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In this paper, the development of two-dimensional metal dichalcogenide WO3-WS2 nanoplates for highly selective oxygen sensing application was reported. A facile precipitation method to produce self-assembled WO3 nanoplates and one-step solid-state synthesis of self-assembled WO3-WS2 nanoplates was described. X-ray diffraction (XRD) confirms the formation of WO3 and WO3-WS2 hybrid structure. The as-synthesized nanoplates were investigated for sensing applications of ethanol, methanol, n-butanol, LPG, and O2 gas. Study revealed that both as-synthesized WO3 and WO3-WS2 nanoplate sensors are highly selective for oxygen sensing application. Response percentage of WO3 nanoplates and WO3-WS2 nanoplates measured at 500-ppm oxygen concentration was 40% and 95% respectively. The measured response time and recovery times of WO3-WS2 nanoplate sensor was shorter than WO3 nanoplate sensor at all concentrations. The improved performance of as-synthesized WO3-WS2 nanoplates was attributed to the formation of deeper depletion layer between WS2 and WO3 p-n junction which provide additional adsorption sites for oxygen species.

CuS nanoparticles synthesized by solid-state reaction were used to remove Mordant Orange (MO), Acridine Orange (AO), and Safranin-O (SO) from water. Average diameter, band gap and surface area of CuS nanoparticles were 50 nm, 3.2 eV and 1.52 m2/g respectively. CuS nanoparticles removed 22%, 45%, 51% SO, AO, and MO in 180 min respectively. Addition of H2O2 resulted in 100% removal of dyes in 180 min in ambient light and 75% dye removal in dark. H2O2 also increased apparent reaction rate constant (Kapp). Details of dye removal mechanism by CuS nanoparticles and enhanced dye removal due to H2O2 is provided.

We report detailed ac electrical and structural characterization of manganese cobalt ferrite nanoparticles, prepared by coprecipitation technique. X-ray diffraction (XRD) confirmed single-phase cubic spinel structure of the nanoparticles. Tetrahedral (A) and octahedral (B) group complexes were present in the spinel lattice as determined by Fourier Transform Infrared Spectroscopy (FTIR). Scanning Electron Microscope (SEM) images revealed presence of spherical shape nanoparticles having an average diameter ~50–80 nm. Composition, temperature and frequency dependent ac electrical study of prepared nanoparticles interpreted the role of cationic distribution between A and B sites. Overlapping large polaron tunnelling (OLPT) conduction mechanism was observed from 290 to 200 K. Frequency exponent s was fitted theoretically using OLPT model. High values of Density of States (DOS) of the order of 1022–1024 eV−1 cm−3 were extracted from ac conductivity for different compositions. We found that DOS was dependent on distribution of cations in the tunnel-type cavities along the a and b axis.

SnS nanoflakes were synthesized using a solid state reaction method at 600 °C and their gas sensing properties were investigated. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and Transmission Electron Microscopy (TEM) analysis revealed the formation of a pure, polycrystalline, orthorhombic phase of SnS nanoflakes. The response of the SnS nanoflakes sensor to reducing gases such as acetone and alcohols (ethanol, methanol and 1-butanol) was measured from 25 °C to 200 °C. The response of the SnS nanoflakes sensor was highest for acetone (∼1000% at 100 °C). It was determined that the optimal operating temperature of the SnS nanoflakes sensor was 100 °C for acetone and 1-butanol. Fast response and recovery times of these sensors were observed for all gases. With an increase in temperature from 25 °C to 200 °C, response and recovery times of the SnS nanoflakes sensor were improved for all gases. Finally, the SnS nanoflakes sensor characteristics have been compared to the characteristics of other metal oxide/sulphide nanostructure sensors reported in previous studies. Moreover, the SnS nanoflakes sensor showed good stability and reproducibility at 100 °C for acetone. As acetone in human breath is a marker for diagnosis of diabetes, this work demonstrates a possible use of SnS nanoflakes in diabetes diagnosis.

Orthorhombic phase bismuth sulfide (Bi2S3) nanobelts were prepared via liquid-solid phase reaction method. Bi2S3 nanobelts were observed to be preferentially oriented along the (101) plane. Direct band gap (2.95 eV) and characteristic wavelength (λmax = 342 nm) were extracted through UV-visible spectroscopy. Specific surface area (9.8 m2/g) and pore size (2.5-120 nm) were evaluated through Brunauer-Emmett-Teller (BET) analysis. Relative humidity (RH) sensing properties were studied in the range of 11-97% RH at ambient conditions. The response of the sensor increases linearly with increase in RH. Fast response time (8-10 s) and recovery time (15 s) were observed. Reproducible and large response was also observed between 11 and 97% RH. Small hysteresis (

Two-dimensional pure cubic phase lead sulphide (PbS) nanosheets were synthesized using solid state reaction method at ambient pressure and low temperature ~190 °C. From 210 K–300 K, small polaron hopping conduction mechanism was found to be dominant in PbS nanosheets at frequencies 20 Hz–2 MHz. High values of dielectric constant (~200) and electrical conductivity (of the order of 10−3 S m−1 at 300 K) of PbS nanosheets were extracted suggesting that it is a proficient material for capacitive storage devices. A high value of density of states of the order of 1032 eV−1 cm−3 was obtained for PbS nanosheets. The capacitance-voltage (CV) measurements of PbS nanosheets resulted in a stable butterfly loop due to switching of ferroelectric polarization at 300 K. The permittivity calculated at 0 V capacitance was ~150 and the dielectric loss remained below ~0.50. The polarization-voltage (QV) measurements showed a remnant polarization 23 µC cm−2 in PbS nanosheets. The leakage current density was below 0.5 mA cm−2 in the range ±5 V.