Electrocatalytic properties of Cu-Zr amorphous alloy towards the electrochemical hydrogenation of nitrobenzene

The Cu-Zr amorphous alloy was studied as an electrocatalyst towards the electrochemical hydrogenation of nitrobenzene. The electrocatalyst was activated by chemical etching in HF solution. Resulted changes in the morphology, chemical composition and crystalline structure of the electrocatalyst surface were characterised by scanning electron microscopy, X-ray diffraction and Auger electron spectroscopy. The electrocatalytic properties of the Cu-Zr amorphous alloy were assessed by voltammetric measurements. Due to the formation and aggregation of Zr residue modified Cu nanocrystals on the surface caused by the selective dissolution of Zr components in the chemical etching, the activated amorphous alloy is an effective electrocatalyst for the electrochemical reduction reaction of nitrobenzene with aniline as the main product. The positive shift of the peak potential and accompanying increase in the value of peak current in voltammograms with increasing Cu content and decreasing Zr content of the alloy surface in the chemical etching are indicative of improved electrocatalytic activity. (C) 2002 Elsevier Science B.V. All rights reserved.

Remediation of Persistent Organic Pollutants (POPs) in Two Different Soils

Persistent organic pollutants (POPs) are a set of chemicals that are toxic, persist in the environment for long periods of time, and biomagnify as they move up through the food chain. The most widely used method of POP destruction is incineration, which is expensive and could result in undesirable by-products. An alternative bioremediation technology, which is cheaper and environ-mentally friendly, was tested during this experiment. Two different soil types containing high and low organic matter (OM) were spiked with 100 mg/kg each of pyrene and Aroclor 1248 and planted with three different species of grasses. The objective of the study was to determine residue recovery levels (availability) and potential effectiveness of these plant species for the remediation of POPs. The results showed that recovery levels were highly dependent on the soil organic matter content—very low in all treatments with the high OM content soil compared to recoveries in the low OM soil. This indicates that availability, and, hence, biodegradability of the contaminants is dependent on the organic matter content of the soil. Moreover, the degree of availability was also significantly different for the two classes of chemicals. The polyaromatic hydrocarbon (PAH) recovery (availability) was extremely low in the high organic matter content soil compared to that of the polychlorinated biphenyls (PCBs). In both soil types, all of the plant species treatments showed significantly greater PCB biodegradation compared to the unplanted controls. Planting did not have any significant effect on the transformation of the PAHs in both soil types; however, planting with switchgrass was the best remedial option for both soil types contaminated with PCB.

基于SHAW模型的黄土高原半干旱区农田土壤水分动态模拟

黄土高原半干旱区土壤蒸发强烈,准确地掌握土壤水分动态对于旱地农业水分管理至关重要。应用基于物理基础的一维水热耦合SHAW(The Simultaneous Heat and Water)模型,模拟了陕西子洲岔巴沟流域1964~1967年土壤水分和土壤蒸发的动态特征,以及神木六道沟流域2006年坡地和梯田土壤水分变化。结果表明,除表层土壤水分模拟结果偏差较大,其他土层模拟值与实测值基本吻合,模拟期土壤水分模拟的相对平均绝对误差(Relatively Mean Absolutely Error,RMAE)为5.2%~11.4%。1964~1967年土壤累积蒸发量模拟值与实测值平均相对偏差为0.8%~6.1%,土壤蒸发的模拟值与实测值较为一致。因此,SHAW模型可以用于黄土高原半干旱区农田土壤水分动态规律研究。

应用Vc发酵弃渣防治保护地病害

The prevention and control of tomato plant diseases were conducted in protective ground using Vc fermentation waste residue treated by enzymolysis and ultrasonic wave. The results showed that the seedlings planted for 3 weeks on the protective ground soil continuously cropped tomato plant for 9 years and fertilized 75, 150 and 300 kg·hm -2 grew well. Their biomass were increased by 123%, 164% and 182%, and the disease incidence rates were decreased by 59%, 78% and 85%, respectively. Under application of 300 kg·hm -2 Vc fermentation waste residue, the products of tomato grown for 10 weeks on the soil continuously cropped tomato plant for 9, 6 and 2 years were increased by 60%, 43% and 14%, respectively, and the disease incidence rates were all decreased by 50%.

