C1s Binding Research Articles

The C1s core levels of polycyclic aromatic hydrocarbons and styrenic polymers: A first-principles study.

Understanding core level shifts in aromatic compounds is crucial for the correct interpretation of x-ray photoelectron spectroscopy (XPS) of polycyclic aromatic hydrocarbons (PAHs), including acenes, as well as of styrenic polymers, which are increasingly relevant for the microelectronic industry, among other applications. The effect of delocalization through π aromatic systems on the stabilization of valence molecular orbitals has been widely investigated in the past. However, little has been reported on the impact on the deeper C1s core energy levels. In this work, we use first-principles calculations at the level of many body perturbation theory to compute the C1s binding energies of several aromatic systems. We report a C1s red shift in PAHs and acenes of increasing size, both in the gas phase and in the molecular crystal. C1s red shifts are also calculated for stacked benzene and naphthalene pairs at decreasing intermolecular distances. A C1s red shift is in addition found between oligomers of poly(p-hydroxystyrene) and polystyrene of increasing length, which we attribute to ring-ring interactions between the side-chains. The predicted shifts are larger than common instrumental errors and could, therefore, be detected in XPS experiments.

Roles of hygrothermal aging temperature and time in degradation of the fracture toughness of highly cross‐linked epoxy

AbstractThe evolution of plane‐strain fracture toughness in highly cross‐linked epoxies was assessed for different hygrothermal aging temperatures (25, 50, and 75°C) and durations (0–75 days). The absorption of water increased with hygrothermal aging, but at a diminishing rate and without saturating. A fraction of the absorbed water persisted despite prolonged drying. Thermogravimetric analysis revealed that the epoxy‐decomposition temperature decreased with hygrothermal aging. 13C solid‐state nuclear magnetic resonance spectroscopy indicated an increase in the de‐shielding of carbon atoms in the vicinity of electronegative elements like oxygen with hygrothermal aging severity, indicating the development of intermolecular hydrogen bonding. X‐ray photoelectron spectroscopy tracked the chemical bonding state of carbon by using a narrow scan on the C1s binding energy region. Upon hygrothermal aging, there was a decrease in CC/CC groups, indicating main chain scission through hydrolysis. A simultaneous increase in the CO species indicates the formation of alcohols as hydrolysis reaction products. In this manner, retained water was involved in hydrogen bonding and chemical reactions with the epoxy. With increasing severity of hygrothermal aging, the fracture toughness decreased. This was consistent with fracture surface micrographs that showed a greater distance amongst crack stretch marks in specimens with less toughness.

Probing Intramolecular Interaction of Stereoisomers Using Computational Spectroscopy

Several model stereoisomers such as ferrocene (Fc), methoxyphenol, and furfural conformers are discussed. It was discovered that the Fc IR spectroscopic band(s) below 500cm−1 serve as fingerprints for eclipsed (splitting 17 (471–488)cm−1) and staggered Fc (splitting is ~2 (459–461)cm−1) in the gas phase. It is revealed that in the gas phase the dominance of the eclipsed Fc (D5h) at very low temperatures changes to a mixture of both eclipsed and staggered Fc when the temperature increases. However, in solvents such as CCl4, eclipsed Fc dominates at room temperature (300K) due to the additional solvation energy. Intramolecular interactions of organic model compounds such as methoxyphenols (guaiacol (GUA) and mequinol (MEQ)) and furfural, ionization energies such as the carbon 1s (core C1s), as well as valence binding energy spectra serve this purpose well. Hydrogen bonding alters the C1s binding energies of the methoxy carbon (C(7)) of anti-syn and anti-gauche conformers of GUA to 292.65 and 291.91eV, respectively. The trans and cis MEQ conformers, on the other hand, are nearly energy degenerate, whereas their dipole moments are significantly different: 2.66 Debye for cis and 0.63 Debye for trans-MEQ. Moreover, it is found that rotation around the Cring–OH and the Cring–OCH3 bonds differ in energy barrier height by ~0.50 kcal⋅mol−1. The Dyson orbital momentum profiles of the most different ionic states, 25a′ (0.35eV) and 3a′ (−0.33eV), between cis and trans-MEQ in outer valence space (which is measurable using electron momentum spectroscopy (EMS)), exhibit quantitative differences. Finally, the molecular switch from trans and cis-furfural engages with a small energy difference of 0.74 kcal mol−1, however, at the calculated C(3)(–H⋅⋅⋅O=C) site the C1s binding energy difference is 0.105eV (2.42 kcal mol−1) and the NMR chemical shift of the same carbon site is also significant; 7.58ppm from cis-furfural without hydrogen bonding.

