Chemical Surface Adsorption and Trace Detection of Alcohol Gas in Graphene Oxide-Based Acid-Etched SnO2 Aerogels

A proposed device based on MoSe2-ZnO heterojunctions on rGO for enhanced ethanol gas sensing performances at room temperature

In this research, we report an enhanced sensing response ethanol gas sensing device based on a ternary nanocomposite of molybdenum diselenide-zinc oxide heterojunctions decorated rGO (MoSe2/ZnO/rGO) at room temperature. The sensing performance of the ternary nanocomposite sensing device has been analysed for various concentrations of ethanol gas (1-500 ppm). The gas-sensing results have revealed that for 500 ppm ethanol gas concentration, the sensing device has exhibited an enhanced response value(Rg/Ra)of 50.2. Significantly, the sensing device has displayed a quick response and recovery time of 6.2 and 12.9 s respectively. In addition to this, the sensing device has shown a great prospect for long-term detection of ethanol gas (45 days). The sensing device has demonstrated the ability to detect ethanol at remarkably low concentrations of 1 ppm. The enhanced sensing performance of the ternary nanocomposite sensing device has highlighted the effective synergistic effect between MoSe2nanosheets, ZnO nanorods, and rGO nanosheets. This has been attributed to the formation of two heterojunctions in the ternary nanocomposite sensor: a p-n heterojunction between MoSe2and ZnO and a p-p heterojunction between MoSe2and rGO. The analysis of the results has suggested that the proposed MoSe2/ZnO/rGO nanocomposite sensing device could be considered a promising candidate for the real-time detection of ethanol gas.

Dual-channel MIRECL portable devices with impedance effect coupled smartphone and machine learning system for tyramine identification and quantification

We designed a novel, portable, and visual dual-potential molecularly imprinted ratiometric electrochemiluminescence (MIRECL) sensor for tyramine (TYM) detection based on smartphone and deep learning-assisted optical devices. Molecularly imprinted polymer-Ce2Sn2O7 (MIP-Ce2Sn2O7) layers were fabricated by in-situ electropolymerization method as the capture and signal amplification probe. Oxygen vacancies in Ce2Sn2O7 not only enhance the electrochemical redox capability but also accelerate the energy transfer, thereby enhancing the luminescence of cathode ECL. Under optimal conditions, the ECL signals of MIP-Ce2Sn2O7 at the cathode and the anode response of Ru(bpy)32+ was reduced, thus a wide linear range from 0.01 μM to 1000 μM with the detection limit as low as 0.005 μM. Interestingly, combined with an artificial intelligence image recognition algorithm and the principle of optical signal reading by smartphone, the developed MIRECL sensor has been applied to the portable and visual determination of TYM in aquatic samples, and its practicability has been satisfactorily verified.

One Droplet toward Efficient Alcohol Detection Using Femtosecond Laser Textured Micro/Nanostructured Surface with Superwettability

Alcohol with different concentrations is commonly used in food, industry, and medicine fields all over the world. However, current methods for detecting alcohol concentration are restricted to large sample consumption, additional senergy consuming, or complex operations. Here, inspired by superwettability of lotus leaves, a superhydrophobic and superorganophilic surface is designed on the polydimethylsiloxane (PDMS) for one droplet efficient alcohol detection, which is prepared via femtosecond laser direct writing technology. Meanwhile, the contact angles of droplets with various alcohol concentrations on the laser-treated PDMS (LTP) surface are different. Based on the above characteristic, alcohol concentration through contact angle measurement without any external energy is directly detected, which is simple and efficient. Furthermore, it is worth noting that the LTP surface remains stable wettability after 1000 water-ethanol cycles and 300 days tests in air, indicating strong surface repeatability and stability. Significantly, the LTP surface has a broad potential application in one droplet detecting alcohol concentration, fake or genuine wine, and alcohol molecules. This work provides a new strategy to fabricate a superwetting surface for efficient one droplet alcohol detection.

