IndexXRD analysisVoltometric studies of the modified electrode Study on pH dependenceInterference studiesAnalysis of real samplesConclusionsA scanning electron microscope provides detailed information on the surface of nanoparticles, including morphological characterization, homogeneity and size of particles. Fig. 2 indicates the SEM micrograph of NiTiO3 nanoparticles. As can be seen, the NiTiO3 nanoparticles have a homogeneous morphology with a spherical shape and the average diameter of the nanoparticles is approximately 38.0 nm. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an Original Essay Therefore, XRD analysis was performed to study the crystalline phases of NiTiO3 nanopowders. Fig. 3 shows the XRD spectra of NiTiO3 nanoparticles after heat treatment at 750 °C in air for 2 hours, which is the lowest temperature reported so far for the formation of NiTiO3 nanopowders by the sol–gel method. Sharp and intense peaks of nanoparticles at this temperature represent the fine crystalline rhombohedral NiTiO3 phase, and all peaks were well coordinated associated with the database in JCPDS (file number: 83-0199). The particle size calculated with the Scherrer formula [24] (Eq. 1):D = (0.9λ)/(βcosθ) (1)where λ (0.15418 nm) is the X-ray wavelength , β is the full width at half maximum (FWHM) in radians of the X-ray diffraction peak, θ is the diffraction angle, and D is the average particle size. According to Eq. 1, the average particle size of the NiTiO3 nanopowders was estimated to be approximately 33.0 nm with a value compatible with the SEM results. Characterization of the modified electrode by EISIn this study, the EIS technique was used to indicate the additional effect of nickel titanate nanoparticles on the modified electrode. The EIS plots of modified and unmodified electrodes in [Fe(CN)6]3-/4- (Fe2+/Fe3+) as a negatively charged redox probe are shown in Fig. 4. The value of electron transfer resistance (Rct, diameter of the semicircle ) depends on the dielectric and insulating characteristics of the electrode/electrolyte interface [25]. The results were approximated by an equivalent circuit. As can be observed, the presence of NiTiO3 nanoparticles on the surface of the carbon paste electrode increases the transfer of electrons on the surface of the modified electrode. On the other hand, the modified electrode compared to a bare electrode, had a lower charge transfer resistance. The surface morphology of the bare and modified electrodes was characterized by SEM technique (Fig. 5A and B). As can be seen in Fig. 5A, the surface of the pure graphite electrode is non-uniform and free of any coating. Fig. 5B shows a homogeneous distribution of NiTiO3 nanoparticles on the surface of a modified electrode. Voltammetric studies of the modified electrode The kinetic parameters of NiTiO3/CPE were studied by the cyclic voltammetry (CV) method. The cyclic voltammograms of the modified electrode on the Fe2+/Fe3+ probe solution in the scan rate range of 10.0 to 70.0 mV s-1 are shown in Fig. 6. It can be seen in Fig. 6(c) for scan speed values ​​greater than 300.0 mV s-1 the anode potential is directly proportional to the logarithm of the scan speed. Next, the electron transfer rate constant (ks, s−1) and the transfer coefficientof the charge (α) can be calculated using the Laviron equation (Eq. 2) [26].Log ks = α log (1-α) + (1- α) logα – log (RT/nFv) –α ( 1-α) nαF∆Ep/2.3RT (2)Where v are different scanning speed values ​​and n is the number of electrons involved in the redox reaction. From these expressions, α can be determined by measuring the change in peak potential versus scan speed, and ks can be determined by measuring ΔEp values. Based on these results, the values ​​of α and ks were obtained to be 0.32 and 0.14 s-1, respectively. Application of Nanostructured Modified Sensor in Electrochemical Studies of Monohydroxybenzoic Acid Isomers Oxidation of OHB and PHB on Unmodified and Modified Electrodes The electrochemical behaviors of OHB and PHB were studied by DPV. Fig. 7 shows differential pulse voltammograms of the NiTiO3/CPE and CPE electrodes in a BR buffer solution (pH 5.0) containing 50.0 µM PHB and 50.0 µM OHB. As shown in Figures 7b and c, a significant improvement in the voltammetric responses of NiTiO3/CPE compared to bare CPE demonstrates the effect of nickel titanate nanoparticles on the modified electrode. Therefore, the modified electrode was used for the simultaneous determination of OHB and PHB with high sensitivity and adequate detection limit. Study of pH dependence The electrochemical behavior of OHB and PHB at NiTiO3/CPE was studied in the presence of BR buffer with different pH (from 2.0 to 9.0). ) using differential pulse voltammetry (DPV). Differential pulse voltammograms of the modified electrode toward OHB and PHB were recorded and shown in Figs. 8A and 9A, respectively. As can be seen, the anodic peak potentials of OHB and PHB shift towards negative values ​​with increasing pH. Therefore, protons participate in the OHB and PHB oxidation reaction, and the acidity of the electrolyte has a significant effect on the oxidation. Furthermore, it indicates that the optimal pH 2.0 can be used for individual determination of OHB and PHB (Fig. 8B and 9B). But when OHB and PHB are determined simultaneously at pH 2.0, both have only one peak in DPV (Fig. 10). Therefore, we used another pH value to separate the peaks of the two isomers from each other. As shown in Fig. 11, at pH 5.0 there are two separate peaks with good sensitivity for two isomers. Therefore, a buffer solution with pH = 5.0 was selected for the simultaneous determination of these isomers. Interference studies The ability of the proposed nanostructured sensor for the determination of OHB and PHB in the presence of common interfering substances was studied using the DPV technique. Experiments were conducted by analyzing a standard solution containing 50.0 µM OHB and PHB using an increasing amount of interfering species. The tolerance limit was defined as the concentrations giving an error of less than ±5.0% in the peak oxidation current of OHB and PHB [27]. Some common cations and anions such as Na+, K+, NH4+, Ca2+, Mg2+, Cl-, CO32-, NO3- and I- have been studied for their interference with the detection of OHB and PHB. The results demonstrate that these ions have virtually no noticeable interference with the DPV signals of the NiTiO3/CPE targets. Some organic compounds such as gallic acid, uric acid and dopamine are believed to have no influence on OHB and PHB signals with deviations less than 5%. These results were reported in Table 1. The ability to generate a modified electrode with a stable surface was investigated under optimized experimental conditions, using continuous DPV determination of OHB and PHB. Subsequent measurements of the oxidation currents of 50.0 µM OHB and PHB at the same NiTiO3/CPE were performed over a period of fifteen days. The standard deviation.