Methods for the photoreduction of molecules are provided, the methods comprising illuminating an amino-terminated diamond surface comprising amino groups covalently bound to the surface of diamond with light comprising a wavelength sufficient to excite an electronic transition defined by the energy band structure of the amino-terminated diamond, thereby inducing the emission of electrons from the amino-terminated diamond surface into a sample comprising molecules to be reduced, wherein the emitted electrons induce the reduction of the molecules to form a reduction product; and collecting the reduction product.