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Electrochemical sensor based on epoxy-functionalized BEA nanozeolite and graphene oxide modified glassy carbon electrode for bisphenol E determination

Electrochemical sensor based on epoxy-functionalized BEA nanozeolite and graphene oxide modified... An epoxy-functionalized beta type nanozeolite (BEA)/graphene oxide nanocomposite modified glassy carbon electrode (GCE/BEA/APTMS/GA/GO/NF) has been created for the differential pulse voltammetric determination of bisphenol E (BPE). The modified electrode presented an enhanced current response in comparison with bare GCE. A linear dependence of anodic peak current (I ) and scan rate (ν) was observed, which showed that the electrochemical process was adsorption- controlled. Differential pulse voltammetry (DPV) was employed and optimized for the sensitive determination of BPE. Under the optimized conditions, the anodic peak current was linearly proportional to BPE concentration in the range between 0.07 and 4.81 µM, with a correlation coefficient of 0.995 and limit of detection 0.056 μM (S/N = 3). The electrode showed good repeatability and storage stability, and a low response to interfering compounds. Comparison was made to the determination of bisphenol A. To confirm the electrode analytical performance, recovery tests were performed, and deviations lower than 10% were found. The BEA zeolite-GO nanocomposite proved to be a promising sensing platform for bisphenol determination. Graphical abstract Keywords BEA nanozeolite · Graphene oxide · Bisphenol E · Bisphenol A · Electrochemistry 1 Introduction Bisphenols (BPs) are a known group of endocrine disrupting compounds with adverse effects on human health and the environment [1]. Bisphenol A (BPA), 2, 2-bis (4-hydroxy- phenyl) propane, is the most used among BPs with a wide * Alistair J. Fielding a.j.fielding@ljmu.ac.uk range of applications, such as polycarbonate plastics manufacturing, with potent endocrine-disrupting activity. Extended author information available on the last page of the article Vol.:(0123456789) 1 3 Journal of Applied Electrochemistry Bisphenol E (BPE), 1,1-bis(4-hydroxyphenyl) ethane, which They indicated that the BPs molecular structure influ- has a structure very similar to BPA (Fig. 1) is another impor- enced electrode performance. Recently, Vaghela et  al. tant industrial chemical used as monomer for the production [46] described the preparation of a electrochemical bio- of polycarbonate plastics and epoxy resins [2]. BPE has been electrode containing entrapped tyrosinase in an agarose- reported to have similar acute toxicity and estrogenic activity guar gum-graphene oxide composite cast on indium tita- to that of BPA [, , , , 2–6]. nium oxide (ITO) glass plates. The mechanism of sensing Conventional chromatography, such as liquid chromatog- involved enzymatic oxidation of bisphenols to correspond- raphy (LC) or gas chromatography (GC), sometimes com- ing o-bisphenols and subsequently their reduction on the bined with mass-spectroscopy (MS); LC–MS and GC–MS; designed bioelectrodes at a potential of 80 mV. The limit and/or UV–Vis spectroscopy are sensitive and selective of detection found for BPE was 10 µM. To our knowledge, analytical procedures for the routine determination of BPs. there are no reports of zeolitic nanocomposites applied to Disposable or simple manufactured tools have been widely BPE electrochemical determination. used for environmental analysis in the last couple of years, in The creation of electrodes using zeolite in combination which electrochemical sensors or biosensors stand as good with graphene oxide (GO) has been reported [36]. GO is options due to their wide applicability and feasibility [, , 1, known for its high electronic conductivity, relatively inert 7, 8]. Advances in the area of nanostructured materials, have electrochemistry, biocompatibility, wide potential range made possible the design of a series of different electro- and low cost [47], and can act as a reinforcement for the chemical sensors, where nanocomposites are used to deco- assembling of oxides to form stable sensing platforms rate conventional glassy carbon electrodes (GCE) or screen [48]. These properties in combination with zeolites has printed electrodes (SPE) with reported increased sensitivity led to a great increase of the sensitivity [, , 36, 49, 50]. In a and/or selectivity for the determination of BPs [, , , , , , , , , previous work, we reported the synthesis and characteriza- , 9–19]. Graphene oxide (GO) nanocomposites or hybrids tion of nanozeolites, such as beta type zeolite (BEA), and with other materials [, , , , , , 20–26] are also examples of its alkoxysilane functionalization with (3-aminopropyl) nanomaterials used for this purpose. Surfactants, dendrim- trimethoxysilane (APTMS), followed by cross-linking ers, ionic liquids, among others, are additional materials with glutaraldehyde (GA) [32]. Herein, we report the used for the preparation of electrochemical sensors for BPs application of BEA/APTMS/GA and GO decorated GCE determination [, , , , 27–31]. to bisphenol E determination. Unmodified and modified Among many different materials, micro- and nano-sized nanozeolite and GO suspensions were prepared in etha- zeolites have attracted extensive attention due to their mul- nol and used for GCE coating