This research was supported by the I-CORE Program of the Planning and Budgeting Committee and The Israel Science Foundation (Grant No. 152/11). We thank the Schulich Faculty of Chemistry and the Technion - Israel Institute of Technology for the renovated laboratory and startup package. We also thank the Royal Society of Chemistry for permission in adapting materials from https://dx-doi-org.remotexs.ntu.edu.sg/10.1039/C4TA06164K for use in this manuscript. Dr. Kalisman thanks the Schulich postdoctoral fellowship for their support. We thank Dr. Yaron Kauffmann for his assistance with HR-TEM and HAADF as well as Dr. Kamira Weinfeld for her assistance with XPS characterization.

1. Synthesis of Quantum Dots21
<ol>
	<li>Preparation of TOP:Se Precursor
	<ol>
		<li>Combine 58 mg of Se powder with 0.360 g of Tri-n-octylphosphine (TOP) in a vial with a septum.</li>
		<li>Sonicate the TOP:Se mixture until it is clear with no solids.</li>
	</ol>
	</li>
	<li>Synthesis of CdSe
	<ol>
		<li>Combine 3.0 g trioctylphosphine oxide (TOPO), 280 mg n-octadecylphosphonic acid (ODPA), and 60 mg CdO with a 3 mm x 8 mm cylindrical stir bar in a 25 ml 3-neck round bottom flask equipped with a thermocouple (inserted in a custom glass adapter), a reflux condenser with a T-joint (center neck), and a rubber septum. Assemble all glass-to-glass joints with high temperature vacuum grease. Connect the T-joint to a Schlenk line on one end that can be switched between a clean inert gas and vacuum, while connecting the other end to a bubbler. 
		Caution: CdO is very toxic and should be weighed and added to the round bottom flask inside an enclosed environment such as a glovebox.</li>
		<li>Place the round bottom flask apparatus in a heating mantle, and purge with inert gas.</li>
		<li>Heat the solids in the round bottom flask to 150 &#176;C, making sure to start stirring vigorously once the compounds melt (around 60-80 &#176;C). In order to avoid overshooting the target temperature, heat to 100 &#176;C and then 150 &#176;C once the heating rate slows down or stabilizes.</li>
		<li>Degas the mixture under vacuum (at 150 &#176;C) for at least 1 hr while still stirring. Make sure the T-joint is not open to the bubbler or the oil will get sucked into the flask and Schlenk line. When moving from gas to vacuum be careful to transition slowly to avoid more than a rolling boil.</li>
		<li>Refill the flask with inert gas (and continue to flow gas over the sample) and increase the temperature to 350 &#176;C. The solution should turn clear as it heats up, and excess solids on the flask wall can be collected by careful swirling of the flask.</li>
		<li>Inject 1.5 g of TOP into the flask through the septum. Allow the solution temperature to stabilize before proceeding. 
		Note: Try to minimize the amount of air/moisture injected by keeping the TOP in a septa vial under inert atmosphere, and injecting it as quickly as possible.</li>
		<li>Inject all of the TOP:Se mixture (prepared in section 1.1) into the flask through the septum, using a wide needle to inject the TOP:Se as quickly and uniformly as possible.</li>
		<li>Let the reaction proceed for the desired time, and remove from the heating mantle.
		<ol>
			<li>For very small seeds remove from heat just before injecting. For larger seeds remove the flask from heat immediately after injecting TOP:Se or after waiting up to 3 min. Longer wait result in larger seeds.</li>
		</ol>
		</li>
		<li>Let the reaction cool to approximately 100 &#176;C and inject approximately 5 ml of degassed toluene. Transfer the solution to a vial under inert atmosphere for cleaning. 
		Note: To simplify this process 10 ml of toluene can be placed in a 20 ml vial with a septa under constant flow of inert gas. Use approximately half of this toluene to inject into the cooling mixture, and then transfer the cooled mixture back into this vial.</li>
		<li>Cleaning of seeds
		<ol>
			<li>Put the solution in a 50 ml centrifuge tube.</li>
			<li>Add methanol (approximately 5 ml) to precipitate out the seeds from the toluene mixture.</li>
			<li>Centrifuge at 3,400 x g for 5 min.</li>
			<li>Decant clear supernatant and re-dissolve the pellet in toluene (5-10 ml).</li>
			<li>Repeat steps 1.2.10.2 through 1.2.10.4 at least three times total.</li>
		</ol>
		</li>
		<li>Dilute a small aliquot of the seeds in toluene in order to measure Ultraviolet-Visible (UV-Vis) absorbance between 350-800 nm. Use the peaks to determine the concentration and size of the CdSe seeds as described in the literature22.</li>
	</ol>
	</li>
</ol>
2. Synthesis of Seeded Rods 21
<ol>
	<li>Preparation of TOP:S Precursor
	<ol>
		<li>Combine 1.2 g of S with 15 g of TOP in a vial with a stir bar.</li>
		<li>Stir until clear with no solids (usually at least 24 hr).</li>
		<li>Measure 0.62 g of this mixture into a vial with a septum.</li>
	</ol>
	</li>
	<li>Preparation of TOP:CdSe Precursor
	<ol>
		<li>Measure the appropriate volume of CdSe seeds from step 1 (based on UV-Vis peak) into a vial with a septum. 
		Note: For a calculated concentration of 5x10-5 with 2.25 nm seeds (both values calculated from the UV-Vis spectra22), use 300 &#181;l of solution.</li>
		<li>Evaporate the toluene using a vacuum line until the seeds are dry. Do not leave under vacuum for more than 5-10 min once dry, as this can degrade the quality of the seeds.</li>
		<li>Re-dissolve all of the dried seeds in 0.5 g of TOP.</li>
	</ol>
	</li>
	<li>Synthesis of CdSe@Cds
	<ol>
		<li>Combine 60 mg propylphosphonic acid (PPA), 3.35 g TOPO, 1.080 g ODPA, and 230 mg CdO with a 3 mm x 8 mm cylindrical stir bar in a 25 ml 3-neck round bottom flask equipped with a thermocouple (inserted in a custom glass adapter), a reflux condenser with a T-joint (center neck), and a rubber septum. Assemble all glass-to-glass joints with high temperature vacuum grease. Connect the T-joint to a Schlenk line on one end that can be switched between a clean inert gas and vacuum, while connecting the other end to a bubbler. 
		Caution: CdO is very toxic and should be weighed and added to the round bottom inside an enclosed environment, such as a glovebox. PPA is regulated in some countries and can be replaced by butylphosphonic acid (BPA, 72 mg) or hexylphosphonic acid (HPA, 80 mg), though BPA and HPA usually result in shorter rods.</li>
		<li>Place the round bottom flask apparatus in a heating mantle, and purge with inert gas.</li>
		<li>Heat the solids in the round bottom flask to 120 &#176;C, making sure to start stirring vigorously once the compounds melt (around 60-80 &#176;C). In order to avoid overshooting the target temperature, heat to 90 &#176;C and then 120 &#176;C once the heating rate slows down or stabilizes.</li>
		<li>Degas the mixture under vacuum (at 120 &#176;C) for at least &#189; hr while still stirring.
		<ol>
			<li>Make sure the T-joint is not open to the bubbler or the oil will get sucked into the flask and Schlenk line. When moving from gas to vacuum be careful to transition slowly to avoid more than a rolling boil. Use a cold trap with liquid nitrogen (LN2) for a better vacuum.</li>
		</ol>
		</li>
		<li>Refill the flask with inert gas (and continue to flow gas over the sample) and increase the temperature to 320 &#176;C. The solution should turn clear as it heats up, and excess solids on the flask wall can be collected by careful swirling of the flask.</li>
