Advanced and green ozonation process for removal of clofibric acid in water system: Preparation and mechanism analysis of efficient copper-substituted MCM-48
Graphical abstract
Introduction
In the last few decades, pharmaceuticals and personal care products (PPCPs) continued to release into the aquatic environment due to growing demand, especially in the excessive medical prevention and treatment of some diseases [1]. In China, 70 pharmaceuticals were detected in the five major river watersheds from 2012 to 2013 [2]. These active pharmaceutical ingredients were usually highly persistent and negative impacts on aquatic microorganisms and human health. As the primary metabolite of clofibrate, clofibric acid (CA) of various ng/L in drinking water treatment plant was reported for a long time due to its polar character [3]. A series of reports exhibited that clofibric acid had endocrine disrupting effects in the process of cholesterol synthesis [4]. Scientists took advantage of advanced oxidation processes (AOPs) by generating highly reactive oxidizing radicals with excellent performance to remove and even mineralize these PPCPs even if they were difficult to be degraded in low concentrations [5].
Ozonation was a powerful method to remove clofibric acid and decrease the toxicity, but it had weak mineralization efficiency due to the formation of many refractory intermediates which was difficult to react with ozone. However, this shortage could be overcome by the introduction of efficient catalysts to start advanced oxidation processes (AOP). In the heterogeneous catalytic ozonation system, mineralization and toxic degradation of CA would be improved a lot because of the generation of non-selected reactive oxygen species (ROS) including hydroxyl radicals, superoxide radicals and so on [6], [7]. These highly reactive oxidizing agents were able to react instantaneously and unselectively with various organic compounds [8]. On the other hand, solid catalysts in liquid phase after reaction were cycled and reused, which prevented causing secondary pollution. Therefore, it was expected to design an optional catalyst to achieve quick degradation and mineralization of CA.
The carrier and active component of catalysts should be considered when they were prepared. This family of materials generally called M41S have gained popular in the field of catalytic ozonation, including two-dimensional hexagonal MCM-41 and three-dimensional cubic MCM-48 [9], [10], [11]. In essence, these mesoporous molecular sieves were applied as the carrier of catalysts because they possessed huge surface area and narrow pore size distribution. Moreover, MCM-48 had a gyroid minimal surface and 3D well-organized networks of channel, which favored mass transport [12]. Besides carriers, the selection of active components was also important. The previous works showed that transition metals could be active sites, like Co, Fe, Mn, and Cu, which gained wide utilization in catalytic ozonation field [13], [14], [15], [16], [17]. It was found the CuO/Cu2O, as p-type oxides, also exhibited catalytic efficiency because the redox couple (Cu2+/Cu+) could prompt the electron transfer in the process of reaction and ozone decomposition [18], [19].
Generally, the approach to modifying mesoporous molecular sieves could be classified into two categories: The first one was that active sites were loaded on the surface of carriers, generating weak chemical bond on the surface of catalyst. The second one corresponded to products with strong bond in the framework due to substitution of silicon by metal or other active components. However, metal-leaching of metal loaded catalysts caused secondary pollution. To overcome this, incorporating metal into the framework of MCM-48 became an attractive technology in the process of synthesizing catalysts in this work. Meanwhile, the doping of cooper increased lattice oxygen and generated oxygen vacancies. In turn, the oxygen vacancies enhanced mobility of lattice oxygen and improve catalytic efficiency. The DFT method was employed to study the structure mechanism of catalysts. The highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) energy gap was a simple indicator of chemical reactivity and kinetic stability [20]. The energy separation value of orbitals reflected electron transfer and catalytic capacity of catalysts. Then, role of redox couple, reactive oxygen species, and nature of acidic active sites were also investigated to learn detailed reaction mechanism about catalysts. H2O2 detection and ozone utilization efficiency were discussed to explore catalytic mechanism in the gas-solid-liquid system. Moreover, the possible reaction routes of CA were proposed with presence of Cu substituted MCM-48. Besides oxalic acid, acetic acid and humic acid, 2-hydroxyisobutiric acid was found as the main intermediates with the presence of Cu-MCM-48 during ozonation of CA.
Section snippets
Catalyst preparation
Pure MCM-48 material was synthesized via a hydrothermal method according to previous research [11]. Cu-MCM-48 was prepared with addition of 5 mL cupric nitrate solution before crystallization. The calcined powder-form samples were designated as CuX-MCM-48, and the X represents different molar ratio of Si/Cu (X = 160, 100, 60, 20). For detecting the influence of active components, cupric nitrate was also incinerated at 550 °C for 6 h to get the cupric oxide.
Experiments and analytical methods
Experiments were conducted in a 1.3 L
Characterization of different samples
The small and big angle XRD patterns of MCM-48 and Cu-MCM-48 were shown in Fig. 1(a) and (b), respectively. The small angle XRD of pure MCM-48 and Cu-MCM-48 exhibited double peaks at 2θ smaller than 3°, and some weak peaks between 3.5 and 5.5° were typical MCM-48 phase when the content of copper was little. These peaks were indexed as the (2 1 1), (2 2 0), (4 0 0), (4 2 0), (3 3 2), and (4 3 1) reflections in the cubic Ia3d space of three-dimensional MCM-48 [22]. However, with the excess
Conclusions
In this study, metal modified mesoporous molecular sieves Cu-MCM-48 were prepared, characterized, and tested for their catalytic efficiency for degradation of clofibric acid in the ozonation. The optimal Si/Cu ratio was 60 among these catalysts and CA mineralization reached to 41.1% at 60 min, Cu60-MCM-48 kept good stability in the mild acid system. The reactive oxygen species including hydroxyl radicals and superoxide radicals were examined by quenching experiments, which improved the
Acknowledgements
Authors were greatly indebted to the Science & Technology Office of Guangzhou (201607010276), the PhD Start-up Fund of Natural Science Foundation of Guangdong Province (2017A030310420) and Major Science and Technology Program for Water Pollution Control and Treatment in China (No. 2017ZX07202-004)
References (45)
- et al.
