Elsevier

Applied Surface Science

Volume 489, 30 September 2019, Pages 34-43
Applied Surface Science

Full length article
Analysis of the morphology, structure and optical properties of 1D SiO2 nanostructures obtained with sol-gel and electrospinning methods

https://doi.org/10.1016/j.apsusc.2019.05.090Get rights and content

Highlights

  • The PVP/SiO2 composite nanofibers and SiO2 nanowires obtained using the electrospinning and sol-gel methods

  • The effect of process parameters on their morphology was investigated

  • The effect of share of precursors and process parameters on their optical properties were investigated

Abstract

The aim of the study was the production of ceramic SiO2 nanowires using the sol-gel and electrospinning methods from a PVP/TEOS/AcOH/EtOH solution. The obtained fibrous mats underwent preliminary drying at room temperature. Then, they were subjected to the calcination process in air to obtain pure amorphous silicon dioxide nanowires. A scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS) was used in order to carry out an analysis of the morphology and chemical composition of the resulting nanowires. A high-resolution transmission electron microscope (TEM) was used along with X-ray diffraction analysis (XRD) in order to analyse the structure of the obtained materials. Besides, thermogravimetric analysis (TGA) was performed to show polymer concentration loss in the function of temperature in the obtained two types of PVP/SiO2 nanofibers. The analysis of the optical properties and the energy band gap of the prepared nanowires was determined by spectral analysis using a UV–Vis spectrophotometer. Using the method proposed by the authors and the recorded absorbance spectra determined the banded refractive index n, real n′ and imaginary k part of the refractive index as a function of the wavelength, complex dielectric constant ε, real and imaginary part εr and εi of the dielectric constant as a function of the wavelength of the SiO2 nanowires. The obtained results, which were as follows: energy band gap of 3.93–3.97 eV, complex refractive index coefficient values of 1.52–1.65 and dielectric constant in the range of 2.30–2.73, suggest the possibility to control the morphology and optical properties of the produced nanomaterial.

Introduction

Most likely, the first paper describing the possibilities of obtaining silicon oxide nanofibers with the use of sol-gel and electrospinning methods, was a paper published in 2002 [1]. Its authors, as a base for spinning solution, used 10% solution of poly(vinyl alcohol) in water, to which they added a mixture of tetraethyl orthosilicate (TEOS, which is a precursor of SiO2), (ortho)phosphoric acid (H3PO4) and water, in molar proportions of, respectively, TEOS: H3PO4:H2O 1:0.01:11. Heating of the obtained PVA/SiO2 fibrous mats at temperatures in the range of 400–800 °C for 10 h, contributed to obtaining — irrespective of the employed calcination temperature — one-dimensional, amorphous silicon oxide nanomaterials, with diameters in the range of 200–300 nm.

Results of subsequent studies on obtaining silicon oxide nanofibers with the electrospinning method were published in professional literature only six years later, i.e. in 2008. Chinese research team presented in their paper [2] a method of obtaining mesoporous SiO2 nanofibers from a mixture of tetraethyl orthosilicate, polyvinylpyrrolidone, ethanol, symmetric triblock copolymer Pluronic P123 (H(C2H5O)20(C3H7O)70(C2H5O)OH), ethanol and hydrochloric acid (HCl). The solution was prepared, when 1.5 g of TEOS, 0.5 g of P123 and 1.18 g of PVP were added to 10 ml of ethanol. In order to evoke hydrolysis reaction of TEOS, to the solution prepared in such a way, 0.1 g of hydrochloric acid was added.

