The authors thank their collaborators at RTI International, US Army Natick Soldier RD&#38;E Center, and Edgewood Chemical and Biological Center. They also thank their funding source, the Defense Threat Reduction Agency.

1. Atomic Layer Deposition (ALD) of Al2O3 on Fiber Mats
<ol>
	<li>Place a 2.54 x 2.54 cm2 polypropylene fabric sample in the reactor boat (a thin, rigid, metal mesh holder). A schematic of the reactor is presented in Figure 2.</li>
	<li>Open the pressure gauge. Remove the clasp from the reactor cap. Turn on manual control in the LabView system. Close the carrier nitrogen and gate valve on the ALD reactor. Open the vent nitrogen.</li>
	<li>After removing the reactor cap, load the fabric sample into the ALD reactor. Replace the reactor cap and open the gate valve. Close the vent and open the carrier nitrogen. Turn off manual control.</li>
	<li>Load the recipe for Al2O3 on fabrics. The recipe will alternately dose trimethylaluminum (TMA) for 1.2 s, followed by a 30 s dry nitrogen purge or dose water for 1 s followed by a 60 s dry nitrogen purge. Set the recipe to run 1000 cycles.</li>
	<li>Set the mass flow controller to 20 cfm and the furnace temperature to 90 &#176;C (84 &#176;C on the furnace interface).</li>
	<li>Open the manual valve to the TMA and water. Close the pressure gauge. Replace the clasp on the reactor cap. Press Start on the interface.</li>
	<li>Upon completion of the recipe, open the pressure gauge. Remove the clasp from the reactor cap. Turn on manual control in the system. Close the carrier nitrogen and gate valve on the ALD reactor. Open the vent nitrogen.</li>
	<li>Remove the reactor cap and sample boat. Re-seal the reactor. 
	NOTE: The procedure may be paused at this point.</li>
</ol>
2. Atomic Layer Deposition (ALD) of TiO2 on Polyamide-6 (PA-6) Fiber Mats
<ol>
	<li>Place a 2.54 x 2.54 cm2 PA-6 fabric sample in the reactor boat (a thin, rigid, metal mesh holder).</li>
	<li>Open the pressure gauge. Remove the clasp from the reactor cap. Turn on manual control in the LabView system. Close the carrier nitrogen and gate valve on the ALD reactor. Open the vent nitrogen.</li>
	<li>After removing the reactor cap, load the fabric sample into the ALD reactor. Replace the reactor cap and open the gate valve. Close the vent and open the carrier nitrogen. Turn off manual control.</li>
	<li>Load the recipe for TiO2 on fabrics. The recipe will alternately dose TiCl4 for 1 s, followed by a 40 s dry nitrogen purge or dose water for 1 s followed by a 60 s dry nitrogen purge. Set the recipe to run 300 cycles.</li>
	<li>Set the mass flow controller to 20 cfm and the furnace temperature to 90 &#176;C (84 &#176;C on the furnace interface).</li>
	<li>Open the manual valve to the TiCl4 and water. Close the pressure gauge. Replace the clasp on the reactor cap. Press Start&#160;on the interface.</li>
	<li>Upon completion of the recipe, open the pressure gauge. Remove the clasp from the reactor cap. Turn on manual control in the system. Close the carrier nitrogen and gate valve on the ALD reactor. Open the vent nitrogen.</li>
	<li>Remove the reactor cap and sample boat. Re-seal the reactor. 
	NOTE: The procedure may be paused at this point.</li>
</ol>
3. Solvothermal Synthesis of MIL-96
<ol>
	<li>Add 0.0878 g of H3BTC to an 80 mL glass beaker.</li>
	<li>Add 12 mL of H2O and 12 mL of ethanol to the beaker.</li>
	<li>Stir magnetically for 10 min or until the H3BTC is fully dissolved.</li>
	<li>Place the solution in a Teflon lined pressure vessel.</li>
	<li>Add the Al2O3 coated polypropylene to the solution and prop the fabric on a mesh support so it does not lie flat against the bottom of the vessel.</li>
	<li>Seal the pressure vessel and place it in the furnace at 110 &#176;C for 24 h.</li>
	<li>After allowing the sample to cool, place the fabric sample in a mesh basket in a beaker. Wash twice with ethanol, each for 12 h.</li>
	<li>Sample activation requires heating at 85 &#176;C for 6 h under vacuum, followed by heating at 110 &#176;C for 12 h under vacuum. 
	NOTE: The procedure can be stopped here. All samples should be stored in a desiccator to maintain sample activation.</li>
</ol>
4. Solvothermal Synthesis of UiO-66-NH2
<ol>
	<li>Add 0.08 g of ZrCl4 to a 20 mL glass scintillation vial.</li>
	<li>Add 20 mL of N,N-dimethylformamide (DMF) to the ZrCl4 in 5 mL increments. Cap the vial between increments and allow fumes to dissipate.</li>
	<li>Sonicate the solution for 1 min.</li>
	<li>Add 0.062 g of 2-aminoterephthalic acid to the vial, and magnetically stir the solution for 5 min.</li>
	<li>Add 25 &#181;L of deionized water to the vial.</li>
	<li>Add 1.33 mL of concentrated HCl to the vial.</li>
	<li>Submerge the TiO2 ALD coated fabric swatch in the solution and cap the vial.</li>
	<li>Place the sample in the furnace at 85 &#176;C for 24 h.</li>
	<li>After allowing the sample to cool, place the fabric sample in a mesh basket in a beaker. Wash twice with 80 mL of DMF, each for 12 h. Wash 3 times with 80 mL of ethanol, each for 12 h.</li>
	<li>After removing the fabric swatch, filter the residual MOF powder. Wash twice with 80 mL of DMF, each for 12 h. Wash 3 times with 80 mL of ethanol, each for 12 h.</li>
	<li>Sample activation requires heating at 85 &#176;C for 6 h under vacuum, followed by heating at 110 &#176;C for 12 h under vacuum. 
	NOTE: The procedure can be stopped here. All samples should be stored in a desiccator to maintain sample activation.</li>
</ol>

