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This research studies the effects of volume ratios on the properties of GO/(ZnxNi1−x)O ternary composite prepared by a sol–gel technique. The ratios were produced by keeping the volume of graphene oxide (GO) constant whilst varying the volumes of zinc oxide, ZnO and nickel oxide, NiO to produce GO/ZnO0.2NiO0.8, GO/ZnO0.5NiO0.5, and GO/ZnO0.8NiO0.2 nanocomposites. The structural, morphological, elemental, optical, gas sensing, and photocatalytic properties of the synthesized nanocomposites have been investigated. EDX results confirmed the presence of graphene oxide, nickel oxide, and zinc oxide in the composites. The bandgap energy values exhibited a reduction as compared to the constituent compounds which range from 3.1 to 3.4 eV. Functional groups belonging to carbon, oxygen, nickel, zinc were obtained. The conductivity and activation energy of the ternary composites was also determined. The gas sensing properties were tested for NH3, H2S, and Cl2 at 100 ppm and 10 V; with the highest sensitivity recorded for H2S. The synthesized ternary composites were highly effective in degradation of dye with the efficiencies of 87.3%, 86.7%, and 88.0% respectively, obtained at 0.022 per minute, 0.020 per minute, 0.024 per minute for pseudo-first order rate constant. Results from the characterization show potential application of the composites in gas sensing and photocatalytic devices. [ABSTRACT FROM AUTHOR]

In Mott‐type resistive switching phenomena, which are based on the metal–insulator transition in strongly correlated materials, the presence of an abrupt temperature‐driven transition in the material is considered essential for achieving high‐speed and large‐resistance‐ratio switching. However, this means that the freedom of material/device design in applications is significantly reduced for this type of switching by the strict requirement of transition abruptness. Here, high‐speed, abrupt resistive switching with a switching time of 140 ns is demonstrated in epitaxial films of Ca2RuO4/LaAlO3 (001), which is a material with a nonthermal metal–insulator transition driven by current, despite the complete absence of an abrupt thermal transition in the resistivity–temperature characteristics. Highly smooth negative‐differential‐resistance behavior, very high cycling stability, and an endurance over 106 cycles are also demonstrated in the current–voltage and current–time characteristics, which confirm the nonstochastic nature of the abrupt switching. These results suggest that strict control of the resistivity–temperature characteristics is not necessarily required in a material with a nonthermal‐type metal–insulator transition to obtain high‐speed resistive switching because of the independence of the dynamics from those of the thermal transition, and this phenomenon potentially has important advantages in resistive switching applications. [ABSTRACT FROM AUTHOR]

The AgNPs were synthesized using water-soluble polysaccharides extracted from the Leucaena leucocephala seeds. The UV-visible spectrum of the AgNPs showed a sharp absorption peak at 448 nm. The XRD analysis showed four major peaks of the crystalline AgNPs with planes of a face-centered cubic lattice of silver. The EDS spectrum showed a strong signal peak at ~3 keV. TEM and SEM observations showed the spherical shape of AgNPs with no particle agglomeration, and the size ranged from 8 to 20 nm. AgNPs were highly stable at -14.2 mV by zeta potential measurement. AgNPs showed significant anticancer activity against the cell lines of breast cancer, liver carcinoma, and colon carcinoma with the I C 50 value of 22.5, 12.3, and 8.9 μg mL-1, respectively. AgNPs at 900 μg mL-1 exhibited considerable antifungal activity against ten fungal pathogens. Water-soluble polysaccharide has the ability to synthesize AgNPs keeping strong antitumor, antifungal activities. The AgNPs can slow down spoilage of composite milk samples at different temperatures. In addition, the accuracy of milk-IR-analyses was not affected by different concentrations of AgNPs. [ABSTRACT FROM AUTHOR]

