This work was generously supported by Brown University and the Advanced Energy Consortium. We gratefully thank Dr. Qingbo Zhang for his established synthetic method of iron oxide MFCs.

1. Synthesis of MFCs with control over MFCs&#39; overall diameter and ferrite composition
<ol>
	<li>Wash and thoroughly dry all glassware to be used in the synthesis. The amount of water in the synthesis impacts the dimensions of the MFCs, so it is crucial to ensure the glassware has no residual water in it16,26.
	<ol>
		<li>To wash the glassware, rinse with water and detergent and scrub with a flask brush to remove debris. Thoroughly rinse to remove all detergent and finish with a rinse of deionized water.</li>
		<li>To dry the glassware, shake water droplets off the surface of the glassware and place into an oven at 60&#176;C until completely dry.</li>
		<li>Rinse the polyphenylene-lined (PPL) reactors with 37% hydrochloric acid to remove any debris from previous use. To do this, place the reactors and their caps in a large beaker and fill with hydrochloric acid until the reactors are completely submerged. Let this sit for 30 min before pouring out the hydrochloric acid. Continuously rinse the beaker containing the reactors with water for 1-2 min, and then place the reactors in the oven to dry.</li>
	</ol>
	</li>
	<li>Use an automatic pipette to transfer 20 mL of ethylene glycol into a 50 mL beaker with a magnetic stir bar.</li>
	<li>Weigh out the required amount of iron(III) chloride (FeCl3&#183;6H2O, solid) to achieve a final concentration of 1.3 mM and add it to the beaker. Put the beaker on a stir plate and turn it on at 480 rpm to begin continuous stirring of the beaker. 
	NOTE: As this is a hydrate, it must be measured and added quickly to avoid unwanted absorption of water from the ambient air.</li>
	<li>Weigh 250 mg of polyacrylic acid (PAA, Mw ~6,000, powder) and add it to the beaker. After the addition of PAA, the solution becomes opaque and slightly lighter in color.</li>
	<li>Weigh 1.2 g of urea (CO(NH2)2, powder) and add it to the beaker.</li>
	<li>Using a pipette, add 0.7 mM manganese(II) chloride (MnCl2&#183;6H2O aq, 3.5 M, 0.2 mL) to the beaker.</li>
	<li>Finally, using a pipette add the required amount (0.5 mL) of ultra-pure water to the beaker.</li>
	<li>Let the solution stir for 30 min and notice the color change. It will present as a translucent, dark orange color.</li>
	<li>Transfer the reaction mixture into the polyphenylene lined (PPL) reactor. Note that after the solution has stirred some solids may have accumulated on the sides of the beaker.
	<ol>
		<li>Use a magnet (cubic permanent rare earth magnet, 40 x 40 x 20 mm, hereafter referred to as a &#34;magnet&#34; for all separation and magnetic collection procedures) to drag the stir bar around the walls of the beaker to ensure any solids that have accumulated on the sides are dispersed into the reaction solution.</li>
		<li>Once the solution is mixed and ready, transfer it into the 50 mL PPL lined reactor.</li>
		<li>Use a clamp and lever to seal the reactor in the stainless-steel autoclave as tightly as possible. Clamp the reactor vessel to a stable surface, and using a rod inserted into the cap as a lever, push the reactor to seal. Note that the sealed reactor should not be able to be opened by hand. This is crucial as the high-pressure environment of the oven requires a tight seal on the reactor.</li>
	</ol>
	</li>
	<li>Place the reactor into an oven for 20 h at 215 &#176;C.</li>
	<li>After the hydrothermal reaction is done, remove the reactor from the oven and allow it to cool down to room temperature. The pressure of the oven will enable the reactor to be opened by hand. Note that at this point, the reactor will contain the MFC product dispersed in ethylene glycol with other impurities, such as unreacted polymer, and will be an opaque black solution. The product will be isolated in the following steps.</li>
</ol>
2. Magnetic separation and purification of MFCs
<ol>
	<li>Place 200 mg of steel wool into a glass vial. Fill the glass vial halfway with the reaction mixture from the reactor. Fill the rest of the vial with acetone and shake well. Note that the steel wool increases the magnetic field strength in the vial and will help magnetic separation of the nanoclusters from the solution.</li>
