Gama-Fe2O3 silica-coated 2-(2-benzothiazolyl azo)-4-methoxyaniline for supercapacitive performance http://dx.doi.org/10.5599/jese.1657 521 J. Electrochem. Sci. Eng. 13(3) (2023) 521-536; http://dx.doi.org/10.5599/jese.1657 Open Access : : ISSN 1847-9286 www.jESE-online.org Original scientific paper -Fe2O3 silica-coated 2-(2-benzothiazolyl azo)-4-methoxyaniline for supercapacitive performance Jinan Mohammed Mahmood1, Zaid H. Mahmoud1,, Noor Sabah Al-Obaidi 1 and Ahmed M. Rahima2 1Chemistry Department, College of Science, Diyala University, Iraq 2Chemistry Department, College of Science, Mustansiriyah University, Iraq Corresponding author: zaidhameed_91@yahoo.com Received: December 30, 2022; Accepted: January 30, 2023; Published: February 6, 2023 Abstract Magnetic -Fe2O3@SiO2 core-shell nanocomposite was prepared using Stöber method and functionalized firstly by isopropenyloxytrimethylsilane as a coupling agent to enter active acetylacetone on the surface of nanoparticles, and after that by the synthesized azo dye ligand, 2-(2-benzothiazolyl azo)-4-methoxyaniline. In such a way, -Fe2O3@SiO2-azo dye hybrid nanocomposite was formed. The structure of the synthesized azo dye was evidenced by physical and chemical analysis using melting point, Fourier-transform infrared spectroscopy (FT-IR), CHNS elemental analysis, proton nuclear magnetic resonance (HNMR) and gas chromatography mass spectrometry (GC-MS). The magnetic properties, structure, element composition and morphology characterization of prepared materials (-Fe2O3, -Fe2O3@SiO2, and -Fe2O3@SiO2-azo dye) were investigated by vibrating sample magnetometer (VSM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron spectroscopy (TEM) and field electron scanning electron microscopy- energy dispersive X-ray-mapping techniques. The electrochemical performance of synthe- sized -Fe2O3, -Fe2O3@SiO2, and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline) electrodes were carried out using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). It was shown that the finally prepared -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline) hybrid nanocomposite electrode possesses good storage charge capability of 580 F g-1 at 1 A g-1. Keywords Hybrid nanocomposite; maghemite nanoparticles; azo dye ligand; supercapacitor elec- trode; coatings Introduction Supercapacitor (SC) is a storage energy device with long cycle life, high power density and fast recharge capability, but in spite of many advantages, SCs still suffer from the low density of energy http://dx.doi.org/10.5599/jese.1657 http://dx.doi.org/10.5599/jese.1657 http://www.jese-online.org/ mailto:zaidhameed_91@yahoo.com J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 SUPERCAPACITIVE PROPETIES OF -Fe2O3@SiO2-AZO DYE HYBRID 522 before they could have authentic electric applications [1,2]. SC is composed of two electrodes (anode and cathode), membrane and electrolyte solution. Different metal oxides, sulfides [3], hydroxides [4], and metal complexes [5] have already been studied as electrode materials to improve the capacitance of SC. In order to attain high efficiency, two electrodes should store the energy or charges equally, which means that if one electrode stores charge more than the other, it will cause a difference in the charge balance of the electrodes of SC [6]. Maghemite phase (-Fe2O3) is a one of the auspicious electrode materials because of its natural abundance and large specific capacitance [7,8]. The electrochemical behavior of iron oxide [9] and iron oxide coated by SiO2 have already been examined, but without reporting their supercapacitance or electrochemical performance [10-12]. However, their chemical stability, good theoretical capaci- tance and low cost have