Pd-loaded SnO2 hierarchical nanospheres for a high dynamic range H2S micro sensor

Large-Area Printed Oxide Film Sensors Enabling Ultrasensitive and Dual Electrical/Colorimetric Detection of Hydrogen at Room Temperature

Commercial hydrogen (H2) sensors operate at high temperatures, which increases power consumption and poses a safety risk owing to the flammable nature of H2. Here, a polymer-noble metal-metal oxide film is fabricated using the spin-coating and printing methods to realize a highly sensitive, low-voltage operation, wide-operating-concentration, and near-monoselective H2 sensor at room temperature. The H2 sensors with an optimized thickness of Pd nanoparticles and SnO2 showed an extremely high response of 16,623 with a response time of 6 s and a recovery time of 5 s at room temperature and 2% H2. At the same time, printed flexible sensors demonstrate excellent sensitivity, with a response of 2300 at 2% H2. The excellent sensing performance at room temperature is due to the optimal SnO2 thickness, corresponding to the Debye length and the oxygen and H2 spillover caused by the optimized coverage of the Pd catalyst. Furthermore, multistructures of WO3 and SnO2 films are used to fabricate a new type of dual-signal sensor, which demonstrated simultaneous conductance and transmittance, i.e., color change. This work provides an effective strategy to develop robust, flexible, transparent, and long-lasting H2 sensors through large-area printing processes based on polymer-metal-metal oxide nanostructures.

Engineering a Heterophase Interface by Tailoring the Pt Coverage Density on an Amorphous Ru Surface for Ultrasensitive H2S Detection

Amorphous/crystalline heterophase engineering is emerging as an attractive strategy to adjust the properties and functions of nanomaterials. Here, we reveal a heterophase interface role by precisely tailoring the crystalline Pt coverage density on an amorphous Ru surface (cPt/aRu) for ultrasensitive H2S detection. We found that when the atomic ratio of Pt/Ru increased from 10 to 50%, the loading modes of Pt changed from island coverage (1cPt/aRu) to cross-linkable coverage (3cPt/aRu) and further to dense coverage (5cPt/aRu). The differences in coverage models further regulate the chemical adsorption of H2S on Pt and the electronic transformation process on Ru, which can be proved by ex situ X-ray photoelectron spectroscopy experiments. Notably, a special cross-linkable coverage 3cPt/aRu on ZnO shows the best gas-sensitive performance, in which the operating temperature reduces from 240 to 160 °C compared with pristine ZnO and the selectivity coefficient for H2S gas improves from ∼1.2 to ∼4.6. This is mainly benefit from the maximized exposure of the amorphous/crystalline heterophase interface. Our work thus provides a new platform for future applications of amorphous/crystalline heterogeneous nanostructures in gas sensors and catalysis.

Top-Down Approaches for 10 nm-Scale Nanochannel: Toward Exceptional H2S Detection

Metal oxide semiconductors (MOS) have proven to be most powerful sensing materials to detect hydrogen sulfide (H₂S), achieving part per billion (ppb) level sensitivity and selectivity. However, there has not been a way of extending this approach to the top-down H₂S sensor fabrication process, completely limiting their commercial-level productions. In this study, we developed a top-down lithographic process of a 10 nm-scale SnO₂ nanochannel for H₂S sensor production. Due to high-resolution (15 nm thickness) and high aspect ratio (>20) structures, the nanochannel exhibited highly sensitive H₂S detection performances (R_a/R_g = 116.62, τ_res = 31 s at 0.5 ppm) with selectivity (R_H2S/R_acetone = 23 against 5 ppm acetone). In addition, we demonstrated that the nanochannel could be efficiently sensitized with the p-n heterojunction without any postmodification or an additional process during one-step lithography. As an example, we demonstrated that the H₂S sensor performance can be drastically enhanced with the NiO nanoheterojunction (R_a/R_g = 166.2, τ_res = 21 s at 0.5 ppm), showing the highest range of sensitivity demonstrated to date for state-of-the-art H₂S sensors. These results in total constitute a high-throughput fabrication platform to commercialize the H₂S sensor that can accelerate the development time and interface in real-life situations.