	<li>Place the vial on a magnet for magnetic collection to occur. The result will be a translucent solution with precipitate at the bottom.
	<ol>
		<li>Pour off the supernatant solution while the MFCs are magnetically trapped by the steel wool by holding the magnet to the bottom of the vial while pouring. Ethylene glycol will be mostly removed in this step.</li>
		<li>Start washing with the low ratio of acetone to water and increase the ratio in subsequent washes until pure. Do this 3-4 times.</li>
	</ol>
	</li>
	<li>Remove the vial from the magnet and fill it with water. Shake well to dissolve the MFCs. Now the product will be fully dispersed in water.</li>
	<li>Repeat the previous two steps several times until the aqueous solution of the MFCs produces no bubbles when shaken. The result will be a dark, opaque ferrofluid that will respond strongly to magnets. 
	NOTE: In a typical synthesis with 20 mL of ethylene glycol, approximately 80 mg of MFC product will be obtained.</li>
</ol>
3. Surface functionalization of MFCs toward ultra-high colloidal stability
NOTE: The synthesis of nitro-dopamine and Poly(AA-co-AMPS-co-PEG) can be found in our previous work16. The copolymer is made through free radical polymerization. Add 0.20 g of 2,2&#8242;-Azobis(2-methylpropionitrile) (AIBN), 0.25 g of acrylic acid (AA), 0.75 g of 2-Acrylamido-2-methylpropane sulfonic acid (AMPS), and 1.00 g of Poly(ethylene glycol) methyl ether acrylate (PEG) in 10 mL of N,N-Dimethylformamide (DMF). Heat the mixture in a 70 &#176;C water bath for 1 h and transfer it to a dialysis bag (Cellulose Membrane, 3 kDa) in water. The weight ratio of AA, AMPS, and PEG is 1:3:4. Polymerization for these monomers has a 100% conversion rate as confirmed by freeze drying and weighing.
<ol>
	<li>Combine 10 mL of purified nanoparticles (around 100 mg) in a 20 mL vial with 10 mL of saturated N-[2-(3,4-dihydroxyphenyl)ethyl]nitramide (nitro-dopamine) solution (~1 mg/mL). Wait for 5 min.</li>
	<li>Wash the nitro-dopamine coated MFCs using magnetic separation. Pour out the pale-yellow supernatant. Add water and shake vigorously. Then, pour out water using the magnet to retain the product. Repeat this washing several times leaving the dark brown collection in the vial. 
	NOTE: Prepare a aqueous solution with a concentration of 20 mg/mL, a buffer solution with a concentration of 100 mg/mL, and a poly(AA-co-AMPS-co-PEG) polymer solution with a concentration of 20 mg/mL.</li>
	<li>Mix 1 mL of EDC solution, 1 mL of MES buffer, and 3 mL of the polymer solution. Lightly stir by swirling the mixture, and let it sit for approximately 5 min. It should be a clear and colorless solution when fully combined.</li>
	<li>Add this mixture to the MFC collection and place the vial in an ice bath. Lower the probe sonicator into the solution, and then turn it on (250 watts of power at 20 kHz).
	<ol>
		<li>After a 5 min sonication treatment, add roughly 5 mL of ultra-pure water to the vial while the sonicator is still running. Continue monitoring the vessel to ensure that no product spills. Maintain the ice in the ice-water mixture as some of the initial ice will melt due to the intensity and heat of the sonication.</li>
		<li>Allow the mixture to sonicate for an additional 25 min, for a total of 30 min.</li>
	</ol>
	</li>
	<li>Place the vial on top of a magnet to separate the MFCs and pour out the supernatant solution.</li>
	<li>Wash the modified MFCs with deionized water several times.</li>
	<li>Fill the vial containing the MFCs with ultra-pure water. Pipette this fluid into a vacuum filtration system with a 0.1 &#181;m polyethersulfone membrane filter to remove any irreversibly aggregated MFCs. Make sure to flush the walls of the funnel to minimize any loss of product.</li>
	<li>Vacuum filter the solution. Repeat this process 2-3 times. The result will be a purified aqueous solution of monodispersed MFCs. 
	NOTE: Roughly 10% of the product will be irreversibly aggregated and this material will remain on the filter and should be discarded.</li>
</ol>