This study deals with the synthesis, characterization and gas sensing interrogations of pure and Cr (5 and 15%) doped ZrO2. The conventional precipitation route is committed for the synthesis of the pure and Cr-doped ZrO2 powder and the films were formulated by drop casting mode by exploiting ZrOCl2·8H2O as precursor, CrO3 as doping agent and NH4OH as stabilizing agent. The structural properties, optical properties and electrical properties of the handled samples were anatomized by X-ray diffraction (XRD), scanning electron microscopy, ultraviolet–differential reflectance spectroscopy (UV-DRS) spectroscopy, photoluminescence (PL) studies and current–voltage (I–V) measurement. The structure and size of the crystal were resolved by XRD. The uniform spherical-like morphology of the particles was favoured by SEM investigation. The bandgap of the materials was reckoned by UV-DRS report. The occupancy of oxygen vacancies in the samples was conceded by PL studies. The ohmic contact of the samples with the electrodes has been professed by I–V measurements. The gas sensing competency of the drop casted films were monitored by the exposure of the different concentrations of reducing gases like ammonia, acetone, ethanol, formaldehyde and xylene. The output data render that all the processed samples exhibits a peak response towards ammonia gas, exclusively 15% of Cr-doped ZrO2 sensor shows an utmost gas response of about 48%, excellent response time and recovery time of about 68 and 72 s, respectively, among other samples. Thus, the fusion of Cr stimulates the gas sensing proficiency of ZrO2. [ABSTRACT FROM AUTHOR]

The present paper describes the preparation and characterization of Polyvinyl Alcohol-Polypyrrole-Silver Nanocomposite (PVA-PPy-Ag NC) films. The prepared films were conducting, freestanding, flexible, and robust. Silver nanoparticles (Ag NPs) were synthesized from an aqueous solution of silver nitrate using trisodium citrate as a reductant. The casting solution for the films was prepared by in-situ chemical oxidative polymerization of pyrrole. This was done in the presence of Polyvinyl Alcohol and suspension of pre-synthesized silver nanoparticles. The absorption band at 424 nm in UV-Visible Spectroscopy of silver nanoparticles confirmed the formation of Ag nanoparticles. Scanning Electron Microscopy (SEM) studies revealed that spherical Ag NPs were produced with an average size of ~ 25 nm. The morphological analysis of the synthesized PVA-PPy-Ag nanocomposite films was carried out using Transmission Electron Microscopy (TEM). It was observed in the TEM images that Ag nanoparticles were well dispersed and conjugated in the PVA-PPy matrix. The structure of the produced films was studied by Fourier transform infrared (FTIR) Spectroscopy and X-Ray Diffraction (XRD). X-ray diffraction analysis exhibited the crystalline nature of the silver nanoparticles with a face-centered cubic (fcc) structure. The synthesized PVA-PPy-Ag nanocomposite films can be further utilized as potential material for the fabrication of gas sensors. [ABSTRACT FROM AUTHOR]

Magnetic iron oxide nanomaterials (MIONs) have been extensively investigated for the various important applications. Coprecipitation, hydrothermal, high temperature decomposition of organic precursors, microemulsions, polyol methods, electrochemical methods, aerosol method, sonolysis and green synthesis processes for the fabrication of MIONs have been reviewed. Different characterization methods like XRD, SEM, EDX and TEM for the as prepared MION materials have been studied. Important applications of MIONs in the field of biomedical, nanorobotics and energy devices have also been addressed in this review. Target oriented drug delivery and hyperthermia applications of MIONs have also focused. [ABSTRACT FROM AUTHOR]

In the present work, tracing and Whatman papers were used as substrates to grow zinc oxide (ZnO) nanostructures. Cellulose-based substrates are cost-efficient, highly sensitive and environmentally friendly. ZnO nanostructures with hexagonal structure were synthesized by hydrothermal under microwave irradiation using an ultrafast approach, that is, a fixed synthesis time of 10 min. The effect of synthesis temperature on ZnO nanostructures was investigated from 70 to 130 °C. An Ultra Violet (UV)/Ozone treatment directly to the ZnO seed layer prior to microwave assisted synthesis revealed expressive differences regarding formation of the ZnO nanostructures. Structural characterization of the microwave synthesized materials was carried out by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The optical characterization has also been performed. The time resolved photocurrent of the devices in response to the UV turn on/off was investigated and it has been observed that the ZnO nanorod arrays grown on Whatman paper substrate present a responsivity 3 times superior than the ones grown on tracing paper. By using ZnO nanorods, the surface area-to-volume ratio will increase and will improve the sensor sensibility, making these types of materials good candidates for low cost and disposable UV sensors. The sensors were exposed to bending tests, proving their high stability, flexibility and adaptability to different surfaces. [ABSTRACT FROM AUTHOR]

