Veda Ramaswamy

Synthesis of nanocrystalline SnO2 powder by amorphous citrate route

Abstract Nanocrystalline SnO 2 has been synthesized by liquid mix technique using citric acid as the complexing agent. The tin oxide powder obtained at different calcination temperatures (773–1223 K) is characterized using powder X-ray diffraction (XRD), SEM, TEM, TG-DTG and UV spectroscopic techniques. The material obtained is nanocrystalline, having particle size in the range of 10–14 nm. The technique is cost-effective and yields the desired product at temperatures as low as 773 K.

Photocatalytic decomposition of methylene blue using nanocrystalline anatase titania prepared by ultrasonic technique

Abstract Nanocrystalline particles of pure anatase titania were prepared by sol–gel method at ambient temperature using ultrasonication (Ti-US). The advantages of ultrasonication method are demonstrated as compared to the conventional stirring method of preparation of titania (Ti-S). The physico-chemical properties of the samples were investigated by powder XRD, SEM, TEM, low temperature (77 K) nitrogen sorption, and UV–Vis spectroscopic techniques. More uniform distribution/dispersion of the nanoparticles (SEM), marginally higher surface area, better thermal stability, and phase purity are some of the advantages of preparation of nanocrystalline titania by ultrasonication method. The UV–Vis diffuse reflectance spectra of the samples prepared by ultrasonication method were blue shifted compared to pure anatase due to decrease in particle size. The behavior of anatase titania in photocatalytic decomposition of methylene blue in aqueous medium was studied as a function of the method of preparation and the crystallite size. The nanoparticles prepared by ultrasonication method were more effective than both, the sample prepared by conventional stirring method and commercial Degussa P-25. The higher photocatalytic activity of Ti-US is attributed to the more uniform size of the particles as compared to Ti-S samples.

Factors affecting the preparation of alumina pillared montmorillonite employing ultrasonics

In the preparation of alumina pillared clays, the intercalation step is shown to be completed within a few minutes using ultrasonics, and such materials show enhanced textural properties and improved thermal stability. The role of ultrasonics and various preparative parameters that govern the preparation of alumina pillared montmorillonite are presented. This includes the effect of exchangeable cations (Na, Ca, La), three different pillaring precursors, the concentration of pillaring species, and the concentration of the clay in suspension. It is shown that the exchangeable cations and their mode of binding influence the diffusional rates of the pillaring species. When different pillaring precursors are employed, not much variation in the textural properties of pillared clays is noticed. However, their optimum concentration is essential. It is also observed that this method can handle a concentrated clay suspension for pillaring with alumina. From the kinetics of calcium exchange experiments during pillaring, it was observed that the exchange under conventional conditions is completed instantaneously, while under ultrasonic treatment only 26% of Ca2+ exchange took place instantaneously and further exchange occurred only after ultrasonic treatment. From these observations, it is proposed that the role of ultrasonics in the present synthesis is the acceleration of diffusion of the intercalating aluminium pillaring species followed by an ion exchange process.

Immobilization and characterization of copper chlorophthalocyanine on alumina-pillared montmorillonite

Alumina-pillared montmorillonite (Al-PILC) has been used as the host material for the immobilization of copper-tetra decachlorophthalocyanine (Cu-Cl14Pc) complex using ultrasonic technique. Thermogravimetric (TG)/DTG analysis, BET surface area, XRD, FT-IR and UV–VIS spectroscopic techniques have been used to characterize samples containing different concentrations of copper (0.104–0.152 wt.%) in Al-PILC. The studies reveal that Cu-Cl14Pc is present in the porous structure of Al-PILC and that the immobilized samples prepared by ultrasonication contain better-dispersed Cu-Cl14Pc compared to the sample prepared by normal agitation method. The catalytic activity for the hydroxylation of phenol to catechol and hydroquinone using the immobilized Cu-Cl14Pc and H2O2 is reported. The immobilized copper is the active center in the hydroxylation. The method of preparation and dispersion of Cu-Cl14Pc influence the catalytic activity.

Intercalation of Al oligomers into Ca2+ -montmorillonite using ultrasonics

Enhanced thermal stability and textural properties can be induced into pillared interlayered clays when aluminium oligomers are intercalated into the Ca2+ form of montmorillonite clay using ultrasonics within 20 min at ambient temperature.