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The authors have nothing to disclose.

This work demonstrates a modified polyol synthesis of manganese ferrite nanocrystals clustered together into uniform nanoscale aggregates29. In this synthesis, iron(III) chloride and manganese(II) chloride undergo a forced hydrolysis reaction and reduction, forming molecular MnxFe3-xO4. These ferrite molecules form primary nanocrystals under the high temperature and high pressure in the reactors, ultimately assembling into spherical aggregates termed her...

The inclusion of manganese as a dopant in an iron oxide lattice can, under the appropriate conditions, increase the material&#39;s magnetization at high applied fields as compared to pure iron oxides. As a result, manganese ferrite (MnxFe3-xO4) nanoparticles are highly desirable magnetic nanomaterials due to their high saturation magnetization, strong response to external fields, and low cytotoxicity1,2,3,4,5. Both single domain nanocrystals as well as clusters of these nanocrystals, termed multidomain particles, have been investigated in diverse biomedical applications, including drug delivery, magnetic hyperthermia for cancer treatment, and magnetic resonance imaging (MRI)6,7,8. For example, the Hyeon group in 2017 used single domain manganese ferrite nanoparticles as a Fenton catalyst to induce cancer hypoxia and exploited the material&#39;s T2contrast for MRI tracking9. It is surprising in light of these and other positive studies of ferrite materials that there are few in vivo demonstrations as compared to pure iron oxide (Fe3O4) nanomaterials, and no reported applications in humans9,10.
One immense challenge faced in translating the features of ferrite nanomaterials into the clinic is the generation of uniform, non-aggregating, nanoscale clusters11,12,13,14. While conventional synthetic approaches to monodomain nanocrystals are well developed, multidomain clusters of the type of interest in this work are not easily produced in a uniform and controlled fashion15,16. Additionally, ferrite composition is usually non-stoichiometric and not simply related to the starting concentration of the precursors and this can further obscure systematic structure-function characterization of these materials9,12,13,17. Here, we address these issues by demonstrating a synthetic approach that yields independent control over both the cluster dimension and composition of manganese ferrite nanomaterials.
This work also provides a means to overcome the poor colloidal stability of ferrite nanomaterials18,19,20. Magnetic nanoparticles are generally prone to aggregation due to strong particle-particle attraction; ferrites suffer more from this problem as their larger net magnetization amplifies particle aggregation. In relevant biological media, these materials yield large enough aggregates that the materials rapidly collect, thereby limiting their routes of exposure to animals or people20,21,22. Hilt et al. found another consequence of particle-particle aggregation in their study of magnetothermal heating and dye degradation23. At slightly higher particle concentrations, or increased time of exposure to the field, the effectiveness of the materials was reduced as materials aggregated over time and the active particle surface areas decreased. These and other applications would benefit from cluster surfaces designed to provide steric barriers that precluded particle-particle interactions24,25.
Here we report a synthetic approach to synthesize manganese ferrite clusters (MFCs) with controllable dimensions and composition. These multidomain particles consist of an assembly of primary manganese ferrite nanocrystals that are hard aggregated; the close association of the primary nanocrystals enhances their magnetic properties and provides for an overall cluster size, 50-300 nm, well matched to the optimum dimensions for a nanomedicine. By changing the amount of water and manganese chloride precursor, we can independently control the overall diameter and composition. The method utilizes simple and efficient one-pot hydrothermal reactions that allow for frequent experimentation and material optimization. These MFCs can be easily purified into a concentrated product solution, which is further modified by sulfonated polymers that impart colloidal stability. Their tunability, uniformity, and solution phase stability are all features of great value in applications of nanomaterials in biomedical and environmental engineering.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.1 Micron Vaccum Filtration Filter</td>
			<td>Thermo Fisher Scientific</td>
			<td>NC9902431</td>
			<td>for filtration of aggregated clusters after synthesis and surface coating to achieve a uniform solution</td>
		</tr>
		<tr>
			<td>2-Acrylamido-2-methylpropane sulfonic acid (AMPS, 99%)</td>
			<td>Sigma-Aldrich</td>
			<td>282731-250G</td>
			<td>reagent used in copolymer to surface coat nanoclusters and functionalize them for biological media</td>
		</tr>
		<tr>
			<td>2,2&#8242;-Azobis(2-methylpropionitrile) (AIBN)</td>
			<td>Sigma-Aldrich</td>
			<td>441090-100G</td>
			<td>reagent used in copolymer making as the free ridical generator</td>
		</tr>
		<tr>
			<td>4-Morpholineethanesulfonic acid, 2-(N-Morpholino)ethanesulfonic acid (MES)</td>
			<td>Sigma-Aldrich</td>
			<td>M3671-250G</td>
			<td>acidic buffer used to stabilize nanocluster surface coating process</td>
		</tr>
		<tr>
			<td>Acrylic acid</td>
			<td>Sigma-Aldrich</td>
			<td>147230-100G</td>
			<td>reagent used in copolymer to surface coat nanoclusters and functionalize them for biological media; anhydrous, contains 200 ppm MEHQ as inhibitor, 99%</td>
		</tr>
		<tr>
			<td>Analytical Balance</td>
			<td>Avantor</td>
