Synthesis of Blend Polymer (PVA / PANI)/Copper (1) Oxide Nanocomposite: Thermal Analysis and UV-Vis Spectra Specifications

Copper (1) oxide nanoparticles together with matrix polymers of polyvinyl alcohol (PVA) and polyaniline (PANI) composite films were synthesized, as these materials are of importance in optoelectronic applications. ‎Nanoparticles of Cu2O were produced by chemical precipitation. Polymerization of aniline was carried out through polymerization in an acidic medium. Structural, thermal, and optical properties of PVA+PANI/Cu2O nanocomposite were inspected by x-ray diffraction (XRD), scanning electron microscopy (SEM), fourier-transform infrared (FTIR), differential scanning calorimeter (DSC) and ultraviolet-visible spectroscopy (UVVis spectroscopy). X-ray diffraction peaks at 29.53°, 36.34°, and 42.22° indicated the presence of cuprous oxide nanoparticles, having high dispersions and limited size distributions. The estimated average size of Cu2O nanoparticles was ~ 17.1525 nm. A characteristic‎peak‎at‎around‎2θ‎=‎18.5°‎was attributed to periodical parallel and perpendicular polymer chains, which denoted the formation of PANI. SEM results indicated the symmetrical dispersion of Cu2O nanoparticles inside the hybrid polymer of PVA and PANI matrix, being potentially useful for encapsulation and acting as a good capping agent. FTIR results established the formation of PANI and Cu2O with nanocrystalline nature. DSC results revealed the appearance of one single peak of Tg which decreased with Cu2O content of 4% wt, followed by an increase of that value by increasing Cu2O content up to 16%wt. Thermogram analysis of the PANI and PVA embedded with Cu2O form showed an exothermic peak at (240292)°C affiliated to the cross-linking reaction, while the Tm value of prepared nanocomposites is just about close to that of PVA polymer. The results indicated that there is an increase in thermal stability due to the presence of Cu2O NPS within the matrix of polymers. The distinguishing peaks at 330, 347, and 457 nm which refer to PANI are assigned to π−π* electron transitions among the benzenoid rings. The high absorption intensity of the peak at 470 nm for the blended PVA+PANI having 12% wt of Cu2O NPS is assigned due to the inter-band transitions for electrons of the core copper as well as copper oxide. This points out that the increasing quantity of Cu2O NPs leads to increases in the amounts of highly oxidized structures in PANI and decreases in the doping electrons and length of conjugation throughout the incorporation of Cu2O NPs into PANI matrix. Depending on the practical results, it can be said that these polymeric nanocomposites can be efficiently used in photovoltaic technology applications.


Introduction
Cuprous oxide is a natural p-type semiconductor that is not -noxious and highly plentiful in the crust of the earth. It has a great coefficient of absorption which extends from the violet to green solar spectra, which enables it to convert solar energy to electrical or chemical energy. Cu 2 O is considered as one of the most attractive inorganic systems with a wide range of applications in gas detecting, CO oxidation, photocatalysis, photochemical evolution of H 2 from water, and photocurrent generation [1][2][3]. Cu 2 O nanoparticles can be produced by various processes, such as electrodeposition, chemical method, thermal relaxation, liquidphase reduction, evaporation in vacuum, and green combination. Nanostructures with conducting polymers, like PANI and polypyrrole, along with their nano -dimensional composites, appeared as an attractive field of research that can lead to creating novel materials for recent technologies. The nano-dimensional condition of metal oxide/polymer composites reveals improved electrical and magnetic properties compared with primeval metal oxide and conduction polymers. In addition , these composites exhibit high stability in the air, chemistry, and electricity mediums, for example, transistors (field effect), as well as their ease of production [4,5]. The carriers of charge for the PANI are mostly regarded to be polarons and bipolarons, which are steadied by counter ions combined into the polymer during the preparation. Conductive polymers have lately become an area of widespread attention in the field of organic electronics due to their potential practical application in energy conversion designs such as photovoltaic and solar cells, biosensors, and others [6,7]. They also have a wide array of electrical properties which can make them easily well-ordered by changing their

Al-Khafaji
Iraqi Journal of Science, 2021, Vol. 62, No. 11, pp: 3888-3900 3890 states of oxidation and protonation [8][9][10]. However, the main difficulty related to the successful utilization of PANI is its poor mechanical solubility within aqueous and organic solvents. Enhancement of polyaniline properties can be accomplished either by developing composites and nanocomposites for aniline or blending them with polymers or inorganic materials which exhibit better mechanical and optical properties, along with the stability in the handling of PANI [11,12]. Polyvinyl alcohol (PVA) insulating polymer is acknowledged as a water-soluble and crystalline vinyl polymer within hydroxyl (-OH) groups bonded to the carbon atoms in the backbone of a longchain molecule. The technique of chemical reduction is commonly used for the production of Cu 2 O NPs from Cu 2+ salts. It includes reducing Cu 2+ ions to Cu + with a reducing agent [13].
