Anatase Surface Research Articles

Anatase TiO2 film with dominant (001) facets prepared by radio frequency atmospheric pressure plasma

Anatase TiO2 nanosheets film with dominant (001) facets (TF-1) has attracted widespread research interest owing to wide-ranging industrial applications and fundamental importance. In this work, we prepared TF-1 with well adhesion on quartz substate in a short time (20 min) by radio frequency (RF) pulse-modulated plasma with hydrofluoric acid (HF) as the morphology controlling agent (MCA). Many intercrossed nanosheets were observed on the surface of TF-1 through SEM images, which provides more exposed reactive (001) facets. The degree of truncation (B/A) and the percentage of exposed (001) facets (S001/S) were estimated by XRD patterns and Raman spectra, which have been increased due to the presence of HF. XPS results indicate that F atoms are only adsorbed on anatase surface rather than doped into TiO2 lattice. The functions of HF on the growth of anatase TiO2 nanosheets were studied by density functional theory (DFT), revealing the stabilization effects associated with chemisorbed fluorine (F) atoms over (001) surface, and thus stimulating its preferred growth.

Unveiling photoinduced electron transfer in cobalt(iii)-R-pyridine complexes anchored to anatase nanocrystals: photoluminescence and magnetic studies.

In this study, we synthesized mixed ligand complexes of the cis-[Co(tn)2(Rpy)Br]Br2 type using a novel mechanochemical approach. Characterization involved spectral measurements and single crystal X-ray diffraction analysis, confirming the structure of the cis-[Co(tn)2(4-Mepy)Br]Br2 complex. The single crystal refinement data revealed a monoclinic crystal system with a distorted octahedral geometry. The choice of the sixth ligand influenced the emission and magnetic properties, showing a ferromagnetic character in the Co(iii)-complex environment. We investigated efficient electron transfer to the cobalt(iii) center using TiO2 nanoparticles under UV-light irradiation. The adsorption characteristics of cis-[Co(tn)2(Rpy)Br]Br2 in aqueous 2-propanol varied, leading to surface compound formation. Under UV irradiation, the anatase surface exhibited remarkable adsorption capabilities, facilitating efficient electron transfer to the Co(iii) center and resulting in a high photoefficiency for Co(ii) formation. Our study has put forward a model for interfacial electron transfer (IET), taking into account the overlap between the TiO2 conduction band and the acceptor level of the Co center, as well as the electronic coupling between the donor level of the Ti center and the acceptor level of the Co center. This model sheds light on the accumulation of electrons for reducing the adhered complex ion. The IET process was corroborated by the conversion of 2-propanol into acetone, as verified by 1H NMR technique. Overall, our findings provide novel insights into the role of the Rpy moiety in modifying the structure of the TiO2-cobalt(iii)-Rpy compound and propose a mechanism for IET reactions, thus advancing the field.

In situ Fourier transform infrared-attenuated total reflection spectroscopy and modeling investigation of protein adsorption: Case of expanded bovine serum albumin on titanium dioxide anatase.

The purpose of this experimental and modeling research is to study the pH effect and to determine the surface coverage plus the adsorption constant (Ka) of bovine serum albumin (BSA) protein adsorbed on TiO2 anatase surface, respectively. In situ Fourier transform infrared-attenuated total reflection spectroscopy in a flow-through cell was used to study the BSA adsorption on porous TiO2 anatase films. The experiments were performed in water solution, under different pH values, at a concentration of 10-6 mol/l. Theoretically, we extended the two-state model, based on a system of coupled differential equations, by adding a desorption parameter Kd2, for unfolded state. The model was solved taking into account the adsorption (Ka), desorption (Kd1,2), transformation (Kf) coefficients, and the initial solution protein concentration (C0). The findings clearly illustrated that the solution pH drastically changed the behavior of BSA adsorption, whereas the mathematical analytical solutions allowed us to determine the native state (θ1), the unfolded state (θ2), and the full one (θ) surface coverages. Finally, a good application of the approximated model on the experimental work, expanded BSA adsorbed on TiO2 anatase at pH = 1.7, indicated a value of Ka = (408.36 ± 0.996) × 102 mol-1 l min-1.