Lattice thermal expansion of LaCo1-xCuxO3

Abstract Lattice thermal expansion studies on LaCo 1− x Cu x O 3 ( x =0, 0.02, 0.05, 0.1, 0.3 and 0.5) were carried out by high temperature XRD from room temperature to 1173 K. A linear increase in lattice parameter was observed with increase in copper concentration indicating the substitution of copper in the lattice. The % volume thermal expansion (∇ V ∗100/V) increases with temperature. As the copper concentration increases from 0.0 to 30 mol.%, the % volume thermal expansion decreases from 5.98 to 4.522. The lattice and volume thermal expansion coefficients (TEC), ᾱ a , ᾱ c , and ᾱ v averaged between 298 and 1023 K are calculated using the HTXRD data. ᾱ a, ᾱ c and ᾱ v decreased from 26.78×10 −6 to 18.27×10 −6 K −1 , 27.81×10 −6 to 24.56×10 −6 K −1 and 82.45×10 −6 to 72.9×10 −6 K −1 , respectively, as the copper concentration increased from 0 to 30 mol.%. The decrease in TEC with copper loading is due to the introduction of the covalent character of the Cu–O bond in the otherwise ionic nature of the La–O bond in LaCoO 3 . The larger decrease in ᾱ a as compared to ᾱ c confirms the substitution of more copper in the a–b plane rather than in the c -axis.

Immobilization of bile salt hydrolase enzyme on mesoporous SBA-15 for co-precipitation of cholesterol.

We describe herein a simple and effective strategy for immobilization of bile salt hydrolase enzyme by grafting glutaraldehyde groups inside channels of APTES functionalized SBA-15. The increase in glutaraldehyde concentration prevents leakage of enzyme but showed a steep decrease in enzyme activity in the immobilized matrix. So the degree of cross-linking should be the minimum possible to ensure sufficient stability without loss of activity. Cross-linking carried out with 0.1% glutaraldehyde concentration showed the highest activity, so this was used in all further experiments. Physico-chemical characterizations of the immobilized enzyme were carried out by XRD, N2 adsorption, TEM, FTIR and (29)Si CP-MAS NMR techniques. Immobilized BSH exhibits enhanced stability over a wide pH (3-11) and temperature range (40-80 °C) and retains an activity even after recycling experiments and six months of storage. From our in vivo research experiment toward co-precipitation of cholesterol, we have shown that immobilized BSH enzyme may be the promising catalyst for the reduction of serum cholesterol levels in our preliminary investigation. Enhancement in pH stability at the extreme side of pH may favor the use of immobilized BSH enzyme for drug delivery purpose to with stand extreme pH conditions in the gastrointestinal conditions.

Incorporation of tin into mesoporous silica SBA-15 molecular sieves

Abstract Mesoporous silica SBA-15 molecular sieves have been incorporated with various amounts of Sn by repeated post grafting technique using two different metal precursors viz., Sn acetate and Sn chloride. Physico chemical characterization was done by X-ray fluorescence spectrophotometer (XRF), powder X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy (TEM), FTIR, Sn-Mossbauer and 119Sn MAS NMR spectroscopic methods to understand the chemical nature of incorporated Sn. Higher amounts of Sn could be incorporated into SBA-15 using Sn acetate. Adding dilute HCl to parent SBA-15 in the acetate precursor could have increased the number of silanol groups, thereby facilitating the incorporation of higher amounts of Sn. XRD data indicate a good mesoscopic order. The characteristic hexagonal features of SBA-15 were maintained in Sn-SBA-15 samples. Incorporation of Sn does not affect the original pore structure of the parent SBA-15 event at high Sn loading. The silanol groups on the internal walls of SBA-15 are suggested to be the sites for Sn incorporation. 119Sn NMR shows an isotropic chemical shift at δ=−604 ppm which indicates the presence of Sn in essentially octahedral environment. Sn Mossbauer spectroscopic studies reveal that Sn2+ may form upon reductive treatments and can probably be stabilized atomically in the pore wall, whereas Sn4+ is stabilized as large size entities.

Crystallization of SrCO3 within thermally evaporated fatty acid films: unusual morphology of crystal aggregates

Reaction of CO2 with electrostatically entrapped Sr2+ ions within thermally evaporated stearic acid films leads to the in-situ growth of SrCO3 crystals in highly organized assemblies, the organization possibly occurring due to hydrophobic association of the crystallites covered by a monolayer of stearic acid.

Immobilization of Ntn hydrolases on APTES fuctionalized SBA-15

APTES Functionalized mesoporous silica SBA-15 molecular sieves have been prepared and used for immobilization of Penicillin G acylase. Physico chemical characterization was done by nitrogen adsorption, powder XRD and TEM methods to understand the nature of immobilized PGA enzyme. XRD data indicate a good mesoscopic order. The characteristic hexagonal features of SBA-15 were maintained in PGA immobilized SBA-15 samples. Incorporation of PGA does not affect the original pore structure of the parent SBA-15. The adsorption of PGA on SBA-15 from buffered solutions with a pH value, 7.8 has been studied as a model protein adsorption system. The maximum activity of the immobilized enzyme was observed at pH 7.8, slightly below the isoelectric point of the enzyme. The loading capacity of immobilized PGA is 34 mg protein per 0.5 g of SBA-15. The stability of Penicillin G acylase was enhanced by the physical entrapment in SBA-15.