Enhanced NO2 gas sensor device based on supramolecularly assembled polyaniline/silver oxide/graphene oxide composites

Herein, we report a successful synthesis of supramolecularly assembled polyaniline/silver oxide/graphene oxide composite (PANI/Ag₂O/GO) for enhanced NO₂ gas sensing application. The PANI/Ag₂O/GO composite was synthesized by facile stirring followed by an ultrasonication process. The prepared material was characterized by different techniques such as x-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and Raman-scattering spectroscopy. The detailed analysis revealed that the average crystallite sizes of PANI/Ag₂O and PANI/Ag₂O/GO composites were found to be 37.37 nm and 41.55 nm, respectively. FESEM and TEM analysis showed coral-like rough-surfaced and extensively agglomerated morphology for PANI and ultrathin flexible sheet-like morphology for GO. Ag₂O nanoparticles with diameters 20–30 nm were well incorporated in the GO sheets and PANI matrix in the case of PANI/Ag₂O/GO composites. The synthesized materials were used to make resistive sensor devices that had a high response to NO₂ gas. The fabricated sensors were examined at various temperatures to obtain the optimal sensing temperature. The fabricated NO₂ gas sensor device based on PANI/Ag₂O/GO composite exhibited a highest sensitivity of 5.85 for 25 ppm at an optimized temperature (100 °C) as compared to the pure PANI (2.5) and PANI/Ag₂O composite (3.25). Further, the fabricated sensor device based on PANI/Ag₂O/GO composite was also examined at different NO₂ gas concentrations.     

Fabrication and its characteristics of metal-loaded TiO2/SnO2 thick-film gas sensor for detecting dichloromethane

This study investigated sensitivity of the gas sensor to chemical warfare agents with the various operating temperatures and catalysts. The nano-sized SnO₂ powder mixed with metal oxide (TiO₂) was doped with transition metals (Pt, Pd and In). Thick film of nano-sized SnO₂ powder and TiO₂ was prepared by screen-printing method onto Al₂O₃ substrates with platinum electrode and chemical precipitation method. The physical and chemical properties of sensor material were investigated by SEM/EDS, XRD and BET analyzers. The measured sensitivity to simulant chemical toxic gas is defined as the percentage of resistance of value equation, (R_a − R_g/R_a), that of the resistance (R_air) of SnO₂ film in air and the resistance (R_gas) of SnO₂ film in dichloromethane. The best sensitivity and selectivity of these thick-film sensor were shown with 1 wt.% Pt and 5 wt.% TiO₂ for dichloromethane toxic gas at the operating temperature of 250 °C.     

SnO2 submicron porous cube derived from metal-organic framework for n-butanol sensing at room temperature

SnO₂ is a typical metal oxide semiconductor gas sensitive material, which has been studied deeply. However, pure SnO₂ sensing materials usually have good performance at high operating temperatures. In this study, we reported an n-butanol sensor with high selectivity and fast response based on SnO₂ submicron porous cube prepared by heating and decomposing the Sn-based metal-organic framework material (Sn-MOF) in air at a certain temperature. SnO₂ submicron porous cube prepared at 450 °C shows good response and selectivity for n-butanol. And it has a response (%) of 175% to 100 ppm n-butanol and a relatively fast response/recovery time of 184 s/183 s at room temperature. The (110) crystal plane with sufficient oxygen-rich vacancy can adsorb O₂ and n-butanol molecules more effectively. Therefore, its sensitivity to n-butanol gas can be significantly improved. This work provides a good idea for further research on pure metal oxide semiconductor room temperature gas sensors.     

Process intensification of uniform loading of SnO2 nanoparticles on graphene oxide nanosheets using a novel ultrasound assisted in situ chemical precipitation method

In this paper, a novel ultrasound assisted, solution-based chemical synthesis method for the preparation of SnO₂–graphene nanocomposite is presented. Graphene oxide (GO) was prepared by the modified Hummers–Offeman method in presence of ultrasonic irradiation. Further loading of SnO₂ on GO was carried out with an ultrasound assisted solution-based synthesis route. The prepared GO and SnO₂–graphene nanocomposite were characterized by XRD, TEM, FTIR spectra, TGA and DTA analysis in order to confirm the formation of graphene–SnO₂ nanocomposite. TEM analysis of ultrasonically prepared graphene–SnO₂ composite shows the uniform and fine loading of SnO₂ particles (3–5 nm) on graphene nanosheets. However agglomerated morphology was observed in case of conventionally prepared graphene–SnO₂ composite. The cavitational effects generated due to the ultrasonic irradiations during the synthesis of graphene–SnO₂ composite improve the fine and uniform loading of SnO₂ on graphene nanosheets by oxidation–reduction reaction between GO and SnCl₂·2H₂O compared to conventional synthesis methods. The formed material was used for the preparation of anode in lithium ion batteries and its electrochemical performance was characterized by cyclic voltammetry and charge/discharge cycles. It is found that the capacity of SnO₂–graphene nanocomposite based Li-battery is stable for around 120 cycles, and the battery could repeat stable charge–discharge reaction.     

