Faculty Publications
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Item Retention of high dielectric constant sodium beta alumina via solution combustion: Role of aluminum ions complexation with fuel(Elsevier Ltd, 2018) Gupta, B.; Pujar, P.; Mal, S.S.; Gupta, D.; Mandal, S.In the present study, solution combustion technique has been explored to synthesize Sodium ?-alumina (SBA; NaAl11O17) powder and thin films. Three fuels namely urea, glycine and citric acid have been used to seek the feasibility of synthesizing crystalline SBA powder at low temperature. Also, the effect of nature of fuels used as well as calcination treatment on phase evolution and morphology of the as-combusted powder was investigated. Thermal analysis and X-ray diffraction studies suggest the formation of crystalline SBA powder at temperature as low as 259 °C, using urea in the combustion reaction whereas other fuels resulted in amorphous SBA phase and this variation in phase was found due to difference in exothermicity of the fuel used. Thermodynamic and spectroscopic analyses showed that the exothermicity of fuel depends on various factors like (i) standard heat of formation of fuel and (ii) the complexation offered by fuel to metal cations. Furthermore, sodium ?-alumina thin film capacitor (metal-insulator-metal) was also fabricated using urea via spray combustion synthesis. The sodium ?-alumina thin film showed a high dielectric value (?r) of ~21. © 2017 Elsevier Ltd and Techna Group S.r.l.Item A scalable screen-printed high performance ZnO-UV and Gas Sensor: Effect of solution combustion(Elsevier Ltd, 2020) Manjunath, G.; Pujari, S.; Patil, D.R.; Mandal, S.In the present study, scalable screen-printed Zinc Oxide (ZnO) based sensor was demonstrated to sense ultra-violet irradiation and gases such as ammonia (NH3), ethanol (C2H5OH), liquefied petroleum gas (LPG), chlorine (Cl2) and hydrogen sulphide (H2S). A facile solution combustion synthesis (SCS) route was adopted to synthesize high purity, homogeneous, nanocrystalline and highly reactive ZnO with favourable morphologies, microstructural parameters for the sensing performance using low-cost and less-violent fuels such as urea, citric acid and glycine. Fuel impacts on uniform particle size distribution, bond length, grain size, lattice strain enhanced the gas sensing potential in the synthesized powders. Films were fabricated by depositing synthesized powders on the glass substrate via screen printing approach using Na-carboxy methyl cellulose as a binder, water as a solvent and annealed at 500 °C for 2 h in ambient. Non-stoichiometric, phase pure and adhered thick films with optical band gap (3.17-3.25 eV) imparted gas sensing properties because of recombination of an electron-hole pair and intrinsic defects. ZnO films obtained from glycine-fuel system exposed to 100 ppm of NH3, C2H5OH, Cl2 and 50 ppm of H2S, exhibited good gas sensitivity of ~8, 5, 3 and 10 at an operating temperature of 50, 100, 200 and 100 °C respectively with a faster response and recovery speed. But, high sensitivity ~6 to 100 ppm of LPG at 350 °C in ZnO films from citric acid fuel-system. ZnO films obtained from glycine fuel system showed a high response to UV irradiation for exposing time of 90s. Low cost, high-performance sensor can be fabricated for the dual applications - alarming to prolonged exposure to harmful UV radiation and detection of a series of toxic and damaging gases. © 2019 Elsevier LtdItem A comparative study on enhancer and inhibitor of glycine–nitrate combustion ZnO screen-printed sensor: detection of low concentration ammonia at room temperature(Springer, 2020) Manjunath, G.; Pothukanuri, P.; Mandal, S.We report a comparative study on enhancing and inhibiting the sensing performance of Sr-doped ZnO (Sr0.01 Zn0.99O) and RuO2-activated Sr-doped ZnO heterostructured sensors towards the low concentration (? 