Synthesis and Gas Sensing Properties of Transition Metal Dichalcogenides materials (TMDs)

En el procés de monitorització industrial, el control d'emissions dels cotxes, la seguretat de la qualitat de l'aire interior i exterior i la protecció del medi ambient, la detecció contínua i fiable de diversos gasos és fonamental. Els òxids metàl·lics semiconductors, els materials més utilitzats en aplicacions de detecció de gasos, tenen limitacions substancials com ara un alt consum d'energia, una mala estabilitat a llarg termini, una selectivitat limitada i, sobretot, una alta sensibilitat creuada a la humitat. Els materials nous que permeten un funcionament a baixa temperatura poden resoldre problemes relacionats amb l'energia, donant lloc a xarxes de sensors millors i més fiables. Com a resultat, materials 2D com els dicalcogenurs de metalls de transició (TMD) han sorgit com a opcions viables per a la detecció de gasos. Aquests materials de nova generació tenen el potencial de millorar les propietats de detecció dels materials sensibles als gasos, com ara la sensibilitat, la selectivitat, l'estabilitat i la velocitat (temps de resposta-recuperació). Això es deu a les seves propietats úniques inherents, que inclouen el gruix a nanoescala, una gran superfície específica, abundants llocs de vora actiu i una alta sensibilitat a les molècules de gas a temperatures més baixes i fins i tot a temperatura ambient. La tesi actual intenta augmentar la fabricació d'aquests materials en capes 2D de nova generació i utilitzar-los per a aplicacions de detecció de gasos en aquest camp d'estudi. A més, els materials de detecció de gasos investigats en aquesta tesi tenen el potencial d'abordar l'esmentat anteriorment en la seva forma prístina o després d'alguna funcionalització. En aquest sentit, aquesta tesi proposa sensors de gas quimioresistius basats en diversos materials TMD.En el proceso de monitoreo industrial, el control de emisiones de automóviles, la seguridad de la calidad del aire interior y exterior y la protección del medio ambiente, la detección continua y confiable de varios gases es fundamental. Los óxidos de metales semiconductores, los materiales más utilizados en aplicaciones de detección de gases, tienen limitaciones sustanciales, como un alto consumo de energía, poca estabilidad a largo plazo, selectividad limitada y, sobre todo, alta sensibilidad cruzada a la humedad. Los nuevos materiales que permiten el funcionamiento a baja temperatura podrían resolver los problemas relacionados con la energía, lo que daría como resultado redes de sensores mejores y más fiables. Como resultado, los materiales 2D como los dicalcogenuros de metales de transición (TMD) han surgido como opciones viables para la detección de gases. Estos materiales de próxima generación tienen el potencial de mejorar las propiedades de detección de los materiales sensibles al gas, como la sensibilidad, la selectividad, la estabilidad y la velocidad (tiempo de respuesta-recuperación). Esto se debe a sus propiedades únicas inherentes, que incluyen espesor a nanoescala, gran área de superficie específica, abundantes sitios de borde activos y alta sensibilidad a las moléculas de gas a temperaturas más bajas e incluso a temperatura ambiente. La tesis actual intenta ampliar la fabricación de estos materiales en capas 2D de próxima generación y utilizarlos para aplicaciones de detección de gases en este campo de estudio. Además, los materiales de detección de gases investigados en esta tesis tienen el potencial de abordar lo mencionado anteriormente, ya sea en su forma original o después de alguna funcionalización. En este sentido, esta tesis propone sensores de gas quimiorresistivos basados en varios materiales TMDs.In the industrial monitoring process, car emission control, indoor and outdoor air quality safety, and environmental protection, continuous and reliable detection of various gases is critical. Semiconducting metal oxides, the most extensively used materials in gas sensing applications, have substantial limitations such as high power consumption, poor long-term stability, limited selectivity, and, most notably, high humidity cross-sensitivity. Novel materials that allow for low-temperature operation might solve power-related issues, resulting in better and more reliable sensor networks. As a result, 2D materials like transition-metal dichalcogenides (TMDs) have emerged as viable options for gas sensing. These next-generation materials have the potential to improve gas-sensitive materials' sensing properties such as sensitivity, selectivity, stability, and speed (response-recovery time).This is owing to their inherent unique properties, which include nanoscale thickness, large specific surface area, abundant active edge sites, and high sensitivity to gas molecules at lower temperatures and even at room temperature. The current thesis attempts to scale up the fabrication of these next-generation 2D layered materials and utilise them for gas sensing applications in this field of study. Furthermore, the gas sensing materials investigated in this thesis have the potential to address the aforementioned either in their pristine form or after some functionalization. In this regard, this thesis proposes chemoresistive gas sensors based on several TMDs materials

