Growth of Nanometric Gold Particles in Solution Phase

The time evolution of colloidal gold particles in the nanometric regime has been investigated by employing electron microscopy and electronic absorption spectroscopy. The particle size distributions are essentially Gaussian and show the same time dependence for both the mean and the standard deviation, enabling us to obtain a time-independent universal curve for the particle size. Temperature dependent studies show the growth to be an activated process with a barrier of about 18 kJ mol(-1). We present a phenomenological equation for the evolution of particle size and suggest that the growth process is stochastic.

Electrochemical Determination of L-Dopa in Mucuna pruriens Seeds, Leaves and Commercial Siddha Product Using Gold Modified Pencil Graphite Electrode

In the present work a gold modified pencil graphite electrode (GPGE) was used for the determination of L-dopa present in the aqueous extracts of Mucuna pruriens seeds (MPS), Mucuna pruriens leaves (MPL) and Commercial Siddha Product (CSP). The GPGE shows excellent electrocatalytic activity towards the oxidation of both L-dopa and ascorbic acid (AA), with the separation of peak potential of 98 mV. The differential pulse voltammetric (DPV) results indicated that the detection limit for L-dopa was 1.54 mu M (S/N=3). This method can be successfully applied for the determination of L-dopa in real samples.

Production and properties of carbon fibre/particle reinforced cast metal matrix composites

Carbon fibres/particles can be satisfactory reinforcing material in polymer, ceramic and metal matrices. Carbon fibres/particles reinforced polymer matrix composites and ceramic matrix composites are being used extensively in critical areas of application, but carbon fibre - metal matrix composites have not reached that stage yet. This paper discusses the salient aspects of production and specific properties of carbon fibre/particle reinforced cast metal matrix composites. It is envisaged that these materials will find extensive applications where cost, weight and thermal expansion are the key factors.

Production of biosurfactant “Biosur-Pm” by Pseudomonas maltophila CSV89: characterization and role in hydrocarbon uptake

Pseudomonas maltophilia CSV89, a soil bacterium, produces an extracellular biosurfactant, ''Biosur-Pm''. The partially purified product is nondialyzable and chemically composed of 50% protein and 12-15% sugar, which indicates the complex nature of Biosur-Pm. It reduces the surface tension of water from 73 to 53 x 10(-3) N m(-1) and has a critical micellar concentration of 80 mg/l. Compared to aliphatic hydrocarbons, Biosur-Pm shows good activity against aromatic hydrocarbons. The emulsion formed is stable and does not require any metal ions for emulsification. The kinetics of Biosur-Pm production suggest that its synthesis isa growth-associated and pH-dependent process. At pH 7.0, cells produced more Biosur-Pm with less cell surface hydrophobicity. At pH 8.0, however, the cells produced less Biosur-Pm with more cell surface hydrophobicity and showed a twofold higher affinity for aromatic hydrocarbons compared to the cells grown at pH 7.0. The Biosur-Pm showed a pH-dependent release, stimulated growth of the producer strain on mineral salts medium with 1-naphthoic acid when added externally, and facilitated the conversion of salicylate to catechol. All these results suggest that Biosur-Pm is probably a cell-wall component and helps in hydrocarbon assimilation/uptake.

Potential herblayer production and grazing effects in anthropogenic savanna-grasslands in the moist tropical forests of the Western Ghats of India

The moist tropical forests of the Western Ghats of India are pockmarked with savanna-grasslands created and managed by local agricultural communities. A sample of such savanna-grasslands with differing growing conditions was studied in terms of peak above-ground biomass, monthly growth, and cumulative production under different clipping treatments. The herblayer was found to be dominated by perennial C4 grasses, with Eulalia trispicata, Arundinella metzii and Themeda triandra being common to all sites. Peak biomass ranged between 3.3-5.9 t/ha at sites most favourable for grass production. Across these sites, peak biomass was found to be inversely related to the number of rainy days during the growing season, suggesting that growth may be light-limited. This hypothesis is supported by the observation that growth is most rapid immediately after the easing of the monsoon. Single clips early in the growing season had no negative or a slightly positive effect on production, but mid-season single clips or continuous frequent clipping reduced production by as much as 40%. The results suggest that, while indiscriminate grazing may certainly be deleterious, it is possible to obtain sustained high yields from forest lands managed for grass production without totally excluding grazing.

