Xianfa Zhang

Ionic liquid-assisted synthesis of α-Fe2O3 mesoporous nanorod arrays and their excellent trimethylamine gas-sensing properties for monitoring fish freshness

Large-scale and well-aligned α-Fe2O3 mesoporous nanorod arrays in situ deposited on ceramic tubes have been successfully synthesized by an ionic liquid (IL)-assisted hydrothermal reaction followed by calcination. The mesoporous sizes of the nanorods can be adjusted by changing the calcination temperature. Such an in situ assembled α-Fe2O3 mesoporous nanorod array sensor exhibited not only high sensitivity, short recovery time and good reproducibility to trimethylamine (TMA), but also a good linear relationship in a ppm level concentration range (0.1–100 ppm). Furthermore, the sensor was evaluated for a fast analysis of the primary volatiles of Carassius auratus (0–11 h) which have been analyzed using headspace solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS). Such α-Fe2O3 mesoporous nanorod arrays showed considerable potential in the identification of fish freshness. The superior gas-sensing properties of the obtained nanostructures should be attributed to the uniform mesoporous structure in the ordered nanorod arrays with a large specific surface area, as well as an appropriate amount of residual functionalized ILs, which help the TMA molecules to diffuse and adsorb onto the array surface and assist electron transfer. The formation mechanism of the mesoporous nanorod arrays was also discussed in detail.

High efficient and selective removal of Pb2+ through formation of lead molybdate on α-MoO3 porous nanosheets array

2D hand-like structured α-MoO3 porous nanosheets were grown in-situ onto a capillary by a simple hydrothermal route, on which titanium dioxide seed layer was sol-dip-coated in advance. The α-MoO3 porous nanosheets array exhibits an exceptional lead ion uptake capacity up to 1450.0mg·g-1, and can effectively reduce Pb2+ concentration from 20mg·L-1 to a low level of smaller than 3μg·L-1, well below the acceptable limits in drinking water standards (10μg·L-1) and can efficiently remove 99.9% lead ion within a few minutes at room temperature. Furthermore, α-MoO3 porous nanosheets array also has high selectivity toward Pb2+ better than Cu2+, Zn2+, Cr3+ and Cd2+. The mechanism for adsorption was discussed according to the results of Zeta potential, IR, XPS and XRD analyses. The excellent removal performance of the array to Pb2+ is resulted from the electrostatic adsorption interaction and the formation of new species lead molybdate.

Enhanced H2S Gas-Sensing Performance of Zn2SnO4 Lamellar Micro-Spheres

With the rapid development of industry, the discharge of sulfide gas has been increasing in recent decades, which results in severe air pollution. H2S, as the typical representation of sulfide, is a harmful and toxic acidic gas and widely used in various industries. Even at low concentrations, it can cause hypoxia and seriously threatens the safety of human. When the concentration reaches 1 mg/L (659 ppm) or higher, inflammation or death will occur. According to the U. S. Scientific Advisory Board on Toxic Air Pollutants, the acceptable concentration of H2S in the environment is less than 83 ppb (North Carolina Department of Environment and Natural Resources, 20031). Therefore, it is necessary to fabricate gas sensors which can detect ppb-level H2S in time to reduce the environmental pollution and harm to human. Zinc stannate (Zn2SnO4) is a typical n-type ternary semiconductor, and has been employed as important multifunctional material in the fields of photocatalytic activity (Das et al., 2017), solar cells (Li et al., 2015), lithium ion batteries (Lim et al., 2016), and so forth. Especially, owing to the excellent gas-sensing performance of ZnO and SnO2 (Sukunta et al., 2017; Zhu and Zeng, 2017; Zhu et al., 2018), the application of Zn2SnO4 in the field of gas sensors has attracted extensive attention (An et al., 2015; Zhao et al., 2016; Yang et al., 2017). Up to now, only one case has concerned on the detection of H2S with Zn2SnO4 hollow octahedron (Ma et al., 2012), which showed the response to H2S with the detection limit being 1 ppm at 260 C. Meanwhile, such reported Zn2SnO4 sensor presents poor selectivity. Apparently, the sensor cannot satisfy the need of practical application for the detection of ppb-level H2S, especially in a complex environment involving other interfering gases due to its poor selectivity and higher working temperature. In view of the fact that gas-sensing performance of materials is highly dependent on their micro-structure and surface state (Yu et al., 2017; Zhang et al., 2018), therefore, it would be a meaningful work to prepare Zn2SnO4 with novel morphology to further decrease the working temperature and improve the selectivity and stability, thus performing the detection of ppb-level H2S. In this work, Zn2SnO4 lamellar micro-spheres have been synthesized by a facile ethylenediamine-assisted hydrothermal method followed by calcining at 600C. The diameter of micro-spheres is ∼1μm and they are composed of nanosheets with thickness of ∼85 nm. The sensor fabricated from the micro-spheres shows good response and selectivity to H2S at 170 C, and the lowest detection limit is down to 50 ppb. Moreover, it shows good linear relationship in the range of ppb (50–1000 ppb) and ppm (3–50 ppm) level. Meanwhile, the gas-sensing mechanism is also investigated.

Enhanced H2S gas-sensing performance of Zn2SnO4 hierarchical quasi-microspheres constructed from nanosheets and octahedra

Most of the reported ternary oxides based sensors have not been realized to detect ppb-level H2S till now. In this work, Zn2SnO4 hierarchical quasi-microspheres were prepared through a facile surfactant-free hydrothermal method followed by calcination in air atmosphere. The quasi-microspheres are composed of nanosheets with the thickness of 100 nm and octahedra with the average size of 0.63 μm, respectively. The sensor fabricated from such Zn2SnO4 hierarchical quasi-microspheres shows excellent selective response to H2S at 133 °C with the lowest detection limit of 1 ppb. The gas response exhibits good linear relationship in the concentration range of 1-1000 ppb. Such outstanding H2S sensing property might be attributed to its porous structure, the synergistic effect of the two typical building blocks and the surface adsorbed oxygen, and the possible sensing mechanism is also discussed.