Synthesis,characterization and enhanced acetone sensing performance of Pd loaded Sm doped SnO2 nanoparticles

In the present communication, we have presented a high performance acetone sensor based on Pd loaded Sm doped SnO₂ nanomaterial. The (0.5, 1, 2 and 3) wt% Pd loaded 6 mol% Sm doped SnO₂ nanoparticles were prepared using a co-precipitation method. The characterization of samples was done by using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FEG-SEM), Energy Dispersive Analysis by X-rays (EDAX), High Resolution-Transmission Electron Microscopy (HR-TEM) and Selective Area Electron Diffraction (SAED) techniques. The gas response studies such as sensitivity, selectivity and stability towards liquid petroleum gas, ammonia, ethanol and acetone were measured at 100 ppm concentrations. The results show that optimum Pd loading (2 wt%) results in smaller crystallite size (~3.1 nm), lower operating temperature (200 °C), higher gas response (94%),better selectivity, faster response (~3 s) and quicker recovery (~12 s) towards acetone.     

Bivalent tin ion assisted reduction for preparing graphene/SnO2 composite with good cyclic performance and lithium storage capacity

Co-precipitation method of SnCl₂·2H₂O and graphene oxide (GO) solution was performed to fleetly prepare graphene/SnO₂ composite. The structure and composition of the nanocomposite were detected by means of XRD, SEM, TEM and FT-IR. The GO was reduced by bivalent tin ions to graphene nanosheet (GNS) via solution reaction and SnO₂ nano-crystals with size of 4–6 nm were homogeneously distributed on the matrix of GNS. It was found that the disorder degree of graphene in GNS/SnO₂ composite prepared by the bivalent tin ion assisted reduction method was much lower than that of GNS obtained via pyrolysis reduction. The possible mechanism for this phenomenon was discussed in detail. The N₂ adsorption tests showed an ink-bottle-like pore structure of GNS/SnO₂ and the SnO₂ nanoparticles were confined in the interlayer of GNS without agglomeration. These structural features were desirable and enabled GNS/SnO₂ an excellent anode material in lithium ion battery. The electrochemical tests showed that the composite could deliver a reversible capacity of 775.3 mAh/g and capacity retention of 98% after 50 cycles.     

Tin–Zinc oxide composite ceramics for selective CO sensing

Composite metal oxide gas sensors were intensely studied over the past years having superior performance over their individual oxide components in detecting hazardous gases. A series of pellets with variable amounts of SnO₂ (0–50 mol%) was prepared using wet homogenization of the component oxides leading to the composite tin-zinc ceramic system formation. The annealing temperature was set to 1100 °C. The samples containing 2.5 mol% SnO₂ and 50 mol% SnO₂ were annealed also at 1300 °C, in order to observe/to investigate the influence of the sintering behaviour on CO detection. The sensor materials were morphologically characterized by scanning electron microscopy (SEM). The increase in the SnO₂ amount in the composite ceramic system leads to higher sample porosity and an improved sensitivity to CO. It was found that SnO₂ (50 mol%) - ZnO (50 mol%) sample exhibits excellent sensing response, at a working temperature of 500 °C, for 5 ppm of CO, with a fast response time of approximately 60 s and an average recovery time of 15 min. Sensor selectivity was tested using cross-response to CO, methane and propane. The results indicated that the SnO₂ (50 mol%)-ZnO (50 mol%) ceramic compound may be used for selective CO sensing applications.     

