Reduced graphene oxide-porous In2O3 nanocubes hybrid nanocomposites for room-temperature NH3 sensing

Metal oxide semiconductors (MOS)-reduced graphene oxide (rGO) nanocomposites have attracted great attention for room-temperature gas sensing applications. The development of novel sensing materials is the key issue for the effective detection of ammoniagas at room temperature. In the present work, the novel reduced graphene oxide (rGO)-In₂O₃ nanocubes hybrid materials have been prepared via a simple electrostatic self-assembly strategy. Characterization results exhibit that the intimate interfacial contact between In₂O₃ nanocubes and the rGO sheets are achieved. Particularly, the as-prepared rGO/In₂O₃ nanocomposites displayed high sensitivity, fast response and excellent selectivity towards ammonia (NH₃) at room-temperature, which clearly uncovers the merit of structural design and rational integration with rGO sheets. The superior gas sensing performance of the rGO/In₂O₃ nanocomposites can be attributed to the synergetic effects of rGO sheets and porous In₂O₃ nanocubes. The reported synthesis offers a general approach to rGO/MOS-based semiconductor composites for room-temperature gas sensing applications.     

Single crystal WO3 nanoflakes as quartz crystal microbalance sensing layer for ultrafast detection of trace sarin simulant

Tungsten oxide (WO₃) nanoflakes were synthesized, and characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. Thermogravimetry and X-ray photoelectron spectroscopy demonstrate the existence of strongly bound surface water molecules on the surface of tungsten oxide nanoflakes. WO₃ nanoflake functionalized quartz crystal microbalance sensors were fabricated, and firstly used for detection of trace sarin simulant, dimethyl methylphosphonate (DMMP). The sensors have better reproducibility and stability as well as much shorter response (30 s) and recovery time (73 s) than those functionalized by conventional hydrogen-bond acidic branched copolymers. The strongly bound surface water molecules on the surface of WO₃ nanoflakes are believed to play a key role in achieving such excellent DMMP sensing characteristics.     

Indium-organic framework CPP-3（In） derived Ag/In2O3 porous hexagonal tubes for H2S detection at low temperature

There is a great demand for high-performance hydrogen sulfide（H₂S） sensors with low operating temperatures. Ag/In₂O₃ hexagonal tubes with different proportions were prepared by the calcination of Ag+-impregnated indium-organic frameworks(CPP-3（In）), and the developed sensors exhibit enhanced gassensing performance toward H₂S. Gas sensing measurements indicate that the response of Ag/In₂O₃（2.5 wt%） sensor to 5 ppm H₂S ha...     

Pure and Palladium‐Loaded Co3O4 Hollow Hierarchical Nanostructures with Giant and Ultraselective Chemiresistivity to Xylene and Toluene

Pure and palladium‐loaded Co₃O₄ hollow hierarchical nanostructures consisting of nanosheets have been prepared by solvothermal self‐assembly. The nanostructures exhibited an ultrahigh response and selectivity towards p‐xylene and toluene. The responses (resistance ratio) of the palladium‐loaded Co₃O₄ hollow hierarchical nanostructures to 5 ppm of p‐xylene and toluene were as high as 361 and 305, respectively, whereas the selectivity values (response ratios) towards p‐xylene and toluene over interference from ethanol were 18.1 and 16.1, respectively. We attributed the giant response and unprecedented high selectivity towards methylbenzenes to the abundant adsorption of oxygen by Co₃O₄, the high chemiresistive variation in the Co₃O₄ nanosheets (thickness≈11 nm), and the catalytic promotion of the specific gas‐sensing reaction. The morphological design of the p‐type Co₃O₄ nanostructures and loading of the palladium catalyst have paved a new way to monitoring the most representative indoor air pollutants in a highly selective, sensitive, and reliable manner.     

