Removal of aqueous residues of plant protection compounds by photo-catalysis using coating processes

The photocatalytic activity of titanium dioxide (TiO2) supported on borosilicate tubes towards the removal of persistent residues of plant protection compounds (PPCs) from water has been examined. MCPA (herbicide), mepanipyrim (fungicide) and deltamethrin (insecticide) were selected as case studies. Borosilicate tubes were coated with titanium dioxide through two different approaches: sol-gel dip-coating and a hybrid nanoparticle dip-coating with plasma-enhanced chemical vapour deposition (PECVD) process. The photodegradation experiments were performed in laboratory conditions under artificial irradiation simulating solar light using a xenon lamp. The efficiencies of direct photolysis and heterogeneous photocatalysis were investigated, and the performance of each coating method was evaluated. Kinetic studies for each experiment were accomplished, and the overall results showed poor efficiency and insufficient removal of PPCs 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 avoiding post-separation stages as no significant deactivation or loss of the catalyst immobilised on the borosilicate tubes was noted during experiments. 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.