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N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Catalytic+'+MOF-Cloth+'+Formed+via+Directed+Supramolecular+Assembly+of+UiO-66-NH+2+Crystals+on+Atomic+Layer+Deposition-+Coated+Textiles+for+Rapid+Degradation+of+Chemical+Warfare+Agent+Simulants.">Catalytic ' MOF-Cloth ' Formed via Directed Supramolecular Assembly of UiO-66-NH 2 Crystals on Atomic Layer Deposition- Coated Textiles for Rapid Degradation of Chemical Warfare Agent Simulants.</a> Chemistry of Materials. 29 (11), 4894-4903 (2017).</li><li>L&#243;pez-maya, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Textile+/+Metal+-+Organic-Framework+Composites+as+Self-Detoxifying+Filters+for+Chemical-Warfare+Agents.">Textile / Metal - Organic-Framework Composites as Self-Detoxifying Filters for Chemical-Warfare Agents.</a> Angewandte Chemie International Edition. 54 (23), 6790-6794 (2015).</li><li>Zhao, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conformal+and+highly+adsorptive+metal-organic+framework+thin+films+via+layer-by-layer+growth+on+ALD-coated+fiber+mats.">Conformal and highly adsorptive metal-organic framework thin films via layer-by-layer growth on ALD-coated fiber mats.</a> Journal of Materials Chemistry. 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The authors have nothing to disclose.

The ALD coating strongly influences the adhesion and loading of the MOF. First, depending on the type of substrate and ALD precursor, the ALD layer can either form a distinct outer shell around the fiber, or diffuse into the fiber to create a gradual transition to the metal oxide coating20. The hard shell has been observed on cotton and nylon substrates, while diffusive layers can be observed in polypropylene under proper conditions. Second, the diffusion into the fiber can also be controlled by varying the deposition temperature20,24. Higher temperatures increase the diffusion of the ALD precursors into the fiber. Lastly, the metal oxide coating must be thick enough after diffusion to form a conformal outer coating and provide functional groups and increased surface roughness for the MOF to nucleate18,20. While silicon wafers were used to monitor the ALD growth and estimate film thickness, polymer spin-coated on QCM crystals can serve as a more accurate means to track mass uptake, coupled with FTIR intensities to estimate film thicknesses24. These methods would require more time and materials, but could account for delayed or accelerated nucleation on polymer films, rather than estimating based on the ALD growth on silicon. Alternatively, TEM cross-sectional imaging could be used, but this may result in breaking or compressing the fiber coatings.
Unlike conventional MOF synthesis, the MIL synthesis relies on a metal source anchored on a fiber. Under proper conditions, the Al2O3 coating on polypropylene can diffuse into the fiber, helping to anchor the MOF after synthesis. However, if the metal oxide is fully reacted or if the ALD diffusion is limited, the adhesive forces may be slightly diminished. An example of this is present for the MIL-96 grown using 500 ALD cycles of Al2O3, as shown in the SEM image in Figure 3a. The patchy MOF coverage and loose fragments are evidence of the MOF layer peeling away from the fiber after the metal oxide has been fully reacted, confirmed by the cross-sectional images in Figure 4. For the thicker metal oxide layers, this peeling is not observed. The MOF loading of the MIL is limited by the metal source on the fiber. The MOF loading on the 500 cycle sample was likely low because the Al was fully consumed. The uniform MOF adhesion on the 1000 cycle and 2000 cycle samples, and their cross-sectional images, suggest the Al2O3 was not fully consumed. The loading was limited by the diffusion rate of the trimesic acid organic linker into the Al2O3 and longer synthesis time may reveal a higher MOF loading on the thicker Al2O3 coatings.
Separately from the MOF syntheses on fabrics, Al2O3 powder was used in place of the Al2O3 ALD coating during a MIL-96 synthesis. The powder did not react. To understand the difference in reactivity between the powder and film, the dielectric constants were compared. Using ellipsometry measurements on the film, the refractive index was found to be 1.63, giving a dielectric constant of 2.66, while the literature value of Al2O3 is 1025. This suggests the ALD film is much more likely to form a dipole, making it more reactive. Given the low ALD temperature, this is likely due to hydroxyls remaining in the film creating defects.
The 2000 cycle samples had the highest BET surface area, consistent with a larger mass loading than on the 500 cycle samples. The smaller BET surface area of the MIL-96 on the fibers coated with 500 ALD cycles reflects the small mass loading. The literature value for the BET surface area of synthesized MIL-96 is approximately 600 m2/gMOF7,8. Using the mass measurements and surface areas, the calculated specific surface area of MIL on fabrics was only one tenth of the literature values, though this is improved with thicker ALD base layers. This estimate may be artificially low due to exaggerated mass measurements and insufficient material in the BET.
For the UiO-66-NH2 synthesis, the TiO2 on PA-6 fibers interacts with the backbone of the fiber to change the structural properties while also forming a hard outer shell on the microfibers20,26. The coatings deposited at 50 &#176;C resulted in pealing and poor adhesion after MOF synthesis because the low temperature limited the diffusion of the precursor into the fiber. For metal oxides deposited at 90 &#176;C, this peeling was largely eliminated due to the increased temperature of deposition, though some cracks can still be observed in the film. At 200 &#176;C, the diffusion into the fiber eliminated peeling and cracking, but at the expense of thinning the available TiO2 at the surface of the fiber. The thick outer shells deposited at 50 and 90 &#176;C still resulted in MOF growth, but the MOF growth was very limited on TiO2 deposited at 200 &#176;C, likely because the outermost shell is so thin. The BET surface area of these samples reflects the growth on the TiO2 layers. The UiO-66-NH2 powder surface area was 1325 m2/gMOF, in agreement with literature reported values. Back calculating the MOF surface area from the mass measurements and sample surface areas reveals the MOF powders on fabrics had at best half the surface area per gram MOF. In all cases, while the mass loadings could be misleading, the thicker outer ALD layers correlated to larger BET surface areas post MOF growth, possibly&#160;resulting in better MOF crystallinity as the MOF precursors interacted less with the fibers.
Future studies may examine atomic layer deposition for a variety of metal oxides, including ZnO, ZrO2, and HfO2, which may be applicable for alternative MOF syntheses27. However, some of these processes require much higher deposition temperatures, limiting feasible fabrics for deposition. Additionally, MOFs with much more complex metal centers, such as Zr6 clusters, may be much more difficult to achieve due to the limited mobility of the film. However, in choosing appropriate ALD precursors and temperatures, fluidity of the film may be achieved at higher MOF synthesis temperatures28.

