Natural organic matter (NOM) plays an important role in metal speciation, and complexation reactions between metals and organics play an important role in contaminant bioavailability, reactivity, and mobility in natural systems. However, the chemical complexity of NOM has made it difficult to study using traditional methods. Copper complexation can be used as an indirect probe to study the reactive sites of NOM, which is important for characterizing not only organic matter in general, but also its active sites for metal ion complexation in the soil environment. This study utilizes multiple complementary spectroscopic techniques including Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and synchrotron-based X-ray Absorption Spectroscopy (XAS) at both the Cu K and L-edges. Spectra were collected on various standard Cu(II)-organic acid compounds, mixtures, and Cu(II) reacted with fulvic and humic acids. FTIR and K-edge spectroscopy are both sensitive to coordination environments, but FTIR spectra on NOM cannot be deconvoluted easily and K-edge spectra have difficulties differentiating between N and O bonding groups. In contrast, Cu L-edge XANES measurements provide direct access to core-level bonding orbitals of the metal-ligand complex where distinct shifts in the L<sub>3</sub>-edge correspond to changes in the ligand field, but provide little conformational information. The combined measurement of Cu-NOM systems with multiple approaches produces a clearer understanding of complexation reactions than any technique alone.

In-situ Cu(II)-fulvic acid systems studied using complementary spectroscopic techinques

249th National Meeting (2015)

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