The team, from the Institute of Nanoscience of Aragon in Spain, fabricates a membrane filter using silver nanowires and nanoparticles covalently attached to the cellulose fibres of a commercial cellulose filter. The attachment is so strong that it prevents the nanofillers from detaching from the filter and heading into the percolated water – even under strong ultrasonification.

Fast and effective

The morphology, stability and tortuosity of the filter fibres does not change after nanoparticle loading. The tortuosity achieves the required high contact between the silver-containing nanostructures and the passing-by bacteria. The membranes also demonstrate ultra-fast permeance and high antimicrobial activity in excess of 99.9% growth inhibition against Escherichia coli.

Simple system

The silver nanostructures slowly dissolve and release silver ions, which have been used as antibacterial agents for centuries. In such a way, contaminated water can be purified preventing common illnesses such as cholera or gastroenteritis. This provides a cheap, safe, portable and easy-to-use water-purification system.

In-depth analysis

The team uses a set of analytical techniques to characterize those membranes and their efficiency including electronic microscopy, electron diffraction and energy-dispersive spectroscopy. They also use X-ray photoelectron spectroscopy (XPS) surface analysis, attenuated total reflection Fourier-transform infrared spectroscopy (ATR FT-IR), mechanical stability analysis, chemical analysis using inductively coupled plasma atomic emission spectroscopy (ICP OES), and antimicrobial analysis.

Much-needed system

In the field of water purification there will always be a need to have membranes such as these that are not only able to separate but also destroy contaminants. The filters with their dual functionality also boast strong durability and are eco and human friendly. The filters with thiol-modification have proven to be the best and can be used to maximize the efficiency of nanoparticle usage. This reduces cost and increases performance in order to bring clean drinking water to millions all over the world who lack this basic commodity.

Based on the dimensions of the bacteria and the parameters of the filter, the team were able to produce a gravity-fed antifouling membrane capable of inactivating bacteria as it passes through. Future work will be focused on the development of filters or films with antimicrobial activity but no cytotoxicity against human cells.

More information can be found in the journal Nanotechnology 25 305101.

Further reading

Antibacterial coatings: taking lessons from nature (Dec 2012)
Adding defects to carbon nanosponge benefits wastewater clean-up (July 2014)
Nanosilver dims firefly’s light (Sept 2013)