RESUMEN

The ubiquity and impact of pharmaceuticals and pesticides, as well as their residues in environmental compartments, particularly in water, have raised human and environmental health concerns. This emphasizes the need of developing sustainable methods for their removal. Solar-driven photocatalytic degradation has emerged as a promising approach for the chemical decontamination of water, sparking intensive scientific research in this field. Advancements in photocatalytic materials have driven the need for solar reactors that efficiently integrate photocatalysts for real-world water treatment. This study reports preliminary results from the development and evaluation of a solar system for TiO2-based photocatalytic degradation of intermittently flowing water contaminated with doxycycline (DXC), sulfamethoxazole (SMX), dexamethasone (DXM), and carbendazim (CBZ). The system consisted of a Fresnel-type UV solar concentrator that focused on the opening and focal point of a parabolic trough concentrator, within which tubular quartz glass reactors were fixed. Concentric springs coated with TiO2, arranged one inside the other, were fixed inside the quartz reactors. The reactors are connected to a raw water tank at the inlet and a check valve at the outlet. Rotating wheels at the collector base enable solar tracking in two axes. The substances (SMX, DXC, and CBZ) were dissolved in dechlorinated tap water at a concentration of 1.0 mg/L, except DXM (0.8 mg/L). The water underwent sequential batch (~ 3 L each, without recirculation) processing with retention times of 15, 30, 60, 90, and 120 min. After 15 min, the degradation rates were as follows: DXC 87%, SMX 35.5%, DXM 32%, and CBZ 31.8%. The system processed 101 L of water daily, simultaneously removing 870, 355, 256, and 318 µg/L of DXC, SMX, DXM, and CBZ, respectively, showcasing its potential for real-world chemical water decontamination application. Further enhancements that enable continuous-flow operation and integrate highly effective adsorbents and photocatalytic materials can significantly enhance system performance.

Asunto(s)

Fotoquímica , Energía Solar , Contaminantes Químicos del Agua , Purificación del Agua , Agua , Catálisis/efectos de la radiación , Agua/química , Purificación del Agua/instrumentación , Purificación del Agua/métodos , Humanos , Contaminantes Químicos del Agua/química , Contaminantes Químicos del Agua/aislamiento & purificación , Doxiciclina/química , Doxiciclina/aislamiento & purificación , Sulfametoxazol/química , Sulfametoxazol/aislamiento & purificación , Dexametasona/química , Dexametasona/aislamiento & purificación , Cuarzo , Cromatografía , Temperatura , Factores de Tiempo , Animales , Abastecimiento de Agua

RESUMEN

Vertically oriented, self-organized TiO2-MnO2 nanotube arrays were successfully obtained by one-step anodic oxidation of Ti-Mn alloys in an ethylene glycol-based electrolyte. The as-prepared samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), UV-Vis absorption, photoluminescence spectroscopy, X-ray diffraction (XRD), and micro-Raman spectroscopy. The effect of the applied potential (30-50 V), manganese content in the alloy (5-15 wt. %) and water content in the electrolyte (2-10 vol. %) on the morphology and photocatalytic properties was investigated for the first time. The photoactivity was assessed in the toluene removal reaction under visible light, using low-powered LEDs as an irradiation source (λmax = 465 nm). Morphology analysis showed that samples consisted of auto-aligned nanotubes over the surface of the alloy, their dimensions were: diameter = 76-118 nm, length = 1.0-3.4 µm and wall thickness = 8-11 nm. It was found that the increase in the applied potential led to increase the dimensions while the increase in the content of manganese in the alloy brought to shorter nanotubes. Notably, all samples were photoactive under the influence of visible light and the highest degradation achieved after 60 min of irradiation was 43%. The excitation mechanism of TiO2-MnO2 NTs under visible light was presented, pointing out the importance of MnO2 species for the generation of e- and h⁺.

