Non-Biological Photosynthesis

This paper is concerned with research under way in the De partment of Chemistry of the Massachusetts Institute of Tech nology, on the design of a non-biological photosynthetic process in which water is decomposed by sunlight into the component hydrogen and oxygen, not by the sunlight absorbed by water, but by the sunlight absorbed by inorganic material that has been added to the water. It is desirable first to review briefly some pertinent aspects of the natural process, and the work which led to recognition of the new process as a means of converting solar into chemical energy. Photosynthesis is usually thought of as the process by which living plants absorb sunlight and thereby convert carbon dioxide and water into oxygen and compounds of carbon. The com pounds of carbon produced by the reaction include carbohydrates (such as sucrose) which store up part of the energy of the sun light in the form of chemical energy. This energy can be released when desired by burning the sugar to produce heat and give back carbon dioxide and water. The growing of sugar cane is, in fact, one of the most efficient natural ways to convert solar into chemical energy, as has been pointed out in an earlier paper of this series by Dr. Daniels, The natural process is brought about, as is well known, not by the sunlight absorbed by the carbon dioxide and water which produce the sugar, but by the sunlight absorbed by the chloro phyll in the system. Two aspects of the natural process have been of particular interest. One is the question of how the carbon in the carbon dioxide is reduced to the form in which it is found in sugar ; the other is the question of how the oxygen in water is oxidized to oxygen gas. The problem of learning how the carbon is reduced is difficult to attack experimentally because no sure wray has been found to reduce carbon dioxide photochemically in water solution outside of a living organism.1 The other problem of learning how the oxygen in liquid water