Highly selective photocatalytic CO2 reduction by metal-N4 dynamically generated from atomically dispersed copper

Solar-driven conversion of CO2 into high-value-added chemicals is considered as one of the effective strategies to address global climate change. However, the sluggish charge separation kinetics and poor product selectivity remain the two major bottlenecks restricting photocatalytic CO2 conversion. Herein, we developed an anatase surface modified atomically dispersed Cu (Cu anchored on N-doped carbon skeleton) photocatalyst (TiO2/Cu1NC) based on a “reflux + calcination” method for CO2 photoreduction. Under full spectral illumination, the as-synthesized TiO2/Cu1NC displayed a brilliant CO production rate of 2.59 μmol h−1 (mass of photocatalyst: 5 mg), high selectivity (∼98.5%), and excellent durability using [Ru(bpy)3]Cl2·6H2O as the photosensitizer and triethanolamine as an electron donor. Experiments and density functionalized theory calculations synergistically confirm that the surface-constructed atomically dispersed Cu1NC active sites can accelerate the separation and transfer of photogenerated charge carriers, optimize CO2 adsorption and activation, reduce the formation energy barrier of the key intermediate *COOH during the CO2RR process, and thus enhance the activity and selectivity of CO2RR. This work provides new insights into the surface engineering of atomically dispersed active sites to improve the activity and CO selectivity of CO2 photoreduction.

Electronic Bulk and Surface Properties of Titanium Dioxide Studied by DFT-1/2.

Transparent conductive oxides, such as TiO2, are important functional materials for optoelectronic and photovoltaic devices. We investigate the electronic bulk properties of the TiO2 phases rutile and anatase with the DFT-1/2 method and obtain a quantitatively good description of their electronic band structures. We then applied this method to the (001) surfaces of rutile and anatase and calculated their ionization potentials (IPs) and work functions (WF). To relate these calculated surface properties with values from experiments, we evaluated the effect of varying the oxygen stoichiometry at the surface on both IP and WF.

Understanding the release, migration, and risk of heavy metals in coal gangue: An approach by combining experimental and computational investigations

The lack of understanding on the environmental fate and implications of heavy metals in coal gangue (CG) has restrained its utilization. Conventional extraction methods provide empirical measures of heavy metal speciation, lacking a detailed description of bound strength, which limits long-term risk assessment. In this study, the releasing and migrating behavior of six heavy metals (Cd, As, Pb, Ni, Cu, and Cr) were investigated through an approach by combining experimental and computational investigations. The corresponding mechanisms and risks were understood and discussed on a molecular level. The results suggested that CG is primarily a natural kaolinite α-quartz and anatase mineral. The sequence extraction results showed that heavy metals in CG are mainly distributed in stable silicate and iron manganese oxide-bound states. The toxicity characteristic leaching procedure test advised Cu, Cr, Ni, and Pb had a high toxic level and thus required long-term monitoring and controlling. A quantum chemical calculation demonstrated that the heavy metals were more likely to be embedded in silicate minerals with high binding energy than those binding on the anatase surface. The findings of this research provide a promising approach to comprehensively evaluate the stability mechanism and potential long-term risks of heavy metals in solid waste.

Mechanistic insight on water dissociation on pristine low-index TiO2 surfaces from machine learning molecular dynamics simulations

Water adsorption and dissociation processes on pristine low-index TiO2 interfaces are important but poorly understood outside the well-studied anatase (101) and rutile (110). To understand these, we construct three sets of machine learning potentials that are simultaneously applicable to various TiO2 surfaces, based on three density-functional-theory approximations. Here we show the water dissociation free energies on seven pristine TiO2 surfaces, and predict that anatase (100), anatase (110), rutile (001), and rutile (011) favor water dissociation, anatase (101) and rutile (100) have mostly molecular adsorption, while the simulations of rutile (110) sensitively depend on the slab thickness and molecular adsorption is preferred with thick slabs. Moreover, using an automated algorithm, we reveal that these surfaces follow different types of atomistic mechanisms for proton transfer and water dissociation: one-step, two-step, or both. These mechanisms can be rationalized based on the arrangements of water molecules on the different surfaces. Our finding thus demonstrates that the different pristine TiO2 surfaces react with water in distinct ways, and cannot be represented using just the low-energy anatase (101) and rutile (110) surfaces.

Comparison of H2O Adsorption and Dissociation Behaviors on Rutile (110) and Anatase (101) Surfaces Based on ReaxFF Molecular Dynamics Simulation.

