Highly efficient generation of H2O2 at composite polyaniline/heteropolyanion electrodes: effect of heteropolyanion structure on H2O2 yield

A new highly efficient electrochemical H₂O₂ generating system based on polyaniline film doped with heteropolytungstate anions was developed. The oxygen reduction characteristics of polyaniline–heteropolytungstate composites were investigated using the rotating disk–ring electrode technique. Polyaniline electrode with immobilized heteropolytungstate anions of the Dawson structure (P₂W₁₈O₆₂⁶⁻) exhibits a 75% efficiency of H₂O₂ generation in the acid medium while polyaniline doped with heteropolytungstate anions of the Keggin structure (PW₁₂O₄₀³⁻) reduces O₂ predominantly by four electrons. It was established that the chemosorption of H₂O₂ during the reduction of O₂ governs the efficiency of hydrogen peroxide generation.     

One‐pot synthesis of polyaniline doped with transition metal ions using H2O2 as oxidant

Polyanilines (PANIs) doped with Zn²⁺ and Cu²⁺ were synthesized by H₂O₂ oxidative polymerization of aniline in the presence of corresponding metal chloride in solution. The products were characterized by elemental analysis, UV‐Vis‐NIR, FTIR and Raman spectroscopies. Scanning electron micrograph was employed to examine the morphology of PANIs fabricated in the presence of different transition metals. Experimental results showed that transition metal ions had been successfully incorporated into the polymer, and there was a strong interaction between the transition metal ions and the PANI chains. The electrical conductivity of PANI doped with Zn²⁺ and Cu²⁺ is 0.37 and 0.21 S/cm, respectively, which is higher than that of HCl doping PANI corresponding to 0.052 S/cm. The cyclic voltammetric study has indicated that incorporation of metal ions in PANI backbone results in increasing of specific capacitance compared to that of HCl doping PANI. Copyright © 2014 John Wiley & Sons, Ltd.     

H2O nucleation around Au+

First principles electronic structure calculations have been carried out to investigate the ground state geometry, electronic structure, and the binding energy of [Au(H2O)n]+ clusters containing up to 10 H2O molecules. It is shown that the first coordination shell of Au+ contains two H2O molecules forming a H2O-Au+-H2O structure with C2 symmetry. Subsequent H2O molecules bind to the previous H2O molecules forming stable and fairly rigid rings, each composed of 4 H2O molecules, and leading to a dumbbell structure at [Au(H2O)8]+. The 9th and the 10th H2O molecules occupy locations above the Au+ cation mainly bonded to one H2O from each ring, leading to structures where the side rings are partially distorted and forming structures that resemble droplet formation around the Au+ cation. The investigations highlight quantum effects in nucleation at small sizes and provide a microscopic understanding of the observed incremental binding energy deduced from collision induced dissociation that indicates that [Au(H2O)n]+ clusters with 7-10 H2O molecules have comparable binding energy. The charge on the Au+ is shown to migrate to the outside H2O molecules, suggesting an interesting screening phenomenon.     

Synthesis of aqueous Au core-Ag shell nanoparticles using tyrosine as a pH-dependent reducing agent and assembling phase-transferred silver nanoparticles at the air-water interface

We demonstrate that the amino acid tyrosine is an excellent reducing agent under alkaline conditions and may be used to reduce Ag+ ions to synthesize stable silver nanoparticles in water. The tyrosine-reduced silver nanoparticles may be separated out as a powder that is readily redispersible in water. The silver ion reduction at high pH occurs due to ionization of the phenolic group in tyrosine that is then capable of reducing Ag+ ions and is in turn converted to a semi-quinone structure. These silver nanoparticles can easily be transferred to chloroform containing the cationic surfactant octadecylamine by an electrostatic complexation process. The now hydrophobic silver nanoparticles may be spread on the surface of water and assembled into highly ordered, linear superstructures that could be transferred as multilayers onto suitable supports by the versatile Langmuir-Blodgett technique. Further, tyrosine molecules bound to the surface of Au nanoparticles through amine groups in the amino acid may be used to selectively reduce silver ions at high pH on the surface of the Au nanoparticles, thus leading to a simple strategy for realizing phase-pure Au core-Ag shell nanostructures.     

