Synthesis and electrocatalytic activity of photoreduced platinum nanoparticles in a poly(ethylenimine) matrix

In situ monitoring of cytoplasmic dopamine levels by noble metals decorated carbon fiber tips

Dopamine (DA), a catecholamine neurotransmitter, is crucial in brain signal transmission. Monitoring cytoplasmic DA levels can reflect changes in metabolic factors and provide valuable information for researching the mechanisms involved in neurodegenerative diseases. However, the in-situ detection of intracellular DA is constrained by its low contents in small-sized single cells. In this work, we report that noble metal (Au, Pt)-modified carbon fiber micro-nanoelectrodes are capable of real-time detection of DA in single cells with excellent sensitivity, selectivity, and anti-contamination capabilities. Notably, noble metals can be modified on the electrode surface through electrochemical deposition to enhance the conductivity of the electrode and the oxidation current of DA by 50 %. The nanosensors can work stably and continuously in rat adrenal pheochromocytoma cells (PC12) to monitor changes in DA levels upon K+ stimulation. The functionalized carbon fibers based nanosensors will provide excellent prospects for DA analysis in the brains of living animals.

Effect of Crystal Growth on the Thermodynamic Stability and Oxygen Reduction Reaction Activity of Cu-Pt Nanoparticles

Thermodynamically stable (ordered) platinum-based bimetallic nanoparticle (NP) catalysts are auspicious candidates for catalyzing the oxygen reduction reaction (ORR) in fuel cells. Although the cubic (L1₂) and tetragonal (L1₀) ordered phases have been extensively studied, very little is known about the cubic (D₇) thermally stable/ordered CuPt₇ with regard to its synthesis at room temperature and ORR activity. The typical synthetic approach to the ordered phase (L1₂ and L1₀) has been by thermal annealing of the disordered phase in an inert atmosphere. We demonstrate that by coordinating Cu²⁺ and Pt⁴⁺ ions to amino groups in aqueous polyethyleneimine (PEI) (precursor solution), slow crystal growth by a UV-light assisted photoreduction can be used to achieve ordered CuPt₇ NPs at room temperature. Slow crystal growth produces a relatively expanded lattice (7.766 Å) of CuPt₇ and a lesser ORR activity via a four-electron transfer pathway. Conversely, fast crystal growth through a NaBH₄ assisted chemical reduction produces a disordered CuPt phase at room temperature and a contracted lattice (3.809 Å) that enhances the ORR activity of CuPt via a two-electron transfer pathway. Our comparative observations of CuPt and CuPt₇ support the observation that lattice contraction is critical in the ORR activity of Cu-Pt nanoalloys.

Synthesis of SDS-Modified Pt/Ti3C2Tx Nanocomposite Catalysts and Electrochemical Performance for Ethanol Oxidation

It is well-known that platinum (Pt) is still the preferred material of anode catalyst in ethanol oxidation, however, the prohibitive high cost and CO poisoning of Pt metal impede the commercialization of fuel cells. Therefore, improving the utilization rate of catalysts and reduce the cost of catalyst become one of the most concerned focus in the construction of fuel cells. In this work, the Pt-based catalysts are synthesized by using different content of sodium dodecyl sulfate (SDS) modified-Ti₃C₂T_x support, and the dispersion regulation function of SDS modified-Ti₃C₂T_x supported on Pt nanoparticles is investigated. The structure, composition and morphology of different catalysts are characterized by X-ray diffraction (XRD), X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and high-resolution TEM, respectively. It is found that the Pt nanoparticles in pure Ti₃C₂T_x surface are serious aggregated and show poor dispersion, whereas the Pt nanoparticles in SDS modified-Ti₃C₂T_x have a better dispersion. The electrochemical results revealed that SDS modified-Ti₃C₂T_x supported Pt nanoparticles has higher electrocatalytic activity and stability in both acidic and alkaline ethanol oxidation when the dosage of SDS increases to 100 mg. These findings indicate that the SDS-Ti₃C₂T_x/Pt catalysts show a promising future of potential applications in fuel cells with modification of Ti₃C₂T_x support.

