Faculty Publications
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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 Ammonia gas detection by solution combustion-processed pristine & Ti-doped ZnO transparent films: a reverse effect of doping on gas response(Springer, 2023) Vardhan, R.V.; Manjunath, G.; Pothukanuri, P.; Mandal, S.In this contribution, pure, polycrystalline wurtzite crystal structured, spin-coated pristine ZnO and Ti-doped (1, 2, and 3 wt%) ZnO transparent films were accomplished at 400 °C through a facile solution combustion synthesis method. Crystallinity, roughness, and porosity in the pristine film were relatively higher than in the doped films. The demonstrated films were transparent, with ~ 70 to 90% in the visible region. The room temperature detection of ammonia (NH3) gas (25–100 ppm) was recognized in all the films. The pristine film revealed a superior gas response at every concentration of NH3 gas in contrast to all the doped films; it is probably due to comparatively high crystallinity, porosity, more oxygen vacancy concentration (1.788), and high fraction of adsorbed oxygen (20.55%). The film exhibited the highest gas response of 34.7 at 100 ppm of NH3 gas and a limit of detection of ~ 10.7 ppm with superior selectivity towards NH3 gas. Although doping enhanced the transparency but diminished the NH3 gas response due to the combined effect of deterioration in the mentioned properties achieved in pristine film. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Item Tracing of Ammonia Gas by Solution-Combustion-Derived Pristine and Nb-Doped TiO2 Films: Beneficial Impact of Crystallinity and Adsorbed Oxygen on the Gas Response(Springer, 2023) Vardhan, R.V.; Manjunath, G.; Pothukanuri, P.; Mandal, S.The current work delivers room-temperature ammonia (NH3) gas-detectable pristine, Nb-doped TiO2 air- and vacuum-annealed films obtained through the solution-combustion process. Polycrystalline anatase crystal structured films without any dopant oxide phases were processed at 400°C on glass substrates. The crystallinity was higher in pristine films than in doped films; the morphological features were similar in all the films. The films were > 50% transparent, and the estimated optical energy band gap was greater in doped films than in pristine films. All the films detected NH3 gas (25 ppm to 100 ppm) at room temperature, and the gas response was highly dependent on the crystallinity and relative area fraction of adsorbed oxygen (% of OA). The vacuum-annealed pristine film exhibited a better gas response than the other films at all NH3 gas concentrations due to high crystallinity and % of OA (10.15%). The film demonstrated maximum gas response of ~16 towards 100 ppm of NH3 gas and displayed good selectivity. Even though the doping reduced the crystallite size from ~17 nm to ~9 nm, it also diminished the crystallinity of the films, which significantly impacted the deterioration of their gas response. © 2023, The Minerals, Metals & Materials Society.Item Detection of ethanol gas at room temperature by In2O3-based screen-printed films fabricated through particle-free aqueous solution combustible inks(Institute of Physics, 2024) Vardhan, R.V.; Praveen, L.L.; Manjunath, G.; Pothukanuri, P.; Seikh, A.H.; Alnaser, I.A.; Mandal, S.The current work investigates the room temperature ethanol gas detection capabilities of pristine, Sn-doped, Zn-doped, Sn & Zn co-doped In2O3-based screen-printed films, fabricated using particle-free aqueous solution combustible inks on glass substrates. The fabricated films were pure, polycrystalline with cubic bixbyite crystal structure, porous, and transparent (∼75 to 95%) in the visible range. Relatively high surface roughness was detected in pristine film than in doped films. Ethanol gas was detected by all the films at room temperature. Among all, the pristine film showed a relatively greater gas response at all concentrations of ethanol gas ranging from 25 ppm to 100 ppm. This superior gas response was attributed to comparatively greater oxygen vacancy concentration (OV/OL), relative area fraction of surface adsorbed oxygen (% of OA), and high surface roughness with porosity. The maximum ethanol gas response attained was ∼17 at 100 ppm concentration by the pristine film, which also demonstrated high selectivity to ethanol gas. © 2024 The Author(s). Published by IOP Publishing Ltd.Item Ultra-high ammonia gas response of phase-stabilized (Fe0.2Ni0.2Cr0.2Mn0.2Zn0.2)3O4-? high-entropy spinel oxide sensor array and its machine learning predictions(Elsevier Ltd, 2025) Praveen, L.L.; Upadhyay, B.; Potnuri, R.; Mandal, S.In this work, the gas sensing performance of phase-stabilized (FeNiMnZnCr)3O4 high-entropy spinel oxide (HSO) gas-sensors via screen-printing were investigated, where the HSO powders were synthesized via solution combustion synthesis (SCS) using three different fuels: citric acid, urea, and glucose. Although all HSO powders were obtained at 500 °C, the formation of stable spinel phase was evidenced at 600 °C. Among all fabricated sensors, G-800 gas sensor depicted a stable ultra-high response of ?3471 towards 100 ppm of ammonia gas along with a notable response of ?162 even at 10 ppm (where G means glucose and 800 represents calcination temperature in °C) and it demonstrated a strong device-to-device reproducibility with stability of ?35 days. A synergy of crystallinity and increased porosities from XRD and FESEM micrographs resulted in ultra-high gas-response towards ammonia gas compared to volatile organic compounds such as formaldehyde, methanol, and ethanol). The presence of defect band and oxygen vacancies observed from the Raman and XPS analysis, were complemented by the presence of porosities confirmed from BET surface area analysis. Subsequently, the machine learning (ML) algorithms are applied on sensor signals to estimate the concentration of ammonia gas, and among all the ML classifiers, RFC gave reasonably better predictions in three concentrations regimes with a good classification accuracy of 93.3 ± 5.3 %, 90 ± 7.5 %, and 83.3 ± 13.1 % for G-600, G-700, and G-800, respectively. The proposed ML studies enable accurate detection of hazardous ammonia levels using HSO-based sensors, showing strong potential for integration into diagnostic platforms targeting ammonia breath markers. © 2025 Elsevier B.V.