Cleans Water with Nanotechnology

A new water filter developed in South Africa could provide millions of people with clean drinking water. The filter, about the size and shape of a teabag, would be inexpensive, easy to distribute and simple to use.

Researchers are conducting a final set of tests on a new type of diminutive water filter before industrial production can begin. The microbiologist pours water from a plastic bottle though a high-tech, teabag-sized filter before analyzing it in laboratory at the University of Stellenbosch in South Africa. The filter would be much cheaper than bottled water as well as any other filter on the market. Instead of being filled with black or green tea, the bag contains active carbon granules and is made from nanofibers treated with biocide, which kills bacteria rather than simply filtering them from the water.

This project takes nanotechnology to the poorest of the poor people who live in this world, and it will make a difference in their lives. With some 300 million people in Africa - and over a billion worldwide - living without access to clean drinking water, the need for such a filter is huge. When in mass production, the developers said they expect the teabag to cost just a few South African cents (under half a US cent and under a third of a euro cent).

In addition to being inexpensive the filter is also easy to distribute to rural area and simple to use as it can be placed in an adapter that fits on nearly any regular-sized plastic bottle. Each filter can clean one liter (one quart) of the most polluted water to the point where it is completely safe to drink. Once used, the filter can be disposed of and is biodegradable.

African countries, led by Somalia, Mauritania and Sudan, were ranked to have the most vulnerable water supplies, according to a June report by UK-based risk consultancy firm Maplecroft.

It is simply impossible to build purification infrastructure at every polluted stream. So this filter has taken the solution right at the the people. The water is cleaned right then and there when people drink. The filter is now undergoing testing by the South African Bureau of Standards, after which it can be rolled out to the United Nations and non-governmental organizations that have expressed interest in it.

Advanced Nanogenerators for Versatile Applications

In the last article (http://nanosciencetech.blogspot.com/2010/11/self-powered-nanosensors-based-on-zinc.html) we have discussed about the nano generators basically based on the movement of the zinc oxide nanowires resulting the necessary piezoelectric effect to produce small amount of electricity. This technology can be very much utile in medical sciences, where there is a growing need for the surgery less equipments and supporting technology.

In a recent development, researchers have come up with a technique where they use the freely bendable piezoelectric ceramic thin film nano-materials that can convert tiny movements of the human body (such as heart beats and blood flow) into electrical energy. Thus these devices can be implanted in micro robot which can operate human organs without their battery charged.

The ceramics, containing a perovskite structure, have a high piezoelectric efficiency. Until now, it has been very difficult to use these ceramic materials to fabricate flexible electronic systems due to their brittle property. The research team, however, has succeeded in developing a bio-eco-friendly ceramic thin film nanogenerator that is freely bendable without breakdown.

Nanogenerator technology, a power generating system without wires or batteries, combines nanotechnology with piezoelectrics that can be used not only in personal mobile electronics but also in bio-implantable sensors or as an energy source for micro robots. Energy sources in nature (wind, vibration, and sound) and biomechanical forces produced by the human body (heart beats, blood flow, and muscle contraction/relaxation) can infinitely produce nonpolluting energy.

This technology can be used to turn on an LED by slightly modifying circuits and operate touchable flexible displays. In addition, thin film nano-materials have the property of both high efficiency and lead-free bio compatibility, which can be used in future medical applications.

Self-Powered Nanosensors Based on Zinc Oxide Nanowires

Researchers have created first self-powered nanometer-scale sensing devices by combining a new generation of piezoelectric nanogenerators with two types of nanowire sensors. The new devices can measure the pH of liquids or detect the presence of ultraviolet light using electrical current produced from mechanical energy in the environment.

Based on arrays containing as many as 20,000 zinc oxide nanowires in each nanogenerator, the devices can produce up to 1.2 volts of output voltage, and are fabricated with a chemical process designed to facilitate low-cost manufacture on flexible substrates. Tests done with nearly one thousand nanogenerators -- which have no mechanical moving parts -- showed that they can be operated over time without loss of generating capacity.

The report said that the nanoscale generators, which use the piezoelectric effects, produces electric charges when wires made from zinc oxides are subjected to strain. The strain can be produced by simply flexing the wires. The total current from many wires can be added up to power small devices. The research effort has recently focused on increasing the amount of current and voltage generated and on making the devices more robust.

The zinc oxide nanowires are embedded at the both ends of them in a polymer substrate. As they are compressed in a flexible nanogenerator enclosure, they can then generate current. That eliminates the need of metallic electrode that was required in earlier devices. Because the generators are completely enclosed, they can be used in a variety of environments. The whole system thus can be grown on folded and flexible substrates with temperatures of less than100 degrees Celsius. That will accord lower cost fabrication and growth on just about any substrate.

The nanogenerators are produced using a multi-step process that includes fabrication of electrodes that provide both ohmic and shottky contacts for the nanowires. The arrays can be grown both vertically and laterally. To maximize current and voltage, the growth and assembly requires alignment of crystalline growth, as well as the synchronization of charging and discharging cycles.

Production of vertical nanogenerators begins with growing zinc oxide nanowires on a gold-coated surface using a wet chemical method. A layer of polymethyl-methacrylate is then spun-coated onto the nanowires, covering them from top to bottom. Oxygen plasma etching is then performed, leaving clean tips on which a piece of silicon wafer coated with platinum is placed. The coated silicon provides a Shottky barrier, which is essential for maintaining electrical current flow.

The alternating current output of the nanogenerators depends on the amount of strain applied. At a strain rate of less than two percent per second, 1.2 volts is the produced output voltage. Lateral nanogenerators integrating 700 rows of zinc oxide nanowires produced a peak voltage of 1.26 volts at a strain of 0.19 percent. In a separate nanogenerator, vertical integration of three layers of zinc oxide nanowire arrays produced a peak power density of 2.7 milliwatts per cubic centimeter. By measuring the amplitude of voltage changes across the device when exposed to different liquids, the pH sensor can measure the acidity of liquids. An ultraviolet nanosensor depends on similar voltage changes to detect when it is struck by ultraviolet light.

The new generator and nanoscale sensors open new possibilities for very small sensing devices that can operate without batteries, powered by mechanical energy harvested from the environment. Energy sources could include the motion of tides, sonic waves, mechanical vibration, the flapping of a flag in the wind, pressure from shoes of a hiker or the movement of clothing.