Pure In2O3 nanoparticles are prepared by a facile precipitation method and are further modified by Ag. The synthesized samples are characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, Raman and UV-Vis spectra. The results show the successful heterojunction formation between Ag and In2O3. Gas sensing property measurements show that the 5 mol % Ag-modified In2O3 sensor has the response of 67 to 50 ppm ethanol, and fast response and recovery time of 22.3 and 11.7 s. The response is over one magnitude higher than that of pure In2O3, which can be attributed to the enhanced catalytic activity of Ag-modified In2O3 as compared with the pure one. The mechanism of the gas sensor can be explained by the spillover effect of Ag, which enhances the oxygen adsorption onto the surface of In2O3 and thus give rise to the higher activity and larger surface barrier height. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) comb-like nanostructures were successfully synthesized on the silicon substrate without a catalyst via chemical vapour deposition. The morphology and crystal structure of the product were characterized by scanning electron microscope and X-ray diffractometer. In this research, a simple gas sensor was fabricated based on the principle of change in resistivity due to oxygen vacancies, which makes its surface chemically and electrically active. The fabricated ZnO nanostructures proved to be quite sensitive to low concentration of $$\hbox {H}_{2}\hbox {S}$$ gas at room temperature. The sensitivity and response time were measured as a function of gas concentrations. Small response time (48-22 s) and long recovery time (540 s) were found at $$\hbox {H}_{2}\hbox {S}$$ gas concentrations of 0.1-4 ppm, respectively. ZnO comb-like structures are considered as the most suitable materials for gas sensor fabrication due to their high sensing properties. These nanostructures growth and $$\hbox {H}_{2}\hbox {S}$$ gas sensing mechanism were also discussed. [ABSTRACT FROM AUTHOR]

The density of oxygen vacancies in semiconductor gas sensors was often assumed to be identical throughout the grain in the numerical discussion of the gas-sensing mechanism of the devices. In contrast, the actual devices had grains with inhomogeneous distribution of oxygen vacancy under non-ideal conditions. This conflict between reality and discussion drove us to study the formation and migration of the oxygen defects in semiconductor grains. A model of the gradient-distributed oxygen vacancy was proposed based on the effects of cooling rate and re-annealing on semiconductive thin films. The model established the diffusion equations of oxygen vacancy according to the defect kinetics of diffusion and exclusion. We described that the steady-state and transient-state oxygen vacancy distributions, which were used to calculate the gas-sensing characteristics of the sensor resistance and response to reducing gases under two different conditions. The gradient-distributed oxygen vacancy model had the applications in simulating the sensor performances, such as the power law, the grain size effect and the effect of depletion layer width. [ABSTRACT FROM AUTHOR]

We have examined the effects of oxygen content and thickness in sputtered InSnO (ITO) electrodes, especially for the application of imperceptible amorphous-InGaZnO (a-IGZO) thin-film transistors (TFTs) in humidity sensors. The imperceptible a-IGZO TFT with 50-nm ITO electrodes deposited at Ar:O2 = 29:0.3 exhibited good electrical performances with Vth of −0.23 V, SS of 0.34 V/dec, µFE of 7.86 cm2/V∙s, on/off ratio of 8.8 × 107, and has no degradation for bending stress up to a 3.5-mm curvature. The imperceptible oxide TFT sensors showed the highest sensitivity for the low and wide gate bias of −1~2 V under a wide range of relative humidity (40–90%) at drain voltage 1 V, resulting in low power consumption by the sensors. Exposure to water vapor led to a negative shift in the threshold voltage (or current enhancement), and an increase in relative humidity induced continuous threshold voltage shift. In particular, compared to conventional resistor-type sensors, the imperceptible oxide TFT sensors exhibited extremely high sensitivity from a current amplification of >103. [ABSTRACT FROM AUTHOR]

