Facile synthesis of a porous network-like silver film for electrocatalytic detection of nitrate

We have developed a method for in-situ construction of a porous network-like silver film on the surface of a glassy carbon electrode (GCE). It is based on a galvanic replacement reaction where a layer of copper nanoparticles is first electrodeposited as a sacrificial template. The silver film formed possesses a porous network-like structure and consists of an assembly of numerous nanoparticles with an average size of 200 nm. The electrode displays excellent electrocatalytic activity, good stability, and fast response (within 2 s) toward the reduction of nitrate at a working potential of −0.9 V. The catalytic currents linearly increase with the nitrate concentrations in the range of 0.08–6.52 mM, with a detection limit of 3.5 μM (S/N = 3) and a repeatability of 3.4 % (n = 5).

A facile method was developed for in situ construction of a porous network-like Ag film on a glassy carbon electrode by a galvanic replacement reaction, where a layer of Cu nanoparticles previously electrodeposited as a sacrificial template. Thus-formed Ag film displays excellent electrocatalytic activity, good stability, and fast response (within 2 s) toward nitrate reduction.

     

Facile synthesis of biomass-derived hierarchical porous carbon microbeads for supercapacitors

Using the facile method of solvent evaporation, the leonardite fulvic acids (LFA)-based porous carbon microbeads (PCM) have been successfully prepared at ambient pressure, followed by carbonization and KOH activation (a low mass ratio alkali/LFA = 1.5) in an inert atmosphere. The effects of KOH treatment on pore structures and the formation mechanism of the PCM were discussed. The results showed that the sample exhibited remarkable improvement in textural properties. The activated carbon microbeads had high surface area (2269 m² g^?1), large pore volume (1.97 cm³ g^?1), and displayed excellent capacitive performances, compared with carbon powder. The porous carbon material electrodes with the “porous core structure” behaved superiorly at a specific capacitance of 320 F g^?1 at a current density of 0.05 A g^?1 in 6 M KOH electrolyte, which could still remain 193 F g^?1 when the current density increased to 100 A g^?1. Remarkably, in the 1 M TEABF₄/PC electrolyte, the PCM samples could reach 156 F g^?1 at 0.05 A g^?1, possess an outstanding energy density of 39.50 Wh kg^?1, and maintain at 22.05 Wh kg^?1 even when the power density rose up to 5880 W kg^?1. The balance of structural characteristic and high performance makes the porous carbon microbeads a competitive and promising supercapacitor electrode material.     

Hydrogen evolution assisted deposition of a three-dimensional porous nickel film for the electrocatalytic oxidation of histamine

Microchimica Acta - The authors describe an electrochemical sensor for ultrasensitive voltammetric of histamine (HA) by using a gold electrode that was modified with a film consisting of...     

Facile method for synthesis of hollow porous magnetic microspheres with controllable structure

Hollow porous magnetic microspheres with strong magnetization and controllable structure were prepared via a facile electrostatic self-assembly of the positively charged Fe(3)O(4) nanoparticles onto the surface of the negatively charged poly(N,N'-methylenebisacrylamide-co-methacrylic acid) (P(MBAAm-co-MAA)) microspheres with subsequent removal of the polymer core through calcination at high temperature. The shell thickness was facilely tuned through the ratio between Fe(3)O(4) and polymer, and the void space was conveniently changed through the size of polymer microspheres. The hollow magnetic microspheres possessed high saturation magnetization value (51.38 emu/g) and porous structure with high specific surface area (108.04 m(2)/g). Based on these properties, the drug loading and release behaviors were investigated, which indicated that the hollow magnetic microspheres exhibited a controlled release process.     

Facile synthesis of silver core - silica shell composite nanoparticles

Combining metal nanoparticles and dielectrics (e.g. silica) to produce composite materials with high dielectric constant is motivated by application in energy storage. Control over dielectric properties and their uniformity throughout the composite material is best accomplished if the composite is comprised of metal core - dielectric shell structured nanoparticles with tunable dimensions. We have synthesized silver nanoparticles in the range of 40-100nm average size using low concentration of saccharide simultaneously as the reducing agent and electrostatic stabilizer. Coating these silver particles with silica from tetraalkoxysilanes has different outcomes depending on the alcoholic solvent and the silver particle concentration. A common issue in solution-based synthesis of core-shell particles is heterogeneous nucleation whereupon two populations are formed: the desired core-shell particles and undesired coreless particles of the shell material. We report the formation of Ag@SiO(2) core-shell particles without coreless silica particles as the byproduct in 2-propanol. In ethanol, it depends on the silver surface area available whether homogeneous nucleation of silica on silver is achieved. In methanol and 1-butanol, core-shell particles did not form. This demonstrates the significance of controlling the tetraalkoxysilane hydrolysis rate when growing silica shells on silver nanoparticles.     

