Ultrafine Pt NPs-Decorated SnO2/α-Fe2O3 Hollow Nanospheres with Highly Enhanced Sensing Performances for Styrene

Preparation of Pt/WO3@ZnO hollow spheres for low-temperature and high-efficiency detection of triethylamine

In this work, hollow spherical Pt-loaded WO3/ZnO heterostructured composites were prepared by a chemical liquid phase synthesis method. The morphology, crystal structure and components of the composites were characterized by SEM, TEM, XRD, XPS, etc. The sensing performance for various gases was also tested. Compared with the pristine WO3 (S = 44@225 °C, 50 ppm) gas sensor, the gas sensor that is functionalized with 1 wt% Pt and 0.5 mmol ZnO (1Pt/WZ-2) has a high response of 842-50 ppm at a relatively low temperature of 100 °C for TEA, with a quick response/recovery time of 34/120 s, a lower detection limit of 50 ppb, and good selectivity and moisture resistance. This study provides a highly efficient synthesis method of composite materials for TEA gas detection and the sensitivity mechanism is also discussed in detail.

Layered double hydroxide nanosheets-built porous film-covered Au nanoarrays as enrichment and enhancement chips for efficient SERS detection of trace styrene

Styrene, a prevalent volatile organic compounds (VOCs), is very harmful to atmosphere and humans. Consequently, the development of efficient detection technologies for styrene is of high importance, which is still in challenge! In this work, we crafted a layered double hydroxide (LDH) porous film-coated gold nanoarray, designed to act as a surface enhanced Raman spectroscopy (SERS) chip for the efficient and portable detection of gaseous styrene. This chip features a covering layer composed of cross-linked LDH nanosheets, notable for their porous structure and high specific surface area. When the covering layer is 100-300 nm in thickness, this composite chip has significant enrichment effect and strong SERS performance to gaseous styrene with a lowest detectable concentration below 1 ppb (4.64 ×10-3 mg/m3), and can response within 10 s, showing the rapid response and high sensitivity. Additionally, the chip has strong anti-interference capabilities and maintains excellent response to styrene, even in mixed benzene-VOCs gases. The exceptional SERS performances of this chip is ascribed to its LDH covering layer-induced styrene-enrichment and structurally-enhanced SERS performances. This study provides a simple route and practical chip for the rapid and ultrasensitive SERS-based detection of gaseous styrene, which is also potentially beneficial for the detection of other gaseous VOCs.

Efficient Eu3+-Integrated UiO-66 Probe for Ratiometric Fluorescence Sensing of Styrene and Cyclohexanone

The development of probes with sensitive and prompt detection of volatile organic compounds (VOCs) is of great importance for protecting human health and public security. Herein, we successfully prepared a series of bimetallic lanthanide metal-organic framework (Eu/Zr-UiO-66) by incorporating Eu³⁺ for fluorescence sensing of VOCs (especially styrene and cyclohexanone) using a one-pot method. Based on the multiple fluorescence signal responses of Eu/Zr-UiO-66 toward styrene and cyclohexanone, a ratiometric fluorescence probe using (I₆₁₇/I₃₂₀) and (I₆₁₇/I₃₃₀) as output signals was developed to recognize styrene and cyclohexanone, respectively. Benefitting from the multiple fluorescence response, the limits of detection (LODs) of Eu/Zr-UiO-66 (1:9) for styrene and cyclohexanone were 1.5 and 2.5 ppm, respectively. These are among the lowest reported levels for MOF-based sensors, and this is the first known material for fluorescence sensing of cyclohexanone. Fluorescence quenching by styrene was mainly owing to the large electronegativity of styrene and fluorescence resonance energy transfer (FRET). However, FRET was accounted for fluorescence quenching by cyclohexanone. Moreover, Eu/Zr-UiO-66 (1:9) exhibited good anti-interference ability and recycling performance for styrene and cyclohexanone. More importantly, the visual recognition of styrene and EB vapor can be directly realized with the naked eyes using Eu/Zr-UiO-66 (1:9) test strips. This strategy provides a sensitive, selective, and reliable method for the visual sensing of styrene and cyclohexanone.

