Surface OH Groups Research Articles

Observation of Structure‐Sensitive Decomposition of Cp(allyl)Pd on Pd Nanodots Formed by MOCVD

AbstractThe decomposition kinetics of the organometallic precursor cyclopentadienyl‐allyl‐Pd [Cp(allyl)Pd] on silica and titania substrates (as well as previously deposited Pd) are investigated by continuous metal‐organic (MO)CVD under atmospheric pressure. The substrate particles are freshly generated in an aerosol process with well‐defined and known densities of surface OH groups, and then coated immediately in a second reactor. Time‐resolved data on size and number density of deposited Pd nanodots on the carrier particles are obtained by electron microscopy and used as a means to infer the decomposition kinetics. It is found that decomposition proceeds very rapidly for a few seconds, both by proton‐initiated decomposition on surface OH groups and by autocatalysis, until the Pd nanodots have grown to a size of about 2 nm, where autocatalysis comes to a standstill, regardless of precursor concentration, residence time in the CVD reactor, or decomposition temperature. Proton‐initiated decomposition on OH groups continues to depend measurably on these process parameters in terms of the number density of Pd dots, even after autocatalysis has stopped. Our observations indicate that autocatalysis is structure‐sensitive.

Incorporation of an asymmetry gadolinium porphyrin into mesoporous SBA-15 and the study of luminescence property

The incorporation of an asymmetry gadolinium porphyrin into the mesoporous molecular sieves SBA-15 by reactions of the surface OH group with an F and OH group of the porphyrin. The resultant material was confirmed that the channels of SBA-15 have been filled with porphyrins by XRD, TEM, solid UV/Vis, nitrogen adsorption, leaving the mesopores unaffected. Luminescent properties were studied by solid fluorescence emission and excitation spectra. Results indicate that the luminescence intensity of SBA-15/porphyrin is stronger than the pure porphyrin. We also provided the FTIR results and study the links between silica wall and gadolinium porphyrin after incorporation porphyrin into SBA-15.

Aqueous Solution Synthesis of Crystalline Anatase Nanocolloids for the Fabrication of DSC Photoanodes

The production of anatase nanocolloids via a novel aqueous solution synthesis method is described. The process involves forced hydrolysis of aqueous solution at low temperature leading to fast nucleation of anatase nanoparticles . The isolated nanopowders were found to consist predominantly of anatase as the major phase , possess a very high surface area (up to ), and a relatively elevated surface hydroxyl content in comparison with the P25 reference material. Single-layer ( thick) photoanodes prepared with aqueous-synthesized powders were found to have a specific surface area of and the anatase nanocrystallites to have grown to and assume a higher degree of crystallinity but still carry surface OH groups. The pore size of the film was determined to be . By comparison, the film prepared with P25 nanoparticles had the following properties: , crystallite size, 0.2% surface OH, and pore size. Dye-sensitized solar cell (DSC) devices assembled with the newly fabricated photoanodes showed equivalent photo-electrochemical performance [power conversion efficiency η, short-circuit current voltage , open-circuit voltage , and Fill Factor (FF)] to cells prepared using the benchmark P25 titania powder.

Preparation of WO3/ZnO Composite Photocatalyst and Its Photocatalytic Performance

A series of WO3/ZnO composite photocatalysts with different WO3 concentrations were prepared by a precipitation-grinding method followed by calcination at different temperatures. The prepared samples were characterized by N2 physical adsorption, X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, UV-visible spectroscopy, and photoluminescence spectroscopy. The photocatalytic activity of the samples was evaluated by photocatalytic degradation of acid orange II under UV light (λ = 365 nm) irradiation. The results showed that at the optimal calcination temperature of 600 °C, the WO3/ZnO composite photocatalyst with 2 wt% concentration of WO3 showed about doubled photocatalytic activity compared to pure ZnO. The increase in the photocatalytic activity could be attributed to the coupling of WO3, which suppressed the growth of ZnO particles, increase of the surface area and increased amount of surface OH groups of the sample. The presence of WO3 also restrained the recombination rate of e−/h+ pairs. ：采用沉淀-研磨法制备了一系列不同 WO3 含量的 WO3/ZnO 复合光催化剂, 应用 N2 物理吸附、X 射线衍射、扫描电镜、傅里叶变换红外光谱、紫外-可见光谱和光致发光谱等手段对催化剂进行了表征, 并以 λ = 365 nm 的紫外光为光源, 评价了该催化剂光催化降解酸性橙 II 的活性, 考察了 WO3 的复合对 WO3/ZnO 样品光催化性能的影响. 结果表明, 当复合 2%WO3, 并于 600 °C 焙烧时, 所制备的 WO3/ZnO 催化剂活性最高, 比纯 ZnO 的提高了约一倍. 合适的煅烧温度可以提高催化剂结晶度, 而 WO3 的复合可抑制 ZnO 晶粒的长大, 提高催化剂比表面积和改善催化剂表面羟基数量, 并可抑制光生电子与光生空穴的复合, 从而显著提高其光催化脱色活性.