A facile construction of heterostructured ZnO/Co_3O_4 mesoporous spheres and superior acetone sensing performance

The rapid development of internet and internet of things brings new opportunities for the expansion of intelligent sensors,and acetone as a major disease detection indicator(i.e.,diabetes) making it become extremely important clinical indicator.Herein,uniform mesoporous ZnO spheres were successfully synthesized via novel formaldehyde-assisted metal-ligand crosslinking strategy.In order to adjust the pore structure of mesoporous ZnO,various mesoporous ZnO spheres were synthesized by changing weight percentage of Zn(NO_3)_2·6 H_2 O to tannic acid(TA).Moreover,highly active heterojunction mesoporous ZnO/Co_3 O_4 has been fabricated based on as-prepared ultra-small Co_3 O_4 nanocrystals(ca.3 nm) and mesoporous ZnO spheres by flexible impregnation technique.Profit from nano-size effect and synergistic effect of p-n heterojunction,mesoporous ZnO/Co_3 O_4 exhibited excellent acetone sensing performance with high selectivity,superior sensitivity and responsiveness.Typically,5 wt% Co_3 O_4 embedded mesoporous ZnO sphere showed prominent acetone response(ca.46 for 50 ppm),which was about 11.5 times higher than that in pure ZnO sensing device,and it was also endowed high cyclic stability.The nanocrystals embedded hybrid material is expected to be used as promising efficient material in the field of catalysis and gas sensing.     

Highly sensitive,humidity-tolerant and flexible NO2 sensors based on nanoplate Bi2Se3 film

Recently, two-dimension (2D) materials have fueled considerable interest in the field of gas sensing to cope urgent demands at specific scenarios. Unfortunately, the susceptibility to ambient humidity, and/or fragile operation stability always frustrate their further practicability. To overcome these drawbacks, we proposed one novel flexible gas sensor based on bismuth selenide (Bi₂Se₃) nanoplates for sensitive NO₂ detection at room temperature. The as-prepared Bi₂Se₃ sensor exhibited favorable sensing performance, including remarkable NO₂ selectivity, high response of 120% and fast response time of 81 s toward 5 ppm NO₂, an ultralow detection limit of 100 ppb, and nice stability. Besides, the excellent humidity tolerance and mechanical flexibility endowed Bi₂Se₃ sensors with admirable reliability under harsh working conditions. The first-principles calculation further revealed the insights of extraordinary NO₂ selectivity and the underlying gas-sensing mechanism.     

压电晶体微天平阵列传感器识别毒剂的研究

压电晶体微天平(QCM)阵列传感器在毒剂侦检领域具有广泛的应用前景。本研究建立了QCM阵列传感器毒剂检测系统,以氢键酸性共聚硅氧烷(BSP3)、聚表氯醇(PECH)和乙基纤维素(ECEL)为膜材料制备了对毒剂敏感的QCM阵列传感器,对沙林、芥子气、甲基膦酸二甲酯进行了定量检测,并结合模式识别方法对检测结果进行了分析处理,识别率达到98%以上,为探索QCM阵列传感器对毒剂的定性定量分析提供了方法依据。     

Preparation of homogeneous porous Zn-CoOx and its response to alcohols under relative low operating temperature

A homogeneous porous Co₃O₄-ZnO nanomaterial (Zn-CoO_x) was successfully fabricated by precipitation-annealing route. The as-prepared Zn-CoO_x exhibited good response, reliable reversibility and good selectivity towards alcohols, which attributed to the porous structure and p-n heterojunction formed between Co₃O₄ and ZnO. In particular, the different Fermi levels of Co₃O₄ and ZnO leaded to a further increase the depth of the space charge layer, which improved the gas sensitivity of the material from 10% to 480%. Besides, the continuous Co₃O₄ leaded to a relatively lower operating temperature and resistance. This material preparation method and bimetallic oxides could be widely used in the research and development of metal oxide gas sensitive materials and sensors.     

Facile synthesis of cobalt oxide/reduced graphene oxide composites for electrochemical capacitor and sensor applications

Reduced graphene oxide sheets decorated with cobalt oxide nanoparticles (Co₃O₄/rGO) were produced using a hydrothermal method without surfactants. Both the reduction of GO and the formation of Co₃O₄ nanoparticles occurred simultaneously under this condition. At the same current density of 0.5 A g⁻¹, the Co₃O₄/rGO nanocomposites exhibited much a higher specific capacitance (545 F g⁻¹) than that of bare Co₃O₄ (100 F g⁻¹). On the other hand, for the detection of H₂O₂, the peak current of Co₃O₄/rGO was 4 times higher than that of Co₃O₄. Moreover, the resulting composite displayed a low detection limit of 0.62 μM and a high sensitivity of 28,500 μA mM⁻¹cm⁻² for the H₂O₂ sensor. These results suggest that the Co₃O₄/rGO nanocomposite is a promising material for both supercapacitor and non-enzymatic H₂O₂ sensor applications.     