The experimental data and theoretical concepts on the nature and physicochemical properties of the active centers at the surface of tin dioxide are reported, which are involved in detection of toxic and explosive ambient impurities. The active centers formed at the nanocrystal SnO surface are classified on the basis of their chemical properties, and their role in the interaction of semiconductor nanocrystal oxides with the gases exhibiting the redox properties is confirmed. The chemical modification of the SnO surface aimed at elaborating a controlled amount of specific active centers is shown to be the most efficient method for increasing the selectivity of sensors. Selecting the optimum catalytic modifiers (nanoparticles or clusters of noble metals and their oxides) allows the sensor sensitivity and selectivity of the target gas detection to be increased. [ABSTRACT FROM AUTHOR]

The recent modernization of the livestock industry lags behind the scale of the livestock industry, particularly in indoor environmental monitoring. In particular, the H2S gas concentration in chicken coops affects the growth and reproductive capacity of the chickens and threatens their health. Therefore, the research and development of a low-cost, environmentally friendly sensor that can achieve on-line monitoring of H2S gas has a notably important practical significance. This paper reports the design of an H2S gas sensor, with selection of an electrochemical probe with high accuracy and wide measurement range using the relatively mature technology of electrochemical sensors. Although the probe of the sensor is the main factor that affects the sensor accuracy, the probe must be combined with a specifically designed signal condition circuit that can overcome the lack of an electrode to satisfy the requirements for the interconnection and matching between the output signal and the test instrument. Because the output current of the electrochemical electrode is small and likely to be disturbed by noise, we designed signal-conditioning modules. Through the signal-conditioning circuit, the output signal of the current electrode can be converted into a voltage and amplified. In addition, we designed a power control module because a bias voltage is necessary for the electrode. Finally, after the calibration experiment, the accurate concentration of H2S gas can be measured. Based on the experimental analysis, the sensor shows good linearity and selectivity, comparatively high sensitivity, perfect stability and an extremely long operating life of up to two years. [ABSTRACT FROM AUTHOR]

The present work reports the influence of zinc oxide (ZnO) seed layer annealing temperature on structural, optical and electrical properties of ZnO nanorod arrays, synthesized by hydrothermal method assisted by microwave radiation, to be used as UV sensors. The ZnO seed layer was produced using the spin-coating method and several annealing temperatures, ranging from 100 to 500 °C, have been tested. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and spectrophotometry measurements have been used to investigate the structure, morphology, and optical properties variations of the produced ZnO nanorod arrays regarding the seed layer annealing temperatures employed. After the growth of ZnO nanorod arrays, the whole structure was tested as UV sensors, showing an increase in the sensitivity with the increase of seed layer annealing temperature. The UV sensor response of ZnO nanorod arrays produced with the seed layer annealed temperature of 500 °C was 50 times superior to the ones produced with a seed layer annealed at 100 °C. [ABSTRACT FROM AUTHOR]

A study on the propane gas-sensing properties of Cu-doped ZnO thin films is presented in this work. The films were deposited on glass substrates by sol-gel and dip coating methods, using zinc acetate as a zinc precursor, copper acetate and copper chloride as precursors for doping. For higher sensitivity values, two film thickness values are controlled by the six and eight dippings, whereas for doping, three dippings were used, irrespective of the Cu precursor. The film structure was analyzed by X-ray diffractometry, and the analysis of the surface morphology and film composition was made through scanning electron microscopy (SEM) and secondary ion mass spectroscopy (SIMS), respectively. The sensing properties of Cu-doped ZnO thin films were then characterized in a propane atmosphere, C3H8, at different concentration levels and different operation temperatures of 100, 200 and 300 °C. Cu-doped ZnO films doped with copper chloride presented the highest sensitivity of approximately 6 x 104, confirming a strong dependence on the dopant precursor type. The results obtained in this work show that the use of Cu as a dopant in ZnO films processed by sol-gel produces excellent catalysts for sensing C3H8 gas. [ABSTRACT FROM AUTHOR]

