Degradation Intermediates

Monolithic structured TiO2/aerogel composites were prepared from resorcinol-formaldehyde polymer aerogel (RFA) and its carbon aerogel (RFCA) derivative. A resorcinol-formaldehyde hydrogel was synthesized in a sol-gel reaction and transformed into polymer aerogel by supercritical drying. The RFA was converted to carbon aerogel by pyrolysis at 900 °C in dry N2. Amorphous and crystalline TiO2 layers were grown from TiCl4 and H2O precursors by atomic layer deposition (ALD) at 80 °C and 250 °C, respectively, on both RFA and RFCA. The substrates and the composites were studied by N2 adsorption, TG/DTA-MS, Raman, SEM-EDX and TEM techniques. Their photocatalytic activity was compared in the UV catalyzed decomposition reaction of methyl orange dye.

Kinetic and mechanistic related approaches for mostly titania were intensively studied in the literature. However, combined modelling and kinetic studies are few. Therefore, the present work focuses on modelling the dependence of the degradation kinetics of two model compounds (salicylic acid-SA and methyl orange-MO) on Evonik Aeroxide P25, hydrothermally prepared hierarchical TiO 2 and P25/WO 3 nanostars, obtained also by hydrothermal crystallization. The obtained individual semiconductors and the composites were characterized using XRD, DRS, SEM, while the photocatalytic degradation of the model pollutants were carried out varying the catalyst load, the initial pollutant concentration and incident light intensity. It was found that the degradation kinetics were independent from the hierarchical nature of the material, while significant dependencies of the degradation efficiency was found from the previously mentioned investigation parameters. All these parametric interdependences were successfully studied and a kinetic model was proposed for both bare TiO 2 and TiO 2 /WO 3 composite systems.

TiO2-Au aerogels containing different amounts of gold nanoparticles of different sizes (5 and 16 nm) were successfully synthesized using a sol-gel procedure, and were tested for salicylic acid photodegradation under UV irradiation. The structure and morphology of the obtained materials were investigated using X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption measurements. UV-Vis spectroscopy was used to study the optical properties. The effects of the gold nanoparticles on the TiO2 crystallization process were twofold, as follows: (i) the number of crystallized zones was strongly related to the concentration of the gold nanoparticles, and (ii) the smaller gold particles increased the time taken for the crystallization of the samples. It was found that the noble metal-doped samples exhibited higher degradation rates compared with bare titania. It was found that the most active photocatalyst in each studied system was the sample with the highest concentration of gold nanoparticles. Additionally, the highest degradation rate value was obtained with the smallest Au nanoparticles (46.4  10-3 μmol/(L•s).

Titania/tungsten (VI) oxide/noble metal (gold and platinum) composites were obtained by the means of selective noble metal photodeposition on the desired oxide's surface (either on TiO 2 or on WO 3). The noble metal particles' localization was proved by SEM-EDX, while their size with DRS and TEM. The influence of the noble metal nanoparticles' position was investigated successfully on the light absorption properties, photocatalytic activity toward oxalic acid and photocatalytic hydrogen production. Major differences were observed in the photocatalytic performance of the catalysts in which only the position of the noble metal was changed. Consequently, highly active composites were obtained, that surpassed the reference catalysts' (TiO 2 (Au), TiO 2 (Pt), WO 3 (Au), WO 3 (Pt)) oxalic acid degradation yield and were also quite active for photocatalytic hydrogen production.

Double modifications of TiO2 by doping with WO3 and by dispersing on a SiO2 support were made by the one-pot sol-gel method. Doping with W shifts the TiO2 band gap energy from 3.2 eV to around 3.06 eV. The surface area of the supported W-TiO2/SiO2 material was significantly increased, by approximately 3 times, in comparison to the bare TiO2. The photocatalytic activities of the catalysts were evaluated in the degradation reaction of p-nitrophenol in aqueous solution and basic medium. After 240 min of photodegradation, more than approximately 99% p-nitrophenol could be mineralized with the most active W-TiO2/SiO2 catalyst. Under UV irradiation, p-nitrophenol was initially photodegraded into hydroquinone and benzosemiquinone intermediates, which were further degraded into smaller fragments such as organic carboxylic acids and finally completely mineralized. A proposed photoreaction mechanism was presented based on the key roles of the surface hydroxyl species and superoxide radicals s...