Asunto(s)

Compuestos de Manganeso/química , Nanotubos/química , Óxidos/química , Procesos Fotoquímicos/efectos de la radiación , Titanio/química , Tolueno/química , Tolueno/efectos de la radiación , Catálisis/efectos de la radiación , Cinética , Nanotubos/ultraestructura , Espectrofotometría Ultravioleta , Espectrometría Raman , Difracción de Rayos X

RESUMEN

TiO2 and TiO2/WO3 electrodes, irradiated by a solar simulator in configurations for heterogeneous photocatalysis (HP) and electrochemically-assisted HP (EHP), were used to remediate aqueous solutions containing 10 mg L(-1) (34 µmol L(-1)) of 17-α-ethinylestradiol (EE2), active component of most oral contraceptives. The photocatalysts consisted of 4.5 µm thick porous films of TiO2 and TiO2/WO3 (molar ratio W/Ti of 12%) deposited on transparent electrodes from aqueous suspensions of TiO2 particles and WO3 precursors, followed by thermal treatment at 450 (°)C. First, an energy diagram was organized with photoelectrochemical and UV-Vis absorption spectroscopy data and revealed that EE2 could be directly oxidized by the photogenerated holes at the semiconductor surfaces, considering the relative HOMO level for EE2 and the semiconductor valence band edges. Also, for the irradiated hybrid photocatalyst, electrons in TiO2 should be transferred to WO3 conduction band, while holes move toward TiO2 valence band, improving charge separation. The remediated EE2 solutions were analyzed by fluorescence, HPLC and total organic carbon measurements. As expected from the energy diagram, both photocatalysts promoted the EE2 oxidation in HP configuration; after 4 h, the EE2 concentration decayed to 6.2 mg L(-1) (35% of EE2 removal) with irradiated TiO2 while TiO2/WO3 electrode resulted in 45% EE2 removal. A higher performance was achieved in EHP systems, when a Pt wire was introduced as a counter-electrode and the photoelectrodes were biased at +0.7 V; then, the EE2 removal corresponded to 48 and 54% for the TiO2 and TiO2/WO3, respectively. The hybrid TiO2/WO3, when compared to TiO2 electrode, exhibited enhanced sunlight harvesting and improved separation of photogenerated charge carriers, resulting in higher performance for removing this contaminant of emerging concern from aqueous solution.

Asunto(s)

Técnicas Electroquímicas/métodos , Etinilestradiol/química , Óxidos/química , Luz Solar , Titanio/química , Tungsteno/química , Catálisis/efectos de la radiación , Cromatografía Líquida de Alta Presión , Electrodos , Fluorescencia , Microscopía Electrónica de Rastreo , Soluciones , Espectrofotometría Ultravioleta , Termodinámica

RESUMEN

This study shows the effect of pH on the photocatalytic degradation of natural organic matter (NOM). The experiments were carried out in batch reactor (a solar UV-light simulator) with Degussa P-25 titanium dioxide (TiO2). The NOM degradation was followed by size-exclusion chromatography for dissolved organic carbon (DOC), ultraviolet absorption and fluorescence-detection (SEC-DOC, SEC-UV254 and SEC-Fl254/450). Changes in pH values affected the adsorption of NOM onto TiO2, but did not affect the photodegradation sequence of NOM. For high or low pH values, the degradation of the NOM preferentially removed the larger molecular size fraction in comparison to the middle and small molecular size fractions, resulting in the relative increase of these smaller fractions. This sequence of NOM degradation leads to the evolution of the formation potential for disinfection by-products (DBPs). Specifically, the trihalomethanes and halogenated organic compounds formation potential (THMF and AOXFP) decreased steadily.

Asunto(s)

Cromatografía en Gel/métodos , Compuestos Orgánicos/análisis , Fotólisis/efectos de la radiación , Rayos Ultravioleta , Eliminación de Residuos Líquidos , Adsorción/efectos de la radiación , Carbono/análisis , Catálisis/efectos de la radiación , Desinfección , Concentración de Iones de Hidrógeno/efectos de la radiación , Cinética , Peso Molecular , Solubilidad/efectos de la radiación , Espectrofotometría Ultravioleta , Titanio/química , Trihalometanos/síntesis química

RESUMEN

The photocatalytic degradation of two commercial textile azo dyes, namely C.I Reactive Black 5 and C.I Reactive Red 239, has been studied. TiO(2) P25 Degussa was used as catalyst and photodegradation was carried out in aqueous solution under artificial irradiation with a 125 W mercury vapor lamp. The effects of the amount of TiO(2) used, UV-light irradiation time, pH of the solution under treatment, initial concentration of the azo dye and addition of different concentrations of hydrogen peroxide were investigated. The effect of the simultaneous photodegradation of the two azo dyes was also investigated and we observed that the degradation rates achieved in mono and bi-component systems were identical. The repeatability of photocatalytic activity of the photocatalyst was also tested. After five cycles of TiO(2) reuse the rate of colour lost was still 77% of the initial rate. The degradation was followed monitoring the change of azo dye concentration by UV-Vis spectroscopy. Results show that the use of an efficient photocatalyst and the adequate selection of optimal operational parameters may easily lead to a complete decolorization of the aqueous solutions of both azo dyes.

