Structural relationship between random copolyimides and their carbon fibers

A series of polyimide (PI) fibers synthesized from pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) were prepared by a two-step wet-spinning process. The prepared PI fibers were then carbonized with the increasing temperatures up to 1500 °C under a high-purity nitrogen atmosphere. The effects of ODA/p-PDA molar ratios on the chemical structure, microstructure, chain orientation, and structural evolutions of the PI fibers were systematically investigated. The elemental composition, morphology, and aggregation structure after carbonization were also analyzed. The results showed that different chemical compositions have greatly influenced the aggregation structures of the resulting PI and carbon fibers. The PI fibers showed increased crystallinity and orientation degree with the decreased ODA moieties, while the corresponding PI-based carbon fibers (CFs) exhibited perfect graphitic structures. The CFs derived from PMDA/p-PDA PI backbone with flat chains exhibited a well-defined graphite structure with d ₀₀₂ of 0.349 nm and I _D/I _G of 1.442. In addition, the carbon yield of the prepared PI-based carbon fibers reached more than 95 %.     

Comparative analysis of the factors associated with citation and media coverage of clinical research

Our objective was to study the relationship between the design and content of randomized clinical trials (RCTs) and the subsequent number of citations in the medical literature and attention in online news and social media. We studied RCTs published during 2014 in five highly cited medical journals. This was a retrospective review focusing on characteristics of the individual trials and measures of citation and lay media attention. Primary outcome measures included citation count and Altmetric^® scores (a composite score measuring attention in news, blogs, Twitter^®, and Facebook^®). Two hundred and forty two RCTs were included in the final analysis. Trial characteristics that were positive predictors of citation count included investigation of Hepatitis C treatment (r = 0.35, p < 0.001), private funding (r = 0.24, p < 0.001), mortality-related endpoint (r = 0.22, p < 0.001), and research setting within the United States (r = 0.13, p < 0.001). The trial characteristic that positively predicted Altmetric score was the population size potentially affected (r = 0.39, p < 0.001). The only negative predictor of citation count was the size of the population potentially affected (r = ?0.21, p < 0.001). Negative predictors of the Altmetric score included investigation of Hepatitis C treatment (r = ?0.21, p < 0.001) and private funding (r = ?0.13, p < 0.001). While correlation magnitudes were weak, the predictors of biomedical literature citation and non-academic media coverage were different. These predictors may affect editorial decisions and, given the rising influence of health journalism, further study is warranted.     

Exergo-economic analysis of a 1-MW biomass-based combined cycle plant with externally fired gas turbine cycle and supercritical organic Rankine cycle

This paper deals with exergo-economic modeling and analysis of a 1-MW biomass integrated gasification combined cycle plant that couples an indirectly heated gas turbine (GT) cycle with a supercritical organic Rankine cycle (ORC). The GT produces a fixed net output of 500 kWe, and the organic vapor turbine produces the rest. Saw dust is considered as biomass feed for the gasifier, and toluene acts as ORC working fluid. GT cycle working fluid is heated through a combined combustor-heat exchanger (CHX) unit. Effects of plant parameters, viz. compressor pressure ratio (r _p), gas turbine inlet temperature (TIT) and cold end temperature difference (CETD) of the CHX unit on the thermodynamic and economic performance of the plant are reported. Energy efficiency is maximized at a fixed value of r _p (=6), for all TITs. Higher TIT yields in higher efficiency of the plant. Although increase in CETD lowers the plant efficiency but decreases the size of CHX unit, resulting in the lower capital cost of the unit. Exergo-economic analysis reveals that unit product cost (UPC) is lower at higher TITs and higher r _p values. Levelized unit cost of electricity (LUCE) is also minimized at r _p = 6 for all TITs. Higher TIT also yields lower UPC and LUCE values. Both UPC and LUCE decrease with increase in CETD. For r _p = 6, TIT = 1100 °C and CETD = 300 °C, the plant offers minimum UPC and LUCE values.     

