V. Sudarsan

SnO2:Eu3+ nanoparticles dispersed in TiO2 matrix: Improved energy transfer between semiconductor host and Eu3+ ions for the low temperature synthesized samples

SnO2:Eu3+ nanoparticles uniformly dispersed in TiO2 matrix were prepared at 185°C in ethylene glycol. Unlike in SnO2:Eu3+, significant improvement in the exciton mediated energy transfer between SnO2 and Eu3+ ions was observed when SnO2:Eu3+ nanoparticles are dispersed in TiO2 matrix, and this is attributed to effective shielding of surface Eu3+ ions present in SnO2:Eu3+ nanoparticles from the vibrations of stabilizing ligand by TiO2 matrix. Annealing the samples at high temperatures leads to formation of Sn1−xTixO2, without significantly affecting the energy transfer process between Eu3+ ions and semiconductor host.

Improved photocatalytic activity of indium doped cadmium sulfide dispersed on zirconia

A novel composite photocatalyst of indium doped cadmium sulfide dispersed on zirconium oxide has been synthesized, which shows enhanced photocatalytic activity for hydrogen generation from water. In this system, cadmium sulfide exists as a separate dispersed phase on the zirconia support. Optical absorption spectra indicate a blue shift of absorption edge for CdS and In doped CdS dispersed on ZrO2 compared to pure CdS and indium doped CdS. Among the supported CdS, In doped CdS exhibits better optical absorption property. Photocatalytic studies for hydrogen generation from water show an enhanced activity for CdS dispersed on ZrO2 and indium doping in CdS enhances the activity further. Fluorescence lifetime studies indicate that, in the supported CdS, the charge carriers have higher lifetime than that in the unsupported CdS. Photocurrent response experiments show a relatively higher current output for the In doped CdS dispersed on ZrO2 support. The enhanced photocatalytic activity of this composite sample is attributed to a combination of factors like enhanced lifetime of the photogenerated charge carriers, increased photoresponse and improved surface area. The present study leads to a new observation that the photocurrent response and photocatalytic activity of CdS and indium doped CdS are enhanced when they are dispersed on a support like ZrO2. These composites with Pd as co-catalyst exhibit a large increase in the photocatalytic activity due to the increased availability of electrons on the metal surface by the interfacial transfer of electrons from CdS to Pd, when irradiated.

Structural aspects of B2O3-substituted (PbO)0.5(SiO2)0.5 glasses

Lead borosilicate glasses having general formulae (PbO)0.5 −x(SiO2)0.5(B2O3)x with 0.0 ≤ x ≤ 0.4 and (PbO)0.5(SiO2)0.5 −y(B2O3)y with 0.0 ≤ y ≤ 0.5 have been prepared by a conventional melt–quench method and characterized by 29 Si, 11 B magic angle spinning (MAS) NMR techniques and infrared spectroscopy, as regards their structural features. From 29 Si NMR results, it has been inferred that with increasing concentration of boron oxide, (PbO)0.5 −x(SiO2)0.5(B2O3)x glasses exhibit a systematic increase in the number of Q4 structural units of Si at the expense of Q2 structural units, along with the formation of Si–O–B linkages. On the other hand, for (PbO)0.5(SiO2)0.5−y(B2O3)y glasses, there is no direct interaction between SiO2and B2O3 in the glass network, as revealed by the 29 Si MAS NMR studies. Boron exists in both trigonal and tetrahedral configurations for these two series of glasses and for the (PbO)0.5(SiO2)0.5−y(B2O3)y series of glasses; the relative concentration of these two structural units remains almost constant with increasing B2O3 concentration. In contrast, for (PbO)0.5−x(SiO2)0.5(B2O3)x glasses, there is a slight increase in the number of BO3 structural units above x = 0.2, as there is a competition between SiO2 and B2O3 for interaction with Pb2+, thereby leading to the formation of BO3 structural units. For both series of glasses, the thermal expansion coefficient is found to decrease with increasing B2O3 concentration, the effect being more pronounced for the (PbO)0.5 −x(SiO2)0.5(B2O3)x series of glasses due to the increased concentration of Q4structural units of silicon and better cross-linking as a result of the formation of Si–O–B-type linkages.

Mesoporous SAPO-5 (MESO-SAPO-5): a potential catalyst for hydroisomerisation of 1-octene

Mesoporous silicoaluminophosphate was assembled from microporous SAPO-5 secondary building unit precursors. The resultant material possessed both mesoporous channel properties and microporous wall properties. The catalyst showed promising results for vapour phase isomerisation of 1-octene. The presence of strong acidic sites favoured the formation of considerable skeletal isomerised products at elevated temperatures (400–450 °C). However, the catalytic conversion remains constant and active for several hours.

Enhanced quantum efficiency for Dy3+ Emissions in water dispersible PbF2 nanocrystals

PbF2 nanocrystals found to be a better host for Dy3+ ions to exhibit better quantum efficiency. The optimum dopant concentration is found to be higher than that observed in several bulk materials. The nanocrystals are rendered water dispersible by coating poly(acrylic acid) over their surface.