The article provides an overview of the most relevant characterization results of heterogeneous photo-catalytic materials available in the literature. First, we present a summary of the ex situ utilization of physico-chemical characterization techniques. In the majority of current works, pre and post-reaction samples are subjected to ex situ analysis using a multitechnique approach which attempts to render information about the morphological, structural, and electronic properties of relevance to interpret photoactivity. Details of the effects on physico-chemical observables of the nanostructure and the complex chemical nature (considering mono and multiphase materials with presence of several chemical elements) of typical photo-catalysts will be analyzed. Modern studies however emphasize the use of in situ tools in order to establish activity-structure links. To this end, the first point to pay attention to is to consider carefully the interaction between light and matter at the reaction cell where the characterization is carried out. Operando and spectro-kinetic methodologies will be reviewed as they would render valuable and trusting results and thus will pave the way for the future developments in photocatalysis.

Ti-based electroconductive mixed oxides were deposited onto activated carbon by using three different sol-gel-based multistep synthesis routes. As demonstrated by X-ray diffraction, high crystallinity of the tungsten-loaded rutile was achieved by a sequence of annealing in inert atmosphere at 750°C and a short reductive treatment at 650°C. Formation of the rutile phase on the carbon support before the high temperature treatment has been proved to be the prerequisite for complete W incorporation into the rutile lattice. The structural and compositional properties of the mixed oxides were explored by transmission electron microscopy, temperature programmed reduction and X-ray photoelectron spectroscopy. Anode electrocatalysts were formulated by loading the composite of the activated carbon and the Ti-based electroconductive mixed oxides with 40 wt% Pt. Enhanced CO tolerance along with considerable stability was demonstrated for the electrocatalyst prepared using the Ti 0.7 W 0.3 O 2-C composite material with high degree of W incorporation.

The article provides an overview of the most relevant characterization results of heterogeneous photo-catalytic materials available in the literature. First, we present a summary of the ex situ utilization of physico-chemical characterization techniques. In the majority of current works, pre and post-reaction samples are subjected to ex situ analysis using a multitechnique approach which attempts to render information about the morphological, structural, and electronic properties of relevance to interpret photoactivity. Details of the effects on physico-chemical observables of the nanostructure and the complex chemical nature (considering mono and multiphase materials with presence of several chemical elements) of typical photo-catalysts will be analyzed. Modern studies however emphasize the use of in situ tools in order to establish activity-structure links. To this end, the first point to pay attention to is to consider carefully the interaction between light and matter at the reaction cell where the characterization is carried out. Operando and spectro-kinetic methodologies will be reviewed as they would render valuable and trusting results and thus will pave the way for the future developments in photocatalysis.

TiO2-SiO2-based nanocomposites with highly porous structures are gaining ever increasing attention due to their specific properties and large variability of synthesis pathways together with wide information on the impact of the synthesis on the activity of the catalyst. This thereby offers an alternative approach to traditional/commercially available photocatalysts. In our work TiO2-SiO2 based aerogels were obtained and modified with various amount of Ag nanoparticles, using different synthesis pathways. In the first instance their photocatalytic activity was examined in detail, by observing major differences toward salicylic acid and correlating them with their morphological and structural properties (investigating their mesoporous character, band-gap values, crystallinity grade etc.). Applying different techniques such as diffuse reflectance spectroscopy (DRS), X-ray diffraction measurements (XRD), transmission electron microscopy (TEM), Raman-and X-ray photoelectron spectroscopy (XPS) the nanoparticles and their composite morphological and

In the present research gold and platinum nanoparticles were deposited simultaneously on three different commercial titania photocatalysts (Evonik Aeroxide P25, Aldrich rutile and Aldrich anatase). For the synthesis of the composites two noble metal reduction methods (in situ and impregnation) and three noble metal deposition routes (i.e., by changing their deposition order, Au/Pt, Pt/Au, and Au-Pt simultaneously) were used. The photocatalytic performances of the nanocomposites were evaluated under UV irradiation, through degradation of oxalic acid and photocatalytic hydrogen production. The best performing photocatalyst was obtained by sequential noble metal deposition (first Au followed by Pt) on Evonik Aeroxide P25. The morphological and structural properties were studied/investigated by using DRS, TEM, HRTEM, EDX and XRD. The gold and platinum nanoparticles formed clusters in most of the cases. Furthermore, the ecotoxicity of the composites was investigated using Lemna minor growth inhibition tests using static "lake" approach completed by DLS and ROS indirect measurements. The toxic effect of the composites which showed the highest photocatalytic activity did not differ from that of their commercial counterparts, showing that these nanoparticles were eco-friendly. This result shows the great capacity of these materials to be used in the next future in photocatalytic applications.

