Control of silica-alkyltrimethylammonium bromide mesophases with 1,3,5-trialkylbenzenes under acidic conditions

A multifunctional role of trialkylbenzenes for the preparation of aqueous colloidal mesostructured/mesoporous silica nanoparticles with controlled pore size, particle diameter, and morphology

Both the pore size and particle diameter of aqueous colloidal mesostructured/mesoporous silica nanoparticles (CMSS/CMPS) derived from tetrapropoxysilane were effectively and easily controlled by the addition of trialkylbenzenes (TAB). Aqueous highly dispersed CMPS with large pores were successfully obtained through removal of surfactants and TAB by a dialysis process. The pore size (from 4 nm to 8 nm) and particle diameter (from 50 nm to 380 nm) were more effectively enlarged by the addition of 1,3,5-triisopropylbenzene (TIPB) than 1,3,5-trimethylbenzene (TMB), and the enlargement did not cause the variation of the mesostructure and particle morphology. The larger molecular size and higher hydrophobicity of TIPB than TMB induce the incorporation of TIPB into micelles without the structural change. When TMB was used as TAB, the pore size of CMSS was also enlarged while the mesostructure and particle morphology were varied. Interestingly, when tetramethoxysilane and TIPB were used, CMSS with a very small particle diameter (20 nm) with concave surfaces and large mesopores were obtained, which may strongly be related to the initial nucleation of CMSS. A judicious choice of TAB and Si sources is quite important to control the mesostructure, size of mesopores, particle diameter, and morphology.

Understanding the phase emergence of mesoporous silica

The cylinder-to-vesicle phase transition of mesoporous silica and the inter-dependence of the controlling factors are studied. (3-Mercaptopropyl)trimethoxylsilane (MPTMS) is used to alter the phase outcome of mesoporous silica from the cylindrical MCM-41 to the vesicular phase. Exploiting the phase selection at the critical time point of phase emergence allows investigation of the complex interactions among the ingredients. In this system, orderly cylindrical or vesicular phase directly emerges from the "clumps" of randomly mixed surfactant, co-surfactant, and silica precursor. The phase outcome depends on the exact ratio of the ingredients, provided that enough amounts of MPTMS can diffuse into the clumps before the hardening silica prevents the diffusion.

Design and synthesis of high performance multifunctional ultrathin hematite nanoribbons

1D porous ultrathin nanoribbons of hematite (α-Fe2O3) were prepared by controlled annealing of different oxides and hydroxides of iron obtained from a solvothermal synthesis method. It is found that calcination at a temperature of 500 °C for 150 min decomposes these iron hydroxides into their most stable oxide form, i.e., α-Fe2O3. Driven by different attractive forces, these porous α-Fe2O3 nanoparticles get aggregated in an ordered fashion to form an ultrathin 1D nanoribbon structure, as observed by detailed time dependent TEM and HRTEM analysis. It has been found that the high aspect ratio and porous surface morphology of these nanoribbons have significantly improved their electronic and spintronic properties as manifested by their photocatalysis, gas sensing, electrochemical, and magnetic behaviors. These hematite nanoribbons exhibit a weak ferromagnetic behavior due to surface spin disorder and shape anisotropy. Lateral confinement of electrons increases the band gap of the nanoribbons, as evident from the UV absorption analysis, which in turn improves their photocatalytic degradation efficiency (rate constant ∼0.95 h(-1)) by delaying the electron-hole recombination process. However, their liquid petroleum gas sensing properties have been found to be mainly governed by the improved (porous) surface of the hematite nanoribbons that provides huge interaction sites for the analyte gas. Most of all, these hematite nanoribbons show a significantly enhanced pseudocapacitive performance exhibited by their high specific capacitance of about 145 F g(-1) at a current density of 1 A g(-1), high rate capability, and also long cycle stability (nearly 96% of capacity retention after 1600 charging/discharging cycles).

Highly ordered mesoporous TiO2-Fe2O3 mixed oxide synthesized by sol-gel pathway: an efficient and reusable heterogeneous catalyst for dehalogenation reaction

Highly ordered two-dimensional (2D) hexagonal TiO(2)-Fe(2)O(3) mixed-oxide material MFT-1, which is composed of very tiny nanoparticles, is synthesized using sodium dodecylsulfate (SDS) as a structure-directing agent. Interestingly, synthesis of an ordered mesophase was not possible using SDS as a template for mesoporous pure Fe(2)O(3) or TiO(2) phases. This mesoporous iron-titanium mixed-oxide material has been characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), N(2) sorption, ultraviolet-visible light diffuse reflectance spectroscopy (UV-vis DRS) studies. N(2) sorption analysis revealed high surface areas (126-385 m(2) g(-1)) and narrow pore size distributions (3.1-3.4 nm) for different samples. UV-vis DRS spectra and wide-angle powder XRD patterns indicate that the material is composed of α-Fe(2)O(3) and anatase TiO(2) phases. This TiO(2)-Fe(2)O(3) mixed-oxide material can act as a very efficient and reusable catalyst in the dehalogenation of aromatic chloride-, bromide-, and iodide-tolerating -F, -CN, -CH(3), -OCH(3) and -NO(2) functional groups in the aromatic ring using 2-propanol as the dispersion medium.

Controlled formation of polyamine crystalline layers on glass surfaces and successive fabrication of hierarchically structured silica thin films

The formation of silica films on the glass plate whose surface was precoated by crystalline linear poly(ethylenimine) (LPEI) in advance was systematically investigated via controlling the surface-specific crystallization of the LPEI on the glass plate. Immersing glass substrates into a hot aqueous solution of LPEI containing additives such as transition metal ions and acidic compounds and retaining them on 30 °C for desired periods resulted in the formation of crystalline LPEI layers on the substrates. Subsequently dipping this LPEI-coated glass into silica source solutions afforded successfully hierarchically structured silica film which coated continuously the surface of the substrates. In this two-step process, we found that the formation of hierarchically structured silica films strongly depended on the LPEI layer formed from the LPEI aqueous solutions containing different additives. The LPEI layer formed by changing the kinds of additives and their concentrations provides the differently structured silica films composed of turbine-like structures flatly lying-on and/or vertically standing-on as well as ribbon network structures on the surface of the substrates. Moreover, we functionalized these silica films by the introduction of hydrophobic alkyl chains or emissive Eu(III) complexes and investigated their wettability and emission properties.

Swelling of ionic and nonionic surfactant micelles by high pressure gases

The influence of different solvent environments on the size, shape, and characteristics of surfactant micelles of Pluronic F127 and CTAB was investigated by small-angle neutron scattering (SANS). SANS experiments were undertaken on dilute micellar surfactant solutions of F127 and CTAB that between them were exposed to liquid and supercritical carbon dioxide, liquid propane, ethane, and heptane under various pressures and temperatures. Swelling of the surfactant micelles could be directly related to the solubility of the solvents within the micelles, especially within their cores. Carbon dioxide produced the largest swelling of the Pluronic F127 micelles, compared to propane and ethane, which mirrors the solubility of the gases in the PPO core of the micelles. Conversely, the extent of swelling of the cores of CTAB micelles was greater with propane compared to carbon dioxide, which again relates to the solubility of the solvents in the alkane core of the CTAB micelles.