To airport security personnel, an opaque plastic bottle is a dangerous mystery: Does it carry shampoo or explosives? Now researchers have developed a method that uses Raman spectroscopy to detect and identify concealed hazardous materials.
Current methods for identifying explosives are either invasive, like digging through a passenger’s luggage, or require time-consuming sample preparation. X-ray imaging can hint at dangers but doesn’t provide chemical specifics.
But Raman spectroscopy can give detailed information about chemicals behind a barrier, says Freek Ariese of VU University, in Amsterdam. He and his colleagues thought time-resolved Raman spectroscopy (TRRS) would be ideal. The idea behind TRRS is that, after a laser excites a sample, the first photons back to the spectrometer are those emitted from the molecules on the sample’s surface, because they have the shortest distance to travel. Researchers avoid these signals by closing the gate in front of the spectrometer’s detector for the first few hundred picoseconds after excitation, Ariese says. Then they open the gate in time to receive the photons and chemical information from deep within the sample.
To test TRRS’s ability to detect hidden explosives, the researchers put powdered dinitrotoluene, a byproduct of TNT, in a cuvette and placed it behind a variety of common white plastics up to 5-mm thick. First, they opened the detector gate quickly to collect a spectrum dominated by signal from the plastic. Then they started delaying the opening for longer and longer, until they could see dinitrotoluene’s signature in their spectra. Both the type of plastic and its thickness affected the optimum gating delay—between 300 and 500 ps—but they successfully detected the dangerous material behind all the plastics tested.
David Moore of Los Alamos National Laboratory thinks the use of TRRS is an “interesting experiment” but questions its applicability in the real world. The method won’t work, he says, if the explosives are hidden in metal or cardboard: “If it’s not plastic, the laser won’t go through at all.”
Ariese agrees that metals would stymie his team’s method, but he says simply tuning the laser to different wavelengths could allow researchers to look through other materials.

Read more on Raman Reveals Danger Inside Plastic Bottles…

Powered by sunlight, titanium oxide nanotubes can turn carbon dioxide into methane, which can be harnessed as an energy source, say scientists at Pennsylvania State University.
The nanotubes could dramatically reduce CO2 emissions into the atmosphere and reduce our need for fossil fuels.
“Right now there is lots of talk about burying carbon dioxide, which is ridiculous,” said Craig Grimes of Penn State, who, along with Oomman Varghese, Maggie Paulose and Thomas LaTempa, co-authored a paper on the nanotubes in the journal Nano Letters. “Instead we can collect the waste out of the smoke stack, put it though a converter, and presto, use sunlight to change [CO2] back into fuel.”
The nanotubes are arranged vertically, almost like empty honeycomb. Over the top of the nanotubes sits a thin, reddish-brown layer of copper oxide. Both the copper and titanium oxide act as catalysts, speeding up reactions that take place naturally.
When sunlight hits the copper oxide, carbon dioxide is converted into carbon monoxide. When sunlight hits the titanium oxide, water molecules split apart. The hydrogen freed from the water and the carbon freed from CO2 then recombine to create burnable methane, and the spare oxygen atoms pair up to create breathable oxygen.
The scientists have created thin membranes that cover either 3.8 or 15.5 square inches. So far, those membranes have produced an estimated 66 gallons of methane, said Grimes.
Adding more light and CO2 creates more methane. Grimes estimates that focusing the light collected from 1,100 square feet onto one of the membranes would generate more than 132 gallons of methane on a sunny day.
This is solar power by another name, say Grimes and other scientists. Instead of storing electrons in batteries, Grimes’ idea would store energy chemically.

Read more on Nanotube Tech Transforms CO2 Into Fuel…