resulted in protracted studies targeted to improve the electrochemical properties of iron oxides. The studies reported that as high as 207 F g-1 specific capacitance for iron oxide prepared from ultrasonic method [13]. We believe that incorporating of -Fe2O3 with ligand compounds nanocomposite may be an effective method to enhance electrochemical properties and performance [14,15]. So, the maghemite/ligand hybrid nanocomposite will be more committing elec- trode for supercapacitor than pure maghemite. In this paper, we report the synthesis of azo dye on the surface of silica-coated magnetic maghemite nanoparticles incorporated with 2-(2-benzothiazolyl azo)-4-methoxyaniline ligand as new nanomagnetic electrodes for supercapacitor applications. Experimental Materials In this work, the reagents and solvent were purchased from Fisher Scientific and Sigma-Aldrich with 98 % purity, while other chemical materials were supplied from Fluka. All chemicals were used without purification. Preparation of azo dye ligand A mixture (10 ml ethanol, 2 ml conc. HCl) has been used to melt of (0.335 g, 1 mM) of 2-amino- benzothiazole, and diazotized with 10 % solution of NaNO2 at 5 °C. The mixture was added gradually with stirring to cool ethanolic solution (0.307 g, 1 mM) of 4-methoxyaniline. After that, 25 ml of 1 M NaOH solution was added to the colored mix and azo ligand was precipitated, filtrated and washed various times with (1:1) C2H5OH: H2O, and left to dry. The reaction is shown in Scheme 1. Some other physical characteristics of the synthesized azo-dye are summarized as follows. Color: deep brown. M.P. = 300 °C >. 1H NMR (400 MHz, DMSO-d6):  = 7.00-7.857 (m, 6H), 7.908 (s, 2H) (NH2), 3.426 (s, 3H) (OCH3). IR (cm-1):  (N-H) = 3387-3441,  (C=N) = 1604,  (C=C) = 1504,  (N=N) = 1535 and 1568, as,s CH3 = 1404 and 1387, 1309. max = 240, 354 and 412 nm. Elemental analysis calculated: C 58.92 %, H 3.92 %, N 18.98 %, O 4.98 %, S 10.92 %. Preparation of magnetic -Fe2O3 nanoparticles Potassium ferric oxalate K3[Fe(C2O4)3]3H2O was used as a source for synthesis of -Fe2O3 nanopar- ticles by photolysis method [16-18]. In a 125 W irradiation system, 1 g of ferric complex solution was irradiated for 30 min until a yellow precipitate of ferrous oxalate was formed. The precipitate was decanted, washed with distilled water and dried at 80 °C for 4 h. The dried precipitate was burned at 400 °C for 2 h. J. M. Mahmood et al. J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 http://dx.doi.org/10.5599/jese.1657 523 Scheme 1. Preparation of azo ligand Preparation of -Fe2O3@SiO2@IPTMS The preparation of -Fe2O3@SiO2@ consists of two steps: The first step consists of dispersing 0.5 g of the brown magnetic precipitate of -Fe2O3 in the mixture of water and 2-propanol with a ratio of 1:10 with stirring for 2 h at 22 °C. The mixture of oleic acid (10 ml), ammonium solution (28 %, 5 ml), distilled water (10 ml) and 5 ml of tetraethyl orthosilicate (TEOS) was added to the dispersing mixture under continuous stirring. The product was magnetically isolated and dried at 80 °C for 2 h, and used in the next step. The second step was carried out by dispersing 1 g of -Fe2O3@SiO2 in 50 ml of 70 % ethanol solution by sonication process for 1 h. Then 2 ml of (3-iodopropyl)trimethoxysilane (IPTMS) was added to the mixture under a continuous stirrer. Finally, the product was magnetically isolated and dried at 80 °C for 2 h. Preparation of -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline Firstly, (0.1 g) -Fe2O3@SiO2@acetylacetone (synthesized from refluxed -Fe2O3@SiO2@IPTMS with pentane-2,4-dione in the presence of sodium hydride) was dispersed in 10 ml mixture of water and ethanol with ratio (1:1) for 30 min. Then, 0.2 g of 