Semi shield driven p-n heterostructures and their role in enhancing the room temperature ethanol gas sensing performance of NiO/SnO2 nanocomposites

The demand for the development of gas sensors operable at room temperature is increasing due to the uncountable drawbacks of high temperature gas sensors. This contribution describes the fabrication of room temperature ethanol sensor. The synthesis of NiO semi shielded SnO₂ (NiO/SnO₂) nanocomposites (NCs) was done via a simple two-step process, started with co-precipitation technique and then followed by sol-gel method. High resolution electron microscope (HRTEM) results indicated the semi shielding of NiO on SnO₂ nanoparticles (NPs). Surface morphological studies of the fabricated sensors show the porous nature of the samples which further helps in enhanced sensing response. X-ray photoelectron spectroscope (XPS) results of NiO/SnO₂ NCs revealed the valence states of Ni (+2) and Sn (+4). Excellent gas sensing response of the NiO/SnO₂ sensor towards ethanol at room temperature was observed from the gas sensing studies. The response of NiO/SnO₂ (∼140) was nearly 9 times higher than SnO₂ sensor (∼15) and nearly 11 times higher than NiO sensor (12.98) towards 100 ppm ethanol at room temperature. The observed response and recovery times of NiO/SnO₂ were 23 s and 13 s respectively. The p-n heterostructure formed between p-NiO and n-SnO₂, and high chemical sensitization and catalytic activity of the NiO are the main contributors for the excellent sensing performance of NiO/SnO₂ sensor.     

Improved ethanediol sensing with single Yb ions doped SnO2 nanobelt

Yb-doped SnO₂ nanobelts (Yb–SnO₂ NBs) and pure SnO₂ nanobelts (SnO₂ NBs) are successfully synthesized by thermal evaporation method and their composition and morphology are characterized. The single nanobelt device is fabricated by dual-ion beam deposition system, and the gas sensing performance to ethanediol, methanal, ethanol and acetone is investigated. The results show that the best working temperature of single Yb–SnO₂ NB sensor to ethanediol is 190 °C, which is lower than that of pure counterpart and the highest sensitivity is 10.5 to 100 ppm of ethanediol. In addition, it is found that the response/recovery time is short and the sensor exhibits excellent selectivity and stability. The sensing performance of SnO₂ NB is actually improved by Yb.     

Ultrasound assisted synthesis of polythiophene/SnO2 hybrid nanolatex particles for LPG sensing

Polythiophene (PTP) coated SnO₂ nano-hybrid particles have been synthesized using an ultrasound assisted in situ oxidative polymerization of thiophene monomers. Reference experiments have also been performed in the absence of ultrasound to clearly illustrate the effect of ultrasonic irradiations. FTIR results show broadening and shifting of peaks toward lower wave numbers, suggesting better conjugation and chemical interactions between PTP and SnO₂ particles. Due to strong synergetic interaction between the SnO₂ nanoparticles and polythiophene, this hybrid nanocomposite has the potential application as chemical sensors. It has been observed that PTP/SnO₂ hybrid sensors could detect liquefied petroleum gas (LPG) with high sensitivity at room temperature. PTP/SnO₂ hybrid composite containing 20 wt% SnO₂ showed the maximum sensitivity at room temperature. The sensing mechanism of PTP/SnO₂ hybrid nanocomposites to LPG was mainly attributed to the effects of p–n heterojunction between PTP and SnO₂.     

Highly sensitive acetone sensor based on Eu-doped SnO2 electrospun nanofibers

In this study, a series of undoped and Eu-doped SnO₂ nanofibers were synthesized via a simple electrospinning technique and subsequent calcination treatment. Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were carefully used to characterize the morphologies, structures and chemical compositions of these samples. The results reveal that the as-prepared nanofibers are composed of crystallite grains with an average size of about 10 nm and Eu³⁺ ions are successfully doped into the SnO₂ lattice. Compared with pure SnO₂ nanofibers, Eu-doped SnO₂ nanofibers demonstrate significantly enhanced sensing characteristics (e.g., large response value, short response/recovery time and outstanding selectivity) toward acetone vapor, especially, the optimal sensor based on 2 mol% Eu-doped SnO₂ nanofibers shows the highest response (32.2 for 100 ppm), which is two times higher than that of the pure SnO₂ sensor at an operating temperature of 280 °C. In addition, the sensor exhibits a good sensitivity to acetone in sub-ppm concentrations and the detection limit could extend down to 0.3 ppm, making it a potential candidate for the breath diagnosis of diabetes.     

Preparation of hollow SnO2/ZnO cubes for the high-performance detection of VOCs

Detecting volatile organic compounds is essential to improving the environment and human health. This study prepared a novel composite of hollow SnO₂/ZnO cubes using a self-template hydrothermal method followed by a calcination process. The morphology and structure of the composites were characterized using a series of analysis techniques, and the formation mechanism of a hollow cube-like structure was explored. Compared to the hollow SnO₂ cube sensor, the hollow SnO₂/ZnO cube sensor exhibited a strong response (148–100 ppm formaldehyde), fast response/recovery time (15 s/25 s), good linearity (R² = 0.995), good repeatability, and excellent stability. The superior gas sensing property of the hollow SnO₂/ZnO cubes was attributed to the combined advantages of hollow structures and heterojunctions.     

