Nanoparticle cluster gas sensor: Pt activated SnO2 nanoparticles for NH3 detection with ultrahigh sensitivity

In Situ Encapsulated Pt Nanoparticles Dispersed in Low Temperature Oxygen for Partial Oxidation of Methane to Syngas

Highly dispersed ultra-small Pt nanoparticles limited in nanosized silicalite-1 zeolite were prepared by in situ encapsulation strategy using H2PtCl6·6H2O as a precursor and tetrapropylammonium hydroxide as a template. The prepared Pt@S-1 catalyst was characterized by X-ray diffraction (XRD), inductively coupled plasma (ICP), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), N2 adsorption-desorption, CO adsorption, and TGA techniques and exhibited unmatched catalytic activity and sintering resistance in the partial oxidation of methane to syngas. Strikingly, Pt@S-1 catalyst with further reduced size and increased dispersibility of Pt nanoparticles showed enhanced catalytic activity after low-temperature oxygen calcination. However, for Pt/S-1 catalyst, low-temperature oxygen calcination did not improve its catalytic activity.

Enhanced Humidity Sensing Response of SnO2/Silicon Nanopillar Array by UV Irradiation

In this work, a silicon nanopillar array was created with nanosphere lithography. SnO₂ film was deposited on this nanostructure by magnetron sputtering to form an SnO₂/silicon nanopillar array sensor. The humidity sensitivity, response time, and recovery time were all measured at room temperature (25 °C) with UV or without UV irradiation. As a result, the humidity sensitivity properties were improved by enlarging the specific surface area with ordered nanopillars and irradiating with UV light. These results indicate that nanostructure sensors have potential applications in the field of sensors.

Ultrafine nanoparticles of W-doped SnO2 for durable H2S sensors with fast response and recovery

Ultrafine nanoparticles of W-doped SnO2 with an average diameter of 6 nm were fabricated via a facile hydrothermal method. The material shows a reduced particle size and enhanced response to H2S gas as compared to the pristine SnO2 nanoparticles. The detection limit can be down to 100 ppb while the response time and recovery time of the 5%-doped one are reduced to 17 s and 7 s respectively. In addition, the material shows impressive long-term stability of the response through 40 cycles of injection with 10 ppm H2S, which is attractive for designing a durable hydrogen sulfide sensor. The doping of W results in the reduction of size and modification of the electronic band structure of SnO2, which reduces the response time and recovery time and further improves the sensing durability of the materials.

A Schiff-Base Modified Pt Nano-Catalyst for Highly Efficient Synthesis of Aromatic Azo Compounds

A Schiff-base modified Pt nano-catalyst was prepared via one-pot aldimine condensation and then impregnation-reduction of a platinum precursor, in which the Pt nanoparticles (NPs) with an average size of 2.3 nm were highly dispersed on the support. The as-prepared catalyst exhibited excellent activity and selectivity in the hydrogenation coupling synthesis of aromatic azo compounds from nitroaromatic under mild conditions. The strong metal–support interaction derived from the coordination of nitrogen sites on Schiff-base to Pt NPs enables stabilizing the Pt NPs and achieving the catalytic recyclability. The scheme can also tolerate various functional groups and offer an efficient method for the green synthesis of aromatic azo compounds.

Facile Synthesis of Hierarchical Tin Oxide Nanoflowers with Ultra-High Methanol Gas Sensing at Low Working Temperature

In this work, the hierarchical tin oxide nanoflowers have been successfully synthesized via a simple hydrothermal method followed by calcination. The as-obtained samples were investigated as a kind of gas sensing material candidate for methanol. A series of examinations has been performed to explore the structure, morphology, element composition, and gas sensing performance of as-synthesized product. The hierarchical tin oxide nanoflowers exhibit sensitivity to 100 ppm methanol and the response is 58, which is ascribed to the hierarchical structure. The response and recovery time are 4 s and 8 s, respectively. Moreover, the as-prepared sensor has a low working temperature of 200 °C which is lower than that for other gas sensors of such type has been reported elsewhere. The excellent sensitivity of the sensor is caused by its complex phase mixture of SnO, SnO2, Sn2O3, and Sn6O4 revealed by XRD analysis. The proposed hierarchical tin oxide nanoflowers gas sensing material is promising for development of methanol gas sensor. The as-obtained hierarchical tin oxide nanoflower (HTONF) gas sensor shows excellent gas-sensing performance at low working temperature (200 °C) and high annealing temperature (400 °C).