Molecular stabilization of chemically exfoliated bare MnPS3 layers

Transition metal chalcogenophosphates of general formula MPX₃ have attracted recent interest in the field of 2D materials due to the possibility of tuning their properties upon reaching the 2D limit. Several works address this challenge by dry mechanical exfoliation. However, only a few of them use a scalable approach. In this work, we apply a general chemical protocol to exfoliate MnPS₃. The method employs in the first step chemical intercalation and liquid phase exfoliation and in the second step the addition of molecules used as capping agents on the inorganic layers. Therefore, molecules of different nature prompt the quality of the exfoliated material and its stabilization in an aqueous solution, opening the possibility of using these functionalized layers in several fields. Here we illustrate this possibility in electrochemistry. Thus, we show that when polyethylenimine is used as the capping agent, it is possible to reach a compromise between the stability of high quality MnPS₃ flakes in aqueous suspension and their optimum performance as an electrocatalytic system for HER activity.

Synthesis of FePt Nanoparticles by Photoreduction and Chemical Reduction in Poly(ethyleneimine)

Using poly(ethyleneimine) (PEI) polymer substrates, spherical FePt nanoparticles (NPs) with diameter <10 nm have been synthesized by photoreduction and chemical reduction in aqueous media at room temperature. In the photoreduction approach, PEvI acts as both the template into which the metal ions are coordinated and as a reductant when irradiated by ultraviolet light. In the chemical reduction method, PEI acts as only a template, with NaBH₄ as the reductant. The as-prepared NPs were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometry (VSM). Starting from the same precursor state and relative concentrations, the as-prepared NPs from both methods are spherical, crystalline solid solutions with a chemically disordered face-centered cubic (fcc) structure. The as-prepared NPs from both methods are superparamagnetic with some contribution from a ferromagnetic phase. The photoreduced NPs have broad size distribution of (5 ± 1.0 nm), an expanded lattice (3.913 Å), and relatively lower magnetic moment (0.02 emu/g) compared to the narrower size distribution (4 ± 0.7 nm), shortened lattice (3.890 Å), and a dominant moment (15 emu/g) of the chemically reduced NPs. The difference in the rate of particle formation apparently leads to a low efficiency of FePt NP formation via photoreduction compared to chemical reduction.

New Strategy for High-Performance Integrated Catalysts for Cracking Hydrocarbon Fuels

In this study, we described the synthesis, characterization, and application of hyperbranched polymer-encapsulated metal nanoparticles (HEMNs) as integrated catalysts for the supercritical cracking of hydrocarbon fuels. The metal precursor was extracted into the organic phase using a hydrocarbon-soluble hyperbranched poly(amidoamine) (CPAMAM) and then reduced in situ by NaBH₄ to produce HEMNs with virtually a single-size distribution. The monitoring of the preparation process by UV-vis demonstrated the feasibility of this encapsulation approach, and the successful synthesis of three different types of HEMNs, metal (Pd, Pt, Au)@CPAMAM, reflected the universality of this method. Compared with the existing catalyst octadecylamine-stabilized Pd nanoparticle, Pd@18N, HEMNs were superior in every aspect. The new encapsulation method allowed metal NPs to have a smaller particle size beneficial to their overall specific surface area and a higher proportion of active surface atoms for a better catalytic activity. Moreover, the space-limiting effect of the polymer allowed the three HEMNs to be highly dispersed in decalin and exhibited admirable stability under storage tests for up to 12 months and high-temperature stability tests at 180 °C. During the supercritical cracking of decalin, Pd@CPAMAM possessed a much better catalytic performance than Pd@18N and CPAMAM (which can also be used as a macroinitiator). To obtain the same heat sink of 3.02 MJ/kg, the temperature could be lowered from 725 to 701, 693, and 699 °C for Pd, Pt, and Au HEMNs, respectively. Pt HEMN turned out to be the best due to its excellent catalytic dehydrogenation/cracking performance, with the conversion of decalin increasing from 22.3 to 50.7% and the heat sink rising from 2.18 to 2.62 MJ/kg with the existence of 50 ppm Pt@CPAMAM, at 675 °C. The significant enhancements were ascribed to the synergistic catalysis through the remarkable abilities of nanometals to catalyze dehydrogenation/cracking of fuel, the supercritical stabilization effects from CPAMAM, and the initiation effects of the hyperbranched polymer CPAMAM.

