Corrosion and transformation of solution combustion synthesized Co, Ni and CoNi nanoparticles in synthetic freshwater with and without natural organic matter

Abstract

Pure metallic Co, Ni, and their bimetallic compositions of Co₃Ni, CoNi, and CoNi₃ nanomaterials were prepared by solution combustion synthesis. Microstructure, phase composition, and crystalline structure of these nanoparticles (NPs) were characterized along with studies of their corrosion and dissolution properties in synthetic freshwater with and without natural organic matter (NOM). The nanomaterials consisted of aggregates of fine NPs (3-30 nm) of almost pure metallic and bimetallic crystal phases with a thin surface oxide covered by a thin carbon shell. The nanomaterials were characterized by BET surface areas ranging from ~ 1 to 8 m²/g for the Ni and Co NPs, to 22.93 m²/g, 14.86 m²/g, and 10.53 m²/g for the Co₃Ni, CoNi, CoNi₃ NPs, respectively. More Co and Ni were released from the bimetallic NPs compared with the pure metals although their corrosion current densities were lower. In contrast to findings for the pure metal NPs, the presence of NOM increased the release of Co and Ni from the bimetallic NPs in freshwater compared to freshwater only even though its presence reduced the corrosion rate (current density). It was shown that the properties of the bimetallic nanomaterials were influenced by multiple factors such as their composition, including carbon shell, type of surface oxides, and the entropy of mixing.

Figure 1

Simplified scheme of the SCS process.

Figure 2

SEM images and results of EDS analysis (at.%) of the (a) Co, (b) Co₃Ni, (c) CoNi, (d) CoNi₃, and (e) Ni NPs. The scale bar equals 10 µm.

Figure 3

XRD patterns of the Co and Ni-containing NPs.

Figure 4

TEM images of the (a) Co, (b) Co₃Ni, (c) CoNi, (d) CoNi₃ and (e) Ni NPs. The scale bar equals 10 nm.

Figure 5

XPS calculated elemental content (at.-%) of the Co- and Ni-containing NPs.

Figure 6

Released amount of (a) Co and (b) Ni versus the total amount of each metal within the particle loading of the Co- and Ni-containing NPs after 1, 6, and 24 h of exposure in synthetic FW with and without NOM. (c) enlarged view of the Ni release from the Ni and CoNi₃ NPs.

Figure 7

ATR-FTIR spectra of the Co- and Ni-containing NPs exposed for 3 h in (a) synthetic FW without NOM and (b) FW with NOM.

Figure 8

Typical potentiodynamic curves of the (a) PIGE, (b) Co, (c) Co₃Ni, (d) CoNi, (e) CoNi_3, and (f) Ni NPs in synthetic freshwater with and without NOM (FWN, FW).

Figure 9

Simplified scheme of the SCS NP structure.

Figure 10

Schematic summary of the results of dissolution and corrosion study of SCS-obtained Co–Ni NPs.

Figure 11

Corrosion current density, i_corr, results as a function of Ni content and respective mixing entropy values of the Co- and Ni-containing NPs exposed in FW and FWN solutions. The experimental data is presented as solid lines and the calculated data as dashed lines (via the rule of mixing).