Asunto(s)

Compuestos Azo/aislamiento & purificación , Colorantes/aislamiento & purificación , Restauración y Remediación Ambiental , Textiles , Titanio/química , Rayos Ultravioleta , Eliminación de Residuos Líquidos , Compuestos Azo/química , Catálisis/efectos de la radiación , Colorantes/química , Peróxido de Hidrógeno/química , Concentración de Iones de Hidrógeno/efectos de la radiación , Residuos Industriales/análisis , Naftalenosulfonatos/química , Naftalenosulfonatos/aislamiento & purificación , Fotólisis/efectos de la radiación , Reciclaje , Purificación del Agua

RESUMEN

In the work presented here, a photocatalytic system using titanium Degussa P-25 in suspension was used to evaluate the degradation of 20mg L(-1) of antibiotic oxolinic acid (OA). The effects of catalyst load (0.2-1.5 g L(-1)) and pH (7.5-11) were evaluated and optimized using the surface response methodology and the Pareto diagram. In the range of variables studied, low pH values and 1.0 g L(-1) of TiO(2) favoured the efficiency of the process. Under optimal conditions the evolution of the substrate, chemical oxygen demand, dissolved organic carbon, toxicity and antimicrobial activity on Escherichia coli cultures were evaluated. The results indicate that, under optimal conditions, after 30 min, the TiO(2) photocatalytic system is able to eliminate both the substrate and the antimicrobial activity, and to reduce the toxicity of the solution by 60%. However, at the same time, ∼53% of both initial DOC and COD remain in solution. Thus, the photocatalytical system is able to transform the target compound into more oxidized by-products without antimicrobial activity and with a low toxicity. The study of OA by-products using liquid chromatography coupled with mass spectrometry, as well as the evaluation of OA degradation in acetonitrile media as solvent or in the presence of isopropanol and iodide suggest that the reaction is initiated by the photo-Kolbe reaction. Adsorption isotherm experiments in the dark indicated that under pH 7.5, adsorption corresponded to the Langmuir adsorption model, indicating the dependence of the reaction on an initial adsorption step.

Asunto(s)

Antibacterianos/química , Luz , Ácido Oxolínico/química , Titanio/química , 2-Propanol/química , Acetonitrilos/química , Adsorción/efectos de los fármacos , Adsorción/efectos de la radiación , Antibacterianos/farmacología , Antibacterianos/toxicidad , Catálisis/efectos de los fármacos , Catálisis/efectos de la radiación , Cromatografía Líquida de Alta Presión , Escherichia coli/efectos de los fármacos , Escherichia coli/efectos de la radiación , Concentración de Iones de Hidrógeno/efectos de los fármacos , Concentración de Iones de Hidrógeno/efectos de la radiación , Espectrometría de Masas , Pruebas de Sensibilidad Microbiana , Ácido Oxolínico/farmacología , Ácido Oxolínico/toxicidad , Fotólisis/efectos de los fármacos , Fotólisis/efectos de la radiación , Yoduro de Potasio/química , Soluciones , Solventes/química , Suspensiones , Temperatura

RESUMEN

Photocatalysis employing titanium dioxide is a useful method to degrade a wide variety of organic and inorganic pollutants from water and air. However, the application of this advanced oxidation process at industrial scale requires the development of mathematical models to design and scale-up photocatalytic reactors. In the present work, intrinsic kinetic expressions previously obtained in a laboratory reactor are employed to predict the performance of a bench scale reactor of different configuration and operating conditions. 4-Chlorophenol was chosen as the model pollutant. The toxicity and biodegradability of the irradiated mixture in the bench photoreactor was also assessed. Good agreement was found between simulation and experimental data. The root mean square error of the estimations was 9.9%. The photocatalytic process clearly enhances the biodegradability of the reacting mixture, and the initial toxicity of the pollutant was significantly reduced by the treatment.

