Photocatalytic Cr(VI) reduction and organic-pollutant degradation in a stable 2D coordination polymer

A new coordination polymer, Zn(bpy)L (BUC-21), (H2L = cis-1,3-dibenzyl-2-imidazolidone-4,5-°dicarboxylic acid, bpy = 4,4′-bipyridine), has been synthesized under hydrothermal conditions, and characterized by single-crystal X-ray analysis, Fourier transform infrared spectroscopy, thermogravimetric analyses, CNH elemental analysis and UV-Vis diffuse reflectance spectroscopy. BUC-21 exhibited an excellent performance for photocatalytic Cr(VI) reduction with a conversion efficiency of 96%, better than that of commercial P25 (39%), under UV light irradiation for 30 min. BUC-21 could also be used to conduct photocatalytic degradation of organic dyes including methylene blue, rhodamine B, methyl orange and reactive red X-3B. Also, the photocatalytic activity of BUC-21 remained high across a wide pH range from 2.0 to 12.0. It is interesting to note, however, that BUC-21 was unable to achieve simultaneous reduction of Cr(VI) and degradation of an organic pollutant in a mixed matrix, which can be attributed to the competition between Cr(VI) and the organic dyes for access to the photo-excited electrons.