Femtosecond Laser-Driven Phase Engineering of WS2 for Nano-Periodic Phase Patterning and Sub-ppm Ammonia Gas Sensing.

Laser-driven phase transition of 2D transition metal dichalcogenides has attracted much attention due to its high flexibility and rapidity. However, there are some limitations during the laser irradiation process, especially the unsatisfied surface ablation, the inability of nanoscale phase patterning, and the unexploited physical properties of new phase. In this work, the well-controlled femtosecond (fs) laser-driven transformation from the metallic 2M-WS2 to the semiconducting 2H-WS2 is reported, which is confirmed to be a single-crystal to single-crystal transition without layer thinning or obvious ablation. Moreover, a highly ordered 2H/2M nano-periodic phase transition with a resolution of ≈435 nm is achieved, breaking through the existing size bottleneck of laser-driven phase transition, which is attributed to the selective deposition of plasmon energy induced by fs laser. It is also demonstrated that the achieved 2H-WS2 after laser irradiation contains rich sulfur vacancies, which exhibits highly competitive ammonia gas sensing performance, with a detection limit below 0.1 ppm and a fast response/recovery time of 43/67 s at room temperature. This study provides a new strategy for the preparation of the phase-selective transition homojunction and high-performance applications in electronics.

Engineering SnO2 nanorods/ethylenediamine-modified graphene heterojunctions with selective adsorption and electronic structure modulation for ultrasensitive room-temperature NO2 detection.

Ever-increasing concerns over air quality and the newly emerged internet of things (IoT) for future environmental monitoring are stimulating the development of ultrasensitive room-temperature gas sensors, especially for nitrogen dioxide (NO2), one of the most harmful air pollution species released round-the-clock from power plants and vehicle exhausts. Herein, tin dioxide nanorods/ethylenediamine-modified reduced graphene oxide (SnO2/EDA-rGO) heterojunctions with selective adsorption and electronic structure modulation were engineered for highly sensitive and selective detection of NO2 at room temperature. The modified EDA groups not only enable selective adsorption to significantly enrich NO2 molecules around the interface but also realize a favorable modulation of SnO2/EDA-rGO electronic structure by increasing the Fermi level of rGO, through which the sensing performance of NO2 is synergistically enhanced. The response of the SnO2/EDA-rGO sensor toward 1 ppm NO2 reaches 282%, which exceeds the corresponding SnO2/rGO sensor by a factor of 2.8. It also exhibits a low detection limit down to 100 ppb, enhanced selectivity, and rapid response/recovery kinetics. This approach to designing a novel heterojunction with significantly enhanced chemical and electric effects may shed light on the future engineering of gas-sensing materials.

2D/2D heterojunction of g-C3N4/SnS2: room-temperature sensing material for ultrasensitive and rapid-recoverable NO2 detection.

Heterojunction engineering plays an indispensable role in improving gas-sensing performance. However, rational heterojunction engineering to achieve room-temperature NO2 sensing with both high response and rapid recovery is still a challenge. Herein, a 2D/2D heterojunction of g-C3N4/SnS2 is designed to improve the sensing performance of SnS2 and used for ultrasensitive and rapid-recoverable NO2 detection at room temperature. The pristine SnS2 fails to work at room temperature because of its high resistivity and weak adsorption to NO2. After combination with g-C3N4 nanosheets, the g-C3N4/SnS2-based sensor exhibits an extremely high response (503%) and short recovery time (166 s) towards 1 ppm NO2 at room temperature. The improved sensing performance is primarily attributed to the increased adsorption sites and enhanced charge transfer induced by the 2D/2D heterojunctions with large interface contact area. This achievement of g-C3N4/SnS2 2D/2D heterostructures demonstrates a promising pathway for the design of sensitive gas-sensing material based on a 2D/2D heterojunction strategy.

Enhanced oxygen anions generation on Bi2S3/Sb2S3 heterostructure by visible light for trace H2S detection at room temperature.