Metal-organic frameworks are crystalline structures consisting of reactive metal cluster centers bridged by organic molecule linkers to provide large porosities and surface areas. Their structure, porosity, and functionality can be designed by choosing appropriate clusters and linkers, leading to surface areas as high as&#160;7,000 m2/gMOF1,2. Their high porosity and surface area have made MOFs diversely applicable in adsorption, separation, and heterogeneous catalysis in fields ranging from energy production to environmental concerns to biological processes1,3,4,5,6.
Numerous MOFs have proven successful in selectively adsorbing volatile organic compounds and greenhouse gases or to catalytically degrade chemicals that may prove harmful to human health or the environment. In particular, MIL-96 (Al) has shown to selectively adsorb nitrogenous volatile organic compounds (VOCs) due to the availability of lone pair electrons in the nitrogen groups to coordinate with the weak Lewis acid Al present in the metal clusters7. MIL-96 has also been shown to adsorb gases such as CO2, p-xylene, and m-xylene8,9. MOF adsorption selectivity is dependent on both the Lewis acid of the metal cluster, as well as pore size. The pore size of MIL-96 increases with temperature, resulting in increased adsorption capacity of trimethylbenzene with increased temperature, and presents the opportunity of tuning selectivity with adsorption temperature9.
The second MOF of focus here, UiO-66-NH2 has been shown to catalytically degrade chemical warfare agents (CWAs) and simulants. The amine group on the linker provides a synergistic effect in degrading nerve agents, while preventing agent degradation products from binding irreversibly to the zirconium clusters and poisoning the MOF10. UiO-66-NH2 has catalytically hydrolyzed dimethyl p-nitrophenylphosphate (DMNP) with a half-life as short as 0.7 minutes in buffered conditions, nearly 20 times faster than its base MOF UiO-6611,12.
While these adsorption and catalytic properties are promising, the physical form of the MOFs, primarily bulk powder, can be difficult to incorporate into platforms for gas capture and filtration without adding significant bulk, clogging pores, or reducing MOF flexibility. An alternative is to create MOF functionalized fabrics. MOFs have been incorporated into fabrics in myriad ways, including electrospinning MOF powder/polymer slurries, adhesive mixes, spray coating, solvothermal growth, microwave syntheses, and a layer-by-layer growth method13,14,15,16,17,18. Of these, electrospinning and polymer adhesives can result in blocked functional sites on the MOF as they are encapsulated in the polymer, significantly decreasing adsorption capacity and reactivity. Additionally, many of these techniques fail to create conformal coatings on the fibers due to line of sight difficulties or poor adhesion/nucleation and the reliance on purely electrostatic interactions. An alternative method is to first coat the fabric with a metal oxide to allow for stronger surface interactions with the MOF18,19.
One method of metal oxide deposition is atomic layer deposition (ALD). ALD is a technique for depositing conformal thin films, controllable to the atomic scale. The process utilizes two half reactions that occur only at the surface of the substrate to be coated. The first step is to dose a metal containing precursor, which reacts with hydroxyls on the surface, leaving a metallated surface while excess reactant is purged from the system. The second reactant is an oxygen-containing reactant, typically water, which reacts with the metal sites to form a metal oxide. Again, excess water and any reaction products are purged from the system. These alternating doses and purges can be repeated until the desired film thickness is achieved (Figure 1). Atomic layer deposition is particularly useful because the small-scale vapor phase precursors allow for conformal films on every surface of substrates with complex topology, such as fiber mats. Additionally, for polymers such as polypropylene, the ALD conditions can allow the coating to diffuse into the fiber surface, providing a strong anchor for future MOF growth20.
The metal oxide coating allows for increased nucleation sites on the fibers during traditional solvothermal synthesis by increasing functional groups and roughness18,20. Our group has previously shown the ALD metal oxide base layer is effective for UiO-6X, HKUST-1, and other syntheses through various routes of solvothermal, layer-by-layer, and hydroxy-double salt conversion methods13,17,18,21,22,23. Here we demonstrate two synthesis types. The MIL materials are formed by converting the Al2O3 ALD coating directly to MOF by diffusion of the organic linker. By submerging an Al2O3 ALD coated fiber mat in trimesic acid solution and heating, the organic linker diffuses into the metal oxide coating to form MIL-96. This results in a strongly adhered, conformal MOF coating on every fiber surface. The second synthesis approach calls for typical UiO-66-NH2 hydrothermal synthesis using metal and organic precursors, but adds a metal oxide coated fiber mat on which the MOF nucleates. For both synthesis approaches, the resulting products consist of conformal thin films of MOF crystals strongly adhered to the supporting fabric. In the case of MIL-96, these can be incorporated into filters for adsorption of VOCs or greenhouse gases. For UiO-66-NH2 these fabrics can be easily incorporated into lightweight protective clothing for military personnel, first responders, and civilians for continuous defense against CWA attacks.