Simple Synthesis of Cobalt Carbonate Hydroxide Hydrate and Reduced Graphene Oxide Hybrid Structure for High-Performance Room Temperature NH₃ Sensor

A novel hybrid structure sensor based on cobalt carbonate hydroxide hydrate (CCHH) and reduced graphene oxide (RGO) was designed for room temperature NH₃ detection. This hybrid structure consisted of CCHH and RGO (synthesized by a one-step hydrothermal method), in which RGO uniformly dispersed in CCHH, being used as the gas sensing film. The resistivity of the hybrid structure was highly sensitive to the changes on NH₃ concentration. CCHH in the hybrid structure was the sensing material and RGO was the conductive channel material. The hybrid structure could improve signal-to-noise ratio (SNR) and the sensitivity by obtaining the optimal mass proportion of RGO, since the proportion of RGO was directly related to sensitivity. The gas sensor with 0.4 wt% RGO showed the highest gas sensing response reach to 9% to 1 ppm NH₃. Compared to a conventional gas sensor, the proposed sensor not only showed high gas sensing response at room temperature but also was easy to achieve large-scale production due to the good stability and simple synthesis process.

PdO/SnO2 heterostructure for low-temperature detection of CO with fast response and recovery

In this paper, we developed a simple two-step route to prepare a PdO/SnO₂ heterostructure with the diameter of the SnO₂ and PdO nanoparticles at about 15 nm and 3 nm, respectively.

Pd-Functionalized SnO₂ Nanofibers Prepared by Shaddock Peels as Bio-Templates for High Gas Sensing Performance toward Butane

Pd-functionalized one-dimensional (1D) SnO₂ nanostructures were synthesized via a facile hydrothermal method and shaddock peels were used as bio-templates to induce a 1D-fiber-like morphology into the gas sensing materials. The gas-sensing performances of sensors based on different ratios of Pd-functionalized SnO₂ composites were measured. All results indicate that the sensor based on 5 mol % Pd-functionalized SnO₂ composites exhibited significantly enhanced gas-sensing performances toward butane. With regard to pure SnO₂, enhanced levels of gas response and selectivity were observed. With 5 mol % Pd-functionalized SnO₂ composites, detection limits as low as 10 ppm with responses of 1.38 ± 0.26 were attained. Additionally, the sensor exhibited rapid response/recovery times (3.20/6.28 s) at 3000 ppm butane, good repeatability and long-term stability, demonstrating their potential in practical applications. The excellent gas-sensing performances are attributed to the unique one-dimensional morphology and the large internal surface area of sensing materials afforded using bio-templates, which provide more active sites for the reaction between butane molecules and adsorbed oxygen ions. The catalysis and "spillover effect" of Pd nanoparticles also play an important role in the sensing of butane gas as further discussed in the paper.

Highly sensitive ammonia sensor for diagnostic purpose using reduced graphene oxide and conductive polymer

In this study, we fabricate ammonia sensors based on hybrid thin films of reduced graphene oxide (RGO) and conducting polymers using the Langmuir-Schaefer (LS) technique. The RGO is first prepared using hydrazine (Hy) and/or pyrrole (Py) as the reducing agents, and the resulting pyrrole-reduced RGO (Py-RGO) is then hybridized with polyaniline (PANI) and/or polypyrrole (PPy) by in-situ polymerization. The four different thin films of Hy-RGO, Py-RGO, Py-RGO/PANI, and Py-RGO/PPy are deposited on interdigitated microelectrodes by the LS techniques, and their structures are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results of ammonia sensing experiments indicate that the Py-RGO/PANI film exhibits the highest sensor response of these four films, and that it exhibits high reproducibility, high linearity of concentration dependency, and a very low detection limit (0.2 ppm) both in N₂ and exhaled air environments. The current gas sensor, therefore, has potential for diagnostic purposes because it has the additional advantages of facile fabrication, ease of use at room temperature, and portability compared to conventional high-sensitivity ammonia sensors.

