Infrared Signature of the Cation−π Interaction ... - ACS Publications

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Infrared Signature of the Cation−π Interaction between Calcite and Aromatic Hydrocarbons Haitao Wang,† Daniel J. Grant,‡ Peter C. Burns,†,§ and Chongzheng Na*,† †

Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, Indiana 46556, United States ‡ Department of Chemistry, University of Minnesota, 207 Pleasant Street Southeast, Minneapolis, Minnesota 55455, United States § Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, Indiana 46556, United States S Supporting Information *

ABSTRACT: The cation−π interaction is proposed as an important mechanism for the adsorption of aromatic hydrocarbons having non-zero quadrupole moments by mineral surfaces. Direct evidence supporting such a mechanism is, however, limited. Using the model mineral calcite, we probe the cation−π interaction with adsorbed benzene, toluene, and ethylbenzene (BTE) molecules using attenuated total reflectance Fourier transform infrared spectroscopy. We show that the presence of calcite increases the energy required to excite the synchronized bending of aromatic C−H bonds of BTE molecules. The unique conformation of this vibrational mode indicates that the planar aromatic rings of BTE molecules are constrained in a tilted face-down position by the cation−π interaction, as further confirmed by density functional theory calculations. Our results suggest that the shift of the excitation energy of the aromatic C−H bending may be used as an infrared signature for the cation−π interaction occurring on mineral surfaces. partitioning coefficients deduced from sorption isotherms.13 Obviously, complementary analytical techniques are in need to further advance the knowledge of the cation−π interaction involving mineral surfaces. Fourier transform infrared spectroscopy (FTIR) is a sensitive analytical technique that has been used to study the interactions of aromatic hydrocarbons with metals,14 metal oxides,15 aluminosilicates,16 and silicates.17 To probe molecules adsorbed on a solid surface, a sampling technique called attenuated total reflection (ATR) is often used in conjunction with FTIR.18,19 In ATR−FTIR,20,21 a powder of the solid is pressed on a crystal with a high reflective index serving as a conduit to direct the excitation light by total internal reflection. The light creates an evanescent wave extending out of the crystal and into the powder. The absorption of the excitation light by the powder provides structural information pertaining to the molecules adsorbed on the powder surface.22 For surface-adsorbed aromatic hydrocarbons, as compared to their counterparts in a liquid, interactions such as the cation−π interaction with the surface can vary the energies required for exciting certain modes of molecular vibration.23 However, an infrared (IR) signature distinctively linking ATR−FTIR measurement and the cation−π interaction has not been identified.

1. INTRODUCTION The cation−π interaction can arise from the electrostatic force between a positively charged cation and the quadrupole moment of a neutral molecule with additional contributions from polarization, induction, exchange, and dispersion forces.1,2 Theoretical calculations suggest that the enthalpy of the cation−π interaction can be as high as 80 kJ mol−1, which is approximately 1/5 the enthalpy of a covalent bond and 5 times that of a hydrogen bond.3,4 Given the strength of the cation−π interaction, it is well-recognized as an important mechanism for controlling intermolecular processes, such as biomolecule selfassembly,5 ligand−protein recognition,6 organic synthesis,7 and selectivity of ion channels.8 In comparison, only limited efforts have been devoted to elucidating the mechanism of the cation−π interaction in surface-related processes.9−13 On a surface, the cation−π interaction can be envisioned to occur over the positively charged surface cations and, thus, has been proposed as an important mechanism responsible for the adsorption of aromatic hydrocarbons on mineral surfaces.9,10 Direct evidence supporting the cation−π interaction on a mineral surface is currently limited to measurements made using deuterium nuclear magnetic resonance (2H NMR) spectroscopy.11 The pioneering application of 2H NMR showed that the quadrupole interaction of deuteriated aromatic hydrocarbons with an external magnetic field decreased upon adsorption.12 The extent of the decrease varied with the change of surface cations, following a trend consistent with that of © XXXX American Chemical Society

