Electrochemical Monitoring of Synthetic Dyes in Water Using Modified Electrodes With Perovskite Oxides Integrated Halloysite Nanotubes Composites

ABSTRACT

In this study, a simple ultra‐irradiation technique was employed to synthesize perovskite metal titanates (MTiO₃, where M = Sr, Zn, and Fe) for the electrochemical detection of synthetic dyes Indigo Carmine (IC), Sunset Yellow (SY), and Tartrazine (TRZ). The synthesized nanomaterials were integrated with Halloysite Nanotubes (HNTs) and used to modify screen‐printed carbon electrodes (SPCEs). XRD and HR‐SEM analyses confirmed distinct morphologies: pebble‐like SrTiO₃, hexagonal ZnTiO₃, and flake‐like FeTiO₃. Sensor performance was evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Among the composites, FeTiO₃/HNTs/SPCE exhibited superior sensitivity and selectivity toward all three dyes. The sensor demonstrated a wide linear detection range (0.03–1350 µM) with low detection limits of 0.0011 µM (IC), 0.0205 µM (SY), and 0.0033 µM (TRZ). Real sample analysis in Industrial wastewater and pond water confirmed the sensor's practical applicability, highlighting its potential for environmental safety monitoring.

The perovskite metal Titanate's; MTiO₃ (M = Sr, Zn and Fe) was prepared using green ultrasonication method. FeTiO₃/HNTs/SPCE an electrochemical sensor enhanced for simultaneous detection toward IC, SY and TRZ with wide linear range from 0.03‐1350 µM. The modified electrode exhibits low limits of detection of 0.0011 µM (IC), 0.0205 µM (SY) and 0.0033 µM (TRZ). The fabricated sensor demonstrated a practical applicability in different water samples.

1. Introduction

In recent years, environmental safety has become one of the most critical challenges facing the modern world, as it is essential for sustaining ecosystems and protecting public health. Synthetic dyes are extensively used in various industries such as textiles, paper, plastics, cosmetics, and pharmaceuticals, leading to their frequent discharge into aquatic environments through industrial effluents [1]. However, a number of studies show that excessive usage of synthetic colours, mostly made from coal tar products that contain azo functional groups or biphenyl units, in water, whether allowed or prohibited, can seriously endanger human health [2]. The dye chemicals are Indigo Carmine (IC), Sunset Yellow (SY) and Tartrazine (TA), which are approved for use in beverages, gelatin treats, confections, and snacks, are frequently utilized because of their stability, cost, and accessibility. When taken in excess, tartrazine can result in chromosomal damage, thyroid tumors, dermatitis, migraines, allergies, diarrhea, anxiety, hypersensitivity, and even cancer [3, 4]. The Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization's (WHO) Expert Committee on Food Additives (JECFA) both recommend that daily intake of TRZ not surpass 7.5 mg/kg of body weight EFSA J 7 11. Because of this, various several analytical methods, like an capillary electrophoresis [5], LC‐MS [6], HPLC [7] and spectrophotometry [8], have been used to identify and determine the synthetic organic azo dyes. Although these techniques offer good sensitivity and selectivity for determining IC, SY and TRZ they are more costly than electrochemical approaches, time‐consuming, difficult to use, and need specialized training and sophisticated equipment [9]. Furthermore, because of their feasibility, cost‐effectiveness, mobility, and remarkable sensitivity with selectivity, electrochemical techniques are useful analytical instruments for identifying target compounds [10, 11]. Now a days using metal oxide nanomaterials in electrochemical sensor detection of modified electrode by synthetic dye to excellent sensitivity, minimal amount of material required and real sample analysis [12]. Ying fan et al., developed a Copper iron oxide (CuFe₂O₄/Cu⁰/GCE) based material carried out by square wave voltammetry technique detecting of MG, SY and TRZ [13]. Gimadutdinova et al., has been developed tin oxide and cerium oxide SnO₂‐CeO₂ based nanomaterials using voltametric sensor determination of Sunset Yellow FCF [14]. Tajik S et al. have been used MoO₃/WO₄ nanocomposites using carbon paste electrode incorporated with ionic liquid determination of Tartrazine and carmoisine [15]. Moreover, the food analysis mostly using metal oxide‐based materials by electroanalytical chemistry applications.

The spinel structure formula for MFe₂O₄, M‐ is transition metal like Manganese, Cobalt, Zinc and Copper is mostly used in electronic devices. Mahapatra et al., the gas sensor detection of adulteration in fish samples have been CuFe₂O₄ spinel nanostructured materials. Because of their unique properties, nanomaterials with a wide range of morphologies have been used extensively in many different fields over the past few decades [16]. Nevertheless, the required aggregation of nanomaterials prevents them from fully using their advantages during application. A traditional techniques like drop‐cast of developing carbon paste electrodes frequently require to use the binders like nafion, chitosan, and polyvinylpyrrolidone to utilize nanomaterials as sensing active materials [17]. However, these elements are highly dependent on the morphologies of the materials, leading one to believe that the morphology of CuS may be controlled to modify its electrochemical characteristics. For CuS crystals to have the desired electrochemical sensing capabilities, much research needs be done on morphology‐controlled synthesis. Presently, microwave irradiation is used in the suggested processes for CuS synthesis [18]. Simple coprecipitation method, Sono chemical synthesis, Hydrothermal synthesis and Calcination. However, the majority of them have several disadvantages, including expensive tools, laborious procedures, intricate reaction systems, and the usage of hazardous materials. Given its straightforward operation, high reproducibility, affordability, and environmentally friendly, a one‐step hydrothermal or solvothermal approach would be a better option in this situation for the synthesis of CuS nano or micro‐crystals [19]. Yang et al., developed for instance, used a hydrothermal process of CuS in the hexagonal phase, synthesized with the surfactant hexadecyltrimethylammonium bromide. The CuS was then used as an electrocatalyst for glucose and hydrogen peroxide electrochemical sensing [20].