Electrospun ZnO-SnO2 Composite Nanofibers and Enhanced Sensing Properties to SF6 Decomposition Byproduct H2S

Hydrogen sulfide (H₂S) is an important decomposition component of sulfur hexafluoride (SF₆), which has been extensively used in gas-insulated switchgear (GIS) power equipment as insulating and arc-quenching medium. In this work, electrospun ZnO-SnO₂ composite nanofibers as a promising sensing material for SF₆ decomposition component H₂S were proposed and prepared. The crystal structure and morphology of the electrospun ZnO-SnO₂ samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The composition of the sensitive materials was analyzed by energy dispersive X-ray spectrometers (EDS) and X-ray photoelectron spectroscopy (XPS). Side heated sensors were fabricated with the electrospun ZnO-SnO₂ nanofibers and the gas sensing behaviors to H₂S gas were systematically investigated. The proposed ZnO-SnO₂ composite nanofibers sensor showed lower optimal operating temperature, enhanced sensing response, quick response/recovery time and good long-term stability against H₂S. The measured optimal operating temperature of the ZnO-SnO₂ nanofibers sensor to 50 ppm H₂S gas was about 250°C with a response of 66.23, which was 6 times larger than pure SnO₂ nanofibers sensor. The detection limit of the fabricated ZnO-SnO₂ nanofibers sensor toward H₂S gas can be as low as 0.5 ppm. Finally, a plausible sensing mechanism for the proposed ZnO-SnO₂ composite nanofibers sensor to H₂S was also discussed.

A Reduced GO-Graphene Hybrid Gas Sensor for Ultra-Low Concentration Ammonia Detection

A hybrid structure gas sensor of reduced graphene oxide (RGO) decorated graphene (RGO-Gr) is designed for ultra-low concentration ammonia detection. The resistance value of the RGO-Gr hybrid is the indicator of the ammonia concentration and controlled by effective charge transport from RGO to graphene after ammonia molecule adsorption. In this hybrid material, RGO is the adsorbing layer to catch ammonia molecules and graphene is the conductive layer to effectively enhance charge/electron transport. Compared to a RGO gas sensor, the signal-to-noise ratio (SNR) of the RGO-Gr is increased from 22 to 1008. Meanwhile, the response of the RGO-Gr gas sensor is better than that of either a pristine graphene or RGO gas sensor. It is found that the RGO reduction time is related to the content of functional groups that directly reflect on the gas sensing properties of the sensor. The RGO-Gr gas sensor with 10 min reduction time has the best gas sensing properties in this type of sensor. The highest sensitivity is 2.88% towards 0.5 ppm, and the ammonia gas detection limit is calculated to be 36 ppb.

Density Gradient Strategy for Preparation of Broken In2O3 Microtubes with Remarkably Selective Detection of Triethylamine Vapor

Tubule-like structured metal oxides, combined with macroscale pores onto their surfaces, can fast facilitate gas-accessible diffusion into the sensing channels, thus leading a promoted utilization ratio of sensing layers. However, it generally remains a challenge for developing a reliable approach to prepare them. Herein, this contribution describes a density gradient strategy for obtaining broken In₂O₃ microtubes from the In₂O₃ products prepared using a chemical conversion method. These In₂O₃ microtubes hold a diameter about 1.5 μm with many broken regions and massive ultrafine nanopores onto their surfaces. When employed as a sensing element for detection of triethylamine (TEA) vapor, these broken In₂O₃ microtubes exhibited a significant response toward TEA at 1-100 ppm and the lowest detected concentration can reach 0.1 ppm. In addition, an excellent selectivity of the sensor to TEA was also displayed, though upon exposure of other interfering vapors, including ammonia, methanol, ethanol, isopropanol, acetone, toluene, and hydrogen. Such promoted sensing performances toward TEA were ascribed to the broken configuration (superior gas permeability and high utilization ratio), one-dimensional configuration with less agglomerations, and low bond energy for C-N in a TEA molecule.

