Synthesis of Platinum and Tin Oxide Co‐functionalized Single‐walled Carbon Nanotubes (Pt/SnO2/SWNTs) and their Sensing Properties toward Carbon Monoxide

Pt and SnO₂ were co‐functionalized on single‐walled carbon nanotubes (SWNTs) assembled on microelectrodes by electrochemical deposition where Pt nanoparticle's morphology, size, and density were tuned by controlling the applied potential and time. The systematic study to obtain the optimum condition for Pt‐decorated SnO₂/SWNTs (Pt/SnO₂/SWNTs) were performed and also correlate with its CO sensing performance. Illumination‐dependent sensing performance was examined using red, green and UV LED as light sources at room temperature. Under UV illumination, the sensitivity of Pt/SnO₂/SWNTs was enhanced to 2.1 %/ppm_V of CO with the lower detection limit of 0.05 ppm_V.     

Self‐Assembly of Platinum Nanoparticle/Multiwalled Carbon Nanotube Multilayer Film on Au Substrate Electrode

A novel approach to assemble multilayer films of Pt nanoparticle/multiwalled carbon nanotube (MWNTs) composites on Au substrate has been developed for the purpose of improving the methanol oxidation efficiency by providing high catalytic surface area. MWNTs were firstly functionalized with 4‐mercaptobenzene and then assembled on an Au substrate electrode. Pt nanoparticles were fabricated and attached to the surface of the functionalized MWNTs subsequently. Thus a layer of Pt/MWNT composites were assembled on the Au substrate electrode. Repeating above process can assemble different layers of film of Pt/MWNTs composites on the Au electrode. Cyclic voltammetry shows that the Au electrode modified with two layers of film of Pt/MWNT composites exhibits high catalytic ability and long‐term stability for methanol oxidation. The layer‐by‐layer self‐assembly technique provides an efficient strategy to construct complex nanostructure for improving the methanol oxidation efficiency by providing high catalytic surface area.     

A Non‐Enzymatic Hydrogen Peroxide Sensor Based on Gold Nanoparticles/Carbon Nanotube/Self‐Doped Polyaniline Hollow Spheres

In this study, a novel non‐enzymatic hydrogen peroxide (H₂O₂) sensor was fabricated based on gold nanoparticles/carbon nanotube/self‐doped polyaniline (AuNPs/CNTs/SPAN) hollow spheres modified glassy carbon electrode (GCE). SPAN was in‐site polymerized on the surface of SiO₂ template, then AuNPs and CNTs were decorated by electrostatic absorption via poly(diallyldimethylammonium chloride). After the SiO₂ cores were removed, hollow AuNPs/CNTs/SPAN spheres were obtained and characterized by transmission electron microscopy (TEM), field‐emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). The electrochemical catalytic performance of the hollow AuNPs/CNTs/SPAN/GCE for H₂O₂ detection was evaluated by cyclic voltammetry (CV) and chronoamperometry. Using chronoamperometric method at a constant potential of ?0.1 V (vs. SCE), the H₂O₂ sensor displays two linear ranges: one from 5 µM to 0.225 mM with a sensitivity of 499.82 µA mM^?1 cm^?2; another from 0.225 mM to 8.825 mM with a sensitivity of 152.29 µA mM^?1 cm^?2. The detection limit was estimated as 0.4 µM (signal‐to‐noise ratio of 3). The hollow AuNPs/CNTs/SPAN/GCE also demonstrated excellent stability and selectivity against interferences from other electroactive species. The sensor was further applied to determine H₂O₂ in disinfectant real samples.     

Controlled synthesis of monodisperse sub-100 nm hollow SnO2 nanospheres: a template- and surfactant-free solution-phase route, the growth mechanism, optical properties, and application as a photocatalyst

