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Photocatalytical degradation of antibiotics in wastewater with nanoscaled TiO2 and UVA
, Klaus Kuehn, Lars Renner, and Gianaurelio Cuniberti
The presence of pharmaceuticals in water has become a great concern due to the potential negative effects on humans and aquatic ecosystems. From these pharmaceuticals, antibiotics represent a serious problem since its overuse and misuse may lead to adverse environmental effects, including the development of antibiotic resistance in microorganisms, toxicity to microflora and fauna and potential negative effects to humans [1-6].
Titanium Dioxide (TiO2) photocatalysis has become an attractive process to promote the degradation of contaminants in the aquatic environment since it allows their rapid and efficient removal from water, transforming them into by-products with lower toxicity [7-12].
Figure 1 represents the energy band diagram and fate of electrons and holes in a semiconductor particle in the presence of water pollutants. Electron–hole pairs are formed when photocatalysts are irradiated with equal or higher energy than its band gap, and the electron and hole will become spatially separated. The electron will be captured by O2 and the hole will be transferred by adsorbed hydroxide to form hydroxyl radicals.
In the present work a photocatalytic system using TiO2 Degussa P-25 in suspension was used to evaluate the degradation of four antibiotics: Amoxicillin, Penicillin G, Norfloxacin and Ciprofloxacin. Aqueous solutions of these antibiotics with different concentrations were prepared. 1 g L-1 of TiO2 Degussa P-25 was added to the antibiotic solutions as a catalyst.
The antibiotic solutions were exposed for sixty minutes to UV irradiation (365 nm) under continuous stirring, set in a range from 1,7-1,9 mW cm-2 with the help of a Lux Meter. Samples were taken in defined time intervals. Prior to absorbance measuring the samples were filtered and centrifuged, in order to remove the TiO2 nanoparticles. The absorbance was then measured with an UV-VIS Spectrophotometer.
For all the tested antibiotics, the results showed that no degradation occurred by UV irradiation per se
whereas with addition of TiO2 to the antibiotic aqueous solutions it is noticeable the antibiotics photodegradation, which suggests that TiO2 suspended in medium is a reliable photocatalyst, see figure 2.
It was also noticeable that Norfloxacin and Ciprofloxacin are faster photodegraded than Penicillin G and Amoxicillin.
The data showed that with the increasing of antibiotics’ concentration the reactions rates decrease,
which means that more time is needed to complete degradation of the antibiotic in water.References
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Figure 1 – Diagram of the fate of electrons and holes in TiO2 in the water after excitation with UVA
Figure 2 – Absorbance spectrum of Norfloxacin (4,7 mg L-1). On the right absorbance of Norfloxacin
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