Graphene quantum dots-assisted exfoliation of graphitic carbon nitride to prepare metal-free zero-dimensional/two-dimensional composite photocatalysts

The high aspect-ratio morphology of two-dimensional (2D) nanostructures endues them with distinct advantages for photocatalytic or photoelectrical applications. Although various attempts have been devoted to the liquid exfoliation of graphitic carbon nitride (g-C₃N₄) to obtain ultrathin nanosheets (CNNSs), the high exfoliation efficiency, well preservation of in-planar structure and facile operation cannot be simultaneously realized. Furthermore, functionalization of CNNSs is highly desired to promote the capability of photoabsorption, charge separation and transfer. Herein, we one-step prepared well-dispersed graphene quantum dots (GQDs)-modified CNNSs (GQDs/CNNSs) colloids via a facile and efficient GQDs-assisted exfoliation approach in a normal ultrasonic water bath. The exfoliation procedure was optimized by tuning the dopant in GQDs, ultrasonic time and GQDs dosage. The obtained colloidal GQDs/CNNSs show a typical 2D morphology with lateral size of several 100 nm and ultrathin thickness of 1.5–1.8 nm. What is more, we can tailor the semiconductive behavior of GQDs by heteroatom doping and achieve a p–n-type P-doped GQDs-modified CNNSs colloids. This p–n GQDs/CNNSs material presents the enhanced separation efficiency of photoexcited carriers and photocatalytic activity in comparison with bulky g-C₃N₄ (CN) and other CNNSs materials from acid or alkali exfoliation.     

Effect of hydration on microstructure and property of anodized oxide film for aluminum electrolytic capacitor

Etched aluminum foil for aluminum electrolytic capacitor was first boiled in water for different time to form hydrous film on Al foil and then anodized in H₃BO₄ solution at 530 V to form anodic oxide barrier film as insulating dielectric layer. The obtained films were characterized by field-emission scanning electron microscopy, transmission electron microscope and X-ray diffraction for surface morphology, microstructure and crystallinity examination. Small-current charging, LCR meter and electrochemical impedance spectroscopy were exploited to measure the propertied of the anodized oxide film such as withstanding voltage (U_w), specific resistance (R_ox) and specific capacitance (C_s and C_ox) for its electrochemical performance. The results show that the hydrous film is pseudoboehmite (PB) with a dense inner layer and a fibrous outer layer. The crystallinity of the PB film increases with hydration time. During anodization, the PB film was transformed into anodic oxide (γ′-Al₂O₃) barrier film. Prolonging hydration time promotes transformating PB into γ′-Al₂O₃ and improves the crystallinity of the barrier film, leading to increase in C_s and C_ox and decrease in R_ox and U_w.     

A comparative study of lignocellulosic ethanol productivities by <Emphasis Type="Italic">Kluyveromyces marxianus</Emphasis> and <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

The yeast Saccharomyces cerevisiae is commonly employed in industrial ethanol production, regardless of the capability of Kluyveromyces marxianus strains to produce ethanol at similar or higher levels and on inhibitory conditions. Therefore, in this work strains of S. cerevisiae (ethanol RED and AR5) and K. marxianus (SLP1 and OFF1) were compared for ethanol production from sugarcane bagasse (SCB) and wheat straw (WS) hydrolysates. As it is known, during the lignocellulosic hydrolysis not only free sugars were obtained (SCB, g L^?1: glucose 7.64, xylose 8.38, arabinose 2.43; and WS, g L^?1: glucose 6.07, xylose 6.36, arabinose 2.09) but also growth inhibitors of yeast such as hydroxymethylfurfural and furfural that could modify the fermentation capability. The volumetric ethanol productivity (Q _p) was evaluated, and it was observed that the K. marxianus SLP1 was the most efficient for ethanol production reaching a Q _p of 0.292 and 0.250 g L^?1 h^?1 on SCB and WS hydrolysates, respectively. In contrast, S. cerevisiae AR5 and ethanol RED exhibited a reduced Q _p on SCB, but similar values of Q _p to K. marxianus OFF1 on WS. The results obtained show that it is possible to select K. marxianus yeast strains for ethanol production using SCB and WS hydrolysates obtaining higher Q _p than S. cerevisiae yeast strains. Considering the efficiency of ethanol production and the tolerance to inhibitors, K. marxianus strain SLP1 possesses a great potential as an industrial yeast for lignocellulosic ethanol production.     