Controlled synthesis of low‐dimensional materials, such as nanoparticles, nanorods, and hollow nanospheres, is vitally important for achieving desired properties and fabricating functional devices. We report a systematic investigation of the growth of low‐dimensional sub‐100 nm SnO₂ hollow nanostructures by a mild template‐ and surfactant‐free hydrothermal route, aiming to achieve precise control of morphology and size. The starting materials are potassium stannate and urea in an ethylene glycol (EG)/H₂O system. We found the size of the SnO₂ hollow nanospheres can be controlled by simply adjusting the urea concentration. Investigation of the mechanism of formation of the SnO₂ hollow nanospheres revealed that reaction time, urea concentration, and reaction temperature make significant contributions to the growth of hollow nanospheres. On switching the solvent from EG/H₂O to H₂O or ethanol, the SnO₂ nanostructures changed from nanospheres to ultrafine nanorods and nanoparticles. On the basis of reaction parameter dependent experiments, oriented self‐assembly and subsequent evacuation through Ostwald ripening are proposed to explain the formation of hollow nanostructures. Their size‐dependent optical properties, including UV/Vis absorption spectra and room‐temperature fluorescence spectra, were also studied. Moreover, the studies on the photocatalytic property demonstrate that the fabricated hollow structures have slightly enhanced photocatalytic degradation activity for rhodamine B when exposed to mercury light irradiation compared to solid SnO₂ nanospheres under the same conditions. The synthesized tin oxide nanoparticles display high photocatalytic efficiency and have potential applications for cleaning polluted water in the textile industry.     

Synthesis and Characterization of Gold‐Nanoparticle‐Cored Dendrimers Stabilized by Metal–Carbon Bonds

Synthesis and characterization of gold‐nanoparticle‐cored dendrimers (NCDs), in which the dendrons are attached to the gold core through gold–carbon bonds, are described. Synthesis of these materials involved the simultaneous reduction of HAuCl₄ and a Fréchet‐type dendron with a diazonium group at the focal point, all in an organic solvent such as toluene. These materials possess a nanometer‐sized gold core surrounded by a shell of polyaryl ether dendrons, which are connected radially to the core. The NCDs were characterized by TEM, thermogravimetric analysis (TGA), and IR, UV, and NMR spectroscopic techniques. Average particle diameter of the NCDs ranged from 4.7 to 5.5 nm for the different generations. All NCDs exhibit the characteristic plasmon absorption of gold nanoparticles at 520 nm. Average numbers of dendrons per NCD in AuG_n were calculated using results from TGA and TEM studies. Multiple layering of the dendrons is proposed as a possible reason for the high dendron/NCD value.     

Synthesis of Heterocyclic Compounds Catalyzed by Metal/Metal Oxide‐Multiwall Carbon Nanotube Nanocomposites

Metal/metal oxide‐decorated multiwalled carbon nanotubes (MWCNTs ) have been found to be effective over various catalysts because of the synergistic, hybrid, physical, and chemical properties of such nanotubes. These properties make them highly active catalytic tools with excellent chemoselectivity, low catalyst loading, and high recyclability of the catalyst. Here, we discuss some recent findings related to the following topics: (1) synthesis of metal/metal oxide‐decorated MWCNTs , (2) characterization techniques of heterogeneous nanocomposites, and (3) application of these metal/metal oxide nanocomposites for the synthesis of heterocyclic compounds. This review emphasizes the main requirements for developing new nanocomposites for the synthesis of pharmaceutically important heterocycles.     

Colloid‐Assisted Self‐Assembly of Robust,Three‐Dimensional Networks of Carbon Nanotubes over Large Areas

Natural materials, such as bone and spider silk, possess remarkable properties as a result of sophisticated nanoscale structuring. They have inspired the design of synthetic materials whose structure at the nanoscale is carefully engineered or where nanoparticles, such as rods or wires, are self‐assembled. Although much work has been done in recent years to create ordered structures using diblock copolymers and template‐assisted assembly, no reports describe highly ordered, three‐dimensional nanotube arrays within a polymeric material. There are only reports of two‐dimensional network structures and structures on micrometer‐size scales. Here, we describe an approach that uses plasticized colloidal particles as a template for the self‐assembly of carbon nanotubes (CNTs) into ordered, three‐dimensional networks. The nanocomposites can be strained by over 200% and still retain high conductivity when relaxed. The method is potentially general and so may find applications in areas such as sensing, photonics, and functional composites.