<table border="0" cellpadding="0" cellspacing="0" width="625">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">trimethylaluminum</td>
			<td style="width:123px;">Strem Chemicals</td>
			<td style="width:119px;">93-1360</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">home-built ALD reactor</td>
			<td style="width:123px;">N/A</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">nitrogen cylinder</td>
			<td style="width:123px;">Arc3</td>
			<td style="width:119px;">UN1066</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">trimesic acid</td>
			<td style="width:123px;">Sigma-Aldrich</td>
			<td style="width:119px;">482749-500G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">ethanol</td>
			<td style="width:123px;">Koptec</td>
			<td style="width:119px;">V1001</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">teflon lined autoclave</td>
			<td style="width:123px;">PARR Instrument Company</td>
			<td style="width:119px;">4760-1211</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">isotemp furnace</td>
			<td style="width:123px;">Fisher Scientific</td>
			<td style="width:119px;">F47925</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Zirconium (IV) chloride</td>
			<td style="width:123px;">Alfa Aesar</td>
			<td style="width:119px;">12104</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">2-aminoterephthalic acid</td>
			<td style="width:123px;">Acros Organics</td>
			<td style="width:119px;">278031000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">N,N-dimethylformamide</td>
			<td style="width:123px;">Fisher Scientific</td>
			<td style="width:119px;">D119-4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Hydrochloric Acid</td>
			<td style="width:123px;">Fisher Scientific</td>
			<td style="width:119px;">A481-212</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Polypropylene fiber mats</td>
			<td style="width:123px;">N/A</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Polyamide fiber mats</td>
			<td style="width:123px;">N/A</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

solvothermal synthesis of mil-96 and uio-66-nh2 on atomic layer deposited metal oxide coatings on fiber mats

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven effective in gas adsorption, separations, and catalysis. MOFs are most commonly synthesized as bulk powder, requiring additional processes to adhere them to functional devices and fabrics that risk decreasing the powder porosity and adsorption capacity. Here, we demonstrate a method of first coating fabrics with metal oxide films using atomic layer deposition (ALD). This process creates conformal films of controllable thickness on each fiber, while providing a more reactive surface for MOF nucleation. By submerging the ALD coated fabric in solution during solvothermal MOF synthesis, the MOFs create a conformal, well-adhered coating on the fibers, resulting in a MOF-functionalized fabric, without additional adhesion materials that may block MOF pores and functional sites. Here we demonstrate two solvothermal synthesis methods. First, we form a MIL-96(Al) layer on polypropylene fibers using synthetic conditions that convert the metal oxide to MOF. Using initial inorganic films of varying thicknesses, diffusion of the organic linker into the inorganic allows us to control the extent of MOF loading on the fabric. Second, we perform a solvothermal synthesis of UiO-66-NH2 in which the MOF nucleates on the conformal metal oxide coating on polyamide-6 (PA-6) fibers, thereby producing a uniform and conformal thin film of MOF on the fabric. The resulting materials can be directly incorporated into filter devices or protective clothing and eliminate the maladroit qualities of loose powder.