Chitosan-templated Pt nanocatalyst loaded mesoporous SnO2 nanofibers: a superior chemiresistor toward acetone molecules

In this work, we introduce a chitosan-Pt complex (CS-Pt) as an effective template for catalytic Pt sensitization and creation of abundant mesopores in SnO2 nanofibers (NFs). The Pt particles encapsulated by the CS exhibit ultrasmall size (∼2.6 nm) and high dispersion characteristics due to repulsion between CS molecules. By combining CS-Pt with electrospinning, mesoporous SnO2 NFs uniformly functionalized with the Pt catalyst (CS-Pt@SnO2 NFs) are synthesized. Particularly, numerous mesopores with diameters of ∼20 nm form through the decomposition of CS, while a small SnO2 grain size (14.32 nm) is achieved by the pinning effect of CS. It is observed that CS-Pt@SnO2 NFs exhibit outstanding response (Rair/Rgas = 141.92 at 5 ppm), excellent selectivity, stability, and fast response (12 s)/recovery (44 s) speed toward 1 ppm of acetone at 350 °C and high humidity (90% RH). In addition, by applying an exponential fitting tool to experimental response values toward 0.1-5 ppm of acetone, it is estimated that CS-Pt@SnO2 NFs can detect 5 ppb of acetone with a notable response (Rair/Rgas = 2.9). Furthermore, the sensor array based on CS-Pt@SnO2 NFs, CS-driven SnO2 NFs, polyol-Pt loaded SnO2 NFs, and dense SnO2 NFs obviously classifies simulated diabetic breath and healthy human breath by using a pattern recognition tool. These results clearly demonstrate that mesoporous SnO2 NFs, particularly functionalized with CS-Pt templated nanocatalysts, open up a new class of sensing layers offering high sensitivity and selectivity.

A dual ammonia-responsive sponge sensor: preparation, transition mechanism and sensitivity

PDMS-PU (polydimethylsiloxane-polyurethane) sponge decorated with In(OH)3 (indium hydroxide) and BCP (bromocresol purple) particles is shown to be a room-temperature ammonia sensor with high sensitivity and excellent reproducibility; it can accomplish real-time detection and monitoring of ammonia in the surrounding environment. The superhydrophobic and yellowish In(OH)3-BCP-TiO2-based ammonia-responsive (IBT-AR) sponge changes to a purple superhydrophilic one when exposed to ammonia. Notably, after reacting with ammonia, the sponge can recover its original wettability and color after heating in air. The wettability, color and absorption signal of IBT-AR sponge have been measured for sensing ammonia using the water contact angle, macroscopic observation and UV-vis absorption spectrometry, respectively. The minimum ammonia concentrations that can be detected by the sponge wettability, color and absorption signal are 0.5%, 1.4 ppm and 50 ppb, respectively. This kind of sponge with smart wettability and color is a promising new ammonia detector.

Design of Hetero-Nanostructures on MoS2 Nanosheets To Boost NO2 Room-Temperature Sensing

Molybdenum disulfide (MoS₂), as a promising gas-sensing material, has gained intense interest because of its large surface-to-volume ratio, air stability, and various active sites for functionalization. However, MoS₂-based gas sensors still suffer from low sensitivity, slow response, and weak recovery at room temperature, especially for NO₂. Fabrication of heterostructures may be an effective way to modulate the intrinsic electronic properties of MoS₂ nanosheets (NSs), thereby achieving high sensitivity and excellent recovery properties. In this work, we design a novel p-n hetero-nanostructure on MoS₂ NSs using interface engineering via a simple wet chemical method. After surface modification with zinc oxide nanoparticles (ZnO NPs), the MoS₂/ZnO hetero-nanostructure is endowed with an excellent response (5 ppm nitrogen dioxide, 3050%), which is 11 times greater than that of pure MoS₂ NSs. To the best of our knowledge, such a response value is much higher than the response values reported for MoS₂ gas sensors. Moreover, the fabricated hetero-nanostructure also improves recoverability to more than 90%, which is rare for room-temperature gas sensors. Our optimal sensor also possesses the characteristics of an ultrafast response time of 40 s, a reliable long-term stability within 10 weeks, an excellent selectivity, and a low detection concentration of 50 ppb. The enhanced sensing performances of the MoS₂/ZnO hetero-nanostructure can be ascribed to unique 2D/0D hetero-nanostructures, synergistic effects, and p-n heterojunctions between ZnO NPs and MoS₂ NSs. Such achievements of MoS₂/ZnO hetero-nanostructure sensors imply that it is possible to use this novel nanostructure in ultrasensitive sensor applications.