Oxidative, photo-activated TiO2 nanoparticles in the catalytic acetylation of primary alcohols

A series of TiO2 particles of varying particle sizes from nano to micro scales was treated with three different oxidants (O2, TBHP, and aqueous H2O2) under irradiation conditions to form activated TiO2 particles bearing surface peroxo Ti(O2) species. The resultant, heterogeneous catalysts were tested for photo-catalytic acetylation of 2-phenylethanol by acetic anhydride in 8 different solvents. The best scenario involves the use of 32 nm grade of TiO2 nanoparticles and aqueous H2O2 for pre-activation and the use of CH2Cl2 as the reaction solvent. The 2-phenethyl acetate product can be completely formed in 10 h and isolated in essential quantitative yield. It was also found that catalysts derived from TiO2 nanoparticles are superior to those from ZrO2, Y2O3 and WO3 nanoparticles by using the oxidative, photo-activation protocol. The newly developed heterogeneous catalytic system can be smoothly applied to photocatalytic acetylation of several representative primary aliphatic and aromatic alcohols. The intermediacy of Ti–OH or TiO surface groups was proposed in the photo-catalytic acetylation conditions.

Changes in Surface Property and Catalysis of Mesoporous Nb2O5 from Amorphous to Crystalline Pore Walls

The amorphous inorganic phase of an ordered amorphous mesoporous Nb2O5 with two dimensional hexagonal (2D-hex) structure was crystallized with maintaining the original well arranged porous structure. The difference in surface property between amorphous and crystalline Nb2O5 with similar ordered mesoporous structure was compared. It was found from water adsorption–desorption isotherms and observation by infrared (IR) spectroscopy that the amorphous sample was hydrophilic and that the surface OH groups were acidic. On the other hand, the OH groups on crystalline mesoporous Nb2O5 were non-acidic and inside the pores was less hydrophilic. The surface property was also compared by a catalytic reaction, oxidation of cyclohexe by an aqueous solution of H2O2. The high (95%) selectivity for 1,2-epoxycyclohexane was obtained at 40 °C for 2 h in methanol solvent over crystalline mesoporous Nb2O5 at 12% conversion, while amorphous mesoporous Nb2O5 showed high (68%) selectivity for 1,2-cyclohexanediol in acetonitrile solvent at 60 °C for 2 h at 22% conversion. The differences in selectivity and the optimal solvent between amorphous and crystalline samples were interpreted in terms of the acidic feature of surface OH groups and hydrophilicity. While similar selectivity was observed over non-porous crystalline Nb2O5, much higher conversion over crystalline mesoporous Nb2O5 was attained at the same surface area. Thus, an advantage of mesoporous structure is attributed to the higher contact time of molecules inside the pores to the catalyst surface than those outside the particles. The selective epoxidation of cyclohexene using H2O2 has been recognized as an ideal eco-friendly process. The present catalytic performance of crystalline mesoporous Nb2O5 is regarded as one of the best examples to demonstrate the advantage of mesoporous marerials.

IR spectroscopic study of surface properties of amorphous water ice

The state of the surface of amorphous ice with a specific surface area of about 160 m2/g obtained by the condensation of water vapor at 77 K is studied by IR spectroscopy. As the temperature increases to 130–160 K, absorption bands of surface hydroxyl groups vanish, whereas changes in bands characteristic of hydroxyl groups in the bulk of ice are indicative of a phase transition of ice from amorphous to the polycrystalline structure. The surface sites of amorphous ice are characterized with low-temperature adsorption of carbon monoxide. It is shown that there are two types of CO adsorption sites, free hydroxyl groups and oxygen atoms of surface coordinately unsaturated water molecules. Upon adsorption of nitrogen, methane, and carbon monoxide, in addition to the perturbation of surface OH groups, reversible changes in the spectrum are observed in the region of vibrations of bulk hydroxyls, which indicate that the strength of hydrogen bonds between water molecules in the surface layer of icy particles increases approaching the strength of these bonds in the crystal and that the ice surface becomes less amorphous. These results indicate that the properties of the ice surface layer substantially depend on the presence of adsorbed molecules.