Facile synthesis of silver nanoparticles useful for fabrication of high-conductivity elements for printed electronics

A facile synthesis of stable silver nanoparticles having a particle size of <10 nm is described. The synthesis involved reduction of silver acetate with a substituted hydrazine, such as PhNHNH2, in the presence of a 1-alkylamine, such as C16H33NH2, in toluene at 25-60 degrees C. Spin-coated thin films or printed electronic features of alkylamine-stabilized silver nanoparticles could be easily converted at 120-160 degrees C into highly conductive films or elements with conductivity of 2-4 x 104 S cm-1. Organic thin-film transistors with printed silver source/drain electrodes of this nature exhibited field-effect transistor properties which are similar to those of the devices using vacuum-deposited silver electrodes.     

Boron-iron nanochains for selective electrocatalytic reduction of nitrate

The electrocatalysis of nitrate reduction reaction(NRR) has been considered to be a promising nitrate removal technology.Developing a highly effective iron-based electrocatalyst is an essential challenge for NRR.Herein,boron-iron nanochains(B-Fe NCs) as efficient NRR catalysts were prepared via a facile lowcost and scalable method.The Fe/B ratio of the B-Fe NCs-x can be elaborately adjusted to optimize the NRR catalytic performance.Due to the electron transfer from boron to metal,the metal-metal bonds are weakened and the electron density near the metal atom centers are rearranged,which are favor of the conversion from NO_3~-into N_2.Moreover,the well-crosslinked chain-like architectures benefit the mass/electron transport to boost the exposure of abundant catalytic active sites.Laboratory experiments demonstrated that the optimized B-Fe NCs catalyst exhibits superior intrinsic electrocatalytic NRR activity of high nitrate conversion(～80%),ultrahigh nitrogen selectivity(～99%) and excellent long-term reactivity in the mixed electrolyte system(0.02 mol/L NaCl and 0.02 mol/L Na_2 SO_4 mixed electrolyte),and the electrocatalytic activity of the material shows poor performance at low chloride ion concentration(Nitrate conversion of ～61 % and nitrogen selectivity of ～57% in 0.005 mol/L NaCl and 0.035 mol/L Na_2 SO_4 mixed electrolyte).This study provides a broad application prospect for further exploring the highefficiency and low-cost iron-based functional nanostructures for electrocatalytic nitrate reduction.     

Facile synthesis and catalytic property of porous tin dioxide nanostructures

Porous tin dioxide (SnO(2)) nanostructures consisting of nanoplates are prepared through thermal decomposition of the mixed solution composed of dibutyltin dilaurate and acetic acid. The aggregations of the nanoplates give rise to large macropores with the size of about 100-300 nm. These nanoplates have a wormhole-like porous structure with the size of about 4 nm and possess high surface area. X-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, infrared spectroscopy, and nitrogen sorption have been employed to characterize the obtained porous structures. It is found that the obtained nanostructures exhibit excellent catalytic activity toward methanol decomposition. Such porous structures with high surface area have promising industrial applications as catalysts.     

Comparison of nanostructured silver-modified silver and carbon ultramicroelectrodes for electrochemical detection of nitrate

We report the use of silver (Ag)-modified carbon and Ag ultramicroelectrodes (UMEs) for electrochemical detection of nitrate. We investigated several methods for electrodeposition of Ag; our results show that the addition of a complexation agent (ammonium sulfate) in the Ag deposition solution is necessary for electrodeposition of nanostructured Ag that adheres well to the electrode. The electrodeposited Ag on both types of electrodes has branch-like structures that are well-suited for electrocatalytic reduction of nitrate. The use of UMEs is advantageous; the sigmoidal-shaped cyclic voltammogram allows for sensitive detection of nitrate by reducing the capacitive current, as well as enabling easy quantification of the nitrate reduction current. Both cyclic voltammetry and chronoamperometry were used to characterize the electrodes; and independent of the electrochemical interrogation technique, both UMEs were found to have a wide linear dynamic range (4–1000 μM) and a low limit of detection (3.2–5.1 μM). More importantly, they are reusable up to ∼100 interrogation cycles and are selective enough to be used for direct detection of nitrate in a synthetic aquifer sample without any sample pretreatment and/or pH adjustment.     

Facile synthesis of silver nano particles with highly efficient anti-microbial property

A simple surfactant assisted aqueous solution approach, based on the conventional Tollen’s reaction has been applied for the facile syntheses of silver nano-assembly. Nano particle morphologies strongly depend on the temperature adopted during the synthesis. Two-dimensional (2 D) nano-disks and three-dimensional (3D) nano-globules with “Cauliflower” like morphology were observed. The unique and distinctive feature of the synthesized silver nano particle in solution is its very high anti-microbial activity. This is evident in very low (4 μg/ml) inhibitory concentration (MIC) value for Escherichia coli, Vibrio cholerae, Shigella flexneri, Salmonella typhimurium and three varieties of Staphylococcus aureus. This low MIC value is comparable to that of Penicillin and in the cases of E. coli and S. aureus (ML 422), the MIC value is as low as 2 μg/ml which beats even Penicillin.     

