The Preparation Of TiO₂ Composite Film Sensitized With Quantum Dots And Its Ability To Reduce Emission Of Soil Fumigant Into Atmosphere

Soil fumigation is an important management practice for controlling soil pests in the agricultural production system but can lead to excessive atmospheric emission.Current polymer films can prevent the fumigant from dispersing in the air above the soil.However,the temporality of emission control and second pollution of residual fumigant are key limitations of this technology.When the traditional plastic films were removed or broken,soil fumigant would likely escape into the atmosphere,In this study,TiO₂ composite films sensitized with quantum dots were developed and utilized to photodegrade the soil fumigant 1,3-dichloropropene?1,3-D?and chloropicrin?CP?.CuInS₂/ZnS:Al?CIS/ZnS:Al-TiO₂?composites for 1,3-D photodegradation were synthesized after optimization by using response surface methodology?RSM?.The photodegradation of 1,3-D on the composites was further studied by degradation kinetics and mechanism.Then,the composite film was developed and utilized to reduce the emission of the soil fumigant.The results provided the basis that composites could be used for reduction of fumigants'emisson into the atmosphere.The details were as follows.1.RSM was successfully applied to optimize the synthesis of CIS/ZnS:Al-TiO₂composites.The optimum parameters for maximum 1,3-D photodegradation were a QDs content of 23%,a ZnS:Al coating time of 418 min,and a TGA/TiO₂ molar ratio of 1.6.The ANOVA results demonstrated that the ZnS:Al coating time was the most significant parameter among the investigated factors for 1,3-D photodegradation.The interactions between the TGA/TiO₂ molar ratio and QDs content or the ZnS:Al coating time had significant effects on 1,3-D photodegradation.The obtained model can be adequate to describe the relationship between the degradation efficiency and the synthetic factors through PL spectra,absorption spectra,XRD patterns,and TEM images of QDs.2.The photodegradation mechanism of 1,3-D on CIS/ZnS:Al-TiO₂ composites and stability of composites indicated that 1,3-D photodegradation kinetics could be considered as a pseudo-first-order model.With increasing photocatalyst mass,the dissipation rates of 1,3-D increased,thereby consistently half-time was shortened.Photocatalytic reductive dechlorination was one of the pathways to degrade 1,3-D.1,3-D degradation products included Cl^-analyzed by ion chromatography and propene by the mass spectra identification using GC-MS.When the ZnS:Al coating time was 418 min?the shell thickness was 1.3 nm?,a gradient alloy layer was formed.The high-energy electrons in the core can easily tunnel through the ZnS shell into TiO₂.The electrons were transferred to 1,3-D,resulting in the dehalogenation and the highest degradation efficiency.This new approach involving doping of Al into the ZnS shell not only can enhance the stability of the photocatalyst but also maintain photocatalytic activity.3.Flexible CIS/ZnS:Al-TiO₂ composite was developed and the effects of TiO₂layers and sizes on the emission reduction of 1,3-D were investigated.PET substrate played important role in reducing the emission of 1,3-D.The emission rate became smaller,when the thickness of substrate becomes thicker.PET of 0.1 mm could be the proper subtract for further depositing the composites.When changing the QDs layer,the absorbance of the composite films increased with increasing the QDs layer.When changing the layers and sizes of TiO₂ nanoparticle,the appearance,absorbance,and SEM images were all different.The transmittance of single-layer composite film was the highest.The absorbance of double-layer and double-layer?200⁴00 nm?composite films was higher than the single-layer composite film.There was more cracking and considerably jagged in the double-layer?200⁴00 nm?composite film.The photocatalytic performances of the above composite films were further compared.The half-times of cis-and trans-1,3-D were 2.96 h and 2.20 h,respectively,approximately 99.0%of 1,3-D disappeared in the presence of the double-layer composite film.In the receiving chamber,the concentrations of cis-and trans-1,3-D in the presence of these composite films remained lower than that in the presence of the control.The results indicated that the double-layer composite film can be most effectively utilized to photodegrade and to control the emission of the soil fumigant.4.In the photocatalytic reactor of the mixture of 1,3-D and CP.The degradation rate of CP was the higher than 1,3-D.In the presence of 1,3-D,the degradation rate of CP was accelerated at early times and almost equal after 8 h.The half-time decreased from 0.66 h to 0.40 h.The addition of CP didn't have a significant effect on the degradation rate of 1,3-D in the Telone C-17 product.The control efficiencies of1,3-D were 97.30%and 97.17%,47.10%and 46.93%,as well as 7.88%and 6.80%for D+Film and D+C+Film,D+PET and D+C+PET,as well as D and D+C treatments,respectively.The addition of CP didn't make a difference on the control efficiencies of1,3-D.Covering flexible CIS/ZnS:Al-TiO₂ composite film led to the highest 1,3-D control efficiencies in the soil,improving 1.1 and 11.3 times,compared to the PET and no-film treatments.5.What's more,the CIS/ZnS:Al-TiO₂ composite film could promote the soil fumigation of 1,3-D and the mixture of 1,3-D and CP.After covering the composite film,the soil fumigant can be concentrated under the film,prolong the residence time in the soil.This film covering not only enhanced the control effect of nematodes,reduction rates of nematode ranging from 78.6⁸4.9%to 90.0⁹8.7%,but also improved the weed control effect.