Take Liquid Light, profiled in this New Scientist piece. The New Jersey start-up recently showed off a prototype of its carbon dioxide converter, a coffee table-sized "layer cake of steel and plastic." Their first product will be ethylene glycol, a molecule that is used to make plastic bottles and antifreeze. The company says it has created catalysts that can convert carbon dioxide to over 60 different molecules.
It works like this: a lot of useful molecules, such as methanol (wood alcohol), isopropanol (rubbing alcohol), are butonal (a fuel) are just some combination of carbon, oxygen, and hydrogen atoms. Zapping carbon dioxide with electricity in the presence of different metal catalysts and other gases turns it into a whole range of carbon-based molecules. It's just plain chemistry.
While industrial products won't be that big of a carbon sink (relative to the massive amounts we're emitting into the atmosphere, at least), using carbon dioxide represents a 180º turn from thinking about the gas purely as a waste. We might imagine carbon credits of the future to include an entirely new line of plastic products—from pens to clothing to water bottles—all made of carbon sequestered out of thin air. More here.