Ternary systems based on ZnO/CeO2/Cu2O for the degradation of phenol and carbamazepine
Introduction
The search for new materials that work as photocatalysts is constantly evolving. In recent years, much attention has been paid to various methods for modifying the classic first generation semiconductors such as TiO2. Among the different types of material engineering, the most used are the intrinsic and extrinsic doping, the formation of solid solutions and the creation of heterojunctions at the interface between two materials that have no tendency to form solid solutions. The development of semiconductor-semiconductor composite heterojunctions for efficient photocatalytic pollutant degradation is of great interest. ZnO is one of the most abundant, cheap and non-toxic semiconductor, already employed for degradation of different pollutants [1], [2], [3].
The photocatalytic degradation process depends on various factors: the light-absorption ability of the semiconductor, which in turn depends on its surface area and morphology, optical band gap and in particular the charge separation capability [4]. The photocatalytic performances of ZnO can be improved either through doping with metals or nonmetals or via the preparation of ZnO heterostructures with other semiconductor elements [5]. Composite nanostructures of transition metal oxides are of great interest because of their tunable optical as well as catalytic properties. Recently, our and other [6], [7], [8] research groups started to investigate the role of cerium as dopant of oxides. In our approach, cerium ions are not soluble in the ZnO matrix. This composite system has shown an amazing, unexpected activity in the mineralization of acesulfame K, a so-called emerging pollutant, performed under visible light [9]. This result led us to an in-depth study of this new material. We observed that the CeO2/ZnO system is biphasic and the role of the solid−solid interface plays a crucial role in the photo-activity of the material.
Coupled semiconductors formed by ZnO and other metal oxides or sulfides (e.g., CuO, Cu2O, CdO, CuS, CdS, and ZnS) have been employed as photocatalysts, enhancing the charge carrier separation ability (electrons and holes) between adjacent semiconductors [10]. In particular, cupric and cuprous oxides (CuO and Cu2O) are nontoxic p-type metal oxide semiconductor having an optical band gap in the range from 1.2 to 2.2 eV [11]. Moreover, Cu2O is considered very interesting thanks to its relative band position with respect to the normal hydrogen electrode (NHE) (- 1.2 eV for the conduction band and +1.3 eV for the valence band). It has been demonstrated that it instigates reduction and oxidation of different pollutants via the formation of hydroxyl and superoxide radicals (with formation energies of approximately +1.23 and - 0.28 eV, respectively), which are the main reactive species in photocatalytic reactions [12]. Accordingly, addition of Cu2O to ZnO in a ZnO–Cu2O–CuO nanocomposite configuration could result in photocatalytic activity superior to that of the intrinsic ZnO semiconductor system. As it will be shown below, it is indeed the role of these interfaces (or heterojunctions) that allows a better understanding of this novel promising photocatalytic system. In the present work we prepared nanocomposite systems coupling CeO2/ZnO materials with Cu2O particle with two different synthetic methods. The preparation process influences the surface area and the crystallinity of the photocatalysts affecting also their photocatalytic properties. We tested these materials in the degradation of a classic probe molecule like phenol and of an emergent pollutant such as carbamazepine.
Section snippets
Experimental section
All reactants employed were purchased by Sigma-Aldrich and used without any further purification treatment. Distilled water was used in the synthesis procedures. Synthesis procedure will be described for each system in the following corresponding section.
The investigated samples were mainly prepared via hydrothermal and precipitation synthetic routes, described hereafter.
Structural and optical characterization
The ZnO nanoparticles synthetized via precipitation and hydrothermal methods were analysed from a structural point of view by means of X-ray powder diffraction. The structural analysis of these materials has been already well described elsewhere [2], [15], the diffrattograms have been reported in the Supporting Information section (see Fig. S1), showing the typical pattern of ZnO wurtzitic hexagonal phase (00–036–1451 ICDD pattern) [16].
The optical properties of the synthetized samples were
Conclusions
The formation of heterojunction between ZnO and CeO2 has been observed experimentally in the past, the addition of Cu2O nanoparticles on the surface of the mixed systems leads to the formation of a very active material in the abatement of phenol and carbamazepine molecules. Residual traces of Copper (II) not reduced have been evidenced by UV Vis analysis and EPR measurements. These species seem to be well dispersed over the surface of the semiconductors. The role of these species in the photo
CRediT authorship contribution statement
Erik Cerrato: Conceptualization, Data curation, investigation. Elettra Rebolini: Validation, data curation. Debora Fabbri: Supervision. Paola Calza: Resources, Supervision. Maria Cristina Paganini: Conceptualization, Supervision Writing - original draft, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
Financial support from the Italian MIUR through the PRIN Project 20179337R7, MULTI-e “Multielectron transfer for the conversion of small molecules: an enabling technology for the chemical use of renewable energy” and the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No 765860 (AQUAlity) is gratefully acknowledge-edged.
References (28)
- et al.
Investigation of charge separation in particulate oxysulfide and oxynitride photoelectrodes by surface photovoltage spectroscopy
Chem. Phys. Lett.
(2017) - et al.
ZnO/CdO composite nanorods for photocatalytic degradation of methylene blue under visible light
Mater. Chem. Phys.
(2011) - et al.
Photocatalytic degradation of bisphenol A in the presence of Ce–ZnO: Evolution of kinetics, toxicity and photodegradation mechanism
Mater. Chem. Phys.
(2016) - et al.
Effect of cerium doping on the textural, structural and optical properties of zinc oxide: role of cerium and hydrogen peroxide to enhance the photocatalytic degradation of endocrine disrupting compounds
Mater. Sci. Semicond. Process.
(2015) - et al.
Assessment of the abatement of acelsulfame K using cerium doped ZnO as photocatalyst
J. Hazard. Mater.
(2017) - et al.
Nature inspired ZnO/ZnS nanobranch-like composites, decorated with Cu(OH)(2) clusters for enhanced visible-light photocatalytic hydrogen evolution
Appl. Catal. B Environ.
(2019) - et al.
Controlled structural and compositional characteristic of visible light active ZnO/CuO photocatalyst for the degradation of organic pollutant
Appl. Surf. Sci.
(2017) - et al.
Rare earth ions doped ZnO: synthesis, characterization and preliminary photoactivity assessment
J. Solid State Chem.
(2018) - et al.
The role of Yb doped ZnO in the charge transfer process and stabilization
J. Alloys Compd.
(2020) - et al.
Enhanced photocatalytic hydrogen evolution over Pt supported on mesoporous TiO2TiO2 prepared by single-step sol–gel process with surfactant template
Int. J. Hydrog. Energy
(2006)
Copper nanoparticles: synthesis methods and its light harvesting performance
Sol. Energy Mater. Sol. Cells
Beyond TiO2: cerium-doped zinc oxide as a new photocatalyst for the photodegradation of persistent pollutants
ChemistrySelect
Origin of visible light photoactivity of the CeO2/ZnO heterojunction
ACS Appl. Energy Mater.
Two hybrid Au-ZnO heterostructures with different hierarchical structures: towards highly efficient photocatalysts
Sci. Rep.
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