REVERSIBLE PHOTOREDUCTIVE DEPOSITION AND OXIDATIVE DISSOLUTION OF COPPER IONS IN TITANIUM-DIOXIDE AQUEOUS SUSPENSIONS

Particulate titanium dioxide was used to remove and concentrate Cu(II) ions in aqueous solutions through a cyclic process of photodeposition, separation, and oxidation. Illuminated, nitrogen-purged solutions containing copper sulfate, excess sodium formate (pH 3.6), and titanium dioxide formed a purple Cu-TiO2 species. Cu(II) concentrations in the supernatant were driven from 51 to less-than-or-equal-to 0.018 mug/mL. Upon purging with oxygen, this purple Cu-TiO2 system reverted back to white along with a corresponding increase in the Cu(II) supernatant concentration. The photodeposition step and the air oxidation step were utilized to demonstrate a volume reduction process. Eighty-six percent of the Cu(II) in a synthetic waste stream was concentrated to an organic-free solution having 7% of the initial volume. The remaining waste solution contained only 1% of the initial Cu(II), and in a subsequent step, the remaining formate ion was destroyed using conventional TiO2 photocatalytic oxidation. The overall process demonstrated the ability to separate copper ions from organics using only light and air. The reversible photoreduction deposition of Cu(II) from solution was observed in the pH range 1.84-6.60. The reversible photoreduction deposition of copper(II) was dependent on the organic used to scavenge holes and independent of the copper salt used.