Funding was provided by the Defense Threat Reduction Agency, Physical Science and Technology Division, Protection and Hazard Mitigation technical area. This research was supported in part by an appointment to the Postgraduate Research Participation Program at the Air Force Research Laboratory administered by the Oak Ridge Institute for Science and Education (ORISE) through an interagency agreement between the U.S. Department of Energy and the Air Force Research Laboratory, Materials and Manufacturing Directorate, Airbase Technologies Division (AFRL/RXQ).

1.&#160;Preparation and Calculations
<ol>
	<li>Prepare 1 mM HCl solution using concentrated hydrochloric acid, 37%, and water. 
	Note: Caution should always be used when handling concentrated acids. Concentrated acid should always be added to water, never add water to concentrated acid.</li>
	<li>Determine the desired concentration of TMOS, siloxane precursor, for the microwave reaction. A TMOS concentration of 25 mM will be used for procedural demonstrations.</li>
</ol>
2.&#160;Hydrolysis of TMOS and Preparation of Reaction Solution
<ol>
	<li>For a 25 mM reaction solution of TMOS in acetone, obtain a 50 ml&#160;plastic conical tube, TMOS, and the prepared 1 mM HCl solution.</li>
	<li>Using a micropipetter, add 850 &#181;l&#160;of the 1 mM HCl solution to the plastic conical tube.</li>
	<li>Using a micropipetter, add 150 &#181;l&#160;of TMOS to the plastic conical tube containing the 850 &#181;l&#160;of 1 mM HCl.</li>
	<li>Observe that the mixture of TMOS and acid are originally immiscible, resulting in two clear colorless layers.</li>
	<li>Vortex the solution. A quick burst will cause solution to turn slightly cloudy and pale white. Vortexing the solution again will yield a clear colorless solution. Total vortex time is ~10 sec. At this point, the TMOS is hydrolyzed and in the form of silicic acid.</li>
	<li>Add acetone to the plastic conical tube containing the silicic acid solution and dilute to a total volume of 40 ml. Ensure proper mixing by vortexing the solution after diluting the solution with acetone.</li>
</ol>
Note: Prior to microwave heating, the silicic acid / acetone solution will be stable for several hours. Silica condensation was not observed in similar prepared solutions which were stable for several weeks without any evidence of condensation. Although for best results, reaction solutions should be used upon day of preparation to ensure reproducible results.
3.&#160;Create Microwave Method on Microwave Reactor
<ol>
	<li>Create a microwave method within the provided software for SiO2 NP formation. Typical reaction parameters include: power = 300 W, temperature = 125 &#176;C and time = 60 sec. Using an external laptop the temperature, pressure, and power profiles can be stored, plotted, and compared with future experiments as in Figure 1.</li>
</ol>
4.&#160;Microwave-assisted Synthesis of SiO2&#160;Nanoparticles
<ol>
	<li>Obtain a 10 ml&#160;microwave reaction vial, stir bar, and snap cap.</li>
	<li>Add the stir bar to the vial and using a micropipetter add 5 ml&#160;of the silicic acid/acetone reaction solution to the microwave vial. A reaction volume of 5 ml&#160;should be used to provide adequate headspace to accommodate the generation of pressure from superheated acetone.</li>
	<li>Place the snap cap on 10 ml&#160;vial. Ensure cap seats properly on the vial to reduce loss of solvent when superheated.</li>
	<li>Place vial in microwave reactor.</li>
	<li>Press the start button on the laptop to start the microwave heating procedure. Observe proper placement of pressure head unit. Observe that the proper microwave power settings are correct once the reaction begins: correct power setting, increase in reaction temperature, and generation of reaction pressure. When the reaction time has expired, compressed air will quickly cool the reaction.</li>
	<li>Remove the reaction vial from microwave reactor after cooling.</li>
</ol>
Note: Typically for a 5 ml&#160;reaction, a measured conversion of ~40-50% has been reported19 in the preparation of SiO2 NPs by these microwave-assisted methods.
5.&#160;DLS Size Analysis of Reaction Solutions
<ol>
	<li>Obtain a polystyrene disposable cuvette.</li>
	<li>Add 900 &#181;l&#160;of distilled water to the cuvette.</li>
	<li>Add 100 &#181;l&#160;of reaction solution containing SiO2 NP to the cuvette containing the water and mix.</li>
	<li>Setup procedures for particle measurements by following DLS analyzer software and analyze the solution for particle size.</li>
</ol>
6.&#160;SiO2 NP Cleanup Procedure
<ol>
	<li>Add 1 ml&#160;of SiO2 NP reaction solution to an Eppendorf tube.</li>
	<li>Centrifuge at 15.7k x g for 30-60 min&#160;depending on particle diameter.</li>
	<li>Carefully decant excess solution from SiO2 NP pellet.</li>
	<li>Add 1 ml&#160;fresh acetone and resuspend SiO2 NP by placing in an ultrasonic bath for 5-10 min.</li>
	<li>Repeat (centrifuging, decanting, resuspending) two more times for adequate removal of residual silicic acid.</li>
</ol>
7.&#160;SEM Sample Preparation
<ol>
	<li>Clean the highly polished single crystal silicon wafers in an ultrasonic bath for approximately 30 min prior to use.</li>
	<li>Place the silicon wafers in piranha solution (3:1 conc. H2SO4:30% H2O2) at a temperature of 80 &#176;C for 1 hr after removing from the ultrasonic bath. Wash the silicon wafers with distilled water and dry. 
	Note: Caution should be used when handling concentrated acids, especially piranha solution.</li>
	<li>Drop-cast clean or not clean solutions of SiO2 NPs onto the clean prepared silicon wafer.</li>
	<li>Place prepared samples on silicon wafer in the cylindrical tube of the sputter system.</li>
	<li>Vacuum the cylindrical tube of the sputter system to 40 mTorr.</li>
	<li>Purge the cylindrical tube of the sputter system with Argon gas until a pressure of approximately 200 mTorr is reached.</li>
	<li>Decrease the pressure to 80 mTorr and apply 15 mA of voltage and keep constant. Sputter platinum on prepared samples for 60 sec.</li>
</ol>