			<td>VWR-205AC</td>
			<td>used to weigh out solid chemical reagents for use in synthesis and dilution</td>
		</tr>
		<tr>
			<td>Digital Sonifier and Probe</td>
			<td>Branson</td>
			<td>B450</td>
			<td>used to sonicate nanocluster solution during surface coating to break up aggregates</td>
		</tr>
		<tr>
			<td>Dopamine hydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>H8502-25G</td>
			<td>used in surface coating for ligand exchange reaction</td>
		</tr>
		<tr>
			<td>Ethylene glycol (anhydrous, 99.8%)</td>
			<td>Sigma-Aldrich</td>
			<td>324558-2L</td>
			<td>reagent used as solvent in hydrothermal synthesis of nanoclusters</td>
		</tr>
		<tr>
			<td>Glass Vials (20mL)</td>
			<td>Premium Vials</td>
			<td>B1015</td>
			<td>container for nanocluster solution during washing and surface coating as well as polymer solutions</td>
		</tr>
		<tr>
			<td>Graduated Beaker (100mL)</td>
			<td>Corning</td>
			<td>1000-100</td>
			<td>container for mixing of solid and liquid reagents during hydrothermal synthesis (to be transferred into autoclave reactor before oven)</td>
		</tr>
		<tr>
			<td>Handheld Magnet</td>
			<td>MSC Industrial Supply, Inc.</td>
			<td>92673904</td>
			<td>1/2&#34; Long x 1/2&#34; Wide x 1/8&#34; High, 5 Poles, Rectangular Neodymium Magnet low strength magnet used to precipitate nanoclusters from solution (field strength is increased with steel wool when needed)</td>
		</tr>
		<tr>
			<td>Hydrochloric acid (ACS grade, 37%)</td>
			<td>Fisher Scientific</td>
			<td>7647-01-0</td>
			<td>for removing leftover nanocluster debris and cleaning autoclave reactors for next use</td>
		</tr>
		<tr>
			<td>Hydrothermal Autoclave Reactor</td>
			<td>Toption</td>
			<td>TOPT-HP500</td>
			<td>container for finished reagent mixture to withstand high temperature and pressure created by the oven in hydrothermal synthesis</td>
		</tr>
		<tr>
			<td>Iron(III) Chloride Hexahydrate (FeCl3&#183;6H2O, ACS reagent, 97%)</td>
			<td>ACS</td>
			<td>236489-500G</td>
			<td>reagent used in synthesis of nanoclusters as source of iron (III) that becomes iron (II) in finished nanocluster product (keep dry and weigh out quickly to avoid water contamination)</td>
		</tr>
		<tr>
			<td>Labware Washer Brushes</td>
			<td>Fisher Scientific</td>
			<td>13-641-708</td>
			<td>used to wash and clean glassware before synthesis</td>
		</tr>
		<tr>
			<td>Magnetic Stir Plate</td>
			<td>Thermo Fisher Scientific</td>
			<td>50093538</td>
			<td>for mixing of solid and liquid reagents during hydrothermal synthesis</td>
		</tr>
		<tr>
			<td>Manganese chloride tetrahydrate (MnCl2&#183;4H2O, 99.0%, crystals, ACS)</td>
			<td>Sigma-Aldrich</td>
			<td>1375127-2G</td>
			<td>reagent used in synthesis of nanoclusters as source of manganese</td>
		</tr>
		<tr>
			<td>Micropipette (100-1000&#956;L)</td>
			<td>Thermo Fisher Scientific</td>
			<td>FF-1000</td>
			<td>for transferring liquid reagents such as water and manganese chloride</td>
		</tr>
		<tr>
			<td>N-(3-Dimethylaminopropyl)-N&#8242;-ethylcarbodiimide hydrochloride (EDC)</td>
			<td>Sigma-Aldrich</td>
			<td>25952-53-8</td>
			<td>used in surface coating to assist in ligand exchange of copolymer (keep bulk chemical in freezer and diluted solution in refrigerator)</td>
		</tr>
		<tr>
			<td>N,N-Dimethylformamide (DMF)</td>
			<td>Sigma-Aldrich</td>
			<td>227056-2L</td>
			<td>reagent used in copolymer making as the solvent</td>
		</tr>
		<tr>
			<td>Polyacrylic acid sodium salt (PAA, Mw~6,000)</td>
			<td>PolyScience Inc.</td>
			<td>06567-250</td>
			<td>reagent used in hydrothermal synthesis to initially coat the nanoclusters (eventually replaced in surface coating step)</td>
		</tr>
		<tr>
			<td>Poly(ethylene glycol) methyl ether acrylate</td>
			<td>Sigma-Aldrich</td>
			<td>454990-250ML</td>
			<td>reagent used in copolymer to surface coat nanoclusters and functionalize them for biological media; average Mn 480, contains 100 ppm BHT as inhibitor, 100 ppm MEHQ as inhibitor</td>
		</tr>
		<tr>
			<td>Reagents Acetone, 4L, ACS Reagent</td>
			<td>Cole-Parmer</td>
			<td>UX-78920-66</td>
			<td>used as solvent to precipitate nanoclusters during washing</td>
		</tr>
		<tr>
			<td>Single Channel Pipette, Adjustable 1-10 mL</td>
			<td>Eppendorf</td>
			<td>3123000080</td>
			<td>for transferring ethylene glycol and other liquids</td>
		</tr>
		<tr>
			<td>Steel Wool</td>
			<td>Lowe&#39;s</td>
			<td>788470</td>
			<td>used to increase the magnetic field strength in the vial to aid in precipitation of nanoclusters for washing and surface coating</td>
		</tr>
		<tr>
			<td>Stirring Bar</td>
			<td>Thomas Scientific</td>
			<td>8608S92</td>
			<td>for mixing of solid and liquid reagents during hydrothermal synthesis</td>
		</tr>
		<tr>
			<td>Table Clamp</td>
			<td>Grainger</td>
			<td>29YW53</td>
			<td>for tight sealing of autoclave reactor to withstand high pressure of oven during hyrothermal synthesis</td>
		</tr>
		<tr>
			<td>Urea (ACS reagent, 99.0%)</td>
			<td>Sigma-Aldrich</td>
			<td>U5128-500G</td>
			<td>reagent used in hydrothermal synthesis to create a basic solution</td>
		</tr>
		<tr>
			<td>Vaccum Filtration Bottle Tops</td>
			<td>Thermo Fisher Scientific</td>
			<td>596-3320</td>
			<td>for filtration of aggregated clusters after synthesis and surface coating to achieve a uniform solution</td>
		</tr>
		<tr>
			<td>Vacuum Controller V-850</td>
			<td>Buchi</td>
			<td>BU-V850</td>
			<td>for filtration of aggregated clusters after synthesis and surface coating to achieve a uniform solution</td>
		</tr>
		<tr>
			<td>Vacuum Oven</td>
			<td>Fisher Scientific</td>
			<td>13-262-51</td>
			<td>used to create high temperature and pressure needed for nanocluster formation in hydrothermal synthesis</td>
		</tr>
	</tbody>
</table>