		<li>Cool back down to 120 &#176;C and degas under vacuum as in step 1.2.4.</li>
		<li>Refill and reheat the flask as in step 1.2.5.</li>
		<li>Inject 1.5 g of TOP into the flask through the septum. Allow the solution temperature to stabilize at 340 &#176;C before proceeding. 
		Note: Try to minimize the amount of air/moisture injected by keeping the TOP in a septa vial under inert atmosphere, and injecting it as quickly as possible.</li>
		<li>Inject the TOP:S mixture into the flask through the septum, using a wide needle to inject the TOP:S as quickly and uniformly as possible. Start a timer.</li>
		<li>Exactly 20 sec after injecting the TOP:S, inject the TOP:CdSe mixture into the flask through the septum, using a wide needle to inject the TOP:CdSe as quickly and uniformly as possible. 
		Note: The temperature should have dropped to below 330 &#176;C by this point due to the addition of RT TOP solutions.</li>
		<li>Set the temperature to 320 &#176;C and let the reaction proceed for the desired time (8-15 min), and remove from the heating mantle.</li>
		<li>Let the reaction cool away from the heating mantle and inject approximately 5 ml of degassed toluene when the temperature reaches approximately 100 &#176;C. Transfer the solution to a vial under inert atmosphere for cleaning. 
		Note: To simplify this process 10 ml of toluene can be placed in a 20 ml vial with a septa under constant flow of inert gas. Use approximately half of this toluene to inject into the cooling mixture, and then transfer the cooled mixture back into this vial.</li>
		<li>Cleaning of rods
		<ol>
			<li>Put the solution in a 50 ml centrifuge tube.</li>
			<li>Add methanol (approximately 5 ml) to precipitate out the seeds from the toluene mixture.</li>
			<li>Centrifuge at 3,400 x g for 5 min.</li>
			<li>Decant clear supernatant and re-dissolve the pellet in approximately 10 ml hexane.</li>
			<li>Add 1-2 ml each of n-octylamine and nonanoic acid to the solution. The solution should be transparent.</li>
			<li>Add 5 ml methanol and centrifuge for 5 min at 3,400 x g.</li>
			<li>Repeat steps 2.3.13.4 through 2.3.13.6 at least twice more.</li>
			<li>Re-dissolve pellet in 10 ml of toluene. If the pellet does not easily dissolve, more cleaning steps are likely needed, in which case repeat steps 2.3.13.4 through 2.3.13.6.</li>
			<li>Add approximately 7 ml of IPA, 1 ml at a time, until the solution is slightly cloudy even when mixed.</li>
			<li>Centrifuge for 30 min at 2,200 x g in order to separate longer rods from everything else.</li>
			<li>Re-dissolve pellet in 10-15 ml of toluene.</li>
		</ol>
		</li>
		<li>Dilute a small aliquot of the seeds in toluene in order to measure UV-Vis absorbance and/or photoluminescence (PL) of the rods. 
		Note: Any aliquot volume is acceptable as long as the dilution factor is known, however, a typical dilution factor would be 20. For PL, the absorption should be at or below 0.1 at the chosen excitation wavelength (typically use 450 nm).&#160;</li>
	</ol>
	</li>
</ol>
3. Transfer of Seeded Rods to Aqueous Solution
<ol>
	<li>Preparation of Methanol Solution
	<ol>
		<li>Pour approximately 10 ml of methanol into a centrifuge tube.</li>
		<li>Add approximately 250 mg mercaptoundecanoic acid (MUA) and 400 mg tetramethylammonium hydroxide (TMAH).</li>
		<li>Vortex or let sit until all solids fully dissolved.</li>
	</ol>
	</li>
	<li>Ligand Exchange
	<ol>
		<li>Add methanol (5-10 ml, or enough to precipitate the rods) to &#188; to &#189; of rods synthesized from step 2 in a centrifuge tube. 
		Note: The volume of rods used will be dependent on the amount of toluene used to dissolve the rods for storage. If 10-15 ml are used as suggested in step 2.3.13.11, then 3-6 ml of the rod solution should be appropriate.</li>
		<li>Centrifuge at 3,400 x g for 5 min.</li>
		<li>Decant the clear supernatant.</li>
		<li>Add all of the methanol solution from section 3.1 to the pellet.</li>
		<li>Vortex or shake by hand to fully dissolve. Allow the solution to sit at least 1 hr to allow maximum ligand exchange to occur. 
		Note: The solution should be allowed to sit for at least 1 hr even if it appears to dissolve immediately and completely</li>
		<li>Separate the solution into two halves in two centrifuge tubes. 
		Note: Save the centrifuge tube used for step 3.1 and transfer half of the solution into there.</li>
		<li>Add 20 ml of toluene to each half. If there is a phase separation between the alcohol and toluene add methanol drop wise until the phases recombine.</li>
		<li>Centrifuge at 7,700 x g for 15 min.</li>
		<li>Very carefully decant the clear supernatant from pellet.</li>
		<li>Invert the centrifuge tube carefully in order to dry the sample.</li>
		<li>Add 5 ml ultrapure water to the pellet and store in a vial wrapped well in Al foil (or other opaque covering). 
		Note: Once moved from toluene to water, the rods are not photostable, which is why they are covered. Even if kept in the dark the rods should be used as soon as possible, and it is not recommended to store rods in water for more than one month.</li>
	</ol>
	</li>
</ol>
4. Growth of Iridium Nanocrystalline Particles
<ol>
	<li>Sodium Hydroxide
	<ol>
		<li>In a plastic vial weigh out 1,450 mg NaOH. Dissolve NaOH in 20 ml ultrapure water. Solution should be clear with no solids.&#160;</li>
	</ol>
	</li>
	<li>Sodium Persulfate
	<ol>
		<li>In a plastic vial weigh out 950 mg NaS2O8. Dissolve NaS2O8 in 20 ml ultrapure water. Solution should be clear with no solids.</li>
	</ol>
	</li>
	<li>Sodium Nitrate
	<ol>
		<li>In a plastic vial weigh out 300 mg NaNO3. Dissolve NaNO3 in 18 ml ultrapure water. Solution should be clear with no solids.</li>
	</ol>
	</li>
	<li>Iridium Precursor Solution
	<ol>
		<li>In a plastic vial weigh out 50 mg Na3IrCl6. Dissolve Na3IrCl6 in 5.0 ml ultrapure water. Solution should be transparent brown (like scotch) with no solids.</li>
	</ol>
	</li>
	<li>Preparation of sample
	<ol>
		<li>Place a spectroscopic stirrer in a standard polystyrene cuvette. 
		Note: Because the solution is very basic, quartz and other glass cuvettes should not be used.</li>
		<li>Add 0.20 ml iridium precursor solution from step 4.4.1.</li>
		<li>Add 0.50 ml nitrate solution from step 4.3.1.</li>
		<li>Add 0.30 ml of seeded rods in water from section 3 (trace toluene from the ligand exchange may cause clouding of the cuvette wall).</li>
		<li>Add 0.50 ml of persulfate solution from step 4.2.1.</li>
		<li>Add 0.50 ml of sodium hydroxide solution from step 4.1.1.</li>
	</ol>
	</li>
	<li>Illumination of sample
	<ol>
		<li>Place the cuvette in a holder with stirring capabilities.</li>
		<li>Illuminate with 450 nm light at 100 mW for up to 4 hr. The solution should turn green and later blue.</li>
	</ol>
	</li>
	<li>Collecting sample
	<ol>
		<li>Pour solution (but not stir bar) into a centrifuge tube.</li>
		<li>Centrifuge at 7,700 x g for 10 min.</li>
		<li>Carefully decant the supernatant from the pellet, which should be green or blue depending on the reaction time selected. 
