Efficient near ultraviolet light induced formation of hydrogen by ferrous hydroxide.

The formation of hydrogen on irradiating ferrous ion in aqueous solution or suspension was studied over a wide range of pH. In addition to the known reaction in acid solution which decreases in yield with increasing pH and required far UV light, there is an efficient reaction occurring between pH 6 and 9 which utilizes near UV light. The latter reaction is an approximately linear function of both the concentration of ferrous ion and the light intensity. The quantum yield of hydrogen from the suspension of Fe(OH)2 at pH 7.2 is very high: > or = 0.3. The quantum yield decreases by a factor of five at 1 mole percent of ferric ions. To explain these observations it is proposed that an intermediate formed on excitation of the Fe(OH)2 polymer is further reduced by a neighboring Fe(+2) to form H2. These results support the work of Braterman et al. (1983) which claimed that the near UV driven photooxidation of ferrous ions could be responsible for formation of the Banded Iron Formations on the early earth. The efficient photoreaction observed in the present work could also serve as a source of active reducing equivalents to reduce CO2 and thus provide a solution to a dilemma in the arguments on the role of reduced carbon in the origin of life.