Synthesis, stabilization and characterization of zerovalent iron nanoparticles for remediation of hexavalent chromium - Comparing the hydrazine and sodium borohydride routes

Zerovalent iron nanoparticles (nZVI) have found diverse applications as reducing agents in chemical synthesis, particularly for environmental remediation. The preparation of nZVI using the novel hydrazine reduction route (CMC-nZVI) has been studied in detail in this work. A comparison was made with the conventional sodium borohydride method (ZVIB). The former route was found to be more effective in producing smaller (11-50 nm), relatively uniform nZVI particles with a narrow size distribution and spherical morphology. This particle size is much smaller than that of material prepared via the borohydride route, as hydrazine is a stronger reducing agent. The challenge of stabilizing the nanoparticles was addressed using carboxymethyl cellulose (CMC) coating to prevent aggregation and premature oxidation. Nanoparticles synthesized without CMC capping showed poorer stability and a broader particle size range. The effects of process parameters were investigated in detail. The synthesized nZVI particles were thoroughly characterized using several techniques, including SEM, AFM, XRD, FTIR, SQUID, BET, and XPS. The BET surface area of CMC-nZVI particles was more than four times that of ZVIB, indicating superior reactivity. The hydrazine hydrate route, combined with CMC stabilization, offers a promising approach for the large-scale production of stable nZVI nanoparticles suitable for environmental remediation applications. The potential of nZVI was demonstrated by testing the remediation of Cr(VI)-contaminated soil in the solid phase, where nearly complete reduction was achieved within approximately three hours.