Remediation of aqueous waste streams containing metal ions and organic compounds using semiconductor photocatalysis

Since it was discovered that water could be split photocatalytically into hydrogen and oxygen at n-TiO{dollar}sb2,{dollar} semiconductor photoelectrochemistry has been studied for a variety of processes related to solar energy utilization including organic decomposition and metal photodeposition. Although many examples of metal photodeposition exist, the extent of removal and the potential use of these processes has not been thoroughly studied.; The photodeposition of copper in aqueous solutions using titanium dioxide photocatalysis was studied as a function of organic compound, organic concentration and pH. The photodeposition of copper and subsequent oxidation using air was exploited to demonstrate a volume reduction experiment in which copper was removed from an organic contaminated waste stream and concentrated in an organic free solution.; Nitrogen purged solutions containing copper sulfate, excess sodium formate (pH 3.6) and TiO{dollar}sb2{dollar} illuminated with UV light formed a purple Cu-TiO{dollar}sb2{dollar} species. Cu(II) concentrations were driven from 51 {dollar}mu{dollar}g/mL to below detection limits within 5 minutes. Upon purging with oxygen, the purple Cu-TiO{dollar}sb2{dollar} reverted back to white along with an increase in the Cu(II) supernatant concentration which resulted in 98% recovery of the Cu(II) within 130 seconds.; In a volume reduction experiment, a 2500 mL solution containing formate and 51 {dollar}mu{dollar}g Cu/mL was concentrated to 170 mL of 646 {dollar}mu{dollar}g Cu/mL. The remaining formate ion was then oxidized to carbon dioxide using conventional TiO{dollar}sb2{dollar} photooxidation. TiO{dollar}sb2{dollar} photocatalysis was also used to demonstrate the treatment of a spent electroless copper plating bath.; The effect of various organics on copper photodeposition was investigated as a function of organic concentration and pH. For solutions containing organics in which copper photodeposition did not occur, the addition of formate resulted in copper photodeposition. The photodeposited copper was partially oxidizable when exposed to oxygen except for the Cu-TiO{dollar}sb2{dollar} produced with propiolic acid. The rates of copper photodeposition and subsequent oxidation of the photoreduced copper with oxygen were dependent on the organic hole scavenger.; XPS, EPR and X-ray diffraction were used to determine the reduced copper species. The findings indicated that the reduced copper was a mixture of Cu{dollar}sb2{dollar}O and Cu(0) which was dependent on the organic.