Synthesis of Ag2O Nanocrystals with Systematic Shape Evolution, Investigation of Their Facet Stability to Chemical Etching, and the Formation of Ag2S Nanocages Using the Ag2O Nanocrystal Templates

• Main Authors: Lyu, Lian-Ming, 呂煉明
• Other Authors: Huang, Michael Hsuan-Yi
• Format: Others
• Language: en_US
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/92053617997839314162

博士 === 國立清華大學 === 化學系 === 100 === Silver(I) oxide (Ag2O) is a p-type semiconductor with a reported band gap of 1.46 eV. Ag2O has the same cubic cuprite crystal structure as that of Cu2O. In the first project, we have successfully developed a facile procedure for the synthesis of Ag2O nanocrystals with systematic shape evolution from cubic to octahedral and hexapod structures by adjusting the amounts of NH4NO3, AgNO3, and NaOH solutions added to make the reaction mixture, while keeping their molar ratios constant. The crystals are mostly sub-micrometer-sized. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy characterization have been used to determine their crystalline facets. This work represents one of the first reports to achieve synthesis of Ag2O nanocrystals with systematic shape evolution. In the next study, we used Ag2O nanocubes, rhombicuboctahedra, octahedra, and extended hexapods to examine the relative stability of different crystal faces of Ag2O by selectively etching the least stable faces. NH3 was used as the etchant. By carefully controlling the volume of NH3 solution injected, only a specific face was etched, resulting in the formation of new Ag2O nanostructures. Ag(NH3)2+ formed from dissolved silver ions should drive the etching process while NaOH tunes the reaction equilibrium to control morphology of the etched nanocrystals. The order of facet stability in this reaction was found to be {111} > {110} > {100}. The {100} faces are most easily etched. In the third work, the use of these Ag2O heterostructures as templates for the formation of Ag2O–Ag2S core–shell structures and Ag2S cages with morphology control via nanoscale Kirkendall effect was considered. Cubic and hexapod-shaped Ag2S nanocages were produced from Ag2O nanocrystals of corresponding shapes. Cyclic voltammetry curves and scanning electron microscopy images were taken on cubic Ag2O crystals and cubic Ag2O–Ag2S core–shell structures to examine the effects of electrochemical redox processes on the morphology and composition integrity of the initial particles for the first time.