Parisa S Dorraji et al., was developed ZnO/Cysteic acid on the surface of a glassy carbon electrode. The developed modified electrode facilitated the electron transfer of sunset yellow and Tartrazine using differential pulse voltammetry [21].

In this present work prepared by ultrasonic‐irradiation techniques using Perovskite type nanomaterials such as, SrTiO₃, ZnTiO₃ and FeTiO₃ nanomaterials with Halloysite nanotubes (HNTs). The SrTiO₃ morphology like pebble structure, ZnTiO₃ like hexagonal shape and FeTiO₃ flake's structure. The tubular structure of HNTs arises from a lattice mismatch between adjacent layers of silicon dioxide and aluminium oxide. Their molecular formula is Al₂Si₂O₅ (OH)₄·nH₂O, where n‐indicates the level of hydration or dehydration. Using voltametric techniques, the relationship between the morphologies of transition metals and the electrochemical sensing properties for IC, SY and TRZ by FeTiO₃/HNTs was investigated on the surface of a Screen‐printed carbon electrode. The sensor showed a broad linear detection range (0.03‐1350 µM) with low detection limits of 0.0011 µM (IC), 0.0205 µM (SY), and 0.0033 µM (TRZ). The suggested SrTiO₃, ZnTiO₃ and FeTiO₃ with Halloysite nanotubes (HNTs) are low cost, abundant and easy to fabricate using a gentle, ecofriendly method using environmental detection (Scheme 1).

SCHEME 1.

Schematic representation for environmental detection by MTiO₃ (Sr, Zn and Fe) with Halloysite nanotubes (HNTs) composites.

2. Experimental Procedure

The chemicals, instrumentations, and electroanalytical setup was mentioned in the supporting information (SI).

2.1. Ultrasonic‐Irradiation Method of MTiO₃ (Sr, Zn and Fe)

Perovskite‐type nanomaterials were decorated onto Halloysite nanotubes (HNTs) using ultrasonic‐irradiation techniques. In a typical synthesis, Ti(OBu)₄ was first dissolved in 30 mL of ethyl alcohol under continuous stirring at room temperature to form a yellow solution. Then, 50 mM of iron nitrate was added to the solution. After stirring for 30 min, 50 mL of deionized water was introduced, resulting in a brownish suspension. The reaction mixture was then irradiated with a high‐intensity ultrasonic probe (titanium horn, 20 kHz, 10 s per cycle) at room temperature in air for 2 h. The final nanoparticles were collected by centrifugation, washed several times with ethanol and deionized water, and then dried under vacuum at 70°C for 12 h to obtain the FeTiO₃ nanoparticles. Similarly, other materials (SrTiO₃ and ZnTiO₃) also followed same procedure (Scheme 2).

SCHEME 2.

Schematic diagram of preparation for MTiO₃ (Sr, Zn and Fe) with Halloysite nanotubes (HNTs) composites.

2.2. Modified Electrode at FeTiO₃/HNTs

A typical single‐electrode SPCE (Zensor) was used for the experiment. The whole piece was carried out in a room temperature environment. First, a 15‐min sonication in a 1:1 water and ethanol mixture was used to clean the SPCE surface. Following drying, the SPCE was drop‐coated with 6 µL of FeTiO₃/HNTs in ethyl alcohol and left to dry for 5 min at 55°C.

2.3. Preparation of Real Samples

We are used for real world sample analysis of Industrial wastewater and pond water samples were collected. To prevent altering the water's composition, the samples were collected in previously cleaned polyethylene bottles. All samples were filtered with Whatman grade filter paper before to the electrochemical tests in order to remove the organic matter, suspended particles, and organisms that contribute to the turbidity of the water. A 0.22 µm membrane filter was used to filter the samples a second time in order to exclude any tiny particles that can affect the voltametric readings. To match the ideal conditions for Indigo carmine, Sunset yellow and Tartrazine testing, the pH of the filtered water samples was brought to neutral using a 0.1 m phosphate buffer solution. To produce a range of working concentrations, Indigo carmine, Sunset yellow and Tartrazine stock solutions were made in ethanol and diluted in PB. For a thorough mixing of the new analyte, each added sample was gently vortexed for 40 s. After that the electrochemical measurements were performed on the synthesized FeTiO₃/HNTs/SPCE electrodes.

3. Results and Discussion

3.1. XRD and SEM Analysis

In XRD pattern of Figure 1a shows that the perovskite‐type cubic phase structure of SrTiO₃ appeared peaks indicating at 22.7°, 32.3°, 39.9°, 57.3° and 67.8° correspond to (100), (110), (111), (200), (211) and (220) planes, confirm with (JCPDS card No. 01‐079‐0174) respectively [22]. However, the ZnTiO₃ sample observed diffraction peaks at 23.9, 32.7°, 35.8°, 41.5°, 48.9°, 53.4°, 56.8°, 61.7°, and 63.3°, correspond to (012), (104), (110), (021), (024), (116), (018), (214), and (300) planes of rhombohedral ZnTiO₃, confirm with (JCPDS No. 00‐026‐1500) [23]. The Pure FeTiO₃ observed diffraction peaks, which match well with the orthorhombic structure (JCPDS No.01‐076‐1158). The characteristic diffraction peaks at 18.1°, 25.4°, 37.3°, 49.2°, and 61.7° are allocated to the (012), (020), (110), (024) and (116) reflections, respectively [24]. The XRD pattern of Halloysite nanotubes (HNTs) explains the attributed peaks at diffraction angles at 11.9°, 20.1°, 24.5°, 35.5° and 36.0° which correspond to the reflection planes (001), (110), (002), (122) and (200) diffraction planes. The Halloysite nanotubes (HNTs) d‐spacing value of (001) of 7.40 A° (2θ = 11.9) was found for the Halloysite nanotubes (HNTs) [25]. The Debye‐Scherrer Equation (1) was utilized to measure the crystallite size of the MTiO₃, M‐Transition metal (Sr, Zn and Fe) sample.

