B.C. Yadav

Synthesis and characterization of ZnO–TiO2 nanocomposite and its application as a humidity sensor

A detailed study is reported of the synthesis and characterization of a ZnO–TiO2 nanocomposite and its application as a humidity sensor. Variations of resistance with relative humidity have been observed. The sensitivity of the sensor at different temperatures has also been calculated. Scanning electron micrographs and X-ray diffraction patterns of the sensing material were obtained at different temperatures. The minimum size of nanoparticles is found to be 50 nm at room temperature (19°C). The highest sensitivity observed at room temperature was 18 MΩ/%RH. Kelvin radii, which are the radii of pores, have also been studied; their average value at ambient temperature (19°C) is found to be 8.35 Å.

Synthesis and Characterization of ZnO Nanorods by the Hydroxide Route and Their Application as Humidity Sensors

ZnO nanorods have been synthesized through the hydroxide route, and to that, 10% glass powder was mixed. Pellets of powder were made and exposed to humidity. It is observed that as Relative Humidity (RH%) inside the chamber increases from 5% to 95%, resistance of pellets decreases successively. Further pellets were annealed for 3 hours at temperatures of 150°C, 300°C, 450°C and 550°C in an electric furnace successively. After each and every time of annealing, pellets were exposed to humidity and variations in resistance with humidity have been observed. SEM, XRD and percentage weight loss of the sample have been studied. Average diameter of nanorods is found approximately 50 nm and length around 250–350 nm.

Experimental investigations on NO2 sensing of pure ZnO and PANI–ZnO composite thin films

In the present work, comparative investigations on NO2 gas sensing properties of the hybrid nanocomposite thin films of polyaniline (PANI), ZnO and PANI–ZnO towards NO2 gas at room temperature have been reported. The effect of concentration of PANI in the composite thin films on NO2 gas sensing has been investigated. Structural and surface morphological characterizations have been carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM) respectively. The presence of 5 wt% PANI in the composite films was found to give a maximum sensing response of ∼6.11 × 102 towards 20 ppm NO2 gas having fast response and recovery time of about 2.16 min and 3.5 min respectively.

Ferrite Materials: Introduction, Synthesis Techniques, and Applications as Sensors

ABSTRACT The present review summarizes, in a detailed introduction, the synthesis techniques, structures, classifications, uses, properties, and applications of ferrite materials in the fields of sensors. Morphological and structural studies of ferrite materials were performed. A great advantage of ferrites is their porosity, which is necessary for a sensor. These pores serve as humidity or gas adsorption sites and the sensitivity of sensor depends on the size of these pores. The variation in sensitivity with operating temperature at different concentrations of gas for sensing elements CuFe2O4, CdFe2O4, and ZnFe2O4 is discussed. In addition, resistivity–humidity a characteristic and sensitivity for the MgFe2O4 and Mg0.9Sn0.1Fe2O4 corresponding to different values of percentage of relative humidity is discussed.

Morphological and Humidity Sensing Investigations on Niobium, Neodymium, and Lanthanum Oxides

This paper reports a comparative study of moisture sensing properties of niobium penta oxide, neodymium oxide, and lanthanum oxides. Pellets of these materials were made by using hydraulic pressing machine (M.B. Instruments, New Delhi, India) at a pressure of 616 MPa. These pellets were used as sensing elements and thermally annealed at temperatures 200°C and 400°C successively. After each step of annealing, the sensing element was put within a conventionally designed conductivity holder and exposed to humidity inside a controlled humidity chamber. Variations in resistance with the relative humidity were recorded for each sensing elements made of Nb2O5 , Nd2O3 , and La2O3 , respectively. Sensitivities of samples were compared at different annealing temperatures. Maximum values of sensitivities and linear response of sensors were obtained for samples annealed at 400 °C. Lanthanum oxide revealed the highest sensitivity 20 MΩ/%RH in comparison to other samples. Morphological and X-ray diffraction studies of the samples were performed. Results were found reproducible within ±5% error. No ageing effect was observed during three months.

