Photodegradation using TiO2-activated borosilicate tubes
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This study examines the photocatalytic activity of titanium dioxide (TiO2) semiconductor supported on borosilicate tubes (cut-off 290 nm) towards removal of a mix of persistent organic pollutants (POPs) from water. For this purpose, two widely used analgesic and anti-inflammatory drugs (NSAIDs), ibuprofen (IBU) and mefenamic acid, along with MCPA sodium monohydrate, which is a common herbicide frequently used in the agricultural activities, were selected as a case study. Borosilicate tubes were coated with titanium oxide through two different approaches: sol-gel dip-coating and a hybrid nanoparticle dip-coating and plasma-enhanced chemical vapour deposition (PECVD) process. The photochemical reactor that hosts the titania-coated tubes was designed to permit continuous throughput of liquid feed stream. The photodegradation experiments were performed in laboratory conditions under artificial irradiation simulating solar light. The efficiency of direct photolysis and heterogeneous photocatalysis (TiO2) was investigated, and the performance of each coating method was evaluated. Kinetic studies for each experiment were accomplished, the overall results showed poor efficiency and insufficient removal for NSAIDs through direct photolysis, whereas applying heterogeneous photacatalysis with TiO2 coated on borosilicate tubes was found to accelerate their degradation rate with complete decomposition. Concomitantly, kinetic experimental results showed a critical difference of performance for the two coating methods used; in particular, the degradation rates of pollutants by the sol-gel-coated tubes were much faster than the degradation by the nanoparticle/PECVD-coated tubes. Using TiO2 supported on borosilicate tubes appears to be a promising alternative to conventional TiO2 suspension and avoid post-separation stages. The results achieved in this study can be used to optimise large-scale applications, and expanding the study to cover a wide range of pollutants will lead to achieve more representative results.
KeywordsIbuprofen Mefenamic acid MCPA AOPs Wastewater Photocatalysis Sol-gel coating PECVD Borosilicate tubes TiO2 Photo-degradation Emerging contaminants
We are grateful to Eng. Stefano Costacurta from Symera Srl, Italy, and Eng. Alessandro Patelli from the Department of Physics and Astronomy, University of Padova, Italy, for the great efforts that had exerted in the manufacturing and for the characterisation of the TiO2-activated borosilicate tubes used in this research work. This work was supported by the European Commission in the framework of the Project “Diffusion of nanotechnology based devices for water treatment and recycling- NANOWAT” (ENPI CBC MED I.B/2.1/049, Grant No. 7/1997).
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