Search

Air pollution is a big concern as it causes harm to human health as well as environment. NO2 can cause several respiratory diseases even in low concentration and therefore an efficient sensor for detecting NO2 at room temperature has become one of the priorities of the scientific community. Although two dimensional (2D) materials (MoS2 etc.) have shown potential for NO2 sensing at lower temperatures, but these have poor desorption kinetics. However, these limitations posed by slow desorption can be overcome, if a material in the form of a p-n junction can be suitably employed. In this work, ~150 nm thick SnSe2 thin film has been deposited by thermally evaporating in-house made SnSe2 powder. The film has been studied for its morphological, structural and gas sensing applications. The morphology of the film showed that the film consists of interconnected nanostructures. Detailed Raman studies further revealed that SnSe2 film had 31% SnSe. The SnSe-SnSe2 nanostructured sensor showed a response of ~112% towards 5 ppm NO2 at room temperature (30 °C). The response and recovery times were ~15 seconds and 10 seconds, respectively. Limit of detection for NO2 was in sub-parts per million (sub-ppm) range. The device demonstrated a better response towards NO2 compared to NH3, CH4, and H2. The mechanism of room temperature fast response, recovery and selective detection of NO2 independent of humidity conditions has been discussed based on physisorption, charge transfer, and formation of SnSe-SnSe2 (p-n) nano-junctions. Depositing a nanostructured film consisting of nano-junctions using an industrially viable thermal evaporation technique for sensing a very low concentration of NO2 is the novelty of this work.

Dodecyl benzene sulfonic acid (DBSA) doped polyaniline (PANI) has been synthesized by ex-situ doping inemeraldine base (EB). The optical and functional properties of as synthesized DBSA doped PANI (PANI-DBSA) have been studied by UV-Visible and FTIR spectroscopy, respectively. A chemo-resistive gas sensorwas prepared using spin coated PANI-DBSA thin film for quantitative detection of ammonia (NH 3 ) under ambi-ent conditions (27 C, 50% RH). The sensing characteristics of fabricated sensor were recorded using thedynamic resistance measurement, that revealed high sensitivity in relative response (∼4.5), response time(∼55 sec) and rapid recovery (∼100 sec). The PANI-DBSA thin film sensor shows good linearity ( R =0.996)and repeatability over a wide concentration range of NH 3 from 5 to 250 ppm.KEYWORDS: Conducting Polymers, Polyaniline, Dodecyl Benzene Sulfonic Acid (DBSA), Ammonia. 1. INTRODUCTION Ammonia (NH 3 ) is widely used in the production of fer-tilizer, chemicals, refrigeration systems, medical diagno-sis system, material processing and its global productionexceeds from 100 million tons per annum. Its long-termexposure of about 8 hours and inhalation to higher con-centrations≥5000ppmcancauseserioushealthhazards.

Nanocrystalline composite thin films of Zinc oxide and Tin oxide (ZSO) have been synthesized using chemical route for the efficient trace level (20 ppm) detection of NO2 gas at lower operating temperature. The prepared ZSO sensor structure showed a high sensing response of about 1 578× 103 towards 20 ppm of NO2 gas at a lower operating temperature of 70 C with an average response and recovery time of 3.91 min. and 6.91 min. respectively. The structural, optical and surface morphological properties of the ZSO composite thin film have been studied by X-ray diffraction (XRD), UV-Visible spectroscopy, Atomic Force microscopy (AFM) images and have also been correlated with the observed enhancement in gas sensing properties of prepared sensor structure.

We have studied the role of surface bound anionic species on zinc oxide (ZnO) quantum dots (QDs) for the antibacterial activity against Escherichia coli (E. coli) bacteria. The ZnO QDs with surface adsorbed anionic species of acetate ions and nitrate ions have been synthesized using wet chemical route. X-Ray diffraction studies reveal single-phase hexagonal wurtzite structure of as synthesized ZnO QDs. The particle size was found to be 3-5 nm for acetate adsorbed ZnO QDs and 4-7 nm for nitrate adsorbed ZnO QDs. Minimum inhibitory concentration (MIC) measurements and growth kinetics studies for E-coli show a marked difference in the antibacterial activity of ZnO QDs with both anionic species. The MIC for acetate adsorbed ZnO QDs was found to be 2.5 mM in light and 3 mM in dark. However, nitrate adsorbed ZnO QDs exhibits MIC about 6 mM in light and no significant bacterial growth inhibition was observed upto 30 mM under dark. The enhanced bacterial growth inhibition observed for acetate adsorbed ZnO QDs is attributed to the inherent ability of acetate ions to generate reactive oxygen species. The acetate adsorbed QDs having excellent antibacterial activities suggests its potential application for practical bactericidal realization.