Silica-Driven CO2 Reduction in Water Microdroplets.

Abstract

Carbon dioxide (CO2), the most notorious greenhouse gas responsible for global warming and ocean acidification, could persist in the atmosphere for 50 to 200 years, posing substantial long-term environmental challenges. However, its environmental fate remains not fully clear. This study reveals a previously unrecognized silica-driven CO2 reduction pathway in ubiquitous water microdroplets, enabling the efficient conversion of CO2 primarily into formic acid, along with other C1 and C2 products such as methanol, acetic acid, and ethanol, under ambient conditions. Notably, the reaction proceeds at a rate of 3.24 mmol g-1 h-1, exceeding those reported for microdroplet systems utilizing amine absorbents or metal catalysts. Bonn-Oppenheimer molecular dynamics simulations further reveal that at the gas-water interface, a hydrated electron (H2O·-) reduces CO2 to a CO2·- radical anion, which subsequently abstracts a hydrogen atom from Si-OH sites on SiO2 nanoparticles, yielding HCOO- as the primary product. Simultaneously, SiO2 nanoparticles undergo partial disintegration, exposing fresh surfaces and generating additional Si-OH sites, thereby continuously promoting CO2 conversion. These findings provide critical insights into climate evolution mechanisms, the chemical processes underlying acid rain and aerosol formation, and the advancement of efficient CO2 utilization strategies.