Article pubs.acs.org/Langmuir
Dynamic Adsorption of Catechol at the Goethite/Aqueous Solution Interface: A Molecular-Scale Study Yanli Yang, Wei Yan, and Chuanyong Jing* State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China S Supporting Information *
ABSTRACT: Insights from molecular-level mechanisms of catechol adsorption on goethite can further our understanding of the fate and transport of hydroxyaromatic compounds in the environment. The motivation for our study is to explore the dynamic adsorption process of catechol at the goethite/aqueous interface on the molecular scale. Multiple complementary techniques including macroscopic adsorption experiments, flow-cell ATR-FTIR measurement, 2D IR correlation analysis, and quantum chemical calculations were used to study the adsorption mechanisms. Our results show that the adsorption of catechol was elevated at high pH but was not affected by ionic strength because of the formation of inner-sphere complexes. Catechol adsorbed on goethite in mononuclear monodentate and binuclear bidentate configurations in the pH range of 5 to 9. Partial mononuclear monodentate structures could be converted to binuclear bidentate complexes under basic conditions and with increasing surface coverage. interface.7,8 As a result of these discrepancies, a molecular-level understanding of catechol adsorption at mineral/aqueous interfaces remains to be fully developed. Goethite (α-FeOOH) is a common iron oxide mineral that is widespread in terrestrial soils and sediments. However, few studies have measured the adsorptive behavior of catechol on this model mineral. Previous studies mainly focused on macroscopic observations.9,10 Developing insight into the dynamic process of catechol adsorption at goethite/aqueous interface on the molecular level motivates our experimental and theoretical studies. The objective of this study was to explore the bonding mechanisms of catechol at the goethite/aqueous interface under environmental pH conditions. Multiple complementary techniques including macroscopic adsorption experiments, in situ flow-cell measurements of attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy, 2D infrared (2D IR) correlation analysis, and quantum chemical calculations were used to study the adsorption mechanisms. These results should further our understanding of the fundamental interactions of hydroxyaromatic compounds with iron oxide surfaces.
I. INTRODUCTION Catechol and its derivatives are an important class of chemicals in the environment, accounting for a major fraction of the organic matter in water and soil.1 These hydroxyaromatic compounds are highly reactive and readily adsorb onto metal oxide minerals. The adsorption process retards their migration in aquifers and soils and alters their susceptibility to chemical and biological transformations.2 Therefore, a knowledge of the molecular-level interactions between catechol and oxide minerals is critical to understanding the fate and transport of hydroxyaromatic compounds. Considered to be a model compound, catechol has been studied for its adsorption behavior on metal oxides using Fourier transform infrared (FTIR) spectroscopy. However, no consistent bonding mechanisms and configurations of adsorbed catechol have been recognized. Gulley-Stahl et al.,1 for example, suggested that catechol bound predominately as an outersphere complex on MnO2 and as an inner-sphere complex on Fe2O3, TiO2, and Cr2O3 in a mononuclear monodentate (MM) configuration at pH 5. The binuclear bidentate (B-B) structure3,4 and molecularly adsorbed outer-sphere complex5 were also reported for catechol adsorption on TiO2. In addition, McBride and Wesselink6 indicated that catechol had adsorbed onto the Al2O3 surfaces in the same manner as catechol chelated by Al3+, suggesting the formation of a 1:1 bidentate complex with surface Al (M-B structure). These discrepancies might be attributed to the differences in minerals and experimental protocols, such as pH, catechol loading, and whether the samples were wet or had been dried. In dried samples, the molecular structure might be distorted from the aquatic−solid © 2012 American Chemical Society
II. EXPERIMENTAL SECTION 1. Materials. Catechol (≥99%) was purchased from Sigma-Aldrich and used as received. All chemicals were analytical reagent grade or higher and were used without further purification. Milli-Q water (18.2 Received: April 6, 2012 Revised: September 19, 2012 Published: September 19, 2012 14588