2-(2-benzothiazolyl azo)-4-methoxyaniline was added to the dispersion mixture and refluxed for 10 h. After that, the functionalized magnetic nano- composite was separated by pieces of magnetic bar. Finally, it was washed several times with acetone and distilled water and dried at 80 °C for 3 h. All processes and prepared compounds are summarized in Scheme 2. Electrochemical measurements The electrochemical cell contained three electrodes, i.e., 11 cm pieces of prepared samples as working electrodes, Ag/AgCl (saturated KCl) as the reference electrode and Pt foil as the counter elec- trode. 1 M Na2SO4 was utilized as the electrolyte solution. The active material(s) (85 %), carbon black (10 %) and polyvinyl fluoride (5 %) were mixed by using a few drops of N-methyl-2-pyrrolidione solvent to obtain mixtures that were coated on the foil of graphite substrate (1 cm2) and dried in an oven for 10 h at 70 oC. The mass of active materials (-Fe2O3, -Fe2O3@SiO2, and -Fe2O3@SiO2- azo dye) on each of thus formed working electrodes was approximately 0.5 g. The three electrodes were utilized to examine the pesudocapacitive performance of prepared samples in terms of cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy http://dx.doi.org/10.5599/jese.1657 J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 SUPERCAPACITIVE PROPETIES OF -Fe2O3@SiO2-AZO DYE HYBRID 524 Scheme 2. Steps during preparation of -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline Results and discussion Azo ligand characterization The 2-(2-benzothiazolyl azo)-4-methoxyaniline azo ligand was characterized using fragmentation electron effect. The results of hit mass spectroscopy (Figure 1) illustrated that the molecular weight of the C14H12N4OS ligand is 284 g mol-1. Peak at m/z = 284 is assigned to [M]+ and correlated with the prepared azo ligand. Set of peaks located at 210, 134, 77.2 and 35 are related to other fragmen- tation. The main fraction supported with cracking product is shown in Scheme 3. m / z Figure 1. Mass spectrum of azo ligand 0 50 100 150 200 250 300 350 400 450 500 0 20 40 60 80 100 R e la ti v e A b u n d a n c e m/z 284 210 134 77.2 35 J. M. Mahmood et al. J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 http://dx.doi.org/10.5599/jese.1657 525 Scheme 3. Fragmentation pattern of azo ligand Magnetic properties The magnetic properties of prepared materials were investigated by vibrating sample magnetometry (VSM). The magnetization plots of -Fe2O3, -Fe2O3@SiO2 and -Fe2O3@SiO2-2-(2- benzothiazolyl azo)-4-methoxyaniline are shown in Figure 2. The results show that the saturation magnetization is equal to 25-40 emu g-1 without any hysteresis loop. In addition, the results show quick ascension in magnetization curves without any coercivity and the samples show supermagnetic behavior at room temperature. These magnetic properties of prepared nanoparticles are pivotal in their applications since they prevent aggregation of particles and enable their re-dispersion in the reaction medium in the absence of a magnetic field [19]. -10000 -5000 0 5000 10000 -40 -30 -20 -10 0 10 20 30 40 M a g n e ti z a ti o n , e m u g -1 Applied field, Oe -Fe2O3 -Fe2O3/SiO2 -Fe2O3@SiO2-ligand Figure 2. VSM of prepared electrode materials http://dx.doi.org/10.5599/jese.1657 J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 SUPERCAPACITIVE PROPETIES OF -Fe2O3@SiO2-AZO DYE HYBRID 526 Structure characterization The structure properties of -Fe2O3, -Fe2O3@SiO2 and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-me- thoxyaniline were evaluated by XRD and XPS. The XRD of -Fe2O3, -Fe2O3@SiO2, azo ligand 2-(2-ben- zothiazolyl azo)-4-methoxyaniline, and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline are presented in