Theory meets experiment for unravelling the C1s X-ray photoelectron spectra of pyridine, 2-fluoropyridine, and 2,6-difluoropyridine.

High resolution X-ray photoelectron spectra of a series of substituted pyridines (pyridine, 2-fluoropyridine, and 2,6-difluoropyridine) have been recorded and rationalized by means of a quantum mechanical approach based on the density functional theory including vibronic effects at the Franck-Condon level. The significant chemical shifts of the C1s binding energies induced by fluorine atoms are reproduced quantitatively by our computational model, as well as the vibrational fine structure and the band shapes. Nonsymmetric normal modes play an important role due to the core-hole localization in the presence of equivalent carbon atoms in pyridine and 2,6-difluoropyridine.

Polypyrrole nanostructures//activated carbon based electrode for energy storage applications

In this study, a self-assembled polypyrrole nanostructure with the high electrochemical performance was synthesized via a chemical polymerization method. The structure, morphology and compositional analysis were investigated using Fourier transmission infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). The FTIR analysis of the synthesized samples confirmed the presence of pyrrole chain located at 1313 cm−1. The XPS spectrum showed the presence of C1s and N1s binding energy peaks. The FESEM images confirmed the presence of self-assembled nanostructures with a size range of ~ 200 nm. The effect of various aqueous electrolytes on the electrochemical performance of polypyrrole was studied. Because of its smaller hydration sphere radius, increased molar conductivity and higher ionic mobility, self-assembled polypyrrole nanostructure (P1) delivered a high specific capacitance of 623 F g−1 in 0.5 M H2SO4 electrolyte. Finally, we have fabricated a solid-state symmetric (SSC) and asymmetric supercapacitor (ASC) based on polypyrrole electrode. Among them, the as-assembled P1//activated carbon-based ASC delivered a maximum energy density (25.3 Wh kg−1) and power density (2400 W kg−1) with excellent cycling stability after 40,000 charge/discharge cycles.

Core electron binding energies of adsorbates on Cu(111) from first-principles calculations.

Core-level X-ray Photoelectron Spectroscopy (XPS) is often used to study the surfaces of heterogeneous copper-based catalysts, but the interpretation of measured spectra, in particular the assignment of peaks to adsorbed species, can be extremely challenging. In this study we present a computational scheme which combines the use of slab models of the surface for geometry optimization with cluster models for core electron binding energy calculation. We demonstrate that by following this modelling strategy first principles calculations can be used to guide the analysis of experimental core level spectra of complex surfaces relevant to heterogeneous catalysis. The all-electron ΔSCF method is used for the binding energy calculations. Specifically, we calculate core-level binding energy shifts for a series of adsorbates on Cu(111) and show that the resulting C1s and O1s binding energy shifts for adsorbed CO, CO2, C2H4, HCOO, CH3O, H2O, OH, and a surface oxide on Cu(111) are in good overall agreement with the experimental literature.

Study on the preparation, characterization of a novel solid Lewis acid Al3+-SO42−/MWCNTs catalyst and its catalytic performance for the synthesis of biodiesel via esterification reaction of oleic acid and methanol

