The embodiments disclosed herein relate to hetero-nanostructures for efficient solar energy conversions, and more particularly to the fabrication of titanium dioxide hetero-nanostructures and methods of using same for water splitting. In an embodiment, a hetero-nanostructure includes a plurality of connected and spaced-apart nanobeams linked together at an about 90-degree angle, the plurality of nanobeams including a conductive silicide core having an n-type photoactive titanium dioxide shell. In an embodiment, a device for splitting water to generate hydrogen and oxygen includes a first compartment two-dimensional hetero-nanostructure having a plurality of connected and spaced-apart nanobeams, each nanobeam substantially perpendicular to another nanobeam, the plurality of nanobeams including an n-type photoactive titanium dioxide shell having a highly conductive core; and a second compartment copper-doped titanium dioxide nanostructure, wherein the first compartment and the second compartment are separated by a semi-permeable membrane.