Dr. Valdes-Morales, Hector

Benzothiazoles are emerging chemical pollutants mainly coming from leather, paper and rubber industries; due to their use as: herbicides, corrosion inhibitors, anti-freezers, and vulcanisation accelerators. This article presents experimental data on ozone treatment of benzothiazole contaminated waters. The effect of the initial concentration of benzothiazole, ozone dosage, temperature (10-30 °C), and pH (2-9), on ozonation removal rate were assessed at bench scale. Experimental results show that reaction between ozone and benzothiazole could be approximated to a second-order kinetic law. Kinetic parameters for direct and indirect ozone reactions are estimated and temperature dependence of rate parameters is evaluated. Moreover, an initial degradation pathway of benzothiazole ozonation is proposed.

Natural and synthetic zeolites with different properties (porous structure, SiO2/Al2O3 ratio, acidity and Fe-loading) were evaluated as adsorbents/catalysts for octamethylcyclotetrasiloxane (D4) removal in dynamic adsorption tests. BEA type zeolites, with high content of Lewis and Brønsted sites, promoted the catalytic D4 ring-opening leading on the formation of smaller a-x-silanediols, which are narrower molecules able to diffuse into the channel system. Wet oxidation processes were used for the regeneration of a spent BEA zeolite, including ozonation and Fenton-like treatment. Both treatments were optimized to recover almost completely the D4 uptake of the iron-exchanged Fe-BEA in the first use. Thus, its feasibility to be reused was evaluated in successive adsorption/oxidation cycles, recovering up to 80% in at least three subsequent steps. However, in further cycles the accumulation of D4 and/or by-products led to a successive decline in the catalytic activity of the zeolites, hampering not only the capacity to transform D4 into lineal silanediols, thus reducing the adsorption capacity, but also the catalytic activity towards promoting Fenton-like reactions during regeneration.

In this study, a hydrophobic synthetic zeolite, namely ZSM-5 is chosen as an adsorbent/ catalyst for toluene removal. Experimental results showed that toluene adsorption onto ZSM-5 was favourable, following a Langmuir adsorption isotherm model. ZSM-5 zeolite was regenerated using gaseous ozone at low temperature. Adsorbed toluene was oxidised, releasing mainly CO2 and H2O. Traces of oxidation by-products such as acetic acid and acetaldehyde were formed and remained adsorbed after the oxidativate regeneration with ozone. After four successive cycles of adsorption/ozonation, the adsorption efficiency was not affected (92%–99%). These results showed that volatile organic compound (VOC) removal by adsorption onto ZSM-5 zeolite followed by ozone regeneration could be used as a promising hybrid process for the control of VOC emissions in terms of efficiency.

For several decades, it has been known that ozone emissions are harmful to humans, plants, and animals. Heterogeneous catalytic decomposition is an efficient process for removing ozone from air. This study examines the effect of the zeolite's framework and pore width on efficiency for decomposing gaseous ozone. Four highly hydrophobic zeolites are used: a large cavity zeolite (Faujasite/H‐FAU), a medium pore zeolite with parallel channel (Mordenite/H‐MOR), and two medium pore zeolites with interconnected channels (H‐ZSM‐5/H‐MFI and Na‐ZSM‐5/Na‐MFI). Experiments were conducted in fixed‐bed flow reactors loaded with zeolite at ambient conditions (20 °C and 101 kPa). Zeolite surfaces were analyzed during the experiments in order to understand the influence of physical and chemical surface properties on the ozone decomposition mechanism. A higher amount of ozone is eliminated using H‐MOR, compared with the zeolite samples H‐FAU, H‐MFI, and Na‐MFI. Pore width and micropore framework size distribution (channel and cages) appear to be key factors. A narrow channel or cage, slightly larger than the ozone molecule size, seems to promote ozone interactions with Lewis acid sites. Fourier transform infrared spectroscopy shows that Lewis acid sites (LAS), located on the walls of zeolite pores, decompose ozone. This leads to the formation of atomic oxygen species that could react with another ozone molecule to form dioxygen. Hence, LAS are regenerated, ready to decompose another ozone molecule once more.

Recently, natural zeolites have started to be used as alternative materials for ozone abatement from working environments. In this study, a surface response methodology based on a D-Optimal design is applied to develop a transition-metal-modified natural zeolite that increases ozone removal efficiency. Ozone adsorption and/or decomposition onto natural and cobalt modified natural zeolite were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Results evidenced that ozone is adsorbed and decomposed at strong Lewis acidic sites, whereas ozone adsorption products interact with surface OH groups. Additionally, DRIFTS studies indicate that nitrous species are adsorbed at acidic sites, reducing the capacity to decompose ozone when ozone is generated from air.