Anatase Content Research Articles

Fabrication of Electrospun Porous TiO2 Dielectric Film in a Ti–TiO2–Si Heterostructure for Metal–Insulator–Semiconductor Capacitors

The development of metal–insulator–semiconductor (MIS) capacitors requires device miniaturization and excellent electrical properties. Traditional SiO2 gate dielectrics have reached their physical limits. In this context, high-k materials such as TiO2 are emerging as promising alternatives to SiO2. However, the deposition of dielectric layers in MIS capacitors typically requires high-vacuum equipment and challenging processing conditions. Therefore, in this study, we present a new method to effectively fabricate a poly(vinylidene fluoride) (PVDF)-based TiO2 dielectric layer via electrospinning. Nano-microscale layers were formed via electrospinning by applying a high voltage to a polymer solution, and electrical properties were analyzed as a function of the TiO2 crystalline phase and residual amount of PVDF at different annealing temperatures. Improved electrical properties were observed with increasing TiO2 anatase content, and the residual amount of PVDF decreased with increasing annealing temperature. The sample annealed at 600 °C showed a lower leakage current than those annealed at 300 and 450 °C, with a leakage current density of 7.5 × 10−13 A/cm2 when Vg = 0 V. Thus, electrospinning-based coating is a cost-effective method to fabricate dielectric thin films. Further studies will show that it is flexible and dielectric tunable, thus contributing to improve the performance of next-generation electronic devices.

Green preparation of tertiary-phase titanium oxide nanopowder using Chlorella sp. aqueous extract

Herein, a novel green synthesis of tertiary-phase titanium dioxide nanoparticles (TiO2 NPs) using an aqueous extract of Chlorella sp. was reported for the first time. The TiO2 NPs were prepared using various extract volume concentrations (0, 5, 10, 15 and 20 % v/v) and subsequently calcinated at 600 °C. The X-ray diffraction (XRD) results revealed that the concentration ranging from 5 to 15 % v/v algae extract resulted in mixed phases of anatase, brookite, and rutile, while the extract concentration of 20 % v/v yielded mixed phases of anatase and brookite. The phase transformation from anatase to rutile decreased with increasing extract concentration. Transmission electron microscopy (TEM) images showed that the average grain size of the control TiO2 was 90 nm, whereas that of algae mediated TiO2 NPs was 10–20 nm. The concentration of algae extract was a very significant parameter for the phase transformation and particle size reduction of TiO2 NPs. The tertiary phase 10 % and 15 % algae mediated TiO2 powder also exhibited reaction rate constants (k) similar to the binary phase 20 % TiO2, despite containing lower anatase content. The present work demonstrated the successful synthesis of tertiary phases TiO2 nanopowder using microalgae Chlorella extract as a biogenic capping agent.

Impact of Au on the transition temperature and photocatalytic activity of TiO2

The effect of gold (Au) addition on the anatase to rutile transition temperature (ART) of titanium dioxide (TiO2) was investigated. Concentrations of 2, 4, 8 and 16 mol. % of Au have been synthesised via a sol–gel technique and calcined at various temperatures (500–900 °C). The inclusion of gold improves the ART at 700 °C, maintaining 44.5 % anatase content for 4 % Au. Density functional theory studies indicated that the addition of Au in the anatase phase results in considerable lattice distortions, while Au 4d states and occupied Ti 3d orbitals contribute to the valence-conduction band energy gap upon doping. However, no sign of lattice substitution was observed in the experimental analysis. Instead, we demonstrate that the actual structure is well described by gold nanoparticles deposited on anatase and present a detailed DFT description of gold-modified anatase (101). All Au-TiO2samples exhibit reduced photocatalytic degradation properties compared to the control TiO2 at 500 °C. However, after calcining at 600 °C the addition of Au increases the photocatalytic activity of TiO2 from 49 % to 61 %, at an optimal concentration of 2 % Au-TiO2. The modification of titania with gold does push the transition temperature higher. However, this comes at the cost of reduced activity for 1,4-dioxane degradation, with the unmodified titania sample having better overall photocatalytic activity.