In this paper, a successful and environmentally safe pathway in preparing Cu 2 O nanoparticles is described. This pathway was achieved by chemical precipitation of NPs surrounded by a matrix of PVA and PANI which prepared through polymerization, for the synthesis of nanocomposites at room temperature. The properties of PVA+ PANI /Cu 2 O were examined by means of XRD, SEM, FTIR, DSC, and UV-Vis.

Methodology
Synthesis of inorganic nanoparticles is still a confronting task due to innate difficulties in the control of compositions and morphology. Cupric nitrate and sulfate salts and alkaline compounds (normally NaOH) are regularly utilized in the synthesis of Copper(I) oxide Cu 2 O NPS. The procedure of chemical precipitations was adopted in the present study. Briefly, copper sulphate pentahydrate (CuSO 4 . 5H 2 O; 2.5g) was dissolved in deionized water (20ml). The solution was placed inside a round -bottom flask provided with a refluxing apparatus. The CuSO 4 . 5H 2 O solution was preserved at a suitable temperature of about 100 ºC with dynamic stirring. Then, an amount of 0.8g (0.5 molL -1 ) solid NaOH (platelet) was dissolved in 50 ml deionized water and added to the 20 mL aqueous solution of CuSO 4 by continuous stirring. This resulted in the production of a large amount of blue Cu(OH) 2 precipitate which appeared instantly, where the temperature of crystallization was kept for 10 min. Then, 0.80g ascorbic acid dissolved in 40 mL of the deionized water was added drop by drop to the solution with strong stirring. Subsequently, the precipitates were heated up to 100 ºC for additional 10 min. The solution was centrifuged at 6000 rpm for 30 minutes to separate the distilled water. Then, the product was rinsed with water, followed by ethanol, several times, and dried out in the air at room temperature. The colloidal dispersion of the brown-colored Cu 2 O nanoparticles was prepared. The reaction temperature affects the size and shape of the producing cuprous oxide Cu 2 O nanoparticles. Polyaniline was prepared by following similar procedures used to oxidize 0.2 M aniline hydrochloride with 0.25 M ammonium peroxydisulfate within the aqueous middle [14]. Aniline hydrochloride purum (2.59 g, 20 mmol) was dissolved with distilled water in a volumetric flask to make a 50 mL solution. Ammonium peroxydisulfate (purum; 5.71 g, 25 mmol) was similarly dissolved in water to 50 mL. Both solutions were kept for 1 h at room temperature. Subsequently, they were mixed in a beaker, shortly stirred, and left to polymerize. After 24 h, the PANI precipitate accumulated on the filter was rinsed three times with 100 mL of 0.2 M hydrochloric acid, and similarly with acetone. Polyaniline (emeraldine) hydrochloride powder was dehydrated in the air and then in a vacuum at 60 °C. Extra polymerizations were performed in ice bath of about 0-2 °C. The acidity of the reaction mixture was raised by interchanging 10 mL of water with 10 mL of 10 M HCl in several times. PVA was dissolved utilizing distilled water in a beaker at the heating condition. Then, Cu2O NPs (0, 4, 8, 12, and 16 % wt) were added to about 15% wt of PVA and various percentages of PANI solution. Stirring was continued at a temperature of around 100 ºC for 2 h. The resulting product was cooled at room temperature and dried in a hot air oven to obtain PVA + PANI/ Cu2O nanocomposite samples. Figure 1 clarifies the sequence of this methodology. Thin films of a thickness range of 0.025-0.030 cm were tested using an X-ray diffractometer with radiation of Cu Kα (λ=1.5406 Ǻ) (Shimadzu XRD -6000). The XRD patterns were interpreted by matching the observed identical peaks with the standard pattern provided by JCPDS files. The surface morphology and particle size of the manufactured nanoparticles were examined by SEM (FEI Company, Inspect S50-Model). Moreover, FTIR spectrometer (Shimadzu IRAffinity-1S) was employed at a wavenumber range of 400-4000cm -1 to detect polymeric and some inorganic materials. The thermal transitions behavior of the prepared nanocomposite thin films was revealed by a differential scanning calorimeter (Shimadzu DSC-60) through a heating rate of 10°C/min. The optical UV-Vis spectra were verified in a range of 300 to 1100 nm using Shimadzu spectrophotometer UV-1800.

