Using Nanotubes for Synthetic Photosynthesis

Plants have mastered solar energy via photosynthesis. Plants do not store their energy in batteries, however, they store it using the reduction of molecules. Taking a lesson from plants, researchers at the University of Rochester are using chlorophyll-like macromolecules to reduce water to hydrogen gas, which can be easily stored and burned for clean, on-demand energy. This system is modular in design. The first of three modules is the photoactive center. It is here that light energy (a stream of photons) hits a biological porphyrin derivative, noncovalently bound to a carbon nanotube (CNT), and injects an electron into the CNT. The CNTs traverse a polymer membrane. The aligned CNTs and polymer form the second module. The CNT allows for ballistic electron transfer across an impermeable membrane to the third and final module. Here, the electron in the CNT is injected into an inorganic catalyst where water reduction can occur, producing hydrogen gas. This poster focuses on the first module, and explores biological macromolecule binding to CNTs and electron transfer from zinc-substituted hemes to CNTs. The zinc-substituted heme is covalently attached to a protein or polypeptide containing alpha-helical domains via two thioether bonds. The alpha-helical structure allows for amphipathic solubilization of the CNTs and the zinc-substituted heme serves as a photoactive electron donor. The goal of this project is to produce inexpensive solar energy that will directly produce hydrogen gas, eliminating the need for wires (which have resistance) and batteries (which are expensive).