Highly Responsive and Selective Ethanol Gas Sensor Based on Co3O4-Modified SnO2 Nanofibers

SnO₂ nanofibers were synthesized by electrospinning and modified with Co₃O₄ via impregnation in this work. Chemical composition and morphology of the nanofibers were systematically characterized, and their gas sensing properties were investigated. Results showed that Co₃O₄ modification significantly enhanced the sensing performance of SnO₂ nanofibers to ethanol gas. For a sample with 1.2 mol% Co₃O₄, the response to 100 ppm ethanol was 38.0 at 300℃, about 6.7 times larger than that of SnO₂ nanofibers. In addition, the response/recovery time was also greatly reduced. A power-law dependence of the sensor response on the ethanol concentration as well as excellent ethanol selectivity was observed for the Co₃O₄/SnO₂ sensor. The enhanced ethanol sensing performance may be attributed to the formation of p-n heterojunctions between the two oxides.     

Effect of carbonaceous support between graphite oxide and reduced graphene oxide with anchored Co<Subscript>3</Subscript>O<Subscript>4</Subscript> microspheres as electrode-active materials in a solid-state electrochemical capacitor

Hydrothermally synthesized Co₃O₄ microspheres were anchored to graphite oxide (GO) and thermally reduced graphene oxide (rGO) composites at different cobalt weight percentages (1, 10, and 100 wt%). The composite materials served as the active materials in bulk electrodes for two-electrode cell electrochemical capacitors (ECCs). GO/Co₃O₄–1 exhibited a high energy density of 35 W kg^?1 with a specific capacitance (C _sp) of 196 F g^?1 at a maximum charge density of 1 A g^?1. rGO/Co₃O₄-100 presented high specific power output values of up to 23.41 kW h kg^?1 with linear energy density behavior for the charge densities applied between 0.03 and 1 A g^?1. The composite materials showed Coulombic efficiencies of 96 and 93 % for GO/Co₃O₄–1 and rGO/Co₃O₄–100 respectively. The enhancement of capacitive performance is attributed to the oxygenated groups in the GO ECC and the specific area in the rGO ECC. These results offer an interesting insight into the type of carbonaceous support used for graphene derivative electrode materials in ECCs together with Co₃O₄ loading to improve capacitance performance in terms of specific energy density and specific power.

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Magnetite Nanorods Stabilized by Polyaniline/Reduced Graphene Oxide as a Sensing Platform for Selective and Sensitive Non‐enzymatic Hydrogen Peroxide Detection

In this study, magnetite nanorods stabilized on polyaniline/reduced graphene oxide (Fe₃O₄@PANI/rGO) was synthesized via a wet‐reflux strategy. The possible formation of Fe₃O₄@PANI/rGO was morphologically and structurally verified by field emission scanning electron microscopy (FE‐SEM), Fourier transform infrared (FT‐IR) spectroscopy, Raman spectroscopy, X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS). Furthermore, the thermal stability of Fe₃O₄@PANI/rGO was measured by a thermogravimetric analyzer (TGA); the composite had good thermal stability owing to the ceramic nature of Fe₃O₄. The Fe₃O₄@PANI/rGO has been applied as a potential sensing platform for electrochemical detection of hydrogen peroxide (H₂O₂). By the combined efforts of extended active surface area, active carbon support, more catalytic active sites and high electrical conductivity, the Fe₃O₄@PANI/rGO exhibited an improved performance toward the non‐enzymatic detection of H₂O₂ in 0.5 M KOH with a fast response time (5 s), high sensitivity (223.7 μA mM^?1 cm^?2), low limit of detection (4.45 μM) and wide linear range (100 μM–1.5 mM). Furthermore, the fabricated sensor exhibited excellent recovery rates (94.2–104.0 %) during real sample analysis.     