Figure 3A-D, respectively. The results in Figure 3A show diffraction peaks located at 30.1, 35.6, 43.2, 53.4, 57.1 and 62.5o, which correspond to face-centered cubic (220), (311), (400), (422), (511) and (440) crystalline planes, in agreement with (JCPDS-39-1340). On the other side, the results (Figure 3B) show a new diffraction peak centered at 22.8°, which corresponds to (110) plane of amorphous SiO2. By comparing diffraction peaks of -Fe2O3 and -Fe2O3@SiO2, it was found that the coated SiO2 doesn’t change the structure of -Fe2O3. As can be seen (Figure 3D), the presence of sharp peaks confirms that the structure of -Fe2O3@SiO2 remains crystalline after being coated with a layer of azo ligand [20,21]. 2 / ° Figure 3. XRD patterns of: (A) -Fe2O3, (B) -Fe2O3@SiO2, (C) azo ligand, and (D) -Fe2O3@SiO2-azo ligand The chemical composition of -Fe2O3, -Fe2O3@SiO2 and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)- -4-methoxyaniline was characterized using XPS. The XPS of prepared compounds corresponding to C, N, O, Si, S and Fe energy levels are presented in Figures 4A to 4F. The energy level of C (Figure 4A) shows three peaks located at 283.5, 286.2 and 289.1 eV corresponding to C-C, C=N and C=C bonds, respectively, which confirm bonding C of acetylacetone and N of 2-(2-benzothiazolyl azo)-4-methoxy- aniline ligand [22,23]. The spectrum energy level of N 1s is illustrated at Figure 4B. The spectrum can be deconvoluted to 398.4, 399.5 and 401.2 eV, corresponding to [-C=N-], [-N=N-] and [-NH-], respectively [24]. At 531.8 eV, the energy level spectrum is shown (Figure 4C), which is related to O 1s, confirming the presence of O2- in the composite [25]. As shown in Figure 4D, the characteristic peak of Si 2p is clearly formed at 103.2 eV, which indicates the successful coating of SiO2 around -Fe2O3. 10 20 30 40 50 60 70 2/° (A) (220) (3 11 ) (400) (422) ( 51 1) (4 40 ) (311) (3 11 ) (B) SiO2 (C) (D) Ligand In te ns ity , a .u . J. M. Mahmood et al. J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 http://dx.doi.org/10.5599/jese.1657 527 Binding energy, eV Figure 4. XPS of: (A) C 1s, (B) N 1s, (C) O 1s, (D) Si 2p, (E) S 2p, (F) Fe 2p, -Fe2O3@SiO2-azo dye and (G) survey spectra of -Fe2O3@SiO2 and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline 280 282 284 286 288 290 292 In te n s it y , a .u . Binding energy, eV C-C C=N C=C (A) C 1s 398 399 400 401 402 403 In te n s it y , a .u . Binding energy, eV C=N- N=N -NH- N 1s (B) 526 528 530 532 534 536 538 In te n s it y , a .u . Binding energy, eV Si-O-Fe Si-O-Si Si-O-H O 1s(C) 100 101 102 103 104 105 106 In te n s it y , a .u . Binding energy, eV Si 2p(D) 159 160 161 162 163 164 165 166 167 168 169 170 In te n s it y , a .u . Binding energy, eV S 2p5/2 S 2p3/2 (E) 705 710 715 720 725 730 In te n s it y , a .u . Binding energy, eV 2p 3/2 2p 1/2 Fe 2p (F) 0 200 400 600 800 1000 1200 O 1s In te n s it y ( a .u .) Binding energy (eV) O 1s Si 2p Si 2s Fe 2p S 2p N 1s C 1s (G) http://dx.doi.org/10.5599/jese.1657 J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 SUPERCAPACITIVE PROPETIES OF -Fe2O3@SiO2-AZO DYE HYBRID 528 When comparing the survey spectrum of -Fe2O3@SiO2 and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline (Figure 4e), a new peak centered at 145.67 eV is found, corresponding to level energy spectrum of S 2p. This indicates the successfully incorporated ligand with -Fe2O3@SiO2. On the other side, the survey spectrum of prepared compounds shows a small peak of Fe, which approves the coating of Fe3O4 by SiO2. Morphology characterization The morphology of -Fe2O3, -Fe2O3@SiO2 and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-metho- xyaniline were performed utilizing TEM, FESEM and EDX-mapping. TEM images of