Doping of photoactive TiO2 films by DC plasma electrolytic oxidation: Effect of transition metals

Several beneficial features maintain TiO2 in the top list of viable materials for photocatalytic purposes. However, its relatively large band-gap (3.0–3.2 eV) still hampers practical applications under sunlight. This work explores Direct Current (DC) Plasma Electrolytic Oxidation (PEO) of titanium as a fast, easily-scalable and single-step tool to synthesise doped TiO2 photoanodes with controlled morphology, crystalline structure and thickness. Zn-, Cu- and Fe-doped crystalline TiO2 films were obtained in H2SO4 aqueous solutions containing ZnSO4, CuSO4 and FeSO4 precursors, respectively. As-prepared TiO2 films showed a porous and homogeneous sponge-like surface morphology, typical of PEO-produced oxides, and a crystalline phase structure consisting of a mixture of anatase and rutile phases. The anatase content varied in the 54–100 % range and correspondingly the band-gap energy was in the 2.85–3.07 eV range. Doped oxides prepared with a low concentration of the metal precursors showed monochromatic incident-photon-to-current-efficiency (IPCE) values exceeding those obtained with pristine TiO2 by up to 24 %, best performing in the order Zn- > Cu- > Fe-doped TiO2. Photocurrent under polychromatic UV-Vis irradiation showed an analogous trend and the estimated efficiency of solar-light harvesting was in the 0.3–4 % range, with Zn- ≈ Cu- > Fe-doped TiO2. Although the superior performance of the PEO-prepared metal-doped TiO2 could not be fully confirmed by photoelectrocatalytic oxidation tests of organics, the present investigation showed the viability of DC PEO for the synthesis of metal-doped TiO2 photoanodes.

Synthesis of porous TiO2 and Fe-doped TiO2 films for photocatalysis by a cooling enhanced plasma electrolytic oxidation approach

Porous TiO2 films are widely used in photocatalysis for pollutant remediation and synthetic chemistry applications, and the homogeneity and stability of the films are important parameters. Here, we show that porous TiO2 and Fe-doped TiO2 (Fe-TiO2) films on Ti foils with homogeneous structure and well-controlled doping can be synthesized by a cooling enhanced plasma electrolytic oxidation (CPEO) method. The anatase content within pristine TiO2 films and the concentration of Fe dopant in Fe-TiO2 films can be manipulated by simply adjusting the synthetic parameters, leading to an optimum photocatalytic performance under both UV and visible light irradiation for the decomposition of methylene blue.

APPLICATION OF ACTIVATING INFLUENCES IN OBTAINING TiO2-PILLARED MONTMORILLONITE WITH IMPROVED PHOTOCATALYTIC PROPERTIES

A new approach to the obtaining of a highly efficient photocatalyst - TiO2-pillared montmorillonite – by hydrothermally activated intercalation of mechanically dispersed bentonite matrix with the polyhydroxocomplexes of titanium is proposed. The material was characterized by the X-ray diffractometry, low-temperature nitrogen adsorption-desorption, scanning electron microscopy, energy dispersive microanalysis, and zeta potential measurement. The use of short-term (up to 3 min) mechanical dispersion in a planetary mill significantly increases the capacity of cation exchange during intercalation, and the photocatalysts obtained after annealing at 500 °C are characterized by significantly higher values of specific surface area and total pore volume compared with mechanically untreated and initial montmorillonite. The average size of TiO2 crystallites is about 10 nm and the content of anatase is over 90%. Mechanical activation leads to a significant change in the ζ-potential of montmorillonite particles from a significantly negative value in the source material to almost zero, which is an additional argument for more efficient intercalation. Hydrothermal treatment leads to the appearance of coral-like formations of titania on the surface of montmorillonite, and after mechanical treatment they significantly increase in size. Adsorption and photocatalytic properties were studied in a quartz reactor using the rhodamine B dye as example. Complete photocatalytic destruction of the dye was achieved within about 100 min (initial concentration of 40 mg/l, amount of photocatalyst 1 g/l, UV lamp power 250 W). Adsorption kinetics is described by pseudo-first and pseudo-second order models. The kinetics of photocatalysis is described by the Langmuir-Hinshelwood model. The high photoactivity is explained both by the improvement of textural properties and the appearance of additional photocatalytic centers due to the defective structure of mechanically activated montmorillonite.

