ZnO@ZIF-8 Core-Shell Structure Gas Sensors with Excellent Selectivity to H2

Abstract

As the energy crisis becomes worse, hydrogen as a clean energy source is more and more widely used in industrial production and people’s daily life. However, there are hidden dangers in hydrogen storage and transportation, because of its flammable and explosive features. Gas detection is the key to solving this problem. High quality sensors with more practical and commercial value must be able to accurately detect target gases in the environment. Emerging porous metal-organic framework (MOF) materials can effectively improve the selectivity of sensors as a result of high surface area and coordinated pore structure. The application of MOFs for surface modification to improve the selectivity and sensitivity of metal oxides sensors to hydrogen has been widely investigated. However, the influence of MOF modified film thickness on the selectivity of hydrogen sensors is seldom studied. Moreover, the mechanism of the selectivity improvement of the sensors with MOF modified film is still unclear. In this paper, we prepared nano-sized ZnO particles by a homogeneous precipitation method. ZnO nanoparticle (NP) gas sensors were prepared by screen printing technology. Then a dense ZIF-8 film was grown on the surface of the gas sensor by hydrothermal synthesis. The morphology, the composition of the elements and the characters of the product were analyzed by X-ray diffraction analysis (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), Brunauer-Emmett-Teller (BET) and differential scanning calorimetry (DSC). It is found that the ZIF-8 film grown for 4 h cannot form a dense core-shell structure. The thickness of ZIF-8 reaches 130 nm at 20 h. Through the detection and analysis of hydrogen (1000 ppm), ethanol (100 ppm) and acetone (50 ppm) from 150 °C to 290 °C, it is found that the response of the ZnO@ZIF-8 sensors to hydrogen has been significantly improved, while the response to ethanol and acetone was decreased. By comparing the change of the response coefficient, when the thickness of ZIF-8 is 130 nm, the gas sensor has a significantly improved selectivity to hydrogen at 230 °C. The continuous increase of the thickness tends to inhibit selectivity. The mechanism of selectivity improvement of the sensors with different thickness of the ZIF-8 films is discussed.

Three-Dimensional Printing of Poly-L-Lactic Acid Composite Scaffolds with Enhanced Bioactivity and Controllable Zn Ion Release Capability by Coupling with Carbon-ZnO

“…The XRD results are shown in Figure 2 d to characterize the phase structure of the samples. It can clearly be seen that the XRD patterns of ZnO and ZIF-8 were consistent with the standard cards [ 42 ], indicating a successful synthesis of the samples. After the carbonization of ZIF-8, the disappearance of the ZIF-8 peaks in the C–ZnO samples suggest a destroyed crystal structure of ZIF-8.…”

Gas Sensing Technology for the Detection and Early Warning of Battery Thermal Runaway: A Review

“…Metal organic frameworks (MOFs), as typical coordination polymers developing rapidly in recent years, exhibit plenty of advantages when used in CO or CO 2 gas sensors, such as special three-dimensional structure, high porosity, low density, large specific surface area, etc. ,− MOFs with unique gas adsorption and separation characteristics can be utilized as a high-performance membrane-sensing material. The limitation effect of MOF membrane can selectively adsorb some gas molecules with small kinetic diameter (e.g., CO or CO 2 ) to thus improve the selectivity of the prepared gas sensors.…”

Surface Conversion of ZnO Tetrapods Produces Pinhole-Free ZIF-8 Layers for Selective and Sensitive H2 Sensing Even in Pure Methane

“…22,23 For example, it has been reported that the ZIF-8 shell leads to a better selectivity to H 2 and a decreasing response toward ethanol and acetone. 19 The combination of ZnO and ZIF-8 for sensing applications has been thoroughly investigated, and a summary of the results is given in Table S1. 8,16,17,19,20,24−27 Important performance parameters are the operation temperature, morphology, and particle size of ZnO, the coating thickness of ZIF-8, and the architecture of the composite, which mutually influence each other.…”

“…18 However, almost all the developed sensors shown in Table S1 respond also to other gases such as CH 4 , CO, and other hydrocarbons, which makes them unsuitable for applications in gas mixtures. Comparing the results of the studies using ZnO nanoparticles 19 with that on micro-and nanorods, 8,[16][17][18]20 it can be assumed that ZnO− MOF−ZnO conjunctions hinder the conductivity of the ZnO semiconductor because the MOF acts as an insulator. Further improvement of the performance could be possible by using single-crystalline low-defect ZnO microrods or tetrapods, adjustment of the layer thickness, and the prevention of textural porosity of the ZIF-8 layer by uneven coating or microcracks.…”