Synthesis of Mesoporous Pt Nanoparticles with Uniform Particle Size from Aqueous Surfactant Solutions toward Highly Active Electrocatalysts

Noble metal nanodendrites: growth mechanisms, synthesis strategies and applications

Inorganic nanodendrites (NDs) have become a kind of advanced nanomaterials with broad application prospects because of their unique branched architecture. The structural characteristics of nanodendrites include highly branched morphology, abundant tips/edges and high-index crystal planes, and a high atomic utilization rate, which give them great potential for usage in the fields of electrocatalysis, sensing, and therapeutics. Therefore, the rational design and controlled synthesis of inorganic (especially noble metals) nanodendrites have attracted widespread attention nowadays. The development of synthesis strategies and characterization methodology provides unprecedented opportunities for the preparation of abundant nanodendrites with interesting crystallographic structures, morphologies, and application performances. In this review, we systematically summarize the formation mechanisms of noble metal nanodendrites reported in recent years, with a special focus on surfactant-mediated mechanisms. Some typical examples obtained by innovative synthetic methods are then highlighted and recent advances in the application of noble metal nanodendrites are carefully discussed. Finally, we conclude and present the prospects for the future development of nanodendrites. This review helps to deeply understand the synthesis and application of noble metal nanodendrites and may provide some inspiration to develop novel functional nanomaterials (especially electrocatalysts) with enhanced performance.

Surfactant-Assisted Synthesis of Pt Nanocubes Using Poly(N-isopropylacrylamide) Nanogels

Poly(N-isopropylacrylamide) (PNIPAM) nanogels were prepared by emulsion polymerization using sodium dodecyl sulfate (SDS) and employed as a capping agent in platinum nanoparticle (Pt NP) synthesis by liquid-phase reduction with hydrogen gas. When the PNIPAM nanogels were used without removing SDS, that is, a slight amount of SDS was included in the reaction solution, Pt nanocubes (NCs) were predominantly produced (>80%). The proportion of the resultant Pt NCs was much higher than that obtained using the PNIPAM linear polymer (∼60%). To clarify the effects of the three-dimensional polymer network and SDS, we synthesized Pt NPs using the PNIPAM nanogel without SDS (SDS-free PNIPAM nanogel) and found that Pt NCs are rarely formed, and most NPs obtained have an irregular shape. When only SDS was used as a capping agent, NCs were hardly obtained, but other polyhedral NPs were formed. Furthermore, the use of SDS together with the PNIPAM polymer led to the decrease in the proportion of the Pt NCs compared with that obtained using only the linear polymer. These results indicate that the enhancement of the Pt NC proportion using the PNIPAM nanogel with SDS is attributable to not only the three-dimensional polymer network of the PNIPAM nanogel but also the assist of SDS as a capping agent.

Facile dual tuning of PtPdP nanoparticles by metal-nonmetal co-incorporation and dendritic engineering for enhanced formic acid oxidation electrocatalysis

Tuning the compositions and morphologies of catalysts is very important for the design of efficient formic acid oxidation reaction (FAOR) electrocatalysts. Herein, unique PtPdP dendritic nanoparticles (PtPdP DNs) with uniform size and open-pore structure are fabricated by a facile method, in which the Pd and P elements are simultaneously incorporated into Pt DNs. The prepared PtPdP DNs show enhanced catalytic activity and stability for FAOR. The improved electrocatalytic activity toward FAOR for the PtPdP DNs is mainly attributed to the synergic enhancement effect of the structural and compositional advantages, which jointly promote the electrocatalytic kinetics and thus enhance the electrocatalytic performance.

Enhanced melanoma cell-killing by combined phototherapy/radiotherapy using a mesoporous platinum nanostructure

BACKGROUND

Metal nanomaterials have a significant potential as photosensitizer and radiosensitizer. The purpose of this study was to evaluate the cytotoxicity of a platinum mesoporous nanostructure (Pt MN) toward a melanoma cancer cell line upon combined laser radiation (808 nm, 1 and 1.5 W cm^-2) and X-ray irradiation (6 MV, 2, 4, and 6 Gy).

METHODS

Pt MN was synthesized by a simple procedure and characterized by field emission scanning and transmission electron microscopy. A mouse malignant melanoma cell line C540 (B16/F10) was treated with Pt MN, laser light and/or X-ray.