One-step synthesis of fluorescent silver nanoparticles with modulated emission wavelength using <Emphasis Type="Italic">oligo</Emphasis>-polyarylene ether nitrile as surface capping agent

It is well-known that the photonic properties of silver nanoparticles are strongly dependent on their sizes, and the photoluminescence is traditionally detected from the silver nanoparticles with ultra-small sizes <2 nm, which are also named as silver nanoclusters. In this work, a facile one-step protocol for synthesis of fluorescent silver nanoparticles with much larger size in the range of 20–70 nm was reported, where the fluorescent polyarylene ether nitrile (PEN) oligomers with different backbone structures were employed as the surface capping agents. It was found that the silver nanoparticles stabilized with PEN oligomer containing both carboxylic and sulfonic side groups (oligo-PEN/CS) exhibited much stronger luminescence when compared to those capped with carboxylated PEN oligomer (oligo-PEN/C). Furthermore, the fluorescence emission wavelength of obtained Ag nanoparticles can be modulated from 490 nm to 600 nm by simply changing the reaction time of silver ions reduction via oligo-PEN/CS at 70 °C in N,N-dimethylformamide (DMF). Based on their tailorable luminescence, the synthesized silver nanoparticles could find potential applications in biochemical sensing and advanced optical devices.     

Impact of Ni dopant on structure and electrical properties of PMN-0.1PT ceramics

The Ni-doped PMN-0.1PT (PMN-0.1PT-xNi) relaxor ferroelectric ceramics were prepared by two-step columbite precursor method, and the effects of Ni dopant on the phase structure, dielectric, ferroelectric and electrostrictive properties were systematically investigated. The introduction of Ni dopant significantly improved the densification and grains size in the ceramics, but also profoundly modified the phase structure. It demonstrated that the substitution of Ni dopant for B-site in PMN-0.1PT lattice could affect electrical properties of PMN-0.1PT binary ceramics. Properly increasing the amount of Ni dopant led to the enhancement of dielectric and ferroelectric and remarkably increased the electrostrictive response. Results in this study indicated that at a composition x of 2.0 mol%, a large strain response could be obtained with maximum strain as high as 0.11% under the low field of 15 kV/mm at room temperature.     

Oscillating cylinder in viscous fluid: calculation of flow patterns and forces

Laminar and large-eddy-simulation (LES) calculations with the dynamic Smagorinsky model evaluate the flow and force on an oscillating cylinder of diameter D = 2R in otherwise calm fluid, for β = D ²/νT in the range 197–61400 and Keulegan–Carpenter number K = U _m T/D in the range 0.5–8 (ν kinematic viscosity, T oscillation period, U _m maximal velocity). Calculations resolving the streakline patterns of the Honji instability exemplify the local flow structures in the cylinder boundary layer (β ~ 197–300, K ~ 2) but show that the drag and inertia force are not affected by the instability. The present force calculations conform with the classical Stokes–Wang solution for all cases below flow separation corresponding to K < 2 (with β < 61400). The LES calculations of flow separation and vortical flow resolve the flow physics containing a large range of motion scales; it is shown that the energy in the temporal turbulent fluctuations (in fixed points) are resolved. Accurate calculation of the flow separation occurring for K > 2 has strong implication for the force on the cylinder. Present calculations of the force coefficients for K up to 4 and β = 11240 are in agreement with experiments by Otter (Appl Ocean Res 12:153–155, 1990). Drag coeffients when flow separation occurs are smaller than found in U-tube experiments. Inertia coefficients show strong decline for large K (up to 8) and moderate β = 1035 but is close to unity for K = 4 and β = 11240. The finest grid has 2.2 × 10⁶ cells, finest radial Δr/R = 0.0002, number of points along the cylinder circumference of 180, Δz/R = 0.044 and a time step of 0.0005T.     

Shock compression of Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>100−<Emphasis Type="Italic">x</Emphasis></Subscript> metallic glasses from molecular dynamics simulations

The shock response of Cu _x Zr_100?x (x = 30, 50 and 70) metallic glasses (MGs) is characterized using large-scale molecular dynamics simulations. A wide range of piston velocities U _p = 0.125–2.5 km/s are simulated corresponding to shock pressures from 3 to 130 GPa. Independent of composition, the metallic glasses exhibit the following shock wave propagation regimes: (1) single elastic shock wave for U _p < 0.25 km/s, (2) split elastic and plastic shock waves for 0.25 < U _p < 0.75 km/s and (3) overdriven plastic shock wave with a narrow elastic precursor for U _p > 0.75 km/s. Within the split wave and overdriven regimes, the amplitude of the elastic precursor increases with increasing shock intensity, thereby indicating a pressure-dependent yield criterion. Hugoniot states are strongly dependent on the Cu content of the MG with Cu₇₀Zr₃₀ exhibiting a much higher resistance to plastic deformation than either Cu₅₀Zr₅₀ or Cu₃₀Zr₇₀.     

