(Fe³⁺)-UVC-(aliphatic/phenolic carboxyl acids) systems for diethyl phthalate ester degradation: A density functional theory (DFT) and experimental study

Diethyl phthalate ester (DEP) can be degraded in Fe³⁺-UV- aliphatic/phenolic carboxyl acids systems, and the degradation can be significantly influenced by different physical chemical properties of the organic acids. In this study, a density function theory (DFT) approach combined with multilinear regression analysis demonstrates that the lowest unoccupied molecular orbital energy (E_LUMO) significantly negatively influenced DEP degradation. The correlation coefficient of the regression is −19.3 mM L⁻¹ h⁻¹. The standardized partial correlation coefficient is −0.674. The aliphatic acids group has higher catalytic ability than the phenolic carboxyl acids group, and by shifting the dominant LUMO configuration from C_3s3d to Fe_4s3d orbitals, Fe³⁺ significantly accelerates the catalytic reactions of the aliphatic acids/UV systems. Further analysis demonstrates that electron withdrawing hydroxyl group on the aliphatic acids increases the photo catalytic effects of aliphatic acids/UV system. This study highlights the important role of E_LUMO of organic acids on their photocatalytic ability towards degradation of organic pollutants.