Identification of cupric and cuprous copper in copper naphthenate-treated wood by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) was used to monitor the modification on copper naphthenate (Cu-N) treated Southern pine and the effect of a post treatment steaming on Cu-N treated samples. The atomic ratio of oxygen to carbon (O-1s/C-1s) decreases with Cu-N treatment, confirming the coverage of the sample surface with Cu-N, which is rich in -CH2- groups. XPS spectra and Auger parameters were successively used to identify and quantify Cu (I) and Cu (II) on the surface of Cu-N treated samples. The peak at 935 eV and the presence of shake up satellites are a good indication of the presence of cupric copper, while the peak at 933 eV and the disappearance of shake-up satellites are attributed to the presence of cuprous copper. The post-treatment steaming of Cu-N treated Southern pine cubes results in the conversion of 52 percent of the cupric copper into cuprous copper on the wood surface.