·L^-1·min^-1)2.05 times.The photocatalytic activity of 4%r GO-(Bi₂O₃-TiO₂)on DEHP was not affected by the substrate's concentration and increased with the increase of the dose of nanomaterials.The activity was strongest at p H=6(k=0.0834 mg·L^-1·min^-1),p H=10(k=0.0753 mg·L^-1·min^-1)and p H=4(k=0.0741 mg·L^-1·min^-1)followed by activity.Besides,4%r GO-(Bi₂O₃-TiO₂)maintained sufficient stability in 5degradation cycles,and the removal rate of DEHP was higher than 80%.(3)Explain the photocatalytic degradation mechanism of TiO₂-based nanomaterials on DEHP.Free radical quenching test results showed that·O₂^-and·OH were the main active oxygen species affecting the photocatalytic degradation of DEHP.Using DMPO as a spin trapping agent,electron spin resonance spectroscopy(EPR)was performed on 4%r GO-(Bi₂O₃-TiO₂)to verify the intensities of the two free radicals.The results showed that the·OH signal was stronger than·O₂^-free radicals and existed the possibility of free radical conversion.According to the ultraviolet photoelectron spectroscopy(UPS),the conduction band(CB)/valence band(VB)value of 4%r GO-(Bi₂O₃-TiO₂)was calculated,and the energy band structure and Z scheme heterojunction structure of 4%r GO-(Bi₂O₃-TiO₂)were determined.Under simulated solar radiation,e^-in Bi₂O₃ CB and h⁺in TiO₂ VB recombined in the internal electric field formed by r GO,and e^-remaining in TiO₂ CB strongly reduced O₂ to form·O₂^-,h⁺retained in Bi₂O₃ VB had a higher reduction potential and reacted with water molecules adsorbed on the surface to form·OH.·O₂^-and·OH quickly attacked the O11 site of DEHP's high Fukui index(f⁰),degraded DEHP through de-esterification,?-oxidation and hydroxylation,and realized the cleavage of the benzene ring to produce short chains such as butyric acid and 3-hydroxybutyric acid to realize mineralization.(4)Determine the in vitro antibacterial activity of TiO₂-based nanomaterials against Pst.DC3000 and summarize the antibacterial mechanism.The Kirby disc diffusion method was qualitatively observed that 4%r GO-(Bi₂O₃-TiO₂)and 6%r GO-(Bi₂O₃-TiO₂)had the largest inhibition zone diameter,were 12.0 mm.Then the inactivation efficiency of 4%r GO-(Bi₂O₃-TiO₂)was obtained by the plate counting method,which was 1 log higher than that of Bi₂O₃-TiO₂,6 log(>99.9999%),much higher than other prepared nanomaterials.Under visible light conditions,the inactivation efficiency of 4%r GO-(Bi₂O₃-TiO₂)with a minimum inhibitory concentration of 1280?g·m L^-1.The results showed that 4%r GO-(Bi₂O₃-TiO₂)could convert a large amount of·O₂^-generated by photocatalysis into H₂O₂ through SOD-like action and then into·OH through POD-like action.The good enzyme-like activity provided the main active factor for antibacterial effect.Observations by SEM showed that a large amount of 4%r GO-(Bi₂O₃-TiO₂)adhered to the bacteria,causing severe deformation of the bacteria's cell shape and rough surface,severe damage to the cell wall,rupture of the cell membrane and leakage of the cytoplasm.At the same time,FTIR determined that 4%r GO-(Bi₂O₃-TiO₂)could tightly bind to the bacterial outer membrane LPS.Under the treatment of 4%r GO-(Bi₂O₃-TiO₂),the extracellular protein content and the conformation changed significantly,the content increased to 620?g·m L^-1,and the protein secondary conformation changed.Besides,the damage degree of 4%r GO-(Bi₂O₃-TiO₂)treatment for 90 min was as high as 91.37%,the cell survival rate at 180 min treatment was only 9.8%,and the accumulation of MDA was significantly increased to 1.0.The virulence genes in the bacteria(hrp S,cor S,iaa L and flg G)expression levels were down-regulated,indicating that 4%r GO-(Bi₂O₃-TiO₂)destroyed the pathogenicity of bacteria.(5)Reveal the mechanism of TiO₂-based nanomaterials inducing tomato disease resistance enhancement.4%r GO-(Bi₂O₃-TiO₂)foliar sprayed on tomato leaves could significantly reduce the pathogenicity of Pst.DC3000 and delay the occurrence of disease symptoms.4%r GO-(Bi₂O₃-TiO₂)significantly improved the growth of leaves and roots of inoculated tomatoes,and the content of photosynthetic pigments(the content of chlorophy?a,b and carotenoids)increased to 0.009,0.008and 0.004 mg·g^-1·FW,respectively.The photosynthetic parameters had also been relatively improved.The thiol content increased significantly under the treatment of 4%r GO-(Bi₂O₃-TiO₂),the metabolism of phenols and the activities of defence-related enzymes(PPO,PAL and POD)increased to 8,60 and 15 U·g^-1·FW,respectively,which indicated that 4%r GO-(Bi₂O₃-TiO₂)significantly enhanced tomato resistance to Pst.DC3000.Besides,the up-regulation of PR-2 and PR-13 genes indicated that the SA pathway activation led to increased plant disease resistance.In summary,the 4%r GO-(Bi₂O₃-TiO₂)developed by this research institute could efficiently degrade DEHP under visible light conditions,achieve the antibacterial properties of Pst.DC3000 in vitro and induce and enhance the resistance of tomatoes to Pst.DC3000.It had the potential to solve DEHP pollution and Pst.DC3000 pollution at the same time.This research provided a scientific theoretical basis for the photocatalysis of aromatic compounds and laid a theoretical foundation for the targeted modification of nanozymes to enhance their antibacterial and control functions.It was an essential meaning for improving the economic benefits of greenhouse agriculture and sustainable agricultural development.