Abstract:
Water is one of the most familiar materials known to humankind. The common perception is that scientists know everything about water. As practitioners of water science and technology, we know there are plenty of questions to be answered. Whenever a new feature/property of water is discovered, our understanding of environmental processes deepens, and textbooks get updated. Recently, it has been claimed that water spontaneously transforms to hydrogen peroxide (H2O2) at the air–water interface of microdroplets (formed via condensation or spraying) without the application of an electric field, energy, or catalyst. This chemical transformation is speculated to be driven by ultrahigh electric fields at the air–water interface. Wide-ranging implications of this water–peroxide coupling on cloud chemistry, seasonality of diseases, the origin of life, and green chemistry have been noted. How water’s covalent bond could break at room temperature and 1 atm pressure in microdroplets challenges our understanding of water science and physical chemistry, in general. In response, we undertook a comprehensive (1.5 years-long) experimental investigation of H2O2 formation in (i) water microdroplets sprayed over a range of liquid flow rates, the (shearing) airflow rates, and the air composition; and (ii) water microdroplets condensed on hydrophobic substrates formed via hot water or humidifier under controlled air composition. In this lecture, I will disentangle the contributions of water, its surface or “skin”, high interfacial electrical fields, experiment-specific conditions such as shockwaves and cavitation, and airborne contaminants on the spontaneous chemical transformation of H2O to H2O2. (For popular science media coverage on this story: https://cen.acs.org/research-integrity/reproducibility/Claims-water-turning-hydrogen-peroxide/100/web/2022/05)
About the Speaker:
Himanshu Mishra is an Associate Professor of Environmental Science and Engineering at KAUST and serves as a Principal Investigator and an Associate faculty member at the Water Desalination and Reuse Center and the Center for Desert Agriculture, respectively. Mishra’s research group develops and applies experimental methods to investigate wetting, surface forces, chemical reactions, and heat and mass transfer at aqueous interfaces. Fundamental insights are then translated into sustainable technologies such as for global food–water–climate security such as SandX and CarboSoil. Mishra has co-authored over 43 peer-reviewed articles and holds twelve granted/pending patents. He also serves as the Chief Scientific Officer at TerraXY Inc., a spin-out from his laboratory.