A study on the direct electrochemistry and electrocatalysis of microperoxidase-11 immobilized on a porous network-like gold film: Sensing of hydrogen peroxide

We have prepared porous and network-like nanofilms of gold by galvanic replacement of a layer of copper particles acting as a template. The films were first characterized by scanning electron microscopy and X-ray diffraction, and then modified with cysteamine so to enable the covalent immobilization of the enzyme microperoxidase-11. The immobilized enzyme undergoes direct electron transfer to the underlying electrodes, and the electrode displays high electrocatalytic activity towards the reduction of oxygen and hydrogen peroxide, respectively, owing to the largely enhanced electroactive surface of the porous gold film. The detection limit of H₂O₂ is 0.4 μM (3 S/N).

Facile synthesis of ultra-long Cu microdendrites for the electrochemical detection of glucose

Ultra-long Cu microdendrites (MDs) were prepared by one-step electrodeposition on a glassy carbon electrode. The results demonstrated that the reduction potential, pH, and temperature of the electrolysis solution, as well as the amount of Cu²⁺ and citrate ions, play important roles in the formation of the Cu MDs. Notably, the X-ray diffraction experiments confirmed that the aggregations of the Cu nanocrystals preferred to grow along (111) direction. In addition, the resulting Cu MDs-modified electrode showed good electrochemical performance as a non-enzyme glucose sensor in alkaline media.     

Facile synthesis and photoelectrochemical performance of the bush-like ZnO nanosheets film

Bush-like ZnO nanosheets film is fabricated on conductive transparent oxide substrates using a facile hydrothermal method without any surfactant or further heat treatment. The morphology, structure and photoluminescence property of the products are characterized in detail. The ZnO nanosheets are composed of numerous grains with the 5 nm average diameter, and most of the sheets present the relative uniform arrangement. These nanosheets construct a porous network which is favorable for the photoelectrochemical properties and applications in dye-sensitized solar cells. The photoelectrochemical performances of the bush-like ZnO nanosheets film are investigated, and a high open-circuit voltage of 0.69 V is achieved.     

Facile synthesis of thick ordered mesoporous TiO2 film for dye-sensitized solar cell use

Crack-free thick ordered mesoporous TiO₂ films with excellent optical quality have been synthesized by combination of “Doctor Blade” technique and a two-step evaporation induced self-assembly (EISA) method. By employing the as-synthesized mesoporous film with the thickness of 7 μm as the photoanode in dye-sensitized solar cell (DSC), a solar conversion efficiency of 6.53% has been obtained at 30 mW cm⁻² light intensity.     

Facile synthesis of porous MnO/C nanotubes as a high capacity anode material for lithium ion batteries

Porous MnO/C nanotubes are synthesized by a facile hydrothermal method followed by thermal annealing, and possess excellent cyclability and high rate capability as an anode for lithium ion batteries.     

Effects of gold nanoparticle and electrode surface properties on electrocatalytic silver deposition for electrochemical DNA hybridization detection

In this paper we report the catalytic effects of various gold nanoparticles for silver electrodeposition on indium tin oxide (ITO)-based electrodes, and successfully apply this methodology for signal amplification of the hybridization assay. The most widely used gold nanoparticle-based hybridization indicators all promote silver electrodeposition on the bare ITO electrodes, with decreasing catalytic capability in order of 10 nm gold, DNA probe-10 nm gold conjugate, streptavidin-5 nm gold, and streptavidin-10 nm gold. Of greater importance, these electrocatalytic characteristics are affected by any surface modifications of the electrode surfaces. This is illustrated by coating the ITO with an electroconducting polymer, poly(2-aminobenzoic acid)(PABA), as well as avidin molecules, which are promising immobilization platforms for DNA biosensors. The catalytic silver electrodeposition of the gold nanoparticles on the PABA-coated ITO surfaces resembles that on the bare surfaces. With avidin covalently bound to the PABA, it is interesting to note that the changes in electrocatalytic performance vary for different types of gold nanoparticles. For the streptavidin-5 nm gold, the silver electrodeposition profile is unaffected by the presence of the avidin layer, whereas for both the 10 nm Au and DNA probe-10 nm gold conjugate, the deposition profiles are suppressed. The streptavidin-5 nm gold is employed as the hybridization indicator, with avidin-modified (via PABA) ITO electrode as the immobilization platform, to enable signal amplification by the silver electrodeposition process. Under the conditions, this detection strategy offers a signal-to-noise ratio of 20. We believe that this protocol has great potential for simple, reproducible, highly selective and sensitive DNA detection on fully integrated microdevices in clinical diagnostics and environmental monitoring applications.     

用于高性能钠离子电容器的高氮掺杂多孔碳纳米纤维的简易合成

选择合适的生物质材料是获得功能碳材料的有效途径之一。通过柠檬酸钾和三聚氰胺一步热解法制备高氮掺杂多孔碳纳米纤维(NPCF)。在电流密度为0.1和1.0 A·g^-1时,NPCF电极的容量分别为218和140 mAh·g^-1。同时,具有NPCF阳极的钠离子电容器(SIC)在1.0 A·g^-1下表现出优异的倍率性能和超长的使用寿命,可循环超过2 500次。