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We have nothing to disclose.

The microwave-assisted methods described in this manuscript are advantageous over conventional heating methods because SiO2 NPs can be synthesized accurately, precisely, and quickly. The following criteria should be followed to eliminate any potential issues associated with SiO2 NPs formation by these microwave-associated techniques: 1) use of a catalyst such as 1 mM HCl, 2) hydrolysis of the TMOS should be completed before addition of acetone, 3) use of an aprotic solvent such as acetone, 4) use of...

Silica nanoparticles (SiO2 NPs) were first synthesized by St&#246;ber1 and through modifications2-7 have become the preferred method for SiO2 NPs synthesis. Typically, St&#246;ber reactions are catalyzed by alkaline conditions where silica sols are formed. Acid-catalyzed reactions are used less frequently than alkaline-catalyzed reactions due to the greater degree of difficulty of hydrolysis of the siloxane precursor. Unlike alkaline-catalyzed reactions, acid-catalyzed reactions preferentially form silica gels.8
Microwave-assisted chemical reactions are an emerging technique within the scientific community and in literature due to the associated benefits to the techniques9-18. Specifically, microwave-assisted techniques have been shown to be advantageous in the synthesis of nanomaterials where the promotion of spontaneous nucleation events is desired. Microwave conditions are advantageous because microwave reactors deliver controlled power quickly to the reaction10. Until recently19, the synthesis of SiO2 NPs using microwave reactors have been used with limited success mainly as a result of issues with reproducibility20-22.
The details and procedural methods often reported in the literature on the synthesis of nanomaterials often tend to be obscure and sometimes seen as an &#34;art-form.&#34; Combining microwave-assisted synthetic techniques and nanomaterial synthesis can compound the subject even further. The purpose of this manuscript is to guide researchers in the synthesis of nanomaterials by microwave-assisted techniques, eliminate obscurity associated with these techniques, and point out common mistakes associated with these techniques.
In a microwave chemical reaction, any molecular species containing a permanent dipole is capable of interacting and perturbing the electromagnetic (EM) field. These species are not limited solely to the reagents and solvents used within the reaction, but can be any substance placed in the EM field i.e. glass vials, salts, ionic liquids.
The ability for a specific substance to effectively convert EM energy into heat is defined as the loss factor of a material or tan &#948;. Solvents are commonly classified by their loss factor where values for tan &#948; &#62; 0.5 are considered high, 0.1 &#62; tan &#948; &#62; 0.5 are considered medium, and tan &#948; &#60; 0.1 are considered low. These loss factors values relate the ability for a particular solvent to couple or absorb microwave energy and convert that energy into heat. Thermal energy is generated through molecular friction of species attempting to align with the oscillating EM field. If solvents with high tan &#948; values are used within a reaction, the solvent will dominate the microwave absorption events, masking the precursor or reagents, leading to bulk heating as a result of the solvent strongly coupling with the EM field.