SYNTHESIS AND STUDY OF Ag-TiO2 NANOPARTICLES FOR APPLICATION IN SELF-CLEANING FABRICS

In this work, the Ag-TiO2 nanocomposite was prepared by sol-gel method and characterized using the Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and UV-Vis spectroscopy. The Ag+/Ti4+ ratio significantly influences the phase transition of TiO2 from anatase to rutile in the nanocomposite: the anatase content decreases from 94.9% to 52.6% as this ratio increases from 1.0 to 4.0 %. The initial Ag+/Ti4+ ratio of 1.0 % was chosen for further research due the highest content of TiO2 in the anatase phase. The nanoparticles are fairly monodisperse and have a spherical shape with an average size of about 18-24 nm. Self-cleaning fabric polyester (PET) was modified successfully with Ag-TiO2 nanoparticles by an immersed method. The nanocomposite of Ag and anatase TiO2 was coated by binder in 100-200 nm in size which coating onto the surface of fabric demonstrated self-cleaning surface with different mechanisms: hydrophobic surface as “lotus leaf” effect, photocatalytic degradation Rhodamine B under solar irradiation. The PET fabric coated with the Ag-TiO2 composite demonstrates stronger antibacterial activity (inhibition zone of 1.3 cm) compared to the fabric coated with TiO2 alone (inhibition zone of 0.8 cm). The results showed that after 6 h of irradiation, the photocatalytic activity of the Ag-TiO2/PET fabric sample is significantly better than that of the TiO2/PET fabric sample. The ability to change from hydrophobic to hydrophilic is especially promising to the interest in self-cleaning surfaces, the textile industry, and environmental cleanup.

Investigating the crystallization behavior of TiO2 during annealing: Molecular dynamics simulations

TiO2 is a dielectric material with excellent photocatalytic and photochemical properties. The conversion of TiO2 from an amorphous to crystalline phase significantly improves the photocatalytic activity of TiO2. However, the crystallization behavior of TiO2 during annealing has been little studied in the field of molecular dynamics. In this paper, the crystallization behavior of TiO2 during annealing under different conditions was analyzed using molecular dynamics simulation. To investigate the phase transition process of TiO2, the melting point temperature of the system was calculated by mean square displacement at about 2400 K. The effect of size on structural stability was explored. The radial distribution function and x-ray diffraction curves revealed that the anatase phase appeared over 800 K. Moreover, with the increase in annealing temperature, the anatase content in TiO2 first increased and then decreased, and the rutile phase gradually increased. At a specific temperature, a structure is formed where rutile and anatase coexist. Anatase atoms compete with rutile atoms, and by increasing the temperature, anatase is converted to rutile. The amorphous structure is reduced at high temperatures, improving the crystalline quality. The crystallization behavior of the amorphous structure can improve the photocatalytic efficiency of TiO2. TiO2 nanometers have good prospect for application. Therefore, studying the crystallization behavior of TiO2 is essential.