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MΩ) was boiled for 60 min and cooled with nitrogen purging to remove CO2. Goethite was prepared according to the modified method of Schwertmann and Cornell11 as shown in the Supporting Information (SI). The mineral was identified as goethite by X-ray powder diffraction (Rigaku D/MAX 2500, Japan). Examination by transmission electron microscopy (Hitachi-7500, Japan) showed the morphology of goethite as well-crystallized needles. The BET surface area (84.7 m2/g) was determined with ASAP2000 (Micromeritics Instrument Corp., USA). The point of zero charge (PZC) of goethite was determined to be 8.9 with a Zetasizer Nano ZS (Malvern Instruments, U.K.). 2. Macroscopic Adsorption and Dissolution Measurements. Adsorption envelope experiments were performed to determine adsorbed catechol and dissolved Fe as a function of the final solution pH. Suspension samples containing 5 g/L goethite, with or without 1 mM catechol in the presence of 0.01 or 0.1 M NaCl, were adjusted to pH values in the range of 4.5 to 9.2 with NaOH and HCl. After mixing on an end-over-end rotator for 12 h in the dark, samples were passed through a 0.22 μm membrane filter for dissolved catechol and Fe analysis. The concentration of catechol was determined by highperformance liquid chromatography (HPLC, Shimadzu LC-20A, Japan) with UV−visible detection at 284 nm. Analytical separations were performed using a Hypersil Gold C18 column (150 mm × 4.6 mm i.d., particle size 5 μm, Thermo Fisher Scientific Inc.). The mobile phase was a mixture of citric buffer (20 mM, pH 3.5) and methanol (80:20 v/v). The flow rate was 1 mL/min, and the column temperature was set at 40 °C. The concentration of soluble Fe was measured using an inductively coupled plasma optical emission spectrometer (ICP-OES, PerkinElmer Optima 7000 DV, USA) with the analytical wavelength at 259 nm. 3. ATR-FTIR Spectroscopy Study. FTIR measurements were performed with a Nicolet 6700 spectrometer equipped with a liquidnitrogen-cooled MCT detector, a liquid pump (LC-3A, Shimadzu Corporation, Japan), and a 45° ZnSe crystal mounted in a flow cell (Pike Technologies, USA). A total of 256 scans with a resolution of 4 cm−1 were averaged for each spectrum. Data collection and spectral analysis, such as subtraction, normalization, and baseline correction, were carried out using Omnic software (Thermo Fisher Scientific Inc., USA). In addition, the number and location of FTIR peaks were verified using the second derivative. A Gaussian line shape was used in the curve-fitting analysis of the overlapped peaks ranging from 1510 to 1460 cm−1 and 1300 to 1180 cm−1.7,12,13 NaCl was used as the background electrolyte with a fixed concentration of 0.1 M. A 0.1 M catechol solution was prepared in background electrolyte at pH 5, 7, 9, and 11. The ATR-FTIR spectra of the aqueous catechol solutions were obtained by subtracting the spectrum of catechol-free background electrolyte solutions at the same pH from the catechol spectrum. The spectra of catechol adsorbed at the interface were measured with the goethite film on the ZnSe crystal. The film was deposited on the ZnSe crystal by applying 400 μL of a goethite suspension (1 g/L) and drying in an oven at 50 °C for 1 h. Prior to use, the film was rinsed with ultra pure water to remove loosely deposited particles. The 0.1 M NaCl solution at a predetermined pH was passed through the flow cell at a rate of 0.4 mL/min until there was no further change in the spectra. A background spectrum was collected that consisted of the absorbance of the ZnSe crystal and deposited goethite. The solution was then changed to 1, 3, 4, and 8 mM catechol solutions in 0.1 M NaCl at the same pH as that of the electrolyte. Spectra were recorded as a function of time for 4 h. 4. Two-Dimensional IR Correlation Analysis. Two-dimensional correlation spectroscopy was utilized to identify the number of surface complexes and to assign peaks belonging to each surface complex.14−16 The 1D IR spectra in the wavenumber range of 1600 to 1050 cm−1 from 20 to 240 min were baseline corrected and smoothed. The average spectrum was used as a reference.17 Synchronous and asynchronous correlation spectra were calculated with the 2D Shige program (Shigeaki Morita, Kwansei-Gakuin University, 2004−2005).