To describe the MOF/fabric materials, we delineate two terms related to measured surface area. First, projected surface area, cm2projected, refers to the macroscopic size of the fabric swatch as measured with a ruler, i.e., the area of the sample&#39;s projected shadow. The second surface area of interest is the BET surface area, calculated from a nitrogen isotherm obtained at 77 K. These values are given in units of m2/gFabric, m2/gMOF, or m2/gMOF+Fabric, corresponding respectively to the measured or estimated total surface area per gram of sample for the fabric before MOF loading, the MOF itself, or the fabric after loading with MOF. For ALD coated fabrics and MIL-96 coated fabrics, the surface areas were calculated from a partial pressure range of 0.05 to 0.3. For samples containing UiO-66-NH2, surface areas were calculated using a partial pressure range of 0.02 to 0.08, due to the presence of microporosity. All samples had correlation coefficients of 0.995 or higher. Fit parameters are listed for each sample in Table 1. The specific surface area of a MOF on fabric, m2/gMOF, is calculated using measured mass and surface area of MOF on fabric:
<img alt="Equation" src="/files/ftp_upload/57734/57734eq1v2.jpg" />
After coating fabrics with 1000 cycles of Al2O3 ALD, the polypropylene fabric appeared visually unchanged, although some additional stiffness could be felt by hand. Ellipsometry of monitor silicon wafers revealed 1100 &#177;15 &#197; of Al2O3 growth using a Cauchy model. The ALD coating resulted in a mass gain of 1.16 mgAl2O3/cm2projected. This process was repeated with 500 and 2000 cycles of Al2O3, resulting in 600 &#177;15 and 2010 &#177;40 &#197; on the monitor silicon wafers. The mass increase was 0.65 mgAl2O3/cm2projected and 2.26 mgAl2O3/cm2projected on the 500 and 2000 cycle samples respectively. The BET surface area of the Al2O3(1000) coated polypropylene was 4.7 m2/gFabric.
Following the MOF synthesis, the resulting solution was clear and free of loose MOF powder, indicating strong MOF and ALD adhesion on the fiber. After washing and drying, the sample mass increase on the 500, 1000, and 2000 cycle samples was 40, 73, and 77% of the mass of the initial samples, respectively. Parallel exposure of Al2O3 coated fabric samples to synthesis conditions in the absence of MOF linker or metal-cluster precursors revealed an inherent mass gain of 10-20%, suggesting the mass measurements exaggerate the MOF loading. Examination with scanning electron microscopy (SEM) showed conformal MOF crystal thin films on all fibers, resembling a cobblestone pattern (Figure&#160;3b&#8211;3c). When the Al2O3 was reduced to 500 cycles, the film began to break apart as the MOF formed, resulting in a patchy coating (Figure 3a). A bare polypropylene sample with no Al2O3 coating was also exposed to MIL-96 synthesis conditions (Figure 3d), but XRD showed no detectable MOF present on the fibers. Cross-sectional images of these samples revealed the 500 cycle Al2O3 base layer completely reacted, while a fraction of the Al2O3 base layer remained for the 1000 and 2000 cycle samples (Figure&#160;4d&#8211;4f). Cross-sections of the original Al2O3 ALD coated polypropylene are shown in Figure&#160;4a-4c. In the 24 hour reaction time, approximately 80&#177;20 nm of Al2O3 reacted or was potentially etched away in the acidic synthesis conditions. Electron dispersion spectroscopy images of the cross-section revealed the carbon based polypropylene core and predominantly Al2O3 shell (Figure 5). X-ray diffraction patterns of the MOF coated fabric, matching the simulated PXRD pattern of MIL-96, are shown in Figure 6. The measured surface area after MOF growth was 6.0 m2/gMOF+Fabric, 6.7 m2/gMOF+Fabric, and 19.9 m2/gMOF+Fabric, for the 500, 1000, and 2000 cycle samples respectively. Adsorption and desorption isotherms are shown in Figure 7.
The PA-6 fiber mats appeared slightly yellowed after deposition of 300 cycles of TiO2, but the mat felt nearly unchanged in stiffness. Ellipsometry revealed 175 &#177;15 &#197; of TiO2 for ALD at 50, 90, or 200 &#176;C on the monitor silicon. The ALD mass loading was 0.17, 0.20, and 0.25 mgTiO2/cm2projected area PA-6 for the 50, 90, and 200 &#176;C samples. The BET surface area of the PA-6 fabric coated with 300 cycles of TiO2 at 90 &#176;C was 8.2 m2/gFabric.
Following solvothermal MOF synthesis, XRD patterns revealed UiO-66-NH2 was present on the fibers (Figure 8). The MOF mass gain on the 50, 90, and 200 &#176;C samples was 2.4, 78, and 0%. A parallel exposure of TiO2 coated nylon to synthesis conditions in the absence of MOF metal-cluster or linker precursors revealed a mass gain of 10-20%. Additionally, fabric was easily torn during the MOF synthesis and the acidic conditions may etch the TiO2 film, leading to uncertainties in the MOF loading. SEM images showed the MOF coatings on each sample, with flaky coatings on the 50 &#176;C samples, dense coatings on the 90 &#176;C samples, and sparse coatings on the 200 &#176;C samples (Figure&#160;9a&#8211;9c). An uncoated PA-6 sample was also exposed to UiO-66-NH2 synthesis conditions, resulting in a relatively sparse coating of MOF crystals (Figure 9d). The measured BET surface areas after MOF synthesis were 16.0 m2/gMOF+Fabric, 19.8 m2/gMOF+Fabric, and 4.67 m2/gMOF+Fabric, for the 50, 90, and 200 &#176;C samples respectively. Adsorption and desorption isotherms are shown in Figure 10.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/57734/57734fig1v2.jpg" /> 