29Si MAS NMR and microhardness studies of some lead silicate glasses with and without modifiers

Abstract Lead silicate glasses having different mole ratios of SiO2 to PbO and containing different amounts of alkali/alkaline earth metal oxides were prepared by conventional melt-quench method. The different structural units of Si present in these glasses were identified by 29Si MAS NMR. Addition of PbO above 50 mol% to SiO2 and Na2O up to 15 mol% in (SiO2)0.5(PbO)0.5 glasses has been found to give similar 29Si MAS NMR patterns, characteristic of depolymerised silicon structural units (Q2 and Q1), which interconnect the extended Pb–O–Pb network in the glass. The microhardness values of lead silicate glasses show systematic decrease with increase in lead oxide contents. The microhardness values of lead silicate glasses having SiO2 to PbO mole ratio 6.9 and containing different amounts of alkali/alkaline earth metal oxides, have been found to vary in a complex manner. For higher concentrations of alkali/alkaline earth metal oxides, microhardness values have been found to decrease, probably due to conversion of more rigid covalent Q4, and Q3 structural units to less rigid Q2 and Q1 structural units.

Nature of the Pd–CNT interaction in Pd nanoparticles dispersed on multi-walled carbon nanotubes and its implications in hydrogen storage properties

Oleyl amine stabilised Pd nanoparticles have been prepared by reverse micro-emulsion method and supported on multi walled CNTs. TEM studies have confirmed that Pd nanoparticles, having sizes in the range of 3–5 nm, are well dispersed on the CNTs. Based on 13C MAS NMR and TG-DTA studies it is inferred that the Pd nanoparticles interact with CNT support to form sp3 carbon species, which get effectively dispersed on the CNTs. Such finely dispersed Pd nanoparticles facilitate the spillover of hydrogen to the CNT support and improve the hydrogen storage capacity.

Barium borosilicate glass as a matrix for the uptake of dyes

Barium borosilicate (BBS) and sodium borosilicate (SBS) glass samples, prepared by the conventional melt-quench method, were used for the uptake of Rhodamine 6G dye from aqueous solution. The experimental conditions were optimized to get maximum uptake and was found to be 0.4 mg of dye per gram of BBS glass sample. For the same network former to modifier ratio, barium borosilicate glasses are found to have improved extent of uptake for the dye molecules from aqueous solutions compared to sodium borosilicate glasses. Based on 29Si MAS NMR studies on these glasses, it is inferred that significantly higher number of non-bridging oxygen atoms present in barium borosilicate glasses compared to sodium borosilicate glasses is responsible for its improved uptake of Rhodamine 6G dye. 11B MAS NMR studies have confirmed the simultaneous existence of boron in BO3 and BO4 configurations in both barium borosilicate and sodium borosilicate glasses. The luminescence studies have established that the dye molecule is incorporated into the glass matrix through ion exchange mechanism by replacing the exchangeable ions like Na+/Ba2+ attached with the non-bridging oxygen atoms present in the glass.

Structural, luminescence and EPR studies on SrSnO3 nanorods doped with europium ions

The present study describes the structural and luminescent properties of SrSnO(3) nanorods containing Eu(3+) ions. Based on Rietveld refinement of XRD patterns corresponding to both undoped and europium doped SrSnO(3) nanorods, it is inferred that the average bond lengths of Sr-O1 linkages, which have a square planar geometry around Sr(2+) in the SrO(12) polyhedra present in SrSnO(3), remained unaffected with Eu(3+) incorporation into the lattice. However, the average bond lengths of shorter Sr-O2 linkages increase and longer Sr-O2 linkages decrease with Eu(3+) doping into the SrSnO(3) lattice. A lack of variation in the lattice parameters of SrSnO(3) with doped Eu(3+) ions is explained based on mutually compensating changes in the average bond lengths of the Sr-O2 linkages in the unit cell. Luminescence studies have confirmed that Eu(3+) ions occupy the centrosymmetric Sr(2+) site only up to 2 at%, beyond which Eu(3+) ions exist in a significantly distorted environment (grain boundaries). Beyond 3%, incorporation of Eu(3+) ions into the SrSnO(3) lattice leads to the formation of a Eu(2)Sn(2)O(7) phase. From the EPR studies it is confirmed that around 5% of the incorporated Eu(3+) ions get converted to Eu(2+) ions and they occupy Sr(2+) sites in the lattice.

Lanthanide-ion-assisted structural collapse of layered GaOOH lattice.

GaOOH nanorods were prepared by hydrolysis of Ga(NO(3))(3)·xH(2)O by urea at ~100 °C in the presence of different amounts of lanthanide ions like Eu(3+), Tb(3+), and Dy(3+). On the basis of X-ray diffraction and vibrational studies, it is confirmed that layered structure of GaOOH collapses even when very small amounts of lanthanide ions (1 atom % and more) are present in the reaction medium during the synthesis of GaOOH nanorods. The incorporation of lanthanide ions at the interlayer spacing of the GaOOH lattice, followed by its reaction with OH groups that connect the layers containing edge-shared GaO(6) in GaOOH, is the reason for the collapse of the layered structure and associated amorphization. This leads to the formation of finely mixed hydroxides of lanthanide and gallium ions. These results are further confirmed by steady-state luminescence and excited-state lifetime measurements carried out on the samples. The morphology of the nanorods is maintained upon heat treatment at high temperatures like 500 and 900 °C, and during this process, the finely mixed lanthanide and gallium hydroxides facilitate diffusion of lanthanide ions into the Ga(2)O(3) lattice, as revealed by the existence of strong energy transfer with an efficiency of more than 90% between the host and lanthanide ions.