An ammonia detecting mechanism for organic transistors as revealed by their recovery processes

Organic thin film transistor (OTFT) based gas sensors have demonstrated promising applications, owing to their advantages of high selectivity and room temperature operation, accompanied by their low cost, large scale manufacture, and flexibility. However, the understanding of the sensing mechanism is far from clear. Herein, we reveal the sensing mechanism of an organic transistor sensor for ammonia (NH3) detection through studying the recovery behavior in various atmospheres. Inspired by the significant difference in the recovery of the transistor sensor in N2 and in air, we deduced that the operation mechanism should not only involve the NH3-film interaction. Among a series of recovery processes, only upon exposure to wet air can the sensors completely recover in a certain time. Such a phenomenon, coupled with the transistor's performance evolution under vacuum, directly evidenced the existence of a pre-doping effect in the transistor by water (H2O) in ambient air. As a result, the response to the NH3 analyte is actually a de-doping process via reaction with the H2O. The full recovery in wet air is attributable to re-doping by H2O. Density functional theory (DFT) calculations were employed to assist the understanding of such a sensing mechanism. This study could help in the understanding of the sensing processes in many organic semiconductor based sensors.

Optochemical properties of gas-phase protonated tetraphenylporphyrin investigated using an optical waveguide NH3 sensor

5,10,15,20-Tetraphenylporphyrin (TPP) was synthesized, and a glass optical waveguide (OWG, which restricts and maintains the light energy in a specific, narrow space and propagates along the space axially) was coated with a gas-phase protonated TPP thin film to develop a sensor for NH3 gas detection. The results show that the TPP thin film agglomerated into H-based J-type aggregates after H2S gas exposure. The molecules in the protonated TPP film OWG sensor acted as NH3 receptors because the gas-phase protonated TPP film morphologically changed from J-type aggregates into free-base monomers when it was deprotonated by NH3 exposure. In this case, H2S gas could be used to increase the relative amount of J-type aggregates in the TPP film and restore the sensor response. The reversible surface morphology of the TPP film was analyzed by 1H NMR spectroscopy, atomic force microscopy, and UV-vis spectroscopy.

Ultra-sensitive NH3 sensor based on flower-shaped SnS2 nanostructures with sub-ppm detection ability

Layered metal dichalcogenides (LMDs) semiconducting materials have recently attracted tremendous attention as high performance gas sensors due to unique chemical and physical properties of thin layers. Here, three-dimensional SnS₂ nanoflower structures assembled with thin nanosheets were synthesized via a facile solvothermal process. When applied to detect 100ppm NH₃ at 200°C, the SnS₂ based sensor exhibited high response value of 7.4, short response/recovery time of 40.6s/624s. Moreover, the sensor demonstrated a low detection limit of 0.5ppm NH₃ and superb selectivity to NH₃ against CO₂, CH₄, H₂, ethanol and acetone. The excellent performance is attributed to the unique thin layers assembled flower-like nanoarchitecture, which facilitates both the carrier charge transfer process and the adsorption/desorption reaction. More importantly, it was found that the sensor response enhanced with increasing oxygen content in background and was improved by 3.57 times with oxygen content increasing from 0 to 40%. The increased response is owing to the enhanced binding energies between SnS₂ and NH₃ moleculers. Theoretically, density functional theory was employed to reveal the NH₃ adsorption mechanism in different background oxygen contents, which opens a new horizon for LMD based structures applied in various gas sensing fields.

