The objective of this work is to continue studies on the mechanism for the conversion of mercuric ions in solution to a mercury metal agglomerate absorbed on the titanium dioxide photocatalyst. Past Studies have indicate good potential for mercuric ion removal from water by semiconductor photocatalytic degradation. Absorbed photons with energy greater than or equal to the band gap energy excite electrons from the valence band to the conduction band. Mercury ions are reduced to metallic mercury as they take up the electrons, but the species which are oxidized to fill the holes is still debated and is appears to be very dependent on the pH of the solution. It is also likely that the redox reaction occurring at the surface of the TiO 2 should depend on the mercuric salt dissolved in the solution.
Mercuric chloride is largely a molecular substance while mercuric nitrate is an ionic substance.
Tanaka and others 1 completed one of the first studies using TiO 2 to eliminate mercury ions from acidic solutions. Serpone and others 2 studied mercuric and methyl mercury chloride salts in solution. The pH decreased to 3. When Cl - ion was added to the solution, some mercury was removed, but after 20 minutes it began to go back into solution. At pH 7, all of the mercury was removed from the solution after 20 minutes of light exposure, but with more light exposure, the mercury went back into solution.