pH Switchable Emulsions Based on Dynamic Covalent Surfactants

Dynamic covalent surfactants were designed to prepare pH switchable emulsions. A dynamic covalent bond between nonamphiphilic building blocks (polyethylenimine (PEI) and benzaldehyde (B)) was introduced to form the dynamic covalent surfactant PEI-B. The dynamic nature of covalent bond in PEI-B was confirmed by ¹H NMR and fluorescence probe analysis. Stable emulsions were successfully prepared with interfacial active PEI-B at pH 7.8 with various water/paraffin oil ratios under sonication. When lowering the pH to 3.5, a complete phase separation was observed as a result of breaking dynamic covalent bond in the interfacial active PEI-B. After tuning the pH back to 7.8, stable emulsion was obtained again due to the reformation of the dynamic covalent bond and hence interfacial active PEI-B. The emulsification and demulsification were dependent on the formation and breaking of dynamic covalent bond in PEI-B. Such pH-triggered emulsification and demulsification can be switched at least three times. Application of dynamic covalent surfactants will open up a novel route for preparing responsive emulsions.

High-yield synthesis of sub-10 nm Pt nanotetrahedra with bare ⟨111⟩ facets for efficient electrocatalytic applications

Unlike other shapes, the design of tetrahedral Pt nanocrystals (Pt-NTd), which have the largest number of Pt(111) surface atoms and highest catalytic activities toward the electron transfer reactions, has widely been considered a synthetic challenge due to their thermodynamic instability. Here, we show that, by inducing their nucleation on functionalized carbon, Pt NTds can be obtained with tunable sizes and high yields. The carbon support anchors the nanocrystals early and prevents their oriented attachment leading to nanowire formation. Therein, an in situ generated amine is crucial for stabilization of Pt-NTds, which can later be removed to expose the Pt(111) facets for higher catalytic efficiency. The bare nanocrystals exhibit much improved stability and electrocatalytic activity characteristic of Pt(111) toward oxygen reduction reaction (ORR) and methanol and formic acid oxidation reactions. For example, ∼90% of their activity was retained after 5000 potential cycles, while the ORR onset potential was recorded to be very high, 1.01 V vs reversible hydrogen electrode (RHE).

Polyvinylpyrrolidone (PVP) in nanoparticle synthesis

The versatile role of PVP in nanoparticle synthesis is discussed in this Perspective article.

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.

Layer-by-layer assembled multilayers of polyethylenimine-stabilized platinum nanoparticles and PEDOT:PSS as anodes for the methanol oxidation reaction

Polyethylenimine-capped platinum nanoparticles (PEI-capped Pt NPs) are synthesized by photoreduction and qualified as a component for electrostatic layer-by-layer assembly and subsequent electrocatalysis. The PEI-capped Pt NPs are characterized for size and charge using scanning force microscopy, transmission electron microscopy, dynamic light scattering and zetapotential. Well-defined multilayers are produced via thin film electrostatic assembly of PEI-capped Pt NPs with the conducting polymer: poly(3,4-ethylenedioxythiophene):poly(p-styrenesulfonate) [(PEDOT:PSS)(-)Na(+)]. The composite thin films are subsequently characterized by ultraviolet-visible spectroscopy, scanning force microscopy, inductively coupled plasma mass spectroscopy and thermogravimetric analysis. The layer-by-layer deposition process was found to proceed in a controlled manner which permits the fabrication of stable and uniform multilayer thin films. [PEI-capped Pt NPs/(PEDOT:PSS)] multilayers were found to be an active catalyst coating for the oxidation of methanol and a 20 bilayer film proceeds with a stable level of catalyst activity for over 1000 oxidation cycles.

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.

