H2O + CO2 with nanotubes= CH4 and O2. That's the basic formula of research done at Penn State. Scientists there make the hollow catalytic nanotubes from titania (titanium dioxide). Each tube is 135 nanometres wide and a tenth of a millimetre long.
The research at Penn State has also found that tintania nanotubes prvide more efficient solar energy conversion as well. The university press release expalins the experimental process that produces more efficient solar panels than those now in common use. The febrication is faster than what it takes to make the widely used silicon panels.