Typically, polar solvents are used in SiO2 NP synthesis to ensure reagent solubility and for donation of labile protons23. Common solvents used in SiO2 NP syntheses are alcohol solvents such as ethanol, methanol or 2-propanol. These solvents all have high tan &#948; values (0.941, 0.799, and 0.659 for ethanol, 2-propanol and methanol, respectively) making them poor solvent choices for microwave-assisted chemical reactions of SiO2 NPs as they efficiently couple with the EM field. It is our belief that microwave-assisted reactions are most effective when low tan &#948; solvents are used in combination with polar molecular precursors in synthetic reactions. These circumstances allow for the molecular precursors to couple with the EM field, providing molecular heating, while the solvent interacts minimally. For microwave-assisted reactions in this manuscript, acetone is used as an alternative to the commonly used alcohol solvents associated with SiO2 NPs synthesis. Acetone is considered a low loss factor solvent (tan &#948; = 0.054), which limits the solvent interactions within the EM field allowing selective microwave absorption with the reactants meditating silica condensation reactions.
In this manuscript, we outline the procedures associated with the microwave-assisted synthesis of SiO2 NPs which are accurate, precise and quick. SiO2 NP growth is achieved by effective coupling of the precursor with the EM field while the solvent has a minimal role in heating. Hydrolysis of the siloxane precursor is achieved by using hydrochloric acid, which leads to slower rates of hydrolysis and limits further condensation reactions. Alkaline-catalyzed reactions have much faster reaction rates and can complicate growth processes when used with microwave-assisted techniques. The resultant SiO2 NPs synthesized by these techniques range in diameters from 30 nm up to diameters greater than 250 nm. SiO2 NP size is controlled by varying the precursor concentration and exposure time to the microwave radiation.

<table><tbody><tr><td>Tetramethylorthosilicate</td><td>Sigma Aldrich</td><td>218472</td><td></td></tr><tr><td>Hydrochloric acid, 37%</td><td>Sigma Aldrich</td><td>435570</td><td></td></tr><tr><td>Acetone</td><td>Fisher</td><td>A949SK</td><td></td></tr><tr><td>Sulfuric acid</td><td>EMD Millipore</td><td>SX1244</td><td></td></tr><tr><td>Hydrogen peroxide, 30%</td><td>EMD Millipore</td><td>HX0635</td><td></td></tr><tr><td>Discover microwave reactor</td><td>CEM</td><td></td><td></td></tr><tr><td>10 ml Borosilicate reaction vial</td><td>CEM</td><td>908035</td><td></td></tr><tr><td>10 ml Snap cap</td><td>CEM</td><td>909210</td><td></td></tr><tr><td>3 mm Stir bar</td><td>Fisher Scientific</td><td>14-513-65</td><td></td></tr><tr><td>Highly polished silicon wafers</td><td>Broker</td><td>SP064483</td><td></td></tr><tr><td>S4800 SEM</td><td>Hitachi</td><td></td><td></td></tr><tr><td>Zetasizer Nano90</td><td>Malvern</td><td></td><td></td></tr><tr><td>Polystyrene cuvette, (10 mm x 10 mm x 45mm)</td><td>Sarstedt</td><td>67.754</td><td></td></tr><tr><td>5415D centrifuge</td><td>Eppendorf</td><td></td><td></td></tr><tr><td>Hummer 6.2 sputter system</td><td>Anatech</td><td></td><td></td></tr></tbody></table>

