Effect of surfactant lengths on gas-liquid oxygen mass transfer from a single rising bubble

Hierarchical ion interactions in the direct air capture of CO2 at air/aqueous interfaces

The direct air capture (DAC) of CO2 using aqueous solvents is plagued by slow kinetics and interfacial barriers that limit effectiveness in combating climate change. Functionalizing air/aqueous surfaces with charged amphiphiles shows promise in accelerating DAC; however, insight into these interfaces and how they evolve in time remains poorly understood. Specifically, competitive ion interactions between DAC reagents and reaction products feedback onto the interfacial structure, thereby modulating interfacial chemical composition and overall function. In this work, we probe the role of glycine amino acid anions (Gly-), an effective CO2 capture reagent, that promotes the organization of cationic oligomers at air/aqueous interfaces. These surfaces are probed with vibrational sum frequency generation spectroscopy and molecular dynamics simulations. Our findings demonstrate that the competition for surface sites between Gly- and captured carbonaceous anions (HCO3-, CO32-, carbamates) drives changes in surface hydration, which in turn tunes oligomer ordering. This phenomenon is related to a hierarchical ordering of anions at the surface that are electrostatically attracted to the surface and their ability to compete for interfacial water. These results point to new ways to tune interfaces for DAC via stratification of ions based on relative surface propensities and specific ion effects.

Synergistic Assembly of Charged Oligomers and Amino Acids at the Air-Water Interface: An Avenue toward Surface-Directed CO2 Capture

Interfaces are considered a major bottleneck in the capture of CO2 from air. Efforts to design surfaces to enhance CO2 capture probabilities are challenging due to the remarkably poor understanding of chemistry and self-assembly taking place at these interfaces. Here, we leverage surface-specific vibrational spectroscopy, Langmuir trough techniques, and simulations to mechanistically elucidate how cationic oligomers can drive surface localization of amino acids (AAs) that serve as CO2 capture agents speeding up the apparent rate of absorption. We demonstrate how tuning these interfaces provides a means to facilitate CO2 capture chemistry to occur at the interface, while lowering surface tension and improving transport/reaction probabilities. We show that in the presence of interfacial AA-rich aggregates, one can improve capture probabilities vs that of a bare interface, which holds promise in addressing climate change through the removal of CO2 via tailored interfaces and associated chemistries.

Mercury removal from flue gas by a MoS2/H2O heterogeneous system based on its absorption kinetics

An enhanced MoS₂/C₁₀TAB/H₂O system was built and investigated for Hg⁰ removal based on strengthening the Hg⁰ gas-liquid mass transfer. The results showed that adding 7 mg/L C₁₀TAB can improve the Hg⁰ removal efficiency from 76.5 to 88.7% as decrease of the solution surface tension. Keeping 2000 rpm of stirring rate accelerated the renewal rate of gas-liquid interface, thereby enhancing Hg⁰ removal. SO₂ slightly promoted the Hg⁰ removal efficiency to 91% because of the absorption of SO₂ causing a decrease in the solution pH from 6.9 to 4.3. NO participated in Hg⁰ removal reactions but not removed in this system which visibly enhanced the Hg⁰ removal efficiency to 94%. The Hg mass transfer kinetics were analyzed to determine how C₁₀TAB promoted Hg⁰ removal. The Hg-TPD, Hg fate, and species results revealed that Hg⁰ was first oxidized to Hg²⁺, then bonded with S to generate HgS and enrich on the MoS₂. Therefore, improving the Hg⁰ gas-liquid mass transfer can enhance Hg⁰ removal in MoS₂/H₂O system, which can provide reference for purification of other insoluble pollutants in absorption system.