Rust triggers rapid reduction of Cr6+ by red phosphorus: The importance of electronic transfer medium of Fe3.

Abstract

Red phosphorus (P) is one of the metalloid materials, with five external electrons, it should be an excellent electron donor. However, the activity of red P to reduce Cr6+ is limited. Due to electrostatic repulsion, it is difficult for the electrons on the red P to transfer to the chromate anion (Cr6+). Interestingly, we found that Fe3+ derived from rust, waste iron or Fe3+ reagents can be used as the electron transport medium to solve the electron transport obstacles between red P and Cr6+. As a result, the reduction of Cr6+ by red P/rust system takes only 20min, which is far lower than the 140min of red P. The reduction rate of Cr6+ in the red P/rust system is about 12.3 times that of red P. The reaction mechanism is that red P is not easy to access chromate anions but can easily adsorb Fe3+. The adsorbed Fe3+ will be reduced to Fe2+ by red P, and the regenerated Fe2+ will diffuse into the solution to rapidly reduce Cr6+. Therefore, this work provides an alternative waste iron reuse pathway and also sheds light on the important role of electron medium in reduction reaction.