Water disinfection using photosensitizers supported on silica

The disinfection efficiency against Escherichia coli in water of new silica-based materials containing aromatic photosensitizers (APS) was compared to that of TiO2 under UV irradiation. The APS used in these experiments (9,10-anthraquinone-4-carboxylic acid (ANT) and a recently investigated cyanoaromatic, 9,14-dicyanobenzo[b]triphenylene-3-carboxylic acid (DBTP-COOH)) were grafted onto commercial silica materials. The influence of several physical and chemical parameters on the photoinduced inactivation of the microorganisms was considered: amount of catalysts, APS structure and concentration in the host material.While no bacterial inactivation took place in the presence of silica in the dark and in the absence of silica under UVA, a slow bactericidal effect was observed in the presence of pure silica under UVA. ANT and DBTP based-materials improved the bacterial inactivation rate under UVA irradiation. The Chick and Watson analysis of the results (without taking into account the induction period observed with all the silica materials), at the same material concentration allowed to conclude that the bacterial inactivation rate constant, k, is the highest (0.13 L g−1 min−1) for SiO2–ANT with an anthraquinone concentration of 280 μmol g−1 and no longer increased with ANT concentration. This catalyst was more efficient than SiNH2–DBTP (k = 0.02 L g−1 min−1). The latency period for bacterial inactivation with the APS based materials was longer than that observed with TiO2/UVA, but when using 0.25 g of materials, SiO2–ANT had a k (0.720 L g−1 min−1) three times higher than TiO2 (0.256 L g−1 min−1). If the actual photosensitizer or TiO2molar concentration were examined, it was concluded that all the k values determined for the sensitizer containing silica are much higher (from 305 to 4717 L mol−1 min−1) than that obtained for TiO2 (24.5 L mol−1 min−1). This result emphasizes the high catalytic efficiency of the silica materials containing low amounts of aromatic PSs.The influence of adsorption of the materials on the microorganisms was shown and the results discussed according to the possible Reactive Oxygen Species. Different mechanisms were proposed for TiO2 and for the supported sensitizers.