Shape-controlled synthesis of noble metal nanoparticles and their impact on the photocatalytic activity of semiconductor oxides is continuously gaining more and more attention. Hence, commercial titania-based TiO 2-Pd nanocomposites were synthetized and characterized, using spherical and cubical Pd nanoparticles. The obtained photocatalysts were analyzed using optical (DRS) as well as morphological and structural (XRD, HR-TEM) methods in order to understand their properties. The effects of the Pd nanoparticles' shape on different commercial titania-based catalysts were highlighted in terms of photocatalytic efficiencies toward model organic pollutants (phenol and oxalic acid), evolution of reaction intermediates (hydroquinone, pyrocatechol and resorcinol) and photocatalytic H 2 production. It was found that both geometries (spherical, cubic) can enhance the activity of the base photocatalyst, although each Pd morphology modified the ratio of the primary degradation intermediates. Moreover, the photocatalytic hydrogen production of the spherical nanoparticles proved to be more efficient as the cubic ones. The observed activity differences were attributed to a possible change in the electron-transfer process, induced by the different Pd morphologies.

As shape tailoring is gaining more attention in the field of photocatalysis, exploration of the impact of 34 noble metal (Pt) nanoparticles' morphology on the activity of TiO 2-Pt nanocomposites is inevitable. 35 Spherical and polyhedral Pt nanoparticles have been synthesized by chemical reduction, while Aldrich 36 anatase, Aldrich rutile, and Aeroxide P25 were used as base photocatalysts. The nanocomposites were 37 analyzed using DRS, XRD, and HRTEM to uncover morphological, optical, and structural peculiarities of 38 the composite photocatalysts. The importance of the Pt nanoparticles' geometry was proven at three 39 levels: (i) UV light-driven photodegradation of three model pollutants: phenol, methyl orange, and oxalic 40 acid; (ii) the primary degradation intermediates' evolution profile in the case of phenol degradation; and 41 (iii) photocatalytic H 2 production.

TiO2-SiO2-based nanocomposites with highly porous structures are gaining ever increasing attention due to their specific properties and large variability of synthesis pathways together with wide information on the impact of the synthesis on the activity of the catalyst. This thereby offers an alternative approach to traditional/commercially available photocatalysts. In our work TiO2-SiO2 based aerogels were obtained and modified with various amount of Ag nanoparticles, using different synthesis pathways. In the first instance their photocatalytic activity was examined in detail, by observing major differences toward salicylic acid and correlating them with their morphological and structural properties (investigating their mesoporous character, band-gap values, crystallinity grade etc.). Applying different techniques such as diffuse reflectance spectroscopy (DRS), X-ray diffraction measurements (XRD), transmission electron microscopy (TEM), Raman-and X-ray photoelectron spectroscopy (XPS) the nanoparticles and their composite morphological and

In the present work, the influence of a gold nanoparticle's shape was investigated on the commercially available Evonik Aeroxide P25. By the variation of specific synthesis parameters, three differently shaped Au nanoparticles were synthetized and deposited on the surface of the chosen commercial titania. The nanoparticles and their composites' morphological and structural details were evaluated, applying different techniques such as Diffuse Reflectance Spectroscopy (DRS), X-ray Diffraction (XRD), and Transmission Electron Microscopy (TEM). The influence of the Au nanoparticles' shape was discussed by evaluating their photocatalytic efficiency on phenol and oxalic acid degradation and by investigating the H2 production efficacy of the selected composites. Major differences in

Synthesis of composites based on TiO 2 aerogel and Ag nanoparticles. Existence of mixed crystalline structure consisting of brookite and anatase phases. Composites visible photocatalytic activity reduces as brookite phase content raises. Ag nanoparticles addition enhances the visible photocatalytic activity.

