Fundamental Mechanistic Studies on the Ultrasonic Treatment of Problematic Water Pollutants and Toxins
Abstract
Problematic organic pollutants in industrial and drinking water sources are a leading cause of water scarcity. Among the advanced oxidation processes, sonolytic degradation has received considerable attention because it combines oxidation processes initiated by reactive oxidant species and a pyrolysis processes associated with the high temperatures produced during cavitation. The degradation of the semi-volatile compound, MCHM, was rapid and followed pseudo-first order kinetics. The Freundlich kinetic model for heterogeneous systems was successfully applied to describe the non-uniform distribution of MCHM at the gas-liquid interface during ultrasonic treatment. Two primary products were confirmed by GC-MS. Computational studies were also applied to assist in a better understanding of the conformational effects and the pyrolytic pathways. The first-generation antihistamine, diphenhydramine (DPH), was also readily degraded by ultrasound. The heterogeneous process was best fit to a Langmuir-Hinshelwood kinetic model, which indicated a uniform partitioning at the gas-liquid interface. The degradation of DPH was achieved primarily via the addition reaction with hydroxyl radicals to the aromatic rings. Computational studies supported the observed products and the proposed reaction pathways for the pyrolytic and oxidation degradation pathways. Ultrasound was shown to be a rapid and effective method to remediate cetirizine (CET), a second-generation antihistamine. Addition of different hydroxyl radical scavengers into the solution prior to treatment as the competition studies indicated that CET reacted with hydroxyl radicals at the gas-liquid interface and the bulk solution. When the solution was saturated by O2, CET degraded the most rapidly. Degradation products were confirmed by LC-MS analyses. Treatment of the emerging problematic perfluorinated alkyl substance, “GenX” with steady state gamma-radiation under various conditions did not lead to significant degradation. However, “GenX” does react with eaq- at near diffusion-controlled rate, k = 5×1010 M-1·s-1. Titanium dioxide photocatalysis did not lead to appreciable degradation of “GenX” under a variety of conditions even in the presence of oxalic acid or ethanol as the valence band hole quencher. Sonolysis was a promising method and led to the effective mineralization of “GenX” under argon saturated conditions. A detailed computational study of the pyrolytic degradation pathways was carried out using density function in Gaussian 09.
Subject Area
Analytical chemistry|Environmental Studies
Recommended Citation
Cui, Danni, "Fundamental Mechanistic Studies on the Ultrasonic Treatment of Problematic Water Pollutants and Toxins" (2018). ProQuest ETD Collection for FIU. AAI27736466.
https://digitalcommons.fiu.edu/dissertations/AAI27736466