		Note: The pellet can now be collected or dispersed in a polar solvent through sonication for use in other experiments.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Maeda, K., 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=Photocatalyst+releasing+hydrogen+from+water.">Photocatalyst releasing hydrogen from water.</a> Nature. 440 (7082), 295-295 (2006).</li><li>Jacobson, M. Z., Colella, W. G., Golden, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cleaning+the+Air+and+Improving+Health+with+Hydrogen+Fuel-Cell+Vehicles.">Cleaning the Air and Improving Health with Hydrogen Fuel-Cell Vehicles.</a> Science. 308 (5730), 1901-1905 (2005).</li><li>Hoffmann, M. R., Martin, S. T., Choi, W., Bahnemann, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Environmental+Applications+of+Semiconductor+Photocatalysis.">Environmental Applications of Semiconductor Photocatalysis.</a> Chem. Rev. 95 (1), 69-96 (1995).</li><li>Dukovic, G., Merkle, M. G., Nelson, J. H., Hughes, S. M., Alivisatos, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photodeposition+of+Pt+on+Colloidal+CdS+and+CdSe/CdS+Semiconductor+Nanostructures.">Photodeposition of Pt on Colloidal CdS and CdSe/CdS Semiconductor Nanostructures.</a> Adv. Mater. 20 (22), 4306-4311 (2008).</li><li>Menagen, G., Macdonald, J. E., Shemesh, Y., Popov, I., Banin, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Au+Growth+on+Semiconductor+Nanorods:+Photoinduced+versus+Thermal+Growth+Mechanisms.">Au Growth on Semiconductor Nanorods: Photoinduced versus Thermal Growth Mechanisms.</a> J. Am. Chem. Soc. 131 (47), 17406-17411 (2009).</li><li>Alemseghed, M. G., Ruberu, T. P. A., Vela, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+Fabrication+of+Colloidal+Semiconductor-Metal+Hybrid+Heterostructures:+Site+Selective+Metal+Photo+Deposition.">Controlled Fabrication of Colloidal Semiconductor-Metal Hybrid Heterostructures: Site Selective Metal Photo Deposition.</a> Chem. Mater. 23 (15), 3571-3579 (2011).</li><li>Frame, F. A., 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=Photocatalytic+Water+Oxidation+with+Nonsensitized+IrO2+Nanocrystals+under+Visible+and+UV+Light.">Photocatalytic Water Oxidation with Nonsensitized IrO2 Nanocrystals under Visible and UV Light.</a> J. Am. Chem. Soc. 133 (19), 7264-7267 (2011).</li><li>Iwase, A., Kato, H., Kudo, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Novel+Photodeposition+Method+in+the+Presence+of+Nitrate+Ions+for+Loading+of+an+Iridium+Oxide+Cocatalyst+for+Water+Splitting.">A Novel Photodeposition Method in the Presence of Nitrate Ions for Loading of an Iridium Oxide Cocatalyst for Water Splitting.</a> Chemistry Letters. 34 (7), 946-947 (2005).</li><li>Kalisman, P., Kauffmann, Y., Amirav, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photochemical+oxidation+on+nanorod+photocatalysts.">Photochemical oxidation on nanorod photocatalysts.</a> J. Mater. Chem. 3 (7), 3261-3265 (2015).</li><li>Ryu, W. H., 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=Crystalline+IrO2-decorated+TiO2+nanofiber+scaffolds+for+robust+and+sustainable+solar+water+oxidation.">Crystalline IrO2-decorated TiO2 nanofiber scaffolds for robust and sustainable solar water oxidation.</a> J. Mater. Chem. A. 2 (16), 5610-5615 (2014).</li><li>Nakagawa, T., Bjorge, N. S., Murray, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrogenerated+IrOx+Nanoparticles+as+Dissolved+Redox+Catalysts+for+Water+Oxidation.">Electrogenerated IrOx Nanoparticles as Dissolved Redox Catalysts for Water Oxidation.</a> J. Am. Chem. Soc. 131 (43), 15578-15579 (2009).</li><li>Talapin, D. V., 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=Seeded+Growth+of+Highly+Luminescent+CdSe/CdS+Nanoheterostructures+with+Rod+and+Tetrapod+Morphologies.">Seeded Growth of Highly Luminescent CdSe/CdS Nanoheterostructures with Rod and Tetrapod Morphologies.</a> Nano Lett. 7 (10), 2951-2959 (2007).</li><li>Carbone, L., 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=Synthesis+and+Micrometer-Scale+Assembly+of+Colloidal+CdSe/CdS+Nanorods+Prepared+by+a+Seeded+Growth+Approach.">Synthesis and Micrometer-Scale Assembly of Colloidal CdSe/CdS Nanorods Prepared by a Seeded Growth Approach.</a> Nano Lett. 7 (10), 2942-2950 (2007).</li><li>Amirav, L., Alivisatos, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photocatalytic+Hydrogen+Production+with+Tunable+Nanorod+Heterostructures.">Photocatalytic Hydrogen Production with Tunable Nanorod Heterostructures.</a> J. Phys. Chem. Lett. 1 (7), 1051-1054 (2010).</li><li>Nakibli, Y., Kalisman, P., Amirav, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Less+Is+More:+The+Case+of+Metal+Cocatalysts.">Less Is More: The Case of Metal Cocatalysts.</a> J. Phys. Chem. Lett. 6, 2265-2268 (2015).</li><li>Lupo, M. G., 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=Ultrafast+Electron-Hole+Dynamics+in+Core/Shell+CdSe/CdS+Dot/Rod+Nanocrystals.">Ultrafast Electron-Hole Dynamics in Core/Shell CdSe/CdS Dot/Rod Nanocrystals.</a> Nano Lett. 8 (12), 4582-4587 (2008).</li><li>Raino, G., 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=Probing+the+Wave+Function+Delocalization+in+CdSe/CdS+Dot-in-Rod+Nanocrystals+by+Time-+and+Temperature-Resolved+Spectroscopy.">Probing the Wave Function Delocalization in CdSe/CdS Dot-in-Rod Nanocrystals by Time- and Temperature-Resolved Spectroscopy.</a> ACS Nano. 5 (5), 4031-4036 (2011).</li><li>Talapin, D. V., Lee, J. S., Kovalenko, M. V., Shevchenko, E. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prospects+of+Colloidal+Nanocrystals+for+Electronic+and+Optoelectronic+Applications.">Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications.</a> Chem. Rev. 110 (1), 389-458 (2010).</li><li>Kraus, R. M., 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=Room-Temperature+Exciton+Storage+in+Elongated+Semiconductor+Nanocrystals.">Room-Temperature Exciton Storage in Elongated Semiconductor Nanocrystals.</a> Phys. Rev. Lett. 98 (1), 017401 (2007).</li><li>She, C., Demorti&#232;re, A., Shevchenko, E. V., Pelton, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+Shape+to+Control+Photoluminescence+from+CdSe/CdS+Core/Shell+Nanorods.">Using Shape to Control Photoluminescence from CdSe/CdS Core/Shell Nanorods.</a> J. Phys. Chem. Lett. 2 (12), 1469-1475 (2011).</li><li>Manthiram, K., Beberwyck, B. J., Talapin, D. V., Alivisatos, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Seeded+Synthesis+of+CdSe/CdS+Rod+and+Tetrapod+Nanocrystals.">Seeded Synthesis of CdSe/CdS Rod and Tetrapod Nanocrystals.</a> J. Vis. Exp. (82), (2013).</li><li>Yu, W. W., Qu, L., Guo, W., Peng, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Experimental+Determination+of+the+Extinction+Coefficient+of+CdTe,+CdSe,+and+CdS+Nanocrystals.">Experimental Determination of the Extinction Coefficient of CdTe, CdSe, and CdS Nanocrystals.</a> Chem. Mater. 15 (14), 2854-2860 (2003).</li><li>Miao, M. S., Seshadri, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rh2O3+versus+IrO2:+relativistic+effects+and+the+stability+of+Ir4.">Rh2O3 versus IrO2: relativistic effects and the stability of Ir4.</a> J. Phys. Condens. Matter. 24 (21), 215503 (2012).</li><li>Amirav, L., Alivisatos, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Luminescence+Studies+of+Individual+Quantum+Dot+Photocatalysts.">Luminescence Studies of Individual Quantum Dot Photocatalysts.</a> J. Am. Chem. Soc. 135 (35), 13049-13053 (2013).</li><li>Vaneski, A., Schneider, J., Susha, A. S., Rogach, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aqueous+synthesis+of+CdS+and+CdSe/CdS+tetrapods+for+photocatalytic+hydrogen+generation.">Aqueous synthesis of CdS and CdSe/CdS tetrapods for photocatalytic hydrogen generation.</a> APL Materials. 2 (1), 012104 (2014).</li></ol>

