Chemiresistive gas sensor based on Mo0.5W0.5S2 alloy nanoparticles with good selectivity and ppb-level limit of detection to ammonia.

Transition metal dichalcogenides (TMDs) are promising materials for chemiresistive gas sensor, while TMD alloys (two chalcogenide or/and metal elements) with tunable electronic structures have drawn little attention in gas sensing. Herein, Mo0.5W0.5S2 alloy nanoparticles (NPs) were prepared by a facile sonication exfoliation method and then tested for ammonia sensing. The crystal structure, geometric morphology, and elemental composition of Mo0.5W0.5S2 NPs were investigated. The gas sensing measurements demonstrated Mo0.5W0.5S2 NPs with good response to ammonia at 80 °C with a limit of detection down to 500 part per billion (ppb). The sensor also displayed good stability as well as superb selectivity to ammonia in the presence of interferences, such as methanol, acetone, benzene, and cyclohexane. The theoretical calculations revealed Mo and W atoms at edges (such as Mo0.5W0.5S2 (010)) of sheet-like NPs as the active sites for ammonia adsorption. Electrons donated by the adsorbed ammonia were combined with holes in p-type Mo0.5W0.5S2 NPs, and the concentration of the main charge carrier was reduced, resulting in resistance enhancement.

Density Functional Investigation on α-MoO3 (100): Amines Adsorption and Surface Chemistry.

The (100) surface of α-MoO3 should possess overwhelmingly more exposed Mo atoms than the (010), and the exposed Mo has been extensively considered as an active site for amine adsorption. However, α-MoO3 (100) has drawn little attention concerning the amine sensing mechanism. In this research, adsorption of ammonia (NH3), monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA) is systematically investigated by density functional theory (DFT). All four of these molecules have high affinity to α-MoO3 (100) through interaction between the N and the exposed Mo, and the affinity is mainly influenced by both the characteristics of the molecules and the geometric environment of the surface active site. Adsorption and dissociation of water and oxygen molecule on stoichiometric and defective α-MoO3 (100) surfaces are then simulated to fully understand the surface chemistry of α-MoO3 (100) in practical conditions. At low temperature, α-MoO3 (100) must be covered with a large number of water molecules; the water can desorb or dissociate into hydroxyl groups at high temperature. Oxygen vacancy (VO) can be generated through the annealing process during sensor device fabrication; VO must be filled with an O2 molecule, which can further interact with adsorbed water nearby to form hydroxyl groups. According to this research, α-MoO3 (100) must be the active surface for amine sensing and its surface chemistry is well understood. In the near future, further reaction and interaction will be simulated at α-MoO3 (100), and much more attention should be paid to α-MoO3 (100) not only theoretically but also experimentally.

Water-Dispersible CsPbBr3 Perovskite Nanocrystals with Ultra-Stability and its Application in Electrochemical CO2 Reduction.

Thanks to the excellent optoelectronic properties, lead halide perovskites (LHPs) have been widely employed in high-performance optoelectronic devices such as solar cells and light-emitting diodes. However, overcoming their poor stability against water has been one of the biggest challenges for most applications. Herein, we report a novel hot-injection method in a Pb-poor environment combined with a well-designed purification process to synthesize water-dispersible CsPbBr3 nanocrystals (NCs). The as-prepared NCs sustain their superior photoluminescence (91% quantum yield in water) for more than 200 days in an aqueous environment, which is attributed to a passivation effect induced by excess CsBr salts. Thanks to the ultra-stability of these LHP NCs, for the first time, we report a new application of LHP NCs, in which they are applied to electrocatalysis of CO2 reduction reaction. Noticeably, they show significant electrocatalytic activity (faradaic yield: 32% for CH4, 40% for CO) and operation stability (> 350 h).

Defect Engineering in Ultrathin SnSe Nanosheets for High-Performance Optoelectronic Applications.

