This work was fully funded by Hong Kong University Grants Committee - Institutional Development Scheme (IDS) Collaborative Research Grant, grant number UGC/IDS(C)14/B(E)01/19, the Faculty Development Scheme (FDS), grant number UGC/FDS25/E08/20 and partially funded by the Institutional Development Scheme (IDS), grant number UGC/IDS(R)25/20.
<div></div>
.

CAUTION: Readers are advised to carefully check the properties and toxicities of the chemicals described in this paper for the proper chemical handling from the relevant material safety data sheets (MSDS). Some of the chemicals used are detrimental to health, and special cares are to be taken. The impact of nanomaterials on human health is unknown and could pose safety and health risks. Inhalation and contact through the skin with these materials should be avoided. Safety precautions shall also be exercised, such as rele...

We have nothing to disclose.

The pyrolysis method has become one of the powerful strategies in the synthesis of one-dimensional nanomaterial on various heteroatom-doped solid supports with controlled sizes of NPs. For example, the nanospace-confined pyrolysis strategy was reported by Guo et al.56. Briefly, the pre-treated MWCNTs, cobalt, and phosphorus precursors were pyrolyzed&#160;at 800 &#176;C under N2 atmosphere, and the CoP NPs supported on N-CNT can be obtained. The presence of the micro-pores can act as the...