The authors have nothing to disclose.

The synthesis of CdSe seeds and CdSe@CdS seeded rods has been well studied21,24,25. Slight modifications to the amounts, temperatures, and times for steps of the synthesis of these substrate particles can be used to tune their length, diameter, and/or morphology. The synthetic protocol described herein yields highly photoluminescent seeded-rods of uniform dimensions.
The ligand exchange procedure allows for the use of seeded rods in polar environments, in this case water. At the final stages of the ligand exchange, when the pellet is being collected for dissolution (after precipitation by toluene) the pellet often adheres poorly to the surface of the centrifuge tube. It is very important to decant and dry this pellet very carefully, otherwise there is a risk of throwing out or contaminating the pellet that has been formed. Seeds and rods in toluene and methanol are easy to precipitate and collect through the use of a non-solvent, however, once rods are put in water they are very hard to collect or move if they are soluble. This difficulty comes from the immiscibility of water with non-polar non-solvents such as toluene and hexane.
Once iridium oxide has been grown on the surface of seeded rods they become much harder to deal with as they aggregate. This made working with them and then analyzing them a challenging endeavor. Sonication in methanol or water produces a suspension that can be maintained by stirring.
Dried samples were used for XRD analysis. XRD patterns taken after different illumination times showed a growing peak near 2&#952;=23&#176; (Figure 2), indicating time dependent growth of a crystalline material. High resolution spectra taken for clean rods, and rods after 2 hr of photochemical growth of iridium oxide were also taken. Signal from the CdSe@CdS rod sample shows a match with the expected pattern for CdS [PDF# 00-006-0314], with missing peaks attributed to the preference for the clean rods to lay flat on the substrate. Signal from CdSe@CdS rods after growth of iridium oxide show the characteristic CdS peaks, along with extra peaks, including the one seen in Figure 2. Peaks in the XRD pattern were very small (see Figure 2), and required long scans (at least 8 hr) because of the small crystallite size. Some peaks match well with IrO2 [PDF# 00-015-0870], while others match well with Rh2O3 [PDF# 01-076-0148] (which has been theorized to have a structure nearly identical to Ir2O3 &#8212; the pattern for Ir2O3 is not reported in the JCPDS database because it is relatively unstable23). Similar to the XPS data, this XRD data confirms the presence of IrO2, and suggests the iridium growth is a mix of IrO2 and Ir2O3.
Photochemical oxidation as a synthetic tool expands the methods by which chemists can create new hybrid materials. While new synthetic procedures must be developed for photodeposition of each target material, our works shows that photochemical oxidation is possible with cadmium chalcogenide materials. It offers unique means of material processing that can be applied to the intelligent design of complex photocatalysts. It might allow for production of materials in a nonequilibrium state (e.g., formation of the metastable phase Ir2O3), presumably due to the unique atomic-level interaction between the deposit and the substrate. In addition, intermediates produced during the various redox reactions might have interesting effect on the oxide formation; bring about photochemical co-deposition to produce exclusive complex materials. The synthetic method described herein is the first time oxidative photodeposition has been realized with CdS. We anticipate that this synthetic methodology will ultimately allow for the development of stable and efficient solar driven photocatalysis of water.

