Search results for "mesoporous silica"
showing 10 items of 135 documents
Morphology and properties of poly(methyl methacrylate) (PMMA) filled with mesoporous silica (MCM-41) prepared by melt compounding
2016
This paper reports on the morphologies of poly(methyl methacrylate) (PMMA)/mesoporous silica (MCM-41) composites prepared by melt compounding with various MCM-41 contents in the range of 0.1–5 wt%, the interactions between the polymer and filler in these composites, and their thermomechanical, mechanical and thermal degradation properties. The composites formed transparent films at low filler loadings (\0.5 wt%) because of well-dispersed, unagglomerated particles. The presence of polymer did not alter the pore dimensions in the MCM-41 structure and it maintained its hexagonal structure, even though the polymer chains partially penetrated the pores during composite preparation. The PMMA inte…
Temperature dependence of magnetization reversal in Co and Fe3O4 nanowire arrays
2005
Abstract In this paper, we investigate the magnetization reversal of cobalt and magnetite nanowires, 4 nm in diameter, synthesized within the pores of mesoporous silica thin films. A SQUID magnetometer was used to study the magnetic properties of the nanowire arrays over a broad temperature interval, T= 1.8–300 K. The magnetization reversal process was found to be strongly temperature dependent. While a coherent rotation may occur at room temperature, a process involving the formation of domain structures takes place as the temperature decreases down to 1.8 K.
Optimization of MCM-41 type silica nanoparticles for biological applications: Control of size and absence of aggregation and cell cytotoxicity
2015
Abstract Mesoporous silica nanoparticles were synthesized at high pH using CTAB as a template and TEOS as a silica precursor. It was shown that varying the NaOH concentration between 5 and 27.5 mM allows the size, pore and silica structure of mesoporous nanoparticles to be precisely tuned. In particular, monodisperse nanoparticles with the MCM-41 structure with size ranging from 90 nm to 450 nm were obtained by increasing the NaOH concentration from 12.5 to 22.5 mM. It thus demonstrates that NaOH concentration must range between 12.5 and 15 mM in order to prepare MCM-41 silica nanoparticles with optimal size for nanovectorization. We also found that under usual conditions the aggregation of…
Effects of Pressure, Thermal Treatment, and O2 Loading in MCM41, MSU-H, and MSU-F Mesoporous Silica Systems Probed by Raman Spectroscopy
2015
We present a Raman study of the effects induced by pressure, thermal treatments, and O2 loading in MCM41, MSU-H, and MSU-F representative mesoporous silica. We compared the starting powders with the mechanically pressed tablets produced applying pressures of ∼0.2 and ∼0.45 GPa. The spectra of the three untreated tablets evidence that the main value of the Si-O-Si angle decreases and that in the MCM41 and the MSU-H Si-O-Si hydrolysis occurs, whereas such a process is absent or much less efficient in the MSU-F. Despite their different networks, the three powders tend to crystallize in cristobalite when treatments are at 1000 °C. The MCM41 and MSU-H tablets exhibit behavior similar to their st…
Thalassiosira pseudonana diatom as biotemplate to produce a macroporous ordered carbon-rich material
2008
Abstract Ordered macroporous–mesoporous carbonaceous materials were produced as a direct replica of the Thalassiosira pseudonana diatom by infiltration of the skeleton with furfuryl alcohol. The final carbon-rich material preserves the macropores of the diatom acting as bio-template and new hierarchical macro–mesopores appears as the silica is eliminated through chemical etching. The final solid can be described as an organized array of carbon macrotubes. In order to understand the progressive silica etching and the subsequent effect on the final carbon material, different etching reagents have been used. Moreover, the similar pore topology of T. pseudonana and the well known MCM-41 mesopor…
Magneto-optical Investigations of Nanostructured Materials Based on Single Molecule Magnets Monitor Strong Environmental Effects
2007
The determination of the magnetic properties of molecular magnets in environments similar to those used in spintronic devices is fundamental for the development of applications. Single-molecule magnets (SMMs) are molecular cluster systems that display magnetic hysteresis of dynamical origin at low temperature. As they behave like perfectly monodisperse nanomagnets and show clear macroscopic quantum effects in their magnetic properties, they are extremely appealing candidates for the forthcoming generation of molecular devices: they have been proposed as efficient systems for quantum computation, ultra-high-density magnetic recording media, and molecular spintronic systems. These attractive …
Surfactant-Assisted Synthesis of Mesoporous Alumina Showing Continuously Adjustable Pore Sizes
1999
Porous materials displaying tailor-made pore sizes and shapes are particularly interesting in a great variety of real and potential applications where molecular recognition is needed, such as shape-selective catalysis, molecular sieving, and selective adsorption. Classically, apart from silica, materials most commonly used for catalysis and catalyst supports have been those based on high surface aluminas, owing to their thermal, chemical, and mechanical stability and their low cost. Earlier aluminas with high surface areas (~500 m/g) had been prepared using structure-directing agents. However, they were X-ray amorphous materials and their porosity was purely textural, characterized by wide …
Stable anchoring of dispersed gold nanoparticles on hierarchic porous silica-based materials
2010
The nanometric organization of MOx (M = Co, Zn, Ni) domains partially embedded inside the mesoporous silica walls but accessible to the pore voids, which is achieved through a simple one-pot surfactant-assisted procedure, define optimal anchors for the nucleation and growth of gold nanoparticles, which in turn favours an exceptional thermal stability for the final Au-supported materials. As silica support we have selected a UVM-7 silica having a highly accessible architecture defined by two hierarchic pore systems. The combination of nanometric pore length, tortuous mesopores and MOx inorganic anchors favours the stability of the final Au/CoOx-UVM-7 nanocomposites.
Incorporation of Mn12single molecule magnets into mesoporous silica
2003
The incorporation of four Mn12 derivatives, namely [Mn12O12(O2CR)16(H2O)4] (R = CH3 (1), CH3CH2 (2), C6H5 (3), C6F5 (4)), into the hexagonal channels of the MCM-41 mesoporous silica has been studied. Only the smallest clusters 1 and 2, i.e. those with compatible size with the pores of MCM-41, could enter into the mesoporous silica. Powder X-ray diffraction analysis, HRTEM images and N2 adsorption–desorption isotherm experiments show that the well-ordered hexagonal structure of MCM-41 is preserved and that the Mn12 clusters are inside the pores. The magnetic properties of the MCM-41/2b nanocomposite material obtained in CH2Cl2 indicate that the structure of the cluster is maintained after in…
<title>Metallic and semiconducting nanowires: properties and architectures</title>
2003
Nanowires are expected to play an important role in future electronic, optical devices and nanoelectromechanical devices. Measuring the electrical and mechanical properties of nanowires is however a difficult task due to their small dimensions. Here we report the use of an in-situ microscopy technique, which combines transmission electron microscopy (TEM) with scanning probe microscopy (SPM), to investigate the electrical and mechanical properties of metallic and semiconductor nanowires. Additionally, in this paper we describe a novel approach for synthesizing mesoporous silicas with tunable pore diameters, wall thickness and pore spacings that can be used as tempates for the assembly of se…