Phase Evolution of Cu-S System in Ethylene Glycol Solution: the Effect of Anion and PVP on the Transformation of Thiourea

The transformation mechanisms of thiourea in ethylene glycol solution was systematically investigated in this report, which shows the transformation process is influenced by the anion (NO3-, Cl-, Br-) and polyvinylpyrrolidone (PVP). Thiourea (tu) isomerizes into ammonium thiocyanate when NO3- is present, regardless of the existence of PVP. For Cl-, thiourea coordinates with copper anion to form [Cu(tu)]Cl center dot 1/2H(2)O complex whether PVP is present. When it comes to Br-, thiourea hydrolyzes in the cooperation of PVP or coordinates with copper anion to form [Cu(tu)Br]center dot 1/2H(2)O complex without PVP. The different transformation routes will lead to different phase evolution of the Cu-S system. This work may provide a new understanding of the transformation of thiourea in ethylene glycol solution. The optical properties of the as-prepared copper sulfides exhibit significant stoichiometry-dependent features which may have potential applications in semiconductor photovoltaic devices.