Manganese doped two-dimensional zinc ferrite thin films as chemiresistive trimethylamine gas sensors

Trimethylamine (TMA) is highly toxic and can have lethal effects on living organisms. Detecting the presence of TMA in air is very important because, if the TMA level exceeds the OSHA (Occupational Safety and Health Administration) limit, it may harm the environment and endanger human life. Doping is an appropriate flexible way to change the electrical structures of metal oxide semiconductors (MOSs) and improve their ability to detect toxic gases. In this work, Mn-doped zinc ferrite thin film nanorods with agglomerated morphology were fabricated by a spray pyrolysis technique. For the first time, a comprehensive investigation was done on the gas sensing capabilities of Mn-doped ZnFe2O4 thin films. The findings showed that ZFM1 had the best gas sensing characteristics, with high sensitivity (S = 6.24), good selectivity, and quick recovery, towards 10 ppm TMA at ambient temperature. The alternate Mn-ZF sites are responsible for the rapid recovery because they can significantly increase the concentration of oxygen vacancies in the ZF crystal. 0.1 Mn doped ZnFe2O4 (ZFM1) thin film exhibits greatly enhanced gas sensing properties towards TMA, because of its high surface-to-volume ratio and rough surface with a small nanorod structure. The sensor's response to 10 ppm TMA was measured 13 weeks later for stability testing. The stability test results show that the coated ZFM1 film works well as a TMA gas sensor. This work shows that ZF thin films are effective in detecting TMA in the atmosphere.

pH Controlled Nanostructure and Optical Properties of ZnO and Al-Doped ZnO Nanorod Arrays Grown by Microwave-Assisted Hydrothermal Method

The low-temperature microwave-assisted hydrothermal method was used to successfully grow pure and Al-doped ZnO (AZO) nanorod (NR) arrays on glass substrates. The combined effects of doping and pH on the structural properties, surface chemistry, and optical properties of all samples were investigated. Thermodynamic-based simulations of the growth solution were performed and a growth mechanism, that considers the effects of both the pH and Al-doping, is proposed, and discussed. Tuning the solution pH is key parameter to grow well-aligned, single crystal, highly packed, and high aspect ratio nanorod arrays. Moreover, the optical absorption in the visible range is enhanced by controlling the pH value. The PL spectra reveal a shift of the main radiative emission from the band-to-band into a transition involving deep defect levels of Zinc interstitial Zni. This shift is caused by an enhancement of the non-radiative components (phonon relaxation) at high pH values. The production of well-ordered ZnO and AZO nanorod arrays with visible-active absorption/emission centers would increase their potential use in various applications.

Direct and catalyst-free synthesis of ZnO nanowires on brass by thermal oxidation

In this research work, nanowires were grown on brass (Cu - 37.2 wt% Zn) substrate by thermal oxidation. The substrate was oxidized at temperatures ranging from 350 °C to 600 °C in the presence of varying concentrations of O₂ (1%-100%) in N₂ flown at a rate of 200 sccm. The oxidized brass surface was characterized by field emission scanning electron microscope equipped with energy dispersive x-ray spectroscope and transmission electron microscope. Four different types of morphological variations such as thin, thick with branches, circular-flake and flat-cone shape nanostructures were observed during oxidation at different conditions. However, the prevalence of thin and thick morphology with branches was more prominent and found in all growth conditions. The length and diameter of the nanowires varied from 1 to 30 μm and 50 to 500 nm, respectively, whereas the length of the branches varied from 1 to 3 μm. The composition of the nanowires was ZnO possessing of hexagonal wurtzite structure. The selected area diffraction confirms that the nanowires grew along 〈1 1 [Formula: see text] 0〉 directions. Based on the results, a stress induced mechanism is proposed for the growth of ZnO nanowires on Cu - 37.2 wt% Zn substrate.

Enhanced Gas-Sensing Properties for Trimethylamine at Low Temperature Based on MoO3/Bi2Mo3O12 Hollow Microspheres

Most reported trimethylamine (TMA) sensors have to operate at high temperature, which will consume energy highly. To detect TMA at low temperature, it is necessary to modify the existing materials or develop new materials. In this paper, the sensor based on MoO₃/Bi₂Mo₃O₁₂ hollow microspheres can work at low operating temperature of 170 °C, which were prepared via a simple solvothermal route. The phase and morphology of the product were characterized by an X-ray diffraction meter, a scanning electron microscope and a transmission electron microscope. The surface chemistry of the MoO₃/Bi₂Mo₃O₁₂ sensor was studied with an X-ray photoelectron spectroscope to investigate the TMA sensing mechanism. The MoO₃/Bi₂Mo₃O₁₂ sensor ( S = 25.8) had a higher response to 50 ppm TMA than those of MoO₃ hollow spheres ( S = 10.8) and Bi₂Mo₃O₁₂ sensors ( S = 4.8) at 170 °C. In contrast to the pure MoO₃ and Bi₂Mo₃O₁₂ sensors, the MoO₃/Bi₂Mo₃O₁₂ sensor exhibited an obviously enhanced gas-sensing property for TMA, which might be due to the heterostructure formed between MoO₃ and Bi₂Mo₃O₁₂ and the hollow morphology. It is the first time for MoO₃/Bi₂Mo₃O₁₂ to apply in gas sensors, which might take an important step in the application of MoO₃/Bi₂Mo₃O₁₂ or Bi₂Mo₃O₁₂ in the field of gas sensing.