New photocatalysts based on mixed-metal pyridine dicarboxylates

New photocatalytically active isostructural two-dimensional mixed metal-pyridine dicarboxylates, [M(H2O)3Co{C5N1H3(COO) 2}3])∞], M = Gd (1), Dy (2) and Y (3) have been prepared under hydrothermal conditions. The structure consists of a network of MO6(H2O)3, CoO3N3 polyhedral units connected by the pyridine dicarboxylates forming two-dimensional layers, which are arranged in an AAAA... fashion. The photocatalytic studies on 1 - 3 indicate that they are active catalysts for the degradation of simple organic dyes, such as Remazol brilliant blue R (RBBR) and Orange G (OG) in the presence of UV light. The compounds have also been characterized by powder XRD, IR, TGA, UV-Vis and magnetic studies

Synthesis, structure and ionic conductivity in scheelite type Li_0.5Ce_0.5-xLn_xMoO₄ (x = 0 and 0.25, Ln = Pr, Sm)

Scheelite type solid electrolytes, Li0.5Ce0.5-xLnxMoO4 (x = 0 and 0.25, Ln = Pr, Sm) have been synthesized using a solid state method. Their structure and ionic conductivity (σ) were obtained by single crystal X-ray diffraction and ac-impedance spectroscopy, respectively. X-ray diffraction studies reveal a space group of I41/a for Li0.5Ce0.5-xLnxMoO4 (x = 0 and 0.25, Ln = Pr, Sm) scheelite compounds. The unsubstituted Li0.5Ce0.5-xLnxMoO4 showed lithium ion conductivity ∼10−5-10−3 Ω−1cm−1 in the temperature range of 300-700°C (σ = 2.5 × 10−3 Ω−1cm−1 at 700°C). The substituted compounds show lower conductivity compared to the unsubstituted compound, with the magnitude of ionic conductivity being two (in the high temperature regime) to one order (in the low temperature regime) lower than the unsubstituted compound. Since these scheelite type structures show significant conductivity, the series of compounds could serve in high temperature lithium battery operations

Supercritical fluid extraction of organic pollutants from soil combined with adsorption onto activated carbon

Vita.A novel process has been developed for the remediation of soils contaminated with organics. In this process, the organics are continuously extracted from soil and deposited on to activated carbon. The feasibility of this process is governed by the extraction efficiency of organics from soil by supercritical carbon dioxide and the affinity of activated carbon to the organics in the presence of supercritical carbon dioxide. These factors are controlled by the adsorption/desorption phenomena in supercritical fluids. Four model pollutants, naphthalene, phenanthrene, hexachlorobenzene and pentachlorophenol were investigated in this study. The adsorption isotherms of these organics on soil and carbon was measured using frontal analysis chromatography and modeled using the Freundlich isotherm. The amount of organic adsorbed on soil and carbon increased with temperature and was found to be independent of the solubility of the organic in supercritical carbon dioxide. The heats of adsorption of the organics on soil and carbon were found to be 1-5 and 4-8 kcal/mol, respectively, suggesting physical adsorption. The desorption profiles of these organics from soil and carbon were obtained by the same technique. The mass balance closures indicated that the organics could be completely extracted from soil and carbon indicating physical adsorption. The decontamination process was investigated by two models. A simple model, neglecting mass transfer resistances and axial dispersion, was able to predict the amount of carbon dioxide required to attain a certain decontamination level. However, it could not simulate the shape of the experimental desorption profiles satisfactorily. A rigorous model, which accounted for the axial dispersion, effective diffusion, and external mass transfer was highly successful in predicting the shape of the desorption profiles. A perturbation analysis of the parameters indicated that the adsorption equilibrium was the most significant parameter in all the systems investigated. An economic feasibility analysis of the proposed process indicated the process was feasible and the cost for 99% decontamination of a ton of soil contaminated with 1000 ppm of organic was found to be 60-200 dollars, which is lower than the competing technologies

Thermodynamic modeling of the solubilities of fatty acids in supercritical fluids

Modeling the solubilities of fatty acids is important because these compounds are used in various industries. In this work, a thermodynamic model based on Redlich-Kwong equation of state with Kwak-Mansoori mixing rules was used to model the solubilities of fatty acids in supercritical carbon dioxide. The model uses only one adjustable parameter and this parameter varies linearly with the chain length of the fatty acid. Therefore, this model can be potentially used to predict the solubilities of various fatty acids in supercritical carbon dioxide

Scientific publishing: Rising cost of monopolies

A recent editorial in Current Science discusses the issues of access to research journals. This article examines the issue of cost rise and discusses a study undertaken at the Indian Institute of Science (IISc), Bangalore

Kinetics of the ultrasonic degradation of poly (alkyl methacrylates)

The influence of the alkyl group substituents on the ultrasonic degradation of poly (alkyl methacrylate)s, namely poly (methyl methacrylate) (PMMA), poly (ethyl methacrylate) (PEMA) and poly (butyl methacrylate) (PBMA) was studied. The rate coefficient increased with an increase in the number of carbon atoms in the alkyl group: thus the order of degradation was PBMA > PEMA > PMMA. This was attributed to the scission of the main chain, which increases with the length of the side chain. The ultrasonic degradation of PBMA was investigated in various solvents, at different temperatures and at different ultrasound intensities. The degradation rate coefficients increased logarithmically with the decrease in vapor pressure and increased linearly with an increase in viscosity of the solvent and ultrasound intensity. The effect of three different initiators, benzoyl peroxide (BPO), dicumyl peroxide (DCP) and azo-bisisobutyronitrile (AIBN) on the ultrasonic degradation of PBMA was also studied. The degradation of the polymer decreased in the presence of the initiator. A continuous distribution model was developed for the radical mechanism involved in degradation and was used to determine the degradation rate coefficients of PBMA in presence of initiator. The model indicated that the degradation rate coefficient of the interaction of the PBMA radical with the initiator is independent of the dissociation constant of the initiator

Dynamics of Molecular Weight Distributions for Polymer Scission

The dynamics of molecular weight distributions (MWDs) for polymer degradation is of interest to various applications. The time evolutions of MWDs can be determined by solving the governing population balance equations, which are generally solved by moment techniques wherein the initial distribution is represented by a gamma distribution. The evolution of MWD is determined by the time dependence of the gamma distribution parameters. The population balance equations (PBEs) can also be solved numerically by converting them to partial differential equations (PDEs). The degradation rate coefficient in the PBE depends on the molecular weight x as $(x - x_o)^{\lambda}$ or as a quadratic polynomial in x. The solutions obtained with the moment technique, which are inaccurate for certain cases, are compared with the solutions determined by solving the PDEs. The utility of the numerical scheme is also discussed for cases where the initial distribution cannot be represented satisfactorily by a gamma distribution