G. Sarala Devi

HYDROGEN SULFIDE SENSOR BASED ON TIN OXIDE DEPOSITED BY SPRAY PYROLYSIS AND MICROWAVE PLASMA CHEMICAL VAPOR DEPOSITION

Spray pyrolysis and microwave plasma chemical vapor deposition techniques have been employed successfully for the deposition of CuO impregnated SnO2 films suitable for sensing hydrogen sulfide and methyl mercaptan. The observed change in conductivity of these films upon exposure to H2S gas in air has been explained on the basis of the band theory of solids.

High sensitivity and selectivity of an SnO2 sensor to H2S at around 100 °C

Abstract The effect of preparation conditions on the sensitivity of tin-oxide-based semiconducting gas sensors has been studied by appropriately engineering the base material. The incorporation of CuO as an additive has significantly improved the sensing character of the sensor element. These sensor elements have been made sensitive to low concentrations (about 10 ppm and less) of hydrogen sulphide in air. Further, the operating temperature for maximum sensitivity has been considerably reduced to about 90–100 °C. These elements have been tested for cross sensitivity to other gases and confirmed unambiguously to be specifically sensitive to H 2 S, which is detected with maximum sensitivity. A plausible mechanism is proposed to explain this behaviour.

SnO2:Bi2O3 based CO sensor: Laser-Raman, temperature programmed desorption and X-ray photoelectron spectroscopic studies

Abstract The sensitivity and selectivity of tin oxide (SnO2) based gas sensors towards carbon monoxide (CO) was improved by doping the base material with Bi2O3 and Sb2O3. Laser-Raman studies of the compound confirm the formation of bismuth stannate (Bi2Sn2O7) above 800°C, which seems to be acting as a molecular sieve allowing only CO gas to react with the sensor surface, thereby imparting selectivity to the sensor. The chemisorption of oxygen on SnO2:Bi2O3 was investigated over a wide range of temperatures from room temperature to 800°C by means of Temperature Programmed Desorption (TPD) and X-ray Photoelectron Spectroscopic (XPS) studies which were carried out to establish the exact chemical species present on the sensor surface before and after the reaction.

Vapour phase O-alkylation of phenol over alkali promoted rare earth metal phosphates

The vapour phase synthesis of anisole by O-alkylation of phenol with methanol was investigated over lanthanum, cerium, samarium, and antimony phosphate catalysts promoted with cesium hydroxide. Among various catalysts investigated, the cesium promoted samarium phosphate provided better activity and selectivity. The effect of temperature, contact time, time-on-stream, reusability, and up-scaling of the catalyst were also studied. These studies clearly reveal that the Cs-Sm combination is the superior catalyst for selective O-alkylation of phenol with methanol. The unpromoted catalysts provided more C-alkylated side products. Incorporation of cesium suppressed the formation of side products. The X-ray diffraction analysis of various samples revealed that there is no change in the crystalline composition of the catalysts up on addition of cesium promoter. However, the surface acidity of the catalyst was observed to decrease after the incorporation of cesium promoter as revealed by the temperature programmed desorption study of anhydrous ammonia.

Nickel-Impregnated Silica Nanoparticle Synthesis and Their Evaluation for Biocatalyst Immobilization

In the present investigation, impact of nickel-impregnated silica paramagnetic particles (NSP) as biocatalyst immobilization matrices was investigated. These nanoparticles were synthesized by sol–gel route using a nonionic surfactant block co polymer [poly (ethylene glycol)-block-poly-(propylene glycol)-block-poly (ethylene glycol)]. Diastase enzyme was immobilized on these particles (enzyme-impregnated NSP) as model enzyme and characterized using Fourier-transform infrared spectroscopy and X-ray crystallography. Analysis of enzyme-binding nature with these nanoparticles at different physiological conditions revealed that binding pattern and activity profile varied with the pH of the reaction mixture. The immobilized enzyme was further characterized for its biocatalytic activity with respect to kinetic properties such as Km and Vmax and compared with free enzyme. Paramagnetic nanoparticle-immobilized enzyme showed more affinity for substrate compared to free one. The nature of silica and nickel varied from amorphous to crystalline nature and vice versa upon immobilization of enzyme. To the best of our knowledge, this is the first report of its kind for change of nature from one form to other under normal temperatures upon diastase interaction with NSP.

Room temperature synthesis of colloidal platinum nanoparticles

Efficient preparation of stable dispersions of platinum nanoparticles from platinous chloride (K2PtCl4) was achieved by simultaneous addition of capping polymer material. The size of platinum nanoparticles was controlled by changing the ratio of concentration of capping polymer material to the concentration of platinum cation used. The morphology of colloidal particles were studied by means of UV-visible spectrophotometry and transmission electron microscopy (TEM). Particle size increased with low reagent concentration. The change in absorption spectra with the particle size was observed, i.e. blue shift attributed to decrease in particle size

Correlation between structural properties and gas sensing characteristics of SnO2 based gas sensors

Undoped polycrystalline tin oxide sintered in the temperature range 500–1000 °C has been comprehensively characterized with respect to its response to CO, methane and H2. Results obtained at an operating temperature of 300 °C show that increasing the sintering temperature leads to a gradual increase in CO sensitivity which reaches a maximum after sintering at 800 °C.

Boron nitride thin films on Si(100) by metal organic chemical vapour deposition

Abstract Crystalline boron nitride thin films have been deposited on silicon substrates by MO-CVD at different temperatures using a single source III–V precursor in N2 ambient. The deposited films are characterized by XRD and IR techniques. XRD confirms that the films are mostly polycrystalline with (111), (200), (004), (103) oriented cubic and hexagonal phases of boron nitride. IR also shows a mixture of cubic and nexagonal boron nitride phases.

Effect of pH on Synthesis of Single-Phase Titania (TiO2) Nanoparticles and its Characterization

In the present study, we investigated the effect of pH on phase transition of TiO2 nanoparticles synthesized by sol-gel protocol and identification by various techniques as x-ray diffraction, energy dispersive x-ray spectroscopy (EDX), Raman spectroscopy, scanning electron microscopy, etc. Corresponding TiO2 phase change from rutile to anatase and mixture of both anatase and rutile phases by tuning the pH of the reaction mixture is clear from x-ray diffraction studies. The presence of (101) and (110) planes corresponded to anatase and rutile phases of TiO2, respectively.

MOCVD growth of boron nitride films from single source III–V precursor

The sp2 and sp3 phases of boron nitride (BN) have been deposited on Si and Ni substrates by low pressure MO-CVD (metal organic chemical vapour deposition) at 450 °C from diethylaminoborane and the films were characterised by Fourier transform infrared (FTIR) and X-ray diffraction (XRD); a plausible mechanism of CVD is proposed from gas-phase decomposition studies, and to our knowledge this is the first report of the growth of BN by MO-CVD using a single source.