Developing low-cost and highly efficient catalysts for renewable energy production remains one of the most critical and challenging problems to relieve the energy crisis. However, it is far from practical applications due to several concerns, such as large-scale production methods with reliable performance, high production cost, and long-standing stability to extend the service life of catalysts. Industry sectors, like transport and logistics, require energy production for vehicles and equipment with long operation hours, high powered energy supply, and minimal refueling time in achieving efficient operations1,2,3. Therefore, effective strategies have been extensively exploited to address the above technical challenges. For example, by regulating the electronic structure of the metal active sites and catalyst supports, designing the specific architecture of the metal nano-catalysts, fine-tuning metal compositions, functional group modification of anchored support, and varying the morphology to increase the number of intrinsic active sites. In the past few decades, nanoparticles (NPs) have dominated the fields of various heterogeneous catalysis, and the catalytic activities can be effectively tuned by varying the size of the NPs. Only until in recent years, highly dispersed single-atom catalysts (SACs) emerged to have excellent properties towards many catalytic&#160;reactions due to their unique electronic structure and coordination environment. Particularly, SACs have already demonstrated superior performances in energy conversion such as electrochemical reactions (HER, ORR, OER) and electrochemical energy systems (e.g., supercapacitors, rechargeable batteries)4,5,6. While both NPs and SACs have their respective&#160;advantages and limitations in catalytic applications, there do exist reactions that require both NPs and SACs in order to boost catalytic reactivity. For example, Ru NPs supported on Ni- and N-co-doped carbon nanotube superstructure could facilitate the high catalytic wet air oxidation of acetic acid7. This synergistic effect was also demonstrated by Pd1+NPs/TiO2 catalysts for highly selective ketone and aldehydes hydrogenation at room temperatures8. In order to accelerate the field of synergistic NPs and SACs catalysis and explore more on their catalytic applications, a facile way of catalyst synthesis is highly desirable, and the introduction of high loadings of the atomically dispersed active site remains a challenge due to the high tendency of the aggregation of SACs9.
Several methods have been utilized to synthesize SACs for applications in the hydrogenation of nitroarenes10, oxygen reduction reaction and hydrogen evolution reaction11,12, lithium-oxygen batteries13.The most common strategy is the bottom-up approach, in which the metal precursors were absorbed, reduced, and immobilized on the defects of the corresponding support. Mononuclear metal complexes could also be first attached to the functional group of supports, followed by subsequent removal of the organic ligands, thus creating active metal sites for the catalytic process. Atomic layer deposition (ALD) is probably the most frequently used procedure for bottom-up fabrication by depositing a thin layer of film on the substrate with repeated exposure of reactants. Although the catalyst size could be precisely controlled and the reactivity could be greatly improved14, the purity of the substrate was rather demanding, and the metal loading was relatively low, thus resulting in high production costs for practical applications. Various methods such as direct impregnation, co-precipitation, and deposition-precipitation, have been employed to immobilize metal nanoparticles onto the support surfaces, such as metal oxide and nitride, through surface charging effects. However, increasing metal loading usually leads to significant agglomeration and cluster formation of the metal atoms or nanoparticles. Therefore, usually, a very diluted metal solution is required, thus leading to low SACs loadings of the catalysts15. Amine ligands such as phenanthroline have been employed to undergo pyrolysis with metal precursors to prepare atomically dispersed metal catalysts with highly active Co-Nx active sites for the selective dehydrogenation of formic acid. However, the metal loading was relatively low (2-3 wt%) due to the limited number of available N atoms in the amine precursors16.
In the past few decades, hydrogen has been regarded as a potential alternative to replace fossil fuels or hydrocarbons, such as coal, natural gas, and gasoline, due to the advantage of zero-emission of the former. Until now, about 94% of commercial hydrogen is still produced from the reforming process of fossil fuels, in which the process releases a great deal of greenhouse gas17. Therefore, hydrogen production from renewable resources such as water electrolysis is a way to solve the problem of depleted fossil resources and severe carbon emissions. However, the low hydrogen production efficiency has hindered their wider applications. Thus, to overcome this kinetic energy barrier for water-splitting, numerous efficient electrocatalysts have been discovered in the past decade18. Another issue is the storage problem due to the gaseous and explosive nature of hydrogen gas at ambient conditions. Physical storage methods such as compression will require the hydrogen to be compressed up to 700-800 bar, and cryogenic storage by liquefaction will require low temperature at -253 &#176;C19. Although commercialized hydrogen fuel cell-powered vehicles have been successfully demonstrated, the storage problem is yet to be solved if the technology is to be used in wider applications, such as miniature devices and mini-fuel cells. Thus, storage methods of using chemical H materials have been one of the hot focuses in hydrogen energy research. Some examples of