The number of studies regarding sol-gel made titania powders is quite high, and nearly all of them use the calcination as the crystallization process. However, several papers are not providing crucial information regarding the calcination parameters, such as, heat treatment atmosphere, heating rate or heat treatment time. Furthermore, nearly no investigations were done regarding short calcination times and fast heating rates. The present paper points out the missing or under-evaluated aspects in the literature and demonstrates their importance throughout simple experiments. First of all, the influence of the calcination atmosphere and the applied flow rate (in tubular furnaces) was proven by demonstrating the inhomogeneity of the obtained samples. Secondly, the major influence of the chosen calcination time and rate was proven by obtaining fast heat treated titania powders. Their activity varied significantly with the applied calcination time, achieving two activity maxima. Also, the obtained activity trend shows that by varying the calcination time highly active titanias can be obtained (more active than Evonik Aeroxide P25).

In the present study, a morpho-structural analysis of heat treated TiO 2-WO 3-Au aerogel composites is presented. Simultaneously, the influence of the loaded Au nanoparticles on the morphological and structural characteristics of the TiO 2-WO 3 aerogel is also analyzed. X-ray diffraction data (XRD) and Raman spectroscopy measurements indicated that TiO 2 crystallizes mainly in anatase phase, while the WO 3 structure remains amorphous. The morphological features of the samples, i.e. crystallites mean size, particle size distribution, and specific surface area of the pores, are investigated by using XRD, transmission electron microscopy (TEM), and N 2 adsorption/desorption, respectively. The results indicate a decrease in size of the titania crystallites as the tungsten oxide content increases. The diffuse reflectance spectra modified by applying a Kubelka-Munk transformation reveal that the presence of gold nanoparticles improves the material's response in the visible domain.

Titania/tungsten (VI) oxide/noble metal (gold and platinum) composites were obtained by the means of selective noble metal photodeposition on the desired oxide's surface (either on TiO 2 or on WO 3). The noble metal particles' localization was proved by SEM-EDX, while their size with DRS and TEM. The influence of the noble metal nanoparticles' position was investigated successfully on the light absorption properties, photocatalytic activity toward oxalic acid and photocatalytic hydrogen production. Major differences were observed in the photocatalytic performance of the catalysts in which only the position of the noble metal was changed. Consequently, highly active composites were obtained, that surpassed the reference catalysts' (TiO 2 (Au), TiO 2 (Pt), WO 3 (Au), WO 3 (Pt)) oxalic acid degradation yield and were also quite active for photocatalytic hydrogen production.

Titanium dioxide photocatalysts were prepared by a newly developed synthesis method that involves rapid heating with short, medium and long exposures of the sol-gel prepared amorphous starting materials (RHSE, RHME and RHLE series) at different temperatures and calcination times. These materials were characterized by various methods, such as XRD, TEM, DRS, IR, nitrogen adsorption and XPS techniques. The detailed study of these catalysts revealed that at low calcination temperatures (e.g. 400 • C) the highest activity will be achieved if a long calcination (90-120 min) is applied because of the surface purification from the deposited organics. At higher temperatures (e.g. 550 • C) shorter calcination times (5-10 min) proved to be effective to achieve high UV activity. At this temperature an unidentified oxygen type was detected from the O1s XPS of the samples which seems to be related to the presence of Ti 3+. At 600 • C both short (10 min) and medium calcination (30-90 min) times were found to be beneficial for the phenol degradation under UV irradiation due to the very effective sensitization (10 min of calcination) and surface OH-group preservation (60 min of calcination).

In this study the efficiency of different bare, doped and composite photocatalysts were compared, under UV and visible light irradiation in order to show a detailed picture of the relative performance of the best photocatalysts developed in our laboratories and the mostly investigated reference titanias. The syntheses of our photocatalysts were optimized in order to achieve maximum photocatalytic activity under UV and visible light irradiation. Non doped commercial (Aeroxide P25, Aldrich anatase) and synthesized titanias (produced by sol-gel and flame hydrolysis techniques) and nitrogen, iron, iodine doped and silver or gold deposited titanium dioxides were investigated with two model pollutants (phenol and oxalic acid) under identical experimental conditions. The material properties of these selected photocatalysts were thoroughly characterized by X-ray diffraction, diffuse reflectance spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy and BET methods. The highest degradation rate of phenol was determined for the flame made titania sample with relatively low specific surface area (20 m 2 /g) when UV irradiation was applied. In contrast with that, our nitrogen doped photocatalyst with high specific surface area (139 m 2 /g) was the best for phenol degradation under visible light irradiation. Although the most efficient oxalic acid mineralization occurred with noble metal photodeposited samples under UV irradiation, this type of modification was detrimental when VIS irradiation is applied. The decomposition rate of oxalic acid was high under VIS irradiation using the iron and nitrogen doped photocatalysts. For both substrates and irradiation conditions our best photocatalysts were found to be significantly more active than Aeroxide P25 TiO 2. Intermediate studies revealed that phenol degradation resulted in dihydroxy benzene intermediates, such as pyrocatechol and hydroquinone both under UV and visible light irradiation with our TiO 2-N photocatalyst. The results of this comparative study could promote the determination of the optimal synthesis conditions of titanium dioxide based photocatalysts for a given organic pollutant in water.