Effect of inter-electrode spacing on structural and electrical properties of RF sputtered AlN films

An attempt has been made to correlate the morphological and electrical properties of RF sputtered aluminum nitride (AlN), with target to substrate distance (D _ts) in sputter chamber. AlN films, having thickness around 3,000 Å, were deposited on silicon substrates with different D _ts values varying from 5 to 8 cm. XRD results indicated that the crystallinity of c-axis oriented films increase significantly with decrease in D _ts and the FTIR absorption band of the films became prominent at shorter D _ts. The surface roughness increased from 1.85 to 2.45 nm with that in D _ts. A smooth surface with smaller grains was found at shorter D _ts. The capacitance–voltage (C–V) measurements revealed that the insulator charge density (Q _in) increased from 3.3 × 10¹¹  to 7.3 × 10¹¹ cm^?2 and the interface state density (D _it) from 1.5 × 10¹¹  to 7.3 × 10¹¹ eV^?1cm^?2 with the increase in D _ts.     

Mapping farm animal welfare research in an enlarged Europe: international collaboration,bibliometric output,research resources and relation to economic indices

Against the background of divergent political developments across Europe, farm animal welfare (FAW) science has evolved during the last three decades as an inter-disciplinary research area. Recent achievements include pan-European research projects and the implementation of animal welfare assessment systems on-farm. The aim of this study was mapping activities for FAW science and investigating geographical differences in FAW research in Europe (EU28 + candidate countries and the European Economic Area) with regard to available resources (e.g. human resources, infrastructure, funding) and research output (e.g. collaborations and publications). Further, we enquired if economic attributes such as the Coefficient of National Innovation Capacity (NIC) were associated with the reported available resources and research output factors (publications and collaborations) of FAW research. Based on questionnaires sent out to a wide researcher network in regions of an enlarged Europe, we found differences with regard to ‘input factors’ such as human resources, animal and laboratory facilities and national and international research funding and ‘output factors’ such as inter/national collaboration, participation in EU-funded projects related to FAW and number of publications. Respondents were allocated to 4 Western and 4 Eastern geographical clusters of countries (‘hubs’). There were a larger number of researchers, students and technical staff per laboratory in Western compared to Eastern hubs. A pronounced difference was found for funding, as 35% of respondents in the Eastern hubs stated that they lack funded FAW projects compared to 4% in the West. In general, respondents from the Western hubs stated significantly more often that they run projects in the field of FAW research (p = 0.034). Furthermore they were significantly more involved in EU-funded schemes, such as FP7 (EU’s Research and Innovation Funding Programme for 2007–2013) with 24% (p = 0.013) and in ERA-NET Cofund projects (European Research Area—Coordination of Research Programmes) with 5.7% (p = 0.042). The average sum of impact factors from 5 self-named citations was 3.0 ± 2.8 (mean, SD) in the Eastern hubs and 7.5 ± 4.4 in the Western Hubs. When investigating associations of the economic status of EU countries with resource factors and achievements in FAW research, the ‘Coefficient of National Innovation Capacity (NIC)’ was moderately correlated with the input factors for FAW research such as the average number of PhDs currently employed in the institutions (r _s = 0.66; p < 0.001) and the total number of employed researchers (r _s = 0.56; p < 0.01). Stronger associations were found between the scientific output and the economic ranking, here represented by the cumulative impact factor of their published papers (r _s = 0.74; p < 0.001), and between the number of EC-project reports published in CORDIS 2015 with NIC (r _s = 0.67; p < 0.001). We conclude that due to economic disadvantages as represented by the lower NIC or rare participation in EU-funding schemes, the Eastern Hubs could not reach the same level of output factors as the Western Hubs, which negatively impacts on the number of young researchers (PhDs) and impact factors, thus resulting in lower visibility and influence.     