Photocatalysis presents an attractive and promising solution for renewable energy generation and other environmental applications such as water treatment and air purification1-3. Overall water splitting, driven by solar energy, could be a source of clean and renewable hydrogen fuel; however, despite decades of research, systems that are sufficiently stable and efficient for practical use have not yet been realized.
Both photodeposition and semiconductor-mediated photocatalysis rely on the same mechanism of separating photo-generated electron-hole pairs and driving them to the surface where they can initiate redox reactions. The similarities between these two processes make photodeposition an attractive synthetic tool for the field of photocatalysis4-6. This method is expected to take photocatalyst production to new and unexplored frontiers. It might potentially offer pristine control over the spatial arrangement of the different components in a heterostructures, and advance the ability to construct sophisticated nanoparticle systems. Ultimately the method will bring us one step closer to realizing an efficient photocatalyst for direct solar-to-fuel energy conversion.
We investigated the growth of IrO2 as a co-catalyst, as it is known to be an efficient catalyst for water oxidation7-11. A tunable structure of quantum dot (CdSe) embedded in a rod (cadmium sulfide)12,13 was used as our photocatalyst substrate14,15. It is currently undetermined whether the oxidative pathway occurs via a mediated pathway, or by a direct hole attack. Here, our knowledge and control over the photogenerated holes in the semiconductor heterostructure can be harnessed for a mechanistic study of oxidation reactions. This is made possible by the substrate architecture, which facilitates localization of confined holes16,17 and formation of a distinct oxidation reaction site on the rod. The use of nanoscale materials with localized charge carrier can be exploited for mechanistic studies of redox reactions by simple examination of the products. In this way photodeposition can be used as a unique probe of both reduction and oxidation reaction pathways. This is one example of the new and exciting possibilities afforded by the combination of photodeposition and cutting edge colloidal synthesis18-20.
The quest to develop an efficient photocatalyst for water splitting and renewable energy conversion has become an important thrust within the materials community. This has spurred worldwide interest in CdS, which is known to be highly active for hydrogen production, though it is hampered by photochemical instability. Our work here treats the Achilles heel of the material. IrO2 decorated CdSe@CdS rods demonstrate remarkable photochemical stability under prolonged illumination in pure water.

