Cellulose polymorphism study with sum-frequency-generation (SFG) vibration spectroscopy: identification of exocyclic CH2OH conformation and chain orientation

Sum-frequency-generation (SFG) vibration spectroscopy is a technique only sensitive to functional groups arranged without centrosymmetry. For crystalline cellulose, SFG can detect the C6H₂ and intra-chain hydrogen-bonded OH groups in the crystal. The geometries of these groups are sensitive to the hydrogen bonding network that stabilizes each cellulose polymorph. Therefore, SFG can distinguish cellulose polymorphs (I_β, II, III_I and III_II) which have different conformations of the exocyclic hydroxymethylene group or directionalities of glucan chains. The C6H₂ asymmetric stretching peaks at 2,944 cm^?1 for cellulose I_β and 2,960 cm^?1 for cellulose II, III_I and III_II corresponds to the trans-gauche (tg) and gauche-trans (gt) conformation, respectively. The SFG intensity of the stretch peak of intra-chain hydrogen-bonded O–H group implies that the chain arrangement in cellulose crystal is parallel in I_β and III_I, and antiparallel in II and III_II.     

Solid phase extraction studies on cellulose based chelating resin for separation,pre-concentration and estimation of Cu2+and Ni2+

Chelating resins based on biopolymers, specifically cellulose, offers a green analytical method for determination of metal ions at trace levels present in various samples. It offers a fast, accurate and simple method for separation and pre-concentration of metal ions at low concentrations, prior to their determination by instrumental method. Cellulose based chelating resin (CELL-GLY) has been synthesised by immobilising glycine on it. CELL-GLY was used for the determination of trace amounts of Cu²⁺ and Ni²⁺ from aqueous solutions before their determination by FAAS. The preparation of CELL-GLY involves simple steps, based on natural and easily available biopolymer cellulose, which makes its use as chelating resin is a green method. The Cu²⁺ and Ni²⁺ can be quantitatively recovered from the CELL-GLY in the pH range 4.8–6.9 and 6.9-7.8 respectively with a recovery of more than 95% for each of these metal ions. Recovery of these metal ions using CELL-GLY was quantitative up to 35 °C. The detection limits for copper and nickel by FAAS were 1.20 ppb and 1.40 ppb, respectively. The method was successfully employed for the determination of trace amounts of Cu²⁺ and Ni²⁺ in various samples.     

Assessing the feasibility study of highly efficient and selective co-sequestration process for cesium and strontium utilizing calix-crown and crown-ether based combined solvent systems

Journal of Radioanalytical and Nuclear Chemistry - Efficient and selective extraction of 137Cs and 90Sr from high level liquid waste (HLLW) is of utmost importance in the back end nuclear fuel...     

Study of photon-induced L3 vacancy alignment for elements La to U

Alignment of photon-induced L₃ vacancies is studied in rare earth and highZ elements at energies of experimental interest, near thresholds to 60 keV, under nonrelativistic dipole approximation. Numerical calculations of the matrix element are undertaken to produce theoretical data for comparison with the experimental findings. The A₂ values being s>0.1 at photoelectron energies <20 keV are certainly higher than 5–8% uncertainties quoted in experimental results. Present findings are from a very basic model, hydrogen-like and can further be treated as reference to observe the impact of screening, relativistic, multipole and retardation corrections to the model     

A DFT study of the conformational and electronic properties of echinatin,a retrochalcone,and its anion in the gas phase and aqueous solution

Structural Chemistry - Echinatin (Ech), a characteristic retrochalcone isolated from liquorice, a widely used herbal medicine, has been investigated in detail in terms of its conformational and...     

Adsorption of Safranin-T from wastewater using waste materials- activated carbon and activated rice husks

Textile effluents are major industrial polluters because of high color content, about 15% unfixed dyes and salts. The present paper is aimed to investigate and develop cheap adsorption methods for color removal from wastewater using waste materials activated carbon and activated rice husk-as adsorbents. The method was employed for the removal of Safranin-T and the influence of various factors such as adsorbent dose, adsorbate concentration, particle size, temperature, contact time, and pH was studied. The adsorption of the dye over both the adsorbents was found to follow Langmuir and Freundlich adsorption isotherm models. Based on these models, different useful thermodynamic parameters have been evaluated for both the adsorption processes. The adsorption of Safranin-T over activated carbon and activated rice husks follows first-order kinetics and the rate constants for the adsorption processes decrease with increase in temperature.     

Chemical oscillations in the uncatalyzed bromate oxidation of hydroquinone and nitrophenols

Chemical oscillatory behavior in the uncatalyzed bromate oxidation of hydroquinone and nitrophenols is reported. The reaction is strongly inhibited by stirring. Effect of one-electron redox couples (EZ catalysts) on the system is described.

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A class of finite difference schemes for interface problems with an HOC approach

In this paper, we propose a new methodology for numerically solving elliptic and parabolic equations with discontinuous coefficients and singular source terms. This new scheme is obtained by clubbing a recently developed higher‐order compact methodology with special interface treatment for the points just next to the points of discontinuity. The overall order of accuracy of the scheme is at least second. We first formulate the scheme for one‐dimensional (1D) problems, and then extend it directly to two‐dimensional (2D) problems in polar coordinates. In the process, we also perform convergence and related analysis for both the cases. Finally, we show a new direction of implementing the methodology to 2D problems in cartesian coordinates. We then conduct numerous numerical studies on a number of problems, both for 1D and 2D cases, including the flow past circular cylinder governed by the incompressible Navier–Stokes equations. We compare our results with existing numerical and experimental results. In all the cases, our formulation is found to produce better results on coarser grids. For the circular cylinder problem, the scheme used is seen to capture all the flow characteristics including the famous von Kármán vortex street. Copyright © 2016 John Wiley & Sons, Ltd.     

A novel confocal optical pulse stretcher for laser pulses

We present an analytical and experimental study of a novel confocal optical pulse stretcher (COPS). The simple and passive pulse stretcher consists of two concave mirrors and a scraper beam-splitter and its optical configuration ensures a perfect spatial overlapping of laser pulses at the beam-splitter. The pulse stretcher is compact and suitable for laser pulses of large divergences. The confocal optical pulse stretcher is demonstrated on a pulsed copper vapour laser to convert a 40 ns (1/e² % points) pulse into a 55 ns with reduction of peak power by a factor of 1.375 without loss of pulse energy.