Synthesis of visible light-active nanostructured TiOx (x < 2) photocatalysts in a flame aerosol reactor

Titanium dioxide is a wide band gap (3.2 eV) semiconductor which is photo-active when irradiated with UV light. For wider scale use of TiO₂ as a photocatalyst, its activity needs to be extended to the visible light region (constituting 45% of total incident solar energy). A diffusion flame aerosol reactor (FLAR) with an oxygen lean environment in the particle formation zone has been used to synthesize oxygen deficient titanium suboxide (TiO_x with x < 2) nanoparticles. Using a standard-based electron energy loss spectroscopy (EELS) technique, the non-stoichiometry (x in TiO_x) in the flame synthesized particles has been quantified with high accuracy (uncertainty less than 3%). Under an oxygen lean environment in the particle formation zone, the non-stoichiometry in the TiO_x particles is a function of the flame temperature. The value of x in the flame synthesized TiO_x nanoparticles is in the range of 1.88 < x < 1.94. Diffuse reflectance spectra confirmed that the oxygen deficient TiO_x particles absorbed visible light. Visible light activity of the TiO_x particles is demonstrated by photocatalytic degradation of methyl orange solution under visible light illumination.     

Understanding interfacial polycondensation: Experiments on polyurea system and comparison with theory

Interfacial polycondensation, with its multiphase character and the involvement of several rate and equilibrium processes, presents unique challenges to our ability to understand and design processes for achieving desired properties. In a recent study [1], we have presented a detailed model for the process and shown that it explains the salient features as reported in the literature for several interfacial systems. In the present paper, we report extensive experimental studies on the polyurea system and their comparison with the model. Two geometries - the spherical geometry of the microcapsule and the flat-film geometry - have been used to study qualitative and quantitative features of the polycondensation and the nature of the film that forms. While some aspects, such as the manner in which the solvent influences the kinetics, confirm earlier findings, inadequacies have been identified in the sample preparation protocols followed in earlier work, because of which property estimations may carry a large error. Improved protocols have accordingly been developed and used to study the development of film properties in time and as a function of the important preparation variables. Detailed molecular weight distributions have been determined using a GPC technique and used to derive important properties of the polyurea (such as Mark-Houwink parameters) as well as to gain insights into mechanisms. The data have been used to determine the rate parameters in the Dhumal and Suresh [1] model. The predictions of the model, as far as trends are concerned, are shown to be satisfactory given the level of uncertainty about parameter values and the complexity of the system being studied. Where discrepancies exist, the reasons have been established and the areas for improvement of the model identified. The findings reported are of interest to applications such as controlled release and membrane separations, in which permeation rate through the membrane is of importance and depends upon various membrane properties like crystallinity, morphology, etc.     

Structure,growth, and morphology in para nitroaniline dispersed polymethyl methacrylate guest‐host NLO composites

The structure, growth, and morphology of composite films made by dispersing para nitroaniline (PNA) in poly(methyl methacrylate) (PMMA) was investigated with respect to different crystallization methods, composition, and application of electric field. The wide‐angle X‐ray diffraction scans showed large variations in intensity of different reflections, especially the Okl with composition and in the presence of an electric field. In addition, it also showed the occurrence of a new crystalline structure, possibly due to complex formation between PNA and PMMA. The presence of this complex was further confirmed by infrared spectroscopy and thermal analysis. In a certain range of composition (30 to 40 % PNA), spherulitic morphology was observed, which otherwise consisted of needle‐shaped crystals dispersed in amorphous matrix. The transparency of these films also depended strongly on the crystallization conditions, and highly transparent films could be obtained, even at high PNA content by application of electric field. These various results could be explained on the basis of the intermolecular interaction between PNA and PMMA, as well as preferential growth direction and orientation of the PNA crystals. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3522–3534, 1999     

Assessment of bulb pungency level in different Indian cultivars of onion (Allium cepa L.)

Onion (Allium cepa L.) is an important vegetable crop consumed primarily for its ability to enhance the flavor of other foods. The quality of onion depends on its pungency. While highly pungent onions are popular in India, less pungent ones are preferred in other countries. However, the variability in pungency in bulbs of different cultivars however has not been investigated. The present investigation was therefore undertaken to determine the pungency in three popular Indian onion cultivars viz. N-2-4-1, B-780 and Phule Safed. Randomly selected bulb samples of the cultivars were analyzed for the content of pyruvic acid, total soluble solids (TSS) and reducing, non-reducing and total sugars. The red variety N-2-4-1 showed higher level of pungency, while other two varieties were comparatively less pungent.     