A novel solid Lewis acid catalyst Al3+-SO42−/MWCNTs was prepared by impregnating multi walled carbon nanotubes (MWCNTs) with concentrated sulfuric acid and Al3+. The physical and chemical properties of Al3+-SO42−/MWCNTs was characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, X-ray fluorescence spectroscopy, NH3 temperature programmed desorption, X-ray photoelectron spectroscopy and pyridine adsorption IR spectra. The catalytic activities of SO42−/MWCNTs, Al3+-SO42−/MWCNTs and Al3+-SO42−/SWCNTs, Al3+-SO42−/C were compared when they were respectively applied for the catalytic synthesis of biodiesel via esterification reaction of oleic acid and methanol. Results showed that Al3+-SO42−/MWCNTs had the highest catalytic activity: the conversion ratio of oleic acid reached 95% when reaction temperature was 65°C, mass ratio of catalyst to reactants was 0.9wt% and molar ratio of methanol to oleic acid was 12:1 after 7h. The high catalytic activity of Al3+-SO42−/MWCNTs can be ascribed to the flow and escape of electronic is very easily in the tubular structure of MWCNTs since it has low C1s binding energy. It will stimulate a stronginteraction between Al3+ and SO42−, accompanied with the formation of a stable coordination bond, which increased the crystallization degree of Al3+-SO42−/MWCNTs catalyst and improved the combination stability of SO42− and MWCNTs. In addition, SO band can exert strong electron induced effect, which leads to the increasing of the valence electron layer density of Al element, reduces the shielding effect of outer electrons on core electrons and increases the binding energy of core electrons. It directly affects the electronic state of S and Al and changes the chemical state of SO42−, enhances the absorption capacity of Al3+ and increases the imbalance of the system. Eventually, it changed the original acidity of the Al3+-SO42−/MWCNTs catalyst and enhanced its Lewis acidity. Hence, the acid site of Al3+-SO42−/MWCNTs is mainly comprised by Lewis acid, which is favorable for the avoiding of the occurrence of hydration of Brönsted acid active sites.

Acquisition of C1 inhibitor by Bordetella pertussis virulence associated gene 8 results in C2 and C4 consumption away from the bacterial surface.

Whooping cough, or pertussis, is a contagious disease of the respiratory tract that is re-emerging worldwide despite high vaccination coverage. The causative agent of this disease is the Gram-negative Bordetella pertussis. Knowledge on complement evasion strategies of this pathogen is limited. However, this is of great importance for future vaccine development as it has become apparent that a novel pertussis vaccine is needed. Here, we unravel the effect of Virulence associated gene 8 (Vag8) of B. pertussis on the human complement system at the molecular level. We show that both recombinant and endogenously secreted Vag8 inhibit complement deposition on the bacterial surface at the level of C4b. We reveal that Vag8 binding to human C1-inhibitor (C1-inh) interferes with the binding of C1-inh to C1s, C1r and MASP-2, resulting in the release of active proteases that subsequently cleave C2 and C4 away from the bacterial surface. We demonstrate that the depletion of these complement components in the bacterial surrounding and subsequent decreased deposition on B. pertussis leads to less complement-mediated bacterial killing. Vag8 is the first protein described that specifically prevents C1s, C1r and MASP-2 binding to C1-inh and thereby mediates complement consumption away from the bacterial surface. Unravelling the mechanism of this unique complement evasion strategy of B. pertussis is one of the first steps towards understanding the interactions between the first line of defense complement and B. pertussis.

The Electronic Structure of Saturated NaCl and NaI Solutions in Contact with a Gold Substrate

The near ambient pressure X-ray photoelectron spectroscopy set up installed recently at SOLEIL synchrotron facility is used to study the electronic structure of NaCl and NaI saturated solutions formed on a gold substrate. The binding energies of the solution constituents are measured with respect to the Fermi level of the gold substrate. The C1s binding energy of the aliphatic contaminant floating at the surface of the solution is an evidence that the Fermi level in the metal and in the solution are aligned. The use of the Fermi level common energy reference is an added value with respect to previous works realized with micro-jets that were calibrated in energy with respect to vacuum level. We observe that the water valence molecular levels binding energies, and hence the Fermi positioning in the gap of the liquid, the Na+ 2s binding energy and even the work function are independent of the nature of the anions. The secondary electron energy distribution curves show that the work functions of the two solutions are equal within experimental uncertainty. We discuss this point considering the different ion distributions at the surface (related to the different size and polarizability of the anions), and the possible contribution of carbon contaminants. We compare the WF values extracted from the secondary electron edges to alternative measurements using the binding energy of the gas phase O1s or 1b1 spectra (referenced to the gold Fermi level). The ionization energies (referenced to the vacuum level), that we obtain by adding the work function to the measured binding energies, are in good accord with previously published works using micro-jets, obtained, however, at much lower solute concentration. Finally we discuss the origin of the Fermi level pinning in the liquid band gap and consider the possibility that the H+/H2 redox level is aligned with the metal Fermi level.

