Oxidative degradation of quinazoline in supercritical water: a combined ReaxFF and DFT study

Quinazoline (Qu) is a representative heterocyclic compound in chemical wastewater. In this work, the supercritical water oxidation of Qu is investigated using molecular dynamics simulations based on the ReaxFF reactive force field combined with density functional theory (DFT) method. The detailed reaction pathways, transformation routes of nitrogen element, and kinetic behaviours are systematically analyzed at the atomistic level. Simulation results show that the increment of temperature and O2 molecule accelerates the reaction rate and facilitates the complete destruction of Qu. The pyrimidine ring in Qu can be attacked by the OH radical, O2 molecule, and H2O molecule, thereby causing three main pathways for the pyrimidine ring-opening reaction. The aromatic ring undergoes a ring rearrangement process and opens under the attack of active O2 molecules. DFT calculations demonstrate that the supercritical water cluster can decrease the cracking energy of chemical bonds and accelerate the degradation rate of Qu. In addition, the transformation routes of nitrogen element during reaction are described. NH3 is found to be the primary N-containing product after ring-opening reactions and is an intermediate for the production of N2. Finally, the value of activation energy is obtained as 123.0 kJ/mol, which is reasonably consistent with the experimental results.