Photocatalytic abatement of VOCs by novel optimized TiO 2 nanoparticles

In this work, photocatalytic degradation of different VOCs has been investigated using novel TiO 2 nanoparticles (TNP) at near room temperature. The TNP was synthesized in a vortex reactor by sol–gel process with controlled operating parameters. The final product was optimized through an effective control of the calcination temperatures (400–700 °C) and times (1–7 h). The optimized 10–20 nm particle size TNPs exposed a high specific surface area (151 m 2/g), which was three times higher than the commercial Degussa P 25 TiO 2 material. It also showed rather pure crystalline anatase with small rutile traces, confined band gap energy, relatively more Ti 3+ on the surface, and higher OH surface groups as characterized by X-ray diffraction (XRD), Raman spectroscopy, specific surface area analysis, diffuse reflectance ultraviolet–visible spectroscopy (DR/UV–vis), Fourier transformed-infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The optimized TNP showed superior photocatalytic degradation of ethylene at ambient temperature, as tested in an ad hoc designed Pyrex glass photocatalytic reactor. It was found that the mixed phase of the optimized TNP with a high surface area might induce the adsorption of ethylene and water and generate OH groups which act as oxidizing agents on the TNPs surface, leading to higher photocatalytic activity. The effects of different factors, including adsorption, flow rates, concentrations, catalyst weight and reaction temperature were studied in detail for ethylene, propylene, and toluene oxidation. Moreover, higher photocatalytic activity for VOCs abatement was obtained than the Degussa P 25 TiO 2 due to the above-mentioned characteristics.

Evaluation of catalyst prepared in microchannel with in situ FT-IR microscopy

In situ characterization of silicon micro channel reactor with supported platinum alumina catalyst prepared on the channel wall was conducted with FT-IR microscope under propane flow, propene flow and cyclohexane flow. Surface π-allylic species along with surface OH group were observed at 373K under propane or propene flow. These species were rather stable under N2 flow and H2 flow. The reactor was active for dehydrogenation of cyclohexane to produce benzene and cyclohexene. In situ FT-IR observation under flow of cyclohexane at 473K, decrease of reactant, increase of products, a maximum of π-allylic and CC species were observed from inlet toward outlet. The maximum absorbance of the intermediate shifted with flow rate. These suggested consecutive reaction path and existence of film resistance.

The influence of rapid heat treatment in still air on the photocatalytic activity of titania photocatalysts for phenol and monuron degradation

Titanium dioxide photocatalysts were prepared by a new synthesis method that involves rapid heating with short and medium exposures of the sol–gel prepared amorphous starting materials at different temperatures and calcination times (RHSE and RHME series). Samples were also synthesized using conventional calcination methods (applying slow heating and long exposure times, SHLE series). Both sets of samples were characterized by various methods, such as TG-DTA, XRD, SEM, TEM, DRS, FT-IR, TOC and XPS techniques and by sedimentation experiments. The RHSE and RHME samples have good crystallinity and consist of anatase and rutile mixtures. The photocatalytic activity of catalysts was studied in suspensions using phenol and monuron as model substrates. The best UV performance was found for the RHME sample prepared at 600°C with 60min of exposure. This sample has high UV activity and is comparable to Aeroxide P25 TiO2 reference photocatalyst for both substrates. The RHSE and RHME samples significantly exceeded the performance of SHLE samples. The loss of surface OH groups during long time calcination was assumed to have a negative effect on the activity of SHLE samples due to a high degree of aggregation of the particles in aqueous solutions. The improved photocatalytic performance is attributed to the higher level of absorption of light in the near-UV range. This new more economic treatment strategy could have major impact on materials engineering of UV and VIS active photocatalysts prepared via sol–gel methods, especially using acetic acid and aqueous solution of ammonia.

