The structural relaxation, electronic structures, formation energies and transition energy levels of monoclinic HfO2 with neutral and charged oxygen vacancies have been studied using the first principles calculation b...The structural relaxation, electronic structures, formation energies and transition energy levels of monoclinic HfO2 with neutral and charged oxygen vacancies have been studied using the first principles calculation based on density-functional theory and generalized gradient approximation. The results show that oxygen vacancies with different charge states can be formed in m-HfO2 under both oxygen-rich and oxygen-poor conditions. Especially, lower formation energy is obtained in poor oxygen environment. In the presence of oxygen vacancies with different charge states, extra levels can be observed at different positions in the band gap. And the most stable charge states are obtained for varying Fermi levels in the HfO2 band gap. It is found that oxygen vacancy in m-HfO2 has a negative-U behavior.展开更多
In this work,the relationship between electronic structure and hemocompatibility of oxygen deficient rutile TiO2-x was studied by both theoretical calculation and experimental study. Based on the local density functio...In this work,the relationship between electronic structure and hemocompatibility of oxygen deficient rutile TiO2-x was studied by both theoretical calculation and experimental study. Based on the local density functional theory,first-principals method was performed to calculate the electronic structure of rutile TiO2 with different oxygen vacancy concentration. In the range of less than 10% of (or equal) physically realistic O vacancy concentration,the band gap of rutile TiO2 increases with increasing O vacancy concentration,leading the TiO2 changes from a p-type to an n-type semiconductor. The valance band of TiO2 is predominated by O 2p orbital,while the conduction band is occupied by Ti 3d orbital for different O vacancy concentration. The O vacancy results in the occupation of electrons at the bottom of conduction band of TiO2,and the donor density increases with increasing O vacancy concentration. When materials come in contact with blood,the n-type semiconductor feature of oxygen deficient TiO2-x with the bottom of conduction band occupied by electrons would prevent charge transfer from fibrinogen into the surface of materials,thus inhibiting the aggregation and activation of platelets,therefore improving the hemocompatibility of rutile TiO2-x.展开更多
Recently,NO_x emissions in the cold-start period have been a great challenge in eliminating diesel vehicle exhaust.In this study,a type of NO_x adsorption-selective catalytic reduction(AdSCR)bifunctional catalyst was ...Recently,NO_x emissions in the cold-start period have been a great challenge in eliminating diesel vehicle exhaust.In this study,a type of NO_x adsorption-selective catalytic reduction(AdSCR)bifunctional catalyst was developed to remove NO_x in the cold-start period by constructing additional NO_x adsorption sites on the surface of the selective catalytic reduction of NO_x with NH_(3) catalyst.The AdSCR catalyst exhibited both NO_x adsorption-storage performance and NH_(3)-SCR activity.The amount of oxygen vacancies directly affected the adsorption performance of NO_x on the catalyst surface.In this study,H_(2)O_(2)with different pH values was employed to adjust the electronic structure of the CeZrO_(2) support and construct oxygen vacancies on the surface of CeZrO_(2),which contributed to improving NO_x adsorption and storage on the WO_(3)/CeZrO_(2)(W/CZ)catalyst below 200℃.The catalytic performance results show that CZ supports modified by alkaline H_(2)O_(2) rather than acidic and neutral H_(2)O_(2) significantly improve the NO_x adsorption capacity without decreasing the NH3-SCR activity.The characterization results show that the CZ support modified by alkaline H_(2)O_(2)possesses more surface oxygen vacancies and chemisorbed oxygen than CZ supports modified by acidic and neutral H_(2)O_(2).Oxygen vacancies are not only the active sites of NH_(3)-SCR,but also the active sites of NO_x adsorption.Therefore,the W/CZ catalyst modified by alkaline H_(2)O_(2)exhibited an excellent AdSCR performance.This study proposes a novel perspective to address the issue of NO_x emissions from diesel vehicles during the cold start period.展开更多
基金supported by the National Natural Science Foundation of China (No.51202196)the Northwestern Polytechnical University (NPU) Foundation for Fundamental Research (No.JC201111)+1 种基金the Research Fund of the State Key Laboratory of Solidification Processing (NWPU,(No.58-TZ-2011)the 111 Project (No.B08040)
文摘The structural relaxation, electronic structures, formation energies and transition energy levels of monoclinic HfO2 with neutral and charged oxygen vacancies have been studied using the first principles calculation based on density-functional theory and generalized gradient approximation. The results show that oxygen vacancies with different charge states can be formed in m-HfO2 under both oxygen-rich and oxygen-poor conditions. Especially, lower formation energy is obtained in poor oxygen environment. In the presence of oxygen vacancies with different charge states, extra levels can be observed at different positions in the band gap. And the most stable charge states are obtained for varying Fermi levels in the HfO2 band gap. It is found that oxygen vacancy in m-HfO2 has a negative-U behavior.