PdO and PtO doped WS2 boosts NO2 gas sensing characteristics at room temperature

In this work tungsten disulphide nanostructures loaded with platinum-oxide (PtO), or palladium-oxide (PdO) were grown directly onto alumina substrates. This was achieved using a combination of aerosol-assisted chemical vapour deposition (AA-CVD) method with atmospheric pressure CVD technique. At first, tungsten oxide nanowires loaded with either PtO or PdO nanoparticles were successfully co-deposited via AA-CVD followed by sulfurization at 900 °C in the next step. The morphological, structural, and chemical characteristics were investigated using FESEM, TEM, XRD, XPS and Raman spectroscopy. The results confirm the presence of PdO and PtO in the WS2 host matrix. Gas sensing attributes of loaded and pristine WS2 sensors were investigated, at room temperature, towards different analytes (NO2, NH3, H2 etc.). Both pristine and metal-oxide loaded WS2 gas sensors show remarkable responses at room temperature towards NO2 detection. Further, the loaded sensors demonstrated stable, reproducible, ultrasensitive, and enhanced gas sensing response, with a detection limit below 25 ppb. Additionally, the effect of ambient humidity on the sensing response of both loaded and pristine sensors was investigated for NO2 gas. The response of PtO loaded sensor considerably decreased in humid environments, while the response for pristine and PdO loaded sensors increased. However, slightly heating (at 100 °C) the sensors, suppresses the influence of humidity. Finally, the long-term stability of different sensors is investigated, and the results demonstrate high stability with repeatable results after 6 weeks of gas sensing tests. This work exploits an attractive pathway to add functionality in the transition metal dichalcogenide host matrix

Spontaneous in-flight assembly of magnetic nanoparticles into macroscopic chains

Knowing the interactions controlling aggregation processes in magnetic nanoparticles is of strong interest in preventing or promoting nanoparticles’ aggregation at wish for different applications. Dipolar magnetic interactions, proportional to the particle volume, are identified as the key driving force behind the formation of macroscopic aggregates for particle sizes above about 20 nm. However, aggregates’ shape and size are also strongly influenced by topological ordering. 1-D macroscopic chains of several micrometer lengths are obtained with cube-shaped magnetic nanoparticles prepared by the gas-aggregation technique. Using an analytical model and molecular dynamics simulations, the energy landscape of interacting cube-shaped magnetic nanoparticles is analysed revealing unintuitive dependence of the force acting on particles with the displacement and explaining pathways leading to their assembly into long linear chains. The mechanical behaviour and magnetic structure of the chains are studied by a combination of atomic and magnetic force measurements, and computer simulation. The results demonstrate that [111] magnetic anisotropy of the cube-shaped nanoparticles strongly influences chain assembly features.The authors acknowledge the financial support from European Commission H2020 project DAFNEOX (Grant No. 645658). I. S. and Z. K. acknowledge the support of Ministry of Education, Science, and Technological Development of Republic of Serbia – projects ON171017 and III45018. Financial support from Spanish Ministry of Economy and Competitiveness through the Severo Ochoa Programme for Centres of Excellence in R&D (SEV-2015-0496), RTI2018-099960-B-I00, and MAT2015-71664-R, co-financed by the European Regional Development Fund, is gratefully acknowledged. I.S. and C.G. acknowledge the financial support received from Proyecto CONICYT PIA/Basal FB 0821 and CONICYT MEC80170122. A.P., V.F. and Z.K. thank Senzor-INFIZ (Serbia) for the cooperation provided during their respective secondments. Numerical calculations were run on the PARADOX supercomputing facility at the Scientific Computing Laboratory of the Institute of Physics Belgrade.We acknowledge support of the publication fee by the CSIC Open Access Support Initiative through its Unit of Information Resources for Research (URICI)Peer reviewe

An ultrasensitive room-temperature H2S gas sensor based on 3D assembly of Cu2O decorated WS2 nanomaterials