prepared com- pounds are shown in Figures 5A to 5C. Figure 5. TEM images of (A) -Fe2O3, (B) -Fe2O3@SiO2, (C)-Fe2O3@SiO2-azo ligand; FESEM images of (D)-Fe2O3, (e) -Fe2O3@SiO2, (f)-Fe2O3@SiO2-azo ligand, and SAED images of: (g) -Fe2O3, (h)-Fe2O3@SiO2-azo ligand J. M. Mahmood et al. J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 http://dx.doi.org/10.5599/jese.1657 529 The results (Figure 5A) clearly display agglomerates of spherical -Fe2O3 nanoparticles with 11 nm grain size. TEM images illustrate the core-shell system structure of -Fe2O3@SiO2 and confirm the perfect coating of -Fe2O3 nanoparticles by SiO2, as shown in Figure 5B. On the other side, the results (Figure 5C) illustrate the complete surrounding of 2-(2-benzothiazolyl azo)-4-methoxyaniline layer around -Fe2O3@SiO2, which indicates success in the preparation of the final compound. The microscope evaluation of -Fe2O3, -Fe2O3@SiO2 and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4- methoxyaniline were investigated using FESEM. The FESEM images of prepared compounds are shown in Figure 5d-f. The results (Figure 5D) show that the magnetic -Fe2O3 particles were formed in uniform shapes with apparent agglomeration due to their magnetic properties. Added SiO2 to magnetic -Fe2O3 makes the shapes of catalyst nanoparticles spherical (Figure 5e). The FESEM images of -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline show nanocomposite with a small agglomeration of particles, which may be back to fictionalized of -Fe2O3 by 2-(2- benzothiazolyl azo)-4-methoxyaniline layer. The results of FESEM are in agreement with XRD and TEM results. The lattice fingers of -Fe2O3 and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-metho- xyaniline are shown in Figure 5g-h. The results show the highly crystalline nature of -Fe2O3@SiO2- azo, as well as the well-organized dots and ring (Figure 5h), prove the crystalline nature of synthesized material that could be beneficial in structure retention for long-term stability. On the other side, a large number of gleam spots (Figure 5h) compared with pure -Fe2O3 (Figure 6g) elucidates the coating of -Fe2O3 by SiO2 [27,28]. The chemical composition of -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline was investigated by element mapping patterns, while compositions of -Fe2O3 and -Fe2O3@SiO2 were carried out by EDX analysis. The EDS spectrum result (Figure 6) of -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline shows detectable singles back to Fe, O, Si, S, N and S, as well as the weight percentage of detecting elements, suggesting that the nanocomposite was successfully prepared Figure 6. EDS spectrum of -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline and mapping of Fe, Si, S, N, O, C The EDX spectra of -Fe2O3 and -Fe2O3@SiO2 are shown in Figure 7. Clear peaks related to Fe and O without other peaks are evident in Figure 7A, which indicates the successful preparation of pure ferric oxide. A new peak related to Si can be detected from EDS analysis after the coating of Fe2O3 by SiO2 (Figure 7B). http://dx.doi.org/10.5599/jese.1657 J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 SUPERCAPACITIVE PROPETIES OF -Fe2O3@SiO2-AZO DYE HYBRID 530 Figure 7. EDX spectra of: (A) -Fe2O3 and (B) -Fe2O3@SiO2 BET analysis The specific area, mean size of particles and the volume of pores for -Fe2O3 and -Fe2O3@SiO2-2- -(2-benzothiazolyl azo)-4-methoxyaniline were investigated using BET analysis, and the results are summarized in Table 1. The results show that the surface area of -Fe2O3 and -Fe2O3 functionalized by SiO2 and azo compound was 99.3 and 275.5 m2/g, respectively, meaning that the functionalized compound has higher surface area due to the presence of silica and azo