In-situ chemical conversion approach for growth of magnesium-aluminium-layered double hydroxide thin films: Room temperature NO₂ sensing

The direct deposition of layered double hydroxide on a substrate is highly desirable for a gas sensor. In this work, we demonstrate the direct deposition of magnesium-aluminum-layered double hydroxide (MA-LDH) thin film (TF) by chemical conversion of magnesium oxide (MgO) TF. The chemical conversion of MgO TFs produces well-crystalline, porous microsheets composed of an interconnected nanoparticle network of MA-LDH, which provides an enhanced surface area with a highly accessible framework, making MA-LDH TFs promising candidates for efficient gas sensor electrodes. Furthermore, the resulting MA-LDH TFs are tested as resistive sensor electrodes to detect different oxidizing (SO₂, Cl₂, and NO₂) and reducing (LPG, CO, CO₂, H₂, H₂S, and NH₃) gases. The MA-LDH TF exhibited excellent selectivity towards NO₂ gas with a maximum response of 54 % at room temperature (300 ± 2 K) compared to pristine MgO TFs (14 %) at 473 K for 100 ppm. Also, it exhibits a quick response time of 10 s, a detection limit of 0.02 ppm, and prolonged stability. Of prime interest is that the MA-LDH sensor displayed high tolerance to humidity conditions. The excellent NO₂ sensing performance of the MA-LDH TFs is attributed to the expanded surface area, which is composed of porous microsheets formed by interconnected nanoparticles network. The direct deposition of an interconnected microsheet network provides abundant active adsorption sites, thereby enhancing gas sensing efficiency.