Doped Aerogels Research Articles

Preparation of Basic Yellow Doped Nanomaterial and Its Usage in Latent Fingermark Development

Basic yellow has shown great application in chemical and biological field as a dye. Ethanol-based basic yellow solution is used to enhance the deposit of superglue-developed fingermarks in forensic science. However, the potential applications of basic yellow doped nanomaterials in forensic science, latent fingermark development in particular, were still unclear. In this study, we have succeeded in trapping basic yellow in silicon dioxide-based nanomaterials, doped aerogels, using the sol–gel method. We have tested the detection for latent fingermarks left under different conditions. The results indicated that the basic yellow doped aerogels applicable for latent fingermark development on various forensic relevant materials, including metal foil, glass, plastic, and paper, etc. The procedure of preparation and fingermark labeling results of these new basic yellow doped nanomaterials are presented in this study.

Design of multifunctional magnetic hybrid silica aerogels with improved properties

A streamlined synthesis approach is proposed to develop a multifunctional magnetite doped hybrid silica aerogel by taking advantage of the versatility of the sol-gel process and flexibility of the crosslinking reaction. To this avail, magnetite NPs, at concentrations from 0.05 to 0.2 mg/mL, were mixed at the nanoscale with the initial solution containing the silica precursors and the crosslinker. For an effective and sustainable linkage of magnetite to the silica network, the surface of the magnetite was chemically coated with an active silylation agent to compatibilize the surface chemistry of these nanoparticles with the chemistry of silica. It has been shown that at a certain dopant concentration, the magnetite doped aerogels gained several interesting improvements in the final properties over their undoped counterparts, particularly an increase in the compressive strength (up to 2.6 MPa, with ca. 3× increase) with only a marginal increase in the density (up to ∼ 0.29 g cm−3, with 20% increment) and decrease in the active surface area (down to ∼ 49 m2 g−1 and 7% reduction). Importantly, a good deal of improvement regarding the thermal insulation performance for doped aerogels has been obtained due to the opacification behavior of the magnetite dopants at temperatures above 300 K. The significant improvements concerning the physical and mechanical properties combined with the magnetic properties (up to 11 emu g−1 at room temperature) make these multifunctional hybrid aerogels suitable for some applications, ranging from selective magnetic separation for environmental cleaning and magnetic drug delivery to catalysis, etc.

Synthesis of MWCNTs doped sodium silicate based aerogels by ambient pressure drying

The successful incorporation of multiwalled carbon nanotubes (MWCNTs) into silica aerogels prepared by sol–gel method is reported herein. Pure silica aerogels prepared using sodium silicate precursor by ambient pressure drying are so fragile that they cannot be used easily. MWCNTs were used as reinforcements to improve the mechanical properties of silica aerogels. Results show that inserting small amounts of MWCNTs in the gels causes enhanced dimensional stability of silica aerogels. The silica aerogels were prepared by doping MWCNTs in silica matrix before gelation. The influence of MWCNTs on some microstructural aspects of silica matrix has been studied using nitrogen adsorption–desorption isotherms. From SEM study it is confirmed that the silica particles get capped on the surface of MWCNTs suggesting an enhanced toughness. Further, FTIR, Raman, EDAX, thermal conductivity and hydrophobicity studies of these doped aerogels were carried out. By addition of MWCNTs, silica aerogels were formed with 706 m2/g BET and 1,200 m2/g Langmuir surface areas and 149o contact angle. Low density (0.052 g/cc) and low thermal conductivity (0.067 W/m K) MWCNTs doped silica aerogels were obtained for the molar ratio of Na2SiO3::H2O::MWCNTs::citric acid::TMCS at 1::146.67::2.5 × 10−3::0.54::9.46 respectively with improved mechanical strength.

