Investigation of Matrix Effects in Laboratory Studies of Catalytic Ozonation Processes

Abstract

A systematic study investigating the effects of water matrices on heterogeneous catalytic ozonation processes was conducted in a semibatch reactor at initial pH 7.00 ± 0.20. Specifically, three matrices commonly used in laboratory studies were tested: deionized (DI) water, phosphate buffered solution, and tetra-borate buffered solution. Three metal oxide catalysts on SiO2 support, CuO/SiO2, Fe2O3/SiO2, and MnO2/SiO2 (all ∼4.5% metal loading), were synthesized and used as representative solid catalysts. Oxalate was selected as the model compound as it is a common end product in aqueous ozonation processes and also a typical refractory compound to conventional chemical oxidation. Hydroxyl radical (•OH) is generally accepted as the main reactive species in catalytic ozonation processes and can react with oxalate by electron transfer. Catalytic ozonation of oxalate in different water matrices were carried out in a laboratory experimental setup where ozone concentrations in the feed gas and off gas line were continuously monitored. Decomposition tests with and without catalysts in different matrices were also conducted in batch homogeneous reactors to probe the matrix effects on ozone decomposition and interactions between ozone and the catalysts. Moreover, t-butanol (TBA) and methanol were added as the •OH probe compounds to investigate the oxalate degradation mechanisms in various matrices. It was found that the effects of water matrices on catalytic ozonation were multifaceted, including process performance, catalysts stability, and mechanism and reaction pathways. These matrix effects can be ascribed to the influence of inorganic anions such as phosphate and borate on ozone decomposition, competitive adsorption on the catalyst surface, and generation of reactive species during catalytic ozonation processes.

Kinetic Modeling-Assisted Mechanistic Understanding of the Catalytic Ozonation Process Using Cu–Al Layered Double Hydroxides and Copper Oxide Catalysts

“…The variation in the contributions of radical and nonradical mediated processes with the nature and concentration of target organic as well as the catalyst dosage may contribute to the discrepancies in the mechanisms of the HCO process reported in various earlier studies. 10,16,61,62 The significant variability in controlling processes as a function of reaction conditions is particularly evident for the degradation of HCOO − in the presence of CuO where surface reaction control is evident at higher catalyst loadings and low HCOO − concentrations while degradation reactions in solution dominate at higher HCOO − concentrations.…”

Plasmon-enhanced Catalytic Ozonation for Efficient Removal of Recalcitrant Water Pollutants

“…This may be explained by the fact that 0.5 wt % AgMnFe 2 O 4 prepared in our study has a pH pzc of 6.98 (Table S1). Catalysts usually have the maximum ozone decomposition capability when surface hydroxyl groups are mostly zero-charged, ,, and consequently the ATZ removal efficiency was increased. As the main reactive oxidant, a higher O 3 dose led to a faster ATZ removal (Figure S9B).…”

“…To start an experiment, catalysts, atrazine, and 150 mL of ozone solution were added into the reactor, and the mixture was continuously stirred at 500 rpm at room temperature (22 ± 2 °C). Unless otherwise noted, experiments were conducted in unbuffered deionized (DI) water to eliminate the interfering effects of other inorganic ions . The initial pH was adjusted to a desired value using NaOH, and the pH evolution during the experiments was monitored.…”

Carbocatalytic ozonation toward advanced water purification

“…However, opposite conclusions were derived in another study. 290 The discrepancies in these studies might be explained by the combined effects of ionic strength, which inuences the solubility and mass transfer of O 3 , the reaction rates of ROS, and the interactions of O 3 and organics on catalyst surface. It was reported that the solubility and mass transfer of O 3 decrease as ionic strength grows, especially when Cl À , CO 3 2À and PO 4 3À are present, while SO 4…”

“…299,300 Notably, the induced alkalinity with the presence of CO 3 2À and PO 4 3À as basic anions would promote the base activation of O 3 and affect the surface charge of the catalyst. 287,290 Therefore, special attention should be paid to the variation in solution pH with the presence of basic anions. In the most of current studies, individual effects of inorganic anions on the activation of O 3 have been well evaluated.…”