Occurrences of pharmaceuticals in drinking water sources of major river watersheds, China
Ecotox Environ. Safe
(2015) - et al.
Pharmaceuticals and personal care products (PPCPs) in surface and treated waters of Louisiana, USA and Ontario, Canada
Sci. Total Envrion.
(2003) - et al.
Ozonation and H2O2/UV treatment of clofibric acid in water: a kinetic investigation
J. Hazard Mater. B
(2003) - et al.
Catalytic ozonation and methods of enhancing molecular ozone reactions in water treatment
Appl. Catal. B
(2003) - et al.
The efficiency and mechanisms of catalytic ozonation
Appl. Catal. B
(2010) - et al.
Synthesis of cerium-doped MCM-41 for ozonation of p-chlorobenzoic acid in aqueous solution
Appl. Catal. B
(2012) - et al.
Catalytic ozonation of p-chlorobenzoic acid over MCM-41 and Fe loaded MCM-41
Chem. Eng. J.
(2012) - et al.
Heterogeneous catalytic ozonation of clofibric acid using Ce/MCM-48: preparation, reaction mechanism, comparison with Ce/MCM-41
J. Colloid Interface Sci.
(2017) - et al.
Clofibric acid degradation by catalytic ozonation using hydrotalcite-derived catalysts
Appl. Catal. B
(2014) - et al.
Mechanism for enhanced degradation of clofibric acid in aqueous by catalytic ozonation over MnOx/SBA-15
J. Hazard Mater.
(2015)
Novel magnetically separable nanomaterials for heterogeneous catalytic ozonation of phenol pollutant: NiFe2O4 and their performances
Chem. Eng. J.
Activity assessment of direct synthesized Fe-SBA-15 for catalytic ozonation of oxalic acid
Sep. Purif. Technol.
Influence of the surface hydroxyl groups of MnOx/SBA-15 on heterogeneous catalytic ozonation of oxalic acid
Chem. Eng. J.
Decomposition of ozone using carbon-supported metal oxide catalysts
Appl. Catal. B
Functionalization with amine-containing organosilane of mesoporous silica MCM-41 and MCM-48 obtained at room temperature
Ceram. Int.
Catalytic performance of Al-MCM-48 molecular sieves for isopropylation of phenol with isopropyl acetate
Chin. J. Catal.
Resolving surface chemical states in XPS analysis of first row transition metals, oxides and hydroxides: Sc, Ti, V, Cu and Zn
Appl. Surf. Sci.
Microstructural and electrical properties of CuAlO2 ceramic prepared by a novel solvent-free ester elimination process
J. Alloy Compd.
Transition metal (Cu, Cr, and V) modified MCM-41 for the catalytic wet air oxidation of aniline
Micropor. Mesopor. Mater.
Characterization of MCM-41 mesporous melocular sieves containing copper and zinc and their catalytic performance in the selective oxidation of alcohols to aldehydes
Micropor. Mesopor. Mater.
Mechanism of hydroxylation of metal oxide surfaces
J. Colloid Interface Sci.
Effect of pH on MnOx/GAC catalyzed ozonation for degradation of nitrobenzene
Water Res.
Cited by (34)
Highly dispersed copper oxide on silica: Towards an efficient catalyst for continuous glycerol dehydration to acetol
2023, Applied Catalysis A: GeneralIntensification of the photodegradation efficiency of an emergent water pollutant through process conditions optimization by means of response surface methodology
2023, Journal of Environmental ManagementCitation Excerpt :Thus, an enhancement of the mineralization rate is expected for longer irradiation time because of the transformation of these oxidized reaction intermediates into CO2 and H2O. Similar results were previously reported by Li et al. (2019) for the removal of clofibric acid by advanced ozonation. The results obtained in our study prove that TiO2/UV-A photocatalysis is a suitable process for the mineralization of CAc.
Efficient catalytic ozonation via Mn-loaded C-SiO<inf>2</inf> Framework for advanced wastewater treatment: Reactive oxygen species evolution and catalytic mechanism
2023, Science of the Total EnvironmentCitation Excerpt :Thus the binary support catalysts combine the advantages of carbonaceous catalysts and metal-based materials, and NiCAF was proven to be highly feasible in pilot tests (Wei et al., 2019). SiO2 is also regarded as a viable core material and the application of silica-based catalysts for decomposing refractory organics in HCO has bloomed in recent years due to its large specific surface area, abundant disordered pore structure and ample morphology for metal dispersion (Li et al., 2019). Still, there is a lack of investigation with different cores of binary-support catalysts such as SiO2 (Zhang et al., 2016).
Preparation of Mn-FeO<inf>X</inf>/ZSM-5 by high-gravity method for heterogeneous catalytic ozonation of nitrobenzene
2022, Journal of Cleaner Production