Monolayer Co3O4 Inverse Opals as Multifunctional Sensors for Volatile Organic Compounds

Monolayers of periodic porous Co₃O₄ inverse opal (IO) thin films for gas‐sensor applications were prepared by transferring cobalt‐solution‐dipped polystyrene (PS) monolayers onto sensor substrates and subsequent removal of the PS template by heat treatment. Monolayer Co₃O₄ IO thin films having periodic pores (d≈500 nm) showed a high response of 112.9 to 5 ppm C₂H₅OH at 200 °C with low cross‐responses to other interfering gases. Moreover, the selective detection of xylene and methyl benzenes (xylene+toluene) could be achieved simply by tuning the sensor temperature to 250 and 275 °C, respectively, so that multiple gases can be detected with a single chemiresistor. Unprecedentedly high ethanol response and temperature‐modulated control of selectivity with respect to ethanol, xylene, and methyl benzenes were attributed to the highly chemiresistive IO nanoarchitecture and to the tuned catalytic promotion of different gas‐sensing reactions, respectively. These well‐ordered porous nanostructures could have potential in the field of high‐performance gas sensors based on p‐type oxide semiconductors.     

Synthesis of 2D/2D Structured Mesoporous Co3O4 Nanosheet/N‐Doped Reduced Graphene Oxide Composites as a Highly Stable Negative Electrode for Lithium Battery Applications

Mesoporous Co₃O₄ nanosheets (Co₃O₄‐NS) and nitrogen‐doped reduced graphene oxide (N‐rGO) are synthesized by a facile hydrothermal approach, and the N‐rGO/Co₃O₄‐NS composite is formulated through an infiltration procedure. Eventually, the obtained composites are subjected to various characterization techniques, such as XRD, Raman spectroscopy, surface area analysis, X‐ray photoelectron spectroscopy (XPS), and TEM. The lithium‐storage properties of N‐rGO/Co₃O₄‐NS composites are evaluated in a half‐cell assembly to ascertain their suitability as a negative electrode for lithium‐ion battery applications. The 2D/2D nanostructured mesoporous N‐rGO/Co₃O₄‐NS composite delivered a reversible capacity of about 1305 and 1501 mAh g^?1 at a current density of 80 mA g^?1 for the 1st and 50th cycles, respectively. Furthermore, excellent cyclability, rate capability, and capacity retention characteristics are noted for the N‐rGO/Co₃O₄‐NS composite. This improved performance is mainly related to the existence of mesoporosity and a sheet‐like 2D hierarchical morphology, which translates into extra space for lithium storage and a reduced electron pathway. Also, the presence of N‐rGO and carbon shells in Co₃O₄‐NS should not be excluded from such exceptional performance, which serves as a reliable conductive channel for electrons and act as synergistically to accommodate volume expansion upon redox reactions. Ex‐situ TEM, impedance spectroscopy, and XPS, are also conducted to corroborate the significance of the 2D morphology towards sustained lithium storage.     

Enhanced Supercapacitor Performance Using a Co3O4@Co3S4 Nanocomposite on Reduced Graphene Oxide/Ni Foam Electrodes

To avoid an enormous energy crisis in the not-too-distant future, it be emergent to establish high-performance energy storage devices such as supercapacitors. For this purpose, a three-dimensional (3D) heterostructure of Co₃O₄ and Co₃S₄ on nickel foam (NF) that is covered by reduced graphene oxide (rGO) has been prepared by following a facile multistep method. At first, rGO nanosheets are deposited on NF under mild hydrothermal conditions to increase the surface area. Subsequently, nanowalls of cobalt oxide are electro-deposited on rGO/Ni foam by applying cyclic-voltammetry (CV) under optimized conditions. Finally, for the synthesis of Co₃O₄@Co₃S₄ nanocomposite, the nanostructure of Co₃S₄ was fabricated from Co₃O₄ nanowalls on rGO/NF by following an ordinary hydrothermal process through the sulfurization for the electrochemical application. The samples are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained sample delivers a high capacitance of 13.34 F cm⁻² (5651.24 F g⁻¹) at a current density of 6 mA cm⁻² compared to the Co₃O₄/rGO/NF electrode with a capacitance of 3.06 F cm⁻² (1230.77 F g⁻¹) at the same current density. The proposed electrode illustrates the superior electrochemical performance such as excellent specific energy density of 85.68 W h Kg⁻¹, specific power density of 6048.03 W kg⁻¹ and a superior cycling performance (86% after 1000 charge/discharge cycles at a scan rate of 5 mV s⁻¹). Finally, by using Co₃O₄ @Co₃S₄/rGO/NF and the activated carbon-based electrode as positive and negative electrodes, respectively, an asymmetric supercapacitor (ASC) device was assembled. The fabricated ASC provides an appropriate specific capacitance of 79.15 mF cm⁻² at the applied current density of 1 mA cm⁻², and delivered an energy density of 0.143 Wh kg⁻¹ at the power density of 5.42 W kg⁻¹.     