As highly sensitive H2S gas sensors, Au- and Ag-catalyzed SnO2 thin films with morphology-controlled nanostructures were fabricated by using e-beam evaporation in combination with the glancing angle deposition (GAD) technique. After annealing at 500 °C for 40 h, the sensors showed a polycrystalline phase with a porous, tilted columnar nanostructure. The gas sensitivities (S = Rgas/Rair) of Au and Ag-catalyzed SnO2 sensors fabricated by the GAD process were 0.009 and 0.015, respectively, under 5 ppm H2S at 300 °C, and the 90% response time was approximately 5 s. These sensors showed excellent sensitivities compared with the SnO2 thin film sensors that were deposited normally (glancing angle = 0°, S = 0.48). [ABSTRACT FROM AUTHOR]

Applications of alumina and nickel oxide in various fields specially in solar energy conversion technology encouraged us to study physical properties of such materials. Hence after the deposition of the thin films on glass substrate by spray pyrolysis, using X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-visible spectrophotometry, various physical properties were investigated. Different optical quantities such as optical band gap, refractive index, extinction coefficient, dielectric constants, volume and surface energy loss functions and optical conductivity were determined. Within this paper for different nickel to aluminium ratio (from 20/80 to 80/20 ratio) at specific substrate temperatures (300°C), decrease of optical transmittance with nickel content was notable. Using the transmittance data, other optical quantities were achieved by a numerical approximation method. We also observed an increase in the volume energy loss (VELF) more than the surface energy loss (SELF) and simultaneously a decrease trend prevailed according to nickel amount. On the basic of the XRD results, the amorphous phase changed by the presence of more nickel and according to SEM, more obvious nanosized spherical grains at higher nickel ratios can be observed. [ABSTRACT FROM AUTHOR]

The main objective of the paper was the analysis of the properties of SnO2|WO3 heterocontact as well as the determination of its response to 50 ppm of hydrogen sulphide. It was noticed that the sensitivity of the sensor being tested to hydrogen sulphide depended significantly on the polarization direction. When its parameters were compared with those of sensors the gas-sensitive layer of which was made only from one type of metal oxide, a high impact of the heterocontact on the electric charge transport was noticed. The value of the activation energy of the electric conductivity is clearly dependent on the polarization direction. A mechanism of physicochemical processes occurring in a planar sensor with a heterocontact was suggested, and three areas differing in the width of depleted layer, where the inter-phase boundary of SnO2|WO3 had the most essential impact on the parameters of the sensor being tested, were distinguished and described. [ABSTRACT FROM AUTHOR]

The possibility of creating resonant ultraviolet (UV) sensors based on the structure of ZnO nanorods/La3Ga5SiO14 microbalance (LCM) has been investigated. The principle of sensor operation is based on the desorption of oxygen from the surface of ZnO nanorods upon irradiation with UV light and an increase in the concentration of charge carriers that leads to an increase in the capacitance of the structure of ZnO nanorods/LCM. It has been shown that UV radiation intensity affects the resonance oscillation frequency of the LCM sensor. After the end of irradiation, the reverse process of oxygen adsorption on the surface of ZnO nanorods occurs, and the resonance frequency of the sensor oscillations returns to the initial value. [ABSTRACT FROM AUTHOR]

Development of sensor materials based on metal oxide semiconductors (MOS) for selective gas sensors is challenging for the tasks of air quality monitoring, early fire detection, gas leaks search, breath analysis, etc. An extensive range of sensor materials has been elaborated, but no consistent guidelines can be found for choosing a material composition targeting the selective detection of specific gases. Fundamental relations between material composition and sensing behavior have not been unambiguously established. In the present review, we summarize our recent works on the research of active sites and gas sensing behavior of n-type semiconductor metal oxides with different composition (simple oxides ZnO, In2O3, SnO2, WO3; mixed-metal oxides BaSnO3, Bi2WO6), and functionalized by catalytic noble metals (Ru, Pd, Au). The materials were variously characterized. The composition, metal-oxygen bonding, microstructure, active sites, sensing behavior, and interaction routes with gases (CO, NH3, SO2, VOC, NO2) were examined. The key role of active sites in determining the selectivity of sensor materials is substantiated. It was shown that the metal-oxygen bond energy of the MOS correlates with the surface acidity and the concentration of surface oxygen species and oxygen vacancies, which control the adsorption and redox conversion of analyte gas molecules. The effects of cations in mixed-metal oxides on the sensitivity and selectivity of BaSnO3 and Bi2WO6 to SO2 and VOCs, respectively, are rationalized. The determining role of catalytic noble metals in oxidation of reducing analyte gases and the impact of acid sites of MOS to gas adsorption are demonstrated. [ABSTRACT FROM AUTHOR]