$$\mathbf{D}=\frac{0.9\lambda }{\beta \cos \theta }$$ (1)

where, λ is X‐ray wavelength (0.154 nm), and β is the Full Width at Half Maximum peak expanding, θ is diffraction angle. In Figure 1b The XRD patterns of SrTiO₃ exhibit identical diffraction patterns like SrTiO₃ without any extra peak related to HNTs as dispersed perfectly into the SrTiO₃. However, a slightly increased peak intensities were observed demonstrating the creation of composite structure among and SrTiO₃. In ZnTiO₃/HNTs pattern observed peaks intensities a slightly increased compared to pure ZnTiO_3. However, FeTiO₃/HNTs diffraction peaks was demonstrating the peaks are slightly decreased compare with pure HNTs_. The FeTiO₃/HNTs composites are enhance essential to electrochemical sensor applications.

FIGURE 1.

(a) XRD analysis of SrTiO₃, ZnTiO₃, FeTiO₃ and HNTs. (b) XRD analysis of Composites. (c) SEM analysis of SrTiO₃. (d) SEM analysis of HNTs. (e) SEM analysis of SrTiO₃/HNTs. (f) SEM image of ZnTiO₃. (g) SEM image of HNTs. (h) SEM image of ZnTiO₃/HNTs. (i) SEM image of FeTiO₃. (j) SEM analysis of HNTs. (k) SEM analysis of FeTiO₃/HNTs.

The morphological analysis into differences between three metal oxides, and the MTiO₃/HNTs composites was determined using Scanning electron microscopy (SEM). The morphology of HNTs shows like a tube shape structure. Due to the increased number of edges, electron exchange is significantly enhanced. In the case of SrTiO₃, the observed morphology resembles a unique, pebble‐like structure. At lower magnification, the entire pebble formation appears to be on the micrometre size, as shown in Figure 1c [22]. At lower magnification, the structure appears to be uniformly assembled from thin, tube‐like, sharp‐edged petals. These petals are nanometre‐sized and collectively form the overall morphology. as shown in Figure 1d. After forming a composite with HNTs, the tube was distributed over the SrTiO₃ pebbles without altering their original morphology. Higher magnification clearly shows the tubes spread across the pebble surfaces, indicating strong interaction between SrTiO₃ and HNTs, as shown in Figure 1e. As with ZnTiO₃, the obtained morphology looks like a hexagonal arrangement the micrometre size in the low magnification, as shown in Figure 1f [26]. As in the lower magnification, it seems uniformly sized tube‐like structure were aggregated a whole structure; the thickness of the tube structure was sized in micrometres, as shown in Figure 1g. Afterward, making a composite with HNTs, the tube was spread over the ZnTiO₃ hexagonal with no damage to the morphology. At higher magnification, it is evident that the tube not only expanded across the hexagonal structure but also penetrated into the petals, indicating a strong interaction between ZnTiO₃ and HNTs in Figure 1h. For FeTiO₃ the observed morphology appeared as a unique flake‐like formation. At lower magnification, the structure was in the micrometre range and exhibited an orderly arrangement as shown in Figure 1i [27]. At lower magnification, the tube‐like structures appeared to be uniformly aggregated and arranged into a cohesive formation. The edges of the tube‐shaped petals were measured in micrometres, as shown in Figure 1j [28]. After making the composite, in the higher magnification, it clearly visualized that the tube only spread upon the flakes but also entered in‐between the petals, as shown in Figure 1k.

However, an elemental analysis (EDX) were measured by the pointer ID analysis, the expected elements were confirmed with the estimated atomic percentage, for SrTiO₃/HNTs there is evidence in the presence of Sr = 29.4%, Ti = 15.7%, Si = 7.2%, Al = 6.0% and O = 41.8%, as shown in Figure S1a, for ZnTiO₃/HNTs there is evidence in the presence of the atomic percentage, Zn = 20.3%, Ti = 10.8%, Si = 24.3%, Al = 5.9% and O = 38.7%, as shown in Figure S1b and for FeTiO₃/HNTs there in the presence of Fe = 13.4%, Ti = 13.2%, Si = 15.2%, Al = 9.8% and O = 48.4%, as shown in Figure S1c.

3.2. TEM Analysis

To analyse the morphology carried out by high resolution transmission electron microscopy (HR‐TEM). In the resulting SrTiO₃ nanoparticles take on an irregular cubic structure with high magnification shown in Figure S2a [29]. From the HR‐TEM analysis, it's clearly visible that HNTs is a large surface tubular like structure in the higher magnification TEM images, it can clearly be seen that the tubular was in transparent formation, in Figure S2b. Furthermore, the HR‐TEM of SrTiO₃/HNTs shows the SrTiO₃ was irregular cubic structure, upon to HNTs tubular like shape, as seen in the lower magnification image shown in Figure S2c,d. The morphology analysis same of the ZnTiO₃ where irregular shape at the lower magnification image shown in Figure S2e [30]. For TEM analysis of the HNTs was tubular shape like was formed with at the lower magnification, the tubular was formed by the aggregation of nanoparticles, as clearly visible in Figure S2f [31]. The composite of ZnTiO₃/HNTs was carried out by HR‐TEM analysis ZnTiO₃ is aggregated shape and HNTs, where tubular petals at higher magnification shown in Figure S2g,h. From the TEM analysis of FeTiO₃ is irregular spherical shape in the low magnification shown in Figure S2i [32]. The morphology of HNTs is tubular‐like structure at the different magnification in Figure S2j. In the Composite of the FeTiO₃/HNTs conformed by TEM analysis in FeTiO₃ is irregular spherical structure and HNTs is the tubular like shape at the higher magnification was a good crystallinity shown in Figure S2k‐l.