Synthesis of thiol-capped gold nanoparticle with a flow system using organosilane as a reducing agent

Synthesis of thiol-capped gold nanoparticle is carried out by mixing of a THF solution of HAuCl₄·4H₂O and ⁿC₁₂H₂₅SH with a THF solution of triethylsilane in a flow system that consists of polytetrafluoroethylene tubing. The effect of residence time and reaction temperature on the particle size is examined.     

Synthesis of polyaniline/Au composite nanotubes and their high performance in the detection of NADH

Polyaniline (PANI)/Au composite nanotubes were synthesized and developed as an electrode material for a nicotinamide adenine dinucleotide (NADH) sensor. A MnO₂ self-degradable template method was used to prepare the tube-like PANI nanomaterial. By introducing PANI nanotubes into Au colloid, Au nanoparticles (NPs) were successfully decorated onto the surface of PANI nanotubes through electrostatic effects. The morphology, composition, and optical properties of the resulting products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-vis) absorption spectra, and thermogravimetric analysis (TGA). In addition, the obtained PANI/Au composites were used as catalysts for the electrochemical oxidation of NADH. Cyclic voltammogram (CV) experiments indicated that PANI/Au-modified glassy carbon electrode showed a higher electrocatalytic activity towards the oxidation of NADH in a neutral environment. Differential pulse voltammogram (DPV) results illustrated that the fabricated NADH sensor had excellent anti-interference ability and displayed a wide linear range from 4?×?10^?4 to 8?×?10^?3 M with a detection limit of 0.5?×?10^?7 M.     

Preparation and photoelectrochemical characterization of nano-particulate TiO2 and polyaniline composite films on Au

TiO₂ and polyaniline(PANI) composite film was obtained by electrochemical methods^[1] and investigated for solar energy conversion application. A strong rectifying effect was found in the cyclic voltammogram of the film in dark when the scan speed was slow enough (5 mV/s) and a quasi-reversible voltammogram of the film was observed when the scan speed was fast (100 mV/s). The results of both the cyclic voltammograms and the SEM images of the composite film show that the PANI film is almost completely covered with nano-particulate TiO₂. Two anodic photocurrent bands and a cathodic band was observed in the spectra of the photocurrent of the TiO₂/PANI/PATP(p-aminothiophenol)/Au film in 0.05 mol/L Fe(CN)₆^3-/Fe(CN)₆^4- solution. The band at 300~400 nm (3.1~4.1 eV) can be ascribed to the photocurrent band of TiO₂ particles and the bands at 450~730 nm (1.7~2.8 eV) can be ascribed to those of the PANI. The partially-oxidized PANI has internal photoemission function and the insulating matrix of PANI is verified to be reduced PANI with a 3.33 eV bandgap energy. The flat-band potentials of partially-oxidized PANI and TiO₂/PANI composite film in 1.0 mol/LHClO₄ solution are determined as 0.87 V and 0.09(SHE) from Mott-Schottky plots, respectively.     

Precipitation of dispersed silver particles using acetone as reducing agent

A novel environmentally friendly solution-based method for preparing dispersed silver particles is described. The simple and convenient approach consists in heating silver oxide particles dispersed in a highly alkaline water/acetone mixture. The data presented clearly show that acetone reduces completely and rapidly Ag(2)O particles to metallic silver at 60°C. A mechanism explaining the provenance of the electrons responsible for the reduction of silver is proposed.     