Photocatalytic performance of Nd–TiO2 coatings: effect of voltage and frequency

Neodymium (Nd)–titanium dioxide (TiO2) micro-arc oxidation (MAO) coatings were formed in a phosphate-based electrolyte with the addition of neodymium (III) oxide (Nd2O3) using suitable voltages and frequencies. Scanning electron microscopy results revealed that the coatings varied with different voltages and frequencies. Furthermore, composition analysis showed the neodymium–titanium dioxide coatings were mainly composed of anatase and rutile phases. Meanwhile, the anatase content increased and then decreased. In addition, X-ray photoelectron spectroscopy results indicated that the titanium (Ti) 2p spin–orbit components of the neodymium–titanium dioxide coatings shifted toward a higher binding energy, suggesting that some of the neodymium (Nd3+) ions combined with the titanium dioxide lattice, leading to dislocation. Furthermore, photocatalytic experiment results showed that the photocatalytic activity of neodymium–titanium dioxide coatings can be greatly enhanced with a moderate amount of neodymium ions. However, an excessive amount of neodymium ions does not improve the photocatalytic activity further.

Material Design of Bimetallic Catalysts on Nanofibers for Highly Efficient Catalytic Reduction of 4-Nitrophenol.

In this study, CuO-TiO2 nanofiber catalysts were fabricated by an electrospinning process, followed by thermal annealing at various temperatures ranging from 300 to 700 °C. The phase transformation from CuO to metallic Cu was carried out through immersion treatment in NaBH4 solution. The resulting CuO-TiO2 and Cu-CuO-TiO2 nanofibrous mats were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Brunauer-Emmett-Teller (BET) analysis. The results revealed that the crystalline phase composition of the nanofibrous mats considerably affected the efficiency of photocatalytic reduction, where the CuO-TiO2 catalysts with a predominant anatase content was found to be more photoactive than the rutile phase. Similarly, the presence of both Cu and CuO species was more beneficial for promoting the activity of fibers by acting as an interim location for facilitating the electron transfer. The fabricated Cu-CuO-TiO2 nanofibrous mat with a ratio presented high conversion (∼99%) within several minutes with the apparent pseudo-first-order rate constant of 0.42 and 0.50 min-1 in the absence and presence of UV light irradiation as well as excellent stability in recycling runs with a stable conversion efficiency of 97% or higher over five successive catalytic cycles.

A facile impregnation synthesis of Ni-doped TiO2 nanomaterials for dye-sensitized solar cells

This study reports a facile impregnation method for synthesizing Ni-doped TiO2 nanomaterials using P25-TiO2 as a starting material. The as prepared nanomaterials were subjected to structural and optical characterizations and subsequently employed in photovoltaic studies. X-ray diffraction (XRD) and Raman studies confirmed that Ni doping did not alter the anatase and rutile contents of P25-TiO2. Also, the presence of the constituent dopants and their ionic states were confirmed by Energy-Dispersive X-ray (EDX) and X-ray photoelectron (XPS) spectroscopies. Topographic Atomic Force Microscopic (AFM) images illustrated that Ni doping had increased the surface roughness of the TiO2. Optical characterization by UV-Visible spectroscopy revealed that the Ni doping had caused red shift in light absorption due to reduced TiO2 bandgap and improved the dye adsorption on TiO2 films. Then, the photocurrent–photovoltage property of the fabricated devices was investigated and the optimized 0.10 wt% Ni-doped TiO2 photoanode based device exhibited pronounced power conversion efficiency (PCE) of 6.29% under air mass (AM) 1.5 conditions (100 mWcm−2, 1 sun). Improved charge transport properties were also observed by the electrochemical impedance spectroscopic (EIS) study for the device with optimized Ni-doped TiO2 compared to the control device.

Reduced Graphene Oxide/Waste-Derived TiO2 Composite Membranes: Preliminary Study of a New Material for Hybrid Wastewater Treatment