3.3. XPS Analysis at FeTiO₃/HNTs

The X‐ray photoelectron spectroscopy (XPS) analysis, the overall survey spectrum of the FeTiO₃/HNTs were carried out using X‐ray photoelectron spectroscopy (XPS) analysis, the overall survey spectrum of FeTiO₃/HNTs as shown in Figure 2a. From the FeTiO₃/HNTs, the Fe 2p narrow spectrum reveals that there are two peaks Fe 2p_3/2 and Fe 2p_1/2 were seen at 709.8 and 723.7 eV, shown in Figure 2b. For the Ti 2p narrow spectrum reveals that there are two peaks were seen at 456.9 and 462.5 eV, whereas two significant peaks corresponding to Ti 2p_3/2 were seen at 456.9 eV and Ti 2p_1/2 were seen at 462.5 eV are contributed by Ti³⁺, respectively Figure 2c [33]. For the Si 2p narrow spectrum reveals that whereas one significant peak corresponding to Si 2p were seen at 101.8 eV respectively, Figure 2d. In the Al 2p spectrum reveals the corresponding peaks at 73.5 eV respectively shown in Figure 2e [34]. In the O 1s spectrum reveals the corresponding peaks at 530.8 and 528.0 eV can be assigned to hydroxyl groups and lattice oxides, which illuminate the pure FeTiO₃ and composite of FeTiO₃/HNTs respectively, as a good interaction of the other material formation shown in Figure 2f.

FIGURE 2.

(a) Overall XPS Survey spectrum of the FeTiO₃/HNTs. (b) High resolution XPS spectra of Fe 2p, (c) Ti 2p, (d) Si 2p, (e) Al 2p. (f) O 1s.

Similarly, SrTiO₃/HNTs as shown in Figure S3a. In SrTiO₃/HNTs, the Sr 3d narrow spectrum reveals that there are two peaks Sr 3d_5/2 and Sr 3d_3/2 were seen at 131.7 and 133.5 eV, shown in Figure S3b [35]. For the Ti 2p narrow spectrum reveals that there are two peaks were seen at 457.1 and 462.9 eV, whereas two significant peaks corresponding to Ti 2p_3/2 were seen at 457.1 eV and Ti 2p_1/2 were seen at 462.9 eV are contributed by Ti³⁺, respectively shown in Figure S3c. For the Si 2p narrow spectrum reveals that whereas one significant peak corresponding to Si 2p were seen at 101.8 eV respectively Figure S3d. In the Al 2p spectrum reveals the corresponding peaks at 73.9 eV respectively shown in Figure S3e. In the O 1s spectrum reveals the corresponding peaks at 530.8 and 528.0 eV can be assigned to hydroxyl groups, and lattice Oxide, which illuminate the pure SrTiO₃ and composite of SrTiO₃/HNTs shown in Figure S3f.

Similarly, the elemental composition of ZnTiO₃/HNTs was carried out using X‐ray photoelectron spectroscopy (XPS) analysis, the overall survey spectrum of ZnTiO₃/HNTs as shown in Figure S4a. From the ZnTiO₃/HNTs, the Zn 2p narrow spectrum reveals that there are two peaks Zn 2p_3/2 and Zn 2p_1/2 were seen at 1020.1 and 1043.2 eV, shown in Figure S4b [36]. For the Ti 2p narrow spectrum reveals that there are two peaks were seen at 457.2 and 462.8 eV, whereas two significant peaks corresponding to Ti 2p_3/2 were seen at 457.2 eV and Ti 2p_1/2 were seen at 462.8 eV are contributed by Ti³⁺, respectively Figure S4c. For the Si 2p narrow spectrum reveals that whereas one significant peak corresponding to Si 2p were seen at 101.7 eV respectively Figure S4d. In the Al 2p spectrum reveals the corresponding peaks at 73.5 eV respectively shown in Figure S4e. In the O 1s spectrum reveals the corresponding peaks at 530.7 and 528.6 eV can be assigned to hydroxyl groups and lattice Oxides, which illuminate the pure ZnTiO₃ and composite of ZnTiO₃/HNTs respectively. Figure S4f.