Received: February 14, 2015 Revised: May 13, 2015

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DOI: 10.1021/acs.langmuir.5b00610 Langmuir XXXX, XXX, XXX−XXX

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Figure 1. IR spectra of (a) calcite, (b, d, and f) liquids of BTE, and (c, e, and g) calcite surfaces absorbed with BTE molecules. Each spectrum is presented with a full scan from 400 to 4000 cm−1 on the left and an expanded view from 640 to 770 cm−1 on the right. The wavenumber range for the right panels is highlighted on the left panels in gray. The bands of the aromatic C−H out-of-plane bending of BTE molecules are fitted with Lorentzian models. On the basis of the shifts, the Lorentzian fits are marked as I for the first layer of surface-bound molecules and E for the extended layers of surface-bound molecules, as compared to L for the molecules in liquids. The absorbance is scaled, so that the spectra could be plotted together. The inset structures represent the synchronized out-of-plane aromatic C−H bending modes (⊕, C; ⊖, H; and X = CH3 for toluene and C2H5 for ethylbenzene). The powder was sifted using standard sieves (270 and 325) to select for particles having diameters from 45 to 53 μm [nominal diameter of 49 (±4) μm]. Reagent-grade liquids of BTE were purchased from Sigma-Aldrich (>99.99%). The liquids were dried using a 4 Å molecular sieve (Fisher Scientific), which reduced the water content below 5 ppb, as measured by the Karl Fischer titration (Aqua Counter 300). Before mixing with BTE, the calcite powder was baked at 300 °C for 24 h to remove water from the surface of the particles without changing their structure and chemistry.24 The dehydrated powder was cooled to room temperature in a vacuum desiccator (Bel-Art) to avoid interactions with water vapor before mixing with BTE compounds. To facilitate the deconvolution of the IR spectrum, the dehydrated powder was rehydrated in humid air overnight to saturate the calcite surface with water molecules. This was performed by spreading the powder evenly at the bottom of a sealed chamber that contained a small beaker of deionized (DI) water. The dehydrated calcite powder (400 mg) was mixed with 100 μL of BTE liquid in a dry glass vial. The vial was then sealed and placed in an oven at 60 °C for 1.5 h. The elevated temperature facilitated the dispersion of BTE molecules and created a uniform surface coverage of BTE molecules on the calcite particles. The rehydrated powder was mixed with the BTE liquid at room temperature to prevent drying of the hydrated calcite. To probe the cation−π interaction at the calcite−BTE interface, approximately 35 mg of the BTE-wetted powder was placed on the diamond crystal element of a FTIR spectrometer equipped with an

Here, we report the characterization of cation−π interactions between benzene, toluene, and ethylbenzene (BTE) compounds and calcite (CaCO3) using ATR−FTIR. Calcite is a model rhombohedral carbonate mineral that is the main component of oil-trapping chalk formations and a major component of soils, sediments, and atmospheric dust particles. BTE compounds are important constituents of organic solvents and liquid fuels that are widely used in industrial processes and consumer products. We show that the adsorption of BTE molecules on calcite results in a significant increase of the energy required to excite the out-of-plane aromatic C−H vibration (δC−H), providing a prominent analytical signature for probing the cation−π interaction on mineral surfaces. The connection between δC−H vibration and the cation−π interaction is further supported by density functional theory (DFT) calculations.