In synchronous spectra, autopeaks were introduced by changing the band intensity over time. The cross peak showed correlation features between the two IR bands. A positive cross peak indicates that these two peaks increase or decrease simultaneously, whereas a negative cross peak arises when the change in peak intensity was in the opposite direction. Asynchronous spectra show only cross peaks. An asynchronous cross peak exhibits the uncorrelated response of the two IR bands, which are delayed or accelerated during the dynamic adsorption process. In other words, these two peaks change independently and thus may arise from different surface complexes or different functional groups of the same surface complex.17,18 5. Quantum Chemical Calculations. Geometry optimization and IR frequencies were calculated using the Gaussian 09 program19 with B3LYP hybrid density function theory (DFT). The 6-31+G** basis set for C, H, and O was used with a scale factor of 0.9642, and the LanL2DZ basis set was employed for Fe with a scale factor of 0.9612.20 The edge-sharing dioctahedral cluster was used to calculate the vibrational frequencies of catechol on goethite surfaces.21,22 The solvation effect was considered by using an implicit continuum model (IEFPCM) combined with H2O molecules that were added explicitly around catechol, catecholate monoanion, and the surface complexes.21,23
III. RESULTS AND DISCUSSION 1. Macroscopic Adsorption Studies. The adsorption behaviors of catechol on goethite as a function of pH and ionic strength are shown in Figure 1A. The catechol surface coverage increased as the pH increased and reached 2.4 μmol/m2 (i.e., nearly 100% catechol adsorption) at pH >8.5. Previous studies1,9,24 also reported the preferential adsorption of catechol on iron oxides under basic conditions. The phenolic hydroxyl group (ph−OH) of catechol begins to deprotonate at
Figure 1. (A) Adsorption of catechol on goethite as a function of pH in 0.01 and 0.1 M NaCl solution. (B) Total dissolved Fe concentration in the presence and absence of catechol with ionic strength at 0.01 and 0.1 M NaCl. The initial concentrations of catechol and goethite were 1 mM and 5 g/L, respectively. The detection limit of the analytical technique is 5 μg/L. 14589
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pH 7, forming the catecholate monoanion, whereas the uncharged catechol molecule is predominant under acidic and neutral conditions (pKa1 = 9.45, Figure 2A). Meanwhile, the
Table 1. Peak Positions and Assignments for Catechol (H2CAT) and the Catecholate Monoanion (HCAT−) pH 5
pH 7
H2CATa
pH 9
pH 11
HCAT−a
assignment
1103 1199
1103 1199
1075 1175
1103
1136
1261 1276 1377
1261 1276 1375
1239 1251 1367
1103 1199 1224 1259 1278 1373
1224 1258 1284 1358 1457
1189 1244 1254 1314 1430
1471
1471
1450
1515 1598
1515 1598
1491 1600
1488 1503 1598
1463 1547 1571
δ(CH) δ(OH) ν(CO) ν(CO) ν(CO) δ(OH), ν(CC) ν(CC) ν(CC), δ(CH) ν(CC) ν(CC), δ(CH) ν(CC), ν(CO)
1471 1488 1515 1598
a
Peak assignments were based on theoretical calculations. The solvation effect was simulated in combination with IEFPCM and four explicit H2O molecules.