     

贵金属纳米颗粒在玻碳电极上的层层组装

采用表面活性剂二辛酯琥珀酸磺酸钠(AOT, sodiumbis(2-ethylhexyl)sulfosuccinate)微乳法可以制备得到各种贵金属纳米颗粒(包括银、金、铂以及钯),其性质利用紫外-可见吸收光谱、透射电镜、X-射线衍射、傅立叶变换红外光谱以及Zeta电位分析进行了表征。通过层层自组装方法,将带有负电荷的Pt纳米颗粒和聚阳离子(聚烯丙基氯化铵, PAH)自组装到玻碳电极上,并研究了该修饰电极对甲醇的电催化氧化性质。     

Densely Packed,Ultra Small SnO Nanoparticles for Enhanced Activity and Selectivity in Electrochemical CO2 Reduction

Controlling the selectivity in electrochemical CO₂ reduction is an unsolved challenge. While tin (Sn) has emerged as a promising non‐precious catalyst for CO₂ electroreduction, most Sn‐based catalysts produce formate as the major product, which is less desirable than CO in terms of separation and further use. Tin monoxide (SnO) nanoparticles supported on carbon black were synthesized and assembled and their application in CO₂ reduction was studied. Remarkably high selectivity and partial current densities for CO formation were obtained using these SnO nanoparticles compared to other Sn catalysts. The high activity is attributed to the ultra‐small size of the nanoparticles (2.6 nm), while the high selectivity is attributed to a local pH effect arising from the dense packing of nanoparticles in the conductive carbon black matrix.     

Metallopolymer–Peptide Hybrid Materials: Synthesis and Self‐Assembly of Functional,Polyferrocenylsilane–Tetrapeptide Conjugates

Conjugates of poly(ferrocenyldimethylsilane) (PFDMS) with Ac‐(GA)₂‐OH, Ac‐A₄‐OH, Ac‐G₄‐OH and Ac‐V₄‐OH have been prepared by reaction of the tetrapeptide units with the amino‐terminated metallopolymer. The number average degree of polymerisation (DP_n) of the PFDMS was approximately 20 and comparable materials with shorter (DP_n≈10) and/or amorphous chains have been prepared by the same procedure. Poly(ferrocenylethylmethylsilane) (PFEMS) was employed for the latter purpose. All conjugates were characterised by GPC, MALDI‐TOF MS, NMR and IR spectroscopy. With the exception of Ac‐V₄‐PFDMS₂₀, all materials exhibited some anti‐parallel β‐sheet structure in the solid state. The self‐assembly of the conjugates was studied in toluene by DLS. The vast majority of the materials, irrespective of peptide sequence or chain crystallinity, afforded fibres consisting of a peptidic core surrounded by a PFS corona. These fibres were found in the form of cross‐linked networks by TEM and AFM. The accessibility of the chemically reducing PFS corona has been demonstrated by the localised formation of silver nanoparticles on the surface of the fibres.     

A Polypyrrole‐Imprinted Electrochemical Sensor Based on Nano‐SnO2/Multiwalled Carbon Nanotubes Film Modified Carbon Electrode for the Determination of Oleanolic Acid

A sensitive molecularly imprinted electrochemical sensor with specific recognition ability for oleanolic acid was synthesized by modification of multiwalled carbon nanotubes (MWNTs) decorated with tin oxide nanoparticles (nano‐SnO₂/MWNTs) and polypyrrole‐imprinted polymer on a carbon electrode. The morphology and electrochemical performance of the imprinted sensor were investigated by using scanning electron microscope (SEM), X‐ray diffraction (XRD), cyclic voltammetry (CV), linear sweep voltammetry (LSV) and amperometric i–t curve. The results showed that the imprinted sensor displayed excellent selectivity toward oleanolic acid. A linear relationship between the response currents and oleanolic acid concentrations ranging from 5.0×10^?8 g/L to 2.0×10^?5 g/L was obtained for the imprinted sensor. The limit of detection (LOD) of the imprinted sensor toward oleanolic acid was calculated as 8.6×10^?9 g/L at a signal to noise ratio (S/N) of 3. This imprinted sensor was successfully applied to the determination of oleanolic acid in Acitinidia deliciosa root samples.     

