Enhanced removal of trace Cr(VI) from neutral and alkaline aqueous solution by FeCo bimetallic nanoparticles

The reactivity of zero valent iron (Fe 0 ) for removing Cr(VI) is self-inhibiting under neutral and alkaline conditions, due to the precipitation of ferrous hydroxide on the surface of Fe 0 . To overcome this difficulty, we incorporated a second metal (Co) into Fe 0 to form FeCo bimetallic nanoparticles (FeCo BNPs), which can achieve higher activity and significant improvement in the reaction kinetics for the removal of Cr(VI) compared with Fe 0 . The FeCo BNPs were synthesized by a hydrothermal reduction method without using any templates. The characterization analysis indicated that the products were highly uniform in large scale with 120–140   nm size in diameter. The obtained FeCo BNPs exhibited a remarkable removal ability for Cr(VI) in the pH range of 5.3–10.0. Especially, FeCo BNPs were able to reduce trace Cr(VI) (1.0   mg   L −1 , pH   =   7.5) down to about 0.025   mg   L −1 within 1   h. XPS analysis confirmed that Cr(VI) was reduced to Cr(III) by FeCo BNPs, while Fe and Co was oxidized, implying a chemical reduction process. The enhanced removal of trace Cr(VI) could be originated from the introduction of Co, which not only served as a protecting agent against surface corrosion by galvanic cell effect, but also enhanced the efficient flow of electron transfer between iron and Cr(VI). All the results primarily imply that FeCo BNPs can be employed as high efficient material for wastewater treatment.