Controllable Preparation Of M (Mg / Ni) - Al-LDHs And Study On NO_x Gas Sensitivity

To solve the problems of low sensitivity, poor selectivity and high cost of NO_x semiconductor sensor at room temperature, the layered double hydroxide(LDHs) is prepared using magnesium nitrate, nickel nitrate, aluminum nitrate as raw materials. NO_x gas-sensing properties are improved by optimizing the structure.M(Mg/Ni)-Al–LDHs have been synthesized via a simple, using sodium dodecyl sulfate(SDS) as template agent and inserted anion to control the sample morphology and layer spacing First, the influence of the reaction time, reaction temperature, concentration of SDS, Mg/Al molar ratio and the concentration of urea on the composition and morphology of Mg-Al–LDHs samples are studied. Secondly, the gas-sensing properties are tested. The results show that the sample with higher specific surface area and larger interlamellar spacing can only be prepared under certain conditions. The response of the best Mg-Al–LDHs to 100 ppm NO_x can reach 76% and the response time is only 1.3s at room-temperature and low detection limit of 1 ppm. Moreover, the sensor also exhibits excellent selectivity, stability, and repeatability.3D hierarchical Ni-Al–LDHs is synthesized using SDS as template. And, the influence of morphologic change on the gas-sensing properties of Ni-Al–LDHs is also studied. Comparing with Ni-Al–LDHs without hierarchical structure, it is found that Ni-Al–LDHs with hierarchical structure has a larger specific surface area and layer spacing. The test results show that the gas-sensing properties of Ni-Al–LDHs with hierarchical structure are obviously better than that one without hierarchical structure. The response of Ni-Al–LDHs with hierarchical structure to 100 ppm NO_x can reach 61.2% and the response time is 3.0s at room-temperature. The minimum detection limit can reach 1 ppm. Moreover, the sensor also exhibits excellent selectivity.In conclusion, 3D hierarchical Mg-Al–LDHs and Ni-Al–LDHs gas sensors work well at room temperature, which shows that this kind of sensitive material has potential applications in the field of gas sensor, especially for harmful and toxic NO_x.