3.4. Electrochemical Analyse

3.4.1. Impedance Studies

The effect of intercalated anions on the interfacial properties of MTiO₃/HNTs‐modified SPCEs was thoroughly evaluated using electrochemical impedance spectroscopy (EIS). The EIS measurements were measured in a [Fe(CN)₆]^−3/‐4 redox probe electrolyte solution. Nyquist plots were used to correlate the width of the semicircular arc with the electron transfer resistance. Materials exhibiting low charge transfer resistance (R_ct) typically indicate superior charge transfer capabilities. For instance, the bare SPCE showed an R_ct of 403.8 Ω. Surface modification with suitable electrocatalysts much improved the electrode's conductivity. Anion intercalation influenced the charge transfer resistance and overall ion transport, as displayed by EIS analysis across different modified electrodes. The corresponding R_ct values were 1293.1 Ω for ZnTiO₃, 530.2 Ω for SrTiO₃, 373.7 Ω for FeTiO₃, and 319.1 Ω for HNTs, suggesting that these materials exhibited relatively lower charge transport efficiency compared to the bare electrode, as shown in Figure 3a. In this case, the lowest R_ct values observed for ZnTiO₃/HNTs (1078.2 Ω), SrTiO₃/HNTs (558.6 Ω), and FeTiO₃/HNTs (184.2 Ω) indicate that forming composites with Halloysite nanotubes (HNTs) significantly enhances ion transport on the modified electrode surface. The Nyquist plots were fitted using Randle's equivalent circuit, which includes charge transfer resistance (R_ct), solution resistance (R_s), Warburg impedance (W), and double‐layer capacitance (C_dl), insert image shown in Figure 3b. FeTiO₃/HNTs thus provides increased flow‐carrying accessibility, promoting electrochemical activity.

FIGURE 3.

(a) EIS plot of unmodified and modified electrodes in the probe solution of 0.1 m KCl with 5 mM [Fe(CN)₆]^−3/−4. (b) EIS study of different modified electrodes (inset image: Randle's equivalent circuit). (c) CV studies of unmodified and modified electrodes. (d) CV study of unmodified and modified electrodes in the probe solution of 0.1 m KCl with 5 mM [Fe(CN)₆]^−3/−4 (e) CV studies of different scan rate. (f) Linear plot for square root of (Scan rate)^1/2 vs Current. [Correction added on June 15, 2026, after first online publication: The labels in Figure 3 caption have been corrected from (d) to (c) and from (c) to (d) in this version.]

Furthermore, cyclic voltammograms (CV) of the several modified electrodes were recorded in a solution containing 5 mM [Fe(CN)₆]^−3/−4 and 0.1 m KCl. All modified electrodes exhibited prominent redox peaks, attributed to the quasi‐reversible behaviour of the [Fe(CN)₆]^−3/−4 redox couple. The peak‐to‐peak separation (ΔEp) values were observed as follows: bare SPCE (0.269 V), ZnTiO₃ (0.335 V), SrTiO₃ (0.319 V), FeTiO₃ (0.263 V), and HNTs (0.259 V), respectively, in Figure 3c. And then, the ΔEp of ZnTiO₃/HNTs (0.319 V), SrTiO₃/HNTs (0.289 V), and FeTiO₃/HNTs (0.279 V), respectively, reveals that when compared to other control materials, the composite material has improved its electrochemical performance due to synergetic effect Figure 3d. The obtained CV data demonstrate that the electrochemical response is highly sensitive to the unique properties of the incorporated anions. Among the modified electrodes, FeTiO₃/HNTs exhibits enhanced current and superior electrocatalytic activity compared to the others. The electrochemical surface area was calculated for all modified electrodes, by using the Randles‐Sevcik Equation. (2):

$$\mathbf{Ipa}=\left(2.69\times {10}^5\right)n^{3/2}AC\ast D^{1/2}{v}^{1/2}$$ (2)

where, Ip_a‐anodic peak current, n‐number of transferred redox electrons, A—electrochemical active surface area, D‐diffusion coefficient, C‐concentration of electroactive species and υ ^{1/2 –} scan rate. The electroactive surface area of the bare SPCE was 0.066 cm². For the modified electrodes, the values were as follows: ZnTiO₃‐0.061 cm², SrTiO₃‐0.062 cm², FeTiO₃‐0.075 cm², HNTs‐0.073 cm², ZnTiO₃/HNTs‐0.066 cm², SrTiO₃/HNTs‐0.071 cm², and FeTiO₃/HNTs‐0.103 cm². Among all the electrodes, FeTiO₃/HNTs exhibited the highest electroactive surface area. Additionally, cyclic voltammetry analysis of FeTiO₃/HNTs demonstrated a linear increase in current response with increasing scan rates from 20 to 200 mV/s in an electrolyte solution containing 5 mM [Fe(CN)₆]^{3 −}/^{4 −} and 0.1 m KCl, as shown in Figure 3e. A corresponding linear plot was constructed between the square root of the scan rate and the current (µA), yielding a correlation coefficient (R²) of 0.995 for the anodic peak current (ipa) and 0.996 for the cathodic peak current (i_pc) [37]. It reveals that our fabricated electrode belongs to a diffusion‐controlled process, as shown in Figure 3f. The same analysis was performed on the CV curves at different scan rates for all other electrode materials, and their corresponding linear plots were constructed. Based on the results of both CV and EIS analyses, the FeTiO₃/HNTs‐modified SPCE demonstrated superior performance in the electrochemical process compared to the other materials.

3.4.2. Modified Electrodes at IC, SY and TRZ

The divergence in potential and the upgrade in peak current can be influenced by phosphate buffer solutions. Figure 4a shows the optimizing study, we used Cyclic voltammetry method, for which different loading optimization (2, 4, 6 and 8 µL) 6 µL is gives higher peak current performed with other different loading modified electrode. In Figure 4b Bar graph of different loading modified electrode detection of IC, SY and TRZ. The cyclic voltammetry (CV) technique was utilized to study the electrochemical detection of different modified electrodes such as bare SPCE, ZnTiO₃/HNTs, SrTiO₃/HNTs, and for FeTiO₃/HNTs in an oxidation process in the presence of 200 µM of IC, SY and TRZ, as shown in Figure 4c. The CV processes were performed in a working electrode‐electrolyte 0.1 m PBS in pH (7.0) with a scan rate of 50 mV/s and the current responses were recorded with a potential window of 0.0 to 1.2 V, after which the FeTiO₃/HNTs‐modified SPCE was shown to have the higher current responses related to other modified electrodes which valued as I_pa of IC = 20.17 µA, SY = 13.21 µA and TRZ = 15.17 µA, the histogram for the current response of all modified electrode. As a result of their synergistic interaction with the FeTiO₃ flakes and the HNTs is tube shape promotes efficient electron transport in the modified electrode, improving the electrode conductivity. In Figure 4d the bar diagram of different unmodified and modified electrode detection of IC, SY and TRZ.