stable aqueous suspensions of manganese ferrite clusters with tunable nanoscale dimension and composition

Manganese ferrite clusters (MFCs) are spherical assemblies of tens to hundreds of primary nanocrystals whose magnetic properties are valuable in diverse applications. Here we describe how to form these materials in a hydrothermal process that permits the independent control of product cluster size (from 30 to 120 nm) and manganese content of the resulting material. Parameters such as the total amount of water added to the alcoholic reaction media and the ratio of manganese to iron precursor are important factors in achieving multiple types of MFC nanoscale products. A fast purification method uses magnetic separation to recover the materials making production of grams of magnetic nanomaterials quite efficient. We overcome the challenge of magnetic nanomaterial aggregation by applying highly charged sulfonate polymers to the surface of these nanomaterials yielding colloidally stable MFCs that remain non-aggregating even in highly saline environments. These non-aggregating, uniform, and tunable materials are excellent prospective materials for biomedical and environmental applications.

After hydrothermal treatment, the reaction mixture turns into a viscous black dispersion as can be seen in Figure 1. What results after purification is a highly concentrated MFC solution that behaves like a ferrofluid. The fluid in the vial responds within seconds when placed near a handheld magnet (&#60;0.5 T), forming a macroscopic black mass that can be moved around as the magnet is placed at different locations.
This synthesis yields products whose dimension a...

Watch this Scientific Journal Video about Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition at JoVE.com

Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition

We report a one-pot hydrothermal synthesis of manganese ferrite clusters (MFCs) that offers independent control over material dimension and composition. Magnetic separation allows rapid purification while surface functionalization using sulfonated polymers ensures the materials are non-aggregating in biologically relevant medium. The resulting products are well positioned for biomedical applications.

Manganese ferrite clusters (MFCs) are spherical assemblies of tens to hundreds of primary nanocrystals whose magnetic properties are valuable in diverse ...

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Research

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Chemistry

4.1K Views.  Brown University. We report a one-pot hydrothermal synthesis of manganese ferrite clusters (MFCs) that offers independent control over material dimension and composition. Magnetic separation allows rapid purification while surface functionalization using sulfonated polymers ensures the materials are non-aggregating in biologically relevant medium. The resulting products are well positioned for biomedical applications.

