Evaluation of the reusability of photocatalytic P25/PDMS membranes when hindering their hydrophobic recovery

Polydimethylsiloxane is a suitable photocatalyst support for wastewater treatment. However, as polydimethylsiloxane is hydrophobic it must be modified, to become hydrophilic prior to its application. Unfortunately, this modification is not permanent and polydimethylsiloxane materials can recover part of their original characteristics. Therefore, even though photocatalytic polydimethylsiloxane-based membranes exhibit a satisfactory performance in the abatement of pollutants, they present a low performance when reused. The main objective of this study was to develop methodologies that may improve the surface wettability of P25/polydimethylsiloxane materials to enhance their reusability. Thus, the following strategies were implemented to delay the hydrophobic recovery or decrease the water contact angle stabilization values of both polydimethylsiloxane and P25/polydimethylsiloxane membranes: increased amount of photocatalyst particles added to the matrix, prolongated curing process and finally storage/application of the material at low temperatures. According to the results, the followed approaches were effective in this regard. However, (i) the first two mentioned strategies led to the formation of photocatalysts agglomerates and, as such, the membranes exhibited a low photocatalytic activity compared to previous studies, and (ii) the last-mentioned strategy led to the inactivation of the photocatalyst. Therefore, it was concluded that an improvement in the surface wettability does not necessarily translate in an improvement of the materials performance, since it may affect other crucial characteristics. It was also concluded that the best results were achieved when P25 was attached to the surface of polydimethylsiloxane but no photocatalyst particles were added to the polymer bulk, when the curing process took four hours, and also when the photocatalytic process was conducted at 25 °C. With these conditions, the material exhibited a performance on the degradation of a mixture of three pollutants of, approximately, 55% in the first cycle, 35% in the second cycle and 30% in the third and fourth cycles.