2. EXPERIMENTAL SECTION High-quality calcite was purchased from Ward’s Science (Rochester, NY). The structure of the calcite was verified using X-ray diffraction (Bruker Advance). The elemental impurities in calcite were determined to be less than 0.19% (see Table S1 of the Supporting Information) by inductively coupled plasma mass spectrometry (Thermo Scientific Element 2) after digestion in concentrated nitric acid. Calcite was ground into a powder using a mortar and a pestle. B

DOI: 10.1021/acs.langmuir.5b00610 Langmuir XXXX, XXX, XXX−XXX

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Figure 2. Change of the absorption intensity associated with the aromatic C−H out-of-plane bending with time for (a) benzene, (b) toluene, and (c) ethylbenzene. The normalized absorption, A, is obtained by dividing the band areas of the C−H out-of-plane bending for the first (I) and extended (E) layers of BTE molecules by the band areas of the calcite band between 700 and 720 cm−1. The solid line is an average of A for the first layer, and the dashed curves are fitted to exponential functions.

wavenumber of κB = 667 cm−1 for liquid benzene, κT = 726 cm−1 for liquid toluene, and κE = 744 cm−1 for liquid ethylbenzene. These features do not overlap with any vibrational absorption from calcite (Figure 1a) and, thus, are specific for BTE compounds. Upon the adsorption of BTE by calcite (panels c, e, and g of Figure 1), the wavenumbers of δC−H vibration are shifted to greater values, indicating that the simultaneous bending of aromatic C−H bonds are constrained by the calcite surface. This suggests that the BTE molecules are adsorbed on the calcite surface in a face-down position. This orientation is equivalent to placing a calcium cation directly above the aromatic ring of a BTE molecule, favoring the cation−π interaction. Each of the δC−H bands associated with surface-bound BTE molecules can be deconvoluted into two separate bands. As shown in the right panel of panels c, e, and f of Figure 1, we interpret the two deconvoluted bands as the absorption from the first (I) and extended (E) layers of adsorbed molecules. Least-squares regression using the Lorentzian function gives the mean wavenumbers of κB(I) = 680 cm−1, κT(I) = 731 cm−1, and κE(I) = 745 cm−1 for the first layers of adsorbed molecules and κB(E) = 673 cm−1, κT(E) = 728 cm−1, and κE(E) = 744 cm−1 for the extended layers. The devolution of δC−H bands into I and E layers is supported by the changes of their intensities with time. As shown in Figure 2, the absorption intensities of all of the E bands (normalized to the calcite band at 712 cm−1) decrease continuously as BTE molecules evaporate (at approximately 0.2 g m−2 s−1).29 In comparison, the absorption intensities of all of the I bands remain stable until the end of measurement. The deconvulation of δC−H bands supports the hypothesis that the first adsorption layers of BTE molecules interact with the calcite surface strongly through the cation−π interaction. Under this interaction, the electron-poor surface calcium draws π electrons from the aromatic ring. The electron-withdrawing effect extends to and strengthens the aromatic C−H bonds, resulting in an increase of excitation energy, as shown by an increased wavenumber of the δC−H absorption band.37,38 In addition, the electron densities of aromatic rings are reduced, making it difficult for the C−H carbon atoms on the ring to follow the motion of bonded hydrogen atoms through a partial transition from the sp2 hybridization to the sp3 hybridization.30 In contrast, there is no cation−π interaction in the extended adsorption layers. The relatively small amount of increase in excitation energy may be attributed to the increase of the liquid

ATR assembly (Bruker Tensor 27). The instrument was enclosed and operated in a fume hood. IR spectra were acquired immediately after the powder was transferred from the sealed vial onto the diamond crystal. The acquisition continued until the signals for surface-bound BTE molecules completely disappeared as a result of evaporation. Spectra ranging from 400 to 4000 cm−1 were acquired with a resolution of 1 cm−1. To identify the IR absorption bands unique to surface-bound molecules, spectra were also obtained for pure BTE liquids and the pristine calcite powder for comparison. All spectra were referenced to the bare diamond crystal. Geometry optimizations and single-point calculations were performed using the Gaussian program package.25 To do so, a BTE molecule was placed on top of the 1014̅ cleavage surface of a calcite slab consisting of 18 CaCO3 units.26 Calculations were performed with the M06 functional and a 6-31G* basis set on all atoms.27,28 Full geometry optimizations of benzene, toluene, and ethylbenzene were performed in D6h, C1, and Cs symmetries, respectively. For the calcite− BTE structures [C 6 H 6 (CaCO 3 ) n , C 6 H 5 (CH 3 )(CaCO 3 ) n , and C6H5(C2H5)(CaCO3)n, where n = 18], constrained geometry optimizations (with fixed terminal CO3) were performed without imposing any symmetry constraint. The calcite surface was held fixed while BTE geometries were fully optimized. Analytical harmonic frequencies were calculated only for BTE compounds to ensure that each was a minimum energy structure not characterized by any imaginary frequency.