We have investigated the preparation of zinc and tungsten mesoporous titanates materials from a sol-gel method using a block copolymer as amphiphile. The mesoporous network is created through a soft templating method. Samples have been characterized by SAXS, XRD, nitrogen adsorption-desorption, XPS, TEM, EDX, Raman and UV-Vis spectroscopies. The presence of tungsten induces the formation of orthorhombic crystal phase WO 3 besides the titania network and inhibits the formation of anatase, which is the predominant structure in the Zn-TiO 2 materials. No trace of ZnO is detected by XRD and Raman. However XPS suggests the presence of zinc ions in the mesoporous network and their linkage with oxygen atoms. The zinc oxide could therefore either be randomly dispersed or amorphous on the material surface. XPS and EDX also reveal that the tungsten clusters are located at the surface of the tungsten mesoporous titanates. Studies of the Kubelka-Munk function showed that at low Zn content, the band gap energy is in the range of the anatase one and the photocatalytic efficiency of the corresponding zinc titanates is similar to the one of the pure titania mesoporous material. Beyond the addition of 1 mol.% of tungsten, the titanates present a band gap energy in the range 2.7-2.8 eV, close to the value of the orthorhombic WO 3. For both kinds of titanates, the decrease of the band gap reduces their capacity for the photodegradation of methyl orange.

The conversion of methane into methanol is one of the great challenges in the photocatalysis. In this investigation WO3/TiO2 photocatalysts was synthesized by sodium borohydride (NaBH4) method. The tungsten concentration was studied in the range of 5 to 20 atomic ratio. XRD results revealed a TiO2 anatase phase and WO3 peaks near the background noise. However, WO3 presence has been highlighted by Raman spectroscopy, indicating the existence of both orthorhombic and amorphous phase. The photocatalyst experiments showed that all materials enable the methanol production in UVC irradiation, and only the materials with WO3 content produced the alcohol in white light irradiation. The high conversion was observed for WO3(10)/TiO2(90) with 3.5 mmol h-1. The conversion of methane to methanol was most promising using WO3(10)/TiO2(90) due high conversion and no other products observed in FTIR spectra.

Highly ordered ZnO doped WO3 thin films with good crystalline quality are prepared using RF magnetron sputtering technique and its structural and morphological properties are studied using various characterisation tools such as XRD, micro-Raman, XPS, FESEM and EDX analysis. X-ray diffraction studies reveal the enhancement of crystalline quality of the films with increase in ZnO doping concentration up to 5 wt%, beyond which the crystalline quality gets deteriorated. A phase modification from single monoclinic WO3 phase to a mixed monoclinic WO3 and W18O49 phases is observed for films with higher ZnO doping concentrations. Morphological analysis shows that a smooth surface for pure film whereas the ZnO doped films presents a dense distribution of grains of larger sizes with well-defined grain boundary.

One weight percent of differently sized Au nanoparticles were deposited on two commercially available TiO2 photocatalysts: Aeroxide P25 and Kronos Vlp7000. The primary objective was to investigate the influence of the noble metal particle size and the deposition method on the photocatalytic activity. The developed synthesis method involves a simple approach for the preparation of finely-tuned Au particles through variation of the concentration of the stabilizing agent. Au was deposited on the TiO2 surface by photo-or chemical reduction, using trisodium citrate as a size-tailoring agent. The Au-TiO2 composites were synthetized by in situ reduction or by mixing the titania suspension with a previously prepared gold sol. The H2 production activities of the samples were studied in aqueous TiO2 suspensions irradiated with near-UV light in the absence of dissolved O2, with oxalic acid or methanol as the sacrificial agent. The H2 evolution rates proved to be strongly dependent on Au particle size: the highest H2 production rate was achieved when the Au particles measured ~6 nm.