Figure 1.&#160;Schematic of Al2O3 ALD process: In the first step, precursor dosing, trimethyl aluminum precursor reacts with the hydroxyl terminated surface. The excess precursor is then purged from the system, resulting in a uniform aluminum-dimethyl terminated surface. During the water dose step the water reacts to replace the methyl groups, resulting in a newly hydroxyl terminated surface. In the last step of the cycle, the excess water is purged from the system. <a href="/files/ftp_upload/57734/57734fig1v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/57734/57734fig2.jpg" /> 
Figure 2.&#160;ALD reactor schematic: The system is a home-built, hot-walled viscous flow reactor with a dry nitrogen carrier gas. The precursor lines are wrapped with heat tape, while the actual deposition zone holding the mesh sample boat is located within a furnace. The system is operated under vacuum at ~1.8 Torr. <a href="/files/ftp_upload/57734/57734fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/57734/57734fig3.jpg" /> 
Figure 3.&#160;SEM images of PP with (a) Al2O3(500)/MIL-96, (b) Al2O3(1000)/MIL-96, (c) Al2O3(2000)/MIL-96, and (d) no ALD coating after exposure to the MIL-96 synthesis conditions. <a href="/files/ftp_upload/57734/57734fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/57734/57734fig4.jpg" /> 
Figure 4.&#160;SEM images of the cross-section of PP with (a) Al2O3 (500), (b) Al2O3 (1000), (c) Al2O3 (2000), (d) Al2O3 (500)/MIL-96, (e) Al2O3 (1000)/MIL-96, (f) Al2O3 (2000)/MIL-96. <a href="/files/ftp_upload/57734/57734fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/57734/57734fig5.jpg" /> 
Figure 5.&#160;EDS images of the cross-section of PP/Al2O3 (500)/MIL-96 reveals the carbon based polypropylene core with the predominantly Al2O3 shell. <a href="/files/ftp_upload/57734/57734fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/57734/57734fig6.jpg" /> 
Figure 6.&#160;(black)&#160;Simulated PXRD pattern of MIL-96,&#160;(red)&#160;XRD pattern of Al2O3 coated polypropylene, (green)&#160;MIL-96 on Al3O3 (500) coated polypropylene, (bue)&#160;MIL-96 on Al3O3 (1000) coated polypropylene, (purple)&#160;MIL-96 on Al3O3 (2000) coated polypropylene&#160;and (gray)&#160;bare PP after exposure to MIL-96 synthesis conditions. <a href="/files/ftp_upload/57734/57734fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/57734/57734fig7v2.jpg" /> 
Figure 7.&#160;(grey) N2 adsorption&#160;and desorption isotherms for MIL-96 on 500 cycles of Al2O3 on polypropylene&#160;(blue)&#160;adsorption and desorption isotherms for MIL-96 on 1000 cycles of Al2O3 on polypropylene&#160;(black)&#160;adsorption and desorption isotherms for MIL-96 on 2000 cycles of Al2O3 on polypropylene. <a href="/files/ftp_upload/57734/57734fig7v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/57734/57734fig8v2.jpg" /> 
Figure 8.&#160;(black) Simulated PXRD pattern of UiO-66-NH2,&#160;(red)&#160;XRD pattern of TiO2 coated PA-6, (green)&#160;UiO-66-NH2 on TiO2(50 &#176;C), coated PA-6&#160;(blue)&#160;UiO-66-NH2 on TiO2(90 &#176;C) coated PA-6, (purple) UiO-66-NH2 on TiO2(200 &#176;C) coated PA-6&#160;and (gray) UiO-66-NH2 on bare PA-6. <a href="/files/ftp_upload/57734/57734fig8v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/57734/57734fig9.jpg" /> 
Figure 9.&#160;SEM images of PA-6/TiO2/UiO-66-NH2 with ALD deposition at (a) 50 &#176;C, (b) 90 &#176;C and (c) 200 &#176;C and (d) UiO-66-NH2 on PA-6 with no ALD base coat, demonstrating the higher ALD temperature results in greater diffusion of the ALD precursors into the fiber, altering the MOF adhesion. <a href="/files/ftp_upload/57734/57734fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/57734/57734fig10v2.jpg" /> 
Figure 10.&#160;N2 Adsorption and desorption isotherms for PA-6/TiO2/UiO-66-NH2 with ALD deposition at (grey) 50 &#176;C (blue) 90 &#176;C, and (black)&#160;200 &#176;C. <a href="/files/ftp_upload/57734/57734fig10v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Sample</td>
			<td>C</td>
			<td>Y (g/mmol)</td>
			<td>Slope (g/mmol)&#160;</td>
			<td>Qm (mmol/G)</td>
		</tr>
		<tr>
			<td>PP/Al2O3 (1000)</td>
			<td>6.61</td>
			<td>3.13</td>
			<td>17.59</td>
			<td>0.048</td>
		</tr>
		<tr>
			<td>PP/Al2O3 (500)/MIL-96</td>
			<td>7.01</td>
			<td>2.31</td>
			<td>13.588</td>
			<td>0.062</td>
		</tr>
		<tr>
			<td>PP/Al2O3 (1000)/MIL-96</td>
			<td>9.24</td>
			<td>1.58</td>
			<td>13.01</td>
			<td>0.069</td>
		</tr>
		<tr>
			<td>PP/Al2O3 (2000)/MIL-96</td>
			<td>4.06</td>
			<td>1.21</td>
			<td>3.69</td>
			<td>0.2</td>
		</tr>
		<tr>
			<td>Nylon/TiO2 (90 &#176;C)</td>
			<td>2.99</td>
			<td>3.97</td>
			<td>10.57</td>
			<td>0.072</td>
		</tr>
		<tr>
			<td>Nylon/TiO2 (50 &#176;C)/UiO-66-NH2</td>
			<td>63.09</td>
			<td>0.096</td>
			<td>5.99</td>
			<td>0.16</td>
		</tr>
		<tr>
			<td>Nylon/TiO2 (90 &#176;C)/UiO-66-NH2</td>
			<td>599</td>
			<td>0.0082</td>
			<td>4.92</td>
			<td>0.2</td>
		</tr>
		<tr>
			<td>Nylon/TiO2 (200 &#176;C)/UiO-66-NH2</td>
			<td>32.43</td>
			<td>0.644</td>
			<td>20.24</td>
			<td>0.048</td>
		</tr>
	</tbody>
</table>
Table 1.&#160;List of BET fit parameters for each sample.