3. RESULTS We probe the interaction of the calcite surface with BTE using ATR−FTIR. As shown in the left panels of Figure 1, dry calcite powders treated with BTE molecules (c, e, and g) have IR absorption bands attributable to both calcite (a) and BTE molecules (b, d, and f). All of the vibrational modes of surfacebound BTE molecules can be readily identified by comparing them to the vibrational modes of pure BTE liquids. Vibrational modes of pure BTE liquids are listed in Tables S2−S4 of the Supporting Information. Between BTE molecules in liquids and those adsorbed on calcite, significant differences are found for the out-of-plane bending of aromatic C−H bonds, δC−H. In this vibrational mode, all of the aromatic C−H bonds (six for benzene and five for toluene and ethylbenzene) bend together perpendicular to the aromatic ring (i.e., all H atoms go in and out of the paper together), as illustrated by the inset structures (X = CH3 for toluene and CH2CH3 for ethylbenzene). The δC−H vibrational bands for BTE compounds are located between the wavenumbers of 640 and 770 cm−1. This range is shaded in gray in the left panels of Figure 1 and magnified in the right panels. In the absence of calcite (panels b, d, and f of Figure 1), the excitation of δC−H vibration requires light with a C

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Langmuir density next to an adsorbing surface,31 which hinders the δC−H vibration by spatial blockage. To further validate our interpretation of the deconvolution of δC−H vibrational bands, we modify calcite by saturating its surface with water molecules before putting the calcite powder in contact with benzene. The surface modification is performed by leaving the calcite powder in an atmosphere with nearly 100% relative humidity overnight. Under such conditions, more than four layers of water molecules can condense on the calcite surface.32−34 As shown in Figure 3a, the success of water

cation−π interaction energy upon the solvation of metal cations suggested by ab initio calculations.36 The ATR−FTIR results presented above suggest that the shifts of δC−H bands can be used as an IR signature for probing the cation−π interaction between mineral surfaces and aromatic hydrocarbons. On calcite, the shift is most sensitive for the adsorption of benzene with a shift of ΔκB(I) = 13 cm−1, followed by a reasonable sensitivity for toluene of ΔκT(I) = 5 cm−1. The sensitivity for ethylbenzene is the lowest among the three BTE compounds, with ΔκE(I) = 1 cm−1. The reduction of ΔκT(I) and ΔκE(I) compared to ΔκB(I) can be attributed to the substitution effect. In toluene and ethylbenzene, the substitution of hydrogen by alkyls increases the aromatic π electron density through the inductive electron-donating effect. The electrondonating effect of alkyl substitution balances the electronwithdrawing effect of the surface calcium, leading to the observed reduction in the IR shifts of δC−H bands. To visualize the cation−π interaction, DFT calculations are performed to verify the orientation and position of a BTE molecule on the calcite surface. As shown in Figure 4, the calcite surface is represented by a slab consisting of two layers of 3 × 3 CaCO3 units with an overall neutral charge. A BTE molecule is then placed on top of the calcite slab for geometry optimization. Calculations performed without structural constraints and with full relaxation of the BTE−calcite complexes have resulted in the dissociation of terminal CO3 units, possibly because of the limited size of the calcite slab. Because the calcite surface is not expected to reconstruct significantly upon the adsorption of BTE molecules, the structure of the CaCO3 slab is constrained while the BTE molecules are being fully optimized. As shown in Figure 4, all three BTE molecules are similarly arranged with their aromatic rings facing the exposed surface calcium cations. Each surface calcium ion is connected with five oxygen atoms from four surface carbonate ions and one carbonate ion underneath; therefore, each of them has one empty orbital from the 4s3d5 hybridization exposed at the surface with 1/3 of an elementary charge. The aromatic rings of BTE molecules are oriented perpendicular to the empty orbital under the cation−π interaction, so that their π electrons can enter the empty orbital of the surface calcium atom. The aromatic rings are not centered over the calcium atoms but