Nano-Jewels in Biology. Gold and Platinum on Diamond Nanoparticles as Antioxidant Systems Against Cellular Oxidative Stress

Diamond nanoparticles (DNPs) obtained by explosive detonation have become commercially available. These commercial DNPs can be treated under Fenton conditions (FeSO(4) and H(2)O(2) at acidic pH) to obtain purer DNP samples with a small average particle size (4 nm) and a large population of surface OH groups (HO-DNPs). These Fenton-treated HO-DNPs have been used as a support of gold and platinum nanoparticles (≤2 nm average size). The resulting materials (Au/HO-DNP and Pt/HO-DNP) exhibit a high antioxidant activity against reactive oxygen species induced in a hepatoma cell line. In addition to presenting good biocompatibility, Au/HO- and Pt/HO-DNP exhibit about a two-fold higher antioxidant activity than glutathione, one of the reference antioxidant systems. The most active material against cellular oxidative stress was Au/HO-DNP.

Photocatalytic Degradation of Ethylene Emitted by Fruits with TiO2 Nanoparticles

The photocatalytic degradation of ethylene (emitted by fruits) by novel TiO2 nanoparticles (TNPs), at 3 °C, has been investigated to consider the possibility of its use for the cold storage of fruits. TNP exhibits a high specific surface area, a good anatase-to-rutile mixed phase ratio, and more surface OH groups than commercially available Degussa P 25, as characterized by nitrogen adsorption, static light scattering, energy dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. TNPs, tested in an ad-hoc designed Pyrex glass photocatalytic reactor, showed higher photodegradation activity of ethylene than Degussa P 25. The superior characteristics of TNPs, compared to Degussa P 25, might induce the adsorption of ethylene and water and the generation of OH groups which act as oxidizing agents on the TNP surface, leading to higher photocatalytic activity. In the absence of water the photocatalytic degradation of ethylene reduced significantly. Moreover, a positive effect was observed when UV light was converged on the catalyst and an increase in ethylene degradation was achieved when UV light converging pipes and lens were used.

Probing the nanoscale architecture of clay minerals

AbstractIn recent years, experimental and theoretical methods have provided new insights into the size, shape, reactivity, and stability of clay minerals. Although diverse and complex, the surface chemistry of all clay minerals is defined spatially on a common scale of nanometres. This review is organized around the nanoscale architecture of clay minerals examined at several different length scales. The first, and perhaps most important, is the length scale associated with Hbonding in clay minerals. Hbonding interactions define the size and shape of 1:1 phyllosilicates and dominate the surface chemistry of many clay minerals. Structural and surface OHgroups contained within and on the surface of clay minerals provide a type of ‘molecular reporter group’ and are sensitive to subtle changes in their local environment. Examples of OH-reporter group studies in clay minerals, and the spatial scales at which they provide diagnostic information, are examined. The second length scale considered here is that associated with clay–water and clay–organic interactions. Inorganic and organic solutes can be used to explore the surface chemistry of clay minerals. Similar to the use of reporter groups, molecular probes have diagnostic properties that are sensitive to changes in their molecular environment. Clay–water interactions occur at a length scale that extends from the size of the H2O molecule (~0.3 nm) to the larger scales associated with clay-swelling (>10 nm). Similarly, clay–organic interactions are also defined, in part, on the basis of their molecular size, in addition to the type of chemical bonding interactions that take place between the organic solute and the clay surface. Examples illustrating the use of clay–water and clay–organic solute interactions as molecular probes are presented. The largest scale to be considered is that of the particles themselves, with scales that approach micrometres. Recent developments in the synthesis and characterization of ultrathin hybrid films of clay minerals provide complementary information about the nature and distribution of active sites on clay minerals, as well as providing new opportunities to exploit the surface chemistry of clay minerals in the design of functional materials.