Bismuth sulfide (Bi2S3) possesses unique properties that make it a promising material for effective hydrogen sulfide (H2S) detection at room temperature. However, when exposed to light, the oxygen anions (O2-(ads)) adsorbed on the surface of Bi2S3 can react with photoinduced holes, ultimately reducing the ability to respond to H2S. In this study, Bi2S3/Sb2S3 heterostructures were synthesized, producing photoinduced oxygen anions (O2-(hv)) under visible light conditions, resulting in enhanced H2S sensing capability. The Bi2S3/Sb2S3 heterostructure sensor exhibits a two-fold increase in sensing response to 500 ppb H2S under in door light conditions relative to its performance in darkness. Additionally, the sensing response of the Bi2S3/Sb2S3 sensor (Ra/Rg= 23.3) was approximately five times higher than pure Bi2S3. The improved sensing performance of the Bi2S3/Sb2S3 heterostructures is attributable to the synergistic influence of the heterostructure configuration and light modulation, which enhances the H2S sensing performance by facilitating rapid charge transfer and increasing active sites (O2-(hv)) when exposed to visible light.

Synergy of S-vacancy and heterostructure in BiOCl/Bi2S3-x boosting room-temperature NO2 sensing.

The special physicochemical properties of Bi2S3 nanomaterial endow it to be exceptional NO2 sensing properties. However, sensors based on pure Bi2S3 cannot detect trace NO2 at room temperature effectively due to the scanty active sites and poor charge transfer efficiency. Herein, vacancy defect and heterostructure engineering are rationally integrated to explore BiOCl/Bi2S3-x heterostructure with rich S vacancies to enhance NO2 sensing performance. The optimized sensor based on S-vacancy-rich BiOCl/Bi2S3-x heterostructure exhibited a high response value (Rg/Ra = 29.1) to 1 ppm NO2 at room temperature, which was about 17 times compared to the pristine Bi2S3. Meanwhile, the BiOCl/Bi2S3-x sensor also exhibited a short response time (36 s) towards 1 ppm NO2 and a low theoretical detection limit (2 ppb). The superior response value of S-vacancy-rich BiOCl/Bi2S3-x heterostructures was ascribed to the improved electron migration at the heterointerface and the additional exposed active sites caused by the S vacancies in Bi2S3-x. Additionally, the sensors based on S-vacancy-rich BiOCl/Bi2S3-x heterostructures showed good long-term stability, outstanding selectivity, and good flexibility. This study offers an effective method for synergistically engineering defect and heterostructure to enhance gas sensing properties at room temperature.

Targeting tumor energy metabolism via simultaneous inhibition of mitochondrial respiration and glycolysis using biodegradable hydroxyapatite nanorods.

Tumor cells obtain energy supply from the unique metabolic pathways of mitochondrial respiration and glycolysis, which can be used interchangeably to produce adenosine triphosphate (ATP) for survival. To simultaneously block the two metabolic pathways and sharply cut off ATP supply, a multifunctional "nanoenabled energy interrupter" (called as HNHA-GC) was prepared by attaching glucose oxidase (GOx), hyaluronic acid (HA), and 10-hydroxycamptothecin (CPT) on the surface of degradable hydroxyapatite (NHA) nanorods. After targeted delivery of HNHA-GC to the tumor site by HA, the tumor-selective acid degradation of HNHA-GC as well as the subsequent deliveries of Ca2+, drug CPT, and GOx take place. The released Ca2+ and CPT induce mitochondrial dysfunction by Ca2+ overload and chemotherapy respectively, while the GOx-triggered glucose oxidation inhibits glycolysis by starvation therapy (exogenous effect). The generated H2O2 and released CPT increase the intracellular reactive oxygen (ROS) level. Moreover, the generated H+ and enhanced ROS promote Ca2+ overload by accelerating the degradation of HNHA-GC and preventing intracellular Ca2+ efflux, respectively (endogenous effect). As a result, the HNHA-GC displays a promising therapeutic modality for simultaneously cutting off mitochondrial and glycolytic ATP production through a combination of Ca2+ overload, chemotherapy, and starvation therapy.

