CuO nanoparticles were synthesized by aqueous precipitation method and CuO doped PVA nanocomposites (1 wt, 2 wt, 3 wt, 4 wt and 5 wt) were prepared by solution casting method. The pellets of CuO nanoparticles and films of CuO doped PVA nanocomposites were used for electrical studies in the frequency range of 50 Hz to 5 MHz and in the temperature range of 303 to 338 K. The dielectric constant decreases while the AC electrical conductivity increases with increasing frequency and also with increase in temperature. XRD study confirms the crystalline nature of CuO nanoparticles and the average crystallite size is found to be around 8 nm. The peak widths in XRD pattern of PVA-CuO nanocomposites are broadened by incremental addition of CuO nanomaterials which implies an increase in the amorphous character of PVA-CuO nanocomposites that result in greater ionic diffusivity and high ionic conductivity. It is clear from UV-Vis spectral analysis that, increase in CuO concentration decreases the optical band gap from 4.978 eV to 3.03 eV. The FTIR (3700 - 650 cm -1) spectra of nanocomposite films are observed with changes by the addition of CuO nanomaterials.
Nanotechnology is rapidly evolving and expanding that has aroused growing media with public interest since from the past decade which has broad applications in many research areas, development and industrial activity. Development of new nanomaterials is a major theme of all of these programmes. It is established that inorganic addition to poly vinylalcohol (PVA) modifies its properties. This is of particular interest to science and technology and also it has many applications in modern engineering [
In semiconductor physics copper oxide is of good interest which forms two well-known stable oxides, i.e., cupric oxide (CuO) and cuprous oxide (Cu2O). These two oxides have different physical properties and electrical properties. They also differ in colors and crystal structures. The possibility of low cost production methods and the good electrochemical properties make CuO to be one of the best materials for electrical, optical, sensing and so forth. CuO nanostructures have a wide range of applications in gas- sensors [
CuO nanoparticles are synthesized by aqueous precipitation method using copper (II) acetate [Cu(CH3COO)2⋅H2O)] as parent and sodium hydroxide (NaOH) as a decreasing agent. In short, 0.2 M copper (II) acetate solution (300 ml) and glacial acetic acid (CH3COOH) (1 ml) were added to a round-bottom flask and heated to boil under magnetic stirrer. In a flask, 15 ml of 3 M NaOH solution was poured. The colour of the solution turned from blue to black immediately and a black suspension formed simultaneously. The reaction was carried out under stirring and boiling for 3 hr. The mixture was cooled to room temperature and centrifuged by which a wet CuO precipitate was obtained. The precipitate was filtered and washed with distilled water and absolute ethanol for several times. The resulting product was dried at 80˚C for 8 hr to obtain the dry powder of CuO nanoparticles. The yield of prepared CuO nanoparticles was 75%.
Pure PVA film and films doped with CuO nanoparticle at different concentrations were prepared by the solution casting method. First, the PVA stock solution was prepared and to this solution 1 wt, 2 wt, 3 wt, 4 wt and 5 wt of CuO nanoparticles was mixed and stirred vigorously by using magnetic stirrer until transparent PVA-CuO multi component dispersion was obtained. Further, ultrasonification was done for complete dispersal of CuO in PVA solution. Appropriate mixtures of PVA and CuO solution were mixed and poured on to a level clean glass plate and left to dry at room temperature for about 48 hr. The dried films were peeled off from the glass plate and cut into suitable pieces for characterization.
The AC conductivity studies and dielectric studies were carried out in the frequency range from 50 Hz to 5 MHz by using HIOKI 3532-50 LCR HITESTER Version 2.4 and in the temperature range of 303 to 338 K. The structural and morphological studies of CuO nanoparticles and CuO doped PVA nanocomposites were carried out using XRD and FTIR (3700 - 650 cm−1) analysis. The optical absorbance (A) of the samples was measured as function of wavelength (λ) ranging from (200 - 800 nm) using computerized Spectrophotometer 2080 UV-Visible instrument.
The electrical properties of PVA-CuO nanocomposites films are influenced mainly by the synthesis technique, grain size, cation distribution etc. In the present studies, dielectric and AC conductivity studies have been undertaken on the as prepared CuO nanoparticles and CuO doped PVA nanocomposites. In particular, measurement of AC conductivity studies and dielectric constant
Material’s conductivity depends on its overall characteristics such as its chemical composition, crystal structure, and purity. The continuous currents measurements provide only total conductivity. However, simultaneous data on conductivity and on the material’s electrode interface effects can be partially offset by impedance measurements. Impedance measurements are a flexible tool for electrical characterization of materials. The Ohmic contacts were made using air drying silver paint on opposite faces of the prepared nanocomposite films and measurements are taken. The measured conductance G(ω) was used to calculate the AC conductivity of the sample.
where, G(ω) is the measured conductance, A is the area of the sample and d is the thickness of the sample.