Fabrication of nanoporous Cu-Pt(Pd) core/shell structure by galvanic replacement and its application in electrocatalysis

We describe a general strategy to fabricate a new type of nanoporous core/shell structured bimetallic nanocomposites with controllable metal components. Nanoporous copper (NPC) obtained by dealloying Cu/Al alloy is used as both reducing agent and three-dimensional substrate. Electron microscope and X-ray diffraction characterizations demonstrated that a simply galvanic-replacement reaction with H(2)PtCl(6) aqueous solution can easily generate nanoporous core/shell structure with a thin Pt/Cu alloy shell and Cu (or Pt/Cu alloy) core. The morphology and crystal structure evolution of the nanocomposites are studied and discussed in detail. The as-prepared bimetallic PtCu nanocomposites show greatly enhanced catalytic activity and stability toward methanol electro-oxidation as compared with commercial Pt/C catalyst. This facile in situ preparation strategy is also suitable for large-scale production of this novel and inexpensive catalyst.

Strategies for the fabrication of porous platinum electrodes

Porous platinum is of high technological importance due to its various applications in fuel cells, sensors, stimulation electrodes, mechanical actuators and catalysis in general. Based on a discussion of the general principles behind the reduction of platinum salts and corresponding deposition processes this article discusses techniques available for platinum electrode fabrication. The numerous, different strategies available to fabricate platinum electrodes are reviewed and discussed in the context of their tuning parameters, strengths and weaknesses. These strategies comprise bottom-up approaches as well as top-down approaches. In bottom-up approaches nanoparticles are synthesized in a fi rst step by chemical, photochemical or sonochemical means followed by an electrode formation step by e.g. thin fi lm technology or network formation to create a contiguous and conducting solid electrode structure. In top-down approaches fabrication starts with an already conductive electrode substrate. Corresponding strategies enable the fabrication of substrate-based electrodes by e.g. electrodeposition or the fabrication of self-supporting electrodes by dealloying. As a further top-down strategy, this review describes methods to decorate porous metals other than platinum with a surface layer of platinum. This way, fabrication methods not performable with platinum can be applied to the fabrication of platinum electrodes with the special benefit of low platinum consumption.

Electron and phonon transport in Au nanoparticle decorated graphene nanoplatelet nanostructured paper

Monodispersed Au nanoparticles are synthesized on the surface of exfoliated graphene nanoplatelets (GNP) in the presence of polyethyleneimine (PEI) with microwave assisted heating. A highly structured layered Au/GNP "paper" with good flexibility and mechanical robustness is prepared by vacuum assisted self-assembly. The thermal and electrical conductivity of the hybrid paper with and without the Au nanoparticles are investigated after different experimental processing conditions including thermal annealing and cold compaction. Annealing effectively decomposes and removes the adsorbed PEI molecules and improves thermal contact between Au/GNP particles, whereas cold compaction reduces porosity and induces stronger alignment of the Au/GNP within the hybrid paper. Both approaches lead to improvement in electrical and thermal conductivity. It is also found that adjacent GNP particles are electrically connected by the Au nanoparticles but thermally disconnected. It is believed that phonons are scattered at the Au/GNP interfaces, whereas electrons can tunnel across this interface, resulting in a separation of electron and phonon transport within this hybrid paper.

Core-crosslinked compartmentalized cylinders

We present a detailed study on the preparation of compartmentalized cylindrical nanoparticles via a templated approach: the polybutadiene part of a linear polybutadiene-block-poly(2-vinyl pyridine)-block-poly(tert-butyl methacrylate) block terpolymer, B420V280T790, having a bulk microstructure with PB cylinders covered by a P2VP double helix and embedded in a PtBMA matrix was selectively crosslinked. Subsequent sonication-assisted dissolution and chemical modifications such as quaternization (P2VP to P2VPq) and ester hydrolysis (PtBMA to poly(sodium methacrylate), PMANa) resulted in core-crosslinked cylinders soluble in organic and aqueous media. Different amounts of crosslinker and the influence of the sonication treatment on size and shape of the cylindrical aggregates were investigated. The cylinders always exhibit a compartmentalized corona. Under certain conditions, in particular quaternization of P2VP in mixtures of THF and MeOH, the helical arrangement of the P2VPq shell could be preserved even in solution, whereas in most other cases randomly distributed P2VP/P2VPq patches were observed. In aqueous solution at high pH, intramicellar interpolyelectrolyte complex (im-IPEC) formation occurred between the positively charged P2VPq shell and the negatively charged PMANa corona. We further show that different noble metal nanoparticles can be generated either selectively within the im-IPEC compartments (Pd) or randomly distributed among shell and corona of the cylinders (Au and Pt).