Results and Discussion
X-ray diffraction assays infer a great deal of information about the crystal structure, crystallite orientation, and size of desired regions within materials. Figure 2 displays the Xray diffraction patterns of PVA, PANI. their homopolymer blend, and their Cu 2 O/(PANI + PVA) nanocomposites at RT and scan ranges of 10° ≤ 2θ ≤ 80° and 5° ≤ 2θ ≤ 80°, respectively. X-ray diffraction pattern of PVA 85%wt and PANI 15%wt blend (sample 5) is shown in Figure (2a). Inthispattern,onemainbroadpeakappearedaroundthediffractionangleof2θ= 19.72°, corresponding to the (101) crystal plane of PVA. Also, the presence of the distinct crystalpeakat2θ=15.280°,whichisindicativeofthesemi -crystalline nature of PVA, was noticed. The crystallite nature of PVA results from the powerful intermolecular interactions between PVA chains through hydrogen bonds [13]. Besides, the XRD pattern reflects the characteristic peak around the diffraction angle 2θ = 18.5°, which can be attributed to the parallel and vertical cyclic polymer chains of PANI. The peak at about 2θ = 20° is a confirmation of the distance between individual benzene rings within adjacent chains. Thepeakcenteredaround2θ=25°canbeappointed to the scattering of the PANI chains at inter-level spacing. The peakat2θ=13.90°infers that the PANI polymer also has a certain degree of crystallinity (partial crystallization) [15,16]. It is also clear from Figure (  structure. For the semicrystalline-amorphous mixtures, the amorphous component may strongly adjust the crystallization behavior of the components. The miscibility of the amorphous components of the two homopolymers is likely. Thus, it can be suggested that the crystalline formulas in PVA do not prevent mixing between amorphous regions of polymers (conventional semi-crystalline) in blend systems [2,17].
The X-ray diffraction patterns of Cu 2 O/(PANI + PVA) nanocomposites prepared with 16% wt% were studied in Figure ( These nanoparticles revealed good crystallinity due to having sharp peaks in the XRD pattern and broadening peaks indicating that the crystallite size is small. The crystallite size of the prepared Cu 2 O nanoparticles was calculated using Scherrer's equation [18]. Crystallite size calculation by XRD is a generally accepted quantitative method in the scientific community. The average size of copper oxide nanoparticles is estimated to be around 17.1525 nm. In the XRD pattern, the locations of the peaks are in good agreement with references (JCPDS 05-0667). The XRD pattern of the PVA+PANI/Cu 2 O composite determines the diffraction of Cu 2 O nanoparticles, including discrete peaks which can be exquisitely indexed towards crystalline Cu 2 O nanoparticles. From the XRD patterns of the blend and nanocomposites, it was demonstrated that Cu 2 O remains stable in structure even though it is dispersed in PVA + PANI during the polymerization reaction. Figure (2b) shows the presence of the PANI + PVA and Cu 2 O NPS copolymers due to the appearance of peaks obtained from these materials in the nanocomposites. However, the Cu 2 O NPS peak is  The images in Figure 3a and b show 5 separate polyaniline nanoparticles that are uniformly assembled. The particles are rod-shaped, referring to a polyaniline particle of irregular morphology and high heterogeneity within the chain dimensions. The microcrystalline nature of PANI is due to partial agglomeration in the lattice structure. The images in Figure 3a/4 show well-separated, regular, spherical fly ash-shaped Cu2O NPS with an estimated average diameter ranging from 163 to 381 nm, indicating the occurrence of agglomeration. Figure (3a/4) shows Cu 2 O NPS as a good and homogeneous filler that is slowly incorporated into the composite matrix of PVA + PANI due to the strong chemical attraction of Cu and polyaniline nitrogen. Thus, the PVA + PANI polymer blend is an excellent host matrix to avoid the accumulation of copper nanoparticles and is useful for encapsulation, acting as a good covering agent and providing chemical and environmental stability [22,23]. Fourier transform infrared spectroscopy in the wave range of 400-4000 cm was applied to provide auxiliary data on the properties of each element included in the composite mixture of polyvinyl alcohol and polyaniline, along with its Cu 2 O-reinforced nanocomposites, as shown in Figure 4. appointed to the stretching mode for C=O and C=C groups in chains of the polymer. Two strong peaks at 1418 and 1340 cm −1 are recognized to CH2 and vibrations of (CH + OH) groups. Furthermore, the band at peak 1120 cm −1 is appointed to the C-O stretching mode [26,27]. The FTIR spectra of the prepared nanocomposites are shown in Figure (4b). Cu 2 O displays an absorption peak at about 622 cm−1, which determines the Cu(I)-O vibration signal that is well-matched with that of Cu 2 O reported in previous works [21]. This indicates the formation of Cu 2 O particles in the matrix network. DSC technology provides data for glass transition (T g ), melting point (T m ), crystallization temperatures (T c ), as well as specific capacitance (C p ) for each process. Figures 5 and 6 show the heat flux and specific heat curves in the temperature range from 15 °C upward to 300 °C for samples prepared with and without copper oxide nanoparticles, respectively.
