Easing Atmospheric CO2 Levels Using Nanotubes and Sunlight
February 16, 2009 By Laura Mgrdichian
A digital photograph of one of the reaction chambers under natural sunlight. Photo courtesy Craig Grimes.
(PhysOrg.com) -- Researchers at The Pennsylvania State University have determined a way to use arrays of nanotubes in a solar-based process to convert carbon dioxide and water into methane and other hydrocarbon fuels. Their method may provide a new way to reduce carbon-dioxide levels in the atmosphere—rising due to our planet's heavy use of fossil fuels—as well as produce alternative fuels.
The rate of carbon dioxide (CO2) conversion using this method is 20 times higher than that of previously published research. The work is described in the January 27, 2009, online edition of Nano Letters.
"Every 12 days the world consumes about one billion barrels of oil, which represents the release of almost 1 trillion pounds of carbon dioxide into the atmosphere," said the study's lead researcher, Craig Grimes, to PhysOrg.com. "One way of dealing with this problem is by recycling the CO2 into a high-energy-content fuel, but this makes sense only if a renewable energy source, like solar energy, can be used in the process."
This type of solar-based conversion process only works if a photocatalyst—a material that reacts with light—is used to convert the CO2 into hydrocarbons. A photocatalyst that utilizes the most solar energy possible is the best option.
One popular photocatalyst candidate for the job has been titanium dioxide, also called titania, because it can powerfully react with oxygen. But so far, researchers haven't been able to make titania perform adequately despite experimenting with a variety of forms, such as nanoparticles, pellets, and multi-layer films.
Grimes and his colleagues used arrays of titania nanotubes. They created the nanotubes using a technique that incorporates nitrogen into the nanotubes' structures, which the researchers initially thought would help increase the conversion rate (this turned out to be true only in a very limited capacity).
The process also yields a high total surface area compared to other forms of the material, a property that aids in the conversion. To further boost the process, the group scattered an ultra-thin layer of platinum and/or copper "cocatalyst" nanoparticles on the surface of the array.
The nanotubes were as long as 140 micrometers (millionths of a meter) in length and a diameter of about 115 nanometers (billionths of a meter). The total size of each array sample was about 2 centimeters square and the group created several samples.
The researchers made two reaction chambers, each with a window at the top to let in sunlight. They loaded one sample into each chamber and evacuated the air out, producing a vacuum, and sealed them. Next they pumped CO2 through a tank of water and into the chambers, flushing it through via intake and outtake valves for 10 minutes.
This all took place outdoors on sunny or mostly-sunny days on the Penn State campus. The samples were left outside for 2.5 hours, up to a maxiumum of 3.5 hours, between about 12:30 and 4:00 p.m.
Analysis of the chambers' interiors showed that the predominant product of the conversion was methane, with some ethane, propane, butane, pentane, and hexane, along with other materials in very small concentrations. The conversion rates were high, although comparing the results with other published results was rather difficult, according to the group.
"Most of the previous results were achieved using nanoparticles illuminated by ultraviolet light, so we were not exactly comparing apples to apples," said Grimes. "But going by the weight of the material, we could figure out that the rate of hydrocarbon production we achieved is at least 20 times higher than those previous studies."
Grimes and his group attribute their success, in large part, to the cocatalyst particles they used. They think that a homogeneous distribution of both types could further increase the conversion rate.
More information: Nano Lett., 2009, 9 (2), pp 731-737 DOI: 10.1021/nl803258p
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Nov 11, 2009 |
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The immense amount of productive capacity to make even one of these nano-can catalysts would require more energy and generate more waste than makes sense for a ecological program.
Plant trees. Plant gardens. Make the earth green. Breathe.
Aren't these products also polluting when we use them in combustion? Albeit, not as much as coal and oil...
Oh, yes plants only hold the CO2 until they die but by then we are using them to fertilize the next generation of plants... Nice cycle don't you think?
Plants can grow with less water in higher concentations of CO2.
Best way to ease teh CO2 would be natures way imo, plant some forrests and give them a chance to live and die and start the million yr process of turning into fossil fuels again.