preparation of silica nanoparticles through microwave-assisted acid-catalysis

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle diameters ranging from 30-250 nm by varying the reaction conditions. Through the selection of a microwave compatible solvent, silicic acid precursor, catalyst, and microwave irradiation time, these microwave-assisted methods were capable of overcoming the previously reported shortcomings associated with synthesis of silica nanoparticles using microwave reactors. The siloxane precursor was hydrolyzed using the acid catalyst, HCl. Acetone, a low-tan &#948; solvent, mediates the condensation reactions and has minimal interaction with the electromagnetic field. Condensation reactions begin when the silicic acid precursor couples with the microwave radiation, leading to silica nanoparticle sol formation. The silica nanoparticles were characterized by dynamic light scattering data and scanning electron microscopy, which show the materials&#39; morphology and size to be dependent on the reaction conditions. Microwave-assisted reactions produce silica nanoparticles with roughened textured surfaces that are atypical for silica sols produced by St&#246;ber&#39;s methods, which have smooth surfaces.

Temperature, pressure, and microwave power traces for a representative SiO2 NP microwave-assisted reaction are presented in Figure 1. The microwave reaction plot is divided into three sections - ramping, reaction, and cooling. A reaction temperature of 125 &#176;C and reaction time of 60 sec are used in this representative SiO2 NP reaction. During the ramping portion, the power is maximized at 300 W (or near max power) so that the reaction temperature can be reached quickly without ...

Watch this Scientific Journal Video about Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis at JoVE.com

Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Silica nanoparticles were prepared using acid-catalysis of a siloxane precursor and microwave-assisted synthetic techniques resulting in the controlled growth of nanomaterials ranging from 30-250 nm in diameter. The growth dynamics can be controlled by varying the initial silicic acid concentration, time of the reaction, and temperature of reaction.

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

preparation-silica-nanoparticles-through-microwave-assisted-acid

Research

JoVE Journal

Chemistry

18.6K Views.  Oak Ridge Institute for Science and Education. Silica nanoparticles were prepared using acid-catalysis of a siloxane precursor and microwave-assisted synthetic techniques resulting in the controlled growth of nanomaterials ranging from 30-250 nm in diameter. The growth dynamics can be controlled by varying the initial silicic acid concentration, time of the reaction, and temperature of reaction.

Video: Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press. The precursor solution consists of a 1.0:12.0:3.6:3.5 x 10-3 molar ratio of tetramethylorthosilicate (TMOS):methanol:water:ammonia. In each well of the mold, a porous silica sol-gel matrix forms. As the temperature of the mold and its contents is increased, the pressure within the mold rises. After the temperature/pressure conditions surpass the supercritical point for the solvent within the pores of the matrix (in this case, a methanol/water mixture), the supercritical fluid is released, and monolithic aerogel remains within the wells of the mold. With the mold used in this procedure, cylindrical monoliths of 2.2 cm diameter and 1.9 cm height are produced. Aerogels formed by this rapid method have comparable properties (low bulk and skeletal density, high surface area, mesoporous morphology) to those prepared by other methods that involve either additional reaction steps or solvent extractions (lengthier processes that generate more chemical waste).The rapid supercritical extraction method can also be applied to the fabrication of aerogels based on other precursor recipes.

This article describes a rapid supercritical extraction method for fabricating silica aerogels. By utilizing a confined mold and hydraulic hot press, monolithic aerogels can be made in eight hours or less.

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The ...

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 &#176;C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

A &#8220;removable ceramic coating method&#8221; is presented in visual format for the synthesis of non-sintered and metal-terminated monometallic and bimetallic early transition metal carbide and nitride nanoparticles with tunable sizes and crystal structures.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The ...