基金Supported by the National Basic Research Program of China (Grant No. 2005CB623904)National High-Tech Research Program of China (Grant No. 2006AA02A139)National Natural Science Foundation of China (Grant No. 20603027)
文摘In this work,the relationship between electronic structure and hemocompatibility of oxygen deficient rutile TiO2-x was studied by both theoretical calculation and experimental study. Based on the local density functional theory,first-principals method was performed to calculate the electronic structure of rutile TiO2 with different oxygen vacancy concentration. In the range of less than 10% of (or equal) physically realistic O vacancy concentration,the band gap of rutile TiO2 increases with increasing O vacancy concentration,leading the TiO2 changes from a p-type to an n-type semiconductor. The valance band of TiO2 is predominated by O 2p orbital,while the conduction band is occupied by Ti 3d orbital for different O vacancy concentration. The O vacancy results in the occupation of electrons at the bottom of conduction band of TiO2,and the donor density increases with increasing O vacancy concentration. When materials come in contact with blood,the n-type semiconductor feature of oxygen deficient TiO2-x with the bottom of conduction band occupied by electrons would prevent charge transfer from fibrinogen into the surface of materials,thus inhibiting the aggregation and activation of platelets,therefore improving the hemocompatibility of rutile TiO2-x.
基金financially supported by the National Natural Science Foundation of China (No.22072098)Sichuan Science and Technology Program (No.2022ZHCG0125)。
文摘Recently,NO_x emissions in the cold-start period have been a great challenge in eliminating diesel vehicle exhaust.In this study,a type of NO_x adsorption-selective catalytic reduction(AdSCR)bifunctional catalyst was developed to remove NO_x in the cold-start period by constructing additional NO_x adsorption sites on the surface of the selective catalytic reduction of NO_x with NH_(3) catalyst.The AdSCR catalyst exhibited both NO_x adsorption-storage performance and NH_(3)-SCR activity.The amount of oxygen vacancies directly affected the adsorption performance of NO_x on the catalyst surface.In this study,H_(2)O_(2)with different pH values was employed to adjust the electronic structure of the CeZrO_(2) support and construct oxygen vacancies on the surface of CeZrO_(2),which contributed to improving NO_x adsorption and storage on the WO_(3)/CeZrO_(2)(W/CZ)catalyst below 200℃.The catalytic performance results show that CZ supports modified by alkaline H_(2)O_(2) rather than acidic and neutral H_(2)O_(2) significantly improve the NO_x adsorption capacity without decreasing the NH3-SCR activity.The characterization results show that the CZ support modified by alkaline H_(2)O_(2)possesses more surface oxygen vacancies and chemisorbed oxygen than CZ supports modified by acidic and neutral H_(2)O_(2).Oxygen vacancies are not only the active sites of NH_(3)-SCR,but also the active sites of NO_x adsorption.Therefore,the W/CZ catalyst modified by alkaline H_(2)O_(2)exhibited an excellent AdSCR performance.This study proposes a novel perspective to address the issue of NO_x emissions from diesel vehicles during the cold start period.
基金National Natural Science Foundations of China(51202196)Northwestern Polytechnical University Foundation for Fundamental Research(JC201111)"111"Project Foundation(B08040)