Macroporous Pt modified glassy carbon electrode: preparation and electrocatalytic activity for methanol oxidation

Three-dimensional (3D) macroporous Pt (MPPt) with highly open porous walls has been successfully synthesized using the hydrogen bubble dynamic template synthesis and galvanic replacement reaction. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods were adopted to characterize their structures and properties.

A general method for the rapid synthesis of hollow metallic or bimetallic nanoelectrocatalysts with urchinlike morphology

We have reported a facile and general method for the rapid synthesis of hollow nanostructures with urchinlike morphology. In-situ produced Ag nanoparticles can be used as sacrificial templates to rapidly synthesize diverse hollow urchinlike metallic or bimetallic (such as Au/Pt) nanostructures. It has been found that heating the solution at 100 degrees C during the galvanic replacement is very necessary for obtaining urchinlike nanostructures. Through changing the molar ratios of Ag to Pt, the wall thickness of hollow nanospheres can be easily controlled; through changing the diameter of Ag nanoparticles, the size of cavity of hollow nanospheres can be facilely controlled; through changing the morphologies of Ag nanostructures from nanoparticle to nanowire, hollow Pt nanotubes can be easily designed. This one-pot approach can be extended to synthesize other hollow nanospheres such as Pd, Pd/Pt, Au/Pd, and Au/Pt. The features of this technique are that it is facile, quick, economical, and versatile.

Electrochemical corrosion behavior of Mg-5Al-0.4Mn-xNd in NaCl solution

The electrochemical corrosion behavior of Mg-5Al-0.4Mn-xNd (x = 0, 1, 2 and 4 wt.%) alloys in 3.5% NaCl solution was investigated. The corrosion behavior of the alloys was assessed by open circuit potential measure, potentiodynamic polarization, and electrochemical impedance spectroscopy. The electrochemical results show the intermetallic precipitates with Nd behave as less noble cathodes in micro-galvanic corrosion and suppress the cathodic process. During corrosion, Al2O3 and Nd2O3, in proper ratio, is incorporated into the corrosion film, and enhances the corrosion resistance.

Novel Hybrid Electrocatalyst with Enhanced Performance in Alkaline Media: Hollow Au/Pd Core/Shell Nanostructures with a Raspberry Surface

In this paper, a hollow Au/Pd core/shell nanostructure with a raspberry surface was developed for methanol, ethanol, and formic acid oxidation in alkaline media. The results showed that it possessed better electrocatalyst performance than hollow Au nanospheres or Pd nanoparticles. The nanostructure was fabricated via a two-step method. Hollow Au nanospheres were first synthesized by a galvanic replacement reaction, and then they were coated with a layer of Pd grains. Several characterizations such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) were used to investigate the prepared nanostructures.

Large-Scale and Template-Free Growth of Free-Standing Single-Crystalline Dendritic Ag/Pd Alloy Nanostructure Arrays

Large-scale arrays consist of dendritic single-crystalline Ag/Pd alloy nanostructures are synthesized for the first time. A simple galvanic replacement reaction is introduced to grow these arrays directly on Ag substrates. The morphology of the products strongly depended on the reaction temperature and the concentration of H2PdCl4 solution. The mechanism of the formation of alloy and the dendritic morphology has been discussed. These alloy arrays exhibit high surface-enhanced Raman scattering (SERS) activity and may have potential applications in investigation of "in situ" Pd catalytic reactions using SERS. Moreover, electrocatalytic measurements suggest that the obtained dendritic Ag/Pd alloy nanostructures exhibit electrocatytic activity toward the oxidation of formic acid.

