Atomic Layer Deposition(ALD) of Pd Nanoparticles on TiO2NTs for Organochlorinated Compounds Degradation

Author:Lu Zuo Ming

Supervisor:bao jian guo

Database:Doctor

Degree Year:2019

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Pages:139

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With the rapid development of China’s economy and the increasing degree of environmental pollution,a large number of chlorinated organic pollutants have invaded our living environment.China has classified chlorinated organic compounds as priority pollutants.Since such materials are difficult to degrade completely,it is important to find an efficient and environmentally friendly treatment.In this study,two typical pollutants(2,4-dichlorophenol and trichloroethylene)were degraded by electrochemical catalytic.The core step of electrochemical catalytic hydrodechlorination is the production of active hydrogen atoms,and the active hydrogen atom attacks the C-Cl bond on the chlorinated pollutant molecules subsequently,destroys the C-Cl bond and then replaces it.Palladium(Pd)has excellent aggregation and release properties for hydrogen,but the pure palladium is not only costly,but also undergoes a serious agglomeration after electrochemical reaction as an electrode,which greatly reduces the reactivity,so it is necessary to find a good carrier loads palladium nanoparticle.The titanium dioxide nanotube array structure has a large specific region and well-defined geometry,and the titanium dioxide nanotube itself has many adsorption sites,which facilitates the movement of pollutants to the electrode surface,and has excellent performance as a carrier.In this study,Pd nanoparticles were supported on a titania nanotubes via anodization using atomic layer deposition techniques.In the case of an applied current,H+generates electrons at the cathode to generate highly active atomic hydrogen.The hydrogenation substitution reaction occurs directly on the surface of the electrode,and the pollutants are efficiently and rapidly degraded.The research is mainly from the following four aspects:(1)The TiO2 nanotube structure was formed on the titanium substrate by anodization.Pd was deposited on the prepared titanium dioxide nanotubes by atomic layer deposition,and then analyzed by scanning electron microscopy(SEM)and X-ray photoelectron spectroscopy.(XPS),X-ray diffraction(XRD)and X-ray spectroscopy(EDX)were used to characterize the surface microstructure of the loaded electrode and explore the microscopic state of the electrode surface.(2)The prepared Pd-TiO2NTs/Ti(ALD)was used as the cyclic aromatic hydrocarbon structure of 2,4-dichlorophenol in the cathodic degradation solution.Firstly,The electrode was electrochemically characterized by cyclic voltammetry scanning.When there is no 2,4-DCP in the presence of different scanning rates,the electrodes are subjected to multiple scans of the same condition to evaluate the stability of the electrodes.Set different degradation conditions,such as different pH,different electrolytes,different currents,etc.Select the optimal degradation scheme.The electrode was degraded for the service life of 2,4-DCP and the degradation effect was compared with other methods.A fixed volume of the sample analysis solution component was obtained at a fixed time to investigate the reaction mechanism.The main conclusions are as follows:(1)Comparing the TiO2 nanotube electrode after Pd with the cyclic voltammetry(CV)pattern before Pd loading,it was found that Pd can get electrons from the cathode and obviously reduce 2,4-dichlorophenol.The counter electrode was subjected to one hundred continuous scans in the electrocatalytic system,and almost all the curves reached a closed state with little deviation,and the side surface reflected the long-term stability of the electrode under the electrocatalytic system.(2)Establish an electrocatalytic system,the anode is a Pt electrode,the cathode is a prepared Pd-TiO2NTs/Ti(ALD)electrode,and simulated wastewater containing 50mg/L of 2,4-dichlorophenol is added,It is found that the better the dechlorination effect is when the pH decrease in a certain pH range.The dechlorination effect of 2,4-dichlorophenol is different when different electrolytes are added to the solution,and the degradation effect is best when Na2SO4 is used as the electrolyte.2,4-dichlorophenol has good dechlorination effect at room temperature,and dissolved oxygen slightly interferes with the reductive dechlorination effect of 2,4-dichlorophenol.(3)The Pd-TiO2NTs/Ti(ALD)electrode was used as a cathode to degrade 2,4-dichlorophenol.After 60 minutes of reaction,the dechlorination efficiency was 94.1%.Comparing the Pd-TiO2NTs/Ti(ALD)cathode with other cathodes,it was found that the Pd-TiO2NTs/Ti(ALD)cathode prepared by atomic layer deposition technique has better performance in dechlorination efficiency and reuse efficiency.(3)Prepared Pd-TiO2NTs/Ti(ALD)as the chain-like unsaturated olefin structure of trichloroethylene in the cathodic degradation solution.Firstly,the electrode was electrochemically characterized by cyclic voltammetry scanning.Before and after the Pd loading,there were three When vinyl chloride is present and at different scanning rates,the electrodes are subjected to multiple scans of the same condition to evaluate the stability of the electrode.Set different degradation conditions,such as different pH,different electrolytes,different currents,etc.Select the optimal degradation scheme.The service life of the electrode degraded trichloroethylene was evaluated and the degradation effect was compared with other methods.A fixed volume of the sample analysis solution component was obtained at a fixed time to investigate the reaction mechanism.The main conclusions are as follows:(1)Comparing the CV diagram of Pd-TiO2NTs/Ti(ALD)electrode after Pd loading with Pd-TiO2NTs/Ti(ALD)electrode,the Pd load can obtain electrons from the cathode and have obvious reduction effect on trichloroethylene.The irreversibility of reductive dechlorination of trichloroethylene was confirmed by the relationship between the reduction peak current Ip and the square root velocity V1/2 of the scanning speed at different scanning rates.Almost all of the curves of the counter electrode in the electrocatalytic system for one hundred consecutive scans reached a closed state and the offset was small,and the side surface reflected the long-term stability of the electrode under the electrocatalytic system.(2)Establish an electrocatalytic system,the Pt electrode is set as anode,the cathode is a prepared Pd-TiO2NTs/Ti(ALD)electrode,and the simulated wastewater of40 mg/L trichloroethylene is added.It is found that the the better the dechlorination effect is when the pH decrease in a certain pH range.the dechlorination effect of trichloroethylene is different when different electrolytes are added to the solution,and the degradation effect is best when Na2SO4 is used as electrolyte.When the temperature rises,the dechlorination effect rises slightly,and the presence of dissolved oxygen has a slight adverse effect on the reductive dechlorination effect of trichloroethylene.(3)The Pd-TiO2NTs/Ti(ALD)electrode was used as a cathode to degrade trichloroethylene.After 90 minutes of reaction,the dechlorination efficiency was95.0%.Comparing the Pd-TiO2NTs/Ti(ALD)cathode with other cathodes,it was found that the Pd-TiO2NTs/Ti(ALD)cathode prepared by atomic layer deposition technique has better performance in dechlorination efficiency and reuse efficiency.(4)Comparing the dechlorination effect of 2,4-dichlorophenol and trichloroethylene on Pd-TiO2NTs/Ti(ALD)electrode prepared by atomic layer deposition and electrodeposition,it is found that the electrode prepared by atomic layer deposition technology has a long service life.The electrode prepared by the electrodeposition method is better than the electrodeposition method,and the problem that the load between the catalytically active component and the carrier in the electrodeposition method is solved.