Exceptional NH₃ Detection by Cu(cyhdc) MOF Sensor Due to H₂O Coadsorption

Area of Science:

• Materials Science
• Chemical Sensing
• Environmental Monitoring

Background:

• Metal-organic frameworks (MOFs) are increasingly used in electrical impedance sensors for detecting toxic gases.
• Detecting trace ammonia (NH3) is challenging due to its low electrical response.
• MOF selection can enhance electrical response through coadsorption with atmospheric gases like water.

Purpose of the Study:

• To demonstrate a MOF-based sensor for enhanced detection of environmentally toxic ammonia (NH3) gas.
• To investigate the role of water coadsorption in enhancing the sensor's electrical response to NH3.
• To characterize the MOF's structural integrity and adsorption mechanisms.

Main Methods:

• Fabrication and testing of a Cu(cyhdc) MOF-based electrical impedance sensor.
• Exposure of the sensor to varying concentrations of NH3 and relative humidity (RH) at different temperatures.
• Characterization using Thermogravimetric Analysis (TGA), X-ray Photoelectron Spectroscopy (XPS), Fourier-Transform Infrared Spectroscopy (FT-IR), and microstructural analysis.

Main Results:

• The Cu(cyhdc) sensor showed a significant impedance change upon exposure to 5 ppm NH3, particularly at >30% RH.
• Sensor response increased with RH, reaching a 3170× amplification at 92% RH, the highest reported for MOF direct electrical sensors.
• No response to NH3 was observed in the absence of water, and structural integrity was maintained during adsorption.

Conclusions:

• Coadsorption of NH3 and H2O on Cu(cyhdc) MOF significantly enhances electrical detection capabilities.
• The enhanced response is attributed to increased surface capacitance driven by NH3 and H2O coadsorption.
• This study demonstrates a viable strategy for enabling electrical detection of trace toxic gases using MOF sensors and coadsorption effects.