The relationship between structure and reactivity plays a dominant role in water dissociation on the various TiO2 crystallines. To observe the adsorption and dissociation behavior of H2O, the reaction force field (ReaxFF) is used to investigate the dynamic behavior of H2O on rutile (110) and anatase (101) surfaces in an aqueous environment. Simulation results show that there is a direct proton transfer between the adsorbed H2O (H2Oad) and the bridging oxygen (Obr) on the rutile (110) surface. Compared with that on the rutile (110) surface, an indirect proton transfer occurs on the anatase (101) surface along the H-bond network from the second layer of water. This different mechanism of water dissociation is determined by the distance between the 5-fold coordinated Ti (Ti5c) and Obr of the rutile and anatase TiO2 surfaces, resulting in the direct or indirect proton transfer. Additionally, the hydrogen bond (H-bond) network plays a crucial role in the adsorption and dissociation of H2O on the TiO2 surface. To describe interfacial water structures between TiO2 and bulk water, the double-layer model is proposed. The first layer is the dissociated H2O on the rutile (110) and anatase (101) surfaces. The second layer forms an ordered water structure adsorbed to the surface Obr or terminal OH group through strong hydrogen bonding (H-bonding). Affected by the H-bond network, the H2O dissociation on the rutile (110) surface is inhibited but that on the anatase (101) surface is promoted.

Interaction of biomolecules with anatase, rutile and amorphous TiO2 surfaces: A molecular dynamics study.

The adhesion of biomolecules to dental and orthopedic implants is a fundamental step in the process of osseointegration. Short peptide motifs, such as RGD or KRSR, carried by extracellular matrix proteins or coated onto implant surfaces, accelerate cell adhesion and tissue formation. For this reason, understanding the binding mechanisms of adhesive peptides to oxidized surfaces of titanium implants is of paramount importance. We performed molecular dynamics simulations to compare the adhesion properties of 6 peptides, including the tripeptide RGD, its variants KGD and LGD, as well as the tetrapeptide KRSR, its variant LRSR and its truncated version RSR, on anatase, rutile, and amorphous titanium dioxide (TiO2) surfaces. The migration of these molecules from the water phase to the surface was simulated in an aqueous environment. Based on these simulations, we calculated the residence time of each peptide bound to the three different TiO2 structures. It was found that the presence of an N-terminal lysine or arginine amino acid residue resulted in more efficient surface binding. A pulling simulation was performed to detach the adhered molecules. The maximum pulling force and the binding energy were determined from the results of these simulations. The tri- and tetrapeptides had slightly greater adhesion affinity to the amorphous and anatase structure than to rutile in general, however specific surface and peptide binding characters could be detected. The binding energies obtained from our simulations allowed us to rank the adhesion strengths of the studied peptides.

Inducing differences in modification degree and binding mode of organophosphonic acid grafted titania by changing pH and hydrocarbon chain length

Organically modified metal oxide surfaces are of interest in many applications since they combine the advantages of metal oxide supports (structural properties, chemical and mechanical stability) and organic functionalities (for specific surface interactions). Although surface modification with organophosphonic acids (PAs) with an alkyl or aminoalkyl functional group on TiO2 has been investigated previously, knowledge of the synthesis-properties correlation (e.g. the binding mode of the PAs) is still lacking, especially for functional group-surface interactions. These are however important as they can influence functional group availability in applications such as (metal) sorption. In this work, the dependence of modification degree and phosphorus chemical environment on pH and chain length (C1 to C6) was investigated with TGA, ICP-OES, nitrogen/argon sorption, XPS, and solid-state 31P NMR and DFT calculations. The TGA and the ICP-OES results showed a clear impact of pH on surface modification degrees, with a different response for modification with alkyl- and aminoalkylphosphonic acids, featuring a more rapid decrease in modification degrees from pH 2 upwards for the alkylphosphonic acids compared to the aminoalkylphosphonic acids. Moreover, a clear correlation can be found between the aminoalkyl chain length and the NH2/NH3+ ratio. In addition, a positive correlation between the modification degree and the protonation degree of the amine group is observed for aminomethylphosphonic acid (AMPA) and 2-aminoethylphosphonic acid (2AEPA) modified samples, while this is absent for longer alkyl chains. This is supported by DFT calculations that indicate that the most stable binding modes of AMPA and 2AEPA grafted on the anatase (101) surface include hydrogen bonds between NH3+ and the surface oxygen atoms, in contrast, the most stable binding modes for 3-aminopropylphosphonic acid (3APPA), 4-aminobutylphosphonic acid (4ABPA), and 6-aminohexylphosphonic acid (6AHPA) grafted on the anatase (101) surface involve a Lewis acid-base interaction between NH2 and a surface Ti site.