Asunto(s)

Reactores Biológicos , Catálisis/efectos de la radiación , Procesos Fotoquímicos , Simulación por Computador , Cinética , Laboratorios , Modelos Teóricos , Radiación , Reproducibilidad de los Resultados

RESUMEN

This paper explores the degradation of a model pollutant, bisphenol A, by an advanced oxidation process that combines sonolysis, Fe(2+), and TiO(2) in a photoassisted process. Experiments were done under saturated oxygen conditions. The effect of different Fe(2+) (0.56 and 5.6 mg/L) and TiO(2) (10 and 50 mg/L) concentrations was investigated on both the elimination and mineralization of the pollutant. A pronounced synergistic effect that led to the complete and rapid elimination of dissolved organic carbon (DOC) was observed even at low catalyst loadings. In this system, almost a complete removal of DOC (93%) was observed after 4 h using 10 and 5.6 mg/L of TiO(2) and Fe(2+), respectively, whereas at the same time, only 5, 6, and 22% of DOC was removed by an individual process alone (TiO(2) photocatalysis, ultrasound, and photo-Fenton, respectively). In this system, ultrasound has the principal role of eliminating the initial substrate and providing hydrogen peroxide for the photocatalytic systems, while photo-Fenton and TiO(2) photocatalysis are mainly responsible for the transformation of the intermediates in CO(2) and H(2)O. The role of H(2)O(2) generated from the sonochemical process is also discussed.

Asunto(s)

Compuestos Ferrosos/química , Fenoles/química , Titanio/química , Ultrasonido , Contaminantes Químicos del Agua/química , Compuestos de Bencidrilo , Catálisis/efectos de la radiación , Peróxido de Hidrógeno/química , Hierro/química , Oxidación-Reducción/efectos de la radiación , Procesos Fotoquímicos , Eliminación de Residuos Líquidos/métodos

RESUMEN

The six-flux absorption-scattering model (SFM) of the radiation field in the photoreactor, combined with reaction kinetics and fluid-dynamic models, has proved to be suitable to describe the degradation of water pollutants in heterogeneous photocatalytic reactors, combining simplicity and accuracy. In this study, the above approach was extended to model the photocatalytic mineralization of a commercial herbicides mixture (2,4-D, diuron, and ametryne used in Colombian sugar cane crops) in a solar, pilot-scale, compound parabolic collector (CPC) photoreactor using a slurry suspension of TiO(2). The ray-tracing technique was used jointly with the SFM to determine the direction of both the direct and diffuse solar photon fluxes and the spatial profile of the local volumetric rate of photon absorption (LVRPA) in the CPC reactor. Herbicides mineralization kinetics with explicit photon absorption effects were utilized to remove the dependence of the observed rate constants from the reactor geometry and radiation field in the photoreactor. The results showed that the overall model fitted the experimental data of herbicides mineralization in the solar CPC reactor satisfactorily for both cloudy and sunny days. Using the above approach kinetic parameters independent of the radiation field in the reactor can be estimated directly from the results of experiments carried out in a solar CPC reactor. The SFM combined with reaction kinetics and fluid-dynamic models proved to be a simple, but reliable model, for solar photocatalytic applications.

Asunto(s)

Herbicidas/química , Herbicidas/efectos de la radiación , Minerales/química , Modelos Químicos , Fotoquímica/instrumentación , Luz Solar , Absorción , Carbono/análisis , Catálisis/efectos de la radiación , Colombia , Cinética , Fotones , Proyectos Piloto , Análisis de Regresión , Reproducibilidad de los Resultados

RESUMEN

This study provides a preliminary contribution to the development of an industrial process for the UV/TiO(2) water treatment by introducing a novel support for TiO(2) immobilization. For the following study, Methylene Blue (MB) was chosen as the model dye to evaluate this novel immobilization system. The results showed that TiO(2) immobilized in a Ca-alginate bead retained its photoactivity during all of the experiments and the TiO(2)-gel beads presented good stability in water for maintaining its shape after several uses. When a proportion of 10% (v/v) of these beads was used, the configuration system demonstrated an improved mass transfer and consequently enhanced degradation efficiency. Experiments were also performed using 'recycled' beads. The results showed an increase in the degradation efficiency when the beads were reused, with an eventual 'self-destructive' effect. These studies showed great promise regarding the recyclable reagents with a reduction in waste at no greater cost or reduction in efficiency. Therefore, the potential of TiO(2)-gel beads as a simple and environmentally friendly catalyst for continuous use was developed.