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		<tr height="21">
			<td height="21" style="height:21px;width:304px;">Sulfur (S)</td>
			<td style="width:79px;">Sigma</td>
			<td style="width:119px;">84683</td>
			<td style="width:321px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Selenium (Se)</td>
			<td>Sigma</td>
			<td>229865</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cadmium Oxide (CdO)</td>
			<td>Sigma</td>
			<td>202894</td>
			<td>Highly Toxic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">n-Octadecylphosphonic acid (ODPA)</td>
			<td>Sigma</td>
			<td>715166</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Propylphosphonic acid (PPA)</td>
			<td>Sigma</td>
			<td>305685</td>
			<td>Highly regulated in some countries and regions</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Butylphosphonic acid (BPA)</td>
			<td>Sigma</td>
			<td>737933</td>
			<td>Alternative to PPA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hexylphosphonic acid (HPA)</td>
			<td>Sigma</td>
			<td>750034</td>
			<td>Alternative to PPA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Trioctylphosphonic oxide (TOPO)</td>
			<td>Sigma</td>
			<td>346187</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tri-n-octylphosphine, 97% (TOP)</td>
			<td>Sigma</td>
			<td>718165</td>
			<td>Air sensitive</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Spectrochemical Stirbar</td>
			<td>Sigma</td>
			<td><a href="http://www.sigmaaldrich.com/catalog/product/sigma/z363545?lang=en&amp;region=US">Z363545</a></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium Hydroxide</td>
			<td>Sigma</td>
			<td>S5881</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Methanol</td>
			<td>Sigma</td>
			<td>322415</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Toluene</td>
			<td>Sigma</td>
			<td>244511</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hexane</td>
			<td>Sigma</td>
			<td>296090</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Octylamine</td>
			<td>Sigma</td>
			<td>74988</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Nonanoic Acid</td>
			<td>Sigma</td>
			<td>N5502</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Isopropanol</td>
			<td>Sigma</td>
			<td>278475</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mercaptoundecanoic Acid (MUA)</td>
			<td>Sigma</td>
			<td>674427</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Tetramethylammonium Hydroxide (TMAH)</td>
			<td>Sigma</td>
			<td>T7505</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Apiezon H Grease (high temperature grease)</td>
			<td>Sigma</td>
			<td>Z273562</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium Persulfate</td>
			<td>Sigma</td>
			<td>216232</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium Nitrate</td>
			<td>Sigma</td>
			<td>229938</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium Hexachloroiridate(III) hydrate</td>
			<td>Sigma</td>
			<td>288160</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Mounted 455nm LED</td>
			<td>Thorlabs</td>
			<td>M455L3</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Cuvette Holder</td>
			<td>Thorlabs</td>
			<td>CVH100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">25mL 3-neck Round Bottom Flask</td>
			<td>Chemglass</td>
			<td>CG-1524-A-02</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Liebig Condensor</td>
			<td>Chemglass</td>
			<td>CG-1218-A-20</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">T-Joint Adapter</td>
			<td>Chemglass</td>
			<td>AF-0509-10</td>
			<td></td>
		</tr>
	</tbody>
</table>

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).