40% of the catechol dissociated and was converted to the monoanion species; consequently, two bands were resolved at 1488 and 1224 cm−1. These two bands, due to ν(CC) and ν(CO), respectively, were also detected at pH 11, where the catecholate monoanion predominates. The bands centered at 1515 and 1471 cm−1 for the catechol molecule attributable to ν(CC) coupled with the δ(CH) mode shifted to 1503 and 1457 cm−1, respectively. In addition, the peak for the coupled δ(OH) and ν(CC) vibration shifted from 1377 cm−1 at pH 5 to 1358 cm−1 at pH 11 with a significant decrease in intensity. This pH-dependent change was also observed by LanaVillarreal5 and indicated a weak ph−OH band because deprotonation took place more easily under basic pH conditions. The bands at 1276 and 1261 cm−1 for the catechol molecule, which were assigned to the ν(CO) mode, shifted to 1284 and 1258 cm−1, respectively.1,5 The peaks centered at 1103 and 1598 cm−1, corresponding to δ(CH) and ν(CC) coupled with ν(CO), respectively,1,5 remained unchanged for the two different species. Assignments of the bands were consistent with previous studies with one exception: the band at 1224 cm−1 was assigned to ν(CO) instead of δ(OH). The δ(OH) mode in the catechol molecule at 1199 cm−1 (Figure 2B) disappeared upon deprotonation to form the catecholate monoanion. In line with Yost,25 the deprotonation of ph−OH should result in a strong phenolic CO band centered at an increased wavenumber. 3. Spectra of Adsorbed Catechol at an Interface. Figure 3 shows the time-dependent spectra of interfacial species collected from 20 to 240 min at pH 5, 7, and 9 with 1 mM catechol. Compared to the spectra of dissolved catechol (Figure 2B), the shape and position of the peaks of adsorbed catechol changed significantly, suggesting the formation of a covalent bond instead of a weak electrostatic interaction.12 In addition, the shape and position of peaks for adsorbed catechol at pH 5 to 9 were similar even though dissolved catechol species were different, indicating the same interfacial configurations at different pH. The frequencies of the adsorbed spectra at pH 5, 7, and 9 are listed in Table 2. Neither new peaks nor a shift in peak positions was observed from the time-dependent spectra at a given pH. Shoulder peaks were increasingly prominent at 1477, 1276, and 1263 cm−1 along with the reaction time, especially at high pH (Figure 3). Variations in the shape of the overlapped peaks in the ranges of 1510−1460 and 1300−1180 cm−1, as
Figure 2. (A) Distribution of catechol (H2CAT), the catecholate monoanion (HCAT−), and the dianion (CAT2−) in solution as a function of pH at an ionic strength of 0.1 M NaCl. (B) Spectra of the dissolved catechol (0.1 M) as a function of pH in 0.1 M NaCl solution. Spectra were normalized to the peak with the strongest intensity.
goethite surface is negatively charged when the pH is higher than 8.9 (PZC of goethite). However, under basic conditions the adsorption capacity was not reduced by the increased electrostatic repulsion between the catecholate anion and the negatively charged surface. Therefore, the adsorption should involve chemical reactions between the ph−OH and surface sites. In addition, the ionic strength had no detectable effect on the adsorption edge, further confirming that the primary interfacial structures are strongly bound inner-sphere complexes. Nevertheless, spectroscopic analysis and theoretical calculations are required to determine the specific interfacial configurations on the molecular level. 2. ATR-FTIR Spectroscopy and Theoretical Calculations of Dissolved Catechol. The spectra of soluble catechol species from pH 5 to 11 are presented in Figure 2B. The DFToptimized structures of molecular catechol (pH 7, where ph−OH of catechol begins to deprotonate to form monoanion species (Figures 1A and 2A). Correspondingly, the significant increase in adsorption was coupled to the elevated contribution of the B-B structure under high-pH conditions. The effect of catechol surface complexes on the dissolution of goethite in bulk adsorption experiments is illustrated in Figure 1B. Within the pH range of 4.5−9.2, the Fe concentration was below the detection limit of the analytical technique (5 μg/L) in the presence and absence of catechol. The undetectable dissolved Fe could be attributed to two reasons. First, the dissolution of goethite in our system was a consequence of both dissolution due to M-M complexes and inhibition due to B-B configurations.35 The predominant B-B surface complexes may prevent goethite dissolution. Second, dissolution−readsorption processes may occur in our catechol− goethite system, which is similar to the oxalate−goethite system.15 The dissolution of goethite probably occurred in the ATR-FTIR experiments because of the much higher ligand-tosurface ratios. However, the slight dissolution should have no significant impact on the FTIR measurements because no detectable effect was observed during the adsorption process.