ChemInform Abstract: Photocatalytic Hydrogenation, Decomposition and Isomerization Reactions of Alkenes Over TiO2-Adsorbed Water

Photocatalytic reactions of alkenes over TiO2-adsorbed water have been investigated. The products are hydrogenated molecules (CnH2n+2) formed by the addition of two H atoms to the π bond of the alkene (CnH2n, 2⩽n⩽ 4) and lower alkanes (CH4, Cn – 2H2n – 2 and Cn–1H2n) formed by the cooperative addition of an H atom and an OH radical to the π bond followed by decomposition. The photocatalytic isomerization of butenes by surface OH radicals is also observed. The generalized reaction mechanisms for these photocatalytic reactions have been postulated. The initial rate of formation of the hydrogenation product and the sum of the initial rates of formation of lower alkanes per amount of alkene adsorbed are proportional to kH and (kHkOH)1/2, respectively. Here, kH and kOH are rate constants for addition of H atoms and OH radicals to alkene in the vapour phase. For photocatalytic isomerizations, it is found that the isomerization of (E)-but-2-ene to but-1-ene (trans form) which has the same geometrical form is about twice as effective as that between (Z)-but-2-ene and but-1-ene and that the addition of OH to the C(1) position of but-1-ene prevents the isomerization to but-2-enes.

ChemInform Abstract: Characterization of Surface Active Sites of Catalysts with High- Resolution Solid-State NMR

Abstract Results obtained in studies of the surface active sites of heterogeneous catalysts by use of high-resolution solid-state NMR are presented. The 1 H NMR MAS (magic angle spinning) data on chemical shifts of surface OH groups and their interaction with the supported catalytically active complexes are discussed. The relation between the 1 H chemical shift values of OH groups, on the one hand, and characteristics of their acid strength, such as the proton affinity PA OH of the acid residue formed on heterolytic dissociation of the OH groups, on the other hand, is presented. Changes in the intensity of 1 H NMR lines for OH groups of commonly used supports (Al 2 O 3 , TiO 2 , SiO 2 etc.) on interaction with supported oxides suggest the selective interaction of surface OH groups with supported complexes. For the solid heteropolyacid H 3 PW 12 O 40 (HPA) supported on SiO 2 , the binding of the HPA molecule with the SiO 2 surface is most probably multicentred and results in the formation of supported species with different proton structures. Studies of 1 H NMR MAS spectra of zirconium hydrides supported on SiO 2 have revealed the formation of four types of zirconium hydride complex. Solid-state high-resolution 1 H NMR spectra of H 2 S adsorbed on Al 2 O 3 modified with KOH, K 2 CO 3 and HF and on zeolites NaX, NaY and H-ZSM indicate dissociative adsorption of H 2 S which occurs on the coordinatively unsaturated aluminium sites and Na + cations in zeolite cavities. The 1 H and 13 C NMR spectra indicate that adsorbed CH 3 OH reacts more readily with SH − species than with H 2 S adsorbed in the molecular form. Also presented are results of studies on Lewis acid sites in Al 2 O 3 , and zeolites Y and ZSM-5 using the NMR ( 1 H, 13 C and 15 N) of weak adsorbed bases. The formation of Lewis acid sites in HY zeolites during their hydrothermal treatment has been studied by 15 N NMR of adsorbed N 2 O. The strongest Lewis sites are the isolated or weakly associated extralattice Al atoms. The 1 H, 13 C and 15 N NMR chemical shifts of CH 4 , N 2 and N 2 O molecules, as well as 1 H and 15 N relaxation rates of CH 4 and N 2 O adsorbed on a series of HY and H-ZSM zeolites, SiO 2 and Al 2 O 3 , containing controlled amounts of iron impurities, show that unlike SiO 2 , γ-Al 2 O 3 and HY zeolites, the H-ZSM-5 zeolites have strong electron-accepting sites formed by Fe 3+ and probably Al 3+ cations. The possible structure of these sites and the geometry of complexes formed during N 2 O and CH 4 adsorption are discussed. In the final section the results obtained with 109 Ag NMR of supported silver catalysts are presented. The potential of 109 Ag NMR for studying catalysts of this type is discussed.

Role of surface hydroxyl groups in promoting room temperature CO sensing by Pd-modified nanocrystalline SnO 2

SnO 2/Pd nanocomposites were synthesized via sol–gel method followed by variable processing procedures. The materials are sensitive to CO gas in the concentration range 2–100 ppm at room operating temperature. It was shown that modification of nanocrystalline tin dioxide by Pd changes the temperature dependence of sensor response, decreasing the temperature of maximal signal. To understand the mechanism of room temperature CO sensitivity, a number of SnO 2/Pd materials were characterized by XRD, TEM, BET, XPS and TPR techniques. From the results of FTIR, impedance and sensing measurements under variable ambient conditions it was concluded that improvement in CO sensitivity for Pd-modified SnO 2 is due to alteration of CO oxidation pathway. The reaction of CO with surface OH-groups at room temperature was proposed, the latter being more reactive than oxygen species due to the possible chain character of the reactions. It was proposed that Pd additive may initiate chain processes at room temperature.