Land availability and biomass production potential in India

In this paper we have assessed the availability of land and the potential for biomass production in India to meet various demands for biomass, including modern bioenergy. This is estimated by considering the various demands on land and its suitability. The biomass production potential of energy plantations is assessed for different agroecological zones. The total woody biomass production is estimated to be 321 Mt, based on biomass productivity in the range 2 to 17 t/ha/yr for the different agro-ecological zones and considering the conservative estimate of 43 Mha land availability for biomass production. A surplus of 231 Mt of biomass (after meeting the increased demand for fuelwood and timber by the year 2010) is estimated to be available for energy, which has an electricity generation potential of 231 TWh. As a first step, only the feasible physical potential of biomass production is assessed, along with an analysis of barriers. The potential costs and benefits of biomass production strategy are not analysed. (C) 1999 Elsevier Science Ltd. All rights reserved.

Regulation of an 8-kDa peptide involved in testosterone production by luteinizing hormone in rat Leydig cells

Results of Western blot analysis carried out with an interstitial cell extract from male guinea pig and ovarian extract from immature female rats administered equine chorionic gonadotropin (eCG) provide supportive evidence to our earlier suggestion that an 8-kDa peptide is involved in acquisition of steroidogenic capacity by the rat Leydig cells. It was found that though the signal was observed in other tissues such as liver, kidney and lung which do not produce gonadal hormones, the peptide was modulated only by lutenizing hormone (LH) in the rat Leydig cells.

I*(P-2(1/2)) production from CH3I photodissociation at 236 nm

The quantum yield of I*((2)p(1/2)) production from CH3I photolysis at 236 nm in the gas phase has been measured as 0.69 +/- 0.03. The implication is that direct excitation to the (1)Q(1) excited state is significant at this wavelength. The dynamics of I* formation at other excitation energies covering the entire A-band of absorption of CH3I has been discussed in the light of this measurement.

Self-assembled molecular films of tetraamino metal (Co, Cu, Fe) phthalocyanines on gold and silver. Electrochemical and spectroscopic characterization

The formation of molecular films of 2,9,16,23-tetraamino metal phthalocyanines [TAM(II)Pc; M (II) = Co, Cu, and TAM(III)Pc; M = Fe] by spontaneous adsorption on gold and silver surfaces is described. The properties of these films have been investigated by cyclic voltammetry, impedance, and FT-Raman spectroscopy. The charge associated with Co(II) and Co(I) redox couple in voltammetric data leads to a coverage of (0.35+/-0.05) x 10(-10) mol cm(-2), suggesting that the tetraamino cobalt phthalocyanine is adsorbed as a monolayer with an almost complete coverage. The blocking behavior of the films toward oxygen and Fe(CN)(6)(3-/4-) redox couple have been followed by cyclic voltammetry and impedance measurements. This leads to an estimate of the coverage of about 85 % in the case of copper and the iron analogs. FT-Raman studies show characteristic bands around 236 cm(-1) revealing the interaction between the metal substrate and the nitrogen of the -NH2 group on the phthalocyanine molecules.

Strategies for efficient start-up of continuous biooxidation process for refractory gold ores

Strategies for efficient start-up of a continuous process for biooxidation of refractory gold ore and concentrate obtained from Hutti, Gold Mines Limited (HGML), India are discussed in this work. The biooxidation of the concentrate at high pulp density (10%) with wild strain of Thiobacillus ferrooxidans isolated from HGML mines is characterized by significant lag phase (20 days) and incomplete oxidation (35%) even after prolonged operation (60 days). Two strategies, biooxidation with concentrate adapted cells and a step leaching strategy, in which the pulp density is progressively increased from 2% to 10% were considered and the latter resulted in efficient biooxidation of concentrate. Conversion of such a process from batch to continuous operation is shown to result in complete biooxidation of the concentrate and gold extraction efficiency in excess of 90%. (C) 2002 Elsevier Science Ltd. All rights reserved.