The values of the transition temperature, specific heat, and fusion heat associated with each transition, obtained by DSC analysis curves for the blend and doped samples, are listed in Table 1. Sample 5 of the PVA + PANI blend shows two endothermic peaks. The first peak at 44.30 °C is assigned as a thermal effect due to moisture evaporation (water removal), the presence of impurities from the polymer blend sample, and glass transition. The second peak indicates a sharp transition due to an endothermic melting at 210.2 °C with an enthalpy of 0.431J/g. However, the acquired value of T m (210.2 °C) is in agreement with that found by Sakelariou et al. [28].

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Iraqi Journal of Science, 2021, Vol. 62, No. 11, pp: 3888-3900 3895 It is fascinating to show how the heat transfer of PVA + PANI varies after adding varying concentrations of Cu 2 O nanoparticles. It is observed that the DSC thermograms for all samples prepared from PVA+PANI and PVA+PANI/Cu 2 O show one glass transition (T g ) peak, which decreases with the increase in Cu 2 O 4% wt concentration. Then, an increase in the value of T g is observed by increasing the Cu 2 O concentration up to 16 %wt for the prepared nanocomposite samples. We note that the obtained T g values indicate the miscibility of the mixing system. The broadening of the peaks depends on the decrease in the OH content. The PVA hydroxyl groups are largely crosslinked by hydrogen bonding, resulting in maximum temperatures of glass transition (T g ), as in sample 2. The thermal graph of the blend of polyaniline and polyvinyl alcohol shows an exothermic peak at 240-280 ℃ that may be related to cross-linking reactions [29][30][31]. Another exothermic peak can be set at 292℃ which refers to sample 4 with a concentration of 16%wt of copper oxide nanoparticles, due to the cross-linking/oxidation in the backbone compound. The crosslinking in these polymers is irreversible and thus will only be detected when the polymer is first heated. Thus, based on the thermal profile of these materials, we can state that, among polyvinyl alcohol, polyaniline, and the composites of Cu 2 O nanoparticles, cross-linked or oxidative reactions start at a higher temperature than that of the composites, which indicates the stability of the PANI blend composites. The data in Table 1 point out that the melting points (T m ) for the nanocomposite samples are closely around those for the PVA and PANI polymers , indicating the miscibility of the blend system. Also, it seems that the variations in shape and area were due to the diverse degrees of crystallinity found in the samples with different concentrations of Cu2O nanoparticles. The decrease in the heat of fusion and the increase in Tm propose that the crystallinity and faultlessness structure of the crystals are decreased with increasing the degree of cross-linking. This could change the crystalline structure, which might affect polymer-polymer interaction in the amorphous phase; therefore, trouble in the crystals is created, decreasing the enthalpy (heat of fusion) for phase transitions. DSC plot of the nanocomposites showed the presence of a common sharp peak at 230.3℃. This confirms the existence of a monoclinic phase dependent on the copper ion for the oxidation state, which is attributed to Cu 2 O [32][33][34].  We observe distinct peaks at 330, 347, and 457 nm, indicating the -* transition of PANI which is attributed to the benzenoid ring related to the extent of coupling between adjacent phenylene rings in the polymeric chains and the system caused by the accumulation. This leads to increased coupling and thus reduced bandgap. The * benzenoid ring transition and polaron band formation are responsible for the increased electric conductance of the nanocomposites. The intense band decrease at about 300 nm might be due to the n − * transition. The peaks at 400, 420, and 435 nm could be attributed to the polaron -* transition as well as the electron transition from the benzenoid ring to the quinonoid ring [10].