Ultrafast NH3 Sensing Properties of WO3@CoWO4 Heterojunction Nanofibres at Room Temperature

Highly selective detection, quick response times (<5 s), and superior response (|Rn – Ra|/Ra = 1.17) to NH3 gas, particularly at room temperature (RT), are still enormous challenges in gas sensor applications. In this paper, a rational design and facile synthesis for a NH3 sensor have been proposed. Massage ball-like WO3@CoWO4 (Co-W) nanofibres (NFs) were prepared by a facile one-step synthesis utilising an electrospinning approach, followed by appropriate calcination. A Co-W NF sensor with a Co-to-W atomic ratio of 3 : 10 (Co-W-3), which consisted of nano-sized WO3 protrusions (10–15 nm) on submicrometre-sized single crystal CoWO4 particles (100–150 nm) exhibited excellent gas-sensing properties at RT due to the single crystal CoWO4–CoWO4 homojunction structure and distinct massage ball-like WO3–CoWO4 heterojunction. The approach developed in this work will be important for the low-cost and large-scale production of a Co-W-3 ultrafast sensing material with highly promising applications in gas sensors.

Biocarbon-templated synthesis of porous Ni–Co-O nanocomposites for room-temperature NH3 sensors

Mesoporous nickel–cobalt oxide (Ni–Co-O) nanocomposites were fabricated using a mesoporous biocarbon material (BCM), resulting from hemp stem, as a template.

Effect of Mixed Valence States of Platinum Ion Dopants on the Photocatalytic Activity of Titanium Dioxide under Visible Light Irradiation

Titanium dioxide doped with the Pt ion (Pt-TiO₂) was synthesized by a sol-gel method using only water as the solvent and conducting dialysis. The photocatalytic activity for the degradation of 4-chlorophenol (4-CP) on Pt-TiO₂ was not affected by the Brunauer-Emmett-Teller specific surface area under visible light (VL) irradiation. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near-edge structure measurements revealed that only the Pt(IV) ion existed in the TiO₂ bulk and both Pt(II) and Pt(IV) were present near the Pt-TiO₂ surface. Pt(IV) is most likely substituted in the Ti(IV) site of the TiO₂ lattice because of their similar ionic sizes. Quantitative analysis of Pt(II) was performed in the XPS measurements, indicating that the amount of Pt(II) on the surface increased with an increase in the doping amount from 0.2 to 1.0 atom %. We synthesized 0.5 atom % Pt-TiO₂ with various Pt(II)/Pt(IV) ratios by changing the Ti(OC₃H₇)₄ concentration used in the sol-gel synthesis. The 4-CP conversion on Pt-TiO₂ increased linearly with an increase in the Pt(II)/Pt(IV) ratios. A similar relationship was obtained with Pt-TiO₂, which was prepared by a conventional sol-gel method in ethanol-water mixed solvent. Therefore, the Pt(II)/Pt(IV) ratio is a key factor affecting the photocatalytic activity of Pt-TiO₂ under VL irradiation. Our results indicate that controlling the mixed valence states of the doped metal ions is a new strategy to developing highly active metal-ion-doped TiO₂ under VL irradiation.

Key role of surface oxidation and reduction processes in the coarsening of Pt nanoparticles

Particle coarsening is the main cause for thermal deactivation and lifetime reduction of supported Pt nanocatalysts. Here, Atomic Layer Deposition (ALD) was used to prepare a model system of Pt nanoparticles with high control over the metal loading and the nanoparticle size and coverage. A series of samples with distinct as-deposited size and interparticle spacing was annealed under different oxygen environments while Grazing Incidence Small Angle X-ray Scattering (GISAXS) was employed as in situ tool for monitoring the change in average nanoparticle size. The obtained results revealed three morphological stages during the thermal treatment, which can be explained by (I) the formation of a PtO₂ shell on stable Pt nanoparticles at low temperature (below 300 °C), (II) the reduction of the PtO₂ shell at moderate temperature (300 to 600 °C), creating mobile species that trigger particle coarsening until a steady morphological state is reached, and (III) the evaporation of PtO₂ at high temperature (above 650 °C), causing particle instability and coarsening reactivation. The onset temperatures for stages (II) and (III) were found to depend on the initial particle size and spacing as well as on the O₂ partial pressure during annealing, and could be summarized in a morphological stability diagram for Pt nanoparticles. The coarsening model indicates an important role for the reduction of the PtO₂ shell in inducing particle coarsening. The key role of the reduction process was corroborated through isothermal experiments under decreasing O₂ partial pressure and through forced reduction experiments near room temperature via H₂ exposure.