Development of Regular Hydrophobic Silica Aerogel Microspheres for Efficient Oil Adsorption

The objective of this research was to develop new hydrophobic silica aerogel microspheres (HSAMs) with water glass and hexmethyldisilazane for oil adsorption. The effects of the hexmethyldisilazane concentration and drying method on the structure and organic liquid adsorption capacity were investigated. The hexmethyldisilazane concentration of the modification solution did not influence the microstructure and pore structure in a noteworthy manner, which depended more on the drying method. Vacuum drying led to more volume shrinkage of the silica gel microsphere (SGM) than supercritical CO₂ drying, thus resulting in a larger apparent density, lower pore volume, narrower pore size distribution, and more compact network. Owing to the large pore volume and pore size, the HSAMs synthesized via supercritical CO₂ drying had a larger organic liquid adsorption capacity. The adsorption capacities of the HSAMs with pore volumes of 4.04-6.44 cm³/g for colza oil, vacuum pump oil, and hexane are up to 18.3, 18.9, and 11.8 g/g, respectively, higher than for their state-of-the-art counterparts. The new sorbent preparation method is facile, cost-effective, safe, and ecofriendly, and the resulting HSAMs are exceptional in capacity, stability, and regenerability.

Tin Oxide Based Hybrid Nanostructures for Efficient Gas Sensing

Tin oxide as a semiconductor metal oxide has revealed great potential in the field of gas sensing due to its porous structure and reduced size. Especially for tin oxide and its composites, inherent properties such as high surface areas and their unique semiconducting properties with tunable band gaps make them compelling for sensing applications. In combination with the general benefits of metal oxide nanomaterials, the incorporation of metal oxides into metal oxide nanoparticles is a new approach that has dramatically improved the sensing performance of these materials due to the synergistic effects. This review aims to comprehend the sensing mechanisms and the synergistic effects of tin oxide and its composites in achieving high selectivity, high sensitivity and rapid response speed which will be addressed with a full summary. The review further vehemently highlights the advances in tin oxide and its composites in the gas sensing field. Further, the structural components, structural features and surface chemistry involved in the gas sensing are also explained. In addition, this review discusses the SnO2 metal oxide and its composites and unravels the complications in achieving high selectivity, high sensitivity and rapid response speed. The review begins with the gas sensing mechanisms, which are followed by the synthesis methods. Further key results and discussions of previous studies on tin metal oxide and its composites are also discussed. Moreover, achievements in recent research on tin oxide and its composites for sensor applications are then comprehensively compiled. Finally, the challenges and scope for future developments are discussed.

As-Doped h-BN Monolayer: A High Sensitivity and Short Recovery Time SF6 Decomposition Gas Sensor

SF₆ is a common insulating medium of gas-insulated switchgear (GIS). However, it is inevitable that SF₆ will be decomposed due to partial discharge (PD) in GIS, which will cause hidden dangers to the safe and stable operation of equipment. Based on the DFT method, the two-dimensional nano-composite As-doped h-BN (As-BN) monolayer was proposed. By modeling and calculating, the ability of an As-BN monolayer as a specific sensor for SO₂F₂ (compared with an H₂O adsorption system and CO₂ adsorption system) was evaluated by parameters such as the binding energy (E_b), adsorption energy (E_ads), transfer charge (ΔQ), geometric structure parameters, the total density of states (TDOS), band structure, charge difference density (CDD), electron localization function (ELF), sensitivity (S), and recovery time (τ). The results showed that an As-BN monolayer showed strong adsorption specificity, high sensitivity, and short recovery time for SO₂F₂ gas molecules. Therefore, the As-BN monolayer sensor has great application potential in the detection of SF₆ decomposition gases.

Boosting room-temperature ppb-level NO2 sensing over reduced graphene oxide by co-decoration of α-Fe2O3 and SnO2 nanocrystals