The absorption peaks of the low concentration (4% wt) Cu 2 O NPS nanocomposite in figure-(7a) show a blue shift towards PANI with weak adsorption intensity for Cu 2 O. This indicates the formation of the Cu 2 O/PANI nanocomposite due to the incorporation of the Cu 2 O content into the PANI matrix. In figure-(7c), which is dedicated for nanocomposite sample 3 of PVA + PANI blended with 12 wt% Cu 2 O NPS, we observe a high peak of absorption intensity due to electrons between the inter-band transitions of Cu core and Cu oxide. Increasing the amount of Cu 2 O NPS content leads to the severe change of the characteristic peaks of PANI and the absorption peaks of Cu 2 O NPS in the nanocomposites. This indicates that the increasing amount of Cu 2 O NPS increases the amount of highly oxidized structures in PANI [8][9][10]. Figure -7 shows the absorption peaks of high intensity with the blue shift of polyaniline from the positions of the regular peaks, indicating that the addition of Cu 2 O nanoparticles as a filler in the polyaniline and polyvinyl alcohol matrix affects the absorption spectra of the prepared nanocomposites. The less intense absorption peaks are due to Cu 2 O within the nanocomposite, which indicates the interactions between Cu 2 O within the polyaniline and thus shows the polaron construction as well as the charges bipolaron carrier in the nanocomposite [13][14][15]. As stated previously by several researchers, doped composites of PANI polymer regularly display three characteristic absorption bands at ranges of 320−360, 400−450, and 740−950 nm [2,35]. Firstly, the absorbance band develops from π−π*, indicating the electron transitions within the benzenoid section. Secondly and third absorbance bands are connected to the doping levels and the construction of polarons (segments of quinoid ), one by one. For the absorption spectra of PANI +PVA/Cu 2 O samples, a shoulder is centered at around 300nm, and a broadening band is centered at 450 nm. In the visible absorption range, the PVA + PANI/Cu 2 O nanocomposites also have a strong absorption at the wavelength of 591 nm. It should be noted that, in the visible spectra, the morphology, size, and crystallinity of the prepared nanoparticles affect the locations of the resulting optical absorption peaks. Since PVA is a preferred hydrophilic and environmentally-safe polymer, it was selected as a stabilization and dispersion matrix to build a stable Cu 2 O polymer composite structure. It is shown that the introduction of Cu 2 O nanoparticles affects the doping of conductive polyaniline. This effect leads to the interfacial reaction of polyaniline and Cu 2 O NPS. The extinction coefficient designates the properties of a material exposed to light of a given wavelength. It also indicates the absorption variations when an electromagnetic wave propagates through the material. Figure -8 exhibits the extinction coefficient (k) values (k = αλ / 4π), correlated with the absorption coefficient. It can be seen that a high peak of extinction coefficient (k) (0.00047) is reached at 470 nm in the prepared sample 3, with 12% wt of Cu 2 O NPS, which possesses a high adsorption coefficient as explained above.

Conclusions
A novel, simple, and time-and cost-effective method was developed for preparing thick films of polyvinyl alcohol and polyaniline composites supported by cuprous oxide nanoparticles. Cu 2 O nanoparticles were prepared by chemical precipitation and chemical polymerization methods. Aniline was polymerized in the acidic medium at RT. The structural, thermal, and optical properties of the PVA + PANI/Cu 2 O nanocomposites were investigated by XRD, SEM, FTIR, DSC and UV-Vis spectra. The results showed that the prepared Cu 2 O nanoparticles have a highly uniform dispersion and limited size distributions within the nanoscale. The differential scanning calorimeter analysis displayed a single glass transition peak. The melting point values of the nanocomposite samples are very close to those of PVA. Thermal investigation indicated that there is an increase in thermal stability due to the presence of Cu 2 O NPS within the matrix of polymers, compared to that of pure polymers ,i.e thermal degradation happen at higher temperatures. The high absorption intensity peak at 470 nm appeared in the nanocomposite sample 3 due to the inter-band transitions of the Cu core electrons and Cu oxide. This indicates that increasing the amount of Cu 2 O NPS leads to an increase in the quantity of the highly-oxidized structures in PANI and a decrease in the doping electrons and coupling length during the incorporation of Cu 2 O NPS into the PANI matrix.