Microdroplet Separation Mass Spectrometry Resolves the Charge-Dependent Interfacial Catalytic Roles of Microdroplets

Area of Science:

• Environmental Chemistry
• Analytical Chemistry
• Physical Chemistry

Background:

• Microdroplets serve as efficient microreactors, but their full potential is limited by ensemble averaging in conventional analysis.
• Understanding the distinct roles of positive and negative microdroplets is crucial for optimizing chemical processes.

Purpose of the Study:

• To develop and validate a microdroplet separation mass spectrometry method for independent analysis of mixed-charge microdroplets.
• To investigate the charge-dependent degradation efficiency of perfluorooctanoic acid (PFOA) in microdroplets.
• To elucidate the mechanisms behind polarity-dependent microdroplet reactivity and optimize degradation processes.

Main Methods:

• Development of a microdroplet separation mass spectrometry technique to analyze positively and negatively charged microdroplets separately.
• Validation of the method through combined experimental and simulation approaches.
• Application to perfluorooctanoic acid (PFOA) degradation studies, including radical trapping and density functional theory (DFT) analysis.

Main Results:

• The developed method enables online, independent analysis of positively and negatively charged microdroplets.
• Negatively charged microdroplets demonstrated superior degradation efficiency for PFOA compared to positively charged ones.
• Negative interfacial charge stabilizes transition states, facilitating hydroxyl radical (•OH)-driven degradation, a phenomenon observed across various perfluorinated compounds.
• Optimizing the microenvironment through voltage modulation and Fenton's reagent increased PFOA degradation from 38% to 83%.

Conclusions:

• The separation-MS method reliably resolves mixed-charge microdroplet behaviors, offering new insights into interfacial chemistry.
• Charge plays a critical role in microdroplet reactivity, enabling targeted optimization of degradation processes.
• This approach provides a pathway for understanding and enhancing charge-regulated interfacial chemistry in microreactor systems.