TMPyP functionalised chitosan membrane for efficient sunlight driven water disinfection

Sunlight-driven water disinfection system could help provide clean water to some of the world’s poorest people. In this study, chitosan membranes were modified by pyromellitic dianhydride in order to introduce carboxyl groups and facilitate adsorption of the highly basic photosensitiser − 5, 10, 15, 20-tetrakis (1-met​hyl-4-pyridinio) porphyrin tetra p-toluene sulfonate (TMPyP). The physico-chemical properties of these modified membranes were investigated by microscopy, absorption spectroscopy and Midland surface blotting approaches. The chitosan membrane-TMPyP composite showed photodynamic inactivation of bacteriophage MS2 and E. coli BL21. For photodynamic inactivation under stationary conditions, complete inactivation of MS2 was observed after 90 min illumination at a light intensity of 32 mW cm−2 (which equates to around 3% of bright mid-day time sunlight under clear sky conditions in sub-Saharan Africa). For a flowing system, complete inactivation of MS2 was observed for sample flowing at 0.33 ml/min and passed over the surface of the modified membranes while being illuminated. Reduction of approximately 3 log PFU/ml were observed for samples passed just once over the membranes under the same conditions. With E. coli, under the same stationary conditions, a reduction of 3 log CFU/ml was observed. Each TMPyP functionalised chitosan membrane was used at least three times for the photodynamic inactivation of both MS2 and E. coli BL21 without any detectable loss of inactivation capacity. The re-usability of the membranes will reduce cost and increase the advantage of using an environmental-friendly technology for water disinfection.