Construction of Z-scheme heterojunction by coupling Bi2Sn2O7 and BiOBr with abundant oxygen vacancies: Enhanced photodegradation performance and mechanism insight.

Promoting charge migration and enhancing redox ability of photogenerated carriers are important for the development of highly efficient semiconductor-based photocatalyst. Here, BiOBr/Bi2Sn2O7 heterojunction with oxygen vacancies (OVs) was constructed by homogeneously depositing Bi2Sn2O7 nanoparticles on the Vo-BiOBr surface. The experimental results manifested that Vo-BiOBr/Bi2Sn2O7 displayed better performance for rhodamine B, ciprofloxacin, and tetracycline degradation than counterparts without OVs. The characterization results proved OVs played the essential role for enhanced performance via improving the separation efficiency of charge carriers, increasing the visible light harvest, and lowering conduction band position. Moreover, mechanism study revealed that an inner electric field was built at the interface, leading to a Z-scheme path of photogenerated electron. This study provided an efficient strategy for designing highly efficient photocatalyst for solving environmental pollution.

Boosting room-temperature NO2 detection via in-situ interfacial engineering on Ag2S/SnS2 heterostructures.

The effective detection of hazardous gases has become extremely necessary for the ecological environment and public health. Interfacial engineering plays an indispensable role in the development of innovative materials with exceptional properties, thus triggering a new revolution in the realization of high-performance gas sensing. Herein, the rational designed Ag2S/SnS2 heterostructures were synthesized via a facile in-situ cation-exchange method. The coshared S atoms derived from in-situ interfacial engineering enable intimate atomic-level contact and strong electron coupling between SnS2 and Ag2S, which efficiently assist interfacial charge redistribution and transport as confirmed theoretically and experimentally. Benefiting from the high-quality interface of the heterostructures, the resultant Ag2S/SnS2 sensor delivered an ultrahigh response (286%) together with short response/recovery time (17 s/38 s) to 1 ppm NO2. The sensor also demonstrated superior sensing selectivity and reliable repeatability at room-temperature. Such excellent sensing performance could be synergistically ascribed to the junction effect and interfacial engineering of Ag2S/SnS2 heterostructures, which not only modulates the electronic properties of SnS2 but also provides abundant adsorption sites for gas sensing. This study offers guidance for engineering heterostructures with high-quality interface, which might stimulate the exploitation of other novel materials and widen their potential applications.

Synergically engineering defect and interlayer in SnS2 for enhanced room-temperature NO2 sensing.

Defect and interlayer engineering are considered as two promising strategies to alter the electronic structures of sensing materials for improved gas sensing properties. Herein, ethylene glycol intercalated Al-doped SnS2 (EG-Al-SnS2) featuring Al doping, sulfur (S) vacancies, and an expanded interlayer spacing was prepared and developed as an active NO2 sensing material. Compared to the pristine SnS2 with failure in detecting NO2 at room temperature, the developed EG-Al-SnS2 exhibited a better conductivity, which was beneficial for realizing the room-temperature NO2 sensing. As a result, a high sensing response of 410% toward 2 ppm NO2 was achieved at room temperature by using the 3% EG-Al-SnS2 as the sensing material. Such outstanding sensing performance was attributed to the enhanced electronic interaction of NO2 on the surface of SnS2 induced by the synergistic effect of Al doping, S vacancies, and the expanded interlayer spacing, which is directly revealed by the in-suit measurement based on near-ambient pressure X-ray photoelectronic spectroscopy (NAP-XPS). Furthermore, to identify the role of Al doping, S vacancies, and the expanded interlayer spacing in enhancing the NO2 sensing properties, a series of comparative experiments and theoretical calculations were performed.

Boosted charge transfer in dual Z-scheme BiVO4@ZnIn2S4/Bi2Sn2O7 heterojunctions: Towards superior photocatalytic properties for organic pollutant degradation.