RESULTS

Pt MN had a mesoporous structure with a sponge-resemble shape comprised of ensembles of very small adhered particles of <11 nm and about 5-nm pores. While Pt MN represented a low toxicity toward and considerable uptake into the cell line in a concentration range of 10-100 μg mL^-1, laser light radiation alone was also not toxic, and X-ray irradiation alone induced a limited toxicity, Pt MN was toxic against the cells in a dose dependent manner upon laser light radiation, X-ray irradiation, or their combined exposure. The killing efficacy of Pt MN upon X-ray irradiation was more obvious at 72 h post-treatment. The combined exposure (laser radiation followed by X-ray irradiation) led to a deep cell killing and a very low melanoma cell viability (∼1%). Significant melanoma cancer cell killing of Pt MN was due to reactive oxygen species (ROS) production upon combined exposure of laser and X-ray, while cell killing upon laser light radiation was due to heat generation.

CONCLUSION

Pt MN was introduced as a supreme laser/X-ray sensitizer for treatment of cancer with a high ability to produce ROS and a potent impact on decreasing cell viability.

Design synthesis of a controllable flower-like Pt-graphene oxide architecture through electrostatic self-assembly for DNA damage biomarker 8-hydroxy-2′-deoxyguanosine biosensing research

A flower-like Pt-graphene oxide (PtNF-GO) architecture for DNA damage biomarker 8-OHdG biosensing research.

FeOOH-Templated synthesis of hollow porous platinum nanotubes as superior electrocatalysts towards methanol electrooxidation

Porous Pt nanotubes are synthesized via layer-by-layer assembly with FeOOH-nanorods as templates, exhibiting an impressive electrocatalytic performance towards methanol electrooxidation.

Controlled Synthesis of Pt Nanowires with Ordered Large Mesopores for Methanol Oxidation Reaction

Catalysts for methanol oxidation reaction (MOR) are at the heart of key green-energy fuel cell technology. Nanostructured Pt materials are the most popular and effective catalysts for MOR. Controlling the morphology and structure of Pt nanomaterials can provide opportunities to greatly increase their activity and stability. Ordered nanoporous Pt nanowires with controlled large mesopores (15, 30 and 45 nm) are facilely fabricated by chemical reduction deposition from dual templates using porous anodic aluminum oxide (AAO) membranes with silica nanospheres self-assembled in the channels. The prepared mesoporous Pt nanowires are highly active and stable electrocatalysts for MOR. The mesoporous Pt nanowires with 15 nm mesopores exhibit a large electrochemically active surface area (ECSA, 40.5 m(2) g(-1)), a high mass activity (398 mA mg(-1)) and specific activity (0.98 mA cm(-2)), and a good If/Ib ratio (1.15), better than the other mesoporous Pt nanowires and the commercial Pt black catalyst.

Convenient and controllable preparation of a novel uniformly nitrogen doped porous graphene/Pt nanoflower material and its highly-efficient electrochemical biosensing

By employing dopamine as a nitrogen source and reducing agent, the block copolymer P123 as a pore forming agent, and graphene oxide as a carbon precursor, we present, for the first time, a convenient and controllable approach to the preparation of a novel uniformly nitrogen doped porous graphene (N-PGR) material. Using the prepared N-PGR as the supporting material, a novel nitrogen doped porous graphene/Pt nanoflower material (Pt/N-PGR) was obtained by a green and simple method. The characterization results of scanning electron microscopy (SEM), element mapping, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) demonstrate that Pt nanoflowers are uniformly dispersed on nitrogen doped porous graphene. Electrochemical measurements show that Pt/N-PGR-900/GCE exhibits improved electrocatalytic activity towards H2O2 reduction and glucose oxidation. Linear responses are found for H2O2 and glucose in the range of 0.5-40 326 μM and 0.5-133.5 mM with the detection limit (S/N = 3) of 0.2 μM and 0.05 mM, respectively. In addition, Pt/N-PGR-900/GCE exhibits high sensitivity and good anti-interference ability. The superior catalytic activity and selectivity make Pt/N-PGR a promising nanomaterial for application in electrochemical biosensing studies.