The variation of AC conductivity with frequency for pure PVA, CuO and CuO doped PVA nanocomposites is shown in
The dielectric constant is crucial parameter required in the design of electronic and
electrical devices and furthermore, as a function of temperature or frequency, they reveal much information on the chemical or physical state of the polymer [
where, C is the capacitance and
The decrease in dielectric constant with frequency can be attributed to the decrease in polarization with frequency. At very low frequencies (
X-ray diffraction (XRD) technique is used for materials characterization as it provides important information about the internal structure of matter such as crystallite size, nature of the solid sample (amorphous or crystalline), atomic spacing and crystal structure.
The sharp peaks and the crystallite size of CuO nanopowder is calculated by using Debye-Scherrer formula is as shown in the
where, k is the Scherrer constant (k = 0.9), which is related to the crystallite shape, λ and θ are the radiation wavelength and Bragg’s angle, respectively; and β is the full width at half maximum of the diffraction peak.
The peak widths in XRD pattern of PVA-CuO nanocomposites are broadened by incremental addition of CuO nanomaterials is as shown in
Peak | 2θ (degree) | d (Å) | β in degree | β in radians | Ds nm |
---|---|---|---|---|---|
1 2 | 35.25 38.37 | 2.561 2.343 | 0.99 1.06 | 0.0174 0.0185 | 8.36 7.91 |
nature of prepared CuO nanomaterials is observed by the various sharp crystalline peaks in the XRD pattern. The absence of shifting at the locations of the peak in the XRD pattern of PVA-CuO and the absence of the peaks characterizing CuO nanomaterials in all studied PVA-CuO nanocomposites indicates that incorporated CuO nanomaterials lose their structural registry and disperse into the polymer matrix, producing exfoliated nanocomposite, i.e., nano-fillers dispersed into the polymer matrix [
The optical absorption [
where hν is the photon energy, B is the constant and n is the power factor and that takes
Samples | Optical band gap (Eg) in eV |
---|---|
Pure PVA PVA + 1 wt CuO PVA + 2 wt CuO PVA + 3 wt CuO PVA + 4 wt CuO PVA + 5 wt CuO | 4.97 4.88 4.25 4.00 3.90 3.03 |
[
FTIR can be used to analyze a wide range of materials which are in bulk or thin films, liquids, solids, pastes, powders, fibers and other forms. FTIR analysis can give not only qualitative (identification) analysis of materials, but with suitable standards, can be
used for quantitative (amount) analysis. FTIR spectra were recorded for all the prepared PVA-CuO nanocomposites films at room temperature in frequency region 600 - 4000 cm−1 and the spectra is shown in
There are two absorbance bands which appear at around 650 and 3600 - 3100 cm−1 and sharp absorption band at 672.85 cm−1 is associated with Cu-O stretching mode. A broad band in the range of 3500 - 3000 cm−1 is due to the stretching in water molecules associated with CuO. FTIR result suggests the presence of Cu-O bonds and some constitutional water is incorporated in the copper oxide structure. Thus, the formation of copper oxide is confirmed from the FTIR study.
In FTIR spectra of PVA-CuO nanocomposites films, characteristic bands of PVA are observed with two significant changes by the addition of CuO nanomaterials. i.e., slight shifting in vibrational bands and slight changes in intensities of absorption bands at 1753.87 and 1656.47 cm−1. First, the vibrational bands of PVA are slightly shifted by
the addition of CuO nanomaterials. However, the values are within spectra range of pristine PVA. Secondly, structural changes in the PVA molecules due to the addition of CuO nanomaterials are observed by two remarkable changes in the intensity of absorption peaks. These are the increasing the intensity of C=O and C=C bands at 1753.87 cm−1 and 1656.47 cm−1 respectively. Such changes are possible only with a new generation of these groups.
We have prepared pellets of CuO nanoparticles and films of CuO doped PVA nanocomposites. Results of AC electrical conductivity measurements observed in this study indicates an increase of electronic conductivity and decrease of the dielectric constant with the increase in concentration of CuO (1 wt, 2 wt, 3 wt, 4 wt and 5 wt) dispersion in the PVA polymer matrix. The peak widths in XRD pattern of PVA-CuO nanocomposites are broadened by incremental addition of CuO nanomaterials indicating an increase in the amorphous character of PVA-CuO nanocomposites. This amorphous nature results in greater ionic diffusivity and high ionic conductivity. From FTIR analysis, the vibrational bands of PVA are slightly shifted by the addition of CuO nanomaterials which indicates that the considerable interaction exists between PVA matrix and CuO nanomaterials. By UV-Visible studies, the absorption spectrum reveals that the increase in concentration of CuO produces shift in the absorption peak and results in low band gap. Thus, the present study indicates that CuO dispersion tunes the optical absorption property of PVA significantly and consequently makes the PVA film more useful. The prepared PVA-CuO nanocomposites in the present study are expected to be more useful in photonic and electronic device applications.
One of the author’s (A. Manjunath) thanks University Grants Commission (UGC), New Delhi (Minor Research Project) for financial support.
Manjunath, A., Irfan, M., Anushree, K.P., Vinutha, K.M. and Yamunarani, N. (2016) Synthesis and Characterization of CuO Nanoparticles and CuO Doped PVA Nanocomposites. Advances in Materials Physics and Chemistry, 7, 263-273. http://dx.doi.org/10.4236/ampc.2016.610026