Mechanism of Synergistic Effect on Electron Transfer over Co–Ce/MCM-48 during Ozonation of Pharmaceuticals in Water

Abstract

The same amount of metal was deposited on the surface of three-dimensional mesoporous MCM-48 by a facile impregnation–calcination method for catalytic ozonation of pharmaceutical and personal-care products in the liquid phase. At 120 min reaction time, Co/MCM-48 and Ce/MCM-48 showed 46.6 and 63.8% mineralization for clofibric acid (CA) degradation, respectively. Less than 33% mineralization was achieved with Co/MCM-48 and Ce/MCM-48 during sulfamethazine (SMZ) ozonation. In the presence of monometallic oxides modified MCM-48 catalysts, total organic carbon (TOC) removal of diclofenac sodium (DCF) was around 80%. The composite Co–Ce/MCM-48 catalyst exhibited significantly higher activity in terms of TOC removal of CA (83.6%), SMZ (51.7%) and DCF (86.8%). Co–Ce/MCM-48 inhibited efficiently the accumulation of small molecular carboxyl acids during ozonation. A detailed research was conducted to detect the nature of material structure and mechanism of catalytic ozonation by using a series of characterizations. The main reaction pathway of CA was determined by the analysis of liquid chromatography-mass spectrometry, in line with the results of frontier electron density calculations that reactive oxygen species (ROSs) were easy to attack negative regions of pharmaceuticals. The Si–O–Si, Co···HO–Si–O–Si–OH···Ce, and O3···Co–HO–Si–O–Si–OH···Ce–OH···O3 basic units in catalysts were constructed to detect the orbit-energy-level difference. The results revealed that a synergistic effect existed at the interface between cobalt and cerium oxides over MCM-48, which facilitated the ROSs sequence in solution with ozone. Therefore, the multivalence redox coupling of Ce4+/Ce3+ and Co3+/Co2+ along with electron transfer played an important role in catalytic ozonation process.

CeO2 Nanoparticle-Decorated Co3O4 Microspheres for Selective Oxidation of Ethylbenzene with Molecular Oxygen under Solvent- and Additive-Free Conditions

“…For the CeO 2 /Co 3 O 4 samples with loading levels higher than 5 wt %, other broad peaks (λ) located at higher reduction temperatures can be ascribed to the reduction of surface CeO 2 species weakly interacting with Co 3 O 4 . It should be noted that among the series of binary metal oxides, CeO 2 /Co 3 O 4 -3 with good redox property and abundant oxygen vacancies presents the lowest initiating and peak-maximum temperatures, suggesting its excellent reducibility and higher mobility of lattice oxygen . Recent studies have illustrated that catalysts with better reducibility can facilitate the generation of more easily redox species and more active oxygen species for the oxidation reactions. , …”

“…It should be noted that among the series of binary metal oxides, CeO 2 /Co 3 O 4 -3 with good redox property and abundant oxygen vacancies presents the lowest initiating and peakmaximum temperatures, suggesting its excellent reducibility and higher mobility of lattice oxygen. 53 Recent studies have illustrated that catalysts with better reducibility can facilitate the generation of more easily redox species and more active oxygen species for the oxidation reactions. 34,54 The activation of O 2 is a very crucial factor for the redox reactions.…”

Enhancement of Cobalt Concentration Supported on Mesoporous Silica towards the Characteristics and Activities of Catalysts for the Conversion of Waste Coconut Oil into Gasoline and Diesel Oil

“…The broad peak at 15° < 2θ < 30° was observed for all catalysts, corresponding to the amorphous silica phase. The broad peak intensity of Co(1)/MS, Co(2)/MS, and Co(3)/MS decreased with increasing cobalt concentration [19]. This indicates that the impregnation of metal slightly reduced the amorphous area.…”

Copper Foam-Supported CuxO@Fe2O3 Core–Shell Nanotubes: An Efficient Ozonation Catalyst for Degradation of Organic Pollutants

“…Many efforts have been focused on developing efficient and practical catalysts for HCO, and up to the present, a number of transition-metal oxides have been reported to be active toward HCO. − However, few meet the criteria for an excellent HCO catalyst: high activity, good stability, wide applicable pH range, low leaching of metal ions, easy dispersion in and separation from water, and good recyclability. Therefore, the design and synthesis of new catalysts that meet all the requirements of HCO are still a promising but challenging task.…”