Electronic structures of hexane isomers studied using quantum mechanics and graph theory

Electronic and topological properties of hexane ( C 6 H 14) and its five geometric isomers are systematically studied quantum mechanically using several techniques such as positron–electron annihilation gamma-ray spectra, C1s binding energy spectra and carbon nuclear magnetic resonance (NMR) spectra, as well as information derived from graph theory. It is revealed that the Doppler-shift in the gamma-ray spectra of the hexane isomers is in the vicinity of the n-hexane molecule with small structural dependency, in agreement with the fact that the measured Doppler-shifts of other linear alkanes are in the vicinity of hexane. The present study further reveals the electronic structures of hexane isomers, which are deeply rooted into the carbon core electrons, more than mere properties in the valence space. The calculations show that the highest occupied molecular orbitals (HOMOs) of the isomers exhibit less important roles in gamma-ray spectra; whereas the electron–positron annihilation is dominated by the electrons of the lowest occupied valence orbitals (LOVOs) and other valence electrons underneath the HOMO electrons, in agreement with previous findings. The present study further reveals that the C1s binding energies of the isomers exhibit association with the nodes of the isomers using graph theory. That is, more branched carbons likely engage with larger chemical shift, which is indicated by the largest eigenvalues (LEVs) of the adjacency matrix (AM) from graph theory. The chemical shift of the carbon NMR spectra is revealed by the LEVs of the Laplacian matrix (LM) obtained from chemical graph theory.

Differentiation of alkane isomers through binding energy spectra and total momentum cross sections

The C1s binding energy spectra and total orbital momentum cross sections of small saturated alkanes (up to six carbons) and their isomers are investigated and used to differentiate their structural differences. The present study discovers that the impact of isomerization of alkanes on the carbon core shell is more significant than the elongation of the linear carbon chain. C1s binding energies are capable of serving as excellent indicators for isomers, whereas information on valence space such as valence binding energy spectra and valence momentum distributions is more sensitive to the length of the alkane chains. It further reveals that the terminal carbons exhibit smallest IPs for the alkanes but with a similar chemical environment as all their IPs are in the vicinity of 289.50 eV (±0.45 eV). The largest C1s chemical shift for the isomers is 0.88 eV (neopentane) which is nearly three times larger than the linear alkanes which is 0.30 eV. The inner valence bonding energy spectra clearly show a dependence on the number of carbons with a decreasing HOMO–LOMO energy gap of 9.91 eV for methane but 7.63 eV for hexane. The total momentum distributions are also proportional to the number of electrons but the isomers present small differences in the low momentum region which correspond to the long range in coordinate space.

A Molecular Switch Governs the Interaction between the Human Complement Protease C1s and Its Substrate, Complement C4

The complement system is an ancient innate immune defense pathway that plays a front line role in eliminating microbial pathogens. Recognition of foreign targets by antibodies drives sequential activation of two serine proteases, C1r and C1s, which reside within the complement Component 1 (C1) complex. Active C1s propagates the immune response through its ability to bind and cleave the effector molecule complement Component 4 (C4). Currently, the precise structural and biochemical basis for the control of the interaction between C1s and C4 is unclear. Here, using surface plasmon resonance, we show that the transition of the C1s zymogen to the active form is essential for C1s binding to C4. To understand this, we determined the crystal structure of a zymogen C1s construct (comprising two complement control protein (CCP) domains and the serine protease (SP) domain). These data reveal that two loops (492-499 and 573-580) in the zymogen serine protease domain adopt a conformation that would be predicted to sterically abrogate C4 binding. The transition from zymogen to active C1s repositions both loops such that they would be able to interact with sulfotyrosine residues on C4. The structure also shows the junction of the CCP1 and CCP2 domains of C1s for the first time, yielding valuable information about the exosite for C4 binding located at this position. Together, these data provide a structural explanation for the control of the interaction with C1s and C4 and, furthermore, point to alternative strategies for developing therapeutic approaches for controlling activation of the complement cascade.

Core level energy differences between the surface and bulk of organic semiconductor films: The effect of electrostatic polarization energy

The difference in the C1s core level energies between the surface and bulk regions of an organic semiconductor thin film is examined for pentacene and perfluoropentacene (F-pentacene). The experimental method we have recently developed allows us to determine precisely the differences as well as the thickness of the surface region. The C1s binding energies in the outermost layer turn out to be larger than those in the bulk by 0.32eV (pentacene) and 0.25eV (F-pentacene). The results are successfully explained by the interaction energy between the point charge and induced dipole moments suggesting the electrostatic polarization energy plays a main role in the difference of the core level energy.