Watch this Scientific Journal Video about Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats at JoVE.com

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Metal-organic frameworks are effective in gas storage and heterogeneous catalysis, but typical synthesis methods result in loose powders that are difficult to incorporate into smart materials. We demonstrate a method of first coating fabrics with ALD metal oxides, resulting in conformal films of MOF on the fabrics during solvothermal synthesis.

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven ...

solvothermal-synthesis-mil-96-uio-66-nh2-on-atomic-layer-deposited

Nanyang Technological University

Research

JoVE Journal

Chemistry

11.3K Views.  North Carolina State University. Metal-organic frameworks are effective in gas storage and heterogeneous catalysis, but typical synthesis methods result in loose powders that are difficult to incorporate into smart materials. We demonstrate a method of first coating fabrics with ALD metal oxides, resulting in conformal films of MOF on the fabrics during solvothermal synthesis.

Video: Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

Preparation of Highly Porous Coordination Polymer Coatings on Macroporous Polymer Monoliths for Enhanced Enrichment of Phosphopeptides

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous polymer monoliths. The developed approach is based on the preparation of a macroporous polymer containing carboxylic acid functional groups and the subsequent step-by-step solution-based controlled growth of a layer of a porous coordination polymer on the surface of the pores of the polymer monolith. The prepared metal-organic polymer hybrid has a high specific micropore surface area. The amount of iron(III) sites is enhanced through metal-organic coordination on the surface of the pores of the functional polymer support. The increase of metal sites is related to the number of iterations of the coating process.
The developed preparation scheme is easily adapted to a capillary column format. The functional porous polymer is prepared as a self-contained single-block porous monolith within the capillary, yielding a flow-through separation device with excellent flow permeability and modest back-pressure. The metal-organic polymer hybrid column showed excellent performance for the enrichment of phosphopeptides from digested proteins and their subsequent detection using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The presented experimental protocol is highly versatile, and can be easily implemented to different organic polymer supports and coatings with a plethora of porous coordination polymers and metal-organic frameworks for multiple purification and/or separation applications.

A procedure for the preparation of porous hybrid separation media composed of a macroporous polymer monolith internally coated by a high surface area microporous coordination polymer is presented.

We describe a protocol for the preparation of hybrid materials based on highly porous coordination polymer coatings on the internal surface of macroporous ...

Layer-by-layer Synthesis and Transfer of Freestanding Conjugated Microporous Polymer Nanomembranes

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in combination with their outstanding thermal and chemical stability, and low densities. However, their insoluble nature causes problems in their processing since usually applied techniques such as spin coating are not available. Especially for membrane applications, where the processing of CMP as thin films is desirable, the processing problems have hindered their commercial application.
Here we describe the interfacial synthesis of CMP thin films on functionalized substrates via molecular layer-by-layer (l-b-l) synthesis. This process allows the preparation of films with desired thickness and composition and even desired composition gradients.
The use of sacrificial supports allows the preparation of freestanding membranes by dissolution of the support after the synthesis. To handle such ultra-thin freestanding membranes the protection with sacrificial coatings showed great promise, to avoid rupture of the nanomembranes. To transfer the nanomembranes to the desired substrate, the coated membranes are upfloated at the air-liquid interface and then transferred via dip coating.

In this paper we describe the interfacial synthesis of conjugated microporous polymers (CMP) on sacrificial substrates, and the dissolution of the substrate for the preparation of freestanding CMP nanomembranes. In addition, we will describe how the fragile nanomembranes can be transferred to other substrates.

CMP as large surface area materials have attracted growing interest recently, due to their high variability in the incorporation of functional groups in ...

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Here we present a protocol for synthesizing Zn1-xMgxO/Cu2O heterojunctions in open-air at low temperature via atmospheric pressure spatial atomic layer deposition (AP-SALD) of Zn1-xMgxO on cuprous oxide. Such high quality conformal metal oxides can be grown on a variety of substrates including plastics by this cheap and scalable method.

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O ...

Photochemical Oxidative Growth of Iridium Oxide Nanoparticles on CdSe@CdS Nanorods

We demonstrate a procedure for the photochemical oxidative growth of iridium oxide catalysts on the surface of seeded cadmium selenide-cadmium sulfide (CdSe@CdS) nanorod photocatalysts. Seeded rods are grown using a colloidal hot-injection method and then moved to an aqueous medium by ligand exchange. CdSe@CdS nanorods, an iridium precursor and other salts are mixed and illuminated. The deposition process is initiated by absorption of photons by the semiconductor particle, which results with formation of charge carriers that are used to promote redox reactions. To insure photochemical oxidative growth we used an electron scavenger. The photogenerated holes oxidize the iridium precursor, apparently in a mediated oxidative pathway. This results in the growth of high quality crystalline iridium oxide particles, ranging from 0.5 nm to about 3 nm, along the surface of the rod. Iridium oxide grown on CdSe@CdS heterostructures was studied by a variety of characterization methods, in order to evaluate its characteristics and quality. We explored means for control over particle size, crystallinity, deposition location on the CdS rod, and composition. Illumination time and excitation wavelength were found to be key parameters for such control. The influence of different growth conditions and the characterization of these heterostructures are described alongside a detailed description of their synthesis. Of significance is the fact that the addition of iridium oxide afforded the rods astounding photochemical stability under prolonged illumination in pure water (alleviating the requirement for hole scavengers).

A protocol for the photochemical oxidative growth of small crystalline iridium oxide nanoparticles on the surface of CdSe@CdS seeded rod nanoparticles is presented.

We demonstrate a procedure for the photochemical oxidative growth of iridium oxide catalysts on the surface of seeded cadmium selenide-cadmium sulfide ...

Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods. This work outlines a method for depositing SrTiO3 (STO) on germanium using ALD. Germanium has higher carrier mobilities than silicon and therefore offers an alternative semiconductor material with faster device operation. This method takes advantage of the instability of germanium's native oxide by using thermal deoxidation to clean and reconstruct the Ge (001) surface to the 2&#215;1 structure. 2-nm thick, amorphous STO is then deposited by ALD. The STO film is annealed under ultra-high vacuum and crystallizes on the reconstructed Ge surface. Reflection high-energy electron diffraction (RHEED) is used during this annealing step to monitor the STO crystallization. The thin, crystalline layer of STO acts as a template for subsequent growth of STO that is crystalline as-grown, as confirmed by RHEED. In situ X-ray photoelectron spectroscopy is used to verify film stoichiometry before and after the annealing step, as well as after subsequent STO growth. This procedure provides framework for additional perovskite oxides to be deposited on semiconductors via chemical methods in addition to the integration of more sophisticated heterostructures already achievable by physical methods.

This work details the procedures for the growth and characterization of crystalline SrTiO3 directly on germanium substrates by atomic layer deposition. The procedure illustrates the ability of an all-chemical growth method to integrate oxides monolithically onto semiconductors for metal-oxide semiconductor devices.

