Formation of hydrogen peroxide in water microdropletApply
Recent reports on the formation of hydrogen peroxide (H2O2) in water microdroplets produced via pneumatic spraying  or capillary condensation  have garnered significant attention. How covalent bonds in water could break under such mild conditions challenges our textbook understanding of physical chemistry and the water substance. While there is no definitive answer, it has been speculated that ultrahigh electric fields at the air-water interface are responsible for this chemical transformation. We are carrying out a comprehensive experimental investigation of H2O2 formation in (i) water microdroplets sprayed over a range of liquid flow-rates, the (shearing) air flow rates, and the air composition (ii) water microdroplets condensed on hydrophobic substrates formed via hot water or humidifier under controlled air composition. Our experimental results have challenged the putative claims of spontaneous H2O2 generation on the water surface [3, 4]. Additionally, new scientific questions along this theme have emerged that the VSRP intern will contribute to. References: 1. Lee, J. K.; Walker, K. L.; Han, H. S.; Kang, J.; Prinz, F. B.; Waymouth, R. M.; Nam, H. G.; Zare, R. N., Spontaneous generation of hydrogen peroxide from aqueous microdroplets. P Natl Acad Sci USA 2019, 116 (39), 19294-19298. 2. Lee, J. K.; Han, H. S.; Chaikasetsin, S.; Marron, D. P.; Waymouth, R. M.; Prinz, F. B.; Zare, R. N., Condensing water vapor to droplets generates hydrogen peroxide. P Natl Acad Sci USA 2020, 117 (49), 30934-30941. 3. Gallo Jr, A.; Musskopf, N. H.; Liu, X.; Yang, Z.; Petry, J.; Zhang, P.; Thoroddsen, S.; Im, H.; Mishra, H., On the formation of hydrogen peroxide in water microdroplets. Chemical Science 2022, 13 (9), 2574-2583. 4. Musskopf, N. H.; Gallo, A.; Zhang, P.; Petry, J.; Mishra, H., The Air–Water Interface of Water Microdroplets Formed by Ultrasonication or Condensation Does Not Produce H2O2. The Journal of Physical Chemistry Letters 2021, 12 (46), 11422-11429.
Program - Environmental Science and Engineering
Division - Biological and Environmental Sciences and Engineering
Faculty Lab Link - https://www.kaust.edu.sa/en/study/faculty/himanshu-mishra
Center Affiliation - Water Desalination and Reuse Center
Field of Study - Physical Chemistry, Electrochemistry, Analytical Chemistry, Microfluidics, high-speed imaging, chemical kinetics
Desired Project Deliverables
• The intern will conduct a comprehensive experimental investigation of H2O2 formation in (i) water microdroplets sprayed over a range of liquid flow-rates, the (shearing) air flow rates, and the air composition (ii) water microdroplets condensed on hydrophobic substrates formed via hot water or humidifier under controlled air composition. This will also entail a comparative assessment of the various H2O2 detection kits/assays available. • Glovebox experiments will be deployed to quantify H2O2 formation in water microdroplets as a function of the air-borne ozone (O3) concentration. • Effects of atmospherically relevant O3(g) concentrations (10–100 ppb) on the formation of H2O2(aq) will be evaluated. • Effects of the gas–liquid surface area, mixing, and contact duration will be quantified.