Molecular environment of Ni after its use for removal of CMP nanoparticle

X-ray absorption spectroscopy (XAS) is employed to investigate the molecular environment around nickel that, in the form of nickel sulfate solution, has been added to precipitate nanoparticles in chemical mechanical polishing (CMP) waste water. After phase separation, for the liquid-phase sample, both the white line intensity in the normalized Ni K-edge X-ray absorption near edge structure (XANES) spectrum and the amplitude of the extended X-ray absorption fine structure (EXAFS) spectrum are enhanced due to the presence of solvation of water molecules, as compared to the solid-phase sample. Meanwhile, with the presence of water molecules, the coordination number increases; yet the Debye–Waller factor slightly decreases. The lack of chemical reduction of Ni2+ in the CMP solution is suggested as the main reason why the charge neutralization precipitation method through the use of Ni2+ is less effective than the system using Cu2+ to precipitate nanoparticles as previously reported.