Video: Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition

Template Directed Synthesis of Plasmonic Gold Nanotubes with Tunable IR Absorbance

A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) membranes have been under development since the 1990's and have become a common method to template the synthesis of high aspect ratio nanostructures, mostly by electrochemical growth or pore-wetting. Recently, these membranes have become commercially available in a wide range of pore sizes and densities, leading to an extensive library of functional nanostructures being synthesized from AAO membranes. These include composite nanorods, nanowires and nanotubes made of metals, inorganic materials or polymers 3-10. Nanoporous membranes have been used to synthesize nanoparticle and nanotube arrays that perform well as refractive index sensors, plasmonic biosensors, or surface enhanced Raman spectroscopy (SERS) substrates 11-16, as well as a wide range of other fields such as photo-thermal heating 17, permselective transport 18, 19, catalysis 20, microfluidics 21, and electrochemical sensing 22, 23. Here, we report a novel procedure to prepare gold nanotubes in AAO membranes. Hollow nanostructures have potential application in plasmonic and SERS sensing, and we anticipate these gold nanotubes will allow for high sensitivity and strong plasmon signals, arising from decreased material dampening 15.

Solution-suspendable gold nanotubes with controlled dimensions can be synthesized by electrochemical deposition in porous anodic aluminum oxide (AAO) membranes using a hydrophobic polymer core. Gold nanotubes and nanotube arrays hold promise for applications in plasmonic biosensing, surface-enhanced Raman spectroscopy, photo-thermal heating, ionic and molecular transport, microfluidics, catalysis and electrochemical sensing.

A nearly parallel array of pores can be produced by anodizing aluminum foils in acidic environments1, 2. Applications of anodic aluminum oxide (AAO) ...

Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals

We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded synthesis strategy is used in which spherical seeds of CdSe are prepared first using a hot-injection technique. By controlling the crystal structure of the seed to be either wurtzite or zinc-blende, the subsequent hot-injection growth of CdS off of the seed results in either a rod-shaped or tetrapod-shaped nanocrystal, respectively. The phase and morphology of the synthesized nanocrystals are confirmed using X-ray diffraction and transmission electron microscopy, demonstrating that the nanocrystals are phase-pure and have a consistent morphology. The extinction coefficient and quantum yield of the synthesized nanocrystals are calculated using UV-Vis absorption spectroscopy and photoluminescence spectroscopy. The rods and tetrapods exhibit extinction coefficients and quantum yields that are higher than that of the bare seeds. This synthesis demonstrates the precise arrangement of materials that can be achieved at the nanoscale by using a seeded synthetic approach.

A protocol for the seeded synthesis of rod-shaped and tetrapod-shaped multicomponent nanostructures consisting of CdS and CdSe is presented.

We demonstrate a method for the synthesis of multicomponent nanostructures consisting of CdS and CdSe with rod and tetrapod morphologies. A seeded ...

A Simple Method for the Size Controlled Synthesis of Stable Oligomeric Clusters of Gold Nanoparticles under Ambient Conditions

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like oligomeric clusters of these yellow nanoparticles of narrow size distribution are synthesized under ambient conditions via two methods. The delay-time method controls the number of subunits in the oligoclusters by varying the time between the addition of HAuCl4 to alkaline solution and the subsequent addition of reducing agent, NaSCN. The yellow oligoclusters produced range in size from ~3 to ~25 nm. This size range can be further extended by an add-on method utilizing hydroxylated gold chloride (Na+[Au(OH4-x)Clx]-) to auto-catalytically increase the number of subunits in the as-synthesized oligocluster nanoparticles, providing a total range of 3 nm to 70 nm. The crude oligocluster preparations display narrow size distributions and do not require further fractionation for most purposes. The oligoclusters formed can be concentrated &#62;300 fold without aggregation and the crude reaction mixtures remain stable for weeks without further processing. Because these oligomeric clusters can be concentrated before derivatization they allow expensive derivatizing agents to be used economically. In addition, we present two models by which predictions of particle size can be made with great accuracy.

We describe a simple method for producing highly stable oligomeric clusters of gold nanoparticles via the reduction of chloroauric acid (HAuCl4) with sodium thiocyanate (NaSCN). The oligoclusters have a narrow size distribution and can be produced with a wide range of sizes and surface coats.

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like ...

Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates

Functions of clusters in nano or sub-nano scale significantly depend on not only kinds of their components but also arrangements, or symmetry, of their components. Therefore, the arrangements in the clusters have been precisely characterized, especially for metal complexes. Contrary to this, characterizations of molecular arrangements in supramolecular clusters composed of organic molecules are limited to a few cases. This is because construction of the supramolecular clusters, especially obtaining a series of the supramolecular clusters, is difficult due to low stability of non-covalent bonds compare to covalent bonds. From this viewpoint, utilization of organic salts is one of the most useful strategies. A series of the supramolecules could be constructed by combinations of a specific organic molecule with various counter ions. Especially, primary ammonium carboxylates are suitable as typical examples of supramolecules because various kinds of carboxylic acids and primary amines are commercially available, and it is easy to change their combinations. Previously, it was demonstrated that primary ammonium triphenylacetates using various kinds of primary amines specifically construct supramolecular clusters, which are composed of four ammoniums and four triphenylacetates assembled by charge-assisted hydrogen bonds, in crystals obtained from non-polar solvents. This study demonstrates an application of the specific construction of the supramolecular clusters as a strategy to conduct systematical symmetric study for clarification of correlations between molecular arrangements in supramolecules and kinds and numbers of their components. In the same way with binary salts composed of triphenylacetates and one kind of primary ammoniums, ternary organic salts composed of triphenylacetates and two kinds of ammoniums construct the supramolecular clusters, affording a series of the supramolecular clusters with various kinds and numbers of the components.

This article describes construction of a series of hydrogen-bonding supramolecular clusters in crystals using primary ammonium triphenylacetates, which are recrystallized from non-polar solvents. This selective construction of the supramolecular clusters leads to effective systematical symmetric studies about a correlation between the supramolecular clusters and their components.

Functions of clusters in nano or sub-nano scale significantly depend on not only kinds of their components but also arrangements, or symmetry, of their ...

A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) hydrogen fuel cells. Researchers seeking to develop such systems require a method of measuring the generated hydrogen. Herein, we describe a simple, low-cost, and robust method to measure the hydrogen generated from the reaction of solids with aqueous solutions. The reactions are conducted in a conventional one-necked round-bottomed flask placed in a temperature controlled water bath. The hydrogen generated from the reaction in the flask is channeled through tubing into a water-filled inverted measuring cylinder. The water displaced from the measuring cylinder by the incoming gas is diverted into a beaker on a balance. The balance is connected to a computer, and the change in the mass reading of the balance over time is recorded using data collection and spreadsheet software programs. The data can then be approximately corrected for water vapor using the method described herein, and parameters such as the total hydrogen yield, the hydrogen generation rate, and the induction period can also be deduced. The size of the measuring cylinder and the resolution of the balance can be changed to adapt the setup to different hydrogen volumes and flow rates.

The study of methods to generate on-demand hydrogen for fuel cells continues to grow in importance. However, systems to measure hydrogen evolution from the reaction of chemicals with water can be complicated and expensive. This article details a simple, low-cost, and robust method to measure the evolution of hydrogen gas.

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) ...

Determining the Chemical Composition of Corrosion Inhibitor/Metal Interfaces with XPS: Minimizing Post Immersion Oxidation

An approach for acquiring more reliable X-ray photoelectron spectroscopy data from corrosion inhibitor/metal interfaces is described. More specifically, the focus is on metallic substrates immersed in acidic solutions containing organic corrosion inhibitors, as these systems can be particularly sensitive to oxidation following removal from solution. To minimize the likelihood of such degradation, samples are removed from solution within a glove box purged with inert gas, either N2 or Ar. The glove box is directly attached to the load-lock of the ultra-high vacuum X-ray photoelectron spectroscopy instrument, avoiding any exposure to the ambient laboratory atmosphere, and thus reducing the possibility of post immersion substrate oxidation. On this basis, one can be more certain that the X-ray photoelectron spectroscopy features observed are likely to be representative of the in situ submerged scenario, e.g. the oxidation state of the metal is not modified.

A protocol to avoid the oxidation of metallic substrates during sample transfer from an inhibited acidic solution to an X-ray photoelectron spectrometer is presented.

An approach for acquiring more reliable X-ray photoelectron spectroscopy data from corrosion inhibitor/metal interfaces is described. More specifically, ...

Preparation of Polyoxometalate-based Photo-responsive Membranes for the Photo-activation of Manganese Oxide Catalysts

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic polymers, with the aim of photo-activating oxygen-evolving manganese oxide catalysts, which are important components in artificial photosynthesis. The cross-linking technique was applied to obtain a self-standing membrane with a high PW12O403- content. Incorporation and structure retention of PW12O403- within the polymer matrix were confirmed by FT-IR and micro-Raman spectroscopy, and optical characteristics were investigated by UV-Vis spectroscopy, which revealed successful construction of the metal-to-metal charge transfer (MMCT) unit. After deposition of MnOx oxygen evolving catalysts, photocurrent measurements under visible light irradiation verified the sequential charge transfer, Mn &#8594; MMCT unit &#8594; electrode, and&#160;the photocurrent intensity was consistent with the redox potential of the donor metal (Ce or Co). This method provides a new strategy for preparing integrated systems involving catalysts and photon-absorption parts for use with photo-functional materials.

