This paper reports on the swelling and exfoliation behavior of a layered protonic manganese oxide, H(0.13)MnO(2).0.7H(2)O, in a solution of tetrabutylammonium (TBA) hydroxide and the formation and characterizations of unilamellar two-dimensional crystallites of MnO(2). At low doses of TBA ions, layered manganese oxide was observed to undergo normal intercalation, yielding a TBA intercalated phase with a gallery height of 1.25 nm. With a large excess of TBA ions, osmotic swelling occurred, giving rise to a very large intersheet separation of 3.5-7 nm. In an intermediate TBA concentration range, the sample exhibited a broad X-ray diffraction profile with superimposed diffraction features due to intercalation and osmotic swelling. The component responsible for the broad profile was isolated by centrifuging the mixture twice at different speeds, and the recovered colloid was identified as a pile of MnO(2) nanosheets, corresponding to the individual host layer of the precursor layered manganese oxide. Observations by transmission electron microscopy and atomic force microscopy revealed high two-dimensional anisotropy with a lateral dimension of submicrometers and a thickness of approximately 0.8 nm. The nanosheet exhibited broad optical absorption with a peak at 374 nm (epsilon = 1.13 x 10(4) mol(-1) dm(3) cm(-1)). The restacking process of the colloidal MnO(2) nanosheets was followed by aging the colloid at a relative humidity of 95%. The broad diffraction pattern due to the exfoliated sheets weakened with time and eventually resolved into two sharp distinct profiles attributable to a TBA intercalation compound with an intersheet spacing of 1.72 nm and an osmotically swollen hydrate with >10 nm at a very early stage. As drying progressed, the former phase became more abundant without a change in interlayer distance, while the degree of swelling of the latter phase gradually decreased to 2.7 nm that remained unchanged on further aging. Subsequent drying at a lower humidity collapsed the 2.7 nm phase. The resulting single 1.72 nm phase was dehydrated by heating at 150 degrees C to produce a phase with a contracted interlayer spacing of 1.3 nm.

Multilayer ultrathin films composed of exfoliated nanosheets of manganese oxide and poly(diallyldimethylammonium) (PDDA) ions have been fabricated onto various substrates via electrostatic self-assembly technique. Dense monolayer coverage of the substrate surface by the nanosheets was confirmed by atomic force microscopy. UV−vis absorption spectroscopy provided evidence for subsequent growth of multilayer film, exhibiting progressive enhancement of optical absorption due to manganese oxide nanosheets. Evolution of a Bragg peak in the layer-by-layer deposition process also supported the growth of a nanostructured film of PDDA/MnO2 nanosheets with a repeating periodicity of ca. 0.9 nm. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed the inorganic−organic hybrid nature of the obtained multilayer assemblies. Calcination of the films at temperatures above 500 °C removed the polycations, yielding an ultrathin film of manganese oxide Mn2O3. Cyclic voltammogram measurements revealed one reduction peak and two oxidation peaks for a monolayer film, which are attributable to the electrochemical conversion between MnIII and MnIV in manganese oxide nanosheets.

2003 Nanotechnology Nanotechnology V 1505 Redoxable Nanosheet Crystallites of MnO 2 Derived via Delamination of a Layered Manganese Oxide. -Upon contact with aqueous tetrabutylammonium (TBA) ions, the layered compound H0.13MnO2·0.7H2O undergoes various reactions including intercalation, osmotic swelling, and delamination into single sheets, depending on the TBA concentration. Unilamellar crystallites of MnO2, which are only 0.77 nm in thickness and several hundreds of nanometers in lateral size are successfully isolated from other coexisting phases via centrifugation. Slow drying of these colloidal nanosheets proceeds via two different routes, producing the TBA intercalated phase and the osmotically swollen hydrate. -(OMOMO, Y.; SASAKI*, T.; WANG, L.; WATANABE, M.;

Layer-by-Layer Assembly of Multilayer Films Composed of Each Nanosheet: Ti 0.91 O 2 and MnO 2 . The deposition of one layer of Ti 0.91 O 2 nanosheets enhanced the absorbance at 255 nm by 0.139 ± 0.021, and no intrinsic absorption was observed at 372 nm. In contrast, the deposition of one layer of MnO 2 nanosheets provided the absorbance gain at 372 nm by 0.082 ± 0.014 as well as at 255 nm by 0.062 ± 0.007.