Kinetic of sintering of polyethilene glycol and lanthanum dopped aluminum oxide obtained by the sol-gel method

Sintering and crystallization of low-density polyethylene glycol (PEG) and lanthanum, La(III)-doped Al2O3 aerogels prepared from aluminum isopropoxide were investigated. The sintering behavior of non-doped and doped aerogels was examined by following the change of specific surface area with isothermal heat-treatment. The specific surface area and crystalline phases of non-doped and PEG+La(III)-doped aerogels were determined, and the effects of dopants on the sintering and crystallization of Al2O3 aerogels are discussed. Isothermal sintering experiments showed that the sintering mechanism of non-doped and PEG+La(III)-doped Al2O3 aerogels is surface diffusion. The specific surface areas of alumina samples decrease rapidly during the initial period of sintering, and more slowly with prolonged sintering time. The change of the porous structure is correlated with the phase transformation of ?-Al2O3 during calcinations of Al2O3 aerogels. The surface area of non-doped Al2O3 aerogels came to about 20 m2g-1 with heat-treatment at 1100?C because of crystallization of ?-Al2O3 after densification. In the case of heattreatment at 1200?C, the largest surface area was observed for PEG+La(III) doped Al2O3 aerogels and the XRD pattern showed only low ordered ?-Al2O3. These indicate that the addition of PEG+La(III) to boehmite sol prevents Al2O3 aerogels from sintering and crystallizing to the ?-Al2O3 phase. Even after 20 h at 1000?C, PEG+La (III)-doped alumina samples maintain a rather good specific surface area (108 m2 g-1) in comparison to the non-doped, containing mainly ?-Al2O3 and minor amounts of ?-Al2O3. Aluminum-oxides with these structural and textural properties are widely used as a coatings and catalyst supports in the field of various catalysis.

Thermal stability of alumina aerogel doped with yttrium oxide, used as a catalyst support for the thermocatalytic cracking (TCC) process: An investigation of its textural and structural properties

Abstract Undoped and yttria doped alumina aerogel are prepared by the (solution) sol–gel method using a supercritical drying technique. The doping concentrations are in the range of 2.5–20.0 wt.% Y2O3, using yttrium(III) nitrate as a precursor. The effect of yttria doping on the structural and textural properties of alumina aerogel is investigated by BET surface area measurement, X-ray diffraction (XRD), TEM and 27Al MAS NMR. This method of preparation of alumina aerogel provides the most important increases in surface area at 750 °C and up to 1000 °C, when compared to conventional alumina that is obtained via thermal dehydration of boehmite. These results show that the much smaller size of crystallites of alumina aerogel is quite efficient to retard the sintering occurring at these high temperatures. Further improvements in thermal stability are obtained by incorporation of yttrium species during the aerogel preparation. The stabilizing effect goes through a maximum with a yttrium content of ca. 10 wt.%. The presence of yttrium significantly delays the lattice rearrangement into new phases, as normally experienced by the conventional alumina when the temperature increases. These yttrium species induce the formation of distorted tetrahedral Al sites. Such binding effect of Y to Al is clearly detected by 27Al MAS NMR already at 750 °C. However, at 1200 °C, even the doped aerogel cannot withstand the combined effect of sintering and α-phase transformation, so that extremely low surface areas corresponding to those of alumina α-phase and segregated Y-Al2O3 are obtained.

Ostwald ripening of cobalt precipitates in silica aerogels? An ultra-small-angle X-ray scattering study

Monolithic silica aerogels with radial symmetry were synthesized by supercritical drying, doped to 2% and 10% with cobalt, and reduced with hydrogen. All samples were investigated with ultra-small-angle X-ray scattering. The non-doped aerogels have three populations of scatterers with radii of gyration of about 10, 40 and 60–70 Å. The doped aerogels show an additional structure with a radius of gyration ranging from 1050 to 3000 Å. This structure causes intensity oscillations, thus revealing a relatively narrow size distribution. Scattering curves of the 10%-doped aerogels fitted well to a Lifshitz–Slyozov–Wagner particle size distribution, thus revealing that Ostwald ripening might have occurred during aerogel preparation. The same range also shows differences depending on whether the samples were reduced, or in their as-prepared condition. Scattering curves obtained from the cylinder-axis region were different from the scattering curves obtained from the sample boundary, indicating a process-dependent skin effect.