A core-shell structured dual Z-scheme ternary photocatalyst BiVO4@ZnIn2S4/Bi2Sn2O7 was fabricated via hydrothermal and heat-circumfluence strategy. With ZnIn2S4 serving as a bridge to connect BiVO4 and Bi2Sn2O7, the developed ternary catalyst displayed boosted charge transfer and spatial separation capabilities. The effect of mass ratios of BiVO4@ZnIn2S4 and Bi2Sn2O7 on photodegradation efficiency under visible light irradiation was explored. The optimal ternary heterojunction photocatalyst possessed remarkable photocatalytic rate constant for Rhodamine B (RhB) degradation, which was 63 and 12 times higher than that of BiVO4 and Bi2Sn2O7, respectively. In addition, the as-prepared ternary photocatalyst had good universality. Notably, the novel dual Z-scheme photocatalysts could improve the separating/transferring efficiency and reduction/oxidation ability of charge carriers. Meanwhile, the hierarchical structure offered sufficient reaction sites for photodegradation. This work provides a new insight into the rational design of ternary dual Z-scheme photocatalysts.

Increased Active Sites and Charge Transfer in the SnS2/TiO2 Heterostructure for Visible-Light-Assisted NO2 Sensing.

Tin disulfide (SnS2) has been extensively researched as a promising sensing material due to its large electronegativity, suitable band gap, earth abundance, and nontoxicity. However, the poor conductivity and slow response/recovery speed at room temperature greatly hinder its application in high-performance practical gas sensors. Herein, to promote the study of SnS2-based gas sensors, a hierarchical SnS2/TiO2 heterostructure was synthesized and used as a sensing material to detect NO2 with the help of light illumination. Through the synergistic effect of the SnS2/TiO2 heterostructure and 525 nm light activation, the NO2 sensor based on the SnS2/TiO2 heterostructure exhibited a high response factor of 526% toward 1 ppm NO2 and a short response/recovery time of 43/102 s at room temperature due to the enhanced charge transfer and increased adsorption sites, which was superior to the vast majority of other NO2 sensors. An obvious decrease in the surface-adsorbed oxygen content based on the X-ray photoelectron spectroscopy measurement further confirmed that light illumination was helpful to clear the surface of SnS2/TiO2 and thus increased active sites for NO2 sensing. In addition, a flexible SnS2/TiO2 sensor was also fabricated to confirm its potential application in portable and wearable devices.

Tuning the intensity of metal-enhanced fluorescence by engineering silver nanoparticle arrays.

It is demonstrated that silver nanoparticle (SNP) arrays fabricated by combining nanoimprint lithography and electrochemical deposition methods can be used as substrates for metal-enhanced fluorescence, which is widely used in optics, sensitive detection, and bioimaging. The method presented here is simple and efficient at controlling the nanoparticle density and interparticle distance within one array. Furthermore, it is found that the fluorescence intensity can be tuned by engineering the feature size of the SNP arrays. This is due to the different coupling efficiency between the emission of the fluorophores and surface plasmon resonance band of the metallic nanostructures.

SnS2/SnS p-n heterojunctions with an accumulation layer for ultrasensitive room-temperature NO2 detection.

The unique features of SnS2 make it a sensitive material ideal for preparing high-performance nitrogen dioxide (NO2) gas sensors. However, sensors based on pristine tin disulfide (SnS2) fail to work at room temperature (RT) owing to their poor intrinsic conductivity and weak adsorptivity toward the target gas, thereby impeding their wide application. Herein, an ultrasensitive and fully recoverable room-temperature NO2 gas sensor based on SnS2/SnS p-n heterojunctions with an accumulation layer was fabricated. The amounts of SnS2/SnS heterojunctions can be effectively controlled by tuning the ratios of tin and sulfur precursors in the easy one-step solvothermal synthesis. Compared with pristine SnS2, the conductivity of SnS2/SnS heterostructures improved considerably. Such improvement was caused by the electron transfer from p-type SnS to n-type SnS2 because the Fermi level of SnS was higher than that of SnS2. The sensing response of optimized SnS2/SnS toward 4 ppm NO2 was 660% at room temperature, which was higher than most reported sensitivity values of other two-dimensional (2D) materials at room temperature. The superior sensing response of SnS2/SnS heterostructures was attributed to the enhanced electron transport and the increased adsorption sites caused by the SnS2/SnS p-n heterojunctions. Moreover, the SnS2/SnS sensor showed good selectivity and long-term stability. These achievements of SnS2/SnS heterostructured sensors make them highly desirable for practical applications.