FIGURE 4.

(a) CV profiles of different loading modified electrodes in the oxidation reaction of Indigo carmine, Sunset yellow and Tartrazine (200 µM) in PBS (pH 7.0). (b) Bar graph of different loading Vs. Current. (c) CV studies of unmodified and modified electrode on the electrochemical oxidation reaction of Indigo carmine, Sunset yellow and Tartrazine (200 µM) in PBS (pH 7.0). (d) Bar diagram for unmodified and modified electrode.

3.4.3. pH Analysis at FeTiO₃/HNTs Electrode

The electrochemical behaviour of IC, SY, and TRZ was simultaneously investigated at a constant scan rate of 50 mV/s within an optimized potential window range 0.0 to 1.2 V in a PBS electrolyte. The influence of pH, varying from 3.0 to 9.0 in a 0.1 m PB solution, on the performance of the FeTiO₃/HNTs‐modified SPCE for the detection of IC, SY, and TRZ was also examined. Figure 5a the results show that the electrolyte pH value greatly influences the peak position change of IC, SY and TRZ oxidation peaks. To determine the optimal acidity of the medium for the measurement of azo dyes on the provided sensor, the effect of pH on the peak current of IC, SY and TZ was investigated in the 3 to 9 range. As the pH reached, it was found that the redox current of IC, SY and TZ increased as well, peak at pH 7.0. Tartrazine has an azo group, a weak acetate acid group, and two strong sulfonic acid. The molecule is highly hydrophilic, the charge is 2⁻, and only the azo group is protonated at a pH of 7.0. Specifically, as the pH rises from 3.0 to 7.0, the peak anodic current for the simultaneous detection of IC, SY, and TRZ gradually increases. This behaviour can be attributed to proton‐induced cleavage within the molecular structures of IC, SY, and TRZ. The trend continues with a notable rise in redox peak current corresponding to the increasing pH of the electrolyte solution. Enhanced peak current responses are observed at lower pH values (3.0 to 7.0), which is characteristic of an irreversible redox process involving the transfer of an equal number of protons and electrons in an electrically neutral environment. However, at pH 9.0, the peak anodic current responses decrease with further pH increase, likely due to reduced proton availability in the azo dye medium. In such conditions, the absence of protons leads to IC, SY, and TRZ species becoming more positively charged at higher pH values. Notably, for the FeTiO₃/HNTs‐modified electrode, the highest anodic peak current for the detection of IC, SY, and TRZ is achieved at pH 7.0. This pH is considered optimal for electrochemical sensing, as it provides favourable conditions for current response across different pH levels. In Figure 5b, shows the linear graph were plotted for the pH vs potential between anodic peak potentials of Indigo carmine. In Figure 5c, represents the linear graph were plotted for the pH vs potential between anodic peak potentials of Sunset yellow [38]. Similarly Figure 5d also shows the linear graph were plotted for the pH vs potential among anodic peak potentials of Tartrazine, from the slope value cv graph the one electron transfer mechanism of Nernst equation,

$$\mathrm{\Delta }{E}_{P,1/2}=\frac{3.53\ast \mathbf{R}\ast \mathbf{T}}{\mathbf{n}\ast \mathbf{F}}$$ (3)

where, the above equation explain that R, T, and F are the electrochemical factors. The results of the Nernst equation, confirm that the SY and TRZ molecule undergoes one electron transfer mechanism and IC as a two‐electron process. In Figure 5e represents the possible electrochemical mechanism of Indigo carmine, Sunset yellow and Tartrazine. The SY and TRZ targets single electron and proton transfer, and indigo carmine is a two electron and proton transfer by FeTiO₃/HNTs modified electrode.

FIGURE 5.

(a) CV analysis of unmodified and modified electrode for the electrochemical oxidation reaction of Indigo carmine, Sunset yellow and Tartrazine (200 µM) in PBS (pH 7.0). (b–d) the linear plot between pH vs anodic current (blue) and pH vs oxidation potential (E) (red). (e) possible electrochemical mechanism of Indigo carmine, Sunset yellow and Tartrazine.

In Cyclic voltammetry (CV) studies were used to investigate the effect on different concentration of IC, SY and TRZ simultaneous electrochemical sensing. As indicated in to explore the electrochemical behavior of IC, SY and TRZ, the concentration ranged from 100 to 800 µM on FeTiO₃/HNTs‐modified SPCE in the existence of 0.1 m PBS (pH 7.0) with a continuous curve scan rate of 50 mV/s in the potential window of 0.0 to 1.2 V. Figure S5a. presents an increasing the IC, SY and TRZ concentration from 100 to 800 µM, we observed a gradual rise in the oxidation peaks of three targets, as a trend suggests that IC, SY and TRZ molecules enrich readily in the surface of the FeTiO₃/HNTs modified SPCE with increasing concentration. It is important to note that the adsorption of IC, SY and TRZ on the electrode surface is very significant in controlling the electrochemical process. Hence, the sensitivity of the sensor improves with the increase in the concentration of three targets. In Figure S5b, confirm the established linear relationship between IC, SY and TRZ concentration and oxidation peak current, with linear coefficient of IC (R² = 0.980), SY (R² = 0.996) and TRZ (R² = 0.996) respectively. In Figure S5c, the CV responses of the FeTiO₃/HNTs/SPCE were investigated at different scan rates (20 to 160 mV/s) in 0.1 m PBS (pH 7.0), including 200 µM of IC, SY and TRZ. They were collected in the potential range of 0.0 to 1.2 V. It can be showed that with the increase in the scan rate, the peak current also increases, which suggests that the polarization at higher scan rates is much higher than that at lower ones [39]. Figure S5d The calibration plot of the square root of scan rate versus anodic peaks currents (µA), corresponding to IC (R² = 0.974), SY (R² = 0.970) and TRZ (R² = 0.989), respectively, are showing a good linear correlation. The statistical analysis results demonstrate high correlation coefficients and linearly fitted profiles, indicating that the simultaneous of IC, SY and TRZ detection is accomplished on the FeTiO₃/HNTs/SPCE by a diffusion‐controlled process. To the best of our studying, this is consistent with previous reports. These results are exhibit that the FeTiO₃/HNTs‐modified SPCE is a well active material for the precise electrochemical sensor detection of IC, SY and TRZ.

