Heterogeneous Interactions of Prevalent Indoor Oxygenated Organic Compounds on Hydroxylated SiO₂ Surfaces

Abstract

Oxygenated organic compounds (OOCs) are widely found in indoor environments and come from either the direct emissions from indoor activities or the subsequent oxidation of nonoxygenated OCs. Adsorption and partitioning of OCs on surfaces are significant processes in indoor chemistry, yet these interactions specifically involving OOCs are still poorly understood. In this study, we investigate the interactions of three prevalent indoor OOCs (dihydromyrcenol, α-terpineol, and linalool) on an indoor surface proxy (hydroxylated SiO 2 ) by combining vibrational spectroscopy with ab initio molecular dynamics simulations. The adsorption of these compounds on the SiO 2 surface is driven by π hydrogen bonding and O−H hydrogen bonding interactions, with O−H hydrogen bonding interactions being stronger. The results of kinetic measurements suggest that indoor surfaces play a significant role in the removal of these OOCs, especially under moderate and low air exchange. Additionally, indoor surfaces can also serve as a reservoir of OOCs due to their much slower desorption kinetics when compared to other indoor relevant organic compounds such as limonene. Overall, the results gleaned by experiment and theoretical simulations provide a molecular representation of the interaction of OOCs on indoor relevant surfaces as well as implications of these interactions for indoor air chemistry.

Heterogeneous Interactions between Carvone and Hydroxylated SiO2

“…These findings suggested that indoor surfaces can serve as reservoirs of OOCs, which may have negative effects on indoor air quality for a long period of time because of their slow desorption. 26 The impact of relative humidity (RH) also plays a role in gas phase concentrations of organic compounds. In particular, VOCs concentrations in indoor air may increase with the increasing relative humidity (RH) because of the emissions of VOCs by the displacement of water.…”

“…This finding agrees with our previous study, which showed that oxygenated organic molecules (OOCs) form stronger interactions with the SiO 2 surface than other indoor relevant monoterpenes such as limonene with SiO 2 . 26 MD simulations show that the adsorption of carvone on the SiO 2 surface is not only driven by hydrogen bonds between the carvone oxygen and Si−OH sites but also interactions between the carvone oxygen and 3coordinated Si atoms. Our kinetic model suggests that pore sizes need to be considered in controlling the desorption rate of molecules from the porous particles surface, especially the interactions that occur between the molecule functional groups within the pores.…”

“…In another study, the interactions of three prevalent indoor oxygenated organic compounds (OOCs)dihydromyrcenol, α-terpineol, and linaloolwith the hydroxylated SiO 2 surface showed that the OOCs form much stronger bonding with the SiO 2 surface OH groups than limonene due to the O to HO–Si hydrogen bonding and have very slow desorption kinetics. These findings suggested that indoor surfaces can serve as reservoirs of OOCs, which may have negative effects on indoor air quality for a long period of time because of their slow desorption …”

“…Studies on the heterogeneous interactions of prevalent indoor organic molecules on hydroxylated SiO 2 surface (a model for glass surface) that combined vibrational spectroscopy with theory calculations have been previously reported. − These studies show that limonene forms one or two π-hydrogen bonding with the SiO 2 surface hydroxyl (OH) groups, and that the desorption kinetics of limonene from the SiO 2 surface are controlled by the gas diffusion in dry conditions because of the weak π-hydrogen bonding; and the intermolecular interaction between limonene and the SiO 2 surface is stronger than that of other cyclic hydrocarbons such as cyclohexene, benzene, and cyclohexane, while cyclohexane shows the weakest interaction due to its interactions with the SiO 2 surface OH groups only through dispersion forces. , Additional insights from studies of constitutional limonene isomers (γ-terpinene, terpinolene, and α-pinene) and their interactions with SiO 2 surface demonstrated that the strength of the interactions with the SiO 2 surface for limonene, γ-terpinene and terpinolene are comparable . However, α-pinene with one CC bond shows much weaker interactions with SiO 2 surface than that for limonene with two CC bonds. , Since the adsorption of cyclic monoterpenes molecules on the SiO 2 surface is mainly driven by π-hydrogen bonding arising from the CC bonds, and the order of the strength of interaction can be explained by the probability of π-hydrogen bonding formation, the number of CC bonds and the distance distribution between CC bonds play a role in these surface interactions .…”

Interactions of limonene and carvone on titanium dioxide surfaces

“…This implies that polar VOCs are more strongly adsorbed onto TiO 2 surface. [35][36][37][38] For example, the adsorption of different classes of VOCs on TiO 2 (P25) surface follows the order of the strength of the corresponding intermolecular forces: i-octane < toluene < acetone < methyl ethyl ketone < isopropanol < methanol. 36 Additional insights from the studies of C 5 C 7 alkanes interactions with TiO 2 (P25) surface demonstrated that the larger long-chain and more branched molecules have stronger interactions with the TiO 2 surface based on the order of the strength of adsorption: pentane < hexane < i-pentane < i-hexane < heptane.…”