Advances in Noble Metal-Decorated Metal Oxide Nanomaterials for Chemiresistive Gas Sensors: Overview

Highly sensitive gas sensors with remarkably low detection limits are attractive for diverse practical application fields including real-time environmental monitoring, exhaled breath diagnosis, and food freshness analysis. Among various chemiresistive sensing materials, noble metal-decorated semiconducting metal oxides (SMOs) have currently aroused extensive attention by virtue of the unique electronic and catalytic properties of noble metals. This review highlights the research progress on the designs and applications of different noble metal-decorated SMOs with diverse nanostructures (e.g., nanoparticles, nanowires, nanorods, nanosheets, nanoflowers, and microspheres) for high-performance gas sensors with higher response, faster response/recovery speed, lower operating temperature, and ultra-low detection limits. The key topics include Pt, Pd, Au, other noble metals (e.g., Ag, Ru, and Rh.), and bimetals-decorated SMOs containing ZnO, SnO2, WO3, other SMOs (e.g., In2O3, Fe2O3, and CuO), and heterostructured SMOs. In addition to conventional devices, the innovative applications like photo-assisted room temperature gas sensors and mechanically flexible smart wearable devices are also discussed. Moreover, the relevant mechanisms for the sensing performance improvement caused by noble metal decoration, including the electronic sensitization effect and the chemical sensitization effect, have also been summarized in detail. Finally, major challenges and future perspectives towards noble metal-decorated SMOs-based chemiresistive gas sensors are proposed.

Review on recent progress in on-line monitoring technology for atmospheric pollution source emissions in China

Emissions from mobile sources and stationary sources contribute to atmospheric pollution in China, and its components, which include ultrafine particles (UFPs), volatile organic compounds (VOCs), and other reactive gases, such as NH₃ and NO_x, are the most harmful to human health. China has released various regulations and standards to address pollution from mobile and stationary sources. Thus, it is urgent to develop online monitoring technology for atmospheric pollution source emissions. This study provides an overview of the main progress in mobile and stationary source monitoring technology in China and describes the comprehensive application of some typical instruments in vital areas in recent years. These instruments have been applied to monitor emissions from motor vehicles, ships, airports, the chemical industry, and electric power generation. Not only has the level of atmospheric environment monitoring technology and equipment been improving, but relevant regulations and standards have also been constantly updated. Meanwhile, the developed instruments can provide scientific assistance for the successful implementation of regulations. According to the potential problem areas in atmospheric pollution in China, some research hotspots and future trends of atmospheric online monitoring technology are summarized. Furthermore, more advanced atmospheric online monitoring technology will contribute to a comprehensive understanding of atmospheric pollution and improve environmental monitoring capacity.

The Dehydrogenation of H-S Bond into Sulfur Species on Supported Pd Single Atoms Allows Highly Selective and Sensitive Hydrogen Sulfide Detection

The supported metal catalysts on scaffolds usually reveal multiple active sites, resulting in the occurrence of side reaction and being detrimental to the achievement of highly consistent catalysis. Single atom catalysts (SACs), possessed with highly consistent single active sites, have great potentials for overcoming such issues. Herein, the authors used SACs to modulate kinetic process of gas sensitive reaction. The supported Pd SACs, established by a metal organic frameworks-templated approach, promoted greatly the detection capacity to hydrogen sulfide (H₂ S) gas with a very high sensitivity and selectivity. Density functional theory calculations show that the supported Pd SACs not only increased the number of electrons transferring from H₂ S molecules to Pd SACs, but strengthened surface affinity to H₂ S. Moreover, the HS bonds of H₂ S molecules absorbed on Pd atomic sites are more likely to be dehydrogenated directly into sulfur species. Significantly, quasi in situ XPS analysis confirmed the presence of sulfur species during H₂ S detection process, which may be a major cause for such detection signal. Based on these results, a suitable sensing principle for H₂ S gas driven by Pd SACs was put forward. This work will enrich catalytic electronics in chemiresistive gas sensing.

The growth behavior of brain-like SnO2 microspheres under a solvothermal reaction with tetrahydrofuran as a solvent and their gas sensitivity

In this paper, the growth behavior of brain-like SnO2 microspheres synthesized by a tetrahydrofuran (THF) solvothermal method was studied. Unlike water or ethanol as the solvent, THF is a medium polar and aprotic solvent. Compared with other common polar solvents, the THF has no strong irregular effects on the growth process of SnO2. In addition, the viscosity of THF also helps the SnO2 to form a regular microstructure. The growth behavior of the brain-like SnO2 microspheres is controlled by changing the synthesis temperature of the reaction. The SEM and TEM results reveal that the SnO2 forms particles first (125 °C/3 h), and then these nanoparticles connect to each other forming nanowires and microspheres (diameter ≈ 1-2 μm) at 135 °C for 3 h; finally the microspheres further aggregate to form double or multi-sphere structures at 180 °C for 3 h. In this paper, the brain-like SnO2 microspheres obtained at 125 °C for 3 h were selected as sensitive materials to test their gas sensing performance at different operating temperature (50 °C and 350 °C). The H2S was tested at 50 °C which is the lowest operating temperature for the sensor. The combustible gas (H2/CH4/CO) was measured at 350 °C which is the highest temperature for the sensor. They all have extremely high sensitivity, but only H2S has excellent selectivity.