Ultrathin lamellar SnSe is highly attractive for applications in areas such as photonics, photodetectors, photovoltaic devices, and photocatalysis, owing to its suitable band gap, exceptional light absorption capabilities, and considerable carrier mobility. On the other hand, SnSe nanosheets (NSs) still face challenges of being difficult to prepare and their devices having low photoelectric conversion efficiencies. Herein, ultrathin SnSe NSs with controlled Se defects were synthesized with high yield by a facial Li intercalation-assisted liquid exfoliation method. The loss of Se, a narrowing of the band gap, and an increase in lattice disorders involving vacancies, distortions, and phase transition were observed in SnSe NSs prepared with a long lithiation process. Comparing between the 24 and 72 h lithiation samples, the ones processed for a longer time displayed a faster recombination time due to more defect-induced mid-states. Inspiringly, enhancements of 4-10 times were observed for photodetector device parameters such as photocurrent, photoresponsivity, photoresponse speed, and specific detectivity of the 72 h lithiation SnSe NSs. Additionally, these devices show good stability and a broad detection range, from ultraviolet to the near infrared region. Our results provide a promising avenue for the mass production of SnSe NSs with high photoelectric performance and open up opportunities for applications in photonics, optoelectronics, and photocatalysis.

Berlin Green Framework-Based Gas Sensor for Room-Temperature and High-Selectivity Detection of Ammonia.

Ammonia detection possesses great potential in atmosphere environmental protection, agriculture, industry, and rapid medical diagnosis. However, it still remains a great challenge to balance the sensitivity, selectivity, working temperature, and response/recovery speed. In this work, Berlin green (BG) framework is demonstrated as a highly promising sensing material for ammonia detection by both density functional theory simulation and experimental gas sensing investigation. Vacancy in BG framework offers abundant active sites for ammonia absorption, and the absorbed ammonia transfers sufficient electron to BG, arousing remarkable enhancement of resistance. Pristine BG framework shows remarkable response to ammonia at 50-110 °C with the highest response at 80 °C, which is jointly influenced by ammonia's absorption onto BG surface and insertion into BG lattice. The sensing performance of BG can hardly be achieved at room temperature due to its high resistance. Introduction of conductive Ti3CN MXene overcomes the high resistance of pure BG framework, and the simply prepared BG/Ti3CN mixture shows high selectivity to ammonia at room temperature with satisfying response/recovery speed.

Nanosensor-Based Flexible Electronic Assisted with Light Fidelity Communicating Technology for Volatolomics-Based Telemedicine.

Telemedicine provides an attractive vision for tele-monitoring human health conditions and, thus, offers the opportunity for timely preventing chronic disease. A key limitation of promoting telemedicine in clinic application is the lack of a noninvasive med-tech and effective monitoring platform, which should be wearable and capable of high-performance tele-monitoring of health risk. Here we proposed a volatolomics-based telemedicine for continuously and noninvasively assessing human health status through continuously tracking the variation of volatile markers derived from human breath or skin. Particularly, a nanosensor-based flexible electronic was specifically designed to serve as a powerful platform for implementing the proposed cost-effective healthcare. An all-flexible and highly packed makeup (all functional units were integrated in a 2*2*0.19 cm3 plate) enables an electronic, compact configuration and the capability of resisting negative impact derived from customers' daily movement. Notably, the nanosensor-based electronic demonstrates high specificity, quick response rate (t90% = 4.5 s), and desirable low detection limit (down to 0.117 ppm) in continuous tele-monitoring chronic-disease-related volatile marker (e.g., acetone). Assisted by the power saved light fidelity (Li-Fi) communicating technology, a clinic proof on the specifically designed electronic for noninvasively and uninterrupted assessing potential health risk (e.g., diabetics) is successfully implemented, with the accuracy of around 81%. A further increase in the accuracy of prewarning is predicted by excluding the impact of individual differences such as the gender, age, and smoking status of the customer. These promising pilot results indicate a bright future for the tailor-made nanosensing-device-supported volatolomics-based telemedicine in preventing chronic diseases and increasing patients' survival rate.

High Efficiency Mesoscopic Solar Cells Using CsPbI3 Perovskite Quantum Dots Enabled by Chemical Interface Engineering.

