Bimetallic Au and Pd Nanoparticles Modified WO3 Nanosheets for Enhancing the Sensitivity and Selectivity of Formaldehyde Assessment in Aquatic Products.

Formaldehyde, a common illegal additive in aquatic products, poses a threat to people's health and lives. In this study, a novel metal oxide semiconductor gas sensor based on AuPd-modified WO3 nanosheets (NSs) had been developed for the highly efficient detection of formaldehyde. WO3 NS modified with 2.0% AuPd nanoparticles showed a higher response (Ra/Rg = 94.2) to 50 ppm of formaldehyde at 210 °C, which was 36 times more than the pristine WO3 NS. In addition, the AuPd/WO3 gas sensor had a relatively short response/recovery time of 10 s/9 s for 50 ppm of formaldehyde at 210 °C, with good immunity to other interfering gases and good stability for formaldehyde. The excellent gas-sensitive performance was attributed to the chemical sensitization of Au, the electronic sensitization of Pd, and the synergistic effect of bimetallic AuPd, which facilitated the recognition and response of formaldehyde molecules. Additionally, the high sensitivity and broad application prospect of the 2.0% AuPd/WO3 NS composite-based sensor in real sample detection were also confirmed by using the above sensor for the detection of formaldehyde in aquatic products such as squid and shrimp.

Kinetics-Driven Dual Hydrogen Spillover Effects for Ultrasensitive Hydrogen Sensing.

Palladium (Pd)-modified metal oxide semiconductors (MOSs) gas sensors often exhibit unexpected hydrogen (H2 ) sensing activity through a spillover effect. However, sluggish kinetics over a limited Pd-MOS surface seriously restrict the sensing process. Here, a hollow Pd-NiO/SnO2 buffered nanocavity is engineered to kinetically drive the H2 spillover over dual yolk-shell surface for the ultrasensitive H2 sensing. This unique nanocavity is found and can induce more H2 absorption and markedly improve kinetical H2 ab/desorption rates. Meanwhile, the limited buffer-room allows the H2 molecules to adequately spillover in the inside-layer surface and thus realize dual H2 spillover effect. Ex situ XPS, in situ Raman, and density functional theory (DFT) analysis further confirm that the Pd species can effectively combine H2 to form Pd-H bonds and then dissociate the hydrogen species to NiO/SnO2 surface. The final Pd-NiO/SnO2 sensors exhibit an ultrasensitive response (0.1-1000 ppm H2 ) and low actual detection limit (100 ppb) at the operating temperature of 230 °C, which surpass that of most reported H2 sensors.

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.

Pt-functionalized Amorphous RuOx as Excellent Stability and High-activity Catalysts for Low Temperature MEMS Sensors.

The unsaturated coordination and abundant active sites endow amorphous metals with tremendous potential in improving metal oxide semiconductors' gas-sensing properties. However, the amorphous materials maintain the metastable status and easily transfer into the lower-active crystals during the gas-sensing process at high working temperatures, significantly limiting their further applications. Here, a bimetal amorphous PtRu catalyst is developed by accurately regulating the introduction of Pt species into amorphous RuOx supports to realize the highly active and stable H2 S gas-sensing detection. It is found that incorporation of low-concentration Pt species can effectively maintain the amorphous state of initial RuOx and delay the crystallization temperature as high as 100 °C. Further, ex situ XPS and in situ Raman spectroscopy analysis confirm that active Pt species can facilitate H2 S adsorption by strong Pt-S coordination and dissociate the sulfur species to the surrounding support, which contribute to the chemisorption and sensitization of H2 S. Meanwhile, electron transport at the interface between Pt, RuOx and ZnO further activates the reaction process at the surface of the gas-sensitive material. The final PtRu-modified ZnO (PtRu/ZnO) sensor enables the detection of H2 S in the ultra-low concentration range of 15-2000 ppb with remarkable stability.

Multishell SnO2 Hollow Microspheres Loaded with Bimetal PdPt Nanoparticles for Ultrasensitive and Rapid Formaldehyde MEMS Sensors.

Low-cost and real-time formaldehyde (HCHO) monitoring is of great importance due to its volatility, extreme toxicity, and ready accessibility. In this work, a low-cost and integrated microelectromechanical system (MEMS) HCHO sensor is developed based on SnO2 multishell hollow microspheres loaded with a bimetallic PdPt (PdPt/SnO2-M) sensitizer. The MEMS sensor exhibits a high sensitivity to HCHO ((Ra/Rg - 1) % = 83.7 @ 1 ppm), ultralow detection limit of 50 ppb, and ultrashort response/recovery time (5.0/7.0 s @ 1 ppm). These excellent HCHO sensing properties are attributed to its unique multishell hollow structure with a large and accessible surface, abundant interfaces, suitable mesoporous structure, and synergistic catalytic effects of bimetal PdPt. The well-defined multishell hollow structure also shows fascinating capacities as good hosts for noble metal loading. Therefore, PdPt bimetallic nanoparticles can be employed to construct a synergistic sensitizer with a high content and good dispersity on this multishell hollow structure, further exhibiting a reduced working temperature and ultrasensitive detection of HCHO. This PdPt/SnO2-M-based MEMS sensor presents a unique and highly sensitive means to detect HCHO, establishing its great promise for potential application in environmental monitoring.

