Pb(II) deposition-reduction-growth onto iron nanoparticles induced by graphitic carbon nitride

Enhanced stability and prolonged reactivity of nanoparticles are critical factors for successful applications of the nanoscale zero-valent iron (nZVI) technology. In this work, g-C 3 N 4 was employed as a support for distributing, stabilizing nZVI and further changing the composition, microstructure and electronic structure of nZVI due to the interactions between the iron nanoparticles and g-C 3 N 4 sheet. Adjusting the micro-structure of nZVI to enhance the adsorption ability, control the electron transfer, shift IEP negatively, and improve the reactivities and stabilities coordinatively results in stabilized and long-term effective g-nZVI. For example, the accumulated wastewater (i.e., [Pb(II)] = 10 mg/L) treatment volume with g-nZVI in 5 runs is determined to be 50 L, more than twice the treatment capacity of bare nZVI. Besides, more Pb(II) is reduced to metallic Pb by g-nZVI than that by nZVI. Characterizations with spherical-aberration-corrected scanning transmission electron microscopy (Cs-STEM) integrated with X-ray energy dispersive spectroscopy (XEDS), electron energy loss spectroscopy (EELS), Raman spectroscopy, etc. visualize and quantitatively analyze the structural differences and distinctive reactive behaviors of nZVI and g-nZVI. The N-containing functional groups efficiently capture aqueous metal cations, accelerate mass transfer and electron transport from the iron core to surface-attached metal ions. In addition, the nZVI micro-structure change and the formation of covalent bonds between the lone-pair electron of nitrogen and empty orbital of iron apparently reduced the iron corrosion. Results provide direct evidence on the interface chemistry of g-nZVI and further verify the graphitic carbon nitride induces the Pb(II) ions to be deposited, reduced and grown onto iron nanoparticles.