Vertical heterostructure of graphite-MoS2 for gas sensing.

2D materials, given their form-factor, high surface-to-volume ratio, and chemical functionality have immense use in sensor design. Engineering 2D heterostructures can result in robust combinations of desirable properties but sensor design methodologies require careful considerations about material properties and orientation to maximize sensor response. This study introduces a sensor approach that combines the excellent electrical transport and transduction properties of graphite film with chemical reactivity derived from the edge sites of semiconducting molybdenum disulfide (MoS2) through a two-step chemical vapour deposition method. The resulting vertical heterostructure shows potential for high-performance hybrid chemiresistors for gas sensing. This architecture offers active sensing edge sites across the MoS2 flakes. We detail the growth of vertically oriented MoS2 over a nanoscale graphite film (NGF) cross-section, enhancing the adsorption of analytes such as NO2, NH3, and water vapor. Raman spectroscopy, density functional theory calculations and scanning probe methods elucidate the influence of chemical doping by distinguishing the role of MoS2 edge sites relative to the basal plane. High-resolution imaging techniques confirm the controlled growth of highly crystalline hybrid structures. The MoS2/NGF hybrid structure exhibits exceptional chemiresistive responses at both room and elevated temperatures compared to bare graphitic layers. Quantitative analysis reveals that the sensitivity of this hybrid sensor surpasses other 2D material hybrids, particularly in parts per billion concentrations.

Physical and photocatalytic properties of sprayed Dy doped ZnO thin films under sunlight irradiation for degrading methylene blue.

Dysprosium-doped zinc oxide (ZnO) thin films have been prepared through spray pyrolysis onto glass substrates. Cross-sections of the deposited thin films were assessed through Scanning Electron Microscopy (SEM), showing thicknesses between 200 and 300 nm. The thin film roughness was evaluated using the obtained images from the Atomic Force Microscope (AFM) micrographs. The crystallographic structure of the samples was analyzed by X-ray diffraction (XRD) revealing polycrystalline thin films. However, the slight shift towards a higher 2θ angle in Dy-doped ZnO films as compared to the pure ones indicates the incorporation of Dy3+ into the ZnO crystal lattice. The analysis of the oxidation state via X-ray photoelectron spectroscopy (XPS) confirms the incorporation of Dy ions in the ZnO matrix. Besides, UV-Vis-NIR spectrophotometry analysis and photoluminescence (PL) spectroscopy showed that bandgap energy values of ZnO decreased when dysprosium doping increased. Therefore, Dy doped ZnO thin films can be potentially used as a solar-light-driven photocatalyst. Among the different doping yields, the ZnO doped with 6% dysprosium provides the highest degradation rate for methylene blue (MB) under solar irradiation. Specifically, 9% of dye degradation was achieved under sunlight irradiation for 120 minutes.

New optical paper sensor for in situ measurement of hydrogen sulphide in waters and atmospheres.

A novel and low-cost colorimetric sensor for the determination of hydrogen sulphide in environmental samples has been developed. This sensor is based on the immobilization of the reagent N,N-Dimethyl-p-phenylenediamine and FeCl3 in paper support, in which the H2S is adsorbed in order to give rise to the formation of methylene blue as reaction product. The sensor has been applied to determine H2S in water and air samples. Two different sampling systems for H2S caption from the air have been assayed: active and passive sampling. The analytical properties of the different systems have been obtained and compared. The analytical signals, corresponding to the methylene blue, have been obtained measuring the absorbance by conventional reflectance diffuse or using different algorithms for quantifying color intensity. The results obtained with both measurement procedures were comparable, with a detection limit of 1.11 and 1.12mLm(-3) for air samples (active and passive), and 0.5mgL(-1) for water samples. The developed sensor provides good accuracy and precision (RSD<12%) and simplifies significantly the analytical measurements because it avoids the need of preparing derivatization reagents, sample handling and allows in situ measurements. The reaction product obtained is highly stable in this support and no provide any blank signal. Under the optimal conditions, the proposed method exhibit excellent visual sensitivity for the naked eye procedure, making the detection of H2S possible.