As promising sensing materials, reduced graphene oxide (RGO)-based nanomaterials have drawn considerable attention in the fields of gas monitoring owing to their low operating temperature. However, constructing RGO-based room-temperature gas sensors possessing ppb-level limit of detection with high sensitivity remains challenging. In this work, a series of highly sensitive NO₂ sensors were fabricated using α-Fe₂O₃ and SnO₂ co-decorated RGO hybrids (designated as α-Fe₂O₃/SnO₂-RGO) as sensing materials. They were rationally synthesized by a one-pot hydrothermal method. Compared to SnO₂ modified RGO hybrids (SnO₂-RGO with bandgap of 3.88 eV), the bandgap energy of α-Fe₂O₃/SnO₂-RGO hybrids (3.53 eV) was reduced by adding α-Fe₂O_3; the narrower bandgap facilitated the sensing materials to release more electrons and form more oxygen ions at room temperature. Besides, the high carrier migration of RGO, which served as continuous phase, identical structure with ultrasmall particle size of α-Fe₂O₃ and SnO₂ (about 3-6 nm), and abundant chemisorbed oxygen species on the surface (20.8%) of the sensing materials, as well as their suitable bandgap (3.53 eV) in the sensing materials, significantly improved NO₂ response at room temperature. Among the sensors fabricated, α-Fe₂O₃/SnO₂-RGO-15-based NO₂ sensor had the highest response of 7.4 with a short response time of 59 s towards 1 ppm NO₂; it could even reach a response of 2.6 towards 100 ppb NO₂. Notably, α-Fe₂O₃/SnO₂-RGO-15 sample has excellent capability to recognize NO₂, where the response value (7.4) towards 1 ppm NO₂ is about 7 times higher than that of 100 ppm ammonia and common volatile organic compounds (formaldehyde, toluene, ethanol and acetone). Such NO₂ sensor has superior repeatability with negligible response deviation towards 1 ppm NO₂ for four reversible cycles. This makes it to have a great potential application in the field of NO₂ detection.

Electrospinning SA@PVDF-HFP Core-Shell Nanofibers Based on a Visual Light Transmission Response to Alcohol for Intelligent Packaging

A naked-eye detector based on a rapid transmittance response to alcohol was designed to offer real-time and reusable detection of fruit freshness. To ensure the hydrophobicity of the fibrous membrane and high light transmission response to alcohol, fluorine-rich poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with a low refractive index was selected as the shell layer, while sodium alginate (SA) and polyvinyl alcohol (PVA) were selected as the core layer for coaxial electrospinning. The core-shell fibrous detector was obtained by treatment with CaCl₂ to form a stable hydrogel and by water flushing to remove PVA. The interior structure of the fiber and its evolution were investigated with increasing SA concentration, which changed from a nonconcentric structure to a core-shell structure. Without SA, nonconcentric structured fibers were obtained due to high flowability and incompatibility between the organic solvent phase of PVDF-HFP and the aqueous phase of PVA. As the SA concentration increased, the enhanced viscosity and surface tension decreased the asymmetric mobility significantly, which competed with the charge attractive forces from the Taylor cone surface, leading to a core-shell structure. The as-spun membranes were opaque due to light scattering at the interface between air and fiber and became light transparent after immersion in a rotten fruit-containing alcohol and acetic acid due to a decreased light loss. The rapidly responsive, reusable fibrous membranes with over 90% light transparency developed here have high potential for application in visual intelligent packaging to monitor the freshness of fruits and vegetables.

Ultralight MOF-Derived Ni3S2@N, S-Codoped Graphene Aerogels for High-Performance Microwave Absorption

To develop high-performance microwave absorption materials with the features of lightweight, thin thickness, broad bandwidth, and strong absorption, an ultralight Ni₃S₂@N, S-codoped graphene aerogel with a density of 13.5 mg/cm³ has been fabricated by the use of metal-organic frameworks (MOFs) to directly initiate the gelation of graphene oxide strategy. In such a strategy, dual-functional 1D Ni-MOF nanorods not only act as the gelation agent but also afford the doping elements (N and S) originated from the organic species and the precursor for metal sulfide. Due to the synergistic effects of good impedance matching and multiple losses, the optimal reflection loss (RL) of as-prepared Ni₃S₂@N, S-codoped graphene aerogel reaches −46.9 dB at 17.1 GHz with only 2.0 mm and ultralow filling content (1.75 wt%). The maximum effective absorption bandwidth (EAB) reaches 6.3 GHz (11.7–18.0 GHz) at 2.38 mm, covering the whole Ku band. Moreover, the value of EAB with the RL less than −30 dB can be tuned to 12.2 GHz (5.8–18 GHz) at the absorber thickness ranging from 1.9 to 5.0 mm. This work provides insight for rational design and fabrication of multicomponent-containing graphene aerogels, showing the potential application in lightweight and high-performance microwave absorption.