The Enhanced Photocatalytic Performance Of {111} Plane NiO, CoO, Cu ₂ Se And Cu ₂ O / Cu < Its Physical Mechanism Research

Cubic NiO octahedron, CoO octahedron, Cu2Se nanowires and superlattice nanowire with exposed{111} facets were synthesized through thermal decomposition, solvothermal and hydrothermal routes. Morphologies and structures of these products were characterized by means of X-ray diffraction, scanning electron microscopy, field emission scanning electron microscopy, transmission electron microscopy, IR spectrum, X-ray photoelectron spectra and absorption-desorption porosimetry. The growth and formation processes of NiO, CoO, Cu2Se and Cu2O/Cu2Se nanostructures with various geometrical morphologies were studied, and the possible growth mechanisms were proposed. The photocatalyisis degradation organic compounds and photocatalytic H2 evolutionon properties of as-obtained NiO, CoO, Cu2Se and Cu2O/Cu2Se nanostructures with various morphologies were studied, and the relations between morphology, size, exposed facets and properties were investigated. These research results would provide a base for further research on syntheses of NiO, CoO, Cu2Se and Cu2O/Cu2Se nanostructures, the physical and chemicaFproperties of NiO, CoO, Cu2Se and Cu2O/Cu2Se nanostructures and their applications in photocatalysis, photonic and electronic devices and solar cell.(1) The CF ion capped NiO octahedrons were prepared via a simple thermal decomposition. The CFion capped NiO octahedrons were soaked by AgNOsand NH3· H2O solutions, and the phtocatalytic activity of the products for degradation of malachite green under ultraviolet light irradiation were studied. It is found that photocatalytic performances of the Cl-ion capped NiO octahedrons were activated by treatment of AgNO3 and NH3·H2O solutions. The superior photocatalytic activities are attributed to clean{111} facets of the NiO octahedrons without CF ions and the heterojunction between AgCl and NiO. The structure, surface energy of NiO (111), (200) and (220) facets and atomic charge of the NiO (111) facets are studied using periodic density functional theory (DFT). It is found that the{111} facets may show higher reactivity than (200) and (220) facets, and the exposed NiO{111} facets are polar surfaces. A charge separation model between polar NiO{111} surfaces is proposed to explain the enhanced photocatalytic activities.(2) The Cl-CoO octahedrons structure were synthesised by heating CoCl2 aqueous solution at 450℃ in a N2 gas atmosphere. The Cl-CoO octahedrons were processed by AgNO3 and NH3·H2O solution and the phtocatalytic activity of the products for degradation of malachite green under visible light irradiation were studied. It is found that photocatalytic performances were enhanced significantly. The enhanced photocatalytic activities are attributed to the clean CoO{111} facets and the heterojunction between AgCl and CoO. The structure and atomic charge of the exposed CoO{111} facets are studied using periodic density functional theory. The results indicate that the exposed CoO{111} facets are polar surfaces. A charge separation model between polar{111} surfaces is proposed, this model can deepen understanding of the exposed{111} the CoO octahedral structure enhanced photocatalytic property.(3) Cu2Se nanowires with exposed{111} facets and various aspect ratios have been synthesized by a solvothermal reaction of Cu(Ac)2 with Se, NaOH, C2H5OH and C3H8O3, and aspect ratio of the Cu2Se nanowires can be changed by adjusting the reaction time and volume ratio of ethanol to glycerol. The influence of solvent ethanol and glycerol molecules on the geometric shapes was investigated and possible growth mechanism was proposed. The phtocatalytic activity of the Cu2Se nanowires with different aspect ratios and Cu2Se powders for degradation of malachite green under ultraviolet light irradiation was studied, indicating that the photocatalytic activity of the as-prepared Cu2Se nanowires is enhanced by increasing the aspect ratio, percentage of {111} surfaces and TC (111). The structure, surface energy of Cu2Se (111), (121) and (2 02) facets and atomic charge of the Cu2Se (111) facets are studied using periodic density functional theory. It is found that the exposed Cu2Se{111} facets are polar surfaces. Based on the polar structure of the Cu2Se{111} facets, a charge separation model between polar (111) and (m) surfaces is proposed. The internal electric field between polar (111) and (ill) surfaces created by the spontaneous polarization drives charge separation. The reduction and oxidation reactions take place on the positive (111) and negative (m) polar surfaces. The charge separation model can explain clearly the Cu2Se semiconductor nanocrystals with highly photocatalytic activities.(5) Cu2Se nanosheets with exposed{111} facets have been synthesized by a hydrothermal reaction of Cu(Ac)2 with Se, TEA and H2O. Aa and MnO? have been selectively deposited on Cu2Se(111) and (111) facets, and reduction oxidation reaction take place on the (111) and (111) facets. It is further confirmed that the charge separation mechanism of Cu2Se(111) and (111) polar facets(4) Different aspect ratio of the precursor nanowires were synthesized via a hydrothermal reaction of ETA with H2O, Se, KBH4 and Cu foils at 120-200℃ for 12-24 h. Cubic Cu2O/Cu2Se nanowires with exposed{111} facets were obtained by calcining the precursor nanowires in Ar at 350℃ for 2 h. The influence of solvent ethanolamine molecules on the geometric shapes was investigated. The as-prepared Cu2O/Cu2Se nanowires were characterized by means of transmission electron microscopy. It is found that the Cu2O/Cu2Se nanowires are superlattice structure with cubic CU2O and Cu2Se arranged alternately. Use methanol as a sacrificing agent, the photocatalytic H2 production activity of different aspect ratio of Cu2O/Cu2Se nanowires under visible light irradiation was studied. It is found that photocatalytic H2 production activities of the as-prepared Cu2O/Cu2Se nanowires are enhanced by increasing the aspect ratio and TC (111). It is reasonable to conclude that the exposed{111} facets may be highly reactive facets for the activity in H2 evolution. The structure and atomic charge of Cu2O and Cu2Se (111) facets (111), surface energy of Cu2O and Cu2Se (111), (121) and (202) facets are studied using periodic density functional theory. The calculation results have shown that the exposed CU2O and Cu2Se{111} facets are of the polar surfaces. Based on the polar structure of the Cu2O and CuaSe{111) facets, a charge separation model between polar (111) and (111) surfaces is proposed to interpret the enhanced photocatalytic H2 production activities.