Nickel Manganite-Sodium Alginate Nano-Biocomposite for Temperature Sensing

Nanocrystalline nickel manganite (NiMn2O4) powder with a pure cubic spinel phase structure was synthesized via sol-gel combustion and characterized with XRD, FT-IR, XPS and SEM. The powder was mixed with sodium alginate gel to form a nano-biocomposite gel, dried at room temperature to form a thick film and characterized with FT-IR and SEM. DC resistance and AC impedance of sensor test structures obtained by drop casting the nano-biocomposite gel onto test interdigitated PdAg electrodes on an alumina substrate were measured in the temperature range of 20-50 degrees C at a constant relative humidity (RH) of 50% and at room temperature (25 degrees C) in the RH range of 40-90%. The material constant obtained from the measured decrease in resistance with temperature was determined to be 4523 K, while the temperature sensitivity at room temperature (25 degrees C) was -5.09%/K. Analysis of the complex impedance plots showed a dominant influence of grains. The decrease in complex impedance with increase in temperature confirmed the negative temperature coefficient effect. The grain resistance and grain relaxation frequency were determined using an equivalent circuit. The activation energy for conduction was determined as 0.45 eV from the temperature dependence of the grain resistance according to the small polaron hopping model, while the activation energy for relaxation was 0.43 eV determined from the Arrhenius dependence of the grain relaxation frequency on temperature

Nanocrystalline iron-manganite (FeMnO3) applied for humidity sensing

Nanocrystalline iron manganite was synthesized using a sol-gel self-combustion method with glycine as fuel, followed by calcination at 900 °C for 8 hours. Structural characterization was performed using X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). It confirmed the formation of nanocrystalline iron-manganite with a perovskite structure. Humidity sensing properties of bulk and thick film samples of the obtained nanocrystalline iron manganite powder were analyzed. Organic vehicles were added to the powder to form a thick film paste that was screen printed on alumina substrate with test PdAg interdigitated electrodes. Impedance response of bulk and thick film samples was analyzed in a humidity chamber in the relative humidity range 30-90% in the frequency range 42 Hz to 1 MHz in view of applying iron-manganite for humidity sensing applications

Nanocomposite Zn2SnO4/SnO2 Thick Films as a Humidity Sensing Material

Nanocomposite Zn2SnO4/SnO2 powder was obtained by solid state synthesis from homogenized starting nanopowders of ZnO and SnO2, mixed in the 1:1 molar ratio, structurally and morphologically characterized using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Thick film paste was made by adding organic vehicles to the obtained powder. Three to five layers (layer thickness approx. 12 µm) were screen printed on alumina substrate with small test PdAg electrodes and fired at 600oC for 30 minutes. SEM analysis confirmed formation of a porous structure suitable for humidity sensing. Impedance response was studied at the working temperatures of 25 and 50oC in a humidity chamber where the relative humidity (RH) was 30-90% and measured frequency 42 Hz – 1 MHz. With increase in film thickness the overall sensor impedance increased. It reduced at 100 Hz from 36 to 0.25 MΩ (60 µm), from 23.4 to 0.25 MΩ (48 µm) and from 6.8 to 0.02 MΩ (36 µm) at 25 oC, while at 50 oC and also 100 Hz it reduced from 14 MΩ to 0.72 MΩ (48 µm) for RH 30 and 90%, respectively. The response (8 s) and recovery (10 s) was fast, showing that this nanocomposite has potential for application in humidity sensing.© 20XX IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This is the peer-reviewed version of the article: Nikolić Maria Vesna, Dojčinović Milena, Vasiljević Zorka Ž., Luković Miloljub D., Labus Nebojša, "Nanocomposite Zn2SnO4/SnO2 Thick Films as a Humidity Sensing Material" IEEE Sensors Journal, 20, no. 14 (2020):7509-7516, [https://doi.org/10.1109/JSEN.2020.2983135]Published version: [https://hdl.handle.net/21.15107/rcub_dais_8942

Impact of Microstructure on Humidity Influence on Complex Impedance of Iron Manganite

This work deals with our continued research of oxide materials for potential application in gas/humidity sensing. We have made thick film samples using iron manganite powder synthesized by a sol-gel combustion method with a net-like structure, by screen printing on alumina substrate with PdAg interdigitated electrodes. The thick film samples were fired at two temperatures 600 and 800°C. The powder morphology was retained and only the organic compounds in the paste were burnt-out at 600°C, while at 800°C the thick film surface morphology was different where grain growth and individual particles can be observed. We measured complex impedance in a temperature and humidity chamber at room temperature (25°C) in the relative humidity range 30 – 90 % and frequency 100 Hz - 1 MHz. The thick film surface morphology has a significant influence on the effect of humidity on complex impedance. The complex impedance of thick films fired at 600°C was high and did not decrease noticeably with increase in relative humidity (RH), except for RH 80 and 90%, while thick film samples fired at 800°C had an overall lower impedance that reduced more noticeably with increase in RH 40–70% and even more for RH 80 and 90%.This is the peer-reviewed version of the paper:Nikolic, M.V., Vasiljević, Z.Z., Dojčinović, M.P., Vujančević, J., Radovanović, M., 2020. Impact of Microstructure on Humidity Influence on Complex Impedance of Iron Manganite, in: 2020 43rd International Spring Seminar on Electronics Technology (ISSE). Presented at the 2020 43rd International Spring Seminar on Electronics Technology(ISSE), IEEE. [https://doi.org/10.1109/ISSE49702.2020.9120967]Published version: [https://hdl.handle.net/21.15107/rcub_dais_10026

The effect of pH on visible-light photocatalytic properties of pseudobrookite nanoparticles

