| Heavy metal pollution in water environment had brought serious harm to human health and social development. Due to its excellent physical and chemical properties, such as, large specific surface area, atoms lacking coordination, biocompatibility characteristics and had magnetism to easily be separated, Fe3O4 had been widely used to remove the heavy metal in wastewater. Nanocomposites based on Fe3O4 were designed and synthesized in this work. First principles calculations based on density functional theory (DFT) were used to explore their structure and electronic properties. Fe3O4/TiO2 nanocomposites had been prapered and were used to remove Cr (VI) in wastewater. The content as described below:1. By using the first-principle calculations, The cubic Fe3O4 theoretical structure model, as well as Fe3O4 with oxygen deficiency model, was constructed to study the electronic properties, such as geometry and electronic structure, energy structure, density of state, electronic mobility and the migration of the electron-hole pairs. The combination of electron-hole could be determined by effective electronic mass. The effective electronic mass ratio of Fe3O4 bulk was 1.810 and Fe3O4 with oxygen deficiency was 7.368.This suggested that the separation of electronic-hole rate was higher and the photocatalytic properties and adsorption performance were stronger.2. The Fe3O4 with different active surface, such as (111), (001), (110) and (100), had been studied in the paper. The energy structure, density of states and electron mobility were explored to illustrate the physical and chemical activity of facet. The effective electronic mass ratio of Fe3O4 (111), (001), (110), (100) were respectively 2.435,0.1867,0.9587,0.631. And Fe3O4 (111) was the largest than the other surfaces. Therefore Fe3O4 (111) had good photocatalytic properties and adsorption properties. Taken (111) facet of Fe3O4 as example, there were two different oxygen species on Fe3O4 surface which were bridging oxygen and terminal oxygen. We built two kinds of model, one was bridging model, where one cobalt atom or water molecules was linked to one bridging oxygen site. The other was terminal model, where one cobalt atom or water molecules was linked to one terminal oxygen site, and analyzed its adsorption ability. The results showed that the middle of oxygen and the intermediate oxygen of the surface Fe3O4 (111) had high chemical activity.3. The layered structure model was used to construct Fe3O4/TiO2 structural model to explore the geometric structure and electronic properties of nanomaterials. Additionally, Fe3O4/TiO2 nanocomposites were synthesized by using ultrasonic assisted hydrothermal method and used to remove Cr (Ⅵ) in water. When Fe3O4/TiO2 with molar ratio 1:2,Fe3O4/TiO2 nanocomposites had the best adsorption effect to 50 mg/L Cr (Ⅵ) aqueous solution at 25 ℃. After four hours, it reached adsorption equilibrium and adsorption rate could reach 60%.4. First-principles calculations based on DFT were used to study the geometry structure and electronic properties of cube WO3. The band structure, density of states and effective electron mobility rate were explored in this work. The energy gap of WO3was 0.596 eV. The valence band upper was mainly composed of O 2p state, while the bottom of conduction band of WO3 was mainly composed of W 5d. The electrons of O 2p transit to W 5d under irradiation, leaving hole in the O 2p state. And the combination of electron-hole could be determined by effective electronic mass, which could be calculated to be 1.345. It showed that we could make it have a higher electronic-hole separation efficiency through the experiment, which would enhance the photocatalytic activity of WO3. The surface energy of WO3 (001) and its adsorption ability to the nonmetal elements (H、B、C、Si、N、P、O、S、F、Cl、Br、I) were calculated, which indicated that F was the most favorable to be adsorbed on the surface. It revealed that F could be used as surface control agent, which was conductive to the synthesis of new functional materials with specific surface. |
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