Synthesis and characterization of conductive polyaniline/TiO2 composite nanofibers

Fibrillar conductive polyaniline/TiO₂ (PANI/TiO₂) nanocomposites with different TiO₂ amount were synthesized with a template-free in situ polymerization method and characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and conductivity measurement. The morphology determination shows that the PANI/TiO₂ composite nanofibers are relatively uniform with the diameter and length in the range of 20–40 nm and 390–420 nm respectively. It also shows that the TiO₂ of the composite is rutile crystalline and PANI has some degree of crystallinity. The IR measurement indicates that there is a strong interaction between the PANI and TiO₂ nanoparticles, and it has a beneficial effect on the thermal stability of the composite nanofiber. The conductivity of PANI/TiO₂ composites changes with TiO₂ amount and reaches an optimum value of 2.86 S/cm at 11.1 wt% TiO₂. Translated from Journal of Northwest Normal University (Natural Science), 2006, 42(4): 67–70 (in Chinese)     

ChemInform Abstract: H2O Nucleation Around Au+

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Some aspects of metal-support strong interactions in Rh/Al2O3 catalyst under oxidising and reducing conditions

The aim of the Letter is to elucidate the nature of metal-support interaction in the 2 wt% Rh/Al₂O₃ catalyst obtained by annealing Rh–O–Al xerogel at 1113 K in air.XPS, HRTEM, and XRD results reveal that during the Rh–O–Al xerogel annealing in air, rhodium incorporates into forming alumina, which results mostly in Rh⁴⁺/δ-Al₂O₃ solid solution formation.However, in the course of the catalyst reduction at 773 with H₂ and at 823 K with CH₄ the Rh⁴⁺/δ-Al₂O₃ solid solution transforms into Rh–Al alloy. The islands of rhodium form on the surface of the Rh–Al alloy nanocrystallites if the reduction is slow enough.     

Direct Synthesis of H2O2 by a H2/O2 Fuel Cell

Direct synthesis of H₂O₂ solutions by a fuel cell method was reviewed. The fuel cell reactor of [O₂, gas-diffusion cathode electrolyte solutions Nafion membrane electrolyte solutions gas-diffusion anode, H₂] is very effective for formation of H₂O₂. The three-phase boundary (O₂(g)–electrode(s)–electrolyte(l)) in the gas-diffusion cathode is essential for efficient formation of H₂O₂. Fast diffusion processes of O₂ to the active surface and of H₂O₂ to the bulk electrolyte solutions are essential for H₂O₂ accumulation. The maxima H₂O₂ concentrations of 1.2 M (3.5 wt%) and 2.4 M (7.0 wt%) were accomplished by the heat-treated Mn-OEP/AC electrocatalyst with H₂SO₄ electrolyte and by the VGCF electrocatalyst with NaOH electrolyte, respectively, under short circuit conditions.     

Preparation of Superconducting Na(x)(H2O)yCoO2 using NaMnO4 as the deintercalation and oxidation agent

We have used aqueous NaMnO4 solution as the deintercalation and oxidation agent to treat gamma-Na0.7CoO2 powders and to successfully obtain superconducting sodium cobalt oxyhydrates, Nax(H2O)yCoO2, with onset Tc approximately 4.6 K without using highly toxic Br2/CH3CN solution. Chemical analyses indicate that the sodium content x decreases with increasing concentration of NaMnO4 solution and depends slightly on the immersion time. Unlike using a high concentration of aqueous KMnO4 as the deintercalation and oxidation agent, all the hydrated products are the c approximately 19.6 A phase with bilayers of water molecules intercalated between the CoO2 layers and sodium layers because of the absence of K+ in the Na+ layers.     

Au／TS-1@Mesosilica双功能催化材料的制备及其催化丙烯直接环氧化性能

设计制备了一种新型微孔介孔复合核壳结构钛硅分子筛TS-1@Mesosilica（TS-l@Ms）,核为MFI结构钛硅分子筛TS-1,壳层为以非离子表面活性剂P123为模板剂组装形成的介孔氧化硅．壳层氧化硅具有三维蠕虫状孔道结构,有利于微孔和介孔部分的连通及反应物和产物的扩散．通过沉积沉淀法将金纳米粒子负载在壳层介孔孔道,和TS-1中的钛活性中心协同,形成适合于C3H6和H2、O2直接气相环氧化制备环氧丙烷（PO）的双功能催化材料．实验结果表明,Au／TS-1@MS在空速8000mLg-h、温度473K条件下连续反应132h,活性和选择性没有明显下降,丙烯转化率保持在3．7％左右,PO选择性87％以上．     

