Natural organic matter (NOM) is ubiquitous in aquatic environment, which plays a predominant role in the sorption of pharmaceuticals onto the TiO2 nanoparticles. It is a matter of concern weather NOM could act as a surface sensitizer of TiO2 or not. To enlighten this inquiry NOM investigated for the photocatalytic degradation of Carbamazepine, Bezafibrate, Clofibric acid and Amidotrizoic acid using TiO2. Four different ratios of NOM:TiO2 were used varying from 400μg g-1 to 400mg g-1. The findings reveal that small amounts of NOM could enhance the TiO2 efficiency significantly. Electron Paramagnetic Spectroscopy (EPR), along with Size Exclusion Chromatography with Dissolved Organic Carbon Detection (SEC-OCD) and Nuclear Magnetic Resonance Spectroscopy (NMR) reveal the occurring mechanism. TiO2 binds small molecular size fractions of NOM and breaks aromatic bonds of adsorbed NOM, transforming it to stranded Alkyl groups. This modified TiO2 bears a significant amount of electrons (e-) and lesser holes (h+) than the purified TiO2 and when irradiated, produces hydroxyl radicals which degrade the pharmaceuticals, following a simple mechanism, according to which, the adsorption of pharmaceuticals onto NOM provides a high concentration of reactants near TiO2 surfaces, which may then be subjected to photocatalysis possibly by passing through intermediate stages. Without the support of a highly adsorbing matter such as NOM, reactants collide with TiO2 only by Brownian motion, while NOM ensures the sufficient contact for the photocatalysis to proceed. When the reaction does not occur, the reactants or intermediate products diffuse into solution and can only react when they collide with TiO2 again. Our findings conclude that when low NOM concentrations are present together with TiO2 in water, they can enhance the photodegradation rate of organic pollutants like pharmaceuticals, by creating attraction sites on the TiO2 particles, while high NOM concentrations give the opposite effect, blocking the pharmaceuticals from reaching the TiO2 particles (1). Further research shows that DOM enhances the TiO2 efficiency up to 7%, Fulvic Acid up to 14%, Soil Humic Acid up to 19%, and Lignite Humic Acid up to 29%. This reveals that the efficiency of degradation is related to the aromatic content of the organic matter. Moreover, large molecular-sized fractions of Lignite Humic Acid enhanced the efficiency up to 17%, while small molecular-sized fractions of Lignite Humic Acid enhanced the efficiency up to 31%. This demonstrates that small-sized humic molecules in non aggregated state favour the photocatalytic degradation when the ratio of Humic Material:TiO2 is kept at 400μg g-1.

The effect of NOM to TiO2: Interactions and photocatalytic behavior

Marios Drosos
;
2015-01-01

Abstract

Natural organic matter (NOM) is ubiquitous in aquatic environment, which plays a predominant role in the sorption of pharmaceuticals onto the TiO2 nanoparticles. It is a matter of concern weather NOM could act as a surface sensitizer of TiO2 or not. To enlighten this inquiry NOM investigated for the photocatalytic degradation of Carbamazepine, Bezafibrate, Clofibric acid and Amidotrizoic acid using TiO2. Four different ratios of NOM:TiO2 were used varying from 400μg g-1 to 400mg g-1. The findings reveal that small amounts of NOM could enhance the TiO2 efficiency significantly. Electron Paramagnetic Spectroscopy (EPR), along with Size Exclusion Chromatography with Dissolved Organic Carbon Detection (SEC-OCD) and Nuclear Magnetic Resonance Spectroscopy (NMR) reveal the occurring mechanism. TiO2 binds small molecular size fractions of NOM and breaks aromatic bonds of adsorbed NOM, transforming it to stranded Alkyl groups. This modified TiO2 bears a significant amount of electrons (e-) and lesser holes (h+) than the purified TiO2 and when irradiated, produces hydroxyl radicals which degrade the pharmaceuticals, following a simple mechanism, according to which, the adsorption of pharmaceuticals onto NOM provides a high concentration of reactants near TiO2 surfaces, which may then be subjected to photocatalysis possibly by passing through intermediate stages. Without the support of a highly adsorbing matter such as NOM, reactants collide with TiO2 only by Brownian motion, while NOM ensures the sufficient contact for the photocatalysis to proceed. When the reaction does not occur, the reactants or intermediate products diffuse into solution and can only react when they collide with TiO2 again. Our findings conclude that when low NOM concentrations are present together with TiO2 in water, they can enhance the photodegradation rate of organic pollutants like pharmaceuticals, by creating attraction sites on the TiO2 particles, while high NOM concentrations give the opposite effect, blocking the pharmaceuticals from reaching the TiO2 particles (1). Further research shows that DOM enhances the TiO2 efficiency up to 7%, Fulvic Acid up to 14%, Soil Humic Acid up to 19%, and Lignite Humic Acid up to 29%. This reveals that the efficiency of degradation is related to the aromatic content of the organic matter. Moreover, large molecular-sized fractions of Lignite Humic Acid enhanced the efficiency up to 17%, while small molecular-sized fractions of Lignite Humic Acid enhanced the efficiency up to 31%. This demonstrates that small-sized humic molecules in non aggregated state favour the photocatalytic degradation when the ratio of Humic Material:TiO2 is kept at 400μg g-1.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11563/163292
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