In 2009 Wei Shi, et al., presented in their paper [3] a process of obtaining and analysis of photoelectric properties of composite silicon oxide nanofibers, featuring in their volume an evenly dispersed nanoparticles of gold. In this case, the spinning solution was prepared in the form of mixture of TESO, EtOH, H2O and HCl in molar ratio of 2:3:4:5. To a solution prepared in such a way, a polymer solution of PVP/Au nanoparticles/20 ml of EtOH was added in the volume corresponding to molar concentration of 0.8, 1 and 4% in relation to the total solution mass. Also in 2009, Chinese research team from Northeast Normal University presented their method of obtaining and analysis of morphology and structure of composite SiO2/NiO nanofibers with mass relation of particular oxides of 2.33:1 [4]. A year later, a research team of Chinese and US scientists, being the first in the world, presented a paper in Web of Science, in which they proposed a method of obtaining SiO2 nanofibers containing nanoparticles of the same phase [5]. In order to obtain SiO2 nanofibers/SiO2 nanoparticle, three mixtures were prepared: 1.4 g of polyvinylpyrrolidone dissolved in 5 g of N,N‑dimethylformamide with an admixture of 2.5 g of dimethyl sulfoxide (DMSO), 1.5 g of TEOS mixed with 0.6 ml of hydrochloric acid (with weight concentration of 37%) and 0.4 ml of ethanol and SiO2 particles added to 2 ml of ethanol.

The three above solutions were mixed together and formed spinning materials, in which resultant concentration of nanoparticles in relation to final solution mass was, respectively, 0; 1.47; 2.90 and 4.29%. The studied SiO2/SiO2 nanofibers featured diameters in the range of 500 nm–2.5 μm. Authors of the paper indicated future possibilities of silicon oxide nanofibers in stomatological applications.

Another publication in the field of silicon oxide fiber obtainment with the use of sol-gel and electrospinning methods was published in WOS database only after three years, i.e. in 2013. International team of researchers, led by S. S. Batool, consisting in employees of Linköping University and Pakistan Institute of Engineering and Applied Sciences, constructed a relative humidity impedance detector on the bas of SiO2 nanofibers obtained with the use of electrospinning method [6]. In order to obtain nanometric silicon oxide two solutions were employed: 13% mixture of PVP and ethanol and 13% mixture of TEOS in citric acid. Combination of the two mentioned mixtures with ratio of VP/EtOH:TEOS/AcOH = 1:15 constituted a final form of spinning solution. Ceramic silicon oxide nanofibers, obtained with the above-described recipe, featured length of 100 μm and diameter in the range of 150–200 nm. The constructed relative humidity detector, in which the obtained fibres were used, featured high sensitivity, prompt reaction to external factor, good stability and measurement repeatability.

In 2014, a team consisting of scientists from Soochow University and King Saud University confirmed that sensory capabilities of sensors based on silicon oxide fibres may be greatly enhanced through enhancement of porosity of electrospun nanofibers [7]. To this end, three mixtures were prepared, containing polymer solutions consisting in 2.5 g of PVP dissolved in 15 ml of ethanol, to which 3 g of TEOS and 1 ml AcOH were added. To mixtures prepared in such a way, polystyrene nanoparticles ((C8H8)n, PSNs), dispersed in a mixture of deionized water and ethanol (in the form of three different solutions containing, by weight, 7, 14 and 21%) were added. This way, final three spinning solutions were obtained, PVP/EtOH/H2O/AcOH/TEOS/PSNs, with a ratio of TEOS precursor to polystyrene naoparticles amounting to, respectively, 1:1, 1:2 and 1:3. SEM images analysis of the obtained materials, conducted on the basis of at least a hundredfold repeated measurement — both of external diameter of nanoparticles and the obtained pores — proved that diameters of fibres were falling within the range of 500–700 nm.

In 2015, an international team of researchers, led by Xue Zong, and consisting of employees of Jiangnan University, University of Science and Technology of China and South Dakota School of Mines and Technology published a paper [8], in which they described a method of obtaining and properties of electrospun composite SiO2 nanofibers containing eutectic mixtures of fatty acids, which may be used as a material for obtaining and storing thermal energy.