Packing density of HS(CH2)nCOOH self-assembled monolayers

Self-assembled monolayers (SAMs) of HS(CH(2))(n)COOH, n = 5, 10, 15 deposited from ethanol solution onto gold are prepared by five approaches, and their packing densities are evaluated by X-ray photoelectron spectroscopy (XPS) measurements. The five approaches are: (1) direct deposition; (2) acetic-acid-assisted deposition; (3) butyl-amine-assisted deposition; (4) displacement of a preformed HS(CH(2))(n)CH(3) (n = 5, 10, 15) SAMs; and (5) co-deposition with HS(CH(2))(n)CH(3) (n = 5, 10, 15). Packing density metrics are calculated from measurements of SAM and substrate photoemission intensities and their attenuations by two methods. In one case the attenuated photoemissions are expressed as a ratio relative to comparable measurements on an experimental HS(CH(2))(n)CH(3) model system. In the other case a new method is introduced where a calculated attenuation based on theoretical random coil and extended chain models is used as the reference to determine a packing density fraction. Packing densities are also correlated with the S2p(Au-bonded):Au4f peak area ratios and with shifts in the C1s binding energies. SAMs prepared by the direct deposition are a partial multilayer where a second molecular layer is physisorbed onto the SAM and not removable by solvent washing. The addition of acetic acid to the deposition solution disrupts dimer associations of HS(CH(2))(n)COOH in solution and at the surface of the monolayer and yields the most ordered monolayer with the highest density of -COOH groups. The addition of butyl amine results in a labile ammonium carbonate ion pair formation but results in a lower packing density in the SAM. The displacement of the preformed HS(CH(2))(n)CH(3) SAM and the co-deposition of HS(CH(2))(n)CH(3) with HS(CH(2))(n)COOH result in SAMs with little incorporation of the -COOH component.

Epitaxial few-layer graphene: towards single crystal growth

We review our research towards single-crystal growth of epitaxial few-layer graphene (FLG) on SiC substrates. We have established a method for evaluating the number of graphene layers microscopically using low-energy electron microscopy. Scanning probe microscopy in air is also useful for estimating the number-of-layers distribution in epitaxial FLG. The number-of-layers dependence of the work function and C1s binding energy is determined using photoelectron emission microscopy. We investigate the growth processes of epitaxial FLG on the basis of the microscopic observations of surface morphology and graphene distribution. To gain insights into the growth mechanism, we calculate the SiC surface structures with various C coverages using a first-principles scheme. Uniform bilayer graphene a few micrometres in size is obtained by annealing in UHV.

Characterization of oxygen and argon ion flux interaction with PET surfaces by in-situ XPS and ex-situ FTIR

The effects of low (2.5, 0.2 keV) energy reactive oxygen ion bombardment and argon ion bombardment on poly(ethylene terephthalate) thin film (PET) surface chemical composition were studied. PET films have a high potential as a material for biomedical and electrical industries. The source of ions was an ECR Ion Gun with settable acceleration voltages. PET films were sputtered by ion bombardment for variable process time and the modified films were investigated by in-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Fourier transform infrared spectroscopy (FTIR). The significant changes in the chemical composition of surface layers were quantitatively studied by XPS. The ion bombardment scissions the chains in PET film surface layers. Selective sputtering of oxygen atoms from PET surface was observed when argon ion flux used. The 0.2 keV and 2.5 keV argon ion decreased O/C ratio from 0.37 to 0.25, 0.04 respectively. This phenomenon is responsible for the creation of carbon-rich up 96 at.% surface layer and the oxygen in ester bonds is detached first. The oxygen 2.5 keV ion bombardment had similar effect as argon ion bombardment; the ratio O/C was decreased. The ester bond was broken first. But oxygen 0.2 keV ion flux irradiation created an oxygen rich surface; the O/C ratio was in increased from 0.37 to 0.46. The changes in surface conductivity were investigated by shifts in C1s binding energy. Good agreement with atomic concentration of carbon in C–C bonds on the films surface was found. The FTIR analyses identified changes in chemical composition but with no obvious correlation to surface changes. Photons from the ion source irradiating the PET film during ion bombardment probably caused the observed changes in FTIR spectra.