In this work we obtained materials of titanium dioxide whit mixed oxide CoO-TiO2 and WO3-TiO2 (1.0, 3.0, 5.0 %wt). The solids were characterized by; nitrogen physisorption (BET) and porosity (BJH), XRD patterns and UV-Vis spectroscopy. The photoactivity was evaluated using a Pyrex reactor of 200 ml using a solution ethanol-water (1:1 molar ratio) and 0.1 g of catalyst using a high pressure Hg lamp (with a wavelength of 254 nm and an intensity of 2.2 mW/cm 2 encapsulated in a quartz tube. The results showed materials with specific surface area among 89 to 95 m2/g and 41 to 91 m 2 /g with mesopority characteristics. The XRD patterns show the formation of the crystalline anatase phase. The band gap energy (Eg) for the materials were obtained with UV-Vis spectroscopy, the Eg values were lower than 3.2 eV for both mixed oxide. In the water splitting evaluation a maxim in the efficient was found at Co and W at 5 wt.%. The hydrogen produced was 1000 μmol/h and 950 μmol/h respectively, this is a value comparable to respect other works.

Photocatalytic applicability of different TiO₂-based nanomaterials is a current hot topic. Therefore, our interest for the present research was to elucidate the formation of primary and secondary intermediates during the phenol degradation by photocatalysis, in the presence of Au/TiO₂ nanocomposites. The composites consisted of differently shaped gold nanoparticles and commercial titania (Evonik Aeroxide P25). The obtained composites and the noble metal nanoparticles' morphology was investigated by Transmission Electron Microscopy (TEM), their optical properties were explored using Diffuse Reflectance Spectroscopy (DRS), while the crystal structure was characterized by X-ray diffraction (XRD). The photocatalytic activity was investigated by photodegradation of phenol and methyl orange. In case of phenol it was shown that, the formation of degradation intermediates, was dependent on the Au nanoparticles' shape, leading to high amounts of different intermediates as follows: hy...

Hydrogen peroxide was applied during the synthesis to enhance the visible light excitability of nanosized (<10 nm), pure rutile phase titanium dioxides synthesized by a facile, sol-gel method at low temperature. Different amounts of hydrogen peroxide were used during the synthesis to form peroxo groups on the surface of TiO 2-s. As-prepared photocatalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), infrared spectroscopy (IR), and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the catalysts were investigated by phenol, Rhodamine B dye and coumarin degradation under visible light irradiation. Evonik Aeroxide P25 TiO 2 and commercial rutile phase titanium dioxide were used as reference photocatalysts. First order derivative of DRS spectra showed enhanced visible light excitability in the case of Ti:H 2 O 2 = 1:2 ratio (applied during the synthesis). XPS measurements confirmed the formation of peroxo groups in this specific TiO 2. Photocatalytic measurements pointed out that this TiO 2 had by far the best photocatalytic performance, exceeding the photocatalytic activity of Aeroxide P25 and commercial rutile as well. This activity gain was attributed to the presence of peroxo groups on the surface.

TiO 2-Pt aerogel composites have been synthesized by mixing sol-gel titania with Pt colloidal suspensions followed by supercritical drying. The highest specific surface achieved with these materials ranged between 550 and 600 m 2 g-1 before annealing and stayed relatively high, i.e. 162 m 2 g-1 , after calcination. The concentration of Pt nanoparticles ranged between 0.3 to 1.0 % wt. while their size ranged between 5.75 and 6.5 nm. These composites were employed as photocatalysts for room-temperature photocatalytic reforming of ethanol and hydrogen production. The highest hydrogen production rate, 7.2 mmol H 2 h-1 g-1 , was obtained in the case of the smallest and most concentrated metal nanoparticles underlying the importance of the number of active sites on the TiO 2-Pt composites. This rate of hydrogen production is relatively high and reflects the relatively high specific surface of the employed photocatalysts.