Herein, we report for the first time on the fabrication of a hybrid material consisting of Cu2O nanoparticlesdecoratedmultilayeredtungstendisulfide nanostructuresand demonstrate their remarkable gas sensing characteristics towards hydrogen sulfide gas. In the first step, a continuous film of WS2 was deposited directly on commercial alumina substrate by adopting a facile route combining aerosol-assisted chemical vapor deposition with H2 free atmospheric pressure CVD technique. For functionalization an additional step of synthesis was added where copper oxide nanoparticles were grown and deposited directly over as-grown tungsten disulfide at low temperature (i.e., 150 ◦C) using a simple and cost-effective technique. The morphological, structural and chemical characteristicswere investigatedusing FESEM, TEM, and EDX spectroscopy.The gas-sensing studies performed shows that this hybrid nanomaterial has excellent sensitivity towards hydrogen sulfide (11-times increase in response compared to that of pristine WS2 sensor) at moderate temperature (150 ◦C). Additionally, functionalization of pristine WS2 sensor with Cu2O nanoparticles further enhances the gas sensing performance towards the targeted gas even at room temperature (13-times increase in response compared with that of pristine WS2 sensor). Moreover, results obtained from humidity cross-sensitivity of Cu2O-WS2 sensor indicates superior gas sensing response (with a negligible decrease in response) as compared to pristine WS2 sensor, when ambient humidity is increased to 50%, which is rarely found in metal oxide-based sensors. This study could add a significant research value in the gas sensor domain

Three-dimensional assemblies of edge-enriched WSe2 nanoflowers for selectively detecting ammonia or nitrogen dioxide

[Image: see text] Herein, we present, for the first time, a chemoresistive-type gas sensor composed of two-dimensional WSe(2), fabricated by a simple selenization of tungsten trioxide (WO(3)) nanowires at atmospheric pressure. The morphological, structural, and chemical composition investigation shows the growth of vertically oriented three-dimensional (3D) assemblies of edge-enriched WSe(2) nanoplatelets arrayed in a nanoflower shape. The gas sensing properties of flowered nanoplatelets (2H-WSe(2)) are investigated thoroughly toward specific gases (NH(3) and NO(2)) at different operating temperatures. The integration of 3D WSe(2) with unique structural arrangements resulted in exceptional gas sensing characteristics with dual selectivity toward NH(3) and NO(2) gases. Selectivity can be tuned by selecting its operating temperature (150 °C for NH(3) and 100 °C for NO(2)). For instance, the sensor has shown stable and reproducible responses (24.5%) toward 40 ppm NH(3) vapor detection with an experimental LoD < 2 ppm at moderate temperatures. The gas detecting capabilities for CO, H(2), C(6)H(6), and NO(2) were also investigated to better comprehend the selectivity of the nanoflower sensor. Sensors showed repeatable responses with high sensitivity to NO(2) molecules at a substantially lower operating temperature (100 °C) (even at room temperature) and LoD < 0.1 ppm. However, the gas sensing properties reveal high selectivity toward NH(3) gas at moderate operating temperatures. Moreover, the sensor demonstrated high resilience against ambient humidity (Rh = 50%), demonstrating its remarkable stability toward NH(3) gas detection. Considering the detection of NO(2) in a humid ambient atmosphere, there was a modest increase in the sensor response (5.5%). Furthermore, four-month long-term stability assessments were also taken toward NH(3) gas detection, and sensors showed excellent response stability. Therefore, this study highlights the practical application of the 2H variant of WSe(2) nanoflower gas sensors for NH(3) vapor detection

CVD growth of self-assembled 2D and 1D WS2 nanomaterials for the ultrasensitive detection of NO2

Herein, we report for the first time on the facile synthesis of 2D layered WS2 nanosheets assembled on 1D WS2 nanostructures by combining the aerosol assisted chemical vapor deposition (AA-CVD) method with H2-free atmospheric pressure CVD, for an ultrasensitive detection of NO2. This synthesis strategy allows us a direct integration of the sensing material onto the sensor transducer with high growth yield and uniform coverage. Two different WS2 morphologies (nanotriangles and nanoflakes) were prepared and investigated. The results show that the assembly of layered WS2 nanosheets on a 3D architecture leads to an improvement in sensing performance by maintaining a high surface area in an accessible porous network. The sensors fabricated show stable, reproducible and remarkable responses towards NO2 at ppb concentration levels. The highest sensitivity was recorded for WS2 NT sensors, with an unprecedented ultra-low detection limit under 5 ppb. Additionally, this material has demonstrated its ability to detect 800 ppb of NO2 even when operated at room temperature (25ºC). Regarding humidity cross-sensitivity, our WS2 sensors remain stable and functional for detecting NO2 at ppb levels (i.e., a moderate response decrease is observed) when ambient humidity is raised to 50 %. An 8-month long-term stability study has been conducted, which indicates that WS2-NT sensors show a very stable response to NO2 over time