dye and so, higher capacity for adsorption of species on the electrode surface. In addition, the results demonstrated that the mean pore size of -Fe2O3 and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline are 3.9 and 4.3 nm, respectively. According to the IUPAC categories, both prepared electrode materials can be classified into mesopores group [29,30]. Table 1. Nitrogen sorption characteristics of prepared electrode materials Electrode material SBET / m2 g-1 Pore volume, cm3/g Average pore diameter, nm -Fe2O3 99.3 2.66 3.9 -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline 275.5 4.9 4.3 Electrochemical performance The electrochemical properties of -Fe2O3, -Fe2O3@SiO2 and -Fe2O3@SiO2-2-(2-benzo thiazolyl azo)-4-methoxyaniline electrodes were investigated using CV, GCD and EIS techniques. The specific capacitances of three electrodes in the presence 1 M Na2SO4 as electrolyte solution were calculated using cyclic voltammetry data. The CVs of prepared compounds were recorded at different scan rates and within 0-1.2 V potential window, as presented in Figure 8. The CVs of -Fe2O3, - Fe2O3@SiO2 and -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline examined at 10 mV s-1 are shown in Figure 8A. The results demonstrate redox peaks for -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4--methoxyaniline electrode. In addition, the CV result of -Fe2O3@SiO2 showed significant improvement when its surface was modified with 2-(2-benzothiazolyl azo)-4-methoxyaniline, and higher specific capacitance was observed. The CVs of -Fe2O3@SiO2- 2-(2-benzothiazolyl azo)-4- methoxyaniline at different scan rates are presented in Figure 8B. The results show redox peaks until the highest scan rates with slight shifting, which indicates good electrode capability. On the other hand, the separation of current peaks raised with the rising scan rate because the redox peaks change with reversible reactions between the electrode and electrolyte solution [31]. The specific capacitance (Csp) of prepared electrodes was evaluated by using equation )1) [32]: J. M. Mahmood et al. J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 http://dx.doi.org/10.5599/jese.1657 531  =  sp 2 A C m V (1) where A is the area under plot,  / V s-1 scan rate, m / g is the active mass of the electrode, and V is a potential window. The results are shown in Figure 8C. The results exhibit that the modified - Fe2O3@SiO2 by azo ligand (2-(2-benzothiazolyl azo)-4-methoxyaniline) has higher specific capacitance than -Fe2O3@SiO2 and -Fe2O3, because of the interaction between the ferric oxide and azo ligand, which makes the structure of electrode superior and easy for Na2SO4 electrolyte solution accessibility. The specific capacitance of prepared electrodes was also examined at different scan rates 10-100 mV s-1 and the results are also presented in Figure 8C. The results show a reduction in specific capacitance values with increasing scan rate because of difficult redox transition at high scan rate value [33,34]. Figure 8. CVs of (A) -Fe2O3, -Fe2O3@SiO2 and -Fe2O3@SiO2 azo ligand electrodes at 10 mV s-1, and (B) -Fe2O3@SiO2-azo ligand electrode at different scan rates (10-100 mV s-1), (C) specific capacitance of three electrodes at different scan rates The GCD measurements of prepared compounds (-Fe2O3, -Fe2O3@SiO2 and -Fe2O3@SiO2-2-(2- -benzothiazolyl azo)-4-methoxyaniline) were performed at different current densities (0-10 mA g-1) in the presence of 1 M Na2SO4 as the electrolyte solution. The results show that discharge times are decreased with increasing current density due to increased drop voltage. At different current densities, the specific capacitance value was calculated using the following equation [35]:  =  sp I