In this work, a broad overview in the field of strontium titanate (ST, SrTiO3)-, barium titanate (BT, BaTiO3)- and barium strontium titanate (BST, BaSrTiO3)-based gas sensors is presented and discussed. The above-mentioned materials are characterized by a perovskite structure with long-term stability and therefore are very promising materials for commercial gas-sensing applications. Within the last 20 years, the number of papers where ST, BT and BST materials were tested as gas-sensitive materials has ten times increased and therefore an actual review about them in this field has been expected by readers, who are researchers involved in gas-sensing applications and novel materials investigations, as well as industry research and development center members, who are constantly searching for gas-sensing materials exhibiting high 3S parameters (sensitivity, selectivity and stability) that can be adapted for commercial realizations. Finally, the NO2-sensing characteristics of the BST-based gas sensors deposited by the authors with the utilization of magnetron sputtering technology are presented. [ABSTRACT FROM AUTHOR]

Nanocomposites In2O3/Ag obtained by ultraviolet (UV) photoreduction and impregnation methods were studied as materials for CO sensors operating in the temperature range 25–250 °C. Nanocrystalline In2O3 and In2O3/Ag nanocomposites were characterized by X-ray diffraction (XRD), single-point Brunauer-Emmet-Teller (BET) method, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The active surface sites were investigated using Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy and thermo-programmed reduction with hydrogen (TPR-H2) method. Sensor measurements in the presence of 15 ppm CO demonstrated that UV treatment leads to a complete loss of In2O3 sensor sensitivity, while In2O3/Ag-UV nanocomposite synthesized by UV photoreduction demonstrates an increased sensor signal to CO at T < 200 °C. The observed high sensor response of the In2O3/Ag-UV nanocomposite at room temperature may be due to the realization of an additional mechanism of CO oxidation with participation of surface hydroxyl groups associated via hydrogen bonds. [ABSTRACT FROM AUTHOR]

A facile one-step, eco-friendly, and cost-effective approach for the formation of copper oxide (CuO) nanowires by a green method using saponin-rich Sapindus mukorossi fruit extract (SMFE). The physio-chemical characteristics of the synthesized CuO nanowires have been characterized by X-ray Diffractometry (XRD), X-ray Photoelectron Spectroscopy (XPS), FT-IR (Fourier Transform Infrared Spectroscopy, FE-SEM (Scanning Electron Microscopy), and High-Resolution Transmission Electron Microscopy (HR-TEM). Further, the electrocatalytic activity of the CuO nanowires synthesized with SMFE has been investigated, and they have been used as dopamine (DA) sensors. Because of their unique properties, the CuO nanowires/GCE exhibited remarkable electrochemical response for the detection of DA with enhanced current response. The anodic current demonstrated that the CuO nanowires/GCE linearly detects the concentration of DA over the range of 0.1 µM to 0.105 mM of DA with a regression co-efficient of 0.9960. The obtained results illustrated that the synthesized CuO nanowires can easily stimulate the electron transfer reaction between DA and the nanowires modified electrode with the improvement of the conductivity and stability of the electrode. This remarkable electrocatalytic property of CuO nanowires makes it a unique electrochemical sensor for the detection of DA. Furthermore, the sensor is free from the interference of ascorbic acid, uric acid, and other interfering species. Moreover, the anti-interference performance also showed that the CuO nanowires/GCE could be employed for the determination of DA in real samples with good selectivity and sensitivity. [ABSTRACT FROM AUTHOR]