Probing the influence of liquid nitrogen assisted chemical reduction on the nature of passivation layer, magnetic properties, and Cr (VI) remediation performance of nanoscale zero valent iron

Abstract

Zero valent iron nanoparticles synthesis through sodium borohydride assisted chemical reduction of iron salts is a well-established and fast synthesis process. Zero valent iron nanoparticles possess a core shell structure due to formation of a surface passivation layer and this layer is composed of iron oxides and hydroxides. Depending on the synthesis condition the thickness of the passivation layer varies and effective electron transfer process from the metallic core to the outer surface is restricted if the passivation layer is too thick. Here in this work a liquid nitrogen assisted zero valent iron nanoparticles synthesis is illustrated which is fast, cheap, and highly scalable process to tune the physicochemical properties of the passivation layer and thus overall performance of zero valent iron nanoparticles. Zero valent iron nanoparticles nucleated under liquid nitrogen (ZLN) has passivation layer thickness in the range 3–4 nm and showed higher magnetic saturation value (145.32 emu/g) and better Cr (VI) reduction performance than its room temperature counterpart ZRT with a passivation layer thickness in the range 6 − 7 nm. The spherical ZLN nanoparticles showcased a particle size distribution profile in the range 10–120 nm and were able to reduce the concentration of 10 ppm Cr (VI) in about 15 min for a ZLN loading of 1 g/L at a pH value of 7.