A year later, a team of researchers from Amrita University published a paper [9], in which they presented the possibility of using electrospun silicon oxide fibres for binding proteins/DNA. Studies conducted by the authors indicated that one-dimensional SiO2 nanomaterials, obtained with the method of electrospinning of PVP/TEOS/EtOH, may be used for efficient binding of plasmid DNA and BSA (cattle serum albumin). Additionally, electrospun silicon oxide mats are easier to be obtained in comparison to the currently utilised SiO2 nanoparticles, which during obtainment process require hazardous reagents and are much more difficult to be synthesized.

In 2017, a Japanese team from Kagoshima University, being the first in the world, presented two methods of obtaining elastic and conductive composite materials on the basis of electrospun silicon oxide nanofibers and indium tin oxide (ITO) [10]. The prepared SiO2/ITO mats were successfully used as thermally stable, light substrate for production of working electrodes in dye-sensitized solar cell (DSSC). However, efficiency of the cells was lower than the efficiency of conventional DSSCs, produced on FTO/glass substrate.

Within the frames of this elaboration, a broad study of professional literature conducted by us proved that, as of now, there was no attempt to describe an influence of an amount of TEOS precursor in the spinning solution onto morphology, structure and optical properties of one-dimensional SiO2 nanomaterials, obtained with concurrent retention of constant parameters of the electrospinning and calcination process.

Taking into account the above, the aim of this paper is to present an influence of silicon oxide precursor amount in electrospinning solution onto the structure, morphology and chemical content of one-dimensional SiO2 nanostructures obtained with the use of sol-gel and electrospinning methods. Additionally, the paper covers detailed analysis of optical properties of the obtained ceramic nanoparticles, e.g.: energy band gap, refraction of light coefficient and dielectric constant.

Section snippets

Materials

For the preparation of spinning solutions, the following were used: poly(vinylpyrrolidone) (PVP, purity 99%, Mw = 1,300,000 g/mol), ethanol (EtOH, purity 99.8%), acetic acid (AcOH, purity 99.8%) and tetraethyl orthosilicate (TEOS, purity 99%). Ethyl alcohol was provided by Avantor Performance Materials Poland, the remaining reagents and polymer were purchased from Sigma-Aldrich.

Methodology

In the first stage of preparing the spinning solutions, the same two 10% (weight) mixtures of polymer in ethanol were

Analysis of the structure, morphology and chemical composition

An analysis of the morphology and structure of nanofibers prior to the calcination process demonstrated that PVP/SiO2 fibres (Fig. 1a, c – EDS spectra) obtained both from the first spinning solution containing 1 ml of TEOS (Fig. 1a) as well as the fibres with four times the amount of precursor (Fig. 1c) are devoid of structural defects and have a constant diameter along the entire length. This fact testifies to the high viscosity of the manufactured solutions resulting from a uniform dispersion

Conclusions

In the present work, a manufacturing methodology of amorphous SiO2 dielectric nanowires, was described. To obtain one dimensional SiO2 nanostructures, coupling of two method – sol-gel and electrospinning from polymer solution was used. The first step was to obtain thin fibrous PVP/SiO2 mats (Fig. 1a, c – EDS spectra), using an electrospinning method from two spinning solutions that were based on 10% mixture of PVP in ethanol, to which a mixture of AcOH/TEOS precursors in volume ratios of 3:1

Acknowledgements

The research presented in this article was financed by the National Science Centre, Poland based on the decision number 2016/23/B/ST8/02045.

Moreover publication was supported as a part of the Rector's grant in the area of scientific research and development works. Silesian University of Technology, grant no. 10/010/RGJ19/0265 and 10/010/RGJ19/0264.

References (24)

  • S. Wen et al.

    Hierarchical electrospun SiO 2 nanofibers containing SiO 2 nanoparticles with controllable surface-roughness and/or porosity

    Mater. Lett.

    (2010)
  • C. Shao et al.

    A novel method for making silica nanofibres by using electrospun fibres of polyvinylalcohol/silica composite as precursor

    Nanotechnology

    (2002)
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