Generation of Zerovalent Metal Core Nanoparticles Using n-(2-aminoethyl)-3-aminosilanetriol

In this work, a facile one-pot reaction for the formation of metal nanoparticles in a water solution through the use of n-(2-aminoethyl)-3-aminosilanetriol is presented. This compound can be used to effectively reduce and complex metal salts into metal core nanoparticles coated with the compound. By controlling the concentrations of salt and silane one is able to control reaction rates, particle size, and nanoparticle coating. The effects of these changes were characterized through transmission electron microscopy (TEM), UV-Vis spectrometry (UV-Vis), Nuclear Magnetic Resonance spectroscopy (NMR) and Fourier Transform Infrared spectroscopy (FTIR). A unique aspect to this reaction is that usually silanes hydrolyze and cross-link in water; however, in this system the silane is water-soluble and stable. It is known that silicon and amino moieties can form complexes with metal salts. The silicon is known to extend its coordination sphere to form penta- or hexa-coordinated species. Furthermore, the silanol group can undergo hydrolysis to form a Si-O-Si silica network, thereby transforming the metal nanoparticles into a functionalized nanocomposites.

Generation of Zerovalent Metal Core Nanoparticles Using n-2-aminoethyl-3-aminosilanetriol

A novel method for metal core nanoparticle synthesis using a water stable silanol is described.

In this work, a facile one-pot reaction for the formation of metal nanoparticles in a water solution through the use of ...

Preparation of Biomass-based Mesoporous Carbon with Higher Nitrogen-/Oxygen-chelating Adsorption for Cu(II) Through Microwave Pre-Pyrolysis

An environment-friendly technique for synthesizing biomass-based mesoporous activated carbon with high nitrogen-/oxygen-chelating adsorption for Cu(II) is proposed. Bagasse impregnated with phosphoric acid is utilized as the precursor. To pyrolyze the precursor, two separate heating modes are used: microwave pyrolysis and conventional electric-heating pyrolysis. The resulting bagasse-derived carbon samples are modified with nitrification and reduction modification. Nitrogen (N)/oxygen (O) functional groups are simultaneously introduced to the surface of activated carbon, enhancing its adsorption of Cu(II) by complexing and ion-exchange. Characterization and copper adsorption experiments are performed to investigate the physicochemical properties of four prepared carbon samples and determine which heating method favors the subsequent modification for doping of N/O functional groups. In this technique, based on analyzing data of nitrogen adsorption, Fourier transform infrared spectroscopy, and batch adsorption experiments, it is proven that microwave-pyrolyzed carbon has more defect sites and, therefore, time-saving effective microwave pyrolysis contributes more N/O species to the carbon, although it leads to a lower specific surface area. This technique offers a promising route to synthesis adsorbents with higher nitrogen and oxygen content and a higher adsorption capacity of heavy-metal ions in wastewater remediation applications.

Preparation of Biomass-based Mesoporous Carbon with Higher Nitrogen-/Oxygen-chelating Adsorption for CuII Through Microwave Pre-Pyrolysis

Here, we present a protocol to synthesize nitrogen/oxygen dual-doped mesoporous carbon from biomass by chemical activation in different pyrolysis modes followed by modification. We demonstrate that the microwave pyrolysis benefits the subsequent modification process to simultaneously introduce more nitrogen and oxygen functional groups on the carbon.

An environment-friendly technique for synthesizing biomass-based mesoporous activated carbon with high nitrogen-/oxygen-chelating adsorption for Cu(II) is ...

Environment

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three preparation methods are described: (a) the incorporation of metal salts into silica or alumina wet gels using an impregnation method; (b) the incorporation of metal salts into alumina wet gels using a co-precursor method; and (c) the addition of metal nanoparticles directly into a silica aerogel precursor mixture. The methods utilize a hydraulic hot press, which allows for rapid (&#60;6 h) supercritical extraction and results in aerogels of low density (0.10 g/mL) and high surface area (200-800 m2/g). While the work presented here focuses on the use of copper salts and copper nanoparticles, the approach can be implemented using other metal salts and nanoparticles. A protocol for testing the three-way catalytic ability of these aerogels for automotive pollution mitigation is also presented. This technique uses custom-built equipment, the Union Catalytic Testbed (UCAT), in which a simulated exhaust mixture is passed over an aerogel sample at a controlled temperature and flow rate. The system is capable of measuring the ability of the catalytic aerogels, under both oxidizing and reducing conditions, to convert CO, NO and unburned hydrocarbons (HCs) to less harmful species (CO2, H2O and N2). Example catalytic results are presented for the aerogels described.

