Heterogeneous Interactions between Carvone and Hydroxylated SiO₂

Abstract

Oxygenated semivolatile organic compounds are present in indoor air due to the oxidation of monoterpenes and other hydrocarbons. The partitioning of these compounds to indoor surfaces and the formation of organic thin films are of great interest as these surfaces become potential reservoirs for these compounds affecting indoor air composition. Here, we have investigated the interaction of carvone, a limonene oxidation product, with hydroxylated SiO 2 surfaces at 297 ± 1 K with FTIR spectroscopy. The detailed surface interactions were understood through both force field-based molecular dynamics (MD), ab initio molecular dynamics (AIMD) simulations, and electronic structure calculations. The adsorption/desorption kinetics of carvone on hydroxylated SiO 2 have been measured as a function of relative humidity. The desorption kinetics of carvone from the SiO 2 surface are slow, approximately 30 times slower when compared to limonene under dry conditions. Molecular dynamics (MD) simulations reveal that carvone forms O−H hydrogen bonding (carbonyl O to HO−Si) with the isolated hydroxyl groups and oxygen silicon associations (carbonyl O to Si−O−Si) with siloxane bridges that are also on the SiO 2 surface. A kinetic model was applied to further examine the carvone adsorption and desorption kinetics; the experimental measurements can be reproduced by assuming that some carvone molecules become trapped in pores between the SiO 2 particles. Interestingly, relative humidity does not change the desorption kinetics of carvone from the SiO 2 surface. Instead, water molecules adsorb onto the preadsorbed carvone, which hydrates the organic-coated surface. Overall, this study shows how carvone, an oxygenated organic compound, interacts with indoor relevant surfaces and the impact of relative humidity on these interactions. It also demonstrates how chemical transformations (e.g., oxidation) in indoor environments can play an important role in how molecules partition to surfaces and interact with condensed phase water.

Interactions of limonene and carvone on titanium dioxide surfaces

“…The experimental infrared setup has been described previously. [45][46][47] was held in position by nickel jaws inside of the stainless-steel IR cell with BaF 2 windows. The rest of the experimental setup consists of a stainless IR cell (310 3 ml, the optical path length ± of the IR cell is 7 cm), a glass mixing chamber (1329 2 ml), a stainless-steel connection tubing ± (length: 36 inch and I.D.…”

“…The TIP3P water was used to describe the water molecules and details of the CHARMMM compatible force fields for limonene and carvone can be found in our previous work. 46,47,56 All classical molecular dynamics simulations were done with the LAMMPS 57 software package. The equations of motion were integrated using the velocity Verlet algorithm with a 1 fs time step.…”

“…The TIP3P water was used to describe the water molecules and details of the CHARMMM compatible force fields for limonene and carvone can be found in our previous work. 46,47,56…”

“…43,44 Atomistic simulations provide detailed insight into surface interactions, and in our previous work, we have presented studies of hydroxylated SiO 2 (a model for glass surfaces) and indoor relevant organic compounds with great agreement between theory and experiment. [45][46][47] However, TiO 2 presents a unique challenge as there is still outstanding debate over how to model the interactions of water on the TiO 2 surface in a simulation, to either represent the water via a molecular or dissociative association on the surface. [48][49][50][51][52][53] In this study, we have constructed both a non-hydroxylated TiO 2 surface with surface Ti atoms and free water molecules, and a fully hydroxylated TiO 2 with all surface Ti atoms capped with OH groups.…”

“…Our previous studies showed that limonene forms one or two Si-OHÁ Á Áp-hydrogen bonds on the hydroxylated SiO 2 surface, and more than 50% of limonene remains adsorbed within the water and hydroxylated SiO 2 surface through H-OH or Si-OHÁ Á Áp-hydrogen bonding at a relatively high 78% RH when the water coverage is close to three monolayers (MLs); carvone forms a Si-OHÁ Á ÁO hydrogen binding and an oxygen silicon association with siloxane bridge (OÁ Á ÁSi-O-Si) on the hydroxylated SiO 2 surface, and instead of replacing the adsorbed carvone on SiO 2 surface, water adsorbs onto the carvone coverage via H-OHÁ Á ÁO hydrogen binding. [45][46][47] To the best of our knowledge, there are no systematic studies with respect to the adsorption of limonene and its oxidation product carvone on TiO 2 surface or the impact of relative humidity over a wide range of relative humidity conditions. In the present work, we combined transmission FTIR spectroscopy, classical force field-based and ab initio molecular dynamics simulations to investigate the types of surface interactions and relative strengths of limonene and carvone adsorbed on the hydroxylated TiO 2 surface.…”