Restriction of dissolved organic matter on the stabilization of Cu(II) by phosphate.

The precipitation of Cu(II) by phosphate and the influence of dissolved organic matter (DOM) on the precipitation are essential for the fate of Cu(II) in aquatic environments. In this study, the influence of DOM on the reaction of phosphate with Cu(II) was investigated. Here, 51.61%, 29.75%, and 24.32% of the added Cu(II) (50 μM) precipitated without DOM and with the addition of fulvic acid (FA) and humic acid (HA), respectively, owing to the reaction with phosphate (50 μM). Excitation-emission matrix spectroscopy-parallel factor (PARAFAC) and two-dimensional ultraviolet-visible correlation spectroscopy analyses were conducted to characterize the influence of DOM on the precipitation of Cu(II) with phosphate. One humic-like and two protein-like fluorescent components were identified by the PARAFAC model for FA, whereas two humic-like fluorescent components and one protein-like fluorescent component were validated for HA. The humic-like components had primary roles, whereas the protein-like components had secondary roles in limiting the precipitation of Cu(II) with phosphate. Cu(II) binding to DOM chromophores initially occurred at shorter wavelengths, and then at longer wavelengths. Phenolic and carboxylic constituents had important roles, and HA exhibited more binding sites than FA. Therefore, humic-like fluorescent components and chromophores containing phenolic and carboxylic groups and functional groups with peaks at short wavelengths (200–220 nm) were primarily responsible for restricting the precipitation of Cu(II) with phosphate.