Hierarchical SnS2/SnO2 nanoheterojunctions with increased active-sites and charge transfer for ultrasensitive NO2 detection.

SnS2 nanosheets with unique properties are excellent candidate materials for fabricating high-performance NO2 gas sensors. However, serious restacking and aggregation during sensor fabrication have greatly impacted the sensing response. In this study, flower-like hierarchical SnS2 was prepared by a simple microwave method and partially thermally oxidized to form hierarchical SnS2/SnO2 nanocomposites to further improve the sensing performance at low operating temperature. The fabricated SnS2/SnO2 sensor exhibited ultrahigh response (resistance ratio = 51.1) toward 1 ppm NO2 at 100 °C, roughly 10.2 times higher than that of pure SnS2 nanoflowers. The excellent and enhanced NO2 sensing performances of hierarchical SnS2/SnO2 nanocomposites were attributed to the novel hierarchical structure of SnS2 and the nanoheterojunction between SnS2 and the ultrafine SnO2 nanoparticles. The SnS2/SnO2 sensors also exhibited excellent selectivity and reliable repeatability. The simple fabrication of high performance sensing materials may facilitate the large-scale production of NO2 gas sensors.

Selective deposition of organic molecules onto DPPC templates--a molecular dynamics study.

The site-selective deposition of organic molecules onto template structures to create ordered micro/nanoscale arrangements has drawn more and more attention because of the broad possibility, for example, application in organic electronic devices. Here we present a molecular dynamics study toward the selective deposition of organic molecules 3(5)-(9-anthryl) pyrazole (ANP), perylene and sexiphenyl (6P) onto template structures made of the phospholipid L-α-dipalmitoyl-phosphatidylcholine (DPPC) in alternating liquid expanded (LE) and liquid condensed (LC) states. The simulation results indicate, first of all, that the molecules immerge into both LE and LC phases instead of staying on top of them. Furthermore, the simulations replicate the empirically observed higher diffusion constants of the organic molecules on LE phase compared to LC phase of the underlying DPPC layer. Additionally, we propose a possible mechanism for the diffusion barrier between LE/LC phase needed to explain the experimental findings of the selective deposition. Altogether, this study supports the notions suggested by the experiments on the causes of the selective deposition while giving a deeper insight into the molecular processes involved.

Fabrication of split-ring resonators by tilted nanoimprint lithography.

An efficient fabrication technique for large area periodic metallic split-ring arrays has been demonstrated by the combination of tilted nanoimprint lithography and nanotransfer imprinting. The feature size of the split-rings can be adjusted by varying the key geometry parameters of the original imprinting mold. Due to the flexible nature of PDMS molds, these arrays can be patterned on curved surfaces. The molds for nanoimprint lithography and nanotransfer imprinting can be used multiple times without a loss of fidelity.

Creating bicolor patterns via selective photobleaching with a single dye species.

Bicolor fluorescent pattern in thin polymer film is fabricated via a photobleaching process. Dye molecules exhibit monomer emission when they are dispersed inside the polymer and aggregate emission when they are on the surface of the polymer. Thus, a mixed emission of monomer and aggregate can be obtained by evaporating a single dye species on the polymer film. Bicolor pattern in thin polymer film is readily formed by selective photobleaching. This process is particularly attractive for the fabrication of bicolor patterns on flat substrates using a single dye species, which is of potential applications in photonic/electronic devices.

Fabrication of multicolor patterns with a single dye species on a polymer surface.

Multicolored patterns can be fabricated by evaporating a single dye species on a prepatterned polymer substrate. The ratios of dye to polymer are different on protrusion and recess areas of the prepatterned surface, which can result in different aggregates and emissions. The polymer substrate was prepatterned using nanoimprint lithography (NIL) without any further process. This method may provide a facile route for fabricating large-area multicolored patterns.