Swelling of Layered Potassium Ruthenate into Nanosheet Crystallites
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Swelling of Layered Potassium Ruthenate into Nanosheet Crystallites Katsutoshi Fukuda,1 Hisato Kato,2 Wataru Sugimoto,1,2 Yoshio Takasu2 Collaborative Innovation Center for Nanotech Fiber, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan 2 Faculty of Textile Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan
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ABSTRACT The swelling and exfoliation behaviors of layered potassium ruthenate and the resultant unilamellar crystallites of RuO2.10.2- with nanosheet morphology were studied. The reaction of layered H0.2RuO2.1·0.9H2O with tetrabutylammonium hydroxide (TBA+OH-) was found to be extremely sensitive to the interlayer water content. The use of highly hydrous layered protonic ruthenate was essential for obtaining direct exfoliation. The swelling behavior was also affected by the ratio of TBA+ to ion-exchangeable H+ in the layered compound. At low ratios of TBA+/H+≤1, the layered precursor scarcely exfoliated and mostly deposited as an intercalation compound. In the intermediate TBA+/H+ range, an auburn colloidal suspension containing exfoliated nanosheets was formed, while much larger ratios were less favorable for the exfoliation. INTRODUCTION Unilamellar two-dimensional crystallites known as nanosheets are obtained by total exfoliation of various layered oxides with ion-exchange capabilities,1-5 and have attracted significant attention as a unique class of nano-scaled materials in solid state chemistry. These nanosheet crystallites have thickness in the range of molecular scale and lateral size of bulk material. The high structural anisotropy is quite different from that of other nanomaterials, which are usually spherical or rod-like in shape. They often exhibit intriguing physicochemical properties that cannot be attained by bulk materials due to its unique two-dimensionality. Furthermore, the intrinsically negatively charged nanosheets can be easily re-assembled into three-dimensional architectures by various methods. The parent layered material can be synthesized with a vast range of compositions via typical ceramic routes, allowing nanosheets with a comprehensive composition range as long as exfoliation can be accomplished. Such various nanosheets are important inorganic building block for the fabrication of a variety of well-ordered nanostructured materials,6 through which rational design of functionalities can be achieved. Rutile-structured RuO2 has many attractive properties atypical of most oxide systems, including metallic conductivity,7 electrocatalytic activity8 and excellent chemical and electrochemical stability.9 Ruthenate nanosheets10 can be regarded as a new family of two-dimensional crystalline ruthenium dioxide. We have studied these ruthenate nanosheets in terms of their physicochemical properties and applications as high power and energy density supercapacitor electrodes as well as highly active and durable fuel cell co-catalysts.10-12 We have shown that the interlayer nano-space of the layered ruthenate can be utilized for el
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