Large-scale template-free synthesis of ordered mesoporous platinum nanocubes and their electrocatalytic properties

Here we report a facile, one-pot and template-free approach to synthesize mesoporous monocrystalline Pt nanocubes with uniform shapes and sizes, in which small Pt particles with a size of ∼5 nm are three-dimensionally and periodically built up into cubes with a size of ∼50 nm. The forming process is illustrated through a novel meso-crystal self-assembly mechanism. Very interestingly, the mesoporous structures are ordered, which are thought to be beneficial to increase their catalytic activity. Compared with nonporous Pt nanoparticles and porous Pt nanoparticles without order, the ordered mesoporous Pt nanocubes exhibit a highly improved electrocatalytic ability for methanol and formic acid oxidation, and are potentially applicable as electrocatalysts for direct methanol and formic acid fuel cells. Furthermore, this approach can be used to synthesize other Pt-series metallic mesoporous nanoparticles, such as Pd.

Mesoporous Pt nanospheres with designed pore surface as highly active electrocatalyst

A novel strategy for large-scale synthesis of shape- and size-controlled mesoporous Pt nanospheres (MPNs) through a slow reduction reaction in the presence of surfactant is reported here for the first time.

A novel strategy for large-scale synthesis of shape- and size-controlled mesoporous Pt nanospheres (MPNs) through a slow reduction reaction in the presence of surfactant is reported here for the first time. The slow reduction reaction exclusively results in well-defined mesoporous architectures distinctly different from the dendritic constructions reported previously. More importantly, abundant catalytically active sites are created on the highly accessible mesoporous surfaces by the selective adsorption of bromide ions. The MPNs prepared by using the new synthetic route not only show superior electrochemical performance toward methanol oxidation reaction and oxygen reduction reaction, but also exhibit extremely high structural thermostability, which makes them promising catalysts for industrial applications.

Trimetallic PtCuCo hollow nanospheres with a dendritic shell for enhanced electrocatalytic activity toward ethylene glycol electrooxidation

In this work, by utilizing galvanic replacement reaction, a simple method for the synthesis of trimetallic PtCuCo hollow nanospheres with a dendritic shell is demonstrated. The compositions of the nanospheres can be well controlled, and the electrocatalytic activity can also be modulated by adjusting their compositions. Electrocatalytic results show that all of the as-prepared trimetallic PtCuCo nanomaterials show better catalytic performance toward ethylene glycol electrooxidation than the commercial catalyst.

Attachment-based growth: building architecturally defined metal nanocolloids particle by particle

This review highlights the principles and recent mechanistic insight into the synthesis of metal nanostructures using nanoparticles as primary building blocks.

Dendritic Au/Pt and Au/PtCu nanowires with enhanced electrocatalytic activity for methanol electrooxidation

The high-yield synthesis of dendritic Au/Pt and Au/PtCu nanowires is achieved through an effective heterogeneous, epitaxial growth strategy conducted in the water-phase to grow dendritic Pt and PtCu nanoshells on Au nanowires. The synthesized products exhibit excellent electrocatalytic activity towards methanol electrooxidation.

Autocatalysis and selective oxidative etching induced synthesis of platinum-copper bimetallic alloy nanodendrites electrocatalysts

The controllable synthesis of noble metal alloy nanostructures with highly branched morphology has attracted much attention because of their specific physical and chemical properties. This article reports the synthesis of platinum-copper bimetallic alloy nanodendrites (Pt-Cu BANDs) by a facile, one-pot, templateless, and seedless hydrothermal method in the presence of poly(allylamine hydrochloride) (PAH) and formaldehyde (HCHO). The morphology, composition, and structure of Pt-Cu BANDs are fully characterized by various physical techniques, demonstrating Pt-Cu BANDs are highly alloying, porous, and self-supported nanostructures. The formation/growth mechanism of Pt-Cu BANDs is explored and discussed based on the experimental observations. The autocatalytic growth and interdiffusion are responsible for the formation of Pt-Cu alloy whereas selective oxidative etching results in dendritic morphology of Pt-Cu alloy nanostructures. In addition, the electrocatalytic activity and stability of Pt-Cu BANDs for the methanol oxidation reaction (MOR) are investigated by various electrochemical techniques. The synthesized Pt-Cu BANDs show higher electrocatalytic activity and stability than commercially available Pt black.

A universal approach to the preparation of colloidal mesoporous platinum nanoparticles with controlled particle sizes in a wide range from 20 nm to 200 nm

We report a universal method for the preparation of mesoporous Pt nanoparticles with tunable particle sizes by changing the surfactant concentration.

