Synthesis and characterization of high entropy MOFs as enhanced chemiresistive ammonia gas sensor agents

The integration of diverse metals to form high-entropy materials represents a highly effective approach for attaining superior electrochemical properties, attributed to their varied metallic compositions and elevated densities of active sites. A two high-entropy metal-organic framework (HE-MOF-1 and HE-MOF-2) comprising six metals (Mn, Co, Cu, Ni, Zn, and Fe/Zr) and 2-aminoisopthallic acid are efficiently synthesized using a mild solvothermal method. These are characterized by IR, Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM)- Energy-dispersive X-ray spectroscopy (EDX), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), and X-ray Photoelectron Spectroscopy (XPS) techniques. EDX and XPS studies confirm the presence of metals, while the metal ratio of HE-MOF-1 is Mn_5.19, Fe_5.56, Co_7.29, Ni_6.86, Cu_3.38, Zn_3.92 and HE-MOF-2 is Mn_0.023, Co_6.19, Cu_0.03, Ni_6.57, Zn_3.91, Zr_0.01, are analyzed by ICP-OES respectively. The specific surface area of HE-MOF-1 is 118.935 (m²/g) and HE-MOF-2 is 62.9 (m²/g) by Brunauer–Emmett–Teller (BET) analysis and pore size is 3.14 and 2.81 by the Barrett, Joyner, Halenda (BJH) method respectively. Gas sensing studies were performed using a two-probe static method on ammonia, ethanol, acetone, benzene, toluene, and xylene gases. Gas sensing response values of HE-MOF-1, and HE-MOF-2, are 63.4 and 45.19 respectively at 50 ppm concentration and no sensing response towards ethanol, acetone, benzene, toluene, and xylene even at 50 ppm. The shorter response times of 35 s for HE-MOF-1 and 19 s for HE-MOF-2 at lower concentrations highlight the sensor's suitability for rapid detection of low-level ammonia. Response and recovery times were determined using transient response analysis and stability with time is determined.