Here we present protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms. Methods for preparing materials using copper salts and copper-containing nanoparticles are featured. Catalytic testing protocols demonstrate the effectiveness of these aerogels for three-way catalysis applications.

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three ...

Preparation of Functional Silica Using a Bioinspired Method

The goal of the protocols described herein is to synthesize bioinspired silica materials, perform enzyme encapsulation therein, and partially or totally purify the same by acid elution. By combining sodium silicate with a polyfunctional bioinspired additive, silica is rapidly formed at ambient conditions upon neutralization. 
The effect of neutralization rate and biomolecule addition point on silica yield are investigated, and biomolecule immobilization efficiency is reported for varying addition point. In contrast to other porous silica synthesis methods, it is shown that the mild conditions required for bioinspired silica synthesis are fully compatible with the encapsulation of delicate biomolecules. Additionally, mild conditions are used across all synthesis and modification steps, making bioinspired silica a promising target for the scale-up and commercialization as both a bare material and active support medium.
The synthesis is shown to be highly sensitive to conditions, i.e., the neutralization rate and final synthesis pH, however tight control over these parameters is demonstrated through the use of auto titration methods, leading to high reproducibility in reaction progression pathway and yield. 
Therefore, bioinspired silica is an excellent active material support choice, showing versatility towards many current applications, not limited to those demonstrated here, and potency in future applications.

Here, we present a protocol to synthesize bioinspired silica materials and immobilize enzymes therein. Silica is synthesized by combining sodium silicate and an amine &#39;additive&#39;, which neutralize at a controlled rate. Material properties and function can be altered either by in situ enzyme immobilization or post-synthetic acid elution of encapsulated additives.

The goal of the protocols described herein is to synthesize bioinspired silica materials, perform enzyme encapsulation therein, and partially or totally ...

Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) with a 4.6 nm pore size, and ordered silica porous matrix, SBA-15, with a 5.3 nm pore size. This work describes the surface properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the differently ordered porous materials with similar pore sizes. For this purpose, OMC and SBA-15 with highly ordered nanoporous structures are synthesized via impregnation of the silica matrix by applying a carbon precursor and by the sol-gel method, respectively. The porous structure of investigated systems is characterized by an N2 adsorption-desorption analysis at 77 K. To determine the electrochemical character of the surface of synthesized materials, potentiometric titration measurements are conducted; the obtained results for OMC shows a significant pHpzc shift toward the higher values of pH, relative to SBA-15. This suggests that investigated OMC has surface properties related to oxygen-based functional groups. To describe the surface properties of the materials, the contact angles of liquids penetrating the studied porous beds are also determined. The capillary rise method has confirmed the increased wettability of the silica walls relative to the carbon walls and an influence of the pore roughness on the fluid/wall interactions, which is much more pronounced for silica than for carbon mesopores. We have also studied the melting behavior of D2O confined in OMC and SBA-15 by applying the dielectric method. The results show that the depression of the melting temperature of D2O in the pores of OMC is about 15 K higher relative to the depression of the melting temperature in SBA-15 pores with a comparable 5 nm size. This is caused by the influence of adsorbate/adsorbent interactions of the studied matrices.

Here we report the synthesis and characterization of ordered nanoporous carbon (with a 4.6 nm pore size) and SBA-15 (with a 5.3 nm pore size). The work describes the surface and textural properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the materials.

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) ...

