Study On The Crystal Face Effect Of Anatase TiO₂ Photocatalytic Degradation Of Polyacrylamide

As a commonly used material in polymer flooding,the polyacrylamide enhances oil recovery significantly,but its difficult degradation feature is a cause of serious environmental crisis.TiO₂ photocatalytic degradation of polyacrylamide has received widespread attention due to the clean and complete reaction process.This thesis focuses on TiO₂ photocatalytic degradation of polyacrylamide,and discussing the details of TiO₂ crystal plane effect.By using density functional theory,this thesis calculates properties of anatase TiO₂?101?and?001?crystal plane,and its interaction with H2_O and O₂.Anatase TiO₂ with?101?or?001?single plane was synthesized respectively by hydrothermal method,then this catalysts were researched by characterization methods and tested degradation effects.The main content of this thesis can be divided into the following three parts:Part one is confirm the activity species in TiO₂ photocatalytic degradation of polyacrylamide.In process of TiO₂ photocatalytic degradation of polyacrylamide experiment,we set three conditions:adding isopropanol?capture agent of ·H?and not cutting off oxygen?the source of O₂·-?,not adding isopropanol and cutting off oxygen,and adding isopropanol and cutting off oxygen.Comparing with the degradation effects,we concluded that ·OH and O₂ played an important role in the process of TiO₂ photocatalytic degrading polyacrylamide,meanwhile polyacrylamide could not be directly degraded by hole.This work determined research objects for theory calculation of TiO₂ crystal plane effect.Part two is theoretical calculation of the interaction between anatase TiO₂ with low index crystal plane and H2_O,O₂.Based on density functional theory,this thesis systematically researched the structure and properties of?101?and?001?crystal plane,and also discussed the interaction between TiO₂ two typical crystal planes and H2_O?the source of ·OH?,O₂?the source of O₂·-?in the process of TiO₂ photocatalytic degrading polyacrylamide.The forbidden band width of TiO₂?101?crystal plane and?001?crystal plane was 2.78 eV and 1.52 eV respectively,thus the valence electrons of TiO₂ with?001?crystal plane were easier to transit to the conduction,forming photoinduced electron-hole pairs.The adsorption of H2_O on TiO₂?101?crystal plane was-0.956 eV,which is less than the-2.159 eV adsorption on Ti02?001?crystal plane;the stable form of H2_O on TiO₂?101?crystal plane was molecular adsorption,while TiO₂?001?crystal plane was dissociation;Through analyzing the reaction heat of H2_O dissociation on TiO₂ crystal planes,we found the energy of H2_O dissociation on?101?crystal plane was +0.550 eV,which was a endothermic process.The energy of reaction heat of H2_O dissociation on?001?crystal plane was-1.240 eV,which was exothermic process.Therefore,H2_O on TiO₂?001?crystal plane was easier dissociated into the hydroxyl free radicals?·OH?than TiO₂?101?crystal plane.The adsorption of O₂ on TiO₂?101?crystal plane was-0.157 eV,which is less than the-0.958 eV adsorption of TiO₂?001?crystal plane.The adsorption of O₂ on TiO₂?101?and?001?crystal plane were molecular adsorption,no dissociating.After O₂ adsorption,the energy band of TiO₂?101?and?001?crystal plane occurred one impurity level,which cloud reduce the band gap of electronic transiting to conduction band,while the impurity level of TiO₂?001?crystal plane was closer to the valence band.Through Mulliken analysis,after O₂ adsorption,the electronic was transfered from O₂ molecules to the?101?crystal plane,but TiO₂?001?crystal plane was transfering electron to O₂ molecules from crystal plane.Therefore,O₂ on TiO₂?001?crystal plane was easier to form peroxy radical?O₂·-?than TiO₂?101?crystal plane.Part three is synthesis and photocatalytic properties of anatase TiO₂ with low index crystal plane.TiO₂ with?101?crystal plane or?001?crystal plane were respectively synthesized by hydrothermal method,and characterized by a series of technique methods.XRD and Raman analysis showed that two kinds of samples is anatase type.SEM and TEM analysis showed that the TiO₂-101 sample with regular double cone shape had uniform size?about 50 nm × 30 nm?,and was identified as TiO₂ with dominant exposure of?10 1?crystal plane;TiO₂-001 sample with regular nano flake had uniform size?about 100 nm × 100 nm?,and was identified as TiO₂ with dominant exposure of?001?crystal plane.Polyacrylamide degradation and COD determination results indicated the anatase TiO₂ with?001?crystal plane was more excellent than anatase TiO₂ with?101?crystal plane in polyacrylamide photocatalytic.Those results verified the theoretical calculation conclusion of TiO₂?001?crystal plane having high photocatalytic activity.