TiO2 nanoparticles functionalized by Pd nanoparticles for gas-sensing application with enhanced butane response performances

Pd functionalized TiO₂ nanoparticles were synthesized by a facile hydrothermal method. The structure, morphology, surface chemical states and surface area were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N₂ adsorption-desorption isotherms, respectively. The as-synthesized pure and Pd functionalized TiO₂ nanoparticles were used to fabricate indirect-heating gas sensor, and the gas-sensing characteristics towards butane were investigated. At the optimum temperature, the sensors possess good response, selectivity, response/recovery, repeatability as well as long-term stability. Especially for the high response, the response of 7.5 mol% Pd functionalized TiO₂ nanoparticles based sensor reaches 33.93 towards 3000 ppm butane, which is about 9 times higher than that of pure TiO₂ nanoparticles. The response and recovery time are 13 and 8 s, respectively. Those values demonstrate the potential of using as-synthesized Pd functionalized TiO₂ nanoparticles as butane gas detection, particularly in the dynamic monitoring. Apart from these, a possible mechanism related to the enhanced sensing performance is also investigated.

In situ chemoresistive sensing in the environmental TEM: probing functional devices and their nanoscale morphology

In situ transmission electron microscopy provides exciting opportunities to address fundamental questions and technological aspects related to functional nanomaterials, including the structure-property relationships of miniaturized electronic devices. Herein, we report the in situ chemoresistive sensing in the environmental transmission electron microscope (TEM) with a single SnO₂ nanowire device, studying the impact of surface functionalization with heterogeneous nanocatalysts. By detecting toxic carbon monoxide (CO) gas at ppm-level concentrations inside the microscope column, the sensing properties of a single SnO₂ nanowire were characterized before and after decoration with hybrid Fe-Pd nanocubes. The structural changes of the supported nanoparticles induced by sensor operation were revealed, enabling direct correlation with CO sensing properties. Our novel approach is applicable for a broad range of functional nanomaterials and paves the way for future studies on the relationship between chemoresistive properties and nanoscale morphology.

Nanostructured Polypyrrole-Based Ammonia and Volatile Organic Compound Sensors

The aim of this review is to summarize the recent progress in the fabrication of efficient nanostructured polymer-based sensors with special focus on polypyrrole. The correlation between physico-chemical parameters, mainly morphology of various polypyrrole nanostructures, and their sensitivity towards selected gas and volatile organic compounds (VOC) is provided. The different approaches of polypyrrole modification with other functional materials are also discussed. With respect to possible sensors application in medicine, namely in the diagnosis of diseases via the detection of volatile biomarkers from human breath, the sensor interaction with humidity is described as well. The major attention is paid to analytes such as ammonia and various alcohols.

Facile synthesis of nanoparticle packed In2O3 nanospheres for highly sensitive NO2 sensing

Nanoparticle packed In₂O₃ nanospheres are successfully synthesized via a facile one-step solvothermal method followed by annealing.

Superwettability Strategy: 1D Assembly of Binary Nanoparticles as Gas Sensors

Binary 1D nanowires consisting of both SnO₂ nanoparticles and Au nanorods are fabricated through a "substrate-particle solution template" assembling method, which shows highly enhanced gas sensitivity toward acetone under ambient conditions.

A tunable volatile organic compound sensor by using PtOx/GQDs/TiO2 nanocomposite thin films at room temperature under visible-light activation

Pt/GQDs/TiO₂ nanocomposite thin film-based gas sensors show tunable VOC sensing behaviour at room temperature under visible-light activation.

