Resonant-Gravimetric Identification of Competitive Adsorption of Environmental Molecules.

Understanding competitive adsorption relationship among various ambient gases is important in adsorbing-material development for capturing environmentally harmful gas. For example, environmental interfering factors (e.g., moisture) can affect the competitive gas-molecule adsorption that needs to be clarified. Due to a lack of method to quantitatively study the dynamic adsorbing process (e.g., real-time-counting adsorbed molecule number), it is difficult to reveal the competitive adsorption mechanism. Still using conventional "trial-and-error" method hinders the development of high-performance adsorbing materials; thereby new technology is in high demand to address the issue. This study opens up a three-step resonant-gravimetric analysis method by using ultrasensitive resonant cantilevers. The three experimental steps are sequentially for qualitative analysis, quantitative determination, and thermodynamic-level identification about the competitive adsorption relationship among the environmental gas molecules. Previous studies indicate that the zeolitic-imidazolate framework (ZIF) of ZIF-8 nanocrystals has a low affinity to environmental CO2. This conclusion is confirmed in this study by evaluating ZIF-8 with the three experimental steps, sequentially for qualitative judgment of adsorbability, quantitative determination of hydrous molecule structure in real air, and quantitative extraction of thermodynamic enthalpy, ΔH°. By figuring out the competitive interface-adsorption relationship, we verified that ZIF-8 cannot adsorb CO2 in real air. However, for the first time, ZIF-8 is identified as an excellent adsorbent to environmental NO2.