Metal-organic framework (MOF) material, coloured scanning electron micrograph (SEM). MOFs are highly crystalline porous materials made up of 3-D networks of zinc-oxygen clusters connected by organic molecules such as citric acid. Up to 91 per cent of there volume can be made up by the nanoscale pores. Uses of MOFs include gas storage, gas purification, gas separation, or as catalysts. Magnification: x1600 when printed at 10 centimetres wide.