This work reports the preliminary results of the development of composite self-assembling membranes obtained by the combination of reduced graphene oxide (rGO) with commercial Degussa P25 titanium dioxide (TiO2). The purpose is to demonstrate the possibility of combining, in the same self-standing material, the capability to treat wastewater containing both inorganic and organic pollutants by exploiting the established ability of rGO to capture metal ions together with that of TiO2 to degrade organic substances. Moreover, this study also investigates the potential photocatalytic properties of tionite (TIO), to demonstrate the feasibility of replacing commercial TiO2 with such waste-derived TiO2-containing material, fulfilling a circular economy approach. Thus, rGO-TiO2 and rGO-TIO composite membranes, 1:1 by weight, were prepared and characterized by SEM-EDX, XRD, thermogravimetry, as well as by Raman and UV-Vis spectroscopies to verify the effective and homogeneous integration of the two components. Then, they were tested towards 3-mg L-1 aqueous synthetic solutions of Fe3+ and Cu2+ ions to evaluate their metal adsorption ability, with values of the order of 0.1-0.2 mmol gmembrane-1, comparable or even slightly higher than those of pristine rGO. Finally, the ability of the composites to degrade a common organic pesticide, i.e., Imidacloprid®, was assessed in preliminary photocatalysis experiments, in which maximum degradation efficiencies of 25% (after 3 h) for rGO-TiO2 and of 21% (after 1 h) for rGO-TIO were found. The result of tionite-containing membranes is particularly promising and worthy of further investigation, given that the anatase content of tionite is roughly 1/6 of the one in commercial TiO2.

Photocatalytic performance evaluation of flame‐sprayed and polymeric suspension coatings from TiO2 nanoparticles

AbstractBACKGROUNDHeterogeneous photocatalysis offers an interesting alternative to mitigate air pollution by using materials capable of reacting with toxic gases under ultraviolet light. One of these materials is titanium dioxide (TiO2), and thus it is necessary to analyze and improve its photocatalytic response for air depollution, in order to facilitate its use in surface applications.RESULTSThe photocatalytic ability of the synthesized TiO2 particles to remove nitric oxide (NO) was tested, and it was found that both the anatase and rutile phases present in the samples led to a NO abatement capacity of ≈60% η NO. Two different methods to coat surfaces with TiO2 particles were evaluated: thermal spray by oxyacetylene flame and dripping of polymeric suspensions of TiO2. A more detrimental effect on photocatalytic efficiencies was found using polymeric suspension rather than flame‐spraying as coating method. This was despite the anatase transformation to rutile and Ti7O13 that TiO2 particles undergo using the latter process as a consequence of heat transfer from the flame to the particles during the coating formation.CONCLUSIONResults obtained in this research demonstrate that polymeric suspensions inhibit the photocatalytic activity of TiO2 nanoparticles, probably due to the formation of a polymeric matrix on samples that constrains the action of pollutant and testing factors on samples. However, the thermal method can help retain part of the photocatalytic capability to abate NOx, despite depletion in the anatase content resulting from the heat transfer to the TiO2 raw particles sprayed to form coatings. © 2023 Society of Chemical Industry (SCI).

Photovoltaic performances of TiO2/Se heterojunction devices with different crystallographic structures of sputter-deposited TiO2 thin films

This study investigates the impact of sputter-deposited TiO2 n-type window layers with varied crystallographic structures on the power conversion of TiO2/Se photovoltaic devices, one of the most promising indoor photovoltaic energy harvesters and wide-gap top cells in tandem solar cells. Since incident light illuminates from TiO2 n-type window layer of TiO2/Se photovoltaic devices, most of photons carriers is absorbed in the Se layer. It is essential for highly efficient photovoltaic conversion of TiO2/Se devices to improve carrier collection by adequate formation of built-in potential in the Se layer and to reduce recombination by optimizing energy band alignment at TiO2/Se interface. In this study, TiO2 window layers with different contents of anatase and rutile crystallographic structures are applied to TiO2/Se heterojunction devices. Impacts of TiO2 n-type window layers with varied crystallographic structures on the power conversion of TiO2/Se photovoltaic devices are investigated in conjunction with different photoconductivity and energy band structures between anatase and rutile TiO2 thin films. In TiO2/Se photovoltaic devices with anatase/rutile mixture window layer, the power conversion efficiency was increased from 3.04% to 4.48% by combining the high open circuit voltage and high short circuit current, owing to the smaller cliff-type conduction band offset at −0.63 eV and smaller series resistance resulting from fitting the current density–voltage curves.

