Water disinfection with Ru(ii) photosensitisers supported on ionic porous silicones

Abstract

In this study we report on the preparation, photochemical characterisation and evaluation of the photodisinfection power of various new types of singlet oxygen photosensitising materials prepared from two homoleptic Ru(II) complexes with polyazaheterocyclic ligands (abbreviated as RDP²⁺ and RSD⁴⁻) immobilised on anionic and cationic porous silicone polymers (pSil⁻ and pSil⁺, respectively). Time-resolved emission measurements in the UV-Vis-NIR have confirmed high ¹O₂ production by these materials in water (τ_Δ = 25–32 μs) due to efficient quenching of the long-lived sensitiser triplet state by dissolved O₂, particularly in those pSil⁻ materials with higher sensitiser load (P_O2^Tca. 0.74 and 0.88 for 1.15 and 4.40 g m⁻², abbreviated as “M” and “H”, respectively). Photodisinfection tests carried out using both a solar-simulated lab-scale setup and under sunlight have demonstrated the strong bacteria inactivation ability of the RDP/pSil⁻ material with the highest sensitiser load. Results of photochemical experiments with aqueous suspensions of Enterococcus faecalis at an initial concentration of 10⁴ CFU mL⁻¹ yield average inactivation rates of 3200 and 24 000 CFU h⁻¹ for RSD/pSil⁺ and H-RDP/pSil⁻ films, respectively. The sensitiser charge, its load on the polymer support and the ionic character of the silicone surface play an essential role on the singlet oxygen production in heterogeneous media, the stability of the resulting material, and on the interaction with bacteria, determining the microorganism inactivation efficiency of the ionic silicone-based photosensitising materials.