TiO2-SiO2-based nanocomposites with highly porous structures are gaining ever increasing attention due to their specific properties and large variability of synthesis pathways together with wide information on the impact of the synthesis on the activity of the catalyst. This thereby offers an alternative approach to traditional/commercially available photocatalysts. In our work TiO2-SiO2 based aerogels were obtained and modified with various amount of Ag nanoparticles, using different synthesis pathways. In the first instance their photocatalytic activity was examined in detail, by observing major differences toward salicylic acid and correlating them with their morphological and structural properties (investigating their mesoporous character, band-gap values, crystallinity grade etc.). Applying different techniques such as diffuse reflectance spectroscopy (DRS), X-ray diffraction measurements (XRD), transmission electron microscopy (TEM), Raman-and X-ray photoelectron spectroscopy (XPS) the nanoparticles and their composite morphological and

Mono and bicomponent TiO 2 and WO 3 nanoparticles were synthesized inside Vycor Ò glass pores, by cycles of impregnation of the glass with the respective oxide precursor followed by its thermal decomposition. The impregnation-decomposition cycle (IDC) methodology promoted a linear mass increase of the glass matrix, and allowed tuning the nanoparticle size. X-ray diffraction and Raman spectroscopy data allowed identifying the formation of TiO 2 as anatase phase, while WO 3 is a mixture of the c-WO 3 (monoclinic) and d-WO 3 (triclinic) phases. High resolution transmission electron microscopy images revealed that for 3, 5, and 7 IDC, the TiO 2 nanoparticles obtained presented average diameters of 3.4, 4.3, and 5.1 nm, and the WO 3 nanoparticles have 2.9, 4.6, and 5.7 nm sizes. These TiO 2 and WO 3 monocomponent nanoparticles were submitted to IDC with the other oxide precursor, resulting in bicomponent nanoparticles. The broadening and shift of the Raman bands related to titanium and tungsten oxides suggest the formation of hetero-structure core-shell nanoparticles with tunable core sizes and shell thicknesses.

Influence of modification with metals Au and Ag, oxides of Fe, Mg and Ce and their combinations on amorphization of widely used commercial nanosized TiO 2 (Degussa P25) was studied with SR-XRD and EXAFS methods. These systems were chosen taking into account their potential on catalytic properties for biomass to biodiesel transformation, as it was shown in model reaction of liquid phase n-octanol oxidation as well as lowtemperature CO oxidation for "cold start" of the neutralizers of car exhaust gases. Instability of rutile, the most stable TiO 2 phase, in the presence of the additives was found. Application of EXAFS method, rarely used for crystalline structure transfer studies, led to elucidation of this apparent effect, which was explained by higher level of amorphization of rutile than anatase. Literature data indicate that bulky TiO 2 doping leads to either increase of rutile/anatase ratio complete inhibition of anatase to rutile transformation. Dissimilar phase composition changes, revealed in this work for modified nanodispersed TiO 2 , was attributed to size effect.

Effect of a crystalline phase of TiO 2 is investigated in the photodeposition processes of Rh metal nanoparticles on TiO 2 photocatalysts having anatase and rutile phase by means of in-situ time-resolved energy dispersive X-ray absorption fine structure spectroscopy (DXAFS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The important factor was neither its crystallite size nor its specific surface area, and was the crystalline phase. In situ time-resolved DXAFS analysis clarified that the Rh metal nanoparticles with a uniform size appear on both anatase and rutile phases of TiO 2 , whereas the appearance rate of Rh metal nanoparticles decreases with the photoirradiation time only on the rutile phase of TiO 2. The TEM observation and XPS depth analysis revealed that the bare surface of photodeposited Rh metal nanoparticles on the rutile is exposed, although that on the anatase is partially covered with TiO 2 due to strong metal-support interaction (SMSI) between Rh metal nanoparticle and TiO 2-δ .

The influence of gold nanoparticles on the photocatalytic activity (500 W-medium pressure Hg lamp) of TiO 2 anatase for the conversion of benzene to phenol has been studied. Au/TiO 2 samples (Au loading ranging from 0.25 to 2.20 wt%) were prepared by the deposition-precipitation method and characterized by chemical analysis, TEM, XRD, and Raman spectroscopy. Photocatalytic tests revealed that the presence of gold nanoparticles initially decreases the reaction rate but for longer reaction times it becomes beneficial and promotes phenol formation almost doubling the reaction yield with respect to unmodified TiO 2 , without increasing the percentage of hydroquinone, resorcinol and benzoquinone byproducts.

Synthesis of composites based on TiO 2 aerogel and Ag nanoparticles. Existence of mixed crystalline structure consisting of brookite and anatase phases. Composites visible photocatalytic activity reduces as brookite phase content raises. Ag nanoparticles addition enhances the visible photocatalytic activity.

