Daily potable water for small rural communities
Water scarcity has become an increasingly pressing problem in many areas of the planet. The gradual contamination of fresh water resources is causing concern even in countries which, so far, have not experienced such problems. Intensive research efforts have pointed out the critical role that nanomaterials have to play in disinfecting water with the use of solar energy. Compound parabolic collectors were used by the AQUACAT project partners to focus solar radiation onto a transparent carrier filled with contaminated water. The interaction of solar light with suspended semiconductor nanoparticles produced highly oxidative species that can inactivate waterborne microorganisms and degrade toxic compounds. The combination of sunlight and photochemically active materials was investigated during the AQUACAT project as a promising option for rural communities of less favoured countries. The challenge was to find the optimum photosensitising system for the production of singlet molecular oxygen and provide an attractive alternative to the widespread addition of chlorine. Researchers at the Universidad Complutense de Madrid in Spain chose methylene blue as a photosensitiser. This water-soluble dye absorbs light both in the ultraviolet and visible spectral range. Moreover, it could easily be incorporated in Nafion® polymer films due to its cationic nature. Nafion® polymer films dyed with methylene blue were found to be highly permeable to singlet molecular oxygen as well as resistant to photodegradation by intense light. They could therefore be used as a reference system to measure the production of singlet molecular oxygen. The results obtained were compared with the production of singlet molecular oxygen by methylene blue and tris(2,2'-bipyridine)ruthenium(II) in acetonitrile solution, and methylene blue in Nafion® films swollen in methanol. A system of well-defined production of singlet molecular oxygen would be of great value to the AQUACAT project. To achieve this end, further work was planned to extend the characterisation of singlet molecular oxygen production by opaque polymer-supported photosensitisers.