A comprehensive model for kinetics and development of film structure in interfacial polycondensation

A detailed model for interfacial polycondensation (IP) reaction, which accounts for the salient equilibrium and rate processes in reaction and phase separation, is reported here. The modeling of nucleation phenomena is more rational and fundamentally based than so far attempted in the literature on this process. Simpler models are proposed for situations in which one of transport and reaction resistances is the dominant one, and criteria developed that guide the selection of the model. The model explains the empirical findings on different interfacial systems, which have been reported in the literature. An extensive parametric study has been carried out in order to explain the effect of the important dimensionless parameters that arise, and analysis shows that most of the effects observed can be rationalized with respect to certain types of asymptotic behavior. The model makes it possible to predict the time course of development of the important film properties such as thickness, MWD and crystallinity, and to relate these to the preparation conditions and system parameters, as embodied in the different dimensionless parameters. It should therefore be possible to use this model to choose synthesis conditions and system-dependent parameters to achieve desired properties.     

Rapid liquid chromatographic determination of paracetamol and diclofenac sodium from a combined pharmaceutical dosage

A simple, rapid reversed-phase HPLC method for the estimation of paracetamol and diclofenac sodium simultaneously in a combined dosage was developed. A -CN bonded phase columb was used with a mobile phase methanol-potassium dihydrogen phosphate (0.05M), (45:55) pH 3.5 adjusted with phosphoric acid at flow rate of 1.0 ml/min. For accurate quanittaiton, diltiazem hydrochloride was used as an internal standard at 270 nm.     

Empirical predictive modelling of poly-ɛ-lysine biosynthesis in resting cells of Streptomyces noursei

Poly-?-l-lysine (?-PL) biosynthesis was investigated using the resting cell culture technique and nutritional parameters were optimized with response surface methodology (RSM) and an artificial neural network (ANN). ?-PL production in resting cell cultures of Streptomyces noursei NRRL 5126 was compared using RSM and ANN optimization techniques. The predicted ?-PL yield of 924.65 mg/L using ANN simulation was in better agreement with validation experimental results of 918.35±7.56 mg/L than RSM simulation results of 966.24 mg/L. The optimized medium consisted of 3% glucose, 1% ammonium sulphate, and 5 mM citric acid in both a shake flask and a 5 L bioreactor. The shake flask ?-PL production as 1.0 g/L and bioreactor production as 2.36 g/ L was observed. The ANN predictive model was better than the RSM predictive model during nonlinear behavior of the system.     

Analysis of Nifedipine and Related Compounds in Soft Geletin Capsules by Liquid Chromatography

A simple, sensitive, highly specific, stability-indicating, reversed-phase HPLC method for the quantitation of nifedipine and its related compounds such as nitrophenyl pyridine, nitrosophenyl pyridine analogs with average recoveries greater than 100% were obtained using a mobile phase methanol-water (55:45, v/v) at 265 nm.     

In-process rheometry as a PAT tool for hot melt extrusion

Real time measurement of melt rheology has been investigated as a Process Analytical Technology (PAT) to monitor hot melt extrusion of an Active Pharmaceutical Ingredient (API) in a polymer matrix. A developmental API was melt mixed with a commercial copolymer using a heated twin screw extruder at different API loadings and set temperatures. The extruder was equipped with an instrumented rheological slit die which incorporated three pressure transducers flush mounted to the die surface. Pressure drop measurements within the die at a range of extrusion throughputs were used to calculate rheological parameters, such as shear viscosity and exit pressure, related to shear and elastic melt flow properties, respectively. Results showed that the melt exhibited shear thinning behavior whereby viscosity decreased with increasing flow rate. Increase in drug loading and set extrusion temperature resulted in a reduction in melt viscosity. Shear viscosity and exit pressure measurements were found to be sensitive to API loading. These findings suggest that this technique could be used as a simple tool to measure material attributes in-line, to build better overall process understanding for hot melt extrusion.