Versatile photoelectrochemical and electrochemiluminescence biosensor based on 3D CdSe QDs-DNA nanonetwork-SnO2 nanoflower coupled with DNA walker amplification for HIV detection

A novel 3D CdSe quantum dots (QDs)-DNA nanonetwork was assembled to sensitize the mesoporous SnO₂ photoelectrochemical (PEC) substrate, which was coupled with a biped-DNA walker multiple amplification technique to design a versatile electrochemiluminescence (ECL) and PEC biosensor for dual detection of HIV. Firstly, the photosensitive CdSe QDs and SnO₂ nanoflowers have well-matched band-edge energy level, thus their complex can promote effective transfer of the photogenerated carriers, and show better PEC and ECL property. Then, a novel 3D CdSe QDs-DNA nanonetwork was assembled and loaded with a large amount of QDs, which was used as multifunctional PEC and ECL probes. Moreover, the target-triggered biped DNA walker-cascade amplification method was introduced to generate a large amount of output DNA, which was used to link numerous 3D CdSe QDs-DNA nanonetwork probes to the electrode, generating greatly amplified signals for sensitive assay of HIV. The highly photosensitive 3D CdSe QDs-DNA reticulated nanomaterials have high stability and controllability, and display significantly improved PEC and ECL signals of the biosensor. This method opened a new photoelectric nanocomposite of QDs-sensitized SnO₂ nanoflower, and developed a versatile biosensing strategy using the 3D CdSe QD_S DNA sensitization probes for ultra-sensitive detection of biomolecules, which is important for the early diagnosis of diseases.

0D/2D CdS/ZnO composite with n-n heterojunction for efficient detection of triethylamine

It is imperative to seek for novel materials with pronounced gas sensing performance towards triethylamine for the sake of human health. Herein, we successfully fabricate an outstanding triethylamine sensor based on CdS/ZnO composite with 0D/2D structure, which are prepared by in-situ growth of CdS quantum dots on ultra-thin ZnO nanosheets. The ratios between the two ingredients are adjusted and their effect is evaluated. The optimal sample exhibits the lowest operating temperature of 200 °C, the highest response value of ~20 and the fastest response time of 2 s. Besides, it also has the virtues of durable stability, excellent selectivity and superior anti-interference ability. The mechanism behind the aforementioned intriguing performance is investigated by X-ray photoelectron spectroscopy, Kelvin probe and density function theory (DFT) simulation. All the results verify that the enhanced gas sensing properties are derived from splendid 0D/2D structure, n-n heterojunction and large specific surface area. Additionally, this study opens an avenue for designing sensors with 0D/2D structure.

A ratiometric fluorescent probe for the quantitative detection of styrene in air

A ratiometric fluorescent probe (N-butyl-4-(4-amino-styryl)-1,8-naphthalimide) was developed for the quantitative detection of styrene in air. The sensing mechanism was found to involve a Heck reaction between the pretreated probe (diazotization) and styrene. A probe solution absorption method was established to detect gaseous styrene quantitatively.

Edge-exposed MoS2 nanospheres assembled with SnS2 nanosheet to boost NO2 gas sensing at room temperature

SnS₂ nanosheets (NSs) have become an ideal candidate for high performance gas sensors due to their unique sensing properties. However, the restacking and aggregation in the process of sensor manufacturing have great influence on the gas sensing performance. In this study, we synthesized a novel heterojunction of the flower-like porous SnS₂ NSs with edge exposed MoS₂ nanospheres via a facile hydrothermal method and sensitive response has achieved at room temperature (27℃). After functionalization, the SMS-Ⅱ showed excellent response (Ra/Rg = 25.9-100 ppm NO₂), which is 22.3 times higher than that of the pristine SnS₂ NSs. The sensor also has the characteristics of short response time of 2 s, excellent base line recovery (28.2 s), long-term stability and reliability within 16 weeks, good selectivity and low detection concentration of only 50 ppb. The p-n heterojunction formed between the edge-exposed spherical MoS₂ and the 3D flower-like SnS₂ NSs has a synergistic effect, providing a highly active sites for the adsorption of NO₂ gas, which greatly enhance the sensitivity of the sensor. Simple fabrication and excellent gas sensing performance of the SnS₂/MoS₂ heterostructure nanomaterials (NMs) will highly effective for commercial gas sensing application.

