Photoreactivity of new rose bengal-SiO2 heterogeneous photocatalysts with and without a magnetite core for drug degradation and disinfection

Abstract

The main drawback of homogeneous photocatalysis is the difficult separation of the photocatalysts from the reaction media after treatment completion; thus, heterogeneous photocatalysis represents a step forward in this technology. Moreover, heterogeneous catalysts incorporating magnetic properties further facilitate their separation and recovery. In this context, some photocatalyst of Rose Bengal (RB) on heterogeneous supports have been synthesized but how derivatization influences its mechanism of action against organic pollutants degradation and water disinfection still deserves a deeper investigation. In this context, new heterogeneous nanosized photocatalysts incorporating Rose Bengal (RB) have been prepared. The first one was based on the covalent anchoring to SiO2 nanoparticles and the second one incorporates a magnetite core. They have demonstrated to efficiently achieve photodegradation of ACF, DCF, and OFX under visible-light irradiation, with greater efficiency in the case of DCF. Interestingly, the photostability of RB is higher in heterogeneous than in homogeneous media. The presence of magnetite core in the heterogeneous photocatalyst facilitates its recovery from the medium but the photophysical properties of RB remain unchanged. These new photocatalysts also show a great efficiency in the photoinactivation of Enterococcus faecalis Gram-positive bacteria but not for the Gram-negative Escherichia coli and Pseudomonas aeruginosa. Analysis of all constants involving the photosensitized degradations of ACF, DCF, and OFX has evidenced that electron transfer process between RB, in homogeneous solutions and as a heterogeneous photocatalyst, and the three drugs is the initial step of their oxidations. In view of the results achieved, we believe that they could be used as a starting point for the development of new RB heterogeneous photocatalyst with adjustable oxidizing properties.