AUTHOR INFORMATION
Corresponding Author
*Tel: +86-10-62849523. Fax: +86-10-62849523. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
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REFERENCES
This research is supported by the National Natural Science Foundation of China (20921063, 20890112, and 41023005). The use of Deepcomp7000 at the Computer Network Information Center of the Chinese Academy of Sciences is acknowledged.
(1) Gulley-Stahl, H.; Hogan, P. A.; Schmidt, W. L.; Wall, S. J.; Buhrlage, A.; Bullen, H. A. Surface Complexation of Catechol to Metal Oxides: An ATR-FTIR, Adsorption, and Dissolution Study. Environ. Sci. Technol. 2010, 44, 4116−4121. (2) Vasudevan, D.; Stone, A. T. Adsorption of Catechols, 2Aminophenols, and 1,2-Phenylenediamines at the Metal (Hydr)Oxide/Water Interface: Effect of Ring Substituents on the Adsorption onto TiO2. Environ. Sci. Technol. 1996, 30, 1604−1613. (3) Araujo, P. Z.; Morando, P. J.; Blesa, M. A. Interaction of Catechol and Gallic Acid with Titanium Dioxide in Aqueous Suspensions. 1. Equilibrium Studies. Langmuir 2005, 21, 3470−3474. (4) Janković, I. A.; Šaponjić, Z. V.; Č omor, M. I.; Nedeljković, J. M. Surface Modification of Colloidal TiO2 Nanoparticles with Bidentate Benzene Derivatives. J. Phys. Chem. C 2009, 113, 12645−12652. (5) Lana-Villarreal, T.; Rodes, A.; Pérez, J. M.; Gómez, R. A Spectroscopic and Electrochemical Approach to the Study of the Interactions and Photoinduced Electron Transfer between Catechol and Anatase Nanoparticles in Aqueous Solution. J. Am. Chem. Soc. 2005, 127, 12601−12611. (6) McBride, M. B.; Wesselink, L. G. Chemisorption of Catechol on Gibbsite, Boehmite, and Noncrystalline Alumina Surfaces. Environ. Sci. Technol. 1988, 22, 703−708. (7) Hug, S. J. In Situ Fourier Transform Infrared Measurements of Sulfate Adsorption on Hematite in Aqueous Solutions. J. Colloid Interface Sci. 1997, 188, 415−422. (8) Kang, S.; Xing, B. Adsorption of Dicarboxylic Acids by Clay Minerals as Examined by in Situ ATR-FTIR and ex Situ DRIFT. Langmuir 2007, 23, 7024−7031. (9) Evanko, C. R.; Dzombak, D. A. Influence of Structural Features on Sorption of NOM-Analogue Organic Acids to Goethite. Environ. Sci. Technol. 1998, 32, 2846−2855. (10) Evanko, C. R.; Dzombak, D. A. Surface Complexation Modeling of Organic Acid Sorption to Goethite. J. Colloid Interface Sci. 1999, 214, 189−206. (11) Schwertmann, U.; Cornell, R. M. Iron Oxides in the Laboratory: Preparation and Characterization, 2nd ed.; Wiley-VCH: Weinheim, Germany, 2000. (12) Ha, J.; Hyun Yoon, T.; Wang, Y.; Musgrave, C. B.; Brown, J. G. E. Adsorption of Organic Matter at Mineral/Water Interfaces: 7. ATRFTIR and Quantum Chemical Study of Lactate Interactions with Hematite Nanoparticles. Langmuir 2008, 24, 6683−6692. (13) Tan, S.; Sun, X.; Williams, C. T. In Situ ATR-IR Study of Prochiral 2-Methyl-2-Pentenoic Acid Adsorption on Al2O3 and Pd/ Al2O3. Phys. Chem. Chem. Phys. 2011, 13, 19573−19579. (14) Norén, K.; Persson, P. Adsorption of Monocarboxylates at the Water/Goethite Interface: The Importance of Hydrogen Bonding. Geochim. Cosmochim. Acta 2007, 71, 5717−5730. (15) Simanova, A. A.; Loring, J. S.; Persson, P. Formation of Ternary Metal-Oxalate Surface Complexes on α-FeOOH Particles. J. Phys. Chem. C 2011, 115, 21191−21198.
