Methyl functionalization of trimesic acid in copper-based metal-organic framework for ammonia colorimetric sensing at high relative humidity

Exhaled ammonia(NH_(3))can be used as a crucial biomarker of kidney and liver diseases.However,the high humidity in the detection conditions remains a challenge for accurate detection by gas sensors.Herein,a copper-based metal-organic framework(CH_(3)-Cu-BTC)with methyl(CH_(3)^(-))functionalization of trimesic acid was synthesized for NH_(3) colorimetric sensing.The CH_(3)-Cu-BTC exhibited a strong response for 5 ppm NH_(3) with high selectivity under high relative humidity(75%RH).Density functional theory(DFT)simulations indicated that the NH_(3) molecules interacted more strongly with CH_(3)-Cu-BTC than H_(2)O molecules did,and the corresponding color switching was attributed to the lone-pair electron in NH_(3) changing the coordination environment of Cu^(2+)ions,leading to an obviously visible color switching response from ruby green to blue.Based on the tailor-made pore chemistry,the precise detection of trace amounts of NH_(3) in exhaled air was realized through functionalized MOF materials.The strategy used in this study not only offers a new pathway for the rapid detection of low concentration NH_(3) under humid conditions,but also shows a method for early respiration diagnosis of kidney and liver diseases.