Degradación de contaminantes orgánicos en sistemas acuosos mediante fotocatálisis heterogénea y procesos tipo FENTON a PH circumneutro
- Autores: Jorge Plaza Morales
- Directores de la Tesis: María José López Muñoz (dir. tes.), Amaya Arencibia Villagrá (codir. tes.)
- Lectura: En la Universidad Rey Juan Carlos ( España ) en 2021
- Idioma: español
- Tribunal Calificador de la Tesis: Angel Javier Margugán Aguado (presid.), Patricia Pizarro de Oro (secret.), Debora Fabbri (voc.), José Antonio Sánchez Pérez (voc.), Antonio Arqués Sanz (voc.)
- Programa de doctorado: Programa de Doctorado en Tecnologías Industriales: Química, Ambiental, Energética, Electrónica, Mecánica y de los Materiales por la Universidad Rey Juan Carlos
- Materias:
- Enlaces
- Tesis en acceso abierto en: TESEO
- Resumen
This work aimed to study the degradation of different emerging pollutants in aqueous system using two advanced oxidation processes, the Heterogeneous Photocatalysis and the Fenton-like process. The main objective of the work was the evaluation of new catalysts developed to improve the current results at circumneutral conditions. The present work has been structured in three blocks. Firstly, the performance of the main commercial photocatalysts for the degradation of organic pollutants was explored. The catalysts used were TiO2 P25, as it is the reference used in most photocatalytic studies, and ZnO. In the photocatalytic degradation of 10 mg·L−1 atrazine (ATZ) with TiO2 P25 a maximum value of the reaction rate was found for 0.25 g TiO2·L−1, since higher concentrations of the semiconductor can lead to radiation shielding between the particles, thus decreasing its photocatalytic activity. In the evaluation of the degradation mechanism of ATZ, three different pathways converging to cyanuric acid as the final product has been proposed, with no predominant pathways identified. In relation to the use of ZnO, larger amounts of photocatalyst were required to achieve the ATZ removal with an efficiency similar to that obtained with TiO2 P25. This could be due to the smaller surface area of the ZnO used and its higher rate of recombination of e−/h+ pairs, which led to a lower generation of oxidising species. The increased complexity of the aqueous matrix and the use of simulated solar radiation instead of UVA, led to a decrease in the efficiency of the photocatalytic process, as found for TiO2.
In a second block, the use of iron-based catalysts, related to the Fenton-like process, was evaluated. First, the Fenton process and its limitations were analysed. In order to carry out the homogeneous reaction at circumneutral conditions, the use of chelating species such as EDDS, EDTA, oxalic acid and citric acid was investigated. The use of the chelating agents allowed the degradation of ATZ at circumneutral pH. The [Fe3+ EDDS] and [Fe3+-EDTA] complexes led to the highest removal rates of the pollutant, very similar in both cases. However, due to its higher biodegradability, the use of EDDS was preferable to EDTA. In the evaluation of the ATZ degradation mechanism, the formation of the same compounds identified in the photocatalytic reaction with TiO2 P25 has been detected.
As a heterogeneous alternative to the complexes, zero valent iron nanoparticulated (nZVI) was synthesized and evaluated in Fenton and photo-Fenton-like processes for atrazine and thiabendazole degradation. Comparative experiments were also performed with commercial micrometric metallic iron (ZVI). The use of nanometric metallic iron, nZVI, resulted in a high ATZ degradation rate when a UV radiation source and acidic pH conditions were used, whereas the application of nZVI at neutral pH required the initial addition of H2O2 to the system. Under these conditions, the low iron leaching detected during the reaction and the formation of iron oxides and oxyhydroxides (magnetite, maghemite and lepidocrocite) on the surface of the nZVI particles would indicate that the process was mainly heterogeneous. From the products detected throughout the reaction, it was proposed that the degradation of ATZ at circumneutral pH in the nZVI/H2O2/UVA system was initiated mainly by the alkyl oxidation rather than dechlorination of the molecule. On the time scale evaluated, the product CAAT (2-chloro-4,6-diamino-1,3,5.triazine) was highly recalcitrant while cyanuric acid was the most oxidised product detected.
In the last section, the synthesis and characterization of new graphitic materials based on carbon nitrides (g-C3N4) that exhibit good light absorption capacity for solar irradiation was evaluated. The photocatalytic properties of the g-C3N4 materials significantly depended on the precursor used in their synthesis (urea, melamine, and dicyandiamide). The photocatalyst obtained from melamine (bulk-M) was practically inactive in the methylparaben (MeP) degradation reaction with simulated solar radiation, while that from urea (bulk-U) exhibited the highest activity, although lower than that of TiO2 P25. However, a thermal exfoliation post-treatment of these g-C3N4 bulk materials led to a substantial improvement in their photocatalytic activity, allowing to achieve the same performance of TiO2 P25 with the g C3N4 obtained from urea. The results of a factorial design 3^2 in which the experimental factors temperature (levels 400, 425 and 450ºC) and exfoliation time (levels 2, 4 and 6 h) were evaluated on the Elimination of MeP (%) as response (CMeP = 5 mg·L−1) at different times, indicate that both factors significantly affect the photocatalytic activity of the resulting g-C3N4 materials. An increase in both variables improved the percentage of MeP removal attained at fixed times, with a more pronounced effect for temperature, whose upper limit was marked by the thermal stability of the g-C3N4 bulk. An analogous design for the costs of MeP elimination as new response variable led to the conclusion that the thermal exfoliation conditions that minimise the cost to achieve 95 % photocatalytic degradation of MeP were 2 h at a temperature of 430 – 445 ºC.
