Quantitative Analysis of the Structure of Organic Acids and Their Degradation Rates during Ozonation Catalyzed with ZnAl Layered Double Hydroxide

Abstract

ABSTRACT The structure of organic compounds is critical to their degradation rates in various advanced oxidation processes. In this research, 16 organic acids (such as oxalic acid, D-malic acid, oxamic acid, etc.) were used as model contaminants to investigate the mineralization efficiencies of catalytic ozonation with ZnAl layered double hydroxide (ZnAl-LDH). All tests organic acids could be effectively degraded during catalytic ozonation, and good reusability was observed since the unique structure of ZnAl-LDH was kept after the reaction. The effect of temperature on the oxidation of different organic compounds varied based on their molecular structures. In most cases, a proper temperature increase could promote the degradation of organic compounds by catalytic ozonation. The TOC removal kinetic constants had a good linear relationship with the temperature, which proved that the catalytic ozonation of organic matters conformed to the Arrhenius equation, in which the activation energy of various organic acids were between −9.0 and 51.0 kJ·mol−1, and the pre-exponential factors were between 0.003 and 2.45 × 106 min−1. By using linear regression model, it was found that the activation energies of organic acids had a greater correlation with quantum chemical parameters, such as Fukui(0)max, Fukui(+)max, EB3LYP, ELUMO, EHOMO and Bond orders(C-C)max. High correlation of Fukui(0)max and Fukui(+)max indicated the attacking of both free radicals and ozone molecule, respectively. Organic acids with lower energy and C-C bond orders were proved to be simple and readily degradable, and thus much easier to be mineralized during catalytic ozonation.