Facilitating effect of heavy metals on di(2-ethylhexyl) phthalate adsorption in soil: New evidence from adsorption experiment data and quantum chemical simulation.

In terms of researching and treating farmland pollution, interactions between organic and inorganic pollutants are very important aspects. Herein, the effects of heavy metals on di(2-ethylhexyl) phthalate (DEHP) adsorption in soil were investigated. The presence of Cd/Cu increased the adsorption capacity of DEHP (>23%) in a nonlinear manner. Fourier transform infrared spectroscopy revealed that the stretching vibration of soil functional groups changed under different pollution combinations, while quantum chemical simulation, including an independent gradient model and localized orbital locator, proved that outer-orbital complexes could be formed by electrostatic interaction between Cd/Cu and DEHP. The electron transfer process was analyzed by charge decomposition analyses, and these, combined with bond critical point analyses, revealed that metal ions reduced DEHP stability. The binding energy and binding free energy of different combinations were calculated and analyzed, using the key soil organic matter (SOM) information obtained through pyrolysis gas chromatography mass spectrometry. This effectively explained the adsorption behavior, and showed that SOM polar functional groups played an important role in the effect of heavy metals on DEHP adsorption. The study described here has provided a new basis for understanding the multiple interactions, accumulation, and transformation of pollutants in the soil.