Spectroscopic insights into the influence of oxidation on the binding properties of Cu(II) onto biochar-derived dissolved organic matter

The oxidation may change the composition, content, and structure of biochar-derived dissolved organic matter (BDOM) that influences the geochemical behavior of heavy metals (HMs) when biochar is applied. Herein, the binding characteristics of Cu(II) onto BDOM and oxidized BDOM (OBDOM) were investigated using synchronous fluorescence spectra (SFS) and Fourier transform infrared (FTIR) spectroscopy in combination with two-dimensional correlation spectroscopy (2D-COS). The results showed that the content of BDOM300 and BDOM600 decreased by 30.21% and 13.67% respectively after oxidation. Humic-like substances are dominated in the BDOM, which can be preferentially oxidized. Meanwhile, humic-like substances (e.g. 412nm in the BDOM300, 490nm in the OBDOM300, 525nm in the BDOM600, and OBDOM600) can preferentially react with Cu(II). The functional groups, at 1712 cm−1 in the BDOM300, 1631 and 1290cm−1 in the OBDOM300, 1515cm−1 in the BDOM600, 1740 cm−1 in the OBDOM600, played important roles in the complexation between humic-like substances and Cu(II). The logarithmic conditional stability constant (Log K) of the complexes is higher in the OBDOM300 than those in the BDOM300, and higher in the OBDOM600 than those in the BDOM600. The results also indicated that the presence of BDOM promoted the adsorption of Cu(II) by BC300 and BC600, and inhibited the adsorption of Cu(II) by OBC300 and OBC600. Therefore, it is particularly important to insight into the effect of oxidation on the binding properties of Cu(II) and BDOM. This study can provide scientific guidance for the use of biochar in the remediation of HMs.