Functional Characterization of the Recombinant Human C1 Inhibitor Serpin Domain: Insights into Heparin Binding

Variants of the human C1 inhibitor serpin domain containing three N-linked carbohydrates at positions 216, 231, and 330 (C1inhDelta97), a single carbohydrate at position 330 (C1inhDelta97DM), or no carbohydrate were produced in a baculovirus/insect cells system. An N-terminally His-tagged C1inhDelta97 variant was also produced. Removal of the oligosaccharide at position 330 dramatically decreased expression, precluding further analysis. All other variants were characterized chemically and shown to inhibit C1s activity and C1 activation in the same way as native C1 inhibitor. Likewise, they formed covalent complexes with C1s as shown by SDS-PAGE analysis. C1 inhibitor and its variants inhibited the ability of C1r-like protease to activate C1s, but did not form covalent complexes with this protease. The interaction of C1 inhibitor and its variants with heparin was investigated by surface plasmon resonance, yielding K(D) values of 16.7 x 10(-8) M (C1 inhibitor), 2.3 x 10(-8) M (C1inhDelta97), and 3.6 x 10(-8) M (C1inhDelta97DM). C1s also bound to heparin, with lower affinity (K(D) = 108 x 10(-8) M). Using the same technique, 50% inhibition of the binding of C1 inhibitor and C1s to heparin was achieved using heparin oligomers containing eight and six saccharide units, respectively. These values roughly correlate with the size of 10 saccharide units yielding half-maximal potentiation of the inhibition of C1s activity by C1 inhibitor, consistent with a "sandwich" mechanism. Using a thermal shift assay, heparin was shown to interact with the C1s serine protease domain and the C1 inhibitor serpin domain, increasing and decreasing their thermal stability, respectively.

Analysis of Number of Layers in Epitaxial Few-Layer Graphene Grown on SiC towards Single-Crystal Graphene Substrate

We review our research toward single-crystal growth of epitaxial few-layer graphene (FLG) on SiC substrates, in which surface electron microscopy techniques have played essential roles. We have established a method for evaluating the number of graphene layers microscopically using low-energy electron microscopy. The number-of-layers dependence of the work function and C1s binding energy is determined using photoelectron emission microscopy. We use LEEM and thermionic electron emission microscopy to investigate the growth processes of epitaxial FLG. Uniform bilayer graphene a few micrometers in size is obtained by annealing in UHV.

Coordination-Resolved C−C Bond Length and the C 1s Binding Energy of Carbon Allotropes and the Effective Atomic Coordination of the Few-Layer Graphene

Binding energy variation due to the change of atomic coordination has formed the key to the different fascinating properties of carbon allotropes such as graphene nanoribbons, carbon nanotubes, graphite, and diamond. However, determination of the binding energies of these allotropes with a consistent understanding of the effect of bond order variation on the binding energy change has long been a great challenge. Here we show that a combination of the bond order−length−strength correlation theory (Sun, C. Q. Prog. Solid State Chem. 2007, 35, 1) and the photoelectron emission technique has enabled us to quantify the C1s binding energy of atomic carbon and its shift upon carbon allotrope formation. It has been confirmed that the C−C bond contracts spontaneously by up to 30% at the edges of graphene ribbons with respect to the bulk-diamond value of 0.154 nm. The C1s energy shifts positively by values from 1.32 eV for bulk diamond to 3.33 eV for graphene edges with respect to that of 282.57 eV for an isolated carbon atom. The calibration using the bond order−length−strength solution has also enabled estimation of the effective atomic coordination of the few-layer graphene, which is critical for further investigations such as the layer-resolved Raman shift.

On the origin of visible light activity in carbon-modified titania

Characterization of a commercial carbon-modified titania visible light photocatalyst (VLP) reveals a quasi-Fermi level of -0.50 V at pH 7 and characteristic C1s binding energies of 284.8 eV and 286.3 eV as measured by XPS. Treatment with sodium hydroxide affords a soluble brown extract SENSex exhibiting in the IR spectrum intense peaks at 1420 cm(-1) and 1580 cm(-1), tentatively assigned to an arylcarboxylate group. Both the residue and the solution SENSex do not induce significant visible light mineralization of 4-chlorophenol. However, after heating them together in suspension, followed by calcination at 200 degrees C the resulting powder VLPreas exhibits the same quasi-Fermi level and C1s binding energies as the original VLP. Furthermore, within experimental error its visible light activity is identical with that of VLP. These results clearly indicate that, at least for VLP but probably also for other "carbon-doped" titania materials, an aromatic carbon compound and not substitutional or interstitial carbon is the origin of visible light activity.