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Abstract: Edges of 2D transition metal dichalcogenides (TMDs) are well known as highly reactive sites, thus researchers have attempted to maximize the edge site density of 2D TMDs. In this work, metal‐organic framework (MOF) templates are introduced to synthesize few‐layered WS2 nanoplates (a lateral dimension of ≈10 nm) confined in Co, N‐doped hollow carbon nanocages (WS2_Co‐N‐HCNCs), for highly sensitive NO2 gas sensors. WS2 precursors are assembled in the surface cavity of Co‐based zeolite imidazole framework (ZIF‐67) and subsequent pyrolysis produced WS2_Co‐N‐HCNCs. During the pyrolysis, the carbonized ZIF‐67 are doped by Co and N elements, and the growth of WS2 is effectively suppressed, creating few‐layered WS2 nanoplates functionalized Co‐N‐HCNCs. The WS2_Co‐N‐HCNCs exhibit outstanding NO2 sensing characteristics at room temperature, in terms of response (48.2% to 5 ppm), selectivity, response and recovery speed, and detection limit (100 ppb). These results are attributed to the enhanced adsorption and desorption kinetics of NO2 on abundant WS2 edges, confined in the gas permeable HCNCs. This work opens up an efficient way for the facile synthesis of edge abundant few‐layered TMDs combined with porous carbon matrix via MOF templating route, for applications relying on highly active sites. [ABSTRACT FROM AUTHOR]

2D Ru oxide nanosheets (NSs) with optically punched nanoholes are synthesized and integrated on a flexible heating substrate, i.e., silver nanowire (Ag NW)-embedded colorless polyimide (cPI) film, for application in wearable chemical sensors. Multiple discrete pores on the sub-5-nm scale are formed on the basal planes of Ru oxide NSs by irradiation of intense pulsed light. The chemical sensing characteristic of the porous Ru oxide NSs toward nitrogen dioxide (NO2) is investigated under controlled temperatures by applying DC voltage to the Ag NW-embedded cPI film. The improved NO2 responding and recovery kinetics are achieved using the porous Ru oxide NSs with sensitivity of 1.124% at 20 ppm at a film temperature of 80.3 °C. A wireless patch-type sensor module is developed to demonstrate wearable sensing of NO2 using the Ru oxide NSs on Ag NW-embedded cPI heating film. This work paved the new way for application of atomically thin and porous Ru oxide NSs in chemical sensors, which can detect hazardous species in real time. [ABSTRACT FROM AUTHOR]

1D metal-oxide nanotube (NT) structures have attracted considerable attention for applications in chemical sensors due to their high surface area and unique chemical and physical properties. Moreover, bimodal pores, i.e., meso- and macro-sized pores, which are formed on the shell of NTs, can further facilitate gas penetration into the sensing layers, leading to much improved sensing properties. However, thin-walled NTs with bimodal pore distribution have been rarely fabricated due to the limitations of synthetic methods. Here, Ostwald ripening-driven electrospinning combined with sacrificial templating route using polystyrene (PS) colloid and bioinspired protein is firstly proposed for producing both bi-modal pores and catalyst-loaded thin-walled SnO2 NTs. Homogeneous catalyst loading on porous SnO2 NTs is achieved by the protein cage that contains catalysts and PS colloids and protein shells are thermally decomposed during calcination of electrospun fibers, resulting in the creation of dual-sized pores on NTs. Pt catalyst decorated porous SnO2 NTs (Pt-PS_SnO2 NTs) show exceptionally high acetone gas response, superior selectivity against other interfering gases, and very low limit of detection (10 ppb) to simulated diabetic acetone molecules. More importantly, sensor arrays assembled with developed porous SnO2 NTs enable the direct distinction between the simulated diabetic breath and normal breath from healthy people. [ABSTRACT FROM AUTHOR]

Hierarchical SnO2 fibers assembled from wrinkled thin tubes are synthesized by controlling the microphase separation between tin precursors and polymers, by varying flow rates during electrospinning and a subsequent heat treatment. The inner and outer SnO2 tubes have a number of elongated open pores ranging from 10 nm to 500 nm in length along the fiber direction, enabling fast transport of gas molecules to the entire thin-walled sensing layers. These features admit exhaled gases such as acetone and toluene, which are markers used for the diagnosis of diabetes and lung cancer. The open tubular structures facilitated the uniform coating of catalytic Pt nanoparticles onto the inner SnO2 layers. Highly porous SnO2 fibers synthesized at a high flow rate show five-fold higher acetone responses than densely packed SnO2 fibers synthesized at a low flow rate. Interestingly, thin-wall assembled SnO2 fibers functionalized by Pt particles exhibit a dramatically shortened gas response time compared to that of un-doped SnO2 fibers, even at low acetone concentrations. Moreover, Pt-decorated SnO2 fibers significantly enhance toluene response. These results demonstrate the novel and practical feasibility of thin-wall assembled metal oxide based breath sensors for the accurate diagnosis of diabetes and potential detection of lung cancer. [ABSTRACT FROM AUTHOR]

Reported is an electrical transduction platform for real‐time wireless anion sensing using single‐walled carbon nanotubes (SWCNTs) noncovalently functionalized with squaramide‐based anion binding selectors. Systematically studied are anion‐binding properties and efficiency of the electrical transduction of the functionalized SWCNT composites using the squaramide‐based selectors with two similar electron‐withdrawing groups, 3,5‐bis(trifluoromethyl)benzyl (1) and 3,5‐bis(trifluoromethyl)phenyl (2), which induce hydrogen‐bonding interaction with anions and deprotonation of a squaramide N–H proton upon addition of acetate (AcO−), respectively. Charge transduction occurs with AcO− as a result of charge transfer from the deprotonated selector 2, whereas less sensitive transduction is observed with selector 1 via hydrogen‐bonding interaction. These results provide guidelines to efficiently transduce the chemical interaction between selectors and anions to create resistive transduction with functionalized SWCNTs. Electron‐withdrawing groups adjacent to the squaramide as well as proximate cationic pyridyl groups, enhance the anion binding affinity and also lower the selector's pKa. The chemiresistive sensor arrays are readily integrated with a wireless sensing module and demonstrated real‐time sensing of multiple anions with a smartphone readout. [ABSTRACT FROM AUTHOR]

A NO2 sensor based on optically sintered 2D Ru oxide nanosheets applied to a flexible heating substrate composed of a colorless polyimide film with embedded Ag nanowires is described by Hee Jung Park, Il‐Doo Kim, and co‐workers in article number 1606026. A sensitivity of 1.124% at 20 ppm and a wearable wireless sensor is demonstrated. [ABSTRACT FROM AUTHOR]