Penn State researchers have used titanium dioxide nanotubes doped with nitrogen and coated with a thin layer of both copper and platinum for converting a mixture of carbon dioxide and water vapor into methane gas. Using outdoor, visible light, they reported a 20-times higher yield of methane than previously published attempts conducted in laboratory conditions using intense ultraviolet exposures. During the chemical conversion of water and carbon dioxide to methane one carbon dioxide molecule and two water molecules combine to form one methane molecule and two oxygen molecules. However, for the reaction to occur, at least eight photons are required for each molecule. It also requires an efficient photocatalyst that uses the maximum energy available in sunlight. Dual catalysts is the key to efficiently turning carbon dioxide and water vapor into methane.