Direct identification of Cu(II) species adsorbed on rosin-derived resins using electron paramagnetic resonance (EPR) spectroscopy.

Resins derived from natural rosin have been described recently as environmentally-friendly adsorbents with potential uses in the clean-up of wastewaters and the treatment of drinking waters. However, in order to improve the design of these products it is important to understand the chemical mechanisms through which they act. We now describe the combined use of EPR spectroscopy and Cu(II) to probe directly the metal coordination environment after uptake by various rosin-derived products. Clear distinctions are demonstrated between the copper bonding in different adsorbent preparations. Furthermore, in the case of nitrogen cross-linked products, the spectral parameters also provide information on the number of nitrogen atoms in the immediate atomic environment of the copper atom when covalent bonding is involved. This methodology works well for adsorption from solutions containing multiple components, because only those that are paramagnetic are detected, and different types of paramagnetic metal ion produce distinctly different EPR spectra.