Enhanced room-temperature NO2-sensing performance of AgNPs/rGO nanocomposites

A flexible and wearable PET-based chemiresistive H2S gas sensor modified with MoS2-AgCl@AgNPs nanocomposite for the dynamic monitoring of egg spoilage

In this study, a flexible and wearable chemiresistive hydrogen sulfide (H2S) sensor is developed by modifying the MoS2-AgCl@AgNPs (MAAN) nanocomposite on a flexible PET-based Au interdigital electrode (FPAIDE) (MAAN/FPAIDE) to monitor egg spoilage at room temperature inexpensively. A new method is developed for the low-cost batch fabrication of MAAN/FPAIDEs by laser direct writing. The morphology and composition of the synthesized MAAN nanocomposite are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and transmission electron microscopy (TEM). Based on the oxygen adsorption model, a new H2S sensing mechanism is discussed, which is related to the formation of p-n junctions between MoS2 and AgCl and the specific adsorption of H2S by AgNPs on the MAAN sensing layer, causing a decrease in resistance. X-ray photoelectron spectroscopy (XPS) is used to characterize the charge transfer between gas molecules and the MAAN sensing layer and sulfide generation during the response process. The concentration of H2S can be detected down to 27 ppb at 25 °C. Finally, the prepared sensor has been successfully utilized in the real-time monitoring of egg spoilage with satisfactory results, indicating its great potential for the application of fresh food quality and safety supervision and the smart packaging of poultry eggs.

Au- or Ag-Decorated ZnO-Rod/rGO Nanocomposite with Enhanced Room-Temperature NO2-Sensing Performance

To improve the gas sensitivity of reduced oxide graphene (rGO)-based NO2 room-temperature sensors, different contents (0-3 wt%) of rGO, ZnO rods, and noble metal nanoparticles (Au or Ag NPs) were synthesized to construct ternary hybrids that combine the advantages of each component. The prepared ZnO rods had a diameter of around 200 nm and a length of about 2 μm. Au or Ag NPs with diameters of 20-30 nm were loaded on the ZnO-rod/rGO hybrid. It was found that rGO simply connects the monodispersed ZnO rods and does not change the morphology of ZnO rods. In addition, the rod-like ZnO prevents rGO stacking and makes nanocomposite-based ZnO/rGO achieve a porous structure, which facilitates the diffusion of gas molecules. The sensors' gas-sensing properties for NO2 were evaluated. The results reveal that Ag@ZnO rods-2% rGO and Au@ZnO rods-2% rGO perform better in low concentrations of NO2 gas, with greater response and shorter recovery time at the ambient temperature. The response and recovery times with 15 ppm NO2 were 132 s, 139 s and 108 s, 120 s, and the sensitivity values were 2.26 and 2.87, respectively. The synergistic impact of ZnO and Au (Ag) doping was proposed to explain the improved gas sensing. The p-n junction formed on the ZnO and rGO interface and the catalytic effects of Au (Ag) NPs are the main reasons for the enhanced sensitivity of Au (Ag)@ZnO rods-2% rGO.

Ag decoration-enabled sensitization enhancement of black phosphorus nanosheets for trace NO2 detection at room temperature

Black phosphorus (BP), one rising star of two-dimensional (2D) materials, has showcased a huge capability for ppb-level NO₂ detection. However, sluggish reaction kinetics and fragile stability frustrate its further application. In this regard, for the first time we prepared Ag nanoparticles modified BP nanosheets as the sensing layer via one feasible method to recognize trace NO₂ at room temperature. With respect to individual BP, the composition-optimized BP-Ag nanocomposites (BP-Ag-1 sensor) achieved a favorable performance primarily in terms of boosted response (39.9% vs. 11.8%, 100 ppb NO₂), accelerated response speed (190 s vs. 486 s, 100 ppb NO₂) and strengthened operation stability, together with ultralow theoretical detection limit of 0.25 ppb. Furthermore, a protection layer comprised of polylactic acid (PLA) was anchored onto the surface of BP-Ag-1 sensor to keep the water molecules physically from the sensing layer and retain a distinguishable signal toward trace NO₂ at high moisture environments. The introduction of Ag and PLA separately reduced the lone electron pairs from P atoms and suppressed the water penetration into the BP film, thereby offering an alternative way to passivate BP for its optoelectronic applications in the future.

Intrinsically Breathable and Flexible NO2 Gas Sensors Produced by Laser Direct Writing of Self-Assembled Block Copolymers

The surge in air pollution and respiratory diseases across the globe has spurred significant interest in the development of flexible gas sensors prepared by low-cost and scalable fabrication methods. However, the limited breathability in the commonly used substrate materials reduces the exchange of air and moisture to result in irritation and a low level of comfort. This study presents the design and demonstration of a breathable, flexible, and highly sensitive NO₂ gas sensor based on the silver (Ag)-decorated laser-induced graphene (LIG) foam. The scalable laser direct writing transforms the self-assembled block copolymer and resin mixture with different mass ratios into highly porous LIG with varying pore sizes. Decoration of Ag nanoparticles on the porous LIG further increases the specific surface area and conductivity to result in a highly sensitive and selective composite to detect nitrogen oxides. The as-fabricated Ag/LIG gas sensor on a flexible polyethylene substrate exhibits a large response of -12‰, a fast response/recovery of 40/291 s, and a low detection limit of a few parts per billion at room temperature. Integrating the Ag/LIG composite on diverse fabric substrates further results in breathable gas sensors and intelligent clothing, which allows permeation of air and moisture to provide long-term practical use with an improved level of comfort.