New insight into chemical changes between dissolved organic matter and environmental nano-CuO pollutants binding experiment using multi-spectroscopic techniques

Abstract

In this work, the copper oxide nanoparticles (nano-CuO) binding characteristics to dissolved organic matter (DOM) fractions was investigated based on three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy, parallel factor analysis (PARAFAC) and two dimensional correlation spectroscopy (2D-COS). According to the results, the three fluorescence components were obtained from EEM-PARAFAC; furthermore, their related expressed fluorescence intensity reduced with the increase of nano-CuO concentrations. According to the 2D-COS combined with the spectra of synchronous fluorescence, the humic-like fraction fluorescence was more susceptible than protein-like fraction, while the fluorescence changes sequentially occurred in the order as below: protein-like fraction < humic-like fraction. According to two-dimensional Fourier Transformation Infrared correlation spectroscopy (2D-COS-FTIR), DOM's the structural change sequence by nano-CuO binding was in the order as below: 1432 > 1057 > 1600 > 842 > 913 > 1300 cm−1. To be more detailed, DOM binding to nano-CuO's sequential order is COO− antisymmetric stretching > polysaccharide C-O > amide I C-O > aromatic CH in cellulose > C-O stretching of phenolic and deformation of OH. Hetero 2D-COS maps further revealed the close association between the aromatic functional groups and humic-like substances, and between carboxylic groups and protein-like substances. The findings would be beneficial to understand the mechanism of the superior potential of 2D hetero spectral correlation spectroscopy in studying complex interactions with DOM at the molecular level in the soil environment.