High-efficiency and low-cost hybrid nanomaterial as enhancing electrocatalyst: Spongelike AWN core/shell nanomaterial with hollow cavity

A high-efficiency and low-cost spongelike Au/Pt core/shell electrocatalyst with hollow cavity has been facilely obtained via a simple two-step wet chemical process. Hollow gold nanospheres were first synthesized via a modified galvanic replacement reaction between Co nanoparticles in situ produced and HAUCl(4). The as-prepared gold hollow spheres were employed as seeds to further grow spongelike Pt shell. It is found that the surface of this hybrid nanomaterial owns many Pt nanospikes, which form a spongelike nanostructure. All experimental data including scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis-near-infrared spectroscopy have been employed to characterize the obtained Au/Pt hybrid nanomaterial. The rapid development of fuel cell has inspired us to investigate the electrocatalytic properties for dioxygen and methanol of this novel hybrid nanomaterial. Spongelike hybrid nanomaterial mentioned here exhibits much higher catalytic activity for dioxygen reduction and methanol oxidation than the common Pt electrode.

Investigation of heptakis(2,6-di-O-methyl)-beta-cyclodextrin inclusion complexes with flavonoid glycosides by electrospray ionization mass spectrometry

The non-covalent complexes between three flavonoid glycosides (quercitrin, hyperoside and rutin) and heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DM-beta-CD) were investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS). The 1:1 complexation of each flavonoid glycoside (guest) to the DM-beta-CD (host) was monitored in the negative ion mode by mixing each guest with an up to 30-fold molar excess of the host. The binding constants for all complexes were calculated by a linear equation in the order: DM-beta-CD:quercitrin > DM-beta-CD:rutin > DM-beta-CD:hyperoside. A binding model for the complexes has also been proposed based on the binding constants and tandem mass spectrometric data of these complexes.

Analysis of norditerpenoid alkalods in processing Radix Aconiti Lateralis preparata with Radix Glycyrrhizae Preparata by electrospray ionization tandem mass spectrometry

Norditerpenoid alkaloids in the processing of Radix aconiti lateralis preparata with Radix glycyrrhizae preparata was studied by electrospray ionization tandem mass spectrometry. A method of ESI-MS couple with internal standard was applied for semi quantitative analysis of norditerpenoid alkaloids before and after processing. The combined-decoction-to single-decoction-ratios of the relative abundance of toxic hypaconitine, mesaconitine and aconitine were 5. 67%, 4. 05% and 4. 88%, respectively. The chemical changes of processing can been comprehensive observed by ESI-MS/MS analysis. The scientific basis of reducing the toxicity of Radix aconiti lateralis preparata with Radix glycyrrhizae preparata was enlightened by compareing with the single-decotion, the combined-decoction and residue for the compatibility of Radix aconiti lateralis preparata and Radix glycyrrhizae preparata.

Time-dependent DNA condensation induced by amyloid beta-peptide

The major protein component of the amyloid deposition in Alzheimer's disease is a 39-43 residue peptide, amyloid beta (A beta). A beta is toxic to neurons, although the mechanism of neurodegeneration is uncertain. Evidence exists for non-B DNA conformation in the hippocampus of Alzheimer's disease brains, and A beta was reportedly able to transform DNA conformation in vitro. In this study, we found that DNA conformation was altered in the presence of A beta, and A beta induced DNA condensation in a time-dependent manner. Furthermore, A beta sheets, serving as condensation nuclei, were crucial for DNA condensation, and Cu2+ and Zn2+ ions inhibited A beta sheet-induced DNA condensation. Our results suggest DNA condensation as a mechanism of A beta toxicity.

Polyaniline for corrosion prevention of mild steel coupled with copper

Polyaniline emeraldine base/epoxy resin (EB/ER) coating was investigated for corrosion protection of mild steel coupled with copper in 3.5% NaCl solution. EB/ER coating with 5-10 wt% EB had long-term corrosion resistance on both uncoupled steel and copper due to the passivation effect of EB on the metal surfaces. During the 150 immersion days, the impedance at 0.1 Hz for the coating increased in the first 1-40 days and subsequently remained constant above 10(9) Omega cm(2), whereas that for pure ER coating fell below 10(6) Omega cm(2) after only 30 or 40 days. Immersion tests on coated steel-copper galvanic couple showed that EB/ER coating offered 100 times more protection than ER coating against steel dissolution and coating delamination on copper, which was mainly attributed to the passive metal oxide films formed by EB blocking both the anodic and cathodic reactions. Salt spray tests showed that 100 mu m EB/ER coating protected steel-copper couple for at least 2000 h.