Polymer-matrix nanocomposite gas-sensing materials

A new approach has been proposed for producing nanocomposite gas-sensing materials: in situ preparation of a polymer matrix and metal sulfide or oxide nanoparticles through the frontal polymerization of Co(II), Cd(II), Zn(II) and Pb(II) acrylamide complexes. The composition and structure of the nanocomposites thus obtained have been determined using X-ray diffraction, scanning and transmission electron microscopy, and Raman spectroscopy. The nanocomposites have been tested as room-temperature liquefied petroleum gas sensors.

Investigations on humidity sensing of nanostructured tin oxide synthesised via mechanochemical method

In this article, nanocrystalline tin oxide powder was prepared by a mechanochemical method. The synthesised powder was characterised using X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD shows the crystalline nature of the synthesised material. The crystallite size was estimated using Debye–Scherrer equation and its minimum value was 9 nm. Surface morphologies of the sensing pellets were investigated using SEM. Pellets as well as thick films were used as sensing elements for humidity sensing measurement. Thick film was prepared on alumina substrate using screen printing technique. Solid-state pellets as well as films were subjected to humidity-sensing measurements in a specially designed humidity chamber. Variations in resistance with relative humidity (%RH) were measured. The effects of annealing on the surface morphologies as well as on the sensitivity of the sensor were also investigated. Hysteresis and ageing effects on experimental results were found 60% and 64%, respectively, for the sensing element prepared after annealing at 600°C.

Nanostructured ZnFe2O4 thick film as room temperature liquefied petroleum gas sensor

In the present work, thick film of nanostructured zinc ferrite was prepared by screen printing method and its liquefied petroleum gas (LPG) sensing properties were investigated. The structural and surface morphological characterisations of the sample were analysed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The minimum crystallite size of ZnFe2O4 calculated from Scherrers formula is found to be 4 nm. SEM images exhibit the porous nature of the sensing material with a number of active sites. Optical characterisation of the film was carried out by ultraviolet–visible spectrophotometer. The estimated value of band gap of the film was found 1.91 eV. The LPG sensing properties of the zinc ferrite film were investigated at room temperature for different vol.% of LPG. The variations in electrical resistance of the film were measured with the exposure of LPG as a function of time. The maximum values of sensitivity and percentage sensor response were found 16 and 1785, respectively, for 5 vol.% of LPG. These experimental results show that nanostructured zinc ferrite is a promising material for LPG sensor.

Synthesis and porous h-BN 3D architectures for effective humidity and gas sensors

3D (three dimensional) architectures synthesised using an easily scalable solid state method which results in an interconnected network of porous h-BN sheets with boron trioxide are reported in this study. The boron trioxide acts as a nucleating agent for the formation of laterally large nanosheets of h-BN with a low density and increases the specific surface area. The stable form shows improved mechanical properties (experimentally and using MD simulation) and serves as a suitable material for humidity and liquefied petroleum gas (LPG) sensor applications. The sensor shows stability for up to several months without losing its sensitivity.

Experimental investigations on barium titanate nanocomposite thin films as an opto-electronic humidity sensor

This article reports the synthesis and characterisation of Barium titanate (BaTiO3) nanocomposite and its application as opto-electronic humidity sensor. Titanium tetrachloride and barium hydroxide were mixed in molar ratio 1 : 1 in deionised water under continuous stirring at room temperature. Later, sodium hydroxide solution was added to above solution with continuous stirring. Finally, BaTiO3 gel was obtained. The synthesised nano-composite material was characterised using a scanning electron microscope, X-ray diffraction (XRD) and UV-Visible spectrophotometer. SEM image of the composite film shows that the film is porous having uniform grains. From XRD the minimum crystallite size of BaTiO3 was found to be 8 nm using Debye–Scherer formula. UV-Visible absorption spectroscopy was used for optical characterisation of the film. It was found that the optical band gap of the composite material was 3.50 eV. Barium titanate thin film was deposited on the base of an equilateral prism using sol–gel spin coating process at 4000 rpm. The humidity sensing properties of the film was investigated at different angles of incidence. It was observed that the intensity of reflected light increased with an increase in relative humidity (%RH) in the range 5–95% at a particular angle of incidence. Sensing element has maximum sensitivity ∼6 µW/%RH, which is quite significant for sensor fabrication purposes.