Synthesis and characterization of N-doped TiO 2/ZrO 2 visible light photocatalysts

Zirconia and nitrogen-doped TiO 2 powder was synthesized using a polymer complex solution method for the preparation of an enhanced visible light photocatalyst. The produced catalysts were characterized via the Brunauer, Emmett, and Teller method (BET), X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectra, and UV–Vis spectrophotometry analyses. The N-doped TiO 2/ZrO 2 photocatalyst showed a high specific surface area and small crystal sizes. The XPS spectra of the N-doped TiO 2/ZrO 2 sample indicated that nitrogen was doped into the TiO 2 lattice and enhanced the photocatalytic activity. The UV–Vis absorption spectra of the N-doped TiO 2/ZrO 2 sample noticeably shifted to the visible light region compared to that of the TiO 2. The photocatalytic activities of the prepared catalysts were evaluated for the decomposition of gaseous NO x under UV and visible light irradiations. The photocatalytic activities of N-doped TiO 2/ZrO 2 were much greater than those of commercial Degussa P25 in both the UV and visible light regions. The high photocatalytic activity can be attributed to stronger absorption in the visible light region, a greater specific surface area, smaller crystal sizes, more surface OH groups, and to the effect of N-doping, which resulted in a lower band gap energy.

CO 2 reforming of CH 4 over Ni-containing phyllosilicates as catalyst precursors

CO 2 reforming of CH 4 to synthesis gas was investigated on new grounds using Ni-containing phyllosilicates (PS) as catalyst precursors. Ni-containing 1:1 PS and 2:1 PS were synthesized hydrothermally from a gel containing sodium silicate and nickel chloride, then they were reduced under H 2 flow before being used as catalysts. Several complementary techniques including XRD, TG-DTA, FTIR, and TPR were used to evaluate the structural, thermal, spectroscopic and redox properties of the samples, respectively. Ni 2:1 PS were found to be more thermally stable and catalytically active than Ni 1:1 PS. Well crystallized Ni 1:1 PS thermally treated at 700 °C resulted in a transitional 2:1 PS phase. The reduction of structural nickel in thermally stable PS led to the formation of nanometric Ni 0 particles over the surface of the remaining unreduced PS as well as on silica. The unreduced PS structure with surface OH groups appeared as one of the best supports for Ni 0 nanoparticles, resulting in less coke formation, and thereby leading to a high catalytic stability.

Coverage-Dependent Adsorption Mode of Water on Fe3O4(001): Insights from First Principles Calculations

Using density functional theory calculations together with an on-site Coulomb repulsion term (GGA+U), we investigate the adsorption of water on Fe3O4(001). Starting from a single water molecule per (� 2 ×� 2)R45° unit cell, we vary the concentration and configuration of water and hydroxyl groups. Isolated water molecules on the clean surface tend to dissociate heterolytically with an OH group adsorbed on top of an octahedral iron and a proton donated to a surface oxygen. Furthermore, oxygen defects are found to promote strongly water dissociation. The released protons bind to distant surface oxygen to minimize the repulsive interaction between the surface OH groups. At higher coverages, the interplay between adsorbate-adsorbate and adsorbate-substrate interactions and the formation of hydrogen bonds between the surface species result in a crossover to a mixed adsorption mode where every second molecule is dissociated. The energetic trends are related to the underlying electronic mechanisms.

Adsorption and Photocatalytic Decomposition of Toluene on TiO2 Surfaces

We studied the adsorption of toluene and its photodecomposition by TiO2 surfaces under UV irradiation using P-25 samples subjected to two different treatments. In order to shed light on the elementary steps of the photocatalytic decomposition of toluene, we employed X-ray photoelectron spectroscopy (XPS). A higher population of the surface OH-group of TiO2 increased the adsorption reactivity and initial rate of the photodecomposition of toluene. We also identified more efficient accumulation of toluene on the surface of TiO2 with high concentrations of OH-groups via XPS.