A study of the formation, purification and application as a SWNT growth catalyst of the nanocluster [HxPMo12O40[subset]H4Mo72Fe30(O2CMe)15O254(H2O)98].

The synthetic conditions for the isolation of the iron-molybdenum nanocluster FeMoC [HxPMo12O40 [subset]H4Mo72Fe30(O2CMe)15O254(H2O)98], along with its application as a catalyst precursor for VLS growth of SWNTs have been studied. As-prepared FeMoC is contaminated with the Keplerate cage [H4Mo72Fe30(O2CMe)15O254(H2O)98] without the Keggin [HxPMo12O40]n- template, however, isolation of pure FeMoC may be accomplished by Soxhlet extraction with EtOH. The resulting EtOH solvate is consistent with the replacement of the water ligands coordinated to Fe being substituted by EtOH. FeMoC-EtOH has been characterized by IR, UV-vis spectroscopy, MS, XPS and 31P NMR. The solid-state 31P NMR spectrum for FeMoC-EtOH (delta-5.3 ppm) suggests little effect of the paramagnetic Fe3+ centers in the Keplerate cage on the Keggin ion's phosphorous. The high chemical shift anisotropy, and calculated T1 (35 ms) and T2 (8 ms) values are consistent with a weak magnetic interaction between the Keggin ion's phosphorus symmetrically located within the Keplerate cage. Increasing the FeCl2 concentration and decreasing the pH of the reaction mixture optimizes the yield of FeMoC. The solubility and stability of FeMoC in H2O and MeOH-H2O is investigated. The TGA of FeMoC-EtOH under air, Ar and H2 (in combination with XPS) shows that upon thermolysis the resulting Fe : Mo ratio is highly dependent on the reaction atmosphere: thermolysis in air results in significant loss of volatile molybdenum components. Pure FeMoC-EtOH is found to be essentially inactive as a pre-catalyst for the VLS growth of single-walled carbon nanotubes (SWNTs) irrespective of the substrate or reaction conditions. However, reaction of FeMoC with pyrazine (pyz) results in the formation of aggregates that are found to be active catalysts for the growth of SWNTs. Activation of FeMoC may also be accomplished by the addition of excess iron. The observation of prior work's reported growth of SWNTs from FeMoC is discussed with respect to these results.

Effect of surfactant on particle morphology for liquid phase deposition of submicron silica.

Liquid phase deposition (LPD) of silica from soluble silicates has been performed in the presence of dodecyltrimethylammonium bromide (DTAB), sodium dodecyl sulfate (SDS) and sodium dodecylbenzyl sulfate (SDBS). The morphology of the silica varies between semi-ordered uniform spheres to low porosity agglomerates, with the choice and concentration of the surfactants. The agglomerate structures depend on the charge of the surfactant (and hence the retention of micelles under acidic LPD conditions and/or the ionic character of the surfactant solution), the critical micelle concentration (as compared to the concentration of the silica precursor), and the ionic strength of the solution. The application of surfactant micelles as templates for LPD silica is counter to a previous proposal that suggested the ionic strength of the silicate solution would cause the collapse of the ionic vesicles. The size of spherical silica particles is controlled by the relative concentration of the surfactant and the LPD precursor.

Silica coated fullerenols: seeded growth of silica spheres under acidic conditions.

Liquid phase deposition of silica in the presence of fullerenol C60(OH)n, results in the formation of uniform silica spheres, whereas the use of C60 gives large non-uniform agglomerates as a result of homogeneous nucleation. Raman and UV spectroscopy indicate the C60 is retained as the core of the silica spheres.