chemical H storage materials are ammonia borane (AB)20, formic acid (FA)21, ammonia gas22, sodium alanate23, and magnesium hydride24. Among these, AB has a low molecular weight (30.7 g&#183;mol-1), high gravimetric and volumetric densities (196 gH2&#183;kg-1 and 146 gH2&#183;L-1, respectively). Besides, it is an air and moisture stable compound, non-toxic, and highly soluble in water. Metal nanoparticles on various supported materials have been widely used to release the three equivalents of hydrogen from AB, such as platinum- (Pt-), palladium- (Pd-), ruthenium- (Ru-), cobalt- (Co-), and nickel- (Ni-) based catalysts. Co-based heterogeneous catalysts supported on carbon materials are especially attracting much attention due to their low cost, high abundance, and ease of recovery. Several synthetic strategies have been reported, such as the Co NPs supported on branched polyethylenimine-decorated graphene oxide25. The 3D structure with a large surface area ensures the stabilization of Co NPs maintaining at the 2-3 nm size range and prevented the aggregation of NPs. Another strategy is to use N-doped carbon materials to support Co NPs with small sizes. Using Co(salen)26 and Co-MOF27 (metal organic framework) as the precursors, Co NPs of 9.0 nm and 3.5 nm supported on N-doped porous carbon materials have been prepared respectively. The stability towards AB hydrolysis are high and the reactivity can maintain over 95% of the initial activity after 10 reaction runs. Recently, catalysts with hollow micro/nanostructures have been exploited for AB hydrolysis. These materials are conventionally prepared by hydrothermal methods and have been widely used for lithium-ion batteries, supercapacitors, chemical sensors, and heterogeneous catalysis research. Thus, the copper-cobalt synergy towards AB hydrolysis has been demonstrated by the hollow CuMoO4-CoMoO428, which gives a high TOF of 104.7 min-1. Other highly structural-dependent examples include the core-shell CuO-NiO/Co3O429, the CoxCu1&#8722;xCo2O4@CoyCu1&#8722;yCo2O4 yolk-shell type30, and the Ni0.4Cu0.6Co2O4 nanoarrays31 were also found to be active towards AB hydrolysis. Another type of emerging materials known as heterostructured catalysts, such as MXenes and layered double hydroxides (LDHs), are increasingly being exploited for electrocatalytic and photocatalytic reaction32,33,34,35. These materials such as the NiFe-layered double hydroxide36,37 and the CoB-N materials having N-doped carbon-cobalt boride heterointerfaces38 are especially active for oxygen evolution and reduction reaction. In principle, they could be further exploited for hydrogen evolution reactions from hydrogen storage materials such as ammonia borane39. Maximizing the interaction between the catalysts and substrates is also another strategy for AB hydrolysis. Chiang et al. have utilized the surface oxide group of graphene oxide to form an initiated complex species with AB40, thus Ni0.8Pt0.2/GO and rGO demonstrated excellent reactivity towards AB hydrolysis. The use of &#945;-MoC as support for Co and Ni bimetallic catalysts assisted the activation of water molecules and achieved high TOF towards AB hydrolysis, which is four times higher than the commercial Pt/C catalyst41.
Taking advantage of high N contents of the dicyandiamide and related C3N4 materials, a protocol for achieving a facile synthesis of cobalt NPs supported on highly dispersed Co- and N-doped carbon nanotubes is presented herein. The gradual&#160;in-situ formation of Co NPs from the formed atomically dispersed Co during the pyrolysis of C3N4 materials ensure that 1) Co NPs and Co dopants are highly dispersed; 2) Co NPs can be strongly anchored on the doped carbon supports and 3) Co NPs size can be carefully controlled by the temperature and time of the pyrolysis. The as-prepared Co/Co-N-CNT, as a result of the strongly anchored Co NPs and the ability of the Co dopants to lower the adsorption energy of water molecules, was found to have superior stability towards the hydrolysis of AB for hydrogen production. The details of the synthetic protocol of the catalysts and the measurement of the hydrogen production will be the focal point of this report.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Dicyandiamide</td>
			<td>Sigma Aldrich</td>
			<td>D76609</td>
			<td></td>
		</tr>
		<tr>
			<td>Borane-ammonia complex</td>
			<td>Aladdin</td>
			<td>B131882-100g</td>
			<td></td>
		</tr>
		<tr>
			<td>Citric acid, 99%</td>
			<td>Sigma Aldrich</td>
			<td>C0759</td>
			<td></td>
		</tr>
		<tr>
			<td>Cobalt metal standard solution, traceable to SRM from NIST Co(NO3)2 in HNO3 0.5 mol/l 1000 mg/l Co Certipur</td>
			<td>Sigma Aldrich</td>
			<td>1.19785</td>
			<td></td>
		</tr>
		<tr>
			<td>Cobalt(II) acetylacetonate, &#8805; 99%</td>
			<td>Sigma Aldrich</td>
			<td>727970</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrochloric acid, ACS reagent</td>
			<td>Sigma Aldrich</td>
			<td>320331-2.5L</td>
			<td></td>
		</tr>
		<tr>
			<td>ICP-OES</td>
			<td></td>
			<td></td>
			<td>ICP-OES with dichroic spectral combiner (Agilent 5110)</td>
		</tr>
		<tr>
			<td>Muffle furnace</td>
			<td></td>
			<td></td>
			<td>High Performance Hybrid Muffle furnace, Chamber: (360 x 250 x 320) mm, Exterior: (610 x 545 x 500) mm, Power(3100W), Vulcan 3-1750)</td>
		</tr>
		<tr>
			<td>Nitric acid, puriss. p.a., 65.0-67.0%</td>
			<td>Sigma Aldrich</td>
			<td>84378</td>
			<td></td>
		</tr>
		<tr>
			<td>Sulphuric acid, ACS reagent 95-98%</td>
			<td>Sigma Aldrich</td>
			<td>258105</td>
			<td></td>
		</tr>
		<tr>
			<td>Tubular furnace</td>
			<td></td>
			<td></td>
			<td>OTF-1200X with tube size of 60 mm outer diameter (Hefei Kejing)</td>
		</tr>
		<tr>
			<td>Ultrasonic bath</td>
			<td></td>
			<td></td>
			<td>10L Digital Single Frequency 40 kHz Ultrasonic Cleaner (Biobase)</td>
		</tr>
	</tbody>
</table>

