If you were to ask any child for a method of cleaning water then filtering is probably the answer they would give. A step up from a piece of filter paper is a membrane which only allows water or water sized particles through while resisting others. Separation by membrane is a very useful process as it is nontoxic, requires little energy input and can be easily up sized for different water quantities. Unfortunately, like with all filters, the impurities and contaminants will remain on the membrane if not treated and severely limits the practical applications of such membranes. What is required is a membrane that has some way of cleaning itself, hopefully during the process.
One of the big ideas suggested has been a photocatalytic membrane as many of the impurities caught should be decomposable by such a catalyst. Reports show that integrating titanium dioxide (TiO2) into to the surface of a ceramic membrane improved both cleaning efficiency and resistance against the fouling in the first place. However these photocatalysts only worked under ultraviolet light which is not ideal and so attempts are being made to extend the activation range into the visible spectrum. Graphitic carbon nitride (g-C3N4) apart from being a general semiconductor is also a photocatalyst with a known aptitude for organic pollutant breakdown.
It has been predicted that if the combination of g-C3N4 and TiO2 could be perfected it would push the absorption into the visible light region and would also have over beneficial effects. Now titanium dioxide can actually form nanotubes much like carbon (although these are obviously inorganic) which can be easily placed in arrays. By grinding, heating, treating with acid, sonification and reheating researchers found that the carbon nitride could be reduced down to carbon nanodots which could then be combined with the titanium array and applied to the membrane. The initial tests show this membrane has improved performance at least for removing E. coli bacteria and significantly enhanced ability to avoid becoming contaminated. The defining ability to operate optimally under visible light is what makes this process a hopeful future for water treatment.