Development of Photo-Response Extraction for Recovery of Precious Metal Ions

Abstract

The photo-response extraction of precious metal ions was examined, using the azo compound bis(2,2′-dipyridyl-6-yl)diazene (BDPDA), which undergoes reversible trans/cis photoisomerization, adopting the trans configuration under VIS irradiation and being partly photoisomerized to the cis-isomer by UV irradiation. The extraction of platinum ions by BDPDA depended on its configuration, with cis-BDPDA extracting a higher percentage than trans-BDPDA. In the back-extraction, the conversion of BDPDA from cis to trans under VIS irradiation promoted the back-extraction of platinum ions. As a result, platinum ions can be recovered into water without addition of chemicals. These results indicate that the extraction and back-extraction of platinum ions are controllable by controlling the wavelength of irradiation.