pH-Dependent Water Clusters in Photoacid Solution: Real-Time Observation by ToF-SIMS at a Submicropore Confined Liquid-Vacuum Interface

Abstract

Water clusters are ubiquitously formed in aqueous solutions by hydrogen bonding, which is quite sensitive to various environment factors such as temperature, pressure, electrolytes, and pH. Investigation of how the environment has impact on water structure is important for further understanding of the nature of water and the interactions between water and solutes. In this work, pH-dependent water structure changes were studied by monitoring the changes for the size distribution of protonated water clusters by in-situ liquid ToF-SIMS. In combination with a light illumination system, in-situ liquid ToF-SIMS was used to real-time measure the changes of a light-activated organic photoacid under different light illumination conditions. Thus, the proton transfer and pH-mediated water cluster changes were analyzed in real-time. It was found that higher concentration of free protons could lead to a strengthened local hydrogen bonding network as well as relatively larger protonated water clusters in both organic acid and inorganic acid. Besides, the accumulation of protons at the liquid-vacuum interface under light illumination was observed owing to the affinity of organic molecules to the low-pressure gas phase. The application of in-situ liquid ToF-SIMS analysis in combination with in-situ light illumination system opened up an avenue to real-time investigate light-activated reactions. Besides, the results regarding water structure changes in acidic solutions showed important insights in related atmospheric and physiochemical processes.

Ultrathin Silicon Oxide Overlayers Enable Selective Oxygen Evolution from Acidic and Unbuffered pH-Neutral Seawater

“…Furthermore, partial dehydration could help explain the overlayer’s selectivity for the OER over the CER since H 2 O, the reactant for the OER, is the solvent within the aqueous electrolyte and is expected to have a much smaller activation barrier for crossing from the bulk electrolyte into the hydrophilic SiO x overlayer. The most common water cluster sizes at pH 1, (H 2 O) 1–6 , have full dissociation energies of less than 57 kJ mol –1 , suggesting that water’s partial self-dehydration energy is far smaller than the partial dehydration energy of Cl – and Br – .…”

Reversible photo control of proton chemistry

“…18 Hua and coworkers applied mPAHs to mass spectrometry and conducted a real-time study of pH-dependent water clusters. 57 This is an example of using a non-optical instrument to study proton chemistry using an mPAH. mPAHs have also been utilized to drive molecular shuttles with light, 30,58 control foam formation at the air–water interface, 59 and direct the movement of water drops in oil 60 etc.…”

Pore confined time-of-flight secondary ion electrochemical mass spectrometry

“…It was revealed that the hydrogen peroxide oxidation of glyoxal was an important pathway for the formation of organic aerosol under both photochemical aging and dark conditions. 87 In addition, by taking distinct advantage of the capturing elemental and molecular information from the liquid interface, in situ ToF-SIMS has also been applied to identify the transition state of hydrogen peroxide activation in a Fenton reaction 88 and real-time monitor dynamic hydrogen-bond network evolution during a light-activated proton dissociation reaction 89 as well as investigate the ion–solvent and molecular–solvent interactions in various liquids. 90–92 For example, Zhang et al successfully applied in situ ToF-SIMS to obtain direct molecular information on dominant ion clusters in alkaline systems.…”