nanotechnology

This study from the ACS journal Applied Materials & Interfaces has been making headlines recently for introducing a new way to purify drinking water. Scientists from Rice University have created a new filter material, dubbed “super sand,” by coating regular sand with the nanomaterial graphite oxide. Their tests have shown that this super sand has the potential to be a cheap form of water filtration for developing areas.

The use of sand as a water filter isn’t anything new – it’s actually been done for around 6,000 years. However, by combining this old world technique with cutting edge nanotechnology scientists have made sand filtration at least 5 times more efficient. Their report indicates that the modified sand adsorbed 6 times the amount of liquid mercury and 5 times as much heavy metal and organic dye than regular sand.

In addition to the improved filtration capacity, there are other benefits of super sand that increase its prospects for real-world integration. The materials needed to make super sand, graphite and regular sand, are inexpensive and readily available. Another crucial advantage is that super sand can be created around room temperatures. These factors lead experts to believe that super sand could become a cost-efficient and viable method of water filtration in the future.

Check out this interesting article from the NIST Tech Beat explaining how nature may be manufacturing silver nanoparticles all by itself. The article also discusses some ideas as to why it is that silver is such a good antibacterial agent.

Read the NIST article here.

One of the most promising new frontiers in filtration technology involves infusing different membrane types with nanomaterials in order to improve performance or to pass along certain material attributes. Here we will look into one prominent example from recent years, the incorporation of carbon nanotubes (CNTs) into ultrafiltration membranes used in water treatment. We’ll also look at how our stirred cells have aided in this specialized membrane manufacturing process.

First off, what is there to gain by using CNT’s to manufacture water treatment membranes? While scientists have identified several potential advantages for CNT implementation, since the process is still in the R&D phase they have not necessarily been proven in all cases. One key possible benefit is that membranes made with these materials would be much stronger than traditional membranes, thus reducing instances of membrane breakage and fouling, two problems that contribute significantly to high maintenance costs in water treatment. Another unique advantage is that CNTs have antibacterial properties that may reduce biofilm formation and therefore prevent or limit biofouling. Lastly, the process of manufacturing ultrafiltration membranes with CNTs allows the producer to chemically modify the membrane surface which can further reduce fouling by tailoring the membrane for specific organic solutes.

As with standard membrane manufacturing processes, the stirred cell is an ideal piece of equipment for establishing the permeability of the test membranes. For this particular study on the effectiveness of polysulfone ultrafiltration membranes manufactured with CNTs, the cell (an HP4750 in this case) was set to perform dead-end filtration with ultrapure water at 38 bars of pressure (about 551 psi).

The HP4750 Stirred Cell

In order to determine permeability, the HP4750 was directly connected to the pressure regulator of the compressed air tank. Each membrane was compacted at 38 bars until the flow rate was stable (minimum of 30 minutes). Then the flow rate was measured by weighing the permeate as a function of the pressure applied (between 5 and 35 bars). To confirm the results, this test was performed in triplicate.

Permeability is an important test characteristic for determining the membrane’s susceptibility to fouling and its overall efficiency. In the study cited here, researchers found no statistically significant difference in permeability between CNT and non-CNT amended membranes. These findings supported their conclusion that their process for grafting CNTs onto membranes was ineffective. In the conclusion the authors note that because the CNTs only partially dispersed in the host material that they were prevented from taking on the mechanical properties of the CNTs.

While this particular study did not yield the desired results, new methods of integrating nanomaterials onto membranes are constantly being explored and hopefully it’s only a matter of time until these superior membranes become available.

Visit here to read the full study:
http://cohesion.rice.edu/engineering/pedroalvarez/emplibrary/85.pdf