The production of AlN-rich matrix composites by the reactive infiltration of Al alloys in nitrogen

Aluminium nitride (AlN)-Al matrices reinforced with Al2O3 particulate have been fabricated by reactive infiltration of Al-2% Mg alloy into Al2O3 preforms in N-2 in the temperature range of 900-1075 degreesC. The growth of composites of useful thickness was facilitated by the presence of a Mg-rich external getter, in the absence of which composite growth is self-limiting and terminates prematurely. Successful growth of composites has been attributed to the reduction in residual oxygen partial pressure brought about by the reaction with oxygen of highly volatile Mg in the getter alloy. The microstructure of the matrix consists of AlN-rich regions contiguous with the particulate with metal-rich channels in-between, thereby suggesting that nitridation initiates by preferential wicking of alloy along the particle surfaces. The increase in nitride content of the matrix with temperature is consistent with hardness values that vary between similar to3 and 10 GPa. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Self-assembled microtubes and rhodamine 6G functionalized Raman-active gold microrods from 1-hydroxybenzotriazole

1-Hydroxybenzotriazole spontaneously self-assembles to form hollow, linear microtubes initiated by controlled evaporation from water. The tube cavities act as thermo-labile micromoulds for the synthesis of linear gold microrods. Rhodamine 6G-labelled gold microrods, exhibiting surface enhanced resonance Raman activity, have been synthesized using the HOBT microtubes.

Effect of Reagent Addition Rate and Temperature on Synthesis of Gold Nanoparticles in Microemulsion Route

Nanoparticle synthesis in a microemulsion route is typically controlled by changing the water to surfactant ratio, concentration of precursors, and/or concentration of micelles. The experiments carried out in this work with chloroauric acid and hydrazine hydrate as precursors in water/AOT-Brij30/isooctane microemulsions show that the reagent addition rate can also be used to tune the size of stable spherical gold nanoparticles to some extent. The particle size goes through a minimum with variation in feed addition rate. The increase in particle size with an increase in reaction temperature is in agreement with an earlier report. A population balance model is used to interpret the experimental findings. The reduced extent of nucleation at low feed addition rates and suppression of nucleation due to the finite rate of mixing at higher addition rates produce a minimum in particle size. The increase in particle size at higher reaction temperatures is explained through an increase in fusion efficiency of micelles which dissipates supersaturation; increase in solubility is shown to play an insignificant role. The moderate polydispersity of the synthesized particles is due to the continued nucleation and growth of particles. The polydispersity of micelle sizes by itself plays a minor role.

Monodisperse sub-10 nm gold nanoparticles by reversing the order of addition in Turkevich method - The role of chloroauric acid

The Turkevich method for synthesizing gold nanoparticles, using sodium citrate as the reducing agent, is renowned for its ability to produce biocompatible colloids with mean size >10 nm. Here we show that monodisperse gold nanoparticles in the 5-10 nm size range can be synthesized by simply reversing the order of addition of reactants, i.e. adding chloroauric acid to citrate solution. Kinetic studies and electron microscopic characterization revealed that the reactivity of chloroauric acid, initial molar ratio of citrate to chloroauric acid (MR), and reaction mixture pH play an important role in producing monodisperse gold nanoparticles. Reversing the order of addition also enhanced the stabilization of nanoparticles at high MR values. Remarkably, the system exhibits a `memory' of the order of addition, even when the timescale of mixing is much shorter than the timescale of synthesis. (C) 2011 Elsevier Inc. All rights reserved.

Sustainable biomass production for energy in selected Asian countries

This paper presents a synthesis of assessment of sustainable biomass production potential in six Asian countries-China, India, Malaysia, Philippines, Sri Lanka and Thailand, and is based on the detailed studies carried out in these countries under the Asian Regional Research Programme in Energy, Environment and Climate (ARRPEEC). National level studies were undertaken to estimate land availability for biomass production, identify and evaluate the biomass production options in terms of yield per hectare and financial viability, estimate sustainable biomass production for energy, and estimate the energy potential of biomass production in the six Asian countries. Sustainable biomass production from plantation is estimated to be in the range of 182.5-210.5, 62-310, 0.4-1.7, 3.7-20.4, 2.0-9.9 and 11.6-106.6 Mt yr(-1) for China, India, Malaysia, Philippines, Sri Lanka and Thailand, respectively. The maximum annual electricity generation potential, using advanced technologies, from the sustainable biomass production is estimated to be about 27, 114, 4.5, 79, 254 and 195 percentage of the total electricity generation in year 2000 in China, India, Malaysia, Philippines, Sri Lanka and Thailand, respectively. Investment cost for bioenergy production varies from US$381 to 1842 ha(-1) in the countries considered in this study; investment cost for production of biomass varies from US$5.1 to 23 t(-1). (C) 2003 Elsevier Ltd. All rights reserved.