Elsevier

Applied Surface Science

Volume 258, Issue 8, 1 February 2012, Pages 3789-3794
Applied Surface Science

Fabrication and characterization of electrospun orthorhombic InVO4 nanofibers

https://doi.org/10.1016/j.apsusc.2011.12.029Get rights and content

Abstract

The novel orthorhombic InVO4 nanofibers have been successfully synthesized by annealing electrospun precursor fibers. Citric acid was used as a ligand for it could react with metal salts to get a transparent homogeneous precursor solution and homogeneous precursor sol for electrospining. Polyvinyl pyrrolidone (PVP, K-30) was used as a binder and a structure guide reagent because it was one kind of water-soluble polymers. It is easy to gain one-dimensional materials while the viscosity of the citrate/PVP sol was suitable. The structure, morphology and photocatalytic properties of the nanofibers were characterized by X-ray diffraction (XRD), thermogravimetry analysis (TGA), scanning electron microscopy (SEM) analysis, UV–vis spectrophotometer and fluorescence spectrophotometer. The nanofibers calcined at 700 °C were orthorhombic InVO4 with a width in the range of 30–100 nm and length in micron-grade. This one-dimensional pure orthorhombic InVO4 had the higher photocatalytic activity under visible light irradiation. The photo-degradation rate of nitrobenzene aqueous solution under visible light reached 69% after 6 h. It is obvious that the orthorhombic InVO4 nanofibers have a potential application in wastewater-treatment.

Graphical abstract

In this paper, citric acid was used as a ligand for getting a transparent homogeneous precursor solution and further ensured homogeneous precursor sol for electrospining. Polyvinyl pyrrolidone (PVP, K-30) was used as a binder and a structure guide reagent because it could form one-dimensional structure in the electrospinning process if the viscosity of the sol was suitable. Finally, the novel orthorhombic InVO4 nanofibers were prepared successfully by annealing electrospun precursor fibers at 700 °C. Photocatalytic experiment on methyl orange solution under visible light showed that orthorhombic InVO4 nanofibers had a potential application in wastewater-treatment.

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Highlights

► In this paper, orthorhombic InVO4 nanofibers were successfully prepared by annealing the electrospun precursor fibers. ► Citric acid was used as a ligand, it could react with metal salts to get a clear homogeneous precursor solution. ► PVP (K-30), one kind of water-soluble polymers, was used as a binder. Meanwhile, PVP was used as a structure guide reagent.

Introduction

Nowadays, InVO4 has become a promising photo-catalyst with a narrow band gap (Eg = 2.0 eV), which is able to induce hydrolysis of water molecules under visible-light irradiation [1], [2], [3]. InVO4 belongs to a large family of orthovanadate compounds with a general formula M3+VO4 (M3+ = In, Fe, Cr, Al, rare earths) [4], [5] which has two phases: the stable high-temperature orthorhombic InVO4-III (Cmcm) phase and low-temperature metastable monoclinic InVO4-I phase [6], [7]. The structure of InVO4 is composed of chains of the InO6 octahedral linked together by the VO4 tetrahedral [8], and the only difference is that the structure of monoclinic InVO4-I phase consists of compact In4O16 which groups of four edge-shared InO6 octahedra linked to each other by VO4 tetrahedra and the orthorhombic InVO4 is composed of chains of InO6 octahedra which are linked together by VO4 tetrahedra [9]. As a new type of semiconductor, orthorhombic InVO4 has also attracted considerable interests for its special photocatalytic properties [4], [10].

One-dimensional nanostructures, such as nanowires, nanofibers, and nanobelts are expected to play an important role due to their potential applications in nanodevices. Various one-dimensional nanostructured materials have been fabricated by a variety of methods, including templating direction [11], solid-state reaction method [12], hydrothermal treatment [13], etc. Besides, electrospinning is a unique fiber spinning process because it can make fibers with a diameter of 50–500 nm [14]. Single-crystalline InVO4 nanotubes produced by annealing electrospun precursor fibers have been first reported by Yi and Li [15]. To the best of our knowledge, other morphological InVO4 nano-products synthesized by electrospinning technology have not been reported. So, it is very interesting and essential to prepare the InVO4 nanoscale one-dimensional materials via the electrospinning route.

In the present work, the electrospinning technique was used to prepare citrate/PVP composite fibers. Orthorhombic InVO4 nanofibers were obtained by calcining the precursor nanofibers above 700 °C.

Section snippets

Synthesis procedure

NH4VO3 (99.0%) was bought from Shanghai Chemical Reagent Co. Ltd., ethanol of analytical grade was bought from Tianjin Guangcheng Chemical Reagent Co. Ltd. In(NO3)3·4.5H2O with a purity of 99.5% and Polyvinyl pyrrolidone (PVP (K-30), Mw = 4.0 × 104) were purchased from Sinopharm Chemical Reagent Co. Ltd.

A schematic of the electrospinning process is shown in Fig. 1. In a typical experiment for the preparation of the electrospinning solution, 2 mmol In(NO3)3·4.5H2O was dissolved into 10 mL distilled

TG analysis

Fig. 2 shows the typical thermal behavior of the precursor composite nanofibers. The TG curve indicates four different weight loss steps with the increase of temperature in the whole combustion process. The first weight loss (∼16.48%) occurred before 190 °C was mostly attributed to the gradual evaporation of free water and crystal water. The region from 190 to 265 °C with a continuously small weight loss of 5.27% could be ascribed to the decomposition and the complete combustion of nitrate

Conclusion

In summary, the electrospinning method combining with annealing treatment was found to be an effective method for synthesizing InVO4 nanofibers in this work. After calcined the electrospun PVP-precursor nanofibers at 700 °C, orthorhombic InVO4 fibers were obtained. The low ordering ability of the fibers could be attributed to the random stacking of the fiber. The PL spectra proved that the active species in the photocatalytic process were radical dotOH radicals. The UV–vis diffuse reflection spectra

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant No. 50872076 and No. 51172113), the Ministry of Education of Shandong Province (Grant No. J09LD23) and the Key Project of Chinese Ministry of Education (Grant No. 211098). The authors also thank the Analytical Center of Shandong Polytechnic University for the technological support.

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