t C m V (2) 0.00 0.25 0.50 0.75 1.00 -0.010 -0.005 0.000 0.005 0.010 C u rr e n t d e n s it y , A c m -2 Potential, V ---- Fe2O3 ---- Fe2O3@SiO2 ---- Fe2O3@SiO2-azo (A) 0.0 0.2 0.4 0.6 0.8 1.0 1.2 -0.04 -0.02 0.00 0.02 0.04 C u rr e n t d e n s it y , A c m -2 Potential, V (B) 0 10 20 30 40 50 60 70 80 90 100 110 0 100 200 300 400 500 600 S p e c if ic c a p a c ta n c e , F g -1 Scan rate, mVs-1 Fe2O3@SiO2-Ligand Fe2O3@SiO2 Fe2O3 (C) http://dx.doi.org/10.5599/jese.1657 J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 SUPERCAPACITIVE PROPETIES OF -Fe2O3@SiO2-AZO DYE HYBRID 532 where I is the current density in the GCD experiment, t is discharge time, m is the mass of active material (0.5 g) and V is the potential window. The specific capacitance values of prepared compounds at different current densities are summarized in Table 2. Table 2. Specific capacitance values obtained by GCD measurements at different current densities Current density, A g-1 Specific capacitance, F g-1 Electrodes -Fe2O3 -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline 1 273 580 2.5 214 513 5 167 458 10 123 399 The results show that specific capacitance is promoted by incorporating 2-(2-benzothiazolyl azo)- 4-methoxyaniline with -Fe2O3@SiO2 compared with -Fe2O3 electrode because of providing more active sites for transferring electrons inside the electrodes and many sites for storing energy. On the other hand, the results show a decrease in the specific capacitance with increasing current density because there is not enough time for ions to arrive at the surface of the electrode and work in electrochemical reactions [36-39]. The cycling stabilities of -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline and -Fe2O3 electrodes are investigated by GCD measurements (Figure 9) at 10 A/g current density for 1000 cycles. Pure -Fe2O3 electrode shows lower stability compared with the functionalized electrode due to its destruction via large current, discharge and circular charge [39]. After 750 cycles at 10 A g-1, the functionalized electrode exhibited higher stability compared with -Fe2O3, with 92 % of initial capacitance remaining after 1000 cycles, which indicates a good role of the azo compound in the cycle stability of the electrode. Figure 9. Cycling stability of -Fe2O3 and -Fe2O3@SiO2 -azo ligand electrodes From electrochemical measurements, our prepared hybrid nanocomposite shows a very good capability to store the charges and electric energy (580 F g-1) when comparing it with other polymeric and binary oxide compounds (Table 3). It can be noted that the synthesized -Fe2O3@SiO2-2-(2- 0 200 400 600 800 1000 40 50 60 70 80 90 100 C a p a c it a n c e r e te n ti o n , % Number of cycles Fe2O3@SiO2-Azo Fe2O3 J. M. Mahmood et al. J. Electrochem. Sci. Eng. 13(3) (2023) 521-536 http://dx.doi.org/10.5599/jese.1657 533 -benzothiazolyl azo)-4-methoxyaniline) hybrid nanocomposite has interesting electrochemical properties already reported in the literature. Table 3. Specific capacitance for some iron oxide composites (current density = 1 A g-1) Compounds Specific capacitance, F g-1 Reference Iron oxide@SiO2@PolyFc 675 [40] Porous-Fe2O3@C nanowire 280 [41] Iron oxide@SiO2-bis(aminopyridine)-Cu 263 [42] Flexible iron oxide@C/MnO2 306 [43] Iron oxide/reduced graphene oxide 480 [44] -Fe2O3@SiO2-2-(2-benzothiazolyl azo)-4-methoxyaniline 580 This study Conclusion Stöber method was used to prepare -Fe2O3@SiO2 core-shell nanocomposite that was func- tionalized by 2-(2-benzothiazolyl azo)-4-methoxyaniline modified-MNPS, and characterized by dif- ferent techniques such as XRD, XPS, TEM, FESEM-EDX-mapping, while the electrochemical perfor- mance CV, GCD and EIS. 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