Here, we present a protocol to prepare charge transfer chromophores based on a polyoxometalate/polymer composite membrane.

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic ...

Synthesis of In37P20(O2CR)51 Clusters and Their Conversion to InP Quantum Dots

This text presents a method for the synthesis of In37P20(O2C14H27)51 clusters and their conversion to indium phosphide quantum dots. The In37P20(O2CR)51 clusters have been observed as intermediates in the synthesis of InP quantum dots from molecular precursors (In(O2CR)3, HO2CR, and P(SiMe3)3) and may be isolated as a pure reagent for subsequent study and use as a single-source precursor. These clusters readily convert to crystalline and relatively monodisperse samples of quasi-spherical InP quantum dots when subjected to thermolysis conditions in the absence of additional precursors above 200 &#176;C. The optical properties, morphology, and structure of both the clusters and quantum dots are confirmed using UV-Vis spectroscopy, photoluminescence spectroscopy, transmission electron microscopy, and powder X-ray diffraction. The molecular symmetry of the clusters is additionally confirmed by solution-phase 31P NMR spectroscopy. This protocol demonstrates the preparation and isolation of atomically-precise InP clusters, and their reliable and scalable conversion to InP QDs.

Synthesis of In37P20O2CR51 Clusters and Their Conversion to InP Quantum Dots

A protocol for the synthesis of In37P20(O2C14H27)51 clusters and their conversion to indium phosphide quantum dots is presented.

This text presents a method for the synthesis of In37P20(O2C14H27)51 clusters and their conversion to indium phosphide quantum dots. The In37P20(O2CR)51 ...

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

The computational study of the formation and growth of atmospheric aerosols requires an accurate Gibbs free energy surface, which can be obtained from gas phase electronic structure and vibrational frequency calculations. These quantities are valid for those atmospheric clusters whose geometries correspond to a minimum on their potential energy surfaces. The Gibbs free energy of the minimum energy structure can be used to predict atmospheric concentrations of the cluster under a variety of conditions such as temperature and pressure. We present a computationally inexpensive procedure built on a genetic algorithm-based configurational sampling followed by a series of increasingly accurate screening calculations. The procedure starts by generating and evolving the geometries of a large set of configurations using semi-empirical models then refines the resulting unique structures at a series of high-level ab initio levels of theory. Finally, thermodynamic corrections are computed for the resulting set of minimum-energy structures and used to compute the Gibbs free energies of formation, equilibrium constants, and atmospheric concentrations. We present the application of this procedure to the study of hydrated glycine clusters under ambient conditions.

Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry

The atmospheric concentrations of weakly bound molecular clusters can be computed from the thermochemical properties of low energy structures found through a multi-step configurational sampling methodology utilizing a genetic algorithm and semi-empirical and ab initio quantum chemistry.

The computational study of the formation and growth of atmospheric aerosols requires an accurate Gibbs free energy surface, which can be obtained from gas ...

Aqueous Synthesis of Plasmonic Gold-Tin Alloy Nanoparticles

This protocol describes the synthesis of Au nanoparticle seeds and the subsequent formation of Au-Sn bimetallic nanoparticles. These nanoparticles have potential applications in catalysis, optoelectronics, imaging, and drug delivery. Previously, methods for producing alloy nanoparticles have been time-consuming, require complex reaction conditions, and can have inconsistent results. The outlined protocol first describes the synthesis of approximately 13 nm Au nanoparticle seeds using the Turkevich method. The protocol next describes the reduction of Sn and its incorporation into the Au seeds to generate Au-Sn alloy nanoparticles. The optical and structural characterization of these nanoparticles is described. Optically, prominent localized surface plasmon resonances (LSPRs) are apparent using UV-visible spectroscopy. Structurally, powder X-ray diffraction (XRD) reflects all particles to be less than 20 nm and shows patterns for Au, Sn, and multiple Au-Sn intermetallic phases. Spherical morphology and size distribution are obtained from transmission electron microscopy (TEM) imaging. TEM reveals that after Sn incorporation, the nanoparticles grow to approximately 15 nm in diameter.

Author Spotlight: Designing Sustainable Nanomaterials for Advancing Synthesis and Element Mixing

Here, the synthesis of gold (Au) seeds is described using the Turkevich method. These seeds are then used to synthesize gold-tin alloy (Au-Sn) nanoparticles with tunable plasmonic properties.

This protocol describes the synthesis of Au nanoparticle seeds and the subsequent formation of Au-Sn bimetallic nanoparticles. These nanoparticles have ...