Figure 3. IR spectra of (a) hydrated calcite and (b) benzene-covered hydrated calcite. The gray bar marks the region corresponding to the band associated with the aromatic C−H out-of-plane bending of benzene. Each spectrum is presented with a full scan from 400 to 4000 cm−1 on the left and an expanded view from 640 to 770 cm−1 on the right.

adsorption is confirmed by the observation of vibrational bands between 3000 and 3700 cm−1 and at 1646 cm−1, which are associated with the O−H stretching and bending of water molecules, respectively.35 When the wet calcite is used to adsorb benzene, only one δC−H band is found at κB(E) = 673 cm−1 associated with the extended adsorption layers. The absence of the signature band at κB(I) = 680 cm−1 is consistent with the fact that the first layer is now occupied by water molecules. These results are consistent with the reduction of

Figure 4. Positions and orientations of (a) benzene, (b) toluene, and (c) ethylbenzene on calcite optimized at the M06/6-31G* level. Each optimized calcite−BTE complex is shown with a side view on top and the top view at the bottom. Atoms are colored with gray for C, white for H, red for O, and green for Ca. D

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reservoirs.45,46 The low recovery efficiency is attributed to the preferred wetting of carbonate surfaces in reservoir pores by oil, which prevents the displacement of oil by water under capillary pressure and buoyancy through a process called spontaneous imbibition.47 In the past, the adsorption of amphiphilic naphthenates by carbonate surfaces has been proposed as the mechanism responsible for surface hydrophobicity in carbonate reservoirs.48 The strong cation−π interaction shown here suggests that neutral aromatic hydrocarbon molecules, which account for up to 30% of crude oil,49 can also contribute to carbonate surface hydrophobicity. In addition to oil recovery, the cation−π interaction may also have important implications to the transport and transformation of aromatic hydrocarbons in the environment. Aromatic hydrocarbons, such as BTE compounds, can enter soils and sediments by leakage or spills at facilities for producing, delivering, and distributing oil and oil products.50 The leakage and spill of oil and oil products can also release BTE compounds, given their high volatility, into the atmosphere, where they can interact with carbonate-containing aerosol particles originated from dust storms.51−54 Our results suggest that the cation−π interaction is likely to occur under low relative humidity in soils and the atmosphere, where the mineral surface is not completely covered by water. For calcite, the incomplete coverage of the cleavage (1014̅ ) surface occurs under relative humidities below 50%,32−34 a condition that is not difficult to encounter. The simple DFT calculations performed with a single BTE molecule and a slab of 18 CaCO3 units show that BTE molecules are organized in tilted face-down positions next to the calcite surface as a result of the rugged organization of surface calcium and carbonate. The tilted orientation of BTE molecules on calcite is similar to that of aromatic methylene blue adsorbed on mica.55 Preliminary analysis of energetics suggests that direct cation−quadrupole interactions contribute significantly to the total interaction energies for all three BTE molecules adsorbed on calcite. Further elucidation of the nature of the cation−π interaction involving mineral surfaces requires the use of molecular models better than the model that we have used to represent the BTE−calcite system.