3.5. Differential Pulse Voltammetry Studies of IC, SY and TRZ by FeTiO₃/HNTs

In Figure 6a Different pulse voltammetry analysis was performed to evaluate the current response toward electrochemical assessment of IC, SY and TRZ was conducted using an FeTiO₃/HNTs/SPCE in 0.1 M PBS of (pH 7.0) at an applied potential range of 0.2 to 1.0 V. At first the electrochemical anodic I_pa reaction for various concentration of IC, SY and TRZ ranging from 0.03 to 1350 µM on the FeTiO₃/HNTs/SPCE. Figure 6b shows that linear correlation plot from the resulting DPV current responses of IC exhibit a distinct linear regression equation of I_pa (µA) = 0.008X + 1.104 (R² = 0.990), SY = 0.019X + 1.008 (R² = 0.991) and TRZ = 0.007X + 2.060 (R² = 0.990) respectively. In Figure S6a Different pulse voltammetry analysis was performed to evaluate the current response toward electrochemical assessment of IC, SY and TRZ was conducted using an FeTiO₃/HNTs/SPCE in 0.1 M PBS of (pH 7.0) at an applied potential range of 0.2 V to 1.0 V. At first the electrochemical anodic I_pa reaction for various concentration of IC range from 20 to 200 µM and the fixed concentration of 200 µM, SY and TRZ on the FeTiO₃/HNTs/SPCE. Figure S6b shows that linear correlation plot from the resulting DPV current responses of IC exhibit a distinct linear regression equation of I_pa (µA) = 0.107X + 1.904 (R² = 0.977) respectively.

FIGURE 6.

(a) DPV profiles of IC, SY and TRZ on FeTiO₃/HNTs/SPCE with different concentrations (0.03 µM to 1350 µM) at 50 mV/s. (b) Linear plot of the Concentrations IC, SY and TRZ Vs Current. (c) Interference study of IC, SY and TRZ on FeTiO₃/HNTs/SPCE. (d) Corresponding bar diagram of various interferents Vs. relative error (%).

In Figure S6c DPV curves shows that second anodic i_pa reaction for various concentration of SY linear range from 2 to 200 µM and the fixed concentration of 200 µM, IC and TRZ on FeTiO₃/HNTs/SPCE. Figure S6d shows linear plot from the resulting DPV peak current responses exhibit linear regression equation of I_pa (µA) = 0.205X+0.319 (R² = 0.987) respectively. In Figure S6e. Similarly, DPV curves shows that third anodic i_pa reaction for various concentration of TRZ linear range from 2 to 200 µM and the fixed concentration of 200 µM, IC and TRZ on FeTiO₃/HNTs/SPCE. Figure S6f shows linear plot from the resulting DPV peak current responses exhibit linear regression equation of I_pa (µA) = 0.049X+2.036 (R² = 0.960) respectively [40]. These results shows that IC, SY and TRZ do not interfere with the electrochemical detection of each other under the present experimental conditions.

The LOD is calculated from Differential pulse voltammetry using the below given Equation (4),

$$\mathbf{LOD}=3^{\ast }\mathrm{SD}/\mathrm{Y}$$ (4)

where SD is standard deviation of the blank signal concentration of IC, SY and TRZ, Y is the slope of calibration plot from DPV in Figure 6a.

The FeTiO₃/HNTs‐modified SPCE shows a particularly broad linear detection range and a reduced limit of detection for the concurrent quantification of IC, SY and TRZ in comparison to previously reported electrochemical sensors as compared in (Table 1 for IC, Table 2 for SY) and Table S1 for TRZ is provided in the Supplementary Information file.

TABLE 1.

Comparison table of modified electrodes for the detection of indigo carmine from previous reports.

Electrode	Method	Sample	Linear range	LOD	Sensitivity (µA µM−1.cm−2)	Refs.
LB/MWCNTs/GCE	SWV	River water Orange juice Candy	0.1–30 µM	0.019 µM	0.305	[41]
Y2O3@GPE	DPV	Candies	5–300 µM	0.11 µM	−	[42]
PDMCPE	DPV	Water	0.1–1.0 µM	0.0169 µM	—	[43]
SeO2 nanoparticles‐CPB/GCE	DPV	Vitamin tablets	0.02–1.0 µM 1.0–10 µM	0.0043 µM	—	[44]
FeTiO3/HNTs/SPCE	DPV	Industrial wastewater Pond water	0.03–1350 µM	0.0011 µM	0.101	This work

TABLE 2.

Comparison table of modified electrodes for the detection of Sunset yellow from previous reports.