Wireless, Room Temperature Volatile Organic Compound Sensor Based on Polypyrrole Nanoparticle Immobilized Ultrahigh Frequency Radio Frequency Identification Tag

Due to rapid advances in technology which have contributed to the development of portable equipment, highly sensitive and selective sensor technology is in demand. In particular, many approaches to the modification of wireless sensor systems have been studied. Wireless systems have many advantages, including unobtrusive installation, high nodal densities, low cost, and potential commercial applications. In this study, we fabricated radio frequency identification (RFID)-based wireless sensor systems using carboxyl group functionalized polypyrrole (C-PPy) nanoparticles (NPs). The C-PPy NPs were synthesized via chemical oxidation copolymerization, and then their electrical and chemical properties were characterized by a variety of methods. The sensor system was composed of an RFID reader antenna and a sensor tag made from a commercially available ultrahigh frequency RFID tag coated with C-PPy NPs. The C-PPy NPs were covalently bonded to the tag to form a passive sensor. This type of sensor can be produced at a very low cost and exhibits ultrahigh sensitivity to ammonia, detecting concentrations as low as 0.1 ppm. These sensors operated wirelessly and maintained their sensing performance as they were deformed by bending and twisting. Due to their flexibility, these sensors may be used in wearable technologies for sensing gases.

Simultaneous determination of indoor ammonia pollution and its biological metabolite in the human body with a recyclable nanocrystalline lanthanide-functionalized MOF

A Eu(3+) post-functionalized metal-organic framework of nanosized Ga(OH)bpydc(Eu(3+)@Ga(OH)bpydc, 1a) with intense luminescence is synthesized and characterized. Luminescence measurements reveal that 1a can detect ammonia gas selectively and sensitively among various indoor air pollutants. 1a can simultaneously determine a biological ammonia metabolite (urinary urea) in the human body, which is a rare example of a luminescent sensor that can monitor pollutants in the environment and also detect their biological markers. Furthermore, 1a exhibits appealing features including high selectivity and sensitivity, fast response, simple and quick regeneration, and excellent recyclability.

Reversible P–N transition sensing behavior obtained by applying GQDs/Pt decorated SnO2 thin films at room temperature

A GQDs/Pt–SnO₂ thin film presents reversible sensing behavior with switching from p- to n-type acetone sensing performance at room temperature as a function of AC and GC.

Enhanced methanol sensing properties of SnO2 microspheres in a composite with Pt nanoparticles

SnO₂ microspheres in a composite with Pt nanoparticles (0, 0.5, 1.5, 2.5, 5.0 mol% Pt loading) were synthesized by a solvothermal method.

Enhanced CO gas sensing properties of Cu doped SnO2 nanostructures prepared by a facile wet chemical method

Cu doped SnO₂ nanosheets and nanodiscs exhibit highly enhanced CO gas sensing properties and excellent selectivity for CO gas.

Regulable switching from p- to n-type behavior of ordered nanoporous Pt-SnO2 thin films with enhanced room temperature toluene sensing performance

In this work, a nanoporous SnO₂ sensing film is fabricated in situ on a sensing device using a block polymer template and is applied as a chemiresistive gas sensor. The ordered film is capable of detecting 10 ppm toluene at room temperature and shows good stability.

Fabrication of anatase/rutile hierarchical nanospheres with enhanced n/p type gas sensing performance at room temperature

Porous Pt decorated anatase/rutile sensing nanospheres with high crystallinity and large surface area synthesized through psHT treatment present enhanced sensitivity and selectivity to VOCs vapor at room temperature.

Fe3O4/rGO nanocomposite: synthesis and enhanced NOxgas-sensing properties at room temperature

Fe₃O₄nanoparticles-decorated reduced graphene oxide nanocomposites have been successfully synthesized using solvothermal-pyrolytic method. They have superior gas sensing performance with low detection limit, high sensitivity and short response time.

The xylene sensing performance of WO3 decorated anatase TiO2 nanoparticles as a sensing material for a gas sensor at a low operating temperature

Here, the pristine and WO₃ decorated TiO₂ nanoparticles were synthesized by a one-step hydrothermal without the use of a surfactant or template, and used to fabricate gas sensors.

One-step synthesis of flower-shaped WO3 nanostructures for a high-sensitivity room-temperature NOx gas sensor

Flower-shaped WO₃ nanoparticles were successfully synthesized by using a facile hydrothermal method. These particles exhibited excellent room-temperature NO_x gas-sensing performance with high sensitivity, short response time and low detection limit.