In this study, pseudobrookite (Fe2TiO5) nanoparticles were fabricated by a modified sol-gel method using Fe(NO3)39H2O and Ti(OC3H7)4 as starting reagents and ethanol as solvent. Oxalic acid was used as a chelating agent while cetyltrimethyammonium bromide (CTAB) and citric monohydrate were used as surfactants. Structral and morphological characterization using X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) analysis confirmed the formation of pseudobrookite nanoparticles. As synthetized Fe2TiO5 nanoparticles were utilized as photocatalysts for decolorisation of Methylene blue (MB) under visible light irradiation. It was observed that the adsorption of MB onto Fe2TiO5 nanoparticles is strongly dependent on the solution pH. Maximum decolorozation was observed for Fe2TiO5 nanoparticles prepared with CTAB under alcaline conditions (pH=10.5)

Synthesis and characterisation of ZnO synthesized by glycine-nitrate combustion process

One of the ways to get rid of toxic organic compounds that industries release into natural waters is photocatalysis of the decomposition of organic compounds on the surface of heterogenous photocatalysts such as zinc oxide. Zinc oxide is a semiconductor that interacts with UV and near-UV visible light by generating electron-hole pairs which decompose organic molecules. Therefore it is useful to explore different ways of synthesizing zinc oxide and to test quality and quantity of organic decomposition photocatalysis so as to enable the commercial use of the material. Zinc oxide is also a respectable material for use as a photoelectrocatalyst in water oxidation, for example, which can be useful for generating oxygen while using natural sunlight - a clean and abundant energy source. In this project nanocrystalline zinc oxide was synthesized by glycin-nitrate combustion process and the powder was annealed on temperatures of 400 °C and 500 °C. Obtained particles where characterized in detail using X-ray powder diffraction (XRPD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, field emission scanning microscopy (FESEM), photoluminescence spectroscopy (PL) and diffuse reflectance spectroscopy (DRS). The results show that obtained samples are nanocrystalline wurtzite zinc oxide, with particle diameters of 33 nm (annealed at 400 °C) ad 48 nm (annealed at 500 °C). Both samples show significant amount of various crystal defects. Zinc oxide band gap of the samples are determined to be lower than the band gap of the bulk zinc oxide. Photoelectrocatalytic properties were investigated via electrochemical methods: linear voltammetry (LV), chronoamperometry (CA) and impedance spectroscopy (EIS). The results show that material is photostable and reactive to the light. Water oxidation is enhanced by exposing to sunlight. Finally, photocatalytic properties are tested with determining kinetic parameters of phenole and methyl blue decomposition. Zinc oxide nanoparticles are efficient photocatalysts, although sample annealed at 500 °C shows better properties than sample annealed at 400 °C

Structure, morphology and photocatalytic properties of CoxMg1-xFe2O4 (0<x<1) spinel ferrites obtained by sol-gel synthesis

Nanocrystalline cobalt magnesium ferrites with varying cobalt and magnesium content (CoxMg1-xFe2O4, 0<x<1) were synthesized using the sol-gel self-combustion method with citric acid as fuel, followed by calcination at 700 C for 2 hours. Structural characterization was performed using Xray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. It confirmed the formation of agglomerated nanocrystalline ferrites with an inverse cubic spinel structure. The optical band gap energy was determined using UV/Vis spectrophotometry. It reduced with increased Co content. Visible light photocatalytic activity was tested using natural and artificial light sources through a series of experimental degradations of the methylene blue (MB) solution

Photocatalytic degradation of methylene blue and oxytetracycline via sol-gel synthesized pseudobrookite

Fe2TiO5 nanoparticles were synthesized by modified sol-gel method using Fe(NO3)3×9H2O and Ti(OC3H7)4 as starting reagents, oxalic acid as chilate agent and cetyltrimethylammonium bromide as surfactant. The aim of this study was to asses the photocatalytic degradaton of water pollutants, methylene blue and the antibiotic Oxytetracycline (OTC) using natural sunlight irradiation. As prepared nanoparticles were characterized by XRD, BET, FESEM and UV-vis DRS. The optimal operating conditions of photocatalytic degradation of water pollutants were achived by changing the pH of the solution and changing the concentration of photocatalyst

Structure and photocatalytic properties of sol-gel synthesized pseudobrookite

Fe2TiO5 nanopartcles were synthesized by modified sol-gel method with aid of Fe(NO3)3 9H2O and Ti(OC3H7)4 as starting reagents, oxalic acid as chilate agent and cetyltrimethylammonium bromide as surfactant. The aim of this study was to asses the photocatalytic degradaton of the antibiotic Oxytetracycline (OTC) using visible light irradiation. As prepared nanoparticles were characterized by XRD, BET, FESEM and UV-vis DRS. The optimal operating conditions of oxytetracycline photocatalytic degradation were achived by changing the pH of the solution and changing the concentration of photocatalyst

Nanocrystalline SnO2-Zn2SnO4 composite thick films applied as humidity sensors

Starting ZnO and SnO2 nanopowders (<100 nm) were mixed in a suitable ratio and calcined at 1050 °C for 2 hours to obtain nanocrystalline SnO2-Zn2SnO4 composite powder. Structural characterization performed by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) showed that a nanocrystalline composite SnO2-Zn2SnO4 powder was obtained. Thick film paste was made by adding organic vehicles to the powder. Screen printing of four and five layers of thick film paste was performed on two interdigitated test electrode configurations. They were calcined at 500 and 600 °C for 30 minutes. Impedance response was analyzed at several working temperatures (20-60 °C) in the relative humidity range 30-90% and frequency 42 Hz to 1 MHz. Increase in relative humidity lead to a decrease in impedance, especially at lower frequencies. The sensor time delay between absorption and desorption processes was low and the response and recovery times fast showing that the nanocystalline SnO2-Zn2SnO4 composite has potential for application in humidity sensing