Quantitative structure-property relationships on direct photolysis of PCDD/Fs on surfaces of fly ash

Fly ash samples containing polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were generated by combustion of polyvinyl chloride, wood, high-density polyethylene and styrene. By partial least-squares (PLS) regression, quantitative structure-property relationship (QSPR) models were developed for photolysis half-lives (t_1/2) of PCDD/Fs adsorbed on fly ash surfaces and irradiated by UV-B of simulated sunlight. Quantum chemical descriptors computed by PM3 hamiltonian were used as predictor variables. The cross validated Q_cum²value for the optimal QSPR model was 0.678, indicating robustness and good predictive abilities of the model. The QSPR results showed that the stability of the PCDD/F molecules increased with the increase of chlorine atoms in the parent molecules. Increasing the energy of the highest occupied molecular orbital (E_HOMO). the energy of the lowest unoccupied molecular orbital (E_LUMO). E_LUMO + E_HOMO and E_LUMO - E_HOMO values of the PCDD/Fs led to decrease of log t_1/2 values. Increasing the most negative atomic charge on the oxygen atom of PCDD/Fs led to elevated log t_1/2 values. The log t_1/2 values of PCDD/Fs increased with the decrease of the largest negative atomic charge on a carbon atom.