rather are shifted toward the recessed surface oxygen atom bonded to the calcium atom. The methyl group of toluene is positioned next to the recessed surface oxygen and pointing toward an adjacent calcium. The ethyl group of ethylbenzene is arranged similarly as the methyl group of toluene. The geometry parameters for the optimized BTE−calcite structures are listed in Table S5 of the Supporting Information. Overall, the BTE molecules are adsorbed on the calcite surface in tilted face-down positions. The total interaction energies with calcite are estimated to be 36.8, 48.5, and 54.8 kJ mol−1 for BTE from single-point calculations. Each of the interaction energies is expected to include contributions from electronic and dispersive interactions as well as from the interaction between the surface calcium cation and the quadrupole moment of the aromatic ring. Using a simple classical model (see Note S1 of the Supporting Information),37 the cation−quadrupole energy may be estimated from a function of the quadrupole moment Q of a BTE molecule, its distance d to the nearest surface calcium, and the angle θ defining the position of calcium off the center of the aromatic ring E (d , θ ) = −

48Q (3 cos2 θ − 1) d3

(1)

where Q = −8.099, −7.610, and −7.828 Buckingham (1 Buckingham = 1 Debye Å = 3.34 × 10−40 C m) for benzene, toluene, and ethylbenzene, respectively,38 d ≈ 3.4 Å, and θ = 25° (cf. Table S5 of the Supporting Information). Using these values, we obtain EB = 15.0 kJ mol−1 for benzene, ET = 13.2 kJ mol−1 for toluene, and EE = 13.9 kJ mol−1 for ethylbenzene, suggesting that the cation−quadrupole energy is similar for all three BTE compounds. On a relative scale, the cation− quadrupole energy contributes 41, 27, and 25% of the total interaction energy with calcite for benzene, toluene, and ethylbenzene, respectively. The decreasing trend is consistent with the increasing interaction between the substituent group and the surface as the substituent group increases in size.

4. DISCUSSION ATR−FTIR measurements presented above show that BTE molecules placed next to the calcite surface are organized differently from the molecules in bulk liquids, revealing surfaceinduced liquid restructuring under the cation−π interaction. Elucidating the mechanism of liquid restructuring near surfaces is fundamentally important to understand and model heterogeneous systems involving the two phases. Previously, studies employing innovative analytical techniques have revealed surface-induced restructuring of water,39 mercury,40 alkanes,41 alcohols,42 and ionic liquids.43 Through these studies, solvation force,39 hydrogen bonding,39,42 surface tension,40 van der Waals attraction,41 and electrostatic attraction43 have been identified as important surface−liquid interactions responsible for inducing liquid restructuring. Liquid restructuring under the cation−π interaction has not been previously proposed or observed. The revelation of the cation−π interaction as an important mechanism of surface−liquid interaction may help better understand the interfacial processes involved in oil recovery from carbonate reservoirs, where 60% of the world’s oil is stored.44 Clean carbonate minerals have hydrophilic surfaces that should not interact strongly with hydrophobic liquids, such as crude oil. However, conventional technologies, such as water flooding, can only recover 30% of the oil trapped in carbonate

5. SUMMARY Using calcite and BTE compounds as model systems, we have shown that the strong cation−π interaction between a mineral surface and a neutral molecule can lead to an appreciable increase of energy required for the excitation of the out-ofplane aromatic C−H vibration. The increase of excitation energy can be probed using ATR−FTIR, providing a unique signature for recognizing the previously underappreciated noncovalent interaction at the mineral surface. We show that the IR signature is most sensitive for unsubstituted aromatic rings. Alkyl substitution reduces IR sensitivity because of its inductive electron-donating effect.