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared according to the methodology developed by surface organometallic chemistry (SOMC). In this framework, catalytic cycles can be determined by isolating crucial intermediates. All air-sensitive materials are handled under inert atmosphere (using gloveboxes or a Schlenk line) or high vacuum lines (HVLs, &#60;10-5 mbar). The preparation of SiO2-700 (silica dehydroxylated at 700 &#176;C) and subsequent applications (the grafting of complexes and catalytic runs) requires the use of HVLs and double-Schlenk techniques. Several well-known characterization methods are used, such as Fourier-transform infrared spectroscopy (FTIR), elemental microanalysis, solid-state nuclear magnetic resonance spectroscopy (SSNMR), and state-of-the-art dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP-SENS). FTIR and elemental microanalysis permit scientists to establish the grafting and its stoichiometry. 1H and 13C SSNMR allows the structural determination of the hydrocarbon ligands coordination sphere. DNP SENS is an emerging powerful technique in solid characterization for the detection of poorly sensitive nuclei (15N, in our case). SiO2-700 is treated with about one equivalent of the metal precursor compared to the amount of surface silanol (0.30 mmol&#183;g-1) in pentane at room temperature. Then, volatiles are removed, and the powder samples are dried under dynamic high vacuum to afford the desired materials [(&#8801;Si-O-)Hf(&#951;2&#960;-MeNCH2)(&#951;1-NMe2)(&#951;1-HNMe2)]. After a thermal treatment under high vacuum, the grafted complex is converted into metal imido silica complex [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)]. [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] effectively promotes the metathesis of imines, using the combination of two imine substrates, N-(4-phenylbenzylidene)benzylamine, or N-(4-fluorobenzylidene)-4-fluoroaniline, with N-benzylidenetert-butylamine as substrates. A significantly lower conversion is observed with the blank runs; thus, the presence of the imido group in [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is correlated to the catalytic performance.

A new group IV metal catalyst for imine metathesis is prepared by grafting amine metal complex onto dehydroxylated silica. Surface metal fragments are characterized using FT-IR, elemental microanalysis, and solid-state NMR spectroscopy. Further dynamic nuclear polarization surface enhanced NMR spectroscopy experiments complement the determination of the coordination sphere.

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared ...

Microwave-driven Synthesis of Iron Oxide Nanoparticles for Fast Detection of Atherosclerosis

A fast and reproducible microwave-driven protocol has been developed for the synthesis of neridronate-functionalized nanoparticles. Starting from the synthesis of hydrophobic nanoparticles, our method is based on an adaptation from thermal decomposition method to microwave driven synthesis. The new methodology produces a decrease in the reaction times in comparison with traditional procedures. Moreover, the use of the microwave technology increases the reproducibility of the reactions, something important from the point of view of clinical applications. The novelty of this iron oxide nanoparticle is the attachment of Neridronate. The use of this molecule leads a bisphosphonate moiety towards the outside of the nanoparticle that provides Ca2+ binding properties in vitro and selective accumulation in vivo in the atheroma plaque. The protocol allows the synthesis and plaque detection in about 3 hr since the initial synthesis from organic precursors. Their accumulation in the atherosclerotic area in less than 1 hr provides a contrast agent particularly suitable for clinical applications.

Microwave technology enables extremely fast synthesis of iron oxide nanoparticles for atherosclerosis plaque characterization. The use of an aminobisphosphonate in the external side of the nanoparticle provides a fast accumulation in the atherosclerotic area.

A fast and reproducible microwave-driven protocol has been developed for the synthesis of neridronate-functionalized nanoparticles. Starting from the ...

Bioengineering

Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented herein. The novel strategy is based on a facile one-pot pyrolysis treatment of cobalt (II) acetylacetonate and nitrogen-rich organic precursors under Ar atmosphere at 800 &#176;C, resulting in the formation of Co- and N- co-doped carbon nanotube with earthworm-like morphology. The obtained catalyst was found to have a high density of defect sites, as confirmed by Raman spectroscopy. Here, cobalt (II) nanoparticles were stabilized on the atomically dispersed cobalt- and nitrogen-doped carbon nanotubes. The catalyst was confirmed to be effective in the catalytic hydrolysis of ammonia borane, in which the turnover frequency was 5.87 mol H2&#183;molCo-1&#183;min-1, and the specific hydrogen generation rate was determined to be 2447 mL H2&#183;gCo-1&#183;min-1. A synergistic function between the Co nanoparticle and the doped carbon nanotubes was proposed for the first time in the catalytic hydrolysis of ammonia borane reaction under a mild condition. The resulting hydrogen production with its high energy density and minimal refueling time could be suitable for future development as energy sources for mobile and stationary applications such as road trucks and forklifts in transport and logistics.

Here, we present a protocol to synthesize Co nanoparticles supported on carbon nanotubes with Co- and N- dopants for hydrogen productions.

A method for facile synthesis of nanostructured catalysts supported on carbon nanotubes with atomically dispersed cobalt and nitrogen dopant is presented ...