Literature highlights – September 2013

Effect of solvent on TEOS hydrolysis kinetics and silica particle size under basic conditions.

by Malay, Yilgor and Menceloglu from Sabanci University, Istanbul, Turkey
published in J. Sol-Gel Sci. Tech. 2013, 67:351-356

This article provides new evidence for and potential illustrative materials to lecturing on sol-gel chemistry.

In-situ liquid-state 29Si nuclear magnetic resonance was used to investigate the temporal concentration changes during ammonia-catalyzed initial hydrolysis of tetraethyl orthosilicate in different solvents (methanol, ethanol, n-propanol, iso-propanol and n-butanol). Dynamic light scattering was employed to monitor simultaneous changes in the average diameter of silica particles and atomic force microscopy was used to image the particles within this time frame. Solvent effects on initial hydrolysis kinetics, size and polydispersity of silica particles were discussed in terms of polarity and hydrogen-bonding characteristics of the solvents. Initial hydrolysis rate and average particle size increased with molecular weight of the primary alcohols. In comparison, lower hydrolysis rate and larger particle size were obtained in the secondary alcohol. Exceptionally, reactions in methanol exhibited the highest hydrolysis rate and the smallest particle size. Ultimately, our investigation elaborated, and hence confirmed, the influences of chemical structure and nature of the solvent on the formation and growth of the silica particles under applied conditions.

Structural characterization of nano-crystalline Co3O4 ultra-fine fibers obtained by sol-gel electrospinning.

by G. George and S. Anandhan from National Institute of Technology, Mangalore, India
published in J. Sol-Gel Sci. Tech. 2013, 67:256-266

This article gives a richly illustrated example of application of the electrospinning technique, a strongly developing tool in the production of metal oxide fibers.

In this paper, we report the obtention of ultrafine fibers of cobalt oxide (Co3O4) by combining electrospinning method with high-temperature calcinations from the precursor sol of poly(2-ethyl-2-oxazoline) (PEtOx)/cobalt acetate tetrahydrate [Co(CH3COO)2·4H2O] in water. The optimum electrospinning conditions for obtaining precursor composite nanofibers from PEtOx/Co(CH3COO)2·4H2O solution in water, to produce ceramic nanofibers, were studied. The average fiber diameter of the precursor composite fibers measured by scanning electron microscopy (SEM) was approximately 200 nm. Thermogravimetric analysis of PEtOx was performed to estimate the suitable calcination temperature of the precursor fibers. SEM images of the ceramic fibers obtained after calcination revealed the shrinkage in diameter due to complete degradation of the polymer and Co(CH3COO)2·4H2O. Fourier transform infrared spectroscopy was used to ensure the complete pyrolysis of polymer during calcinations of the composite fibers. Crystalline properties of the ceramic fibers were studied by X-ray diffraction and high resolution transmission electron microscopy. The ceramic fibers are polycrystalline with an average grain size of ≈40 nm obtained at a calcination temperature of 773 K. It was observed that the grain sizes increased as the calcination temperature was increased, due to self assembly mechanism.

Titanium alkoxide induced BiOBr-Bi2WO6 mesoporous nanosheet composites with much enhanced photocatalytic activity.

by J. Wang, G. Cao et al. from University of Washington, Seattle, USA<
published in J. Mater. Chem. A 2013, 1:7949-7956

This article presents an unexpected but very impressive evidence for the role of sol-gel matrix in the synthesis of porous photoactive nanocomposite.

Here we report a facile hydrothermal route for the preparation of BiOBr–Bi2WO6 mesoporous nanosheet composites (MNCs) in the presence of titanium isopropoxide, Ti(OiPr)4. High resolution transmission electron microscopy, X-ray diffraction, nitrogen adsorption/desorption analysis and X-ray photoelectron spectroscopy were employed for structural and composition analyses of the MNCs. The photogenerated charge transfer and photocatalytic activity of BiOBr–Bi2WO6 MNCs were investigated by Kelvin probe force microscopy and UV-vis spectroscopy. We propose mechanisms to illustrate how titanium alkoxide induces the formation of mesoporous nanosheet heterostructures and the enhanced photodecomposition efficiency of the dye under low light intensity illumination. Overall, our results suggest that titanium alkoxide is not only strongly involved in the growth of BiOBr (001) facets, but also plays a critical role in the pore evolution of the product. Kelvin probe force microscopy analysis allows us to conclude that the resulting nanocomposites demonstrate high photogenerated charge mobility and a long lifetime. Dye molecules can be rapidly and thoroughly decomposed with the photocatalyst under very low light intensity illumination. The enhanced photocatalytic activity is attributed to well matched band edge positions of BiOBr and Bi2WO6 and the large specific surface area of the MNCs in view of the incorporation of mesopores and the highly exposed BiOBr (001) facet due to the use of Ti(OiPr)4 during the synthesis. The results presented here are expected to make a contribution toward the development of delicate nanocomposites for photocatalytic water purification and solar energy utilization.!divAbstract

Structure-properties relationship in iron oxide-reduced grapheme oxide nanostructures for Li-ion batteries

by Y-E. Sung, N. Pinna et al. from Seoul National University, Seoul, Korea
published in Adv. Funct. Mater. 2013, 23:4293-43025

This article describes how solvothermal synthesis of oxide nanoparticles in the presence of graphene oxide/graphene can offer an approach to advanced materials for energy storage devices.

Non-aqueous sol-gel routes involving the reaction of metal oxide precursors in organic solvents (e.g., benzyl alcohol) at moderate temperature and pressure, offer advantages such as high purity, high reproducibility and the ability to control the crystal growth without the need of using additional ligands. In this paper, a study carried out on a series of iron oxide/reduced graphene oxide composites is presented to elucidate a structure-properties relationship leading to an improved electrochemical performance of such composites. Moreover, it is demonstrated that the easy production of the composites in a variety of temperature and composition ranges, allows a fine control over the final particles size, density and distribution. The materials obtained are remarkable in terms of the particle’s size homogeneity and dispersion onto the reduced graphene oxide surface. Moreover, the synthesis method used to obtain the graphene oxide clearly affects the performances of the final composites through the control of the restacking of the reduced graphene oxide sheets. It is shown that a homogeneous and less defective reduced graphene oxide enables good electrochemical performances even at high current densities (over 500 mAh/g delivered at current densities as high as 1600 mA/g). The electrochemical properties of improved samples reach the best compromise between specific capacity, rate capability and cycle stability reported so far.