Palladium Sub‐Nanoparticle Decorated ‘Bamboo’ Multi‐Walled Carbon Nanotubes Exhibit Electrochemical Metastability: Voltammetric Sensing in Otherwise Inaccessible pH Ranges

A generic approach for the detection of electroactive species in potential ranges that would normally be inhibited due to the stripping of the electrocatalytic material is presented. We demonstrate, via the example of the electrochemical oxidation of hydrazine, that palladium nanoparticle (< 1 nm) decorated bamboo multi‐walled carbon nanotubes exhibit a metastability such that they allow the sensing of hydrazine in the pH range where palladium metal would normally be voltammetrically stripped (oxidized) from the surface of convectional electrodes.     

Kilogram‐Scale Production of SnO2 Yolk–Shell Powders by a Spray‐Drying Process Using Dextrin as Carbon Source and Drying Additive

A simple and general method for the large‐scale production of yolk–shell powders with various compositions by a spray‐drying process is reported. Metal salt/dextrin composite powders with a spherical and dense structure were obtained by spray drying and transformed into yolk–shell powders by simple combustion in air. Dextrin plays a key role in the preparation of precursor powders for fabricating yolk–shell powders by spray drying. Droplets containing metal salts and dextrin show good drying characteristics even in a severe environment of high humidity. Sucrose, glucose, and polyvinylpyrrolidone are widely used as carbon sources in the preparation of metal oxide/carbon composite powders; however, they are not appropriate for large‐scale spray‐drying processes because of their caramelization properties and adherence to the surface of the spray dryer. SnO₂ yolk–shell powders were studied as the first target material in the spray‐drying process. Combustion of tin oxalate/dextrin composite powders at 600 °C in air produced single‐shelled SnO₂ yolk–shell powders with the configuration SnO₂@void@SnO₂. The SnO₂ yolk–shell powders prepared by the simple spray‐drying process showed superior electrochemical properties, even at high current densities. The discharge capacities of the SnO₂ yolk–shell powders at a current density of 2000 mA g^?1 were 645 and 570 mA h g^?1 for the second and 100th cycles, respectively; the corresponding capacity retention measured for the second cycle was 88 %.     

Formation and Properties of Self‐Assembly‐Driven Fluorescent Nanoparticle Sensors

Fluorescent nanoparticles (FNPs) are obtained in water by self‐assembly from a polymeric ionic liquid, fluorescent carboxylate moiety, and a surfactant through two main supramolecular interactions, that is, ionic bonds and hydrophobic/hydrophilic interactions. The hydrophobicity of the surfactant is tunable and a highly hydrophobic surfactant increases the fluorescence intensity and stability of the FNPs. The fluorescence of the FNPs is sensitive to a quenching effect by various ions with high selectivity, and consequently, they may be used as sensors. The self‐assembly approach used to generate the FNPs is considerably simpler than other methods based on more challenging synthetic methods and the flexibility of the approach should allow a wide and diverse range of FNPs to be prepared with specific sensor applications.     

Metal‐Folded Single‐Chain Nanoparticle: Nanoclusters and Self‐Assembled Reduction‐Responsive Sub‐5‐nm Discrete Subdomains

Easy access to discrete nanoclusters in metal‐folded single‐chain nanoparticles (metal‐SCNPs) and independent ultrafine sudomains in the assemblies via coordination‐driven self‐assembly of hydrophilic copolymer containing 9% imidazole groups is reported herein. ¹H NMR, dynamic light scattering, and NMR diffusion‐ordered spectroscopy results demonstrate self‐assembly into metal‐SCNPs (>70% imidazole‐units folded) by neutralization in the presence of Cu(II) in water to pH 4.6. Further neutralization induces self‐assembly of metal‐SCNPs (pH 4.6–5.0) and shrinkage (pH 5.0–5.6), with concurrent restraining residual imidazole motifs and hydrophilic segment, which organized into constant nanoparticles over pH 5.6–7.5. Atomic force microscopy results evidence discrete 1.2 nm nanoclusters and sub‐5‐nm subdomains in metal‐SCNP and assembled nanoparticle. Reduction of metal center using sodium ascorbate induces structural rearrangement to one order lower than the precursor. Enzyme mimic catalysis required media‐tunable discrete ultrafine interiors in metal‐SCNPs and assemblies have hence been achieved.