Bimetallic PtCu Nanocrystal Sensitization WO3 Hollow Spheres for Highly Efficient 3-Hydroxy-2-butanone Biomarker Detection.

As a foodborne bacterium, Listeria monocytogenes (LM) can cause serious diseases and even death to weak people. 3-Hydroxy-2-butanone (3H-2B) has been proven to be a biomarker for exhalation of LM. Detection of 3H-2B is a fast and effective method for determining whether the food is infected. Herein, we present an excellent 3H-2B gas sensor based on bimetallic PtCu nanocrystal modified WO3 hollow spheres. The structure and morphology of the PtCu/WO3 were characterized, and their gas sensitivities were measured by a static testing method. The results showed that the sensor response of WO3 hollow spheres was enhanced by about 15 times after modification with bimetallic PtCu nanocrystal. The maximum response value of the PtCu/WO3 sensor to 10 ppm 3H-2B is as high as 221.2 at 110 °C. In addition, the PtCu/WO3 sensor also exhibited good selectivity to 3H-2B, fast response/recovery time (9 s/28 s), and low limit of detection (LOD < 0.5 ppm). Furthermore, the sensitivity mechanism was studied by monitoring the reaction products by gas chromatography-mass spectrometry. The excellent gas-sensing performance can be attributed to the synergy between PtCu and WO3, including the unique spillover effect of O2 on PtCu nanoparticles, the regulated depletion layer by p-type CuxO to n-type WO3, and their selective catalysis to 3H-2B. Hence, this work offers the rational design and synthesis of highly efficient sensitive materials for the detection of LM for food security.

Tetracycline degradation by Klebsiella sp. strain TR5: Proposed degradation pathway and possible genes involved.

Microorganisms with high tetracycline (TC) degradation efficiencies are required for biological processes for TC-containing wastewater treatment. With multiple enrichment cultures, a TC-degrading strain TR5 was isolated from chicken manure mixture in a large broiler farm, which was identified as Klebsiella pneumoniae by 16S rRNA gene sequencing and biochemical properties. Strain TR5 could degrade TC quickly (∼90% within 36 h) with the initial TC concentration of 200 mg/L under optimized conditions via single-factor experiment coupled with RSM. Strain TR5 could detoxify TC and generate much less toxic products as long as cultured more than one day. Three TC-degrading pathways were proposed based on 8 possible products. A transformant containing a plasmid from TR5 acquired TC-degrading ability, indicating that TC-degrading genes were located on this plasmid. Complete sequencing of pYK5 showed that isomerase-, oxidoreductase-, and transferases-encoding genes were found and were inferred to be involved in TC degradation. TR5 may not degrade TC completely and it can utilize some carbon-containing compounds derived from TC via the effect of formylglutathione hydrolase-encoding gene. Our findings showed that strain TR5 could be a promising agent for wastewater treatment, and genes involved in TC degradation are worthy of further investigations for enzyme preparations development.

Controlled Synthesis of Pt Doped SnO2 Mesoporous Hollow Nanospheres for Highly Selective and Rapidly Detection of 3-Hydroxy-2-Butanone Biomarker.

Listeria monocytogenes (L. monocytogenes) has been recognized as one of the extremely hazardous and potentially life-threatening food-borne pathogens, its real-time monitoring is of great importance to human health. Herein, a simple and effective method based on platinum sensitized tin dioxide semiconductor gas sensors has been proposed for selective and rapid detection of L. monocytogenes. Pt doped SnO2 nanospheres with particular mesoporous hollow structure have been synthesized successfully through a robust and template-free approach and used for the detection of 3-hydroxy-2-butanone biomarker of L. monocytogenes. The steady crystal structure, unique micromorphology, good monodispersit, and large specific surface area of the obtained materials have been confirmed by X-ray diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), Brunauer-Emmett-Teller (BET), and Photoluminescence spectra (PL). Pt doped SnO2 mesoporous hollow nanosphere sensors reach the maximum response of 3-hydroxy-2-butanone at 250°C. Remarkably, sensors based on SnO2 mesoporous hollow nanospheres with 0.16 wt% Pt dopant exhibit excellent sensitivity (Rair/Rgas = 48.69) and short response/recovery time (11/20 s, respectively) to 10 ppm 3-hydroxy-2-butanone at the optimum working temperature. Moreover, 0.16 wt% Pt doped SnO2 gas sensors also present particularly low limit of detection (LOD = 0.5 ppm), superb long-term stability and prominent selectivity to 3-hydroxy-2-butanone. Such a gas sensor with high sensing performance foresees its tremendous application prospects for accurate and efficient detection of foodborne pathogens for the food security and public health.