synthesis of metal nanoparticles supported on carbon nanotube with doped co and n atoms and its catalytic applications in hydrogen production

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

X-ray diffraction patterns (XRD) have been obtained to determine the crystallinity and size of the cobalt NPs. As shown in Figure 1, diffraction peaks corresponding to the (111), (200) and (220) planes (at 2&#952; of 44.2&#176;, 51.5&#176;, and 75.8&#176; respectively) of the cubic phase of metallic cobalt were present in agreement with the JCPDS (Joint Committee for Powder Diffraction Standards) power diffraction file (card # 15-0806)47. The broad peak at 2&#952; of ...

Watch this Scientific Journal Video about Synthesis of Metal Nanoparticles Supported on Carbon Nanotube with Doped Co and N Atoms and its Catalytic Applications in Hydrogen Production at JoVE.com

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

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

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

This protocol is about developing low cost and highly efficient catalyst with reliable performance and longstanding stability. The developed catalyst could be used for renewable energy productions and may even solve the problem of energy crisis. The advantage of this study is to construct both particle and atomically disperse metal atoms on the same catalyst supports, which may perform synergistically for certain types of catalystic reactions.In exploring the potential of renewable energy for vehicles to meet future regulatory and sustainability needs, the rapid development of hydrogen fuel cells and vehicles as well as other related fields has effectively promoted the advancement of hydrogen energy technology. So the objective of this research is to develop a novel hydrogen powered fuel cell prototype using solid hydrogen storage materials for renewable energy to be used in various sectors like transport, logistics, et cetera. Begin by weighing 280 grams of diacid and diamide into an 800 milliliter beaker.Then place the beaker into a muffle furnace and slowly raise the temperature from room temperature to 350 degrees Celsius for the ramp of five degrees per minute. Keep the temperature at 350 degrees Celsius for two hours. Then cool down the furnace by natural cooling.Grind the obtained white solids into fine powder as the carbon nitride materials in the melem form. Begin by mixing and grinding 10 grams of carbon nitride in the melem form with 0.218 grams of cobalt acetyl acetate until the homogenous color is observed. Add six milliliters of citric acid solution in this homogenous mixture and further grind the materials.Dry the materials in an oven at 60 degrees Celsius for six hours. Place these materials into a square shaped crucible and then into a tubular furnace. Heat the materials at a heating rate of 2.6 degrees Celsius per minute from room temperature to 800 degrees Celsius and place it under an argon flow of 100 milliliters per minute for two hours.Slowly cool the furnace by natural cooling, then weigh out the catalyst samples. Set up the water filled inverted cylinder system and 0.1 molar sulfuric acid washing solution. Connect the schlenk flask with the washing solution and the water filled inverted cylinder.Place 0.04 grams of the catalyst into the schlenk flask and sonicate the solution at 40 kilohertz in an ultrasonic bath for six minutes. Then prepare to add 0.04 grams of ammonia borane to 0.948 milliliters of water and inject one milliliter of the solution into the reactor to initiate the hydrolysis reaction. Monitor the drop in the water level as the reaction proceeds and carefully record the production volume at designated times.Plot a graph of the volume of hydrogen production versus time in minutes. Place 0.04 grams of the catalyst and 10 milliliters of water into the schlenk flask and immerse it into the water bath at 40 degrees Celsius. Sonicate the solution at 40 kilohertz in an ultrasonic bath for six minutes, inject one milliliter of the ammonia borane solution to the reactor to initiate the hydrolysis reaction, then record the time for completion of the hydrogen release.Inject one milliliter of the ammonia borane solution to the reactor to initiate the hydrolysis reaction, then record the time for completion of the hydrogen release. Filter off the catalyst by washing it three times with five milliliters of water. Then drive the catalyst in a 60 degree Celsius oven for three hours.Place the catalyst in 10 milliliters of water and sonicate the solution at 40 kilohertz in an ultrasonic bath. Repeat these steps for 10 cycles. Then plot a graph of hydrogen production volume versus cycles.Immerse the schlenk flask containing the catalyst and 0.5 molar sulfuric acid into the oil bath. Stir the reaction for two hours, then filter off the solid using a buchner funnel. Wash the solid three times with 10 milliliters of deionized water each time.Dilute the obtained leachate further to 250 milliliters in a 250 milliliter volumetric flask and collect the metal nanoparticle leached solids by drying at 60 degrees Celsius in an oven. The strong and sharp x-ray defraction piece of metallic cobalt indicate a well-defined crystalline structure, remaining unchanged after recycles. While the structural defects were studied using Raman spectroscopy.The XPS spectrum showed the presence of each element their bonding and the hybridization of carbon atoms during the formation of the carbon nanotube structures. The absorption desorption isotherm demonstrated a specific surface area of 42.02 meters square per gram and the average pore size distribution of 3.6 nanometers. The SEM and HRTEM images depicted the five micrometer tubular structure of cobalt nanoparticles resulting from the catalyzing growth of the nanofiber along with their EDS mapping.The crystal in structure of the cobalt nanoparticle was characterized by selected area electron defraction. The main body of the carbon nanofiber was wrapped by a few layers of carbon of different orientations and defraction rings. The total metal content determined by ICP-OES was found to be 25.1%weight with 9.7%weight of cobalt nanoparticles and 15.4%weight of cobalt dopings on the carbon nanotubes.The catalytic performance of the catalyst was studied and it was found that until the 10th time of ammonia borane edition, there was no obvious decline in the catalytic performance. The rate law of reaction was also studied and the activation energy was determined to be 42.8 kilojoules per mole. Avoid overloading the tubular furnace with catalyst precursors since too many decomposition products may block the tube.Make sure the solids mixture are well mixed. High energy equipment such as milling can be used to facilitate a mixing. These catalysts can be applied in other types of organic transformation reactions and small molecule activation such as hydrogen protection from forming acid, cross reaction, and organic synthesis.

synthesis-metal-nanoparticles-supported-on-carbon-nanotube-with-doped

Research

JoVE Journal

Chemistry

3.2K vues.  Technological and Higher Education Institute of Hong Kong (THEi). Ce protocole consiste à développer un catalyseur à faible coût et très efficace avec des performances fiables et une stabilité à long terme. Le catalyseur développé pourrait être utilisé pour la production d’énergie renouvelable et pourrait même résoudre le problème de la crise énergétique. L’avantage de cette étude est de construire à la fois des atomes métalliques dispersés de particules et atomiquement sur les mêmes supports catalytiques, qui peuvent fonctionner e...