Fluctuation induced conductivity of polycrystalline MgB<Subscript>2</Subscript> superconductor

We report fluctuation-induced conductivity (FIC) of the polycrystalline MgB₂ superconductor in the presence of magnetic field. The results are described in terms of the temperature derivative of the resistivity, dρ/dT. The dρ/dT peak temperature observed for H = 0 Tesla at 39 K remains very distinct under applied fields of 6 Tesla and 8 Tesla at 22 and 20 K respectively. Aslamazov and Larkin (AL) equations are used to explain the anisotropic nature of the polycrystalline MgB₂. The effective coherence length, ξ _p (0) determined experimentally is 55.17 Å, which roughly matches with previously reported experimental work.     

Crystal structure,microstructure and microwave dielectric properties of novel MgAl<Subscript>2</Subscript>Ti<Subscript>3</Subscript>O<Subscript>10</Subscript> ceramic

In the present work, a novel MgAl₂Ti₃O₁₀ ceramic was obtained using a traditional solid-state reaction method. X-ray diffraction and energy dispersive spectrometer showed that the main MgAl₂Ti₃O₁₀ phase was formed after sintered at 1300–1450 °C. With rising the sintering temperature from 1300 to 1450 °C, the bulk density (ρ), relative permittivity (ε _r ) and Q?×?f value firstly increased, reached the maximum values (3.61 g/cm³, 14.9, and 26,450 GHz) and then decreased. The temperature coefficient of resonator frequency (τ _f ) showed a slight change at a negative range of ??94.6 to ??83.7 ppm/°C. When the sintering temperature was 1400 °C, MgAl₂Ti₃O₁₀ ceramics exhibited the best microwave dielectric properties with Q?×?f?=?26,450 GHz, ε _r ?=?14.9 and τ _f ?=???83.7 ppm/°C.     

Synthesis and characterization of ordered mesoporous silica using rosin-based Gemini surfactants

As structure-directing agents, the molecular structure of surfactants is critical for determining the properties of prepared mesoporous materials. Using dehydroabietic acid as a starting material, a series of rosin-based Gemini surfactants (abbreviated as R-n-R, n = 3, 6, 8 and 10, indicating the carbon atom number contained in the spacer) were synthesized and applied as templates in the preparation of ordered mesoporous silica. The structures and morphologies of the samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and N₂ adsorption–desorption. The R-n-R surfactants feature rigid tricyclic hydrophobic groups with large volumes, which are beneficial for the formation of a three-dimensional cubic phase. Furthermore, the spacer length was found to have a tremendous effect on the structure of the prepared mesoporous silica materials. The head group of R-3-R, which has a short spacer, is excessively charged, leading to silica nanoparticles with an irregular morphology and a rather low BET surface area. With longer spacer lengths, R-6-R, R-8-R and R-10-R are conducive to generating silica nanoparticles with a novel dumbbell-like morphology and with higher BET surface areas of 1171, 1096 and 1186 m² g^?1, respectively. The results demonstrate the particularities of the Gemini surfactant structure in the preparation of mesoporous silica nanoparticles with novel morphologies, and the details of the molecular interactions that occur in the condensation of silicate anions are also revealed.     

Extraction of cesium and americium with <Emphasis Type="Italic">p</Emphasis>-alkylcalix[8]arenes from alkaline solutions

Previously unknown isononylcalix[8]arene was synthesized from commercially available isononylphenol. The properties of the product (solubility, extraction ability, tendency to aggregation) were compared with those of the known tert-butylcalix[8]arene. The extraction of ¹³⁷Cs, ^99mTc, and ²⁴¹Am from alkaline carbonate solutions with solutions of p-alkylcalix[8]arenes (alkyl = tert-butyl, isononyl) in tetrachloroethylene was studied. The dependence of the distribution ratios on pH of the aqueous phase in the interval from 11 to 13.9 and on the nature of functional groups in the calixarene core was determined. The composition of extractable solvates of cesium and americium with calix[8]arenes was found. Calix[8]arenes extract cesium from alkaline solutions more efficiently than p-tert-butylphenol, their nonmacrocyclic analog, does. tert-Butylcalix[8]arene exhibits the highest performance, which may be due to formation of aggregates 5.7 ± 0.8 nm in diameter in the organic phase at pH 13.5 of the aqueous phase. The isononyl derivative exists in the monomeric form (particle diameter 1.9 ± 0.5 nm).     

