Photocatalytic reduction of platinum(II and IV) from their chloro complexes in a titanium dioxide suspension in the absence of an organic sacrificial reducing agent

Abstract

The thermodynamics and surface chemistry affecting the photocatalytic reduction of chloro aqua platinum( II) and platinum(IV) complexes as means of platinum recovery from solution are communicated. The photocatalytic reduction rate trends of the cationic, neutral and anionic chloro complexes under acidic conditions in the TiO2 aqueous suspension in air equilibrated solutions, oxygen as well as nitrogen-purged solutions are discussed. Speciation of platinum is used to explain the observed photocatalytic reduction processes and trends. The rate of reduction was found to be highest for the cationic species [Pt(H2O)4]2+ and [PtCl(H2O)3]+ in line with thermodynamic predictions whilst no reduction was observed for the tetrachlorinated [PtCl4]2− complex in each of the three atmospheres. The role of water in the coordination sphere of the platinum(II) chloro aqua complexes is discussed and a comparison is made with the photocatalytic reduction of platinum(IV) from its hexa-chloro compounds without any water in their coordination spheres.