All-inorganic α-CsPbI3 perovskite quantum dots (QDs) are attracting great interest as solar cell absorbers due to their appealing light harvesting properties and enhanced stability due to the absence of volatile organic constituents. Moreover, ex situ synthesized QDs significantly reduce the variability of the perovskite layer deposition process. However, the incorporation of α-CsPbI3 QDs into mesoporous TiO2 (m-TiO2) is highly challenging, but these constitute the best performing electron transport materials in state-of-the-art perovskite solar cells. Herein, the m-TiO2 surface is engineered using an electron-rich cesium-ion containing methyl acetate solution. As one effect of this treatment, the solid-liquid interfacial tension at the TiO2 surface is reduced and the wettability is improved, facilitating the migration of the QDs into m-TiO2. As a second effect, Cs+ ions passivate the QD surface and promote the charge transfer at the m-TiO2/QD interface, leading to an enhancement of the electron injection rate by a factor of 3. In combination with an ethanol-environment smoothing route that significantly reduces the surface roughness of the m-TiO2/QD layer, optimized devices exhibit highly reproducible power conversion efficiencies exceeding 13%. The best cell with an efficiency of 14.32% (reverse scan) reaches a short-circuit current density of 17.77 mA cm-2, which is an outstanding value for QD-based perovskite solar cells.

Acidic Site-Assisted Ammonia Sensing of Novel CuSbS2 Quantum Dots/Reduced Graphene Oxide Composites with an Ultralow Detection Limit at Room Temperature.

Novel CuSbS2 quantum dots (QDs)/reduced graphene oxide (rGO) composites are self-assembled via a hot-injection method, and CuSbS2 QDs exhibit a near monodispersion on the rGO surface. The gas sensors based on CuSbS2 QDs/rGO composites show the relatively good gas responses toward NH3 with an outstanding detection limit of 500 ppb and an average response time of 50 s at room temperature, and visible light illumination is proven to further promote the sensing performance of the composites. The study of the sensing mechanism reveals that the acidic sites on the surface play an extremely important role in NH3 adsorption of the composites, and the reaction between NH3 molecules and the pre-adsorbed oxygen ions finally leads to the generation of NO molecules. The synergistic effect existing between CuSbS2 QDs and rGO, in terms of electron transfer, is certified as well.

Growth kinetics and mechanisms of multinary copper-based metal sulfide nanocrystals.

Multinary copper-based metal sulfide (Cu-M-S) nanocrystals (NCs) usually have high absorption coefficients and near-optimum direct band gaps, which have been considered as novel photo-absorption materials for quantum dot-sensitized solar cells (QDSCs) and hole-transport materials for perovskite solar cells (PSCs). However, the formation and phase transformation mechanisms of Cu-M-S NCs during the solution-based preparing approaches are complicated. Herein, Cu-M-S NCs, including Cu2ZnSnS4 (CZTS), Cu2SnS3 (CTS), CuInS2 (CIS), and CuSbS2 (CAS), have been synthesized through solution-based hot-injection methods. Their formation and phase transformation mechanisms have been studied in terms of the growth kinetics. An effective method has been proposed to investigate the formation mechanisms of Cu-M-S NCs. The results suggest that CZTS, CTS, and CIS NCs are formed through an inter-reaction between metal sulfides rather than the classical cation exchange reactions, and CAS NCs are formed based on the CuxS structure; these findings provide new insights into the formation of Cu-M-S NCs. In addition, the anisotropic or isotropic growth processes during the growth stage have been found to be the key issues in the formation of a zinc blende or wurtzite structure NCs, respectively, which can be controlled by tuning the relative reactivity of metal precursors.

Investigation on the Transformation of Absorbed Oxygen at ZnO {101Ì 0} Surface Based on a Novel Thermal Pulse Method and Density Functional Theory Simulation.

Absorbed oxygen plays a key role in gas sensing process of ZnO nanomaterials. In this work, the transformation of absorbed oxygen on ZnO (101̅0) and its effects on gas sensing properties to ethanol are studied by a novel thermal pulse method and density functional theory (DFT) simulation. Thermal pulse results reveal that the absorbed O2 molecule dissociates into two individual oxygen adatoms by extracting electrons from ZnO surface layers when temperature is above 443 K. The temperature at which absorbed O2 molecule begins to dissociate is the lowest working temperature for gas sensing. DFT simulation demonstrates the dissociation process of O2 at ZnO (101̅0) surface, and the activation energy (Ea) of dissociation is calculated to be 351.71 kJ/mol, which suggests that the absorbed O2 molecule is not likely to dissociate at room temperature. The reactions between ethanol and absorbed O2 molecule, as well as reactions between ethanol and O adatom, are also simulated. The results indicate that ethanol cannot react with absorbed O2 molecule, while it can be oxidized by O adatom to acetaldehyde and then to acetic acid spontaneously. Mulliken charge analysis suggests electrons extracted by O adatom return to ZnO after the oxidation of ethanol.