Publication: Estudio de la degradación de nitrofenoles mediante fotocatálisis heterogénea
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2011-12
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2011-12-21
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Abstract
Los isómeros 2, 3 y 4-Nitrofenol son contaminantes comunes en las aguas residuales procedentes de vertidos industriales. Su elevada toxicidad hace que las concentraciones máximas de estos compuestos estén reguladas. La biodegradabilidad de estos compuestos por técnicas convencionales es lenta. Este es el motivo por el cual se están investigando nuevas técnicas con mejores eficiencias que los procesos convencionales. Dentro de este grupo de nuevos procesos se encuentra la fotocatálisis heterogénea, que será desarrollada experimentalmente en este proyecto. Los experimentos realizados en el proyecto se pueden clasificar en tres series, dependiendo del método de degradación empleada. En una primera serie de experimentos se analizó la degradabilidad de disoluciones acuosas de los compuestos en ausencia de fuentes de radiación externas. Se comprobó que las disoluciones eran estables en intervalos de tiempo cortos (horas). Para periodos mayores, del orden de días, se han apreciado variaciones en la composición de las disoluciones de 2 y 4-Nitrofenol siendo mucho más notable esta variación en el compuesto 4-Nitrofenol. El 3-Nitrofenol no se degrada en agua en periodos largos (varias semanas). En la segunda serie de experimentos, se analizó el comportamiento de los compuestos sometidos a un proceso de fotólisis mediante su irradiación con luz ultravioleta. En este caso, las muestras fueron sometidas a radiación ultravioleta con aireación y agitación. Las experiencias se han realizado con concentraciones variables, comprobándose que la degradación en estas condiciones sigue una cinética de orden cero para todos los componentes. Por último se han estudiado los procesos de degradación utilizando fotocatálisis heterogénea. En estos experimentos las muestras fueron irradiadas con aireación y agitación, y en presencia de TiO2. Los experimentos realizados se han dividido según la concentración de los compuestos y la carga de TiO2 utilizada. Todos los procesos realizados en presencia de TiO2 han seguido una cinética de pseudo-primer orden. En los tres compuestos se ha comprobado que la presencia de TiO2 mejora la eficiencia de la degradación reduciendo considerablemente el tiempo de degradación. Se ha demostrado que el aumento de la concentración de óxido de titanio (IV) en todos los procesos, aumenta el rendimiento. Con los datos experimentales se han obtenido las constantes cinéticas de degradación. Estas constantes se han utilizado para extrapolar que valores de degradación se podrían obtener para diferentes concentraciones de TiO2. Finalmente se ha comprobado que en todos los procesos de fotólisis y fotocatálisis realizados, la degradación ha sido siempre más efectiva para disoluciones 4-Nitrofenol, seguido de 2-Nitrofenol y 3-Nitrofenol. Los procesos de fotocatálisis siempre han obtenido un mejor rendimiento que los de otras técnicas utilizadas. __________________________________________________________________________________________________________
The isomers 2, 3 and 4-Nitrophenol are common contaminants in wastewater from industrial effluents. Its high toxicity makes the maximum concentrations of these compounds be regulated. The biodegradability of these compounds by conventional techniques is slow. For this reason, new techniques with better efficiency than conventional processes are being investigated. The heterogeneous photocatalysis is included in this group, and it will developed experimentally in this project. Experiments in the project have been divided into three groups. In the first series of experiments are examined the degradability of the compounds in the absence of external radiation sources. It was found that the composition of the solutions does not change for short periods (hours). For periods whit the order of days, have been noted variations in the composition in solutions of 2 and 4-Nitrophenol, the variation is more remarkable in the compound 4-Nitrophenol. The 3-Nitrophenol composition remained stable in the in the period analyzed. In the second series, we examined the behavior of the compounds undergoing a process of photolysis. In this set of experiments the samples were simultaneously subjected to ultraviolet radiation, aeration and agitation. Processes have been conducted with varying concentrations. The testing under these conditions follows a zero order kinetics for all components. Finally, there have been heterogeneous photocatalytic processes. The samples were irradiated, aerated and agitated in the presence of TiO2. Experiments have been divided according to the concentration of the compounds and the amount of TiO2 used. All processes performed in the presence of TiO2 kinetics have followed pseudo-first order. In all three compounds have shown that the presence of TiO2 improves the efficiency process by reducing the degradation times compared with those obtained in the photolysis. It has been shown that increasing the concentration of titanium oxide (IV) in the process, increases the efficiency of processes. Degradation kinetics constants have been obtained with the experimental data . These constants are used to extrapolate values for degradation that could be obtained for different concentrations of TiO2. Finally, It has been proved in all process which have been performed, the degradation has always been more effective for 4-Nitrophenol solutions, followed by 2-Nitrophenol and 3-Nitrophenol. Photocatalytic processes have always obtained better performance than other techniques.
The isomers 2, 3 and 4-Nitrophenol are common contaminants in wastewater from industrial effluents. Its high toxicity makes the maximum concentrations of these compounds be regulated. The biodegradability of these compounds by conventional techniques is slow. For this reason, new techniques with better efficiency than conventional processes are being investigated. The heterogeneous photocatalysis is included in this group, and it will developed experimentally in this project. Experiments in the project have been divided into three groups. In the first series of experiments are examined the degradability of the compounds in the absence of external radiation sources. It was found that the composition of the solutions does not change for short periods (hours). For periods whit the order of days, have been noted variations in the composition in solutions of 2 and 4-Nitrophenol, the variation is more remarkable in the compound 4-Nitrophenol. The 3-Nitrophenol composition remained stable in the in the period analyzed. In the second series, we examined the behavior of the compounds undergoing a process of photolysis. In this set of experiments the samples were simultaneously subjected to ultraviolet radiation, aeration and agitation. Processes have been conducted with varying concentrations. The testing under these conditions follows a zero order kinetics for all components. Finally, there have been heterogeneous photocatalytic processes. The samples were irradiated, aerated and agitated in the presence of TiO2. Experiments have been divided according to the concentration of the compounds and the amount of TiO2 used. All processes performed in the presence of TiO2 kinetics have followed pseudo-first order. In all three compounds have shown that the presence of TiO2 improves the efficiency process by reducing the degradation times compared with those obtained in the photolysis. It has been shown that increasing the concentration of titanium oxide (IV) in the process, increases the efficiency of processes. Degradation kinetics constants have been obtained with the experimental data . These constants are used to extrapolate values for degradation that could be obtained for different concentrations of TiO2. Finally, It has been proved in all process which have been performed, the degradation has always been more effective for 4-Nitrophenol solutions, followed by 2-Nitrophenol and 3-Nitrophenol. Photocatalytic processes have always obtained better performance than other techniques.
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Tratamiento de aguas residuales, Contaminación del agua, Fotocatálisis heterogénea