Electrode	Method	Sample	Linear range	LOD	Sensitivity (µA µM−1.cm−2)	Refs.
CuS MF	DPV	Mirinda Jelly Candy	0.1–700 µM	0.006 µM	0.4228	[18]
Eu2O3/Y2O3‐CNTs/GCE	SWV	Soft Drink Pediatric Syrup	4.0 × 10−9‐3.0 × 10−7 M	1.1 × 10−10 M	0.436	[45]
CuFe2O4/Cu0@CFP	SWV	Fruit juice Jelly	0.005–36.0 36.0–200 µM	0.0016 µM	7.3	[13]
La3+/NZF@rGO/ CPE	DPV	Orange, Mango, Pineapple juice	1–140 µM	0.0067 µM	0.114	[39]
ZnO/Cysteic acid/GCE	DPV	Orange juice Peach, gelatin	0.1–3 µM	0.031 µM	—	[21]
FeTiO3/HNTs/SPCE	DPV	Industrial wastewater Pond water	0.03–1350 µM	0.0205 µM	0.240	This work

CuS; Copper sulfide, Eu₂O₃/Y₂O₃ ; Europium‐yttrium oxide, CNTs; Carbon nanotubes, GCE; Glassy carbon electrode, CuFe₂O₄; Copper iron oxide, CFP; Carbon fiber paper, BT‐I; Bismuthiol I, rGO; reduced Graphene Oxide, LB; N‐Diethyl‐p‐phenylenediamine, MWCNT; Multi‐walled carbon nanotubes, Y₂O₃; Yttrium oxide, GPE; Graphite paste electrode, PDMCPE; poly(dopamine) modified carbon paste electrode, CPB; cationic cetylpyridinium bromide. IC; Indigo carmine, SY; Sunset Yellow, TRZ; Tartrazine.

3.6. Interference Study

In Figure 6c the challenge of distinguishing between various phenolic substances that interfere with environmental toxic sample sensing makes this process complex. When the FeTiO₃/HNTs modified SPCE is assessed, substances such as Fructose, Lactose, NaNO₃, Copper metal (Cu), Zinc metal (Zn), Cobalt metal (Co), Sodium (Na), Chloride (Cl) and Catechol are detected as potential interferents. Results from the experiment show the capability of the electrode to favour IC, SY and TRZ reliably [46]. In Figure 6d shows the bar graph of the average current response of different interfering molecules in the presence of IC, SY and TRZ. Therefore, the FeTiO₃/HNTs/SPCE electrode exhibited the ability to distinguish between these interference molecules, indicating that it could be applicable in real‐time sample analysis. Stability studies given in supplementary file in Figure S7a.

3.7. Real Sample Studies

Figure S8a,b to simulate real‐world conditions, the sensor was employed to evaluate the electrode's performance. Initially, unspoked samples of Industrial wastewater and Pond water were analysed, and the results demonstrated satisfactory recovery rates. To further assess the analytical reliability of the FeTiO₃/HNTs/SPCE sensor, differential pulse voltammetry (DPV) measurements were carried out for IC, SY and TRZ in these real samples. Subsequently, known amounts of IC, SY, and TRZ were added to the Industrial wastewater and pond water samples. The observed DPV peaks corresponded well to the presence of IC, SY, and TRZ, confirming the sensor's effectiveness in detecting these analytes in complex sample matrices. The experimental procedure followed protocols previously established in laboratory‐based studies. Based on these findings, we conclude that the FeTiO₃/HNTs/SPCE platform offers an effective and practical approach for detecting IC, SY, and TRZ at pH 7.0 (Table S2).

4. Conclusion

The simple and effective ultrasonic irradiation method was developed for the preparation of three different metal titanates with 3D perovskite network structures which possess favorable functions such as SrTiO₃, ZnTiO₃ and FeTiO₃. They were skillfully integrated with the Halloysite nanotubes (HNTs) in order to modify composite screen‐printed carbon electrodes (SPCEs) for the electrochemical detection of synthetic dyes. A highly electrocatalytic effective composite FeTiO₃/HNTs/SPCE electrode was synthesized on a SrTiO₃ and ZnTiO₃‐based SPCE within our studies toward Indigo Carmine (IC), Sunset Yellow (SY) and Tartrazine (TRZ). The developed sensor exhibited an extensive linear detection range, minimal detection thresholds, and elevated sensitivity. Also, it was possible to detect IC, SY, and TRZ at the same time with high accuracy and without much cross‐interference. The proposed sensor was tested in real environmental samples, such as industrial wastewater and pond water, and it worked very well, showing that it could be used in the real world. These results show that the FeTiO₃/HNTs/SPCE platform could be a simple, sensitive, and effective way to keep an eye on synthetic dyes in complicated mixtures. Despite these encouraging results, it is important to acknowledge certain limitations. The lack of validation through established methods, like High‐Performance Liquid Chromatography (HPLC), along with the absence of long‐term stability tests, may limit wider practical use. Future research will focus on addressing these issues to improve the reliability, accuracy, and usability of the proposed sensing platform in real‐world situations.

Author Contributions

Perumal Murugesan: Investigation, Writing – original draft, Data curation, Software, Methodology. Rajeshwari Yemmi: Data curation, Formal analysis, Methodology. B.E. Kumaraswamy: Conceptualization, Methodology, Formal analysis. Mani Govindasamy: Investigation, Conceptualization, Resources, Methodology, Supervision, Funding acquisition, Writing – review & editing. Mohamed A. Habila: Funding acquisition, Methodology.

Conflicts of Interest

The authors declare no conflict of interest.

Supporting information

Supporting File: smll73941‐sup‐0001‐SuppMat.docx.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.