Morphology genetic 3D hierarchical SnO2microstructures constructed by Sub 5 nm nanocrystals for highly sensitive ethanol-sensor

SnO₂is widely used for ethanol-sensing applications due to its excellent physicochemical properties, low toxicity and high sensitivity. However it is a challenge to construct 3D-hierarchical structures with sub 5 nm primary grain particle, which is the optimized size for ethanol sensor. Herein, genetic tri-level hierarchical SnO₂microstructures are synthesised by the genetic conversion of 3D hierarchical SnS₂flowers assembled by ultrathin nanosheets. The SnS₂nanosheets are morphology genetic converted to porous nanosheets with sub 5 nm SnO₂nanoparticles during the calcination process. When used for the detection of ethanol, the sensor exhibits a high sensitivity of 0.5 ppm (R_a/R_g = 6.8) and excellent gas-sensing response (R_a/R_g= 183 to 100 ppm) with short response/recovery time (12 s/11 s). The excellent gas sensing performance is much better than that of the previous reported SnO₂-based sensors. The highly sensitivity is attributed to the large surface area derived from the recrystallization and volume changes, which offers more active sites during the morphology genetic conversion from SnS₂to SnO₂. Furthermore, the flower-like 3D structure enhances the stability of the materials and is beneficial for the mass diffusion dynamics of ethanol.

Controlled preparation of multiple mesoporous CoAl-LDHs nanosheets for the high performance of NO x detection at room temperature

By fine tuning the metal mole ratio, CoAl-LDHs (CA) with a 2D nanosheet structure were successfully prepared via a one-step hydrothermal method using urea as both precipitator and pore-forming agent. The morphology of CA samples shows uniform and thin porous hexagonal nanosheets. In particular, CA2-1, prepared with the 2 : 1 molar ratio for Co and Al, respectively, has the highest surface area (54 m2 g-1); its average transverse size of platelets is 2.54 μm with a thickness of around 19.30 nm and inter-plate spacing of about 0.2 μm. The sample exhibits a high sensing performance (response value of 17.09) towards 100 ppm NO x , fast response time (4.27 s) and a low limit of detection (down to 0.01 ppm) at room temperature. Furthermore, CA2-1 shows long -term stability (60 days) and a better selectivity towards NO x at room temperature. The excellent performance of the fabricated sensor is attributed to the special hexagonal structure of the 2D thin nanosheets with abundant mesopores, where the active sites provide fast adsorption and transportation channels, promote oxygen chemisorption, and eventually decrease the diffusion energy barrier for NO x molecules. Furthermore, hydrogen bonds between water molecules and OH- could serve as a bridge, thus providing a channel for rapid electron transfer. This easy synthetic approach and good gas sensing performance allow CoAl-LDHs to be great potential materials in the field of NO x gas sensing.

Temperature-controlled resistive sensing of gaseous H2S or NO2 by using flower-like palladium-doped SnO2 nanomaterials

Palladium-doped SnO₂ nanomaterials, with palladium in fractions from 0 to 10 mol% were hydrothermally synthesized and characterized by XRD, FESEM, TEM, and XPS. Their gas sensing properties were studied in two temperature ranges of 75-95 °C and 160-210 °C. The sensor using 5 mol% Pd-doped SnO₂ exhibits temperature-dependent sensing property. NO₂ can be detected at 80 °C, while H₂S is preferably detected at 180 °C. The response to 10 ppm H₂S is 50 times higher than that of the undoped sample. Its detection limit is 500 ppb. For NO₂, the sensor exhibited strong response and a lower detection limit of 20 ppb. In view of the selective detection of H₂S and NO₂ by regulating the temperature, palladium-doped SnO₂ has great prospects in the detection of H₂S and NO₂. Graphical abstract Schematic of the gas sensing mechanism of the S-5% Pd doped SnO_2.

Effect of AuPd Bimetal Sensitization on Gas Sensing Performance of Nanocrystalline SnO2 Obtained by Single Step Flame Spray Pyrolysis

Improvement of sensitivity, lower detection limits, stability and reproducibility of semiconductor metal oxide gas sensor characteristics are required for their application in the fields of ecological monitoring, industrial safety, public security, express medical diagnostics, etc. Facile and scalable single step flame spray pyrolysis (FSP) synthesis of bimetal AuPd sensitized nanocrystalline SnO2 is reported. The materials chemical composition, structure and morphology has been studied by XRD, XPS, HAADFSTEM, BET, ICP-MS techniques. Thermo-programmed reduction with hydrogen (TPR-H2) has been used for materials chemical reactivity characterization. Superior gas sensor response of bimetallic modified SnO2 towards wide concentration range of reducing (CO, CH4, C3H8, H2S, NH3) and oxidizing (NO2) gases compared to pure and monometallic modified SnO2 is reported for dry and humid gas detection conditions. The combination of facilitated oxygen molecule spillover on gold particles and electronic effect of Fermi level control by reoxidizing Pd-PdO clusters on SnO2 surface is proposed to give rise to the observed enhanced gas sensor performance.