The alkylation of light hydrocarbons leads to produce the high octane number gasoline blending components. The homogeneous catalytic alkylation reaction is usually carried out at low temperature in the presence of H 2 SO 4 and HF. The use of heterogeneous catalysis for this reaction is a promising solution for the replacement of hazardous acids to environmentally friendly zeolite catalyst. The alkylation reaction of isobutane with 1-butene was studied on selected zeolite catalysts. The objective of the research was to study the mechanism of the alkylation reaction with taking the rate determining step and irreversible step into consideration.

TiO2-Au aerogels containing different amounts of gold nanoparticles of different sizes (5 and 16 nm) were successfully synthesized using a sol-gel procedure, and were tested for salicylic acid photodegradation under UV irradiation. The structure and morphology of the obtained materials were investigated using X-ray diffraction, transmission electron microscopy, and N2 adsorption-desorption measurements. UV-Vis spectroscopy was used to study the optical properties. The effects of the gold nanoparticles on the TiO2 crystallization process were twofold, as follows: (i) the number of crystallized zones was strongly related to the concentration of the gold nanoparticles, and (ii) the smaller gold particles increased the time taken for the crystallization of the samples. It was found that the noble metal-doped samples exhibited higher degradation rates compared with bare titania. It was found that the most active photocatalyst in each studied system was the sample with the highest concentration of gold nanoparticles. Additionally, the highest degradation rate value was obtained with the smallest Au nanoparticles (46.4  10-3 μmol/(L•s).

Oxidized/partially reduced hexagonal (h-) and monoclinic (m-) WO 3 nanoparticles were tested as photocatalysts both in the aqueous and gas phase. Unlike other semiconductor oxides, WO 3 is unique in that its composition is decisive on photocatalysis, while its crystal structure has only an indirect role.

Introduction The deposition of noble metals on oxide surfaces is a commonly adopted method in heterogeneous catalysis. Noble metal deposited on semiconductor nanoparticles is often found to be beneficial for maximizing the efficiency of photocatalytic reactions [1]. Semiconductor-metal composite nanoparticles facilitate charge rectification and promote interfacial charge transfer processes. Recently, attention has been drawn to the modification of oxide surfaces with gold nanoparticles. Improved photoelectrochemical performance was observed in the case of gold-coated TiO2 films [2]. The improved performance of the nanostructured composite film was attributed to the charging of metal nanoparticles followed by Fermi-level equilibration between the metal and semiconductor in the composite film [3]. However, when the ultraviolet (UV) irradiation was extended for a longer duration (30-60 min), these composite films exhibited a deterioration in photoelectrochemical performance [2]. The po...

Influence of modification with metals Au and Ag, oxides of Fe, Mg and Ce and their combinations on amorphization of widely used commercial nanosized TiO 2 (Degussa P25) was studied with SR-XRD and EXAFS methods. These systems were chosen taking into account their potential on catalytic properties for biomass to biodiesel transformation, as it was shown in model reaction of liquid phase n-octanol oxidation as well as lowtemperature CO oxidation for "cold start" of the neutralizers of car exhaust gases. Instability of rutile, the most stable TiO 2 phase, in the presence of the additives was found. Application of EXAFS method, rarely used for crystalline structure transfer studies, led to elucidation of this apparent effect, which was explained by higher level of amorphization of rutile than anatase. Literature data indicate that bulky TiO 2 doping leads to either increase of rutile/anatase ratio complete inhibition of anatase to rutile transformation. Dissimilar phase composition changes, revealed in this work for modified nanodispersed TiO 2 , was attributed to size effect.

WO3-TiO2 composite materials were obtained using commercial titania (Evonik Aeroxide P25) and hydrothermally crystallized WO3. Different ratios of TiO2/WO3 were investigated, starting at 1 wt.% of WO3 to 50 wt.%. The morphology of WO3 was of the star-like type, and its structure is basically composed of monoclinic crystalline phase. All spectroscopic characteristics of the composites and their derived data (band-gap energy value, light absorption threshold, and IR specific bands) directly varied with the increase of the WO3 content. However, the oxalic acid photodegradation achieved under UV light reached the highest yield for 24 wt.% WO3 content, a result that was attributed to the charge separation efficiency and the surface hydrophilicity. The latter mentioned reason points out the crucial importance of the surface quality of the investigated structure in photocatalytic tests.