IV. CONCLUSIONS In this investigation, adsorption mechanisms of catechol at the goethite/aqueous interface were investigated with multiple complementary techniques. Our spectroscopic and DFT calculation results demonstrated the coexistence of M-M and B-B surface complexes in the pH range of 5 to 9. The ATRFTIR experiments indicated that adsorption in the M-M structure reaches equilibrium in 90−120 min whereas the adsorption in the B-B structure was still increasing at 240 min. In addition, the relative contribution of B-B complexes to the overall adsorption capacity increased with increasing pH and surface coverage. Notably, the M-M structure could partially convert to the B-B structure via proton exchange between the surface and adsorbed catechol under basic conditions and high surface coverage. The results provide insights into catechol surface complexes on the molecular scale that can be used to describe and predict the behaviors of hydroxyaromatic compounds in the environment.
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ASSOCIATED CONTENT
S Supporting Information *
Synthesis and characterization of goethite. Optimized structures for catechol and the catecholate monoanion with explicit water molecules. Comparison of the experimental and calculated frequencies and relative intensities of dissolved catechol. Sensitivity analysis of the DFT calculation. Two-dimensional contour plots obtained from the time-dependent adsorbed spectra at pH 5, 7 and 9. Two-dimensional analysis of the number and shift of the peaks. This material is available free of charge via the Internet at http://pubs.acs.org. 14596
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(16) Lindegren, M.; Loring, J. S.; Persson, P. Molecular Structures of Citrate and Tricarballylate Adsorbed on α-FeOOH Particles in Aqueous Suspensions. Langmuir 2009, 25, 10639−10647. (17) Noda, I.; Ozaki, Y. Two-Dimensional Correlation Spectroscopy: Applications in Vibrational and Optical Spectroscopy; John Wiley & Sons: Chichester, England, 2004. (18) Noda, I. Generalized Two-Dimensional Correlation Method Applicable to Infrared, Raman, and Other Types of Spectroscopy. Appl. Spectrosc. 1993, 47, 1329−1336. (19) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, K.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.; Kobayashi, A.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.; Klene, M.; Knox, J. E.; 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.; Martin, G. J.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Revision B.01; Gaussian, Inc.: Wallingford, CT, 2010. (20) NIST Computational Chemistry Comparison and Benchmark Database; NIST Standard Reference Database Number 101; Johnson, R. D., III, Ed.; Release 15b, August 2011, http://cccbdb.nist.gov/. (21) Kwon, K. D.; Kubicki, J. D. Molecular Orbital Theory Study on Surface Complex Structures of Phosphates to Iron Hydroxides: Calculation of Vibrational Frequencies and Adsorption Energies. Langmuir 2004, 20, 9249−9254. (22) Paul, K. W.; Borda, M. J.; Kubicki, J. D.; Sparks, D. L. Effect of Dehydration on