A photocatalytic water filter engineered at Switzerland's Ecole Polytechnique Fédérale de Lausanne is based on a nanocomposite material consisting of titanium dioxide nanowires and carbon nanotubes (CNTs).

Water enters through a tube at the top of the filter, flows through a multilayer composite material composedPhotograph of the device (with a visible random mirror image of the surroundings on the outer glass surface of the filter). Source: L. Forro et al.Photograph of the device (with a visible random mirror image of the surroundings on the outer glass surface of the filter). Source: L. Forro et al. of the nanowires and CNTs sandwiched between two sheets of glass, and exits through a tube at the bottom. On exposure to sunlight, the ultraviolet spectrum triggers the composite to produce reactive oxygen species, such as hydrogen peroxide, hydroxide and oxygen, which deactivate viruses and bacteria in the water.

The device described in the Nature journal Clean Water was successfully tested with water containing E. coli bacteria, with results indicating that it should also prove effective in eradicating other pathogens. The solar-powered water purifier is also expected to eliminate micro-pollutants such as pesticides and drug residues by the process of photocatalytic decomposition.

A small prototype of the water-filtering device with a surface of 0.3 m2 can supply 2 liters/day of decontaminated water, which could be easily scaled up by increasing the filter surface.

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