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and ...

Aerosol-assisted Chemical Vapor Deposition of Metal Oxide Structures: Zinc Oxide Rods

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, their high cost production and/or incompatibility with microfabrication technologies, due to the use of pre-deposited catalyst-seeds and/or high processing temperatures exceeding 900 &#176;C, represent a drawback for a widespread use of these methods. Here, however, we report the synthesis of ZnO rods via a non-catalyzed vapor-solid mechanism enabled by using an aerosol-assisted chemical vapor deposition (CVD) method at 400 &#176;C with zinc chloride (ZnCl2) as the precursor and ethanol as the carrier solvent. This method provides both single-step formation of ZnO rods and the possibility of their direct integration with various substrate types, including silicon, silicon-based micromachined platforms, quartz, or high heat resistant polymers. This potentially facilitates the use of this method at a large-scale, due to its compatibility with state-of-the-art microfabrication processes for device manufacture. This report also describes the properties of these structures (e.g., morphology, crystalline phase, optical band gap, chemical composition, electrical resistance) and validates its gas sensing functionality towards carbon monoxide.

Columnar zinc oxide structures in the form of rods are synthesized via aerosol-assisted chemical vapor deposition without the use of pre-deposited catalyst-seed particles. This method is scalable and compatible with various substrates based on either silicon, quartz or polymers.

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, ...

Rapid Nanoprobe Signal Enhancement by In Situ Gold Nanoparticle Synthesis

The use of nanoprobes such as gold, silver, silica or iron-oxide nanoparticles as detection reagents in bioanalytical assays can enable high sensitivity and convenient colorimetric readout. However, high densities of nanoparticles are typically needed for detection. The available synthesis-based enhancement protocols are either limited to gold and silver nanoparticles or rely on precise enzymatic control and optimization. Here, we present a protocol to enhance the colorimetric readout of gold, silver, silica, and iron oxide nanoprobes. It was observed that the colorimetric signal can be improved by up to a 10000-fold factor. The basis for such signal enhancement strategies is the chemical reduction of Au3+ to Au0. There are several chemical reactions that enable the reduction of Au3+ to Au0. In the protocol, Good&#39;s buffers and H2O2 are used and it is possible to favor the deposition of Au0 onto the surface of existing nanoprobes, in detriment of the formation of new gold nanoparticles. The protocol consists of the incubation of the microarray with a solution consisting of chloroauric acid and H2O2 in 2-(N-morpholino)ethanesulfonic acid pH 6 buffer following the nanoprobe-based detection assay. The enhancement solution can be applied to paper and glass-based sensors. Moreover, it can be used in commercially available immunoassays as demonstrated by the application of the method to a commercial allergen microarray. The signal development requires less than 5 min of incubation with the enhancement solution and the readout can be assessed by naked eye or low-end image acquisition devices such as a table-top scanner or a digital camera.

Rapid Nanoprobe Signal Enhancement by In Situ Gold Nanoparticle Synthesis

In this work, a protocol for signal enhancement of nanoprobe-based biosensing is presented. The protocol is based on the reduction of chloroauric acid onto the surface of existing nanoprobes that consist of gold, silver, silica or iron-oxide nanoparticles.

The use of nanoprobes such as gold, silver, silica or iron-oxide nanoparticles as detection reagents in bioanalytical assays can enable high sensitivity ...

Molten-Salt Synthesis of Complex Metal Oxide Nanoparticles

The development of feasible synthesis methods is critical for the successful exploration of novel properties and potential applications of nanomaterials. Here, we introduce the molten-salt synthesis (MSS) method for making metal oxide nanomaterials. Advantages over other methods include its simplicity, greenness, reliability, scalability, and generalizability. Using pyrochlore lanthanum hafnium oxide (La2Hf2O7) as a representative, we describe the MSS protocol for the successful synthesis of complex metal oxide nanoparticles (NPs). Furthermore, this method has the unique ability to produce NPs with different material features by changing various synthesis parameters such as pH, temperature, duration, and post-annealing. By fine-tuning these parameters, we are able to synthesize highly uniform, non-agglomerated, and highly crystalline NPs. As a specific example, we vary the particle size of the La2Hf2O7&#160;NPs by changing the concentration of the ammonium hydroxide solution used in the MSS process, which allows us to further explore the effect of particle size on various properties. It is expected that the MSS method will become a more popular synthesis method for nanomaterials and more widely employed in the nanoscience and nanotechnology community in the upcoming years.

Here, we demonstrate a unique, relatively low-temperature, molten-salt synthesis method for preparing uniform complex metal oxide lanthanum hafnate nanoparticles.

The development of feasible synthesis methods is critical for the successful exploration of novel properties and potential applications of nanomaterials. ...

Niobium Oxide Films Deposited by Reactive Sputtering: Effect of Oxygen Flow Rate

Reactive sputtering is a versatile technique used to form compact films with excellent homogeneity. In addition, it allows easy control over deposition parameters such as gas flow rate that results in changes on composition and thus in the film required properties. In this report, reactive sputtering is used to deposit niobium oxide films. A niobium target is used as metal source and different oxygen flow rates to deposit niobium oxide films. The oxygen flow rate was changed from 3 to 10 sccm. The films deposited under low oxygen flow rates show higher electrical conductivity and provide better perovskite solar cells when used as electron transport layer.

Here, we present a protocol for niobium oxide films deposition by reactive sputtering with different oxygen flow rates for use as an electron transport layer in perovskite solar cells.

Reactive sputtering is a versatile technique used to form compact films with excellent homogeneity. In addition, it allows easy control over deposition ...