50 ppm) of ammonia gas at ambient. Sub-microns sized with high specific surface area, high reactive, oxygen-deficient Sr-doped ZnO particles were synthesized at low temperature (196 °C) through facile glycine–nitrate solution combustion synthesis (SCS) method. Porous, adhered screen-printed film of Sr-doped ZnO with optical bandgap (3.22 eV) was dip-coated using 0.02 M RuCl3 aqueous solution to obtain RuO2 activation. Smaller crystallite size and lesser lattice distortion obtained with Sr-doping in ZnO enhance the gas response (S = 71) towards the 50 ppm of ammonia gas at room temperature. RuO2-activated Sr-doped ZnO sensor associated with lesser oxygen vacancies and a lower concentration of chemisorbed oxygen species due to passivation layer and no-spill-over activity of RuO2, which inhibits the gas response from 71 to 3. Sr-doped ZnO-based sensor shows high selectivity towards ammonia against 50 ppm of volatile organic compound (VOCs) vapor. Expeditious sensor kinetics (response time and recovery time) in the Sr-doped ZnO sensor was observed, in which smaller crystallite size offers a shorter distance for the diffusion of oxygen vacancies (Vo). Ultra-high-sensitive and selective sensors with ease and economical fabrication offer feasibility in industries and domestic applications where detection of the less concentration ammonia vapor is crucial. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.Item Structural, compositional and spectral investigation of prawn exoskeleton nanocomposite: UV protection from mycosporine-like amino acids(Elsevier Ltd, 2020) Hadagalli, K.; Kumar, R.; Mandal, S.; Basu, B.The present work explores the use of marine resourced prawn exoskeleton/shell as a new class of naturally occurring composite containing UV absorbing proteins. Mycosporine-like amino acids with a central aromatic ring in the exoskeleton/shell of naturally occurring prawns (Fenneropenaeus Indicus) offer excellent UV protection. The architecture of shell composite constitutes a matrix of chitin-proteins with distinct reinforcements such as spherical calcites (CaCO3), microscopic proteins, and traces of hydroxides/oxides of magnesium. The presence of tryptophan, phenylalanine, and tyrosine, forming the basic building blocks of mycosporines, is confirmed by structural, compositional, and microscopic studies on prawn shells. The UV spectroscopic signatures at 290 and 320 nm provides strong evidence for the highest UV absorption. UV absorption attributes to the presence of mycosporine-like amino acids. Hence, the current exploration of naturally occurring prawn shells directs towards an additive-free sunscreen filter without the generation of detrimental free radicals. © 2020 Elsevier B.V.Item Ultra-sensitive clogging free combustible molecular precursor-based screen-printed ZnO sensors: a detection of ammonia and formaldehyde breath markers(Springer, 2021) Manjunath, G.; Pothukanuri, P.; Mandal, S.It is beneficial to develop the cost-effective, ultra-sensitive ZnO-based sensor for the rapid detection and quantification of the ammonia and formaldehyde breath markers under ambient conditions. Here, one-step solution route was adopted to formulate the aqueous combustible molecular precursor-based clogging free screen-printing ink consisting of zinc nitrate as an oxidizer, glycine as fuel, and eco-friendly binder sodium carboxymethylcellulose. The formulated precursor was deposited on the glass substrates via a screen-printing technique followed by annealing at different temperatures for an hour. Screen printed ZnO sensors processed at 500 °C with high crystallinity, less lattice distortion, low optical bandgap, and high concentration of donor defects showed remarkably high NH3 gas response ~ 336 and a moderate HCHO response ~ 16.4 towards the 5 ppm and 10 ppm of the respective gases. In addition it's LOD values is drawn as 0.6 ppm and 2.9 ppm for NH3 and HCHO gases, respectively, and exhibits superior selectivity towards ammonia. Faster diffusion of oxygen vacancies (Vo) in the smaller crystallites resulted expeditious sensor kinetics in the screen-printed sensor processed at 400 °C. Response and recovery time were recorded to be 50 s and 50 s to the 5 ppm of NH3, respectively. The crystallinity-dominant domain overcomes the adverse effect of larger grains on the gas response of screen-printed ZnO sensor processed at 500 °C. Robust, scalable, and cost-effective screen-printed ZnO conductometric sensors demonstrated here has a potential application in clinical diagnosis, and also in monitoring the NH3 and HCHO gases at low ppm-level. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.