Name: using polystyrene-block-poly(acrylic acid)-coated metal nanoparticles as monomers for their homo- and co-polymerization
Uploaded: 2015-07-09T15:00:00
Description: Watch this Scientific Journal Video about Using Polystyrene-block-polyacrylic acid-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization at JoVE.com

The authors thank the NRF (CRP-4-2008-06), A*Star (SERC 112-120-2011) and MOE (RG14/13) Singapore for financial supports.

Caution: Please consult all relevant material safety data sheets (MSDS). Some chemicals used in these syntheses are corrosive, toxic and possibly carcinogenic. Nanomaterials may have unrecognized hazards as compared to their bulk counterparts. Please use appropriate safety practices when performing reaction, including the use of fume hood and personal protective equipment (safety glasses, gloves, lab coat, full length pants, closed-toe shoes, etc.).
1. Synthesis of Metal Nanoparticles
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<ol>
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The mechanistic details of the syntheses are reported and discussed in the previous publications.20,21 Here we focus on the rationales of the synthetic conditions. For the polymerization of nanoparticles, it is preferred that nanoparticles of uniform size are used. We follow literature procedures to obtain the uniform Au nanoparticles,23 Au nanorods,24 and Te nanowires.25 In general, better size uniformity can be obtained when the nucleation and growth stages are separated.<sup...

Despite great advances in the synthesis of nanoparticles over the past two decades, their orderly assembly remains a great challenge. Our synthetic capabilities in putting the basic building blocks together are of critical importance for the exploration and exploitation of their synergistic effects and collective properties. Thus, developing new reaction pathways and exploring the underlying mechanisms are the stepping stones towards the rational synthesis of complex nanodevices. 
Among the rich structural variety of possible nanoparticle assemblies, one-dimensional (1D) chains have shown useful applications in nanoelectronics, optoelectronics, and biosensors.1-4 Typically, self-assembly of nanoparticles into chain-like structures requires magnetic or electric dipole interactions, anisotropic electrostatic repulsion, or external templates.5-11 For dipole-induced assembly, one needs nanoparticles with permanent dipoles, such as magnetic nanoparticles and semiconductor nanoparticles under special environments.12-15 For nanoparticles with no permanent dipole, it has been shown that the relatively weaker electrostatic repulsion at the ends of the nanoparticle chains can promote the selective attachment of nanoparticle thereon and thus, 1D chain growth.16,17 Because the nanoparticles can aggregate with each other and with the oligomers, the aggregation often follows the intrinsic step-growth mode, leading to short chain length and the lack of control over branching. Lastly, nanoparticles can be adsorbed onto 1D templates to form chains, but usually it is very difficult to achieve secure anchoring and avoid gaps among the nanoparticles. 
With these existing methods, hetero-assembly or &#8220;co-polymerization&#8221; of nanoparticles is particularly difficult. A few pioneer works have demonstrated the &#8220;co-polymerization&#8221; of short nanoparticle chains exploiting magnetic dipole18 or electrostatic repulsion.19
Recently, we reported the homo- and co-polymerization of PSPAA-coated nanoparticles into chains.20,21 This new synthetic pathway involves facile colloidal synthesis and generic use of different types of nanoparticles. It affords ultralong chains without branching and allows ready control of their length and width (single-, double-, and triple-line chains). Most importantly, random- and co-polymers of nanoparticles can be synthesized with improved structural control. In this work, we provide video protocols for the related syntheses, intending to give a detailed demonstration and presentation.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Gold(III) chloride trihydrate, ACS reagent, &#8805;49.0% Au basis 
			&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>G4022</td>
			<td>HAuCl4</td>
		</tr>
		<tr>
			<td>Sodium citrate dihydrate, 99%</td>
			<td>Alfa Aesar</td>
			<td>A12274</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium borohydride, &#8805;99% 
			&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>71321, Fluka</td>
			<td></td>
		</tr>
		<tr>
			<td>Hexadecyltrimethylammonium bromide,&#8805;98%&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>H5882</td>
			<td>CTAB</td>
		</tr>
		<tr>
			<td>Silver Nitrate, 99.9999% trace metals basis</td>
			<td>Sigma-Aldrich</td>
			<td>204390</td>
			<td></td>
		</tr>
		<tr>
			<td>L-ascorbic acid,BioXtra, &#8805;99.0%, crystalline 
			&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>A5960</td>
			<td></td>
		</tr>
		<tr>
			<td>Tellurium dioxide,&#8805;99%&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>243450</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrazine monohydrate, 64-65 %, reagent grade, 98%&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>207942</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly(styrene-b-acrylic acid)(PS154-PAA49)</td>
			<td>Polymer Source</td>
			<td>P4673A-SAA</td>
			<td>PS16000-PAA3500</td>
		</tr>
		<tr>
			<td>Poly(styrene-b-acrylic acid)(PS144-PAA28)</td>
			<td>Polymer Source</td>
			<td>P4002-SAA</td>
			<td>PS15000-PAA1600</td>
		</tr>
		<tr>
			<td>2-Naphthalenethiol, 
			&#160;&#8805;99.0% (GC)&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>88910, Fluka</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium dodecyl sulfate, 99%</td>
			<td>Alfa Aesar</td>
			<td>A11183</td>
			<td></td>
		</tr>
		<tr>
			<td>single wall carbon nanotubes, 99%&#160; ultra-pure</td>
			<td>NanoIntegris</td>
			<td>PC10344a</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydroxide</td>
			<td>Sinopharm</td>
			<td>S1900136</td>
			<td></td>
		</tr>
		<tr>
			<td>1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (sodium salt)&#160;</td>
			<td>Avanti polar lipids</td>
			<td>870160P</td>
			<td>PSH</td>
		</tr>
		<tr>
			<td>N,N-dimethylformamide</td>
			<td>Merck</td>
			<td>SA4s640012</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol, absolute</td>
			<td>Fischer</td>
			<td>E/0650DF/17</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrochloric acid, 37%</td>
			<td>Honey well</td>
			<td>10189005</td>
			<td>Dilute to 1M before use&#160;</td>
		</tr>
	</tbody>
</table>