High performance H2 sensor based on rGO-wrapped SnO2–Pd porous hollow spheres

Hydrogen (H₂) sensors based on metal oxide semiconductors (MOS) are promising for many applications such as a rocket propellant, industrial gas and the safety of storage. However, poor selectivity at low analyte concentrations, and independent response on high humidity limit the practical applications. Herein, we designed rGO-wrapped SnO₂–Pd porous hollow spheres composite (SnO₂–Pd@rGO) for high performance H₂ sensor. The porous hollow structure was from the carbon sphere template. The rGO wrapping was via self-assembly of GO on SnO₂-based spheres with subsequent thermal reduction in H₂ ambient. This sensor exhibited excellently selective H₂ sensing performances at 390 °C, linear response over a broad concentration range (0.1–1000 ppm) with recovery time of only 3 s, a high response of ～8 to 0.1 ppm H₂ in a minute, and acceptable stability under high humidity conditions (e. g. 80%). The calculated detection limit of 16.5 ppb opened up the possibility of trace H₂ monitoring. Furthermore, this sensor demonstrated certain response to H₂ at the minimum concentration of 50 ppm at 130 °C. These performances mainly benefited from the special hollow porous structure with abundant heterojunctions, the catalysis of the doped-PdO_x, the relative hydrophobic surface from rGO, and the deoxygenation after H₂ reduction.     

Synthesis and characterization of mesoporous NiO2/ZrO2-CeO2 catalysts for total methane conversion

This work reports the synthesis and characterization of mesoporous NiO/ZrO₂^-CeO₂ composites. These materials are still being developed due to their excellent morphological and structural properties, especially for solid oxide fuel cells (SOFCs) anodes. A soft chemical route using a polymeric template was utilized to synthesize the samples. The structure after two different calcination processes at 400 °C and 540 °C was studied by X-ray diffraction and Rietveld refinement, before and after NiO loading. Nitrogen adsorption, scanning/transmission electron microscopy and small angle X-ray scattering revealed a nanocrystalline bi-phasic porous material. Temperature programmed reduction experiments showed higher Ni and Ce reduction values for samples calcined at 400 °C and 540 °C, respectively. Methane conversion values in the temperature range studied were similar for both calcination temperatures, showing 50% CH₄ conversion around 550 °C and 80% around 650 °C. However, a sample calcined at 400 °C exhibited better morphological and textural properties leading to an enhancement in NiO and CeO₂ reducibility that might be responsible for an improvement in oxygen surface exchange and gasification of carbon species in catalytic experiments.     

Low-temperature and highly sensitivity H2S gas sensor based on ZnO/CuO composite derived from bimetal metal-organic frameworks

The bimetallic metal-organic frameworks (MOF) Zn/Cu-BTC were prepared by a facile solvothermal method in one step and used as a self-sacrificed template to obtain the ZnO/CuO composites. The composites with different Cu/Zn molar ratios were characterized by XRD, FESEM, and XPS. The ZnO/CuO composite exhibited an octahedral structure, and a p-n heterojunction may be formed between p-type CuO and n-type ZnO. To prove its functional characteristics, the ZnO/CuO composite was used as a sensing material to test its gas sensitivity. The effect of Cu/Zn molar ratios was examined, and the results showed that the optimized ZnO/CuO (1: 0.33) composite based gas sensor exhibited reasonable selectivity to 10 ppm H₂S, operated at 40 °C. The sensitivities were improved by 17.1 times and 327.8 times compared with the pristine CuO and ZnO based gas sensors, respectively. Moreover, the detection limit to H₂S of such sensors could be reduced as low as 300 ppb. The sensing mechanism has been thoroughly studied and such ZnO/CuO composite is an ideal candidate for highly sensitive detection for H₂S with low power consumption in the real application.     

Improved formaldehyde sensor of Zn2SnO4/SnO2 microcubes by compositional evolution and Y2O3 decoration

Zn₂SnO₄/SnO₂(ZTO/SnO₂) and Y doped Zn₂SnO₄/SnO₂(ZTO/SnO₂) microcubes were synthesized by a hydrothermal route at 130?°C and subsequently used for obtaining gas sensors. To evaluate the structure, morphology, chemical state and optical bandgap, our sensors were characterized by XRD, SEM, XPS and UV–vis analysis. Compared with sensors based on ZTO/SnO₂ microcubes, the Y doped ZTO/SnO₂ microcubes had an optimum sensing performance to 100?ppm formaldehyde (HCHO), for instance lower working temperature (210?°C) and better response (46.07). In addition, the enhanced sensing mechanism of Y doped ZTO/SnO₂ microcubes was discussed in detail.     