Synthesis of Peptides from Glycine on Anatases with Different Crystal Facets

Semiconductor minerals are widely present on the surface of Earth, but their roles in the process of peptide formation from amino acids are less studied, especially the role of different crystal facets in the origin of life. In this research, High Performance Liquid Chromatography (HPLC), thermogravimetric analysis (TA/DTA), Nuclear Magnetic Resonance (NMR) and simulation calculations were used to study the condensation of glycine on the surface of anatase with (001) crystal facets and ordinary anatase as well as the reaction mechanism. Combined with TA/DTA and heating experiments (80–130 °C), it was found that anatase with (001) crystal facets and ordinary anatase could both catalyze the condensation of glycine to form corresponding oligopeptides (mainly DKP, Gly2 and Gly3). Anatase with (001) crystal facets shows better catalytic effect, which can reduce the condensation temperature of glycine to 90 °C. With the increase in temperature, the condensation efficiency of anatase with (001) crystal facets for Gly2 is relatively higher, and the maximum yield is about 0.20 mg/m2. The condensation efficiency of ordinary anatase for Gly3 is relatively higher, and the maximum yield is about 0.28 mg/m2. The results of FTIR and simulation calculation show that the electron density of the carboxyl group changes after glycine is adsorbed on the surface of anatase, which is easily subject to the nucleophilic attack of amino groups to promote the condensation reaction. These results can provide reference for the research of condensation of small biomolecules on semiconductor mineral surfaces in the origin of life.

Structural, dynamical and dielectric properties of water in contact with TiO2 surfaces via molecular-dynamics simulations

Undoubtedly, enhancing our knowledge of the dielectric response, structural, translational-librational and dynamics properties of water either in bulk environment or in its interfacial guise are required to provide a detailed understanding of the fundamental properties crucial for the development of more efficient and improved control of photo-energy conversion devices, especially those based on photo-electrochemical (PEC) water splitting. To this end, classical equilibrium molecular-dynamics simulations have been performed to rationalise the intriguing behaviour of bulk water and, in particular, interfacial hydration water layers with both rutile (110) and anatase (101) surfaces of titanium dioxide (TiO2). The dielectric characteristics of interfacial water in the first-adsorbed water layer evince a markedly reduced value in comparison to the bulk water environment, as well as lower self-diffusivity (owing to surface-confinement effects). In addition, this work presents evidence describing behavioural pattern of adsorbed hydration layers which reflects similarities observed in the underlying surface-identity mechanism of titania slabs used, and on how surface atomistic architecture – indeed, ‘surface personality’ – dictates to a large extent the dielectric ‘matching’ of hydration-water layers adsorbed thereon. Further analyses show evidence of strong-roles underpinning the hydrogen-bond network at the water/titania interfaces.

First-Principles Band Alignments at the Si:Anatase TiO2 Interface.

TiO2 has been identified as a promising electron transport layer in Si solar cells. Experiments have revealed that the Si:TiO2 interface undergoes structural changes depending on how it was fabricated. However, less is understood about the sensitivity of electronic properties, such as band alignments, to these changes. Here, we present first-principles calculations of band alignments between Si and anatase TiO2, investigating different surface orientations and terminations. By calculating vacuum-level alignments, we observe a large band offset reduction of 2.5 eV for the O-terminated Si slab compared to other terminations. Furthermore, a 0.5 eV increase is found for the anatase (101) surface compared to (001). We compare the band offsets obtained through vacuum alignment with four different heterostructure models. Even though the heterostructure models contain an excess of oxygen, their offsets agree well with vacuum-level alignments using stoichiometric or H-terminated slabs, and the reduction in band offsets seen for the O-terminated Si slab is not observed. Additionally, we have investigated different exchange-correlation treatments including PBE + U, postprocessing GW corrections, and the meta-GGA rSCAN functional. We find that rSCAN provides more accurate band offsets than PBE, but further corrections are still required to achieve <0.5 eV accuracy. Overall, our study quantifies the importance of surface termination and orientation for this interface.

Modeling stoichiometric and oxygen defective TiO2 anatase bulk and (101) surface: structural and electronic properties from hybrid DFT.