Almost totally useless for carbon sequestration. 99.9% of that carbon is dumped right back into the atmosphere within a decade.
"Almost totally useless for carbon sequestration. 99.9% of that carbon is dumped right back into the atmosphere within a decade."
Make biochar from them. It releases much of the chemical energy and sequesters much of the carbon while creating a soil additive which retains water and nutrients, keeping them from running off into streams.
Not that I am against the described technology. It is worth investigating.
Evolution knows best ? (Unless someone can run experiments for a few hundred million years to find optimal solutions.
Have a nice day
Provided this method can increase areal and temporal conversion efficiency of insolation by a sufficient factor to compensate for the energy required to manufacture and oprate it, it deserves detailed evaluation.
http://www.nytime...tml?_r=1
And, should we convert the CO2 into other hydrocarbons it will end up being burned and release the CO2 into the atmosphere all over again, anyway. What a waste of technology for supposedly saving the planet.
But, if the technology could be applied on the wide scale, it might be possible to at least decrease US dependence on foreign oil if Obama gets his way and no new drilling occurs. :)
If it is viable for use in a closed system, it might help reduce the need for people to use CH4 from other sources. Of course, one cannot get something from nothing. It might not save the planet to use a contraption based upon the technology but it might open up other avenues for the consumer.
Nope. Most of the O2 in the atmosphere comes from the sea and from photosynthesis therein. We could deforest the entire world and still maintain at least 75% of our current atmospheric O2 levels. And, the planet would not overheat anyway. Grass is a more efficient photosynthesizer than trees. More grasses would grow in the absence of trees whose shade often interferes with the growth of grasses.
I'd be hesitant to use methane as our next-gen "fuel of choice", since it's an order of magnitude more potent as a greenhouse gas than CO2. We'd have to be very careful about leaks.
Ca(OH)2 CO2 --> CaCO3 H2O
Trouble is, we get calcium hydroxide from the following reaction:
CaO H2O --> Ca(OH)2
It gets worse. We get calcium oxide from the following reaction:
CaCO3 --> CaO CO2
One common form of the reaction is the slaking of lime, lime being calcium carbonate.
We know how to make calcium carbonate. We just need to find a better reaction/catalyst methodology that does not form a wasteful loop.
Ca(OH)2 plus CO2 --> CaCO3 and H2O
Trouble is, we get calcium hydroxide from the following reaction:
CaO plus H2O --> Ca(OH)2
It gets worse. We get calcium oxide from the following reaction:
CaCO3 --> CaO and CO2
One common form of the reaction is the slaking of lime, lime being calcium carbonate.
We know how to make calcium carbonate. We just need to find a better reaction/catalyst methodology that does not form a wasteful loop.
More than that, use the ethanol to make solid products and so remove greenhouse gases. An answer to everyone's prayer. No cost of supply, no cost to transport the supply, neutral environmental impact, sustainable until the sun burns out. Wow.
We used to do that with oil. We made these interesting little knick-knacks, bottles and things out of plastic and when they were no longer useful we put them in a landfill.
Now we have to recycle(read waste energy making inferior products and finally burn the degraded crap for warmth).
Why? Because "plastics are like unnatural and stuff, and will last for thousands of years. You're like, hurting the Earth Mother Gaia and you're not... uhmm... you're not in tune with nature, man...".
Can we try a "war on hippies" instead of a "war on drugs" this time?
This is never going to happen.
It's unreasonable to expect more than 10% efficiency because it's costly to isolate CO2 out of the air at 380 ppm and any fairly complex molecule requires multiple steps to form; in each step you'll waste a whole bunch of energy because quanta that are above the necessary energy level cannot be used, quanta that are above can be used but all excess energy is waste.
At 10% efficiency you'll need about 25 m^2 in sunny climate for the equivalent of 1 litre of petrol per day(that's about 2400 feet^2 per gallon for you yanks).
This is not about energy. If it's ever cost effective to do this it will be used as feed stock for chemical processes.