New Electrospun ZnO:MoO3 Nanostructures: Preparation, Characterization and Photocatalytic Performance.

Petronela Pascariu,Octavian Ionescu,Niculae Olaru,Mihaela Homocianu,Anton Airinei

doi:10.3390/nano10081476

Petronela Pascariu, Octavian Ionescu + Show 3 more

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https://doi.org/10.3390/nano10081476

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Abstract

New molybdenum trioxide-incorporated ZnO materials were prepared through the electrospinning method and then calcination at 500 °C, for 2 h. The obtained electrospun ZnO:MoO3 hybrid materials were characterized by X-ray diffraction, scanning and transmission electron microscopies, ultraviolet (UV)-diffuse reflectance, UV–visible (UV–vis) absorption, and photoluminescence techniques. It was observed that the presence of MoO3 as loading material in pure ZnO matrix induces a small blue shift in the absorption band maxima (from 382 to 371 nm) and the emission peaks are shifted to shorter wavelengths, as compared to pure ZnO. Also, a slight decrease in the optical band gap energy of ZnO:MoO3 was registered after MoO3 incorporation. The photocatalytic performance of pure ZnO and ZnO:MoO3 was assessed in the degradation of rhodamine B (RhB) dye with an initial concentration of 5 mg/L, under visible light irradiation. A doubling of the degradation efficiency of the ZnO:MoO3 sample (3.26% of the atomic molar ratio of Mo/Zn) as compared to pure ZnO was obtained. The values of the reaction rate constants were found to be 0.0480 h−1 for ZnO, and 0.1072 h−1 for ZnO:MoO3, respectively.

Highlights

Many efforts are being made worldwide to develop new high-performance photocatalytic materials for energy and environmental applications
From the linear plots of ln(C/C0) versus the irradiation time, having a good correlation with the pseudo-first order reaction kinetics (R2 > 0.99), the values of the reaction rate constants were calculated and were found to be: k1 = 0.0480 h−1 (ZnO) and k2 = 0.1072 h−1 (ZnO:MoO3 (S5)), respectively. These results show that after doping with 3.26% molar ratio Mo/Zn, the value of the reaction rate constant increases significantly, doubling its value (k2 = 2 × k1), as compared to that obtained for pure zinc oxide (ZnO)
The X-ray Diffraction (XRD) diffractograms confirmed the hexagonal wurtzite-type structure for pure ZnO, the orthorhombic crystalline structure obtained for MoO3, and a combination of these structures for the ZnO:MoO3 (S5) composite nanostructure

Summary

Introduction

Many efforts are being made worldwide to develop new high-performance photocatalytic materials for energy and environmental applications. Metal oxide semiconductor materials in various shapes and structures, including ZnO, TiO2, CuO, and MgO, have proven to be a good alternative for the degradation of various organic dyes. It is known that ZnO is an oxide semiconductor having a broad direct band gap (3.37 eV), high excitation binding energy (60 meV), and good electrical, mechanical, and optical and photocatalytic properties, comparable to those of TiO2. Molybdenum trioxide (MoO3) is a very interesting transition metal oxide having a wide band gap energy of about 3 eV, distinctive optical properties, and highly visible-light photocatalytic activity [5,6]. The synthesis of ZnO-MoO3 nanostructures (especially by the electrospinning method) and their detailed properties after being incorporated into the ZnO matrix are less reported compared to other semiconductor oxides, such as SnO2, ZnO, TiO2 and In2O3 [7,8]. Similar systems have been obtained by other methods, such as coating of MoO3 altered ZnO, by surface metal impregnation [12], ZnO@MoO3 core/shell nanocables by the electrodeposited method [13], and 1D/1D ZnO@h-MoO3 synthesized via the solid state impregnation-calcination method [14]

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