We present a periodic hybrid DFT investigation of the structural and electronic properties of both stoichiometric and oxygen-defective TiO2 anatase bulk and (101) surface, in singlet and triplet spin states. In all cases, an excellent agreement with available photoelectron spectroscopy data has been obtained, reproducing the offsets of the deep defect levels positions from the conduction band minimum of TiO2 created upon oxygen vacancy (VO) formation. For the bulk, different local structural polaronic distortions around the VO site have been evidenced depending on the spin state considered. Although a similar conclusion has been drawn for the defective surface for the nine different vacancy positions which have been considered, large migration of the twofold coordinated surface O atom has also been evidenced, up to the initial vacancy site in some cases. The very good agreement obtained with available experimental data regarding the offsets from the conduction band minimum of the deep defect levels positions both for the bulk and the (101) surface of TiO2 anatase is encouraging for the application of the proposed hybrid-based computational strategy to TiO2 surface-related processes such as TiO2-based photocatalysis in which oxygen vacancies are known to play a key role. All calculations have been performed with Crystal17, considering different hybrid functionals with both effective core pseudopotentials and all-electron atom-centered basis sets, as well as additional empirical dispersion effects with the D2 and D3 models.

In situ DRIFTS and TPD studies on surface properties affecting SO2-resistance of Pt/TiO2 catalyst in low-temperature CO oxidation

By pre-calcining two TiO2 (P25 and anatase) supports at various temperatures, Pt/TiO2 of different Pt valence states, surface hydroxyls (OH), and peroxide contents were prepared. Pt/Anatase 450 and Pt/P25 450, whose supports were pre-calcined at 450 °C, performed excellently in the CO oxidation catalytic activity test using flue gas without water and SO2. Their low T50 (165 and 175 °C, respectively) and high TOF at 125 °C (0.204 and 0.247 s−1, respectively) of CO oxidation are attributed to the low stability of the adsorbed CO on Pt sites. Furtherly, in the catalytic test using water and SO2-containing flue gas, the catalysts using anatase supports achieved higher performance than P25 supports, showing T50 of 182−186 °C and TOF of 0.202−0.207 s−1 at 165 °C. The in situ DRIFTS study and TPD analysis indicate that OH participates in the sulfate formation. The limited hydroxylation on the anatase surface provides a small amount of OH, thereby mitigating the stable sulfate accumulation. Less stable sulfate on anatase than P25 gives rise to the high activity of anatase-supported catalysts.

Mechanistic Insights into the High Selectivity and Photocatalytic Activity of Brookite TiO2 toward NOX Abatement

TiO2 nanomaterials are promising photocatalysts for NOx depollution from air under sunlight irradiation. It commonly exists in three phases, i.e., anatase, rutile, and brookite. Anatase, rutile, and a mixture of them are heavily studied. Herein, we have tested the photocatalytic activity of the less studied brookite TiO2 for the NOx depollution from the air. Pure brookite and anatase/brookite mixtures have been synthesized and characterized. Interestingly, we found that brookite TiO2 photocatalyst has a comparable photocatalytic activity to that of the benchmark TiO2 P25, and more importantly, it has higher selectivity toward the conversion of NOx into nitrate ions. The selectivity of brookite TiO2 derived from the TALH precursor is 4.6- and 3.5-fold higher than that of pure anatase and TiO2 P25, respectively. Such impressive selectivity has been explained by measuring the content of physically and chemically adsorbed water, the relative density of defects, and the affinity of NO2 and water adsorption on different anatase and brookite surfaces. The EPR results indicated that brookite TiO2 exhibits a higher density of charge-trapping sites (defects) than anatase. The DFT calculation supported that these defects increase the tendency of brookite (001) surface toward the nondissociative adsorption of NO2, whereas the dissociative adsorption of water is preferred on the perfect surface. It seems that the coexistence of dual sites for the adsorption of molecular NO2 and water-dissociated molecules is crucial for the enhanced selectivity of DeNOx to nitrate ions on brookite TiO2.

Density functional theory and molecular dynamics studies on electrical, mechanical, and thermal properties of TiO2 nanoparticles interacting with poly lactic-co-glycolic acid

Poly-lactic poly-co-glycolic acid (PLGA) copolymer is widely used thanks to its biocompatibility, even if could be difficult to find desirable mechanical properties for the polymer matrix. For this reason, inorganic nanoparticles like titanium dioxide (TiO2) can be used to modulate the mechanical properties of systems maintaining their biological capabilities. In this concern, density functional theory (DFT) and molecular dynamics (MD) simulations have been used to study the absorption phenomena of PLGA on surfaces of I4₁/amd (Anatase), P42/mnm (Rutile), and Pbca (Brookite) polymorphs of TiO2 DFT results showed that Anatase TiO2 is the best choice to absorb PLGA in comparison to the other PLGA-TiO2 surfaces. MD simulations remarked a peculiar stabilization pathway of PLGA-TiO2 with Anatase surface along the MD time and the largest increase in both Young's and Bulk's moduli. Finally, the influence of temperature on the mechanical properties of PLGA/A-TiO2 has also been investigated; in particular, MD results revealed that Young’s modulus of nanocomposite and the binding energy decreased by increasing the temperature. The outcomes of the present investigation could be helpful to clarify the potential uses of the PLGA-TiO2 nanocomposites in the biomedical field ranging from bone tissue engineering to drug delivery.