Array of Love-wave sensors based on quartz/Novolac to detect CWA simulants

An array of Love-wave sensors based on quartz and Novolac has been developed to detect chemical warfare agents (CWAs). These weapons are a risk for human health due to their efficiency and high lethality; therefore an early and clear detection is of enormous importance for the people safety. Love-wave devices realized on quartz as piezoelectric substrate and Novolac as guiding layer have been used to make up an array of six sensors, which have been coated with specific polymers by spin coating. The CWAs are very dangerous and for safety reasons their well known simulants have been used: dimethylmethyl phosphonate (DMMP), dipropyleneglycol methyl ether (DPGME), dimethylmethyl acetamide (DMA), dichloroethane (DCE), dichloromethane (DCM) and dichloropentane (DCP). The array has been exposed to these CWA simulants detecting very low concentrations, such as 25 ppb of DMMP, a simulant of nerve agent sarin. Finally, principal component analysis (PCA) as data pre-processing and discrimination technique, and probabilistic neural networks (PNN) as patterns classification technique have been applied. The performance of the sensor array has shown stability, accuracy, high sensitivity and good selectivity to these simulants.     

Dual WO3 based sensors to selectively detect DMMP in the presence of alcohols

A size selective approach to improving selectivity in semiconducting metal oxides (SMO) sensors was obtained by tailoring the architecture of WO₃ powders. The key for achieving high selectivity is based on using a dual sensor configuration where the response on a porous WO₃ powder sensor was compared to the response on a nonporous WO₃ powder sensor. Detection selectivity between methanol and dimethyl methylphosphonate (DMMP) is obtained because the access of a gas molecule in the interior pore structure of WO₃ is size dependent leading to a size dependant magnitude change in the conductivity of SMO sensor.     

Ammonia gas sensor based on a spinel semiconductor,Co<Subscript>0.8</Subscript>Ni<Subscript>0.2</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanomaterial

Thick film of nanocrystalline Co_0.8Ni_0.2Fe₂O₄ was obtained by sol–gel citrate method for gas sensing application. The synthesized powder was characterized by X-ray diffraction (XRD) and transmission electron microscopy. The XRD pattern shows spinel type structure of Co_0.8Ni_0.2Fe₂O₄. XRD of Co_0.8Ni_0.2Fe₂O₄ revels formation of solid solution with average grain size of about 30 nm. From gas sensing properties it observed that nickel doping improves the sensor response and selectivity towards ammonia gas and very low response to LPG, CO, and H₂S at 280 °C. Furthermore, incorporation of Pd improves the sensor response and stability of ammonia gas and reduced the operating temperature upto 210 °C. The sensor is a promising candidate for practical detector of ammonia.     

A Novel Biomimetic Hydrogen Peroxide Biosensor Based on Pt Flowers‐decorated Fe3O4/Graphene Nanocomposite

A sensitive and selective amperometric H₂O₂ biosensor was obtained by utilizing the electrodeposition of Pt flowers on iron oxide‐reduced graphene oxide (Fe₃O₄/rGO) nanocomposite modified glassy carbon electrode (GCE). The morphology of Fe₃O₄/rGO and Pt/Fe₃O₄/rGO was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), respectively. The step‐wise modification and the electrochemical characteristics of the resulting biosensor were characterized by cyclic voltammetry (CV) and chronoamperometry methods. Thanks to the fast electron transfer at the Pt/Fe₃O₄/rGO electrode interface, the developed biosensor exhibits a fast and linear amperometric response upon H₂O₂. The linear range of Pt/Fe₃O₄/rGO is 0.1∼2.4 mM (R²=0.998), with a sensitivity of 6.875 μA/mM and a detection limit of 1.58 μM (S/N=3). In addition, the prepared biosensor also provides good anti‐interferent ability and long‐term stability due to the favorable biocompatibility of the electrode interface. The proposed sensor will become a reliable and effective tool for monitoring and sensing the H₂O₂ in complicate environment.