The Air-Water Interface of Water Microdroplets Formed by Ultrasonication or Condensation Does Not Produce HO.

J Phys Chem Lett

Interfacial Lab (iLab), King Abdullah University of Science and Technology (KAUST), Biological and Environmental Science and Engineering (BESE) Division, Water Desalination and Reuse Center (WDRC), Thuwal 23955-6900, Saudi Arabia.

Published: November 2021

Recent reports on the production of hydrogen peroxide (HO) on the surface of condensed water microdroplets without the addition of catalysts or additives have sparked significant interest. The underlying mechanism is thought to be ultrahigh electric fields at the air-water interface; smaller droplets present larger interfacial areas and produce higher (detectable) HO yields. To gain insights into this phenomenon, we performed condensation experiments and quantified HO formation as a function of the vapor source. Specifically, we compared the HO concentration in water microdroplets condensed from the vapor realized via (i) heating water in the range of 50-70 °C and (ii) ultrasonic humidification (as exploited in the original report). Experimental results revealed that the HO level inside water microdroplets condensed via heating water was below our detection limit (≥0.25 μM), regardless of the droplet size or the substrate wettability. In contrast, water droplets condensed via ultrasonic humidification contained significantly higher (∼1 μM) HO concentrations. We conclude that the ultrasonic humidifiers contribute to HO production, not droplet interfacial effects.

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http://dx.doi.org/10.1021/acs.jpclett.1c02953DOI Listing

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