Sulfate Coordination and Speciation at the Fe(Hydr)Oxide-Water Interface: A Molecular Orbital/Density Functional Theory and Fourier Transform Infrared Spectroscopic Investigation. Langmuir 2005, 21, 11071−11078. (23) Aquino, A. J. A.; Tunega, D.; Haberhauer, G.; Gerzabek, M. H.; Lischka, H. Acid-Base Properties of a Goethite Surface Model: A Theoretical View. Geochim. Cosmochim. Acta 2008, 72, 3587−3602. (24) Gu, B.; Schmitt, J.; Chen, Z.; Liang, L.; McCarthy, J. F. Adsorption and Desorption of Different Organic Matter Fractions on Iron Oxide. Geochim. Cosmochim. Acta 1995, 59, 219−229. (25) Yost, E. C.; Tejedor-Tejedor, M. I.; Anderson, M. A. In Situ CIR-FTIR Characterization of Salicylate Complexes at the Goethite/ Aqueous Solution Interface. Environ. Sci. Technol. 1990, 24, 822−828. (26) Axe, K.; Vejgår den, M.; Persson, P. An ATR-FTIR Spectroscopic Study of the Competitive Adsorption between Oxalate and Malonate at the Water-Goethite Interface. J. Colloid Interface Sci. 2006, 294, 31−37. (27) Chiem, L. T.; Huynh, L.; Ralston, J.; Beattie, D. A. An in Situ ATR−FTIR Study of Polyacrylamide Adsorption at the Talc Surface. J. Colloid Interface Sci. 2006, 297, 54−61. (28) Connor, P. A.; Dobson, K. D.; McQuillan, A. J. New Sol-Gel Attenuated Total Reflection Infrared Spectroscopic Method for Analysis of Adsorption at Metal Oxide Surfaces in Aqueous Solutions. Chelation of TiO2, ZrO2, and Al2O3 Surfaces by Catechol, 8Quinolinol, and Acetylacetone. Langmuir 1995, 11, 4193−4195. (29) Martin, S. T.; Kesselman, J. M.; Park, D. S.; Lewis, N. S.; Hoffmann, M. R. Surface Structures of 4-Chlorocatechol Adsorbed on Titanium Dioxide. Environ. Sci. Technol. 1996, 30, 2535−2542. (30) Sanchez-de-Armas, R.; San-Miguel, M. A.; Oviedo, J.; Marquez, A.; Sanz, J. F. Electronic Structure and Optical Spectra of Catechol on TiO2 Nanoparticles from Real Time TD-DFT Simulations. Phys. Chem. Chem. Phys. 2011, 13, 1506−1514. (31) Yoon, T. H.; Johnson, S. B.; Musgrave, C. B.; Brown, J. G. E. Adsorption of Organic Matter at Mineral/Water Interfaces: I. ATRFTIR Spectroscopic and Quantum Chemical Study of Oxalate
Adsorbed at Boehmite/Water and Corundum/Water Interfaces. Geochim. Cosmochim. Acta 2004, 68, 4505−4518. (32) Liu, L.-M.; Li, S.-C.; Cheng, H.; Diebold, U.; Selloni, A. Growth and Organization of an Organic Molecular Monolayer on TiO2: Catechol on Anatase (101). J. Am. Chem. Soc. 2011, 133, 7816−7823. (33) Li, S.-C.; Wang, J.-G.; Jacobson, P.; Gong, X. Q.; Selloni, A.; Diebold, U. Correlation between Bonding Geometry and Band Gap States at Organic-Inorganic Interfaces: Catechol on Rutile TiO2(110). J. Am. Chem. Soc. 2009, 131, 980−984. (34) Terranova, U.; Bowler, D. R. Adsorption of Catechol on TiO2 Rutile (100): A Density Functional Theory Investigation. J. Phys. Chem. C 2010, 114, 6491−6495. (35) Stumm, W. The Inner-Sphere Surface Complex. In Aquatic Chemistry: Interfacial and Interspecies Processes; Huang, C. P., O’Melia, C. R., Morgan, J. J., Eds.; American Chemical Society: Washington, DC, 1995; p 19.
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