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ASSOCIATED CONTENT

S Supporting Information *

Impurities in calcite (Table S1), vibrational modes of benzene (Table S2), vibrational modes of toluene (Table S3), vibrational modes of ethylbenzene (Table S4), selected geometry parameters of calcite−BTE complexes (Table S5), and estimation of the energy of the cation−quadrupole interaction by classical electrostatics (Note S1). The SupportE

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(16) Haaland, D. M. Fourier transform infrared spectroscopic studies of the adsorption of benzene on alumina and alumina supported platinum. Surf. Sci. 1981, 102, 405−423. (17) Ringwald, S. C.; Pemberton, J. E. Adsorption interactions of aromatics and heteroaromatics with hydrated and dehydrated silica surfaces by Raman and FTIR spectroscopies. Environ. Sci. Technol. 1999, 34, 259−265. (18) Yalamanchili, M. R.; Atia, A. A.; Miller, J. D. Analysis of interfacial water at a hydrophilic silicon surface by in-situ FTIR/ internal reflection spectroscopy. Langmuir 1996, 12, 4176−4184. (19) Jones, Y. K.; Li, Z. H.; Johnson, M. M.; Josse, F.; Hossenlopp, J. M. ATR−FTIR spectroscopic analysis of sorption of aqueous analytes into polymer coatings used with guided SH-SAW sensors. IEEE Sens. J. 2005, 5, 1175−1184. (20) Mudunkotuwa, I. A.; Al Minshid, A.; Grassian, V. H. ATR− FTIR spectroscopy as a tool to probe surface adsorption on nanoparticles at the liquid−solid interface in environmentally and biologically relevant media. Analyst 2014, 139, 870−881. (21) Hind, A. R.; Bhargava, S. K.; McKinnon, A. At the solid/liquid interface: FTIR/ATRThe tool of choice. Adv. Colloid Interface Sci. 2001, 93, 91−114. (22) Colthup, N. B.; Daly, L. H.; Wiberley, S. E. Introduction to Infrared and Raman Spectroscopy, 3rd ed.; Academic Press: London, U.K., 1990. (23) Haq, S.; King, D. A. Configurational transitions of benzene and pyridine adsorbed on Pt{111} and Cu{110} surfaces: An infrared study. J. Phys. Chem. 1996, 100, 16957−16965. (24) Simmons, G.; Bell, P. Calcite−aragonite equilibrium. Science 1963, 139, 1197−1198. (25) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision C.02; Gaussian, Inc.: Wallingford, CT, 2004. (26) Sitepu, H.; O’Connor, B. H.; Li, D. Comparative evaluation of the March and generalized spherical harmonic preferred orientation models using X-ray diffraction data for molybdite and calcite powders. J. Appl. Crystallogr. 2005, 38, 158−167. (27) Zhao, Y.; Truhlar, D. G. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and transition elements: Two new functionals and systematic testing of four M06-class functionals and 12 other functionals. Theor. Chem. Acc. 2008, 120, 215−241. (28) Ditchfie, R.; Hehre, W. J.; Pople, J. A. Self-consistent molecularorbital methods. 9. Extended Gaussian-type basis for molecular-orbital studies of organic molecules. J. Chem. Phys. 1971, 54, 724−728. (29) J. Beverley, K.; H. Clint, J.; D. I. Fletcher, P. Evaporation rates of pure liquids measured using a gravimetric technique. Phys. Chem. Chem. Phys. 1999, 1, 149−153. (30) Kross, R. D.; Fassel, V. A.; Margoshes, M. The infrared spectra of aromatic compounds. II. Evidence concerning the interaction of pelectrons and s-bond orbitals in C−H out-of-plane bending vibrations. J. Am. Chem. Soc. 1956, 78, 1332−1335. (31) Kerisit, S.; Parker, S. C. Free energy of adsorption of water and metal ions on the {10−14} calcite surface. J. Am. Chem. Soc. 2004, 126, 10152−10161.

ing Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.5b00610.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Chongzheng Na acknowledges financial support from the donors of the American Chemical Society Petroleum Research Fund, National Science Foundation Environmental Engineering Program, and Notre Dame Sustainable Energy Initiative. The authors thank Notre Dame Center for Environmental Science and Technology for analytical assistance and Jian Lin for performing ATR−FTIR experiments.

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DOI: 10.1021/acs.langmuir.5b00610 Langmuir XXXX, XXX, XXX−XXX