Sulfate-functionalized hafnium-organic frameworks as a highly effective chemiresistive sensor for low-temperature detection of hazardous NH3 gas

This study proposes a solvothermal method for synthesizing sulfate-functionalized hafnium-organic frameworks (Hf-BTC-SO4) for application in low-temperature NH3 gas sensors. Prior to the gas-sensing studies, solvothermal-processed Hf-BTC-SO4 is characterized using various techniques to obtain structural, elemental, morphological, and thermal stability information. Results of structural and thermal-stability analysis demonstrate that Hf-BTC-SO4 exhibits good crystallinity and high thermal stability with the functionalization of SO4 in the Hf-framework. Microstructural analysis reveals that nanoparticles aggregated to form compact clusters of Hf-BTC-SO4. In addition, Hf-BTC-SO4 has an ultra-high specific surface area of 1100 m2g−1 (with a pore size of 15 Å), suitable for gas detection owing to enhanced surface reactions. Gas-sensing studies confirm that the fabricated Hf-BTC-SO4 sensor exhibits selective detection of NH3 gas at a lower working temperature of 100 ºC. Notably, the Hf-BTC-SO4 sensor detected up to 1 ppm of NH3 (response = 1.41), with excellent response reversibility. The functionalized sulfate bonds and Hf-clusters within the framework form strong bonds with NH3, enhancing their interaction with the metal-organic frameworks. This study can motivate future research on the synthesis of functional organic frameworks for applications in low-temperature NH3 detection devices.