Experimental and theoretical investigation of the catalytic ozonation on the surface of NiO-CuO nanoparticles

Formation of dichloroacetic acid and dichloroacetamide from phenicol antibiotic abatement during ozonation and post-chlor(am)ination

This study investigated the formation of dichloroacetamide (DCAM) and dichloroacetic acid (DCAA) from the abatement of three phenicol antibiotics (PABs, chloramphenicol, thiamphenicol, and florfenicol) during ozonation and post-chlor(am)ination. Results show that the three PABs have a low ozone reactivity (kO3 = 0.11‒0.12 M-1 s-1), and therefore are mainly abated through the hydrogen abstraction mechanism by hydroxyl radicals (•OH) during ozonation. During PAB degradation, the carboxamide moiety in the parent molecules can be cleaved off by •OH attack and thus gives rise to DCAM. The formed DCAM can then be further oxidized by O3 and/or •OH to DCAA as a more stable transformation product (TP). When the three PABs were adequately abated (abatement efficiency of ∼82 %‒95 %), the molar yields of DCAM and DCAA were determined to be 2.79 %‒4.71 % and 32.9 %‒37.2 %, respectively. Furthermore, post-chloramination of the ozonation effluents increased the yields of DCAM and DCAA slightly to 4.20 %‒6.45 % and 39.0 %‒41.1 %, respectively. In comparison, post-chlorination eliminated DCAM in the solutions, but significantly increased DCAA yields to ∼100 % due to the further conversion of DCAM and other ozonation TPs to DCAA by chlorine oxidation. The results of this study indicate that high yields of DCAM and DCAA can be generated from PAB degradation during ozonation, and post-chlorination and post-chloramination will result in very different fates of DCAM and DCAA in the disinfected effluent. The formation and transformation of DCAM and DCAA during PAB degradation need to be taken into account when selecting multi-barrier treatment processes for the treatment of PAB-containing water.

Influence of water molecule on active sites of manganese oxide-based catalysts for ozone decomposition

Developing an efficient approach to decompose ground-level O₃ in humidity is crucial for preventing O₃ pollution in practical application scenes. In this study, MnO_x, CuO, and Cu/MnO_x were synthesized to investigate the influence of H₂O on the variation of active sites during O₃ decomposition. The structural characterizations of the as-synthetic catalysts were measured by N2 physisorption, XRD, SEM, O₂-TPD, H₂-TPR, TG, and FT-IR analyses. In dry conditions, the elimination rate of O₃ followed the sequence of MnO_x > Cu/MnO_x > CuO. The introduction of Cu to MnO_x enhanced the surface area and pore volume of Cu/MnO_x, accordingly diminishing the amounts of surface defects and the participation of sub-surface lattice oxygen for catalytic cycle, indicating that surface defects and oxygen vacancies (V_O) determined the catalytic activity for O₃ decomposition. In humid conditions, the elimination rate of O₃ changed to the sequence of Cu/MnO_x > MnO_x > CuO, with a variation rate compared to dry conditions of -62.9% for MnO_x, 14.2% for CuO, and 27.7% for Cu/MnO_x. The decrease of participant sub-surface lattice oxygen and the accumulation of intermediates in humidity diminished the decomposition of O₃ on MnO_x, while the active species such as superoxide radicals generating from the reaction of H₂O and Cu/MnO_x facilitated the participation of V_O and the desorption of O₂ from the occupied active sites, accelerating the catalytic cycle on Cu/MnO_x. This work developed a deeper understanding of the influence of H₂O on catalytic activity, promoting the performance of MnO_x-based catalysts for practical O₃ decomposition.

Degradation of o-, m-, p-cresol isomers using ozone in the presence of V2O5-supported Mn, Fe, and Ni catalysts

Oxidative degradation of o-, m- and p-cresols using ozone in the presence of V2O5-supported metal (Mn, Fe, Ni) catalysts was studied under ambient reaction conditions. Metal (Mn, Fe, Ni) loaded V2O5 catalysts were prepared using a wet-impregnation method, thereafter, characterized, and analyzed by use of the XRD, FT-IR, SEM-EDX, TEM, and ICP-OES. Results show the effect of the amount of a metal that was loaded on the support, particularly, how it affects the resultant catalysts’ (i) crystallite size, (ii) dispersion of an active metal over the surface of a support, and (iii) catalytic activity. Mn-loaded catalysts were found to be relatively more active for the conversion of individual cresol isomers and the activity of this catalyst was significantly enhanced at a lower Mn to V2O5 ratio (2.5 wt%). Mn(2.5 %)/V2O5 catalyst led to conversions of 66.78, 71.01 and 73.68 % with o-, m-, and p-cresols respectively within 24 h of oxidation. Oxidation products were derivatized by ethanol and a few were positively detected using GC-MS. o-Tolyl acetate and 2,5-dihydroxy toluene were detected from o-cresol, m-tolyl acetate, and 2,3-dihydroxy toluene from m-cresol and p-tolyl acetate and 3,4-dihydroxy toluene from p-cresol oxidation. Dimethyl maleate and dimethyl oxalate were detected as common products in all three isomers’ oxidation.