Enhanced gas sensing properties of hierarchical SnO2 nanoflower assembled from nanorods via a one-pot template-free hydrothermal method

Well-defined three-dimensional (3D) hierarchical tin dioxide (SnO₂) nanoflowers with the size of about 200 nm were successfully synthesized by a simple template-free hydrothermal method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N₂ adsorption-desorption analyses were used to characterize the structure and morphology of the products. The as-synthesized full crystalline and large specific surface area SnO₂ nanoflowers were assembled by one-dimensional (1D) SnO₂ nanorods with sharp tips. A possible self-assembly mechanism for the formation the SnO₂ nanoflowers was speculated. Moreover, gas sensing investigation showed the sensor based on SnO₂ nanoflowers to exhibit high response and fast response-recovery ability to detect acetone and ethanol at an operating temperature lower than 200 °C. The enhancement of gas sensing properties was attributed to their 3D hierarchical nanostructure, large specific surface area, and small size of the secondary SnO₂ nanorods.     

Electrochemically synthesized graphene/polypyrrole composites and their use in supercapacitor

Composite films consisting of polypyrrole (PPy) and graphene oxide (GO) were electrochemically synthesized by electrooxidation of 0.1 M pyrrole in aqueous solution containing appropriate amounts of GO. Simultaneous chronoamperometric growth profiles and frequency changes on a quartz crystal microbalance showed that the anionic GO was incorporated in the growing GO/PPy composite to maintain its electrical neutrality. Subsequently, the GO was reduced electrochemically to form a reduced GO/PPy (RGO/PPy) composite by cyclic voltammetry. Specific capacitances estimated from galvanostatic discharge curves in 1 M H₂SO₄ at a current density of 1 A g^?1 indicated that values for the RGO/PPy composite were larger than those of a pristine PPy film and the GO/PPy composite. In the case of 6 mg mL^?1 GO for the preparation of GO/PPy, a high specific capacitance of 424 F g^?1 obtained at the electrochemically prepared RGO/PPy composite indicated its potential for use as an electrode material for supercapacitors.     

Synthesis of TiO2(B)/SnO2 composite materials as an anode for lithium-ion batteries

A TiO₂(B) nanosheets/SnO₂ nanoparticles composite was prepared by the hydrothermal and chemical bath deposition (CBD) methods, and its electrochemical properties were investigated for use as the anode material of a lithium-ion battery. The as-prepared composites consisted of monoclinic-phase TiO₂(B) nanosheets and cassiterite structure SnO₂ nanoparticles, in which SnO₂ nanoparticles were uniformly decorated on the TiO₂(B) nanosheets. The TiO₂(B)/SnO₂ composites showed a higher reversible capacity and better durability than that of the pure TiO₂(B) for use as a battery anode. The composite electrodes exhibiting a high initial discharge capacity of 2239.1 mAh g⁻¹ and a discharge capacity of more than 868.7 mAh g⁻¹ could be maintained after 50 cycles at 0.1 C in a voltage range of 1.0–3.0 V at room temperature. The results suggest that TiO₂(B) nanosheets coated with SnO₂ could be suitable for use as a stable anode material for lithium-ion batteries. In addition, the coulombic efficiency of the nanosheets remains at an average of 93.1% for the 3rd–50th cycles.     

Facile synthesis of SnO2/NiO nano-composites: Structural,magnetic and catalytic properties

Environmental pollution, one of the major challenges being faced by life forms on our planet, can be controlled to some extent by degrading organic pollutants using heterostructured nanoparticles. This paper reports the fabrication of SnO₂/NiO nano-composites by a simple, environmentally benign and cost effective two – step process via precipitation using tannic acid, a green reagent. Thermal analysis shows the optimum annealing temperature as 500 °C.Fcc structured NiO and tetragonal SnO₂ in the nanocomposite is confirmed from XRD analysis. The interplanar spacing of 0.33 nm in SnO₂ for (111) and 0.20 nm in NiO for (200) planes observed in the HRTEM images confirms the composite formation. The synthesized composites characterized using UV–Vis spectra give band gap energies of the samples. The elemental composition and oxidation states have been supported by EDX and XPS analyses. VSM study carried out at room temperature show enhanced ferromagnetic properties with increase in NiO content. The probe reactions degrading Methylene Blue and Eosin Yellow show the effective catalytic potential of the synthesized SnO₂/NiO nano-composite. Efficient degradation of 98% and 97% could be achieved in 14 and 20 min, respectively, showing suitability as a promising candidate in waste water treatment.