Biological synthesis of silver and gold nanoparticles using apiin as reducing agent

We report a novel strategy for the biological synthesis of anisotropic gold and quasi-spherical silver nanoparticles by using apiin as the reducing and stabilizing agent. The size and shape of the nanoparticles can be controlled by varying the ratio of metal salts to apiin compound in the reaction medium. The resultant nanoparticles were characterized by UV-vis-NIR, transmission electron microscopy (TEM), FT-IR spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The interaction between nanoparticles with carbonyl group of apiin compound was confirmed by using FT-IR analysis. TEM photograph confirming the average size of the gold and silver nanoparticles were found to be at 21 and 39 nm. The NIR absorption of the gold nanotriangles is expected to be of application in hyperthermia of cancer cells and in IR-absorbing optical coatings.     

金纳米棒的表面改性及与H_2O_2的作用

通过调控过氧化氢与金纳米棒相互作用时溶液的H~+和Br~-浓度,考察了过氧化氢刻蚀金纳米棒的条件.通过静电相互作用将聚苯乙烯磺酸钠修饰到带正电的金纳米棒表面,并探讨了表面配体变化对过氧化氢与金纳米棒相互作用的影响,比较了聚苯乙烯磺酸钠浓度改变对过氧化氢刻蚀金纳米棒所引起的等离子体吸收峰的变化.结果表明,过氧化氢与金纳米棒作用过程中,H~+浓度增加可以加快刻蚀反应速率,Br~-起到稳定金离子的作用.采用聚苯乙烯磺酸钠修饰抑制了过氧化氢对金纳米棒的刻蚀,当聚苯乙烯磺酸钠与金纳米棒表面的CTAB完全作用后,复合材料电位接近零,金纳米棒的稳定性降低,继续增加聚苯乙烯磺酸钠的量至电位为负,复合材料稳定性增加.     

Skin Bond Electron Relaxation Dynamics of Germanium Manipulated by Interactions with H2, O2, H2O,H2O2, HF,and Au

Although germanium performs amazingly well at sites surrounding hetero‐coordinated impurities and under‐coordinated defects or skins with unusual properties, having important impact on electronic and optical devices, understanding the behavior of the local bonds and electrons at such sites remains a great challenge. Here we show that a combination of density functional theory calculations, zone‐resolved X‐ray photoelectron spectroscopy, and bond order length strength correlation mechanism has enabled us to clarify the physical origin of the Ge 3d core‐level shift for the under‐coordinated (111) and (100) skin with and without hetero‐coordinated H₂, O₂, H₂O, H₂O₂, HF impurities. The Ge 3d level shifts from 27.579 (for an isolated atom) by 1.381 to 28.960 eV upon bulk formation. Atomic under‐coordination shifts the binding energy further to 29.823 eV for the (001) and to 29.713 eV for the (111) monolayer skin. Addition of O₂, HF, H₂O, H₂O₂ and Au impurities results in quantum entrapment by different amounts, but H adsorption leads to polarization.     

Novel ZnO-Al2O3 composite particles as sorbent for low temperature H2S removal

ZnO-Al₂O₃ composite particles composed of ZnO nanosheets（thickness of 40-80 nm） on alumina particles were prepared by heterogeneous precipitation method using bayerite seed particles.The asprepared composite particles were characterized in terms of crystal structure,morphology,surface area and pore volume.The composite particles were used as sorbent for H₂S adsorption at low temperature, and were compared with pure ZnO sorbent.The composite sorbent showed a greater sulfur adsorption capacity（0.052 g/g） than pure form of ZnO（0.028 g/g）.This significant improvement was mainly attributed to higher surface area,more pore volume and unique morphology in nanoscale,which were also obtained by low cost presented method in this work for synthesis of ZnO sorbent supported on alumina particles.     

Use of t-butyllithium as a reducing agent

Details of the first reported use of an alkyllithium reagent for the reduction of a CO bond are presented.