Hollow TiO2/Poly (Vinyl Pyrrolidone) Fibers Obtained via Coaxial Electrospinning as Easy-to-Handle Photocatalysts for Effective Nitrogen Oxide Removal.

Herein, we present a method for fabricating hollow TiO2 microfibers from Ti (OBu)4/poly (vinyl pyrrolidone) sol-gel precursors and their effects on denitrification as a photocatalyst for air purification. Various sizes of hollow TiO2 fibers were developed using coaxial electrospinning by controlling the core flow rate from 0 to 3 mL h-1. At higher flow rates, the wall layer was thinner, and outer and core diameters were larger. These features are correlated with physical properties, including specific surface area, average pore diameter, and crystalline structure. The increase in the core flow rate from 0 to 3 mL h-1 leads to a corresponding increase in the specific surface area from 1.81 to 3.95 µm and a decrease in the average pore diameter from 28.9 to 11.1 nm. Furthermore, the increased core flow rate results in a high anatase and rutile phase content in the structure. Herein, hollow TiO2 was produced with an approximately equal content of anatase/rutile phases with few impurities. A flow rate of 3 mL h-1 resulted in the highest specific surface area of 51.28 m2 g-1 and smallest pore diameter size of ~11 nm, offering more active sites at the fiber surface for nitrogen oxide removal of up to 66.2% from the atmosphere.

High-temperature treated TiO2modified with 3-aminopropyltriethoxysilane as photoactive nanomaterials

AbstractA series of titanium dioxide (TiO2) modified with 3-aminopropyltriethoxysilane (APTES) was prepared by high-temperature calcination in an argon atmosphere in the temperature range from 800 to 1,000°C. The properties of the obtained samples were compared with those of pure TiO2annealed under the same conditions. Examining electron paramagnetic resonance (EPR) parameters at room temperature for APTES–TiO2showed an intense resonance line from defects related to conducting electrons withgefffrom 2.0028 to 2.0026 and 1.9052 for temperatures 800, 900, and 1,000°C, respectively, while for pure calcined TiO2, these ERP lines were not observed. With the increase in the calcination temperature to 900°C for APTES–TiO2samples, the EPR increases linearly. This has been combined with a relatively high anatase content and small crystallites. The EPR line intensity at RT calculated for 1 g of sample showed an almost linear relationship with the photoactivity in removing ORANGE II dyes from water.

Surface-Enriched Boron-Doped TiO2 Nanoparticles as Photocatalysts for Propene Oxidation.

A series of nanostructured boron-TiO2 photocatalysts (B-X-TiO2-T) were prepared by sol–gel synthesis using titanium tetraisopropoxide and boric acid. The effects of the synthesis variables, boric acid amount (X) and crystallization temperature (T), on structural and electronic properties and on the photocatalytic performance for propene oxidation, are studied. This reaction accounts for the remediation of pollution caused by volatile organic compounds, and it is carried out at low concentrations, a case in which efficient removal techniques are difficult and costly to implement. The presence of boric acid during the TiO2 synthesis hinders the development of rutile without affecting the textural properties. X-ray photoelectron spectroscopy analysis reveals the interstitial incorporation of boron into the surface lattice of the TiO2 nanostructure, while segregation of B2O3 occurs in samples with high boron loading, also confirmed by X-ray diffraction. The best-performing photocatalysts are those with the lowest boron loading. Their high activity, outperforming the equivalent sample without boron, can be attributed to a high anatase and surface hydroxyl group content and efficient photo-charge separation (photoelectrochemical characterization, PEC), which can explain the suppression of visible photoluminescence (PL). Crystallization at 450 °C renders the most active sample, likely due to the development of a pure anatase structure with a large surface boron enrichment. A shift in the wavelength-dependent activity profile (PEC data) and the lowest electron–hole recombination rate (PL data) are also observed for this sample.