using polystyrene-block-poly(acrylic acid)-coated metal nanoparticles as monomers for their homo- and co-polymerization

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are encapsulated in polystyrene-block-poly(acrylic acid) (PSPAA) shells and then used as monomers for their self-assembly. Spherical PSPAA micelles upon acid treatment are known to assemble into cylindrical micelles. Exploiting this tendency, the core-shell nanoparticles are induced to aggregate, coalesce, and then transform into long chains. When more than one type of nanoparticles are used, random and block &#8220;copolymers&#8221; of nanoparticles can be obtained. Detailed procedures are reported for the PSPAA encapsulation of nanoparticles, homo- and co-polymerization of the core-shell nanoparticles, separation and purification of the resulting nanoparticle chains. Transformations of single-line chains into double- and triple-line chains are also presented. The synergy between the polymer shell and the embedded nanoparticles leads to an unusual chain-growth polymerization mode, giving long nanoparticle chains that are distinct from the products of the traditional step-growth aggregation process.

The nanoparticle monomers and chains are characterized by TEM. Figure 1 shows the representative TEM images of the PSPAA encapsulated monomers, confirming the morphologies and sizes (Figure 1). As some monomers typically remain in the sample after the &#8220;polymerization&#8221;, the sample is usually purified and concentrated before being used for TEM characterization. A stain was introduced during the preparation of the TEM samples by mixing the sample solution with 1% ammonium molybd...

Watch this Scientific Journal Video about Using Polystyrene-block-polyacrylic acid-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization at JoVE.com

Using Polystyrene-block-polyacrylic acid-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We report protocols for &#8220;polymerizing&#8221; various types of polymer-encapsulated metal nanoparticles into long chains of &#8220;homo-&#8220; and &#8220;co-polymers&#8221;.

Using Polystyrene-block-poly(acrylic acid)-coated Metal Nanoparticles as Monomers for Their Homo- and Co-polymerization

We present a template-free method for &#8220;polymerizing&#8221; nanoparticles into long chains without side branches. A variety of nanoparticles are ...

using-polystyrene-block-polyacrylic-acid-coated-metal-nanoparticles

Research

JoVE Journal

Chemistry

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

Copper (I) binding by metallochaperone transport proteins prevents copper oxidation and release of the toxic ions that may participate in harmful redox reactions. The Cu (I) complex of the peptide model of a Cu (I) binding metallochaperone protein, which includes the sequence MTCSGCSRPG (underlined is conserved), was determined in solution under inert conditions by NMR spectroscopy.
NMR is a widely accepted technique for the determination of solution structures of proteins and peptides. Due to difficulty in crystallization to provide single crystals suitable for X-ray crystallography, the NMR technique is extremely valuable, especially as it provides information on the solution state rather than the solid state. Herein we describe all steps that are required for full three-dimensional structure determinations by NMR. The protocol includes sample preparation in an NMR tube, 1D and 2D data collection and processing, peak assignment and integration, molecular mechanics calculations, and structure analysis. Importantly, the analysis was first conducted without any preset metal-ligand bonds, to assure a reliable structure determination in an unbiased manner.

Structure and Coordination Determination of Peptide-metal Complexes Using 1D and 2D 1H NMR

The NMR-solution structure of a metallochaperone model peptide with Cu (I) was determined, and a detailed protocol from sample preparation and 1D and 2D data collection to a three-dimensional structure is described.

Copper (I) binding by metallochaperone transport proteins prevents copper oxidation and release of the toxic ions that may participate in harmful redox ...

Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. Isonicotinic acid, or its derivatives, are coupled to variable length diaminoalkane chains under an inert atmosphere in anhydrous DMF or DMSO with the use of a weak base, triethylamine, and a coupling agent, 1-propylphosphonic anhydride. The products precipitate from solution upon formation or can be precipitated by the addition of water. If desired, the ligands can be further purified by recrystallization from hot water. Dinuclear platinum complex synthesis using the bispyridine ligands is done in hot water using transplatin. The most informative of the chemical characterization techniques to determine the structure and gross purity of both the bispyridine ligands and the final platinum complexes is 1H NMR with particular analysis of the aromatic region of the spectra (7-9 ppm). The platinum complexes have potential application as anticancer agents and the synthesis method can be modified to produce trinuclear and other multinuclear complexes with different hydrogen bonding functionality in the bridging ligand.

This protocol describes the use of amide coupling reactions of isonicotinic acid and diaminoalkanes to form bridging ligands suitable for use in the synthesis of multinuclear platinum complexes, which combine aspects of the anticancer drugs BBR3464 and picoplatin.

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. ...

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

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

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

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

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

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

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

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

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

Atom Transfer Radical Polymerization of Functionalized Vinyl Monomers Using Perylene as a Visible Light Photocatalyst

A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The procedure is performed under an inert atmosphere using air- and water-exclusion techniques. The outcome of the polymerization is affected by the ratios of monomer, initiator, and catalyst used as well as the reaction concentration, solvent, and nature of the light source. Temporal control over the polymerization can be exercised by turning the visible light source off and on. Low dispersities of the resultant polymers as well as the ability to chain-extend to form block copolymers suggest control over the polymerization, while chain end-group analysis provides evidence supporting an atom-transfer radical polymerization mechanism.

A method for the atom transfer radical polymerization of functionalized vinyl monomers using perylene as a visible-light photocatalyst is described.

A standardized technique for atom transfer radical polymerization of vinyl monomers using perylene as a visible-light photocatalyst is presented. The ...

Au-Interaction of Slp1 Polymers and Monolayer from Lysinibacillus sphaericus JG-B53 - QCM-D, ICP-MS and AFM as Tools for Biomolecule-metal Studies

In this publication the gold sorption behavior of surface layer (S-layer) proteins (Slp1) of Lysinibacillus sphaericus JG-B53 is described. These biomolecules arrange in paracrystalline two-dimensional arrays on surfaces, bind metals, and are thus interesting for several biotechnical applications, such as biosorptive materials for the removal or recovery of different elements from the environment and industrial processes. The deposition of Au(0) nanoparticles on S-layers, either by S-layer directed synthesis 1 or adsorption of nanoparticles, opens new possibilities for diverse sensory applications. Although numerous studies have described the biosorptive properties of S-layers 2-5, a deeper understanding of protein-protein and protein-metal interaction still remains challenging. In the following study, inductively coupled mass spectrometry (ICP-MS) was used for the detection of metal sorption by suspended S-layers. This was correlated to measurements of quartz crystal microbalance with dissipation monitoring (QCM-D), which allows the online detection of proteinaceous monolayer formation and metal deposition, and thus, a more detailed understanding on metal binding.
The ICP-MS results indicated that the binding of Au(III) to the suspended S-layer polymers is pH dependent. The maximum binding of Au(III) was obtained at pH 4.0. The QCM-D investigations enabled the detection of Au(III) sorption as well as the deposition of Au(0)-NPs in real-time during the in situ experiments. Further, this method allowed studying the influence of metal binding on the protein lattice stability of Slp1. Structural properties and protein layer stability could be visualized directly after QCM-D experiment using atomic force microscopy (AFM). In conclusion, the combination of these different methods provides a deeper understanding of metal binding by bacterial S-layer proteins in suspension or as monolayers on either bacterial cells or recrystallized surfaces.

Au-Interaction of Slp1 Polymers and Monolayer from Lysinibacillus sphaericus JG-B53 - QCM-D, ICP-MS and AFM as Tools for Biomolecule-metal Studies

To obtain basic information on the sorption and recycling of gold from aqueous systems the interaction of Au(III) and Au(0) nanoparticles on S-layer proteins were investigated. The sorption of protein polymers was investigated by ICP-MS and that of proteinaceous monolayers by QCM-D. Subsequent AFM enables the imaging of the nanostructures.

In this publication the gold sorption behavior of surface layer (S-layer) proteins (Slp1) of Lysinibacillus sphaericus JG-B53 is described. These ...

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 ...

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4&#160;paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science &#38; Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites.

Robust functional catechol coatings were produced in one step by direct reaction of the material known as HKUST with synthetic catechols under anaerobic conditions. The formation of homogeneous coatings surrounding the entire crystal is ascribed to the biomimetic catalytic activity of Cu(II) dimers on the external surface of the crystals.

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

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. ...