| Summary: | 碩士 === 國立清華大學 === 化學系 === 101 === CHAPTER 1
Formation of Edge-Truncated Cubic and Truncated Rhombic Dodecahedral Cu2O Nanoframes via Chemical Etching
We report two simple approaches for the formation of edge-truncated cubic and {100}-truncated rhombic dodecahedral cuprous oxide (Cu2O) nanoframes. We used one-pot solution route to synthesize edge-truncated cubic nanoframes. An aqueous solution containing CuCl2, sodium dodecyl sulfate (SDS) surfactant, NH2OH•HCl reductant, NaOH, and HCl were utilized, with the reagents introduced in the order listed. Crystal growth dominates the process in the first hour. Selective acidic etching on the {110} faces by HCl via the addition of ethanol followed by sonication of the solution led to the novel structure of edge-truncated cubic nanoframe with exclusively the etched {110} faces. This is the first time Cu2O edge-truncated cubic nanoframes have been fabricated with diameters of 340–370 nm and a wall thickness of 20–22 nm. To make Cu2O truncated rhombic dodecahedral nanoframes, Cu2O truncated rhombic dodecahedra were used as the sacrificial templates. Careful chemical etching of truncated rhombic dodecahedra was accomplished by injection of an acidic HCl solution to enable face-selective etching over the {110} faces. The resulting {100}-truncated rhombic dodecahedral Cu2O nanoframes with empty {110} faces have a wall thickness of 20–30 nm. The morphologies of these hollow nanoframes were carefully examined by electron microscopy.
CHAPTER 2
Synthesis and Photocatalytic Activity of Ultrasmall Cu2O Cubes, Octahedra and Octapods
We have successfully utilized a feasible method to synthesize ultrasmall Cu2O cubic and octahedral nanocrystals with average edge lengths of 37 and 67 nm, respectively. The nanocrystals were prepared in an aqueous solution of copper acetate (Cu(OAc)2), NaOH and hydrazine (N2H4•H2O) reductant by simply varying the volume of hydrazine added to the reaction mixture. The amount of N2H4 added for cubes and octahedra may influence the truncation degree of Cu2O nanoparticles because N2H4 is a Lewis base. During the crystal growth, crystal faces with a higher growth speed would be eliminated and the crystal morphology was defined by the slowest growing crystal faces. By increasing the amount of N2H4 used, Cu2O octahedral nanocrystals with a higher fraction of {111} faces were produced.
Octapod-shaped Cu2O nanocrystals have also been synthesized via mixing CuCl2, NaOH, sodium dodecyl sulfate (SDS) surfactant and hydroxylamine (NH2OH•HCl) reductant. This is the first time Cu2O octapod-shaped nanocrystals with average sizes of 135 nm are synthesized. TEM and HRTEM images confirmed that the octapods are mainly bounded by the {100} faces with perpendicular crossed depression over their six cubic faces. Optical characterization of these smaller Cu2O nanocrystals showed a weak scattering effect with a broad band centered at 377, 457, and 532 nm respectively for the cubes, octahedra, and octapods. In the photodegradation of negatively charged methyl orange, 70 nm octahedra showed better photocatalytic performance than 135 nm octapods and 460 nm octahedra. The cubes with only the {100} faces were not active. The results clearly demonstrate that the dramatic differences in the catalytic activities of the {100} and {111} faces of Cu2O nanocrystals and that smaller particle sizes with a significantly more surface area of {111} facets are indeed more efficient catalysts.
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