Ultrasensitive xylene gas sensor based on flower-like SnO2/Co3O4 nanorods composites prepared by facile two-step synthesis method

Xylene is a volatile organic compound which is harmful to the human health and requires precise detection. The detection of xylene by an oxide semiconductor gas sensor is an important research direction. In this work, Co₃O₄ decorated flower-like SnO₂ nanorods (SnO₂/Co₃O₄ NRs) were synthesized by a simple and effective two-step method. The SnO₂/Co₃O₄ NRs show high xylene response (R _g/R _a = 47.8 for 100 ppm) and selectivity at the operating temperature of 280 °C, and exhibit high stability in continuous testing. The resulting SnO₂/Co₃O₄ NRs nanocomposites show superior sensing performance towards xylene in comparison with pure SnO₂ nanorods. The remarkable enhancement in the gas-sensing properties of SnO₂/Co₃O₄ NRs are attributed to larger specific surface area and the formation of p-n heterojunction between Co₃O₄ and SnO₂. These results demonstrate that particular nanostructures and synergistic effect of SnO₂ and Co₃O₄ enable gas sensors to selectively detect xylene.

Gas Sensors Based on Chemi-Resistive Hybrid Functional Nanomaterials

Chemi-resistive sensors based on hybrid functional materials are promising candidates for gas sensing with high responsivity, good selectivity, fast response/recovery, great stability/repeatability, room-working temperature, low cost, and easy-to-fabricate, for versatile applications. This progress report reviews the advantages and advances of these sensing structures compared with the single constituent, according to five main sensing forms: manipulating/constructing heterojunctions, catalytic reaction, charge transfer, charge carrier transport, molecular binding/sieving, and their combinations. Promises and challenges of the advances of each form are presented and discussed. Critical thinking and ideas regarding the orientation of the development of hybrid material-based gas sensor in the future are discussed.

A photoelectrochemical immunosensor based on CdS/CdTe-cosensitized SnO2 as a platform for the ultrasensitive detection of amyloid β-protein

An ultrasensitive label-free photoelectrochemical immunosensor was developed to detect amyloid β-protein based on CdS/CdTe-cosensitized SnO₂ nanoflowers.

Rational shape control of porous Co3O4 assemblies derived from MOF and their structural effects on n-butanol sensing

Porous metal oxides are promising materials for VOCs (volatile organic compounds) chemical sensors, because they have large specific surface areas and enough internal space for the fast gas diffusion. Recently, metal-organic framework (MOF) materials with varied shapes and sizes have been regarded as good templates for preparing porous metal oxides. Herein, four kinds of Co-MOFs were prepared by altering the ratios of Co²⁺ ions and 2-methylimidazole at room temperature, which exhibited well-controlled shapes. Then, corresponding porous Co₃O₄ assembled from nanoparticles was acquired by heating Co-MOFs, and showed a good sensing performance for n-butanol, with a response up to 21.0 toward 100 ppm n-butanol. Moreover, it is found that the shape and the size of Co₃O₄ assemblies can significantly influence their sensing performances. For porous Co₃O₄ assemblies, when the nanoparticles are small enough (˜10 nm), a porous structure with a larger proportion of the nanoparticles close to its surface tends to show a better gas-sensing performance. The findings can be used in the design of gas-sensing materials in the future.

Pd-Catalyzed Reaction-Producing Intermediate S on a Pd/In2O3 Surface: A Key To Achieve the Enhanced CS2-Sensing Performances

Although chemiresistive gas sensors, based on metal-oxide semiconductors, have exhibited particular promise for the monitoring of air pollution, they are often limited because of poor selectivity. In that case, to overcome this issue, according to the essence of the gas-sensing process, the method of reforming the surface reaction path on the surface of the sensing materials was used. Here, we report that Pd nanoparticles supported over the In₂O₃ composites, featured with a yolk-shell structure, enable the trace detection of carbon disulfide (CS₂) gas molecules, which are immensely dangerous to humans and animals. Moreover, the prominent enhancement of the gas response and the ultraselective CS₂-sensing characteristic were acquired in comparison with pristine In₂O₃ sensors. Significantly, density functional theory calculations revealed that the Pd supported on In₂O₃ greatly facilitates the adsorption capacity to CS₂, and the intermediate S, produced by Pd-catalyzed desulfurization reaction, on the Pd/In₂O₃ surface during the sensing process is a key to achieving a high CS₂ gas response as well as ultraselectivity, which is well in agreement with the X-ray photoelectron spectroscopy analysis results. On the basis of these results, a new sensing mechanism model for the CS₂-sensing process was put forward.

Construction of flower-like ZnSnO3/Zn2SnO4 hybrids for enhanced phenylamine sensing performance

Novel flower-like ZnSnO₃/Zn₂SnO₄ hybrids were synthesized and showed excellent phenylamine sensing performance.