Interactions of limonene and carvone on titanium dioxide surfaces

Abstract

Limonene, a monoterpene, found in cleaning products and air fresheners can interact with a variety of surfaces in indoor environments. An oxidation product of limonene, carvone, has been reported to...

Comparison of the Adsorption–Desorption Kinetics of Limonene and Carvone on TiO2 and SiO2 Surfaces under Different Relative Humidity Conditions

“…Due to the complexity of pores, all surfaces were modeled without pores. Details of our simulation setup have been described in other work . Two methods were used to calculate the enthalpy of desorption to parameterize the kinetic model.…”

“…18 However, the adsorbed limonene on TiO 2 can be completely displaced by water at 50% RH (∼2 MLs of water) due to the lower O−H surface density on TiO 2 compared SiO 2 . 35 For carvone, there is little change in the amount of adsorbed carvone as a function of RH and little adsorbed water on both SiO 2 and TiO 2 surfaces at even high relative humidity, indicating carvone is blocking sites for water adsorption. 15,35 To better understand the impact of RH, here we applied in situ Fourier transform infrared (FTIR) spectroscopy to monitor the adsorption/desorption kinetics for different surface coverages at different RH ranging from <1 to 78% RH.…”

“…6,15 Similar results were reported for the TiO 2 surface; limonene adsorption is mainly through πhydrogen bonding, whereas carvone adsorption is through a variety of molecular interactions, including carbonyl bonding with Ti 4+ surface atoms, O−H hydrogen bonding, and πhydrogen bonding. 35 Relative humidity has been shown to change these interactions and to decrease the amount of adsorbed VOCs. For example, in an earlier study, we showed that there is still more than 50% of limonene remaining on the hydrated SiO 2 surface through a complex network of π-hydrogen bonding at a high 78% RH (∼3 MLs of water).…”

“…Details of our simulation setup have been described in other work. 35 Two methods were used to calculate the enthalpy of desorption to parameterize the kinetic model. In our previous work, 6 MD simulations have sufficed to calculate the enthalpy of desorption, but due to the nature of the idealized surface, we found enthalpies of desorption for limonene and carvone on surfaces with 0% RH were overestimated using MD simulation methods.…”

“…The peak assignments for the low-relative humidity (<1%) spectrum have been reported previously: the negative peak at 3656 cm −1 and an increase at 3447 cm −1 are associated with the loss of isolated Ti−OH groups and limonene-Ti−OH interactions through hydrogen−π bonding interactions; the peaks at 3085, 3074, 3010 cm −1 are associated with the C−H stretching motion for the sp 3 aliphatic C−H bonds; the peaks at 2968, 2922, 2860, and 2838 cm −1 are for C−H sp 2 stretching motion from alkene and ring; the 1644 cm −1 is assigned to the C�C bond stretching vibrations of the vinyl group and in the ring; and 1454, 1439, and 1378 cm −1 are due to CH 3 and CH 2 bending mode vibrations. 6,18,35 In the 10% RH spectrum, there is an increase in intensity in the range extending from 2800 to 3600 cm −1 due to the adsorbed water O−H stretching band and an increase in the absorption band at 1644 cm −1 , which shifts toward the low frequencies as 1640 cm −1 due to the water bending vibrational mode. 18,35 Figure 3 shows the adsorption−desorption kinetics of limonene at equilibrium pressure of 4, 8, 27, and 55 mTorr under dry conditions (<1% RH).…”