Oxidation and Nanoparticle Formation during Ce(III) Sorption onto Minerals.

The sorption of Ce(III) on three abundant environmental minerals (goethite, anatase, and birnessite) was investigated. Batch sorption experiments using a radioactive 139Ce tracer were performed to investigate the key features of the sorption process. Differences in sorption kinetics and changes in oxidation states were found in the case of the sorption of Ce(III) on birnessite compared to that on other minerals. Speciation of cerium onto all of the studied minerals was investigated using spectral and microscopic methods: high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), and X-ray absorption spectroscopy (XAS) in conjunction with theoretical calculations. It was found that during the sorption process onto birnessite, Ce(III) was oxidized to Ce(IV), while the Ce(III) on goethite and anatase surfaces remained unchanged. Oxidation of Ce(III) by sorption on birnessite was also accompanied by the formation of CeO2 nanoparticles on the mineral surface, which depended on the initial cerium concentration and pH value.

Diffusion of oxygen vacancies formed at the anatase (101) surface: An activation-relaxation technique study

${\mathrm{TiO}}_{2}$ is a technologically important material. In particular, its anatase polymorph plays a major role in photocatalysis, which can also accommodate charged and neutral vacancies. There is, however, scant theoretical work on the vacancy charge and associated diffusion from surface to subsurface and bulk in the literature. Here, we aim to understand +2 charge and neutral vacancy diffusion on anatase (101) surface using 72- and 216-atom surface slabs employing a semilocal density functional and the Hubbard model. The activation-relaxation technique nouveau coupled with quantum espresso is used to investigate the activated mechanisms responsible for the diffusion of oxygen vacancies. The small-slab model overstabilizes the +2 charged topmost surface vacancy, which is attributed to the strong Coulomb repulsion between vacancy and neighboring ${\mathrm{Ti}}^{+4}$ ions. The larger slab allows atoms to relax parallel to the surface, decreasing the +2 charged topmost surface vacancy stability. The calculated surface-to-subsurface barriers for the +2 charged vacancy and diffusion of the neutral vacancy on a slab of 216 atoms are 0.82 and 0.52 eV, respectively. Furthermore, the bulk vacancy prefers to migrate toward the subsurface with relatively low activation barriers 0.19 and 0.27 eV and the reverse process has to overcome 0.38- and 0.40-eV barriers for the +2 charged and the neutral vacancies. This explains the experimentally observed high concentration of vacancies at the subsurface sites rather than in the bulk, and the dynamic diffusion of vacancies from the bulk to the subsurface and from the subsurface to the bulk is highly likely on the surface of anatase (101). Finally, we provide a plausible explanation for the origin of recently observed subsurface-to-surface diffusion of oxygen vacancy from the calculated results.

Interaction of organic pollutants with TiO2: a density functional theory study of carboxylic acids on the anatase (101) surface

Understanding the interaction of the carboxylic group with TiO2 is crucial for photocatalytic degradation of pollutants, because aromatic molecules containing carboxylic acid groups are among the most common micropollutants. This study investigated the interactions of the anatase TiO2 (101) surface with several aromatic carboxylic acids: benzoic, nicotinic, salicylic and anthranilic acid, using dispersion-corrected density functional theory (DFT) calculations. For all the molecules studied, we found higher stabilities of monodentate adsorbed configurations over bidentate. Dispersion was found to have a significant effect on adsorption energies. In particular, dispersion gave rise to a tilted monodentate adsorption configuration, where adsorption through interfacial covalent and hydrogen bonds was additionally stabilised by dispersion interactions of the aromatic ring with the surface. Comparative calculations using DFT with empirical dispersion correction and van der Waals-corrected functionals found the relative stabilities of adsorbed structures to be independent of the method of describing dispersion. Thermodynamic probabilities of different adsorption configurations were evaluated using the Boltzmann distribution, and the tilted dispersion-stabilised structures were predicted to be by far the most abundant. Finally, the optical absorption of TiO2-acid systems was modelled, and TiO2-aromatic acid complexes were found to have their optical absorption extended into the visible range.