Ultrasensitive electrochemical immunosensors for multiplexed determination using mesoporous platinum nanoparticles as nonenzymatic labels

An ultrasensitive multiplexed immunoassay method was developed at a disposable immunosensor array using mesoporous platinum nanoparticles (M-Pt NPs) as nonenzymatic labels. M-Pt NPs were prepared by ultrasonic method and employed to label the secondary antibody (Ab2) for signal amplification. The immunosensor array was constructed by covalently immobilizing capture antibody (Ab1) on graphene modified screen printed carbon electrodes (SPECs). After the sandwich-type immunoreactions, the M-Pt-Ab2 was bound to immunosensor surface to catalyze the electro-reduction of H2O2 reaction, which produced detectable signals for readout of analytes. Using breast cancer related panel of tumor markers (CA125, CA153 and CEA) as model analytes, this method showed wide linear ranges of over 4 orders of magnitude with the detection limits of 0.002 U mL(-1), 0.001 U mL(-1) and 7.0 pg mL(-1) for CA125, CA153 and CEA, respectively. The disposable immunosensor array possessed excellent clinical value in cancer screening as well as convenient point of care diagnostics.

One-pot synthesis of trimetallic Au@PdPt core-shell nanoparticles with high catalytic performance

The development of an efficient synthesis method to produce multimetallic nanoparticles (NPs) with a desirable structure is strongly required to clarify the structure-composition-property relationship of NPs and to investigate their possible applications. However, the controlled synthesis of NPs consisting of multiple (n ≥ 3) noble metal components has been relatively unexplored in comparison to bimetallic NPs. In the present work, we have demonstrated a facile one-pot aqueous approach for the controlled synthesis of trimetallic Au@PdPt core-shell NPs with a well-defined octahedral Au core and a highly crystalline dendritic Pd-Pt alloy shell (Auoct@PdPt NPs). The simultaneous reduction of multiple metal precursors with dual reducing agents, namely, ascorbic acid and hydrazine, gave a fine control over the nucleation and growth kinetics of NPs, resulting in the formation of novel Auoct@PdPt NPs. The prepared NPs showed excellent catalytic performance for methanol electrooxidation, which can be attributed to their optimized binding strength toward adsorbate molecules due to the improved charge transfer between core and shell of the NPs. The present strategy can offer a convenient and valuable way to fabricate multicomponent nanostructures with desired structures and functions.

Dimethylformamide-mediated synthesis of water-soluble platinum nanodendrites for ethanol oxidation electrocatalysis

Herein we describe the synthesis of water-soluble platinum nanodendrites in dimethylformamide (DMF), in the presence of polyethyleneimine (PEI) as a stabilizing agent. The average size of the dendrites is in the range of 20-25 nm while their porosity can be tuned by modifying the concentration of the metal precursor. Electron tomography revealed different crystalline orientations of nanocrystallites in the nanodendrites and allowed a better understanding of their peculiar branching and porosity. The high surface area of the dendrites (up to 22 m(2) g(-1)) was confirmed by BET measurements, while X-ray diffraction confirmed the abundance of high-index facets in the face-centered-cubic crystal structure of Pt. The prepared nanodendrites exhibit excellent performance in the electrocatalytic oxidation of ethanol in alkaline solution. Sensing, selectivity, cycleability and great tolerance toward poisoning were demonstrated by cyclic voltammetry measurements.

Tailored design of architecturally controlled Pt nanoparticles with huge surface areas toward superior unsupported Pt electrocatalysts

Herein, we report a very simple and rapid method to synthesize two types of Pt nanoparticles with open porous structures (i.e., Pt nanodendrites and multiarmed Pt nanostars) in high yield. The present synthesis is performed by a simple sonication treatment of an aqueous solution containing K2PtCl4 and a nonionic block copolymer with branched alkyl chains in the presence of ascorbic acid (AA) at room temperature. Nanodendrites and multiarmed nanostars with different Pt nanostructures are selectively synthesized by simply controlling the dissolved block copolymer amounts in the reactive system. As-prepared 3D Pt nanodendrites and multiarmed Pt nanostars with well-defined morphologies are highly porous and self-supported structures assembled by staggered nanoarms as building blocks, thereby realizing extremely high surface areas (around 80 m(2) g(-1)). The present synthesis has a remarkable advantage in its simplicity for the synthesis of Pt nanocatalysts, in comparison with other previous approaches. Our Pt nanodendrites and Pt nanostars not only improve the active Pt surface area but also show superior electrochemical performance, which make them promising electrocatalysts for future.