Transmission electron micrographs (TEM) were collected in order to see the distribution of iridium oxide on the seeded rods (Figure 1). TEM samples were prepared by pipetting a drop of dissolved particles onto a TEM grid. X-ray diffraction (XRD, Figure 2) and X-ray photoelectron spectra (XPS, Figure 3) were used to characterize the observed growth as a mix of crystalline IrO2 and Ir2O3. Preparation of XRD and XPS samples was done by the drying of particles on glass slides. Enough sample was used so that a thick film developed (Figure 4). The illumination time was found to correspond with the particle size (Figure 5), which can be estimated visually. As the iridium oxide particles grow the color transitions (Figure 4) from yellow-orange (the color of bare rods) to green (medium coverage of ~1 nm particles) to blue (full coverage of ~2 nm particles).
<img alt="Figure 1" src="/files/ftp_upload/53675/53675fig1highres.jpg" /> 
Figure 1. Electron Micrographs of Iridium Oxide Coated Rods. Seeded rods covered in iridium oxide as seen in TEM at lower magnification (A) and higher magnification (B) as well as using high angle annular dark field imaging (C) (adapted from Ref. [9] - Reproduced by permission of The Royal Society of Chemistry). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53675/53675fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/53675/53675fig2highres.jpg" width="700" /> 
Figure 2. X-ray Diffraction Patterns. XRD patterns for (A) bare CdSe@CdS rods (B) CdSe@CdS rods after 2 hr growth of iridium oxide. These XRD patterns show the emergence of crystalline IrO2 and Ir2O3. Indexed patterns for CdS (red) IrO2 (green) and Rh2O3 (blue) are overlaid on the diffraction patterns. Ir2O3 was matched using the powder diffraction file for Rh2O3 because it is too unstable in bulk to characterize, yet has been predicted using theoretical modelling to have an almost identical structure (adapted from Ref. [9] - Reproduced by permission of The Royal Society of Chemistry). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53675/53675fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/53675/53675fig3highres.jpg" width="500" /> 
Figure 3. X-ray Photoelectron Spectrum. XPS was used to support the presence of both IrO2 and Ir2O3. Both plots are from a typical XPS spectrum, for a sample of CdSe@CdS after 2 hr photochemical growth of iridium, over different energy ranges. Signatures of both Ir(III) (at around 65 eV) and Ir(IV) (at around 300 eV) were observed as shown in the spectral peak deconvolutions (adapted from Ref. [9] - Reproduced by permission of The Royal Society of Chemistry). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53675/53675fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/53675/53675fig4highres.jpg" width="700" /> 
Figure 4. Visual Appearance of Sample After Different Growth Times. Powder samples prepared for XRD showing dried particles of (A, orange-red) bare rods (B, green) rods after 2 hr&#160;of illumination (C, blue) rods after 4 hr&#160;of illumination. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53675/53675fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/53675/53675fig5highres.jpg" width="500" /> 
Figure 5. Iridium Oxide Growth Over Time. TEM micrographs, showing the growth of iridium oxide particles over time. (A) Control, kept in the dark. The control shows no iridium oxide growth, and rods of 4-5 nm diameter, unchanged from before the experiment. (B-F) Samples illuminated with unfiltered lamp light for (B) 10 min, (C) 45 min, (D) 2 hr, (E-F) 4 hr. This series shows the progression from small (&#60;0.5 nm) iridium oxide particles, to larger (0.5-2 nm) particles, to a full coating of iridium oxide. The rods that were illuminated for 4 hr&#160;have a total diameter of 9-10 nm, indicating a 2-3 nm thick coating of iridium oxide is present (adapted from Ref. [9] - Reproduced by permission of The Royal Society of Chemistry). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/53675/53675fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Photochemical Oxidative Growth of Iridium Oxide Nanoparticles on CdSe@CdS Nanorods at JoVE.com

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

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 ...

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Nanyang Technological University

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JoVE Journal

Chemistry

9.5K Views.  Technion – Israel Institute of Technology. A protocol for the photochemical oxidative growth of small crystalline iridium oxide nanoparticles on the surface of CdSe@CdS seeded rod nanoparticles is presented.

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

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 ...

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO3 (001) and DyScO3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca2Nb3O10- nanosheets were used, prepared by delamination of their layered parent compound HCa2Nb3O10. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.

Various procedures are outlined to prepare atomically defined templates for epitaxial growth of complex oxide thin films. Chemical treatments of single crystalline SrTiO3 (001) and DyScO3 (110) substrates were performed to obtain atomically smooth, single terminated surfaces. Ca2 Nb3 O10- nanosheets were used to create atomically defined templates on arbitrary substrates.

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain ...

Hydroquinone Based Synthesis of Gold Nanorods

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the synthetic methods for the preparation of gold nanorods are still not fully optimized. In this paper we describe a new, highly efficient, two-step protocol based on the use of hydroquinone as a mild reducing agent. Our approach allows the preparation of nanorods with a good control of size and aspect ratio (AR) simply by varying the amount of hexadecyl trimethylammonium bromide (CTAB) and silver ions (Ag+) present in the "growth solution". By using this method, it is possible to markedly reduce the amount of CTAB, an expensive and cytotoxic reagent, necessary to obtain the elongated shape. Gold nanorods with an aspect ratio of about 3 can be obtained in the presence of just 50 mM of CTAB (versus 100 mM used in the standard protocol based on the use of ascorbic acid), while shorter gold nanorods are obtained using a concentration as low as 10 mM.

This paper describes a protocol for the synthesis of gold nanorods, based on the use of hydroquinone as reducing agent, plus the different mechanisms for controlling their size and aspect ratio.

Gold nanorods are an important kind of nanoparticles characterized by peculiar plasmonic properties. Despite their widespread use in nanotechnology, the ...

In Situ Detection and Single Cell Quantification of Metal Oxide Nanoparticles Using Nuclear Microprobe Analysis

Micro-analytical techniques based on chemical element imaging enable the localization and quantification of chemical composition at the cellular level. They offer new possibilities for the characterization of living systems and are particularly appropriate for detecting, localizing and quantifying the presence of metal oxide nanoparticles both in biological specimens and the environment. Indeed, these techniques all meet relevant requirements in terms of (i) sensitivity (from 1 up to 10 &#181;g.g-1 of dry mass), (ii) micrometer range spatial resolution, and (iii) multi-element detection. Given these characteristics, microbeam chemical element imaging can powerfully complement routine imaging techniques such as optical and fluorescence microscopy. This protocol describes how to perform a nuclear microprobe analysis on cultured cells (U2OS) exposed to titanium dioxide nanoparticles. Cells must grow on and be exposed directly in a specially designed sample holder used on the optical microscope and in the nuclear microprobe analysis stages. Plunge-freeze cryogenic fixation of the samples preserves both the cellular organization and the chemical element distribution. Simultaneous nuclear microprobe analysis (scanning transmission ion microscopy, Rutherford backscattering spectrometry and particle induced X-ray emission) performed on the sample provides information about the cellular density, the local distribution of the chemical elements, as well as the cellular content of nanoparticles. There is a growing need for such analytical tools within biology, especially in the emerging context of Nanotoxicology and Nanomedicine for which our comprehension of the interactions between nanoparticles and biological samples must be deepened. In particular, as nuclear microprobe analysis does not require nanoparticles to be labelled, nanoparticle abundances are quantifiable down to the individual cell level in a cell population, independently of their surface state.