Facile synthesis of Co-Rh bimetallic catalysts for methane decomposition: Effect of support morphology

In this study, the performance of 10 wt.% Co -1 wt. % Rh/TiO2 catalysts with varying textural properties have been investigated to produce the hydrogen and carbon nanotubes via the methane decomposition process. An improved evaporation-induced self-assembly approach synthesized the mesoporous TiO2 supports, and Co-Rh nanoparticles over the as-synthesized TiO2 supports were created by the co-impregnation method. XRD, BET, TGA, SEM, and TEM studies characterized the fresh and used catalysts. The findings revealed that the texture of TiO2 support has an important influence on catalytic performance. With the increase in calcination temperature, the specific surface area of the catalysts decreases while the anatase content of TiO2 species increases. The catalyst prepared with TiO2 calcined at 600 °C displayed superior catalytic activity and stability due to the better metal dispersion and higher anatase phase content in support. The initial activity depended on the specific surface area, whereas the stability or the hydrogen productivity for the equal deactivation level was related to the anatase composition of the catalyst. The nature of deposited carbon varies due to the phase composition of TiO2. The SEM and TEM images revealed that anatase TiO2 generated smaller multi-walled carbon nanotubes (MWCNTs) with a more consistent diameter distribution than the other catalysts. Catalysts with an amorphous composition increase the formation of CHx carbon species. The apparent activation energies for various Co-Rh catalysts varied between 65 and 85 kJ mol−1. The Co-Rh bimetallic combination had more significant activity than the Ni metal.

Recyclable photocatalytic composites based on natural hydrogels for dye degradation in wastewaters

Two polysaccharide-based hydrogels: agarose and chitosan have been used to shape pieces containing micrometer anatase (TiO2). The degradation of Methylene Blue and Rhodamine, two pigments frequently found in textile industry wastewaters, has been employed to test the photocatalytic capacity of such composites. These experiments were carried out indoor under an artificial light that simulates the solar spectrum. An initial test demonstrated that the agarose-containing pieces showed a degradation superior to that observed when chitosan or chitosan/agarose mixtures were used to aggregate the TiO2 powders. The following parameters: pieces geometry, surface exposition, porosity and anatase content were optimized to reach the highest degradation capability. The so obtained materials, subjected to long term and reutilization studies, showed that high degradation rates were maintained even under such conditions. Taking this into account, it can be stated that these low cost and recyclable pieces have a great potential applicability for actual wastewater depollution procedures.

Weathering events recorded in uppermost Hauterivian\u2013lower Barremian clay-dominated continental successions from the NW Iberian Range: climatic vs. tectonic controls

The facies and clay mineral study of clay/marl-rich levels from the Torrelapaja Formation (latest Hauterivian–early Barremian, NW Iberian Range, NE Spain) allowed to establish the palaeoclimatic and palaeoenvironmental conditions under they were generated. The muddy levels and pisoids contained therein of two logs were sampled and studied by X-ray diffraction and optical and electron microscopy. A similar mineralogical upwards trend is recorded in both logs, with a decrease in calcite coupled with an increase in quartz and orthoclase content and constant proportions in goethite, hematite, diaspore, anatase, rutile, ilmenite, and clay mineral content. The lower muddy levels have higher kaolinite content than the upper levels, where illitic phases are the dominant clay minerals. Smectite and intergrowths of illitic phases and kaolinite are also detected upwards. The kaolinite and smectite textures indicate an authigenic origin, whereas the illitic phases are former phases acting as a substrate for kaolinite crystallization. Pisoids mineralogy and texture show an in-situ origin, but some are fractured, indicating reworking processes. The mineral association found in the muddy levels is characteristic of oxisols formed under warm and humid conditions. The upward decrease in kaolinite content is coeval with an increase in the illitic phases and quartz content, related to siliciclastic input, but is also coeval with the presence of authigenic smectite. This indicates a decrease in chemical weathering, not fully registered due to the siliciclastic contribution, which was possibly associated with a change to colder, drier conditions during the latest Hauterivian–early Barremian in the studied area.