C.V. Gopal Reddy

SEMICONDUCTING GAS SENSOR FOR CHLORINE BASED ON INVERSE SPINEL NICKEL FERRITE

Abstract Nickel ferrite, a p-type semiconducting oxide with an inverse spinel structure has been used as a gas sensor to selectively detect chlorine in air. This compound was prepared by two different routes namely, the citrate and co-precipitation method and sensor properties of the resulting compounds from both the methods were compared. X-ray diffraction was used to confirm the structure. The gas sensing characteristics were obtained by measuring the sensitivity as a function of various controlling factors like dopant, concentration of the dopant, operating temperature, concentration of the gas and finally the response time. The sensitivity to chlorine has been compared with that of other interfering gases. A probable explanation has been proposed to explain the selective sensitivity to oxidising gases like chlorine.

LIQUID-PETROLEUM-GAS SENSOR BASED ON A SPINEL SEMICONDUCTOR, ZNGA2O4

Abstract A liquid-petroleum gas sensor has been developed with high selectivity and sensitivity based on an oxygen deficient spinel semiconductor, ZnGa2O4. The operating temperature of the sensor element has been optimised under different operating conditions. Palladium doped zinc gallate sensor, on exposure to LPG at about 320°C showed a change of 4–5 orders in the resistance. The response time also decreases from about 20 min in virgin ZnGa2O4 to less than 1 min in the palladium doped element. The electronic interaction between additive and semiconductor is proposed to account for the sensitisation effects in the sensor element.

Photostabilization of dye on anatase titania nanoparticles by polymer capping

Abstract Nanoparticles of titanium dioxide (TiO2) were prepared by the sol–gel method and characterized by XRD, TEM, FTIR and UV-Visible absorption spectroscopy for their structure, morphology and particle size. Organization, stabilization of the nanoparticles of TiO2 from further growth, and partially inhibiting the photodegradation was achieved by capping with polymers. Photodegradation of dye on TiO2 nanoparticles encapsulated in different polymers has been studied by diffused reflectance UV spectroscopy. The role of the polymer on the photodegradation of TiO2 has been compared and explained.

X-ray photoelectron spectroscopic studies of noble metal-incorporated BaSnO3 based gas sensors☆

Abstract Barium stannate, a semiconducting oxide with cubic perovskite structure prepared by the thermal decomposition method, was incorporated with different noble metal additives. The gas sensing behavior of these materials to various reducing gases like liquefied petroleum gas (LPG), CH 4 and CO have been studied. The gas sensing characteristics established a relation between the sensitivity of the sensor to the different test gases and the work function of the noble metal additive. The results suggest that the greater the work function of the additive, the greater the depletion width of the semiconductor in air and the higher the sensitivity to the reducing gas. X-ray photoelectron spectroscopy studies have been carried out to understand the mechanism of sensing in these oxides. It has been established that in the case of Pd and Ag-incorporated BaSnO 3 it is predominantly the electronic sensitization through a direct interaction between these metals and the semiconductor surface, while in case of Pt-incorporated BaSnO 3 it is the chemical interaction which plays the major role in the gas sensing reaction.

Noble metal additive modulation of gas sensitivity of BaSnO3, explained by a work function based model

Barium stannate, a semiconducting oxide with cubic perovskite structure, has been prepared by the thermal decomposition method. Of its several applications, this material has proved to be one of the successful candidates for chemical sensors to detect toxic and inflammable gases. BaSnO 3 was incorporated with different noble metal additives and the gas sensing behavior of these materials to various reducing gases like LPG, CO and CH 4 have been studied. A model for the electronic interaction between additives and semiconducting BaSnO 3 gas sensors is discussed. The model is based on the depletion layer that is created due to metal-semiconducting oxide contact. Change of the gas sensor characteristics before and after the exposure to the different test gases has been explained on the basis of work function of metal additives. The valence band X-ray photoelectron spectroscopy studies were used to support the results on the gas sensing characteristics in each of the noble metal incorporated BaSnO 3 sensor materials and bring out the difference in the sensing mechanisms in these materials.

Preparation of γ-Fe2O3 by the hydrazine method ☆: Application as an alcohol sensor

Abstract The preparation of γ-Fe 2 O 3 by the thermal decomposition of Fe 3 O 4 obtained from the hydrazine reduction of ferric nitrate was studied employing differential thermal analysis (DTA), and X-ray diffraction (XRD). Here we report a simple technique that does not need any explosive or high-energy reactions to obtain γ-Fe 2 O 3 . The ethanol sensitivity of pure and Pt doped γ-Fe 2 O 3 were investigated by studying the electrical resistance characteristics of sensor elements prepared from this material. The Pt doped sensor elements showed a linear response of sensitivity, in the range of 1–1000 ppm ethanol in air, in the logarithmic scale. γ-Fe 2 O 3 behaves as an n-type basic semiconducting oxide when exposed to ethanol vapors and in turn ethanol probably decomposes via the route of CH 3 CHO to form CO 2 and H 2 O. The maximum sensitivity after Pt incorporation is found at 175°C. The high sensitivity of the sensor to ethanol can be explained on the basis of a catalytic activity that invokes the acid base properties of the test gas and the sensor surface. The response time of the elements to 10 ppm ethanol in air is less than 30 s. Cross sensitivity to other gases like liquefied petroleum gas (LPG), CO, CH 4 , H 2 , H 2 S and NH 3 was also studied.

Tin dioxide nanoparticles prepared by sol-gel method for an improved hydrogen sulfide sensor

Semiconducting tin dioxide incorporated with specific additives has been prepared by the technique of sol-gel to achieve particle sizes in the range of nanometers. This reduced size has been shown to significantly improve the gas sensing characteristics of the sensor elements. Sensitivity of tin dioxide doped with CuO prepared by this method shows an increase in sensitivity over the same composition obtained by conventional hydrolysis method. The results clearly brings out the influence of the crystallite size on the gas sensing characteristics of sensors based on these semiconducting materials.

Preparation and characterization of barium stannate: application as a liquefied petroleum gas sensor†

Barium stannate, BaSnO3, an n-type semiconducting oxide with cubic perovskite structure, has been prepared by the thermal decomposition of barium carbonate (BaCO3) and tin tetrahydroxide (Sn(OH)4). The material was characterized by various physical techniques such as differential thermal analysis (DTA/TG), X-ray diffraction (XRD), BET surface area, Fourier transform infra-red (FT-IR) spectroscopy and scanning electron microscopy (SEM). Of its several applications, this material has proven to be one of the successful candidates for the detection of liquefied petroleum gas (LPG). The sensor has a very good selectivity to detect LPG in comparison to other reducing gases, like carbon monoxide and methane.

Influence of La2O3 loading on SnO2 based sensors

Influence of La2O3 loading on the structural and gas sensing properties of SnO2 have been studied. The effect of different weight percentages of La2O3 (1–10 wt.%) in SnO2, and the effect of calcination temperature on the sensitivity to various reducing gases like LPG, H2 and CH4 has been studied. The structural characteristics have been investigated by X-ray diffraction, and the corresponding crystallite size estimated. In addition to the systematic variation in the crystallite size as a function of the sintering temperature, the role of La2O3 as an effective grain growth inhibitor has been confirmed. Increasing the percentage of La2O3 above 2 wt.% has no added advantage in terms of improving the gas sensing characteristics and also in stabilizing the SnO2 surface. Once the La2Sn2O7 formation temperature is reached, the sensitivity of the sensor decreases marginally. At this temperature the crystallite size also increases very abruptly. All these have been correlated with the formation of the La2Sn2O7, a new phase with standard pyrochlore structure.