Enhanced heterogeneous catalytic ozonation of pharmaceutical pollutants using a novel nanostructure of iron-based mineral prepared via plasma technology: A comparative study

Plasma-treated goethite nanoparticles with high surface area and improved density of surface hydroxyl groups were synthesized from natural goethite (NG) using Argon (PTG-Ar) and Nitrogen (PTG-N₂) as plasma environment to enhance the performance of heterogeneous catalytic ozonation process. Synthesized samples were characterized by FESEM, EDX, TEM, XRD, XPS, BET-BJH, FTIR, AAS and pH_PZC. Results indicated a significantly different morphology for the prepared samples with negligible change in crystal structure. Furthermore, the catalytic activity and synergy factor of the NG and PTG nanocatalysts were evaluated for degradation and mineralization of Sulfasalazine antibiotic (SSZ) as an environmental hazardous contaminant. The highest removal efficiency was achieved 96.05 % under the optimal operating conditions. The kinetic study confirmed the pseudo-first-order reaction for the degradation process. Moreover, the dissolved ozone concentration and effect of organic and inorganic salts were studied in order to assess the reactive oxidant species (ROSs) and catalyst active sites in the process. The mechanism investigation showed the catalytic ozonation of SSZ was mainly performed by successive attacks of hydroxyl radicals (•OH), superoxide radicals (O₂^-) and direct ozone molecules. Environmentally-friendly modification of the NG, negligible iron leaching, successive reusability and superior catalytic activity are the major benefits of the PTG nanoparticles.

Advanced treatment of biologically pretreated coal chemical industry wastewater using the catalytic ozonation process combined with a gas-liquid-solid internal circulating fluidized bed reactor

This paper investigated the performance of the combined system of catalytic ozonation and the gas-liquid-solid internal circulating fluidized bed reactor for the advanced treatment of biologically pretreated coal chemical industry wastewater (CCIW). The results indicated that with ozonation alone for 60min, the removal efficiency of chemical oxygen demand (COD) could reach 34%. The introduction of activated carbon, pumice, γ-Al₂O₃ carriers improved the removal performance of COD, and the removal efficiency was increased by 8.6%, 4.2%, 2%, respectively. Supported with Mn, the catalytic performance of activated carbon and γ-Al₂O₃ were improved significantly with COD removal efficiencies of 46.5% and 41.3%, respectively; however, the promotion effect of pumice supported with Mn was insignificant. Activated carbon supported with Mn had the best catalytic performance. The catalytic ozonation combined system of MnO_X/activated carbon could keep ozone concentration at a lower level in the liquid phase, and promote the transfer of ozone from the gas phase to the liquid phase to improve ozonation efficiency.

Insights into the mechanism of phenolic mixture degradation by catalytic ozonation with a mesoporous Fe3O4/MnO2 composite

Mesoporous Fe₃O₄/MnO₂ is more active than Fe₃O₄ and MnO₂ in catalytic ozonation of phenols mixtures, and it is easily magnetically separated and very stable in recycling at pH 9.

Characterization and reactivity of Mn–Ce–O composites for catalytic ozonation of antipyrine

Mn–Ce–O(8/2) exhibited excellent catalytic activity for the mineralization of antipyrine with ozone, attributed to its high electron transfer ability.

Synthesis of a Fe3O4–CuO@meso-SiO2 nanostructure as a magnetically recyclable and efficient catalyst for styrene epoxidation

A novel Fe₃O₄–CuO@meso-SiO₂ composite was fabricated as a magnetically recyclable and efficient catalyst for olefin epoxidation.

Enhanced ozonation of dichloroacetic acid in aqueous solution using nanometer ZnO powders

Nanometer zinc oxide (ZnO) powders were used as a catalyst to enhance the ozonation for the degradation of dichloroacetic acid (DCAA) in aqueous solution. The batch experiments were carried out to investigate the effects of key factors such as catalyst dosage, ozone dosage, solution pH and tert-butyl alcohol (t-BuOH) on the degradation efficiency of DCAA. Density functional theory (DFT) was adopted to explore the mechanism of generating hydroxyl radical (*OH) on the ZnO surface. The results showed that adsorption and ozonation processes were not effective for DCAA removal, and the addition of ZnO catalyst improved the degradation efficiency of DCAA during ozonation, which caused an increase of 22.8% for DCAA decomposition compared to the case of ozonation alone after 25 min. Under the same experimental conditions, the DCAA decomposition was enhanced by increasing catalyst dosage from 100 to 500 mg/L and ozone dosage from 0.83 to 3.2 mg/L. The catalytic ozonation process is more pronounced than the ozonation process alone at pH 3.93, 6.88, and 10. With increasing the concentration of t-BuOH from 10 to 200 mg/L, the degradation of DCAA was significantly inhibited in the process of catalytic ozonation, indicating that ZnO catalytic ozonation followed *OH reaction mechanism. Based on the experimental results and DFT analysis, it is deduced that the generation of *OH on the ZnO surface is ascribed to the adsorption of molecule ozone followed by the interaction of adsorbed ozone with active sites of the catalyst surface. It is also concluded that ZnO may be an effective catalyst for DCAA removal, which could promote the formation of *OH derived from the catalytic decomposition of ozone.