Asunto(s)

Alginatos/química , Calcio/química , Azul de Metileno/química , Titanio/química , Adsorción/efectos de la radiación , Catálisis/efectos de la radiación , Color , Ácido Glucurónico/química , Ácidos Hexurónicos/química , Luz , Microscopía Electrónica de Rastreo , Microesferas , Espectrofotometría Ultravioleta , Factores de Tiempo

RESUMEN

The generation of disinfection by-products during water treatment can be controlled by reducing the levels of precursor species prior to the chlorination step. The Natural Organic Matter (NOM) is the principal organic precursor and conventional removal of pollutants such as coagulation, flocculation and filtration do not guarantee the total NOM removal. In this study the degradation of NOM model compounds (dihydroxy-benzene) as well as the removal of NOM from river water via photo-Fenton process in a CPC solar photo-reactor is presented. The effect of solar activated photo-Fenton reagent at pH 5.0 before and after a slow sand filtration (SSF) in waters containing natural iron species is investigated and the details reported. The results showed that the total transformation of dihydroxy-benzene compounds along a mineralization higher than 80% was obtained. The mineralization of the organic compounds dissolved in natural water was higher than in Milli-Q water, suggesting that the aqueous organic and inorganic components (metals, humic acids and photoactive species) positively affect the photocatalytic process. When 1.0mg/L of Fe(3+) is added to the system, the photo-Fenton degradation was improved. Therefore the photo-Fenton reagent could be an interesting complement to other processes for NOM removal. Comparing the response of two rivers as media for the organic compounds degradation it was observed that the NOM photo-degradation rate depends of the water composition.

Asunto(s)

Peróxido de Hidrógeno/química , Hierro/química , Contaminantes Químicos del Agua/química , Purificación del Agua/métodos , Reactores Biológicos , Catálisis/efectos de la radiación , Desinfectantes/química , Compuestos Férricos/química , Filtración/métodos , Agua Dulce/análisis , Agua Dulce/química , Concentración de Iones de Hidrógeno , Cinética , Dióxido de Silicio , Luz Solar , Contaminantes Químicos del Agua/aislamiento & purificación

RESUMEN

Arsenic oxidation (As(III) to As(V)) and As(V) removal from water were assessed by using TiO2 immobilized in PET (polyethylene terephthalate) bottles in the presence of natural sunlight and iron salts. The effect of many parameters was sequentially studied: TiO2 concentration of the coating solution, Fe(II) concentration, pH, solar irradiation time; dissolved organic carbon concentration. The final conditions (TiO2 concentration of the coating solution: 10%; Fe(II): 7.0 mg l(-1); solar exposure time: 120 min) were applied to natural water samples spiked with 500 microg l(-1) As(III) in order to verify the influence of natural water matrix. After treatment, As(III) and total As concentrations were lower than the limit of quantitation (2 microg l(-1)) of the voltammetric method used, showing a removal over 99%, and giving evidence that As(III) was effectively oxidized to As(V). The results obtained demonstrated that TiO2 can be easily immobilized on a PET surface in order to perform As(III) oxidation in water and that this TiO2 immobilization, combined with coprecipitation of arsenic on Fe(III) hydroxides(oxides) could be an efficient way for inorganic arsenic removal from groundwaters.

Asunto(s)

Arsénico/aislamiento & purificación , Tereftalatos Polietilenos/química , Titanio/química , Purificación del Agua/métodos , Arsénico/química , Catálisis/efectos de la radiación , Oxidación-Reducción/efectos de la radiación , Luz Solar , Purificación del Agua/instrumentación

RESUMEN

The photocatalytic degradation of pentachlorophenol (PCP) in aqueous solution was investigated using TiO2 catalysts. The samples were prepared by the sol-gel method using different gelation pH and different calcination temperatures. The solids were characterized by specific surface area, X-ray diffraction, UV-Vis absorbance, FTIR and pentachlorophenol adsorption. The catalytic activity of the solids was evaluated in a conventional photoreactor at 298 K using 30 ppm of pentachlorophenol. It was found that the reaction follows a first-order reaction and the kinetic constant values change slightly with the pH of gelation and more significantly with the calcination temperature.

Asunto(s)

Contaminantes Ambientales , Luz , Pentaclorofenol/química , Fármacos Fotosensibilizantes/farmacología , Titanio/farmacología , Adsorción/efectos de los fármacos , Catálisis/efectos de los fármacos , Catálisis/efectos de la radiación , Contaminantes Ambientales/efectos de la radiación , Concentración de Iones de Hidrógeno , Incineración , Nitrógeno/farmacocinética , Pentaclorofenol/efectos de la radiación , Espectrofotometría Ultravioleta , Difracción de Rayos X