Long-wavelength photodiodes based on <Emphasis Type="Italic">n</Emphasis>-GaSb/<Emphasis Type="Italic">n</Emphasis>-GaInAsSb/<Emphasis Type="Italic">p</Emphasis>-AlGaAsSb heterostructures

Photodiodes sensitive in the wavelength ranges 1–2.5 μm and 1–4.8 μm at room temperature have been created on the basis of n-GaSb/n-GaInAsSb/p-AlGaAsSb double-junction heterostructures of two types. The broadband photosensitivity of the diode structures of both types is indicative of the complete separation of photogenerated electron-hole pairs in the staggered n-p heterojunction (n-GaInAsSb/p-AlGaAsSb). The noise characteristics of photodetectors based on the proposed diode structures have been studied. Prospects of the use of these devices in thermophotovoltaic cells for low-temperature radiation sources are considered.     

Influence of silver addition on microstructures and transport properties of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>:Ag<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> composites

In order to obtain high temperature coefficient of resistance (TCR) value of La_0.67Ca_0.33MnO₃:Ag _x (LCMO:Ag _x ) composites, samples with different Ag contents (x?=?0, 0.1, 0.2, 0.25, 0.3, and 0.5) were prepared by sol–gel method. X-ray diffraction analyses indicated that all samples had orthorhombic perovskite structures. As x increased, lattice parameters (a, b, c) and cell volumes underwent slight expansions. Interestingly, the addition of Ag dramatically affected TCR and magneto-resistance (MR) values. Elevated TCR value up to 53.46%·K^?1 at 277 K was observed for LCMO:Ag _x composites with added Ag at the composition of x?=?0.1. Meanwhile, MR value at 263 K reached 71% at the magnetic field of 1 T for samples with Ag composition of x?=?0.25. The increase in Mn⁴⁺/Mn³⁺ ratio and improvement in crystallization caused by added Ag was found responsible for the elevated values of TCR, MR, and T_p. These findings may have practical use in high-performance magneto-resistive manganites.     

Synthesis,nonlinear optical properties and cellular imaging of hybrid ZnS nanoparticles capped with conjugated terpyridine derivatives

A novel organic/inorganic nanohybrids which consisted of ligand L (L = 2-[(2-hydroxy-ethyl)-(4-[2,2′;6′,2″] terpyridin-4′-yl-phenyl)-amino]-ethanol), an optical terpyridine derivative and ZnS nanoparticles (NPs), had been prepared through a solution-phase synthesis technique. The intermolecular interactions at the interface between ZnS and the ligand components were analyzed by FT-IR, far-IR, UV–Vis absorption spectroscopy, XRD and TEM. Particular properties had been shown by fluorescence spectra, fluorescence lifetime, Raman spectrum, aggregation emission and non-linear optical response. The results indicated that the nano-composite L–ZnS NPs had an obvious aggregation-induced emission in ethanol/n-hexane mixtures, and had larger two-photon absorption (TPA) when compared to the free ligand L. The data for the TPA cross-section value (σ = 16,247.8 GM), nonlinear refractive index (γ = 4.46 × 10^?13 cm² W^?1) and the third order nonlinear polarizability [Imχ ⁽³⁾ (esu) = 1.13 × 10^?14] were measured and discussed. Meanwhile, due to the laser irradiation induced charge transfer from the ligand to ZnS NPs, the composite could be potentially applied in vitro and in vivo cellular imaging.     

Cobalt nanoparticles as reusable catalysts for reduction of 4-nitrophenol under mild conditions

Facile reduction of p-nitrophenol to p-aminophenol by sodium borohydride catalysed by cobalt nanoparticles (CoNPs) has been discussed. A simple approach has been made to synthesize highly active and ordered structures of CoNPs. The air-stable nanoparticles were prepared from cobalt sulphate using tetrabutyl ammonium bromide as surfactant and sodium borohydride as reductant. The cobalt nanocolloids in aqueous medium were found to be efficient reusable catalysts for the p-nitrophenol reduction. Palladium nanoparticles prepared from palladium chloride and the same surfactant were found to reduce p-nitrophenol but lose their catalytic efficiency after recovery. Based on chemical and kinetic studies, an attempt has been made to elucidate the mechanism of p-nitrophenol reduction using these nanoclusters.