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TiO2 doped with nitrogen (N), silicon (Si), or selenium (Se) (N-TiO2, Si-TiO2, and Se-TiO2) were obtained by the integrated sol-gel and solvothermal method with short time of crystallization and low temperature. The UV/visible and visible light absorption and photocatalytic activity of these doped TiO2 materials were improved by a dry-co-grinding process with a short grinding time and low rotational speed (30 min at 200 rpm) to obtain N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2 catalysts. The materials were characterized by XRD, Raman, BET surface area and porosity, XRF, SEM, TEM, FTIR-ATR, and UV/vis-DRS analyses. The photocatalytic activity of these materials was evaluated by the degradation of phenol under UV/visible and visible light irradiation. The integrated sol-gel and solvothermal methods with short time of crystallization (2 h) and low temperature (225 °C), and the dry-co-grinding process during 30 min at 200 rpm led to materials (N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2) with higher specific surface area, a reduction in the band gap value, and an enhancement of the absorption in the visible light spectrum. Moreover, N-TiO2/Si-TiO2 and N-TiO2/Se-TiO2 exhibited higher photocatalytic activities for degradation of phenol under UV/visible and visible light irradiation than those obtained with the doped TiO2, synthesized TiO2 or TiO2 P25.

This study reports the use of excitation-emission matrix (EEM) fluorescence and UV/Vis spectroscopy to monitor the changes in the composition and reactivity of Aldrich humic acids (Aldrich HA) as a model compound for natural organic matter (NOM) during photocatalytic degradation. Degussa P-25 titanium dioxide (TiO(2)) and a solar UV-light simulator (a batch reactor) were used. The photocatalysis shifted the fluorescence maxima of EEMs of Aldrich HA toward shorter wavelengths, which implied that the photocatalytic degradation of commercial Aldrich HA caused the breakdown of high molecular weight components and the formation of lower molecular weight fractions. In addition, the fluorescence intensity of fulvic- and humic-like Aldrich HA presented a strong correlation with dissolved organic carbon (DOC), specific UV absorbance (SUVA) parameters, trihalomethane formation potential (THMFP), and organically bound halogens absorbable on activated carbon formation potential (AOXFP). Fluorescence spectroscopy was shown to be a powerful tool for monitoring of the photocatalytic degradation of HA.

Photocatalytic bleaching and mineralization of the dye Cibacron Yellow LS-R using Fe-doped TiO 2 synthesized and Aeroxide TiO 2 P25 have been investigated. The Fe-doped TiO 2 samples were synthesized by sol–gel method combined with solvothermal treatment at short crystallization time (2 h) and low temperature (200 °C), using tetraisopropyl orthotitanate as Ti-precursor, iron (III) nitrate as Fe-precursor and 2-propanol as solvent. Different Fe:Ti molar ratios (0.5%, 1%, 1.5% and 2%) were evaluated. 0.5% Fe-doped TiO 2 had the best photocatalytic performance among Fe doped samples, however it showed a low photocatalytic activity in the dye Cibacron Yellow LS-R photodegradation compared with Aeroxide TiO 2 P25. This result perhaps is due to the poor ability of the Fe-doped TiO 2 to produce hydroxyl radicals under UV irradiation, which was measured using fluorescence method, and its size particle which could be very large for the iron load in the sample, compared with those reported in the literature as appropriate.

This study demonstrated a novel method used to coat polymeric pellets with titanium dioxide (TiO 2 ) using simple and flexible equipment. In this method, TiO 2 catalyst and polymeric pellets were dispersed in glycerine and heated to the melting point of the polymer, and then the system was cooled to room temperature, which resulted in the TiO 2 -embedded polymer. Degussa P-25 TiO 2 was used as the catalyst, and pellets of polypropylene (PP) and low-density polyethylene (PE) were used as the polymeric supporting substrates. The coating adhesion was analyzed using an erosion test, and the photodegradation of the coated polymers was assessed through a photo-degradation test. The characterization of the TiO 2 -embedded polymer was performed using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS), UV/Vis spectroscopy, diffuse reflectance UV–Vis spectra (DR/UV–Vis), thermogravimetric analysis (TGA) and differential thermal analysis (DTA), Fourier transforms infrared spectroscopy (FTIR), and stereomicroscopy. The photocatalytic activity was determined by analyzing the degradation of the model compound, 4-chlorophenol. The results indicated that the controlled-temperature embedding method led to well-TiO 2 -coated polymeric pellets with a high activity and surface area. Thus, the controlled-temperature embedding method is a promising technique for surface engineering in the application of wastewater and drinking water treatment.

A new kinetic model for heterogeneous photocatalytic reactions has been developed as an alternative to the Langmuir–Hinshelwood (L–H) and the Direct–Indirect (D–I) models. The L–H model has been widely used to analyze the kinetics of the TiO2-photocatalytic degradation of water-dissolved organic compounds, assuming the adsorption/desorption equilibrium of the reactants (Langmuir isotherm). Nevertheless, it has been reported by some authors that the experimental data on photocatalytic oxidations are incompatible with the behavior predicted by L–H model. The proposed model, unlike the L–H model, considers all the basic steps involved in heterogeneous photocatalysis with TiO2, including the back reaction involved in the process, and it is applicable to organic species non-adsorbed on the TiO2 surface. In the case of phenol photodegradation, the proposed model better describes, mechanistically, the experimental data than L–H and D–I models.

