(Page 2 of 2)
The researchers also tested the photocatalyst's ability to disinfect in the dark. They shined light on the fibers for 10 hours to simulate exposure to daylight and then stored them in the dark for various times. Even after 24 hours, the photocatalyst still killed bacteria. In fact, just a few minutes of illumination was enough to keep the photocatalyst activated for up to that length of time.
"Typically, when you have a photocatalyst, the activity will stop almost instantaneously when the light is switched off," Shang says. "The chemical species you generate will only last a few nanoseconds. This is an intrinsic drawback of a photocatalytic system, since you require light activation essentially all the time."
The palladium nanoparticles boost the photocatalyst's power in two ways. When photons hit the material, they create pairs of positive and negative charges--holes and electrons. The positively charged holes on the surface of the nitrogen-doped titanium oxide react with water to produce hydroxyl radicals, which then attack bacteria. "What palladium nanoparticles do is they grab electrons away so most of the holes you produce will be able to survive without being neutralized by electrons," says Shang.
As soon as they grab the electrons, the nanoparticles enter a different chemical state and store the negative charges. "When the light is switched off, that charge gets slowly released, and that slow release is what gives us that memory effect," Shang says. "That charge can react with water molecules to produce oxidizing agents again." He says nanoparticles of other transition metals, like silver, also enhance the photocatalyst's effectiveness.
The photocatalyst offers the ability to disinfect at full power during the day and then keep working at night or during power outages. Also, because the disinfection happens quickly, systems could be designed to clean large volumes of water by exposing it to light as the water flows through pipes, Shang says.
Combining light and electrical current removes contaminants from water.
IBM is developing a membrane that is more effective at ridding drinking water of arsenic contaminants.
Promising yes. But has the process been evaluated for biohazards - bits of catalytically reactive nanomaterial in the water supply don't sound like fun. A little light could get through to water in the stomach and do something reactive. Or would you just coat a solid and keep the particles from moving about?
I agree about the bio-hazard angle. For example, what would this photo-catalyst system do to the bacteria in the digestive system? It seems that the catalyst if successful should be carefully confined and controlled within water treatment facilities!
Catalyst contained within filter?
I had the impression that the catalyst was contained within the filter rather than mixed into the water. This would, hopefully, limit concentrations of nano-particles in the water, if I am correct. Otherwise the process also seems very wasteful of catalytic material in addition to unknown biohazards.
Side question. How abundant is palladium? Is there enough for widespread use or is this more a proof-of-principle experiment, perhaps also looking for similar catalysts utilizing more abundant elements.
Caveats aside, sounds like a very interesting and possibly fruitful experiment. The life-saving potential in relief efforts after natural disasters is obvious, as it is in areas lacking pure water supplies.
Also, any antiviral activity?
Re: Catalyst contained within filter?
Estimated Crustal Abundance:
Platinum: 0.005 mg/kg
Gold: 0.004 mg/kg
Silver: 0.075 mg/kg
Palladium: 0.015 mg/kg
Translation: rare, and not cheap. Commonly found in catalytic converters used in cars.
Like all "nano" products toxicity needs to be throughly tested before this idea can ever be used in the water supply. As even if bound in some sort of filter matrix it is goig to get out.
The reproducibility of the photocatalyst?
Due to the narrow band-gap of the Titanium oxynitride or Titanium nitride, it is sure that the nitrogen-doped TiO2 could be used as visible-light photocatalyst.However, nitrogen-doped TiO2 is not stable under the light illuminations, which means it could be gradually transfered to TiO2 and lose their visible-light photocatalytic abilities. So i quite wonder the reproducibility and feasibility of the photocatalyst.
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
Our list of the 50 most innovative companies, including the following:
On Twitter
Become a Fan on Facebook
Subscribe to the Feed
ssintay
11 Comments
Very impressive
This is a very impressive development. Is this temporal stability or "memory effect" induced by the palladium (sliver) nano-particles a well known phenomena? It appears to be a rapid "charging" system for converting photons into electron hole pairs. Any clue on the efficiency of the conversion?
Reply