Research Highlights
Energy-related research highlighted in national and international publications
ClimateWire <http://www.climatewire.net> An E&E Publishing Service
CARBON CAPTURE: Energy-saving process 'scrubs' emissions without
water (Tuesday, August 18, 2009)
Jessica Leber, E&E reporter
An Energy Department researcher has demonstrated a new way to reduce the high cost of capturing carbon dioxide from today's coal burners.
Lab bench experiments show that a waterless liquid molecule could double the amount of CO2 absorbed by current water-based liquids in a scrubber and potentially halve the energy needed to then peel off the CO2 and recycle the liquid for another go-round.
The process -- called "reversible acid gas capture" -- also works with sulfur dioxide and several other harmful pollutants that are in power plant waste streams, according to Dave Heldebrant, a senior research scientist at DOE's Pacific Northwest National Laboratory.
Heldebrant says the approach does away with a major downside of today's most feasible carbon capture option for existing power plants.
For decades, natural gas plants have used amine-based solvents to remove acid gas contaminants, including CO2. Today, big coal-fired power producers such as Atlanta-based Southern Co. are piloting variations of the proven process to handle their smokestack emissions.
But the method has an enormously expensive downside: It consumes about 30 percent of the energy produced by the power plant itself.
How to eliminate an energy hog
Normally, amines are used to bind with CO2 in the flue gas and then, in another chamber, are heated to strip off the CO2. That heat is one big energy hog.
In this process, water is also needed as a solvent and to reduce the solution's corrosiveness. All that water, however, takes even more energy to heat and means that additional liquid must be pumped around -- increasing the "parasitic" energy demand of the capture process.
Eliminating that water, as Heldebrant's organic chemical does, therefore reduces energy demand. "If you've ever watched a pot of water boil, it takes forever to get to temperature. But if you heat oil, it gets hot almost immediately," he said, explaining the theory behind the substitute.
The reusable liquid could be deployed in the same carbon capture infrastructure now being tested for existing plants, and even in newly built plants that will rely on more advanced removal technologies, Heldebrant added.
One pitfall, however, could be the cost of producing the chemical.
Although it is commercially available today, it might cost as much as 10 times more than the most frequently used amine, known as MEA, according to Gary Rochelle, a chemical engineer at the University of Texas, Austin, who works with the amine capture process.
Light at the end of a long research tunnel?
"It is interesting work," said Rochelle. But, he said, because of the chemical's cost and potential real-world inefficiencies, "it's not likely to prove that it solves the problem."
Heldebrant said that the initial high up-front cost could potentially be recouped if the material can be continually recycled with few losses. Still, he noted, a lot more testing is required to put hard numbers to the energy savings and economics of the entire process.
He will present the results of his initial research today to the American Chemical Society. The next step is to increase the volumes in the lab and then to test the concept with real flue gas from a power plant. Heldebrant said he is now in discussions with chemical producers and power companies on how to scale up.
Others are also taking a wait-and-see approach. "It's work that's very early in development, and so it's really hard to make any guesses as to whether it will work for the whole process," said Joan Brennecke, director of the University of Notre Dame Energy Center, noting that it is nearly impossible to eliminate water entirely, since water is in the flue gas itself.
Brennecke is another of many researchers pushing forward technologies to reduce the high energy demand of carbon capture. Funded by a DOE grant, she has worked for several years on a liquid-salt-based capture method that also avoids water, though she estimated that it is also at least a decade away from reaching commercial scale.
"The problem with all of this is that we need a solution today, and all of this is in the research stage," she said. "No matter what, it is going to be painful to do CO2 capture."
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Photosensitization of TiO2 Nanostructures with CdS Quantum Dots: Particulate versus Tubular Support Architectures
David R. Baker 2, Prashant V. Kamat
Advanced Functional Materials Volume 19 Issue 5, pp 805 - 811
Abstract TiO2 nanotube arrays and particulate films are modified with CdS quantum dots with an aim to tune the response of the photoelectrochemical cell in the visible region. The method of successive ionic layer adsorption and reaction facilitates size control of CdS quantum dots. These CdS nanocrystals, upon excitation with visible light, inject electrons into the TiO2 nanotubes and particles and thus enable their use as photosensitive electrodes. Maximum incident photon to charge carrier efficiency (IPCE) values of 55% and 26% are observed for CdS sensitized TiO2 nanotube and nanoparticulate architectures respectively. The nearly doubling of IPCE observed with the TiO2 nanotube architecture is attributed to the increased efficiency of charge separation and transport of electrons.
Cover Page Issue 48
Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvesters
Prashant V. Kamat
J. Phys. Chem. C, 2008, 112 (48), pp 18737–18753
Excited-State and Photoelectrochemical Behavior of Pyrene-Linked Phenyleneethynylene Oligomer†
Yoichiro Matsunaga, Kensuke Takechi, Takeshi Akasaka, A. R. Ramesh, P. V. James, K. George Thomas, and Prashant V. Kamat
J. Phys. Chem. B, 2008
An oligophenyleneethynylene (OPE), 1,4-bis(phenyleneethynyl)-2,5-bis(hexyloxy)benzene (2), is coupled with pyrene to extend the conjugation and allow its use as a light-harvesting molecule [Py-OPE (1)]. The absorption and emission maxima of 1 are red-shifted compared to those of 2. Similar differences in the singlet and triplet excited-state properties are evident. The fluorescence yield of 2 in toluene is 0.53, which is slightly less than the value for the parent OPE (2) of 0.66. The excited singlet and triplet of 1 as characterized from transient absorption spectroscopy exhibit lifetimes of 1.07 ns and 4.0 μs, respectively, in toluene. When 1was cast as a film on a glass electrode (OTE) and excited with a 387-nm laser pulse, we observed the formation of excitons that decayed within a few picoseconds. When 1 was cast as a film on a SnO2-modified conducting glass electrode (OTE/SnO2), a small fraction of excitons dissociated to produce a long-lived charge-separated state. The role of the SnO2 interface in promoting charge separation was inferred from the photoelectrochemical measurements. Under visible light excitation, the OTE/SnO2 electrode was capable of generating photocurrent (∼0.25 mA/cm2) with an incident photon conversion efficiency (IPCE) of ∼6%
ACS Nano podcast and related article: TiO2-Graphene Nanocomposites. UV-Assisted Photocatalytic Reduction of Graphene Oxide,
Graeme Williams,† Brian Seger, and Prashant V. Kamat 
Monday, July 7, 2008
Photo reduction of Graphene Oxide with nano-TiO2
In the articles ASAP of ACS Nano, Williams et al., (from Prashant V. Kamat group - he is also the senior editor of Journal of Physical Chemistry) describes a neat way of reducing the o.6 nm thick graphene oxide with photo activated nano TiO2 (2-7 nm). Graphene is becoming very attractive to many and surely this is another example of that. In the picture, GO means graphene oxide and GR means graphene.
http://www.nanotella.com/2008/07/graphene-oxide-photo-reduction-with.html