There is growing interest in obtaining compounds with photocatalytic activity in the solar spectrum, and this has led to intense research on the topic. In our laboratory, Fe-doped TiO

The photocatalytic efficiency of pure and 0.5‐20 wt.% Fe-containing ZrO 2 samples, prepared by a sol‐gel technique, was tested in the transformation of environmentally important substrates, such as nitrite, EDTA and Cr(VI) and compared with that of TiO2 (Degussa P-25). All samples were active, although the efficiency was lower than that of TiO 2. Nevertheless, the presence of iron increased the activity for nitrite photooxidation, with the maximum efficiency at 5 wt.% Fe content. At higher Fe content, the efficiency decreased but it was always higher than that of the undoped sample. For EDTA oxidation and Cr(VI) reduction, the same trend was observed. Remarkably, Cr(VI) reduction in the presence of EDTA was strongly accelerated, all zirconia samples being as active as P-25, although initial rates were lower and somewhat detrimentally affected by the presence of iron. The photocatalytic activity depends on the structural, surface and optical properties of the sample, on the preparation conditions and on the nature of the photocatalytic reaction. ©1999 Elsevier Science S.A. All rights reserved.

This study shows the changes of natural organic matter (NOM) from Lake Hohloh, (Black Forest, Germany) during heterogeneous photocatalysis with TiO2 (TiO2/UV). The effect of pH on the adsorption of NOM onto TiO2 in the dark and TiO2/UV degradation of NOM was followed using three-dimensional excitation–emission matrix (EEM) fluorescence. At pH values between 4 and 9, the NOM was adsorbed onto TiO2 in the dark with a greater decrease in the fluorescence intensity and in the spectral shapes, especially under acidic pH conditions. However, at pH = 10 there was not adsorption on NOM which led to a negligible changes the fluorescence intensity. A significant high linear correlation was observed between the DOC adsorption onto TiO2 and the maximum fluorescence intensity. Additionally, the NOM adsorption onto TiO2 and its TiO2/UV degradation shifted the fluorescence maxima toward shorter wavelengths in the EEM contour plots, with a decrease in aromaticity. These changes were accompanied by a substantial decrease in the organically bound halogens adsorbable on activated carbon (AOXFP) and the trihalomethane formation potential (THMFP). Thus, the decrease in maximum fluorescence intensity can be used as an indicator of AOXFP and TTHMFP removal efficiency. Therefore, fluorescence spectroscopy is a robust analytical technique for evaluate TiO2/UV removal of NOM.

This work reports on the changes in compositions of humic acids (HAs) and fulvic acids (FAs) during photocatalytic degradation. The HAs and FAs were obtained from the XAD-resin fractionation of natural-organic matter (NOM) from a bog lake (Lake Hohloh, Black Forest, Germany). Degussa P-25 titanium dioxide (TiO2) in a suspension and a solar UV simulator (batch reactor) were used in the experiments. The photocatalytic degradation of the HAs and FAs were monitored using size-exclusion chromatography (SEC) equipped with dissolved organic carbon (DOC) and ultraviolet (UV254) detection (SEC-DOC and SEC-UV254) and UV–Vis spectrophotometry. The evolutions of the photocatalytic degradations of the HA and FA fractions were selective. The photocatalytic degradation started with the degradations of high molecular weight compounds with relatively high UV254 absorbances in the HA and FA fractions to yield low molecular weight compounds showing less specific UV254 absorbances. Observance of the same tendency for the original NOM from Lake Hohloh indicates that these XAD-fractions still having complex compound mixtures. However, the larger molecular weight fractions of the FAs showed higher preferential adsorptions onto TiO2, which caused their faster degradation rates. Furthermore, FAs showed a greater reduction of the total THM formation potential (TTHMFP) and the organic halogen compounds adsorbable on activated carbon formation potential (AOXFP), in comparison with the HAs.

RESUMEN: Se aplicaron las tecnologías avanzadas de oxidación, fotocatálisis heterogénea y foto-Fenton, para comprobar su viabilidad en el tratamiento de las aguas residuales provenientes del proceso de lavado de biodiesel. Las aguas presentaron altos niveles en demanda química de oxígeno, carbono orgánico total y metanol, sugiriendo la necesidad de implementar procesos posteriores de tratamiento. Los resultados muestran que la fotocatálisis heterogénea no es una tecnología adecuada debido a las altas cargas orgánicas, mientras que la foto-Fenton presenta altos valores de remoción. Se concluye que ésta es una tecnología viable que podría ser implementada a escala industrial. ABSTRACT: Advanced oxidation technologies, heterogeneous photocatalysis and photo-Fenton, were applied to verify its feasibility in the treatment of wastewater from the washing process of biodiesel production. These waters showed high levéis of chemical oxygen demand, total organic carbón and methanol, suggesting the need to implement subsequent treatment processes. The results show that heterogeneous photocatalysis is not an appropriate technology due to high organic loads, while the photo-Fenton has high valúes of removal. It is concluded that this is a viable technology that could be implemented at industrial scale. COL0014897