In Situ Detection and Single Cell Quantification of Metal Oxide Nanoparticles Using Nuclear Microprobe Analysis

We describe a procedure for the detection of chemical elements present in situ in human cells as well as their in vitro quantification. The method is well-suited to any cell type and is particularly useful for quantitative chemical analyses in single cells following in vitro metal oxide nanoparticles exposure.

Micro-analytical techniques based on chemical element imaging enable the localization and quantification of chemical composition at the cellular level. ...

Ligand-Mediated Nucleation and Growth of Palladium Metal Nanoparticles

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution of capping ligands during the synthesis reaction, their role in regulating the nucleation and growth rates of colloidal nanoparticles is not well understood. In this work, we demonstrate a mechanistic investigation of the role of trioctylphosphine (TOP) in Pd nanoparticles in different solvents (toluene and pyridine) using in situ SAXS and ligand-based kinetic modeling. Our results under different synthetic conditions reveal the overlap of nucleation and growth of Pd nanoparticles during the reaction, which contradicts the LaMer-type nucleation and growth model. The model accounts for the kinetics of Pd-TOP binding for both, the precursor and the particle surface, which is essential to capture the size evolution as well as the concentration of particles in situ. In addition, we illustrate the predictive power of our ligand-based model through designing the synthetic conditions to obtain nanoparticles with desired sizes. The proposed methodology can be applied to other synthesis systems and therefore serves as an effective strategy for predictive synthesis of colloidal nanoparticles.

The main goal of this work is to elucidate the role of capping agents in regulating the size of palladium nanoparticles by combining in situ small angle x-ray scattering (SAXS) and ligand-based kinetic modeling.

The size, size distribution and stability of colloidal nanoparticles are greatly affected by the presence of capping ligands. Despite the key contribution ...

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.

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.

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

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes

We present the chemoselective synthesis of 1-(iodoethynyl)-4-methylbenzene, 1-(1,2-diiodovinyl)-4-methylbenzene, and 1-methyl-4-(1,2,2-triiodovinyl)benzene as representative examples for the practical chemoselective preparation of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes from the chemoselective iodination of terminal alkynes mediated by hypervalent-iodine reagents. The chemoselectivity was confirmed by using p-tolylethyne as a model substrate to screen a variety of iodine sources and/or the hypervalent-iodine reagents. A combination of tetrabutylammonium iodide (TBAI) and (diacetoxyiodo)benzene (PIDA) selectively generates 1-iodoalkynes, while a combination of KI and PIDA generates 1,2-diiodoalkenes. A one-pot synthesis based on both TBAI-PIDA and KI-PIDA yields the corresponding 1,1,2-triiodoalkenes. These protocols were subsequently applied to the synthesis of synthetically important aromatic and aliphatic 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes, which were obtained in good yield with excellent chemoselectivity.

Herein, detailed protocols for the oxidative iodination of terminal alkynes using hypervalent-iodine reagents are presented, which chemoselectively afford 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes.

We present the chemoselective synthesis of 1-(iodoethynyl)-4-methylbenzene, 1-(1,2-diiodovinyl)-4-methylbenzene, and ...

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. ...

Growth of Gold Dendritic Nanoforests on Titanium Nitride-coated Silicon Substrates

In this study, a high-power impulse magnetron sputtering system is used to coat a flat and firm titanium nitride (TiN) film on silicon (Si) wafers, and a fluoride-assisted galvanic replacement reaction (FAGRR) is employed for the rapid and easy deposition of gold dendritic nanoforests (Au DNFs) on the TiN/Si substrates. Scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy patterns of TiN/Si and Au DNFs/TiN/Si samples validate that the synthesis process is accurately controlled. Under the reaction conditions in this study, the thickness of the Au DNFs increases linearly to 5.10 &#177; 0.20 &#181;m within 15 min of the reaction. Therefore, the employed synthesis procedure is a simple and rapid approach for preparing Au DNFs/TiN/Si composites.

This study presents a feasible procedure for synthesizing gold dendritic nanoforests on titanium nitride/silicon substrates. The thickness of gold dendritic nanoforests increases linearly within 15 min of a synthesis reaction.

In this study, a high-power impulse magnetron sputtering system is used to coat a flat and firm titanium nitride (TiN) film on silicon (Si) wafers, and a ...

Design, Synthesis, and Photochemical Properties of Clickable Caged Compounds

Caged compounds enable the photo-mediated manipulation of the cell physiology with high spatiotemporal resolution. However, the limited structural diversity of currently available caging groups and the difficulties in synthetic modification without sacrificing their photolysis efficiencies are obstacles to expanding the repertoire of caged compounds for live cell applications. As the chemical modification of coumarin-type photo-caging groups is a promising approach for the preparation of caged compounds with diverse physical and chemical properties, we report a method for the synthesis of clickable caged compounds that can be modified easily with various functional units via the copper(I)-catalyzed Huisgen cyclization. The modular platform molecule contains a (6-bromo-7-hydroxycoumarin-4-yl)methyl (Bhc) group as a photo-caging group, which exhibits a high photolysis efficiency compared to those of the conventional 2-nitrobenzyls. General procedures for the preparation of clickable caged compounds containing amines, alcohols, and carboxylates are presented. Additional properties such as the water solubility and cell targeting ability can be readily incorporated into clickable caged compounds. Furthermore, the physical and photochemical properties, including the photolysis quantum yield, were measured and were found to be superior to those of the corresponding Bhc caged compounds. The described protocol could therefore be considered a potential solution for the lack of structural diversity in the available caged compounds.

A protocol for the synthesis and measurement of the photochemical properties of modular caged compounds with clickable moieties is presented.