by a drop coating method. tifunctional properties such as small sizes, biocompatibility, Nafion (NF) polymer was used to complete the coating and high surface area, and the possibility of modulation [32] of guarantee that modifiers did not leach from the electrode their hydrophilicity and hydrophobicity on electrode sur- surface. The intensity of the oxidation peak of BPE was faces for applications of sensing [, , , 33–36] and biosensing significantly increased when using GCE/BEA/APTMS/ [, , , , , , 37–43]. An electrochemical sensor for BPA quanti- GA/GO/NF in comparison with bare GCE or other tested fication using ZrO supported Nano-ZSM-5 nanocomposite modified electrodes. This electrode was then selected for with nanomolar sensitivity has been reported recently [44], further investigation of its electrochemical properties and and used for real sample analysis. analytical performance. Although a wide range of different electrodes have been reported for BPA determination, few works have targeted BPE and/or studied its potential interference proper- ties during electrochemical analytical methods used for 2 Experimental BPs. Lu et al. [45] reported a Metal–Organic Framework (MOF)-based tyrosinase electrochemical sensor for a 2.1 Reagents series of BPs, including BPE, with nanomolar sensitivity. Aluminum isopropoxide (98%), tetraethylammonium hydroxide solution (20%), Cab-O-sil® M-5, graphene oxide (15–20 sheets, 4–10% edge-oxidized), Nafion solution (5 wt%), ethanol (99.8%), inorganic salts, glutaraldehyde solution (25%), (3-aminopropyl)trimethoxysilane (APTMS, 97%), and anhydrous dichloromethane were purchased from Sigma-Aldrich. All chemicals were used without further purification. Fig. 1 Bisphenols A and E structures 1 3 Journal of Applied Electrochemistry the organic templates. Calcinated material hereafter denoted 2.2 Instrumentation BEA. See Figure S1 for XRD patterns and SEM images. The crystallographic structure and morphology of the syn- thetized nanozeolite were determined by X-ray diffraction 2.4 BEA and GO functionalization (XRD) and scanning electron microscopy (SEM). The XRD analyses were performed with a MiniFlex II instru- The BEA was alkoxysilane surface functionalized as previ- ous reported [32]. Initially, 1 g of BEA was suspended in a ment (Rigaku, Tokyo, Japan) equipped with a rotating anode source with flat-plate Bragg–Brentano geometry and solution containing 30 mL of dichloromethane and 1 mL of APTMS, and the suspension stirred for 16  h at room a graphite monochromator, operating at 40 kV and 40 mA, with Cu Kα radiation (wavelength = 1.5418 Å). The powder temperature. The obtained material was then centrifuged (13,400×g) and washed several times with distilled water diffraction patterns were recorded in the 2θ range from 3° to −1 50°, with scanning at a goniometer rate of 2° min . SEM to remove the unreacted APTMS. The final precipitated was dried at 60 °C for 12 h, and denoted BEA/APTMS. images were recorded using a Magellan 400 L instrument (FEI Company), with deposition of a thin coating of gold Finally, the BEA/APTMS functionalized nanozeolite was cross-linked with glutaraldehyde (GA). The experiment onto the samples prior to the analyses. Surface alkoxysilane functionalization was measured using Fourier transform was performed as follows: 1 g of BEA/APTMS nanozeolite was mixed with 20 mL of a 5% glutaraldehyde solution by infrared (FT-IR). FT-IR spectra were acquired using a Perki- nElmer Frontier FT-IR spectrometer equipped with an ATR magnetic stirring for 24 h at room temperature. The GA- functionalized nanozeolite was collected by centrifugation accessory. The samples were scanned 64 times between −1 −1 4000 and 400  cm , at a resolution of 4  cm . (13,400×g) and the solid product was washed three times with distilled water, dried at room temperature, and stored All electrochemical apparatus, including electrodes, was purchased from Metrohm, Netherlands. The electrochemi- under vacuum in order to prevent oxidation. Cross-linked material denoted BEA/APTMS/GA (See Fig. S1 for FT-IR cal process was performed using Autolab potentiostat/galva- nostat equipment (PGSTAT 101), and data processed using characterization). The GO functionalization with APTMS was adapted from Lin et al. [52]. 200 mg GO was dispersed NOVA 2.1.4 software. A three-electrode cell was employed using Ag/AgCl (3  M KCl) as reference electrode and a into 50 mL toluene and sonicated for 30 min. Next, 1.3 mL of APTMS was added and the mixture refluxed under nitro- platinum wire as counter-electrode (all potentials hereafter presented follow this reference). A glassy carbon electrode gen atmosphere at 30  °C for 3  h and then at 100  °C for another 3 h. Following, the reaction product was filtered and (GCE) (3 mm diameter) was used as working electrode in its original form and after surface modification. Bare and modi- washed thrice with toluene to remove the residual APTMS. The filtrate was dried in an over at 40 °C overnight, solid fied electrode surfaces were characterized by SEM using an Inspect S50 microscope (FEI company), with deposition of product denoted GO/APTMS. The GO/APTMS was then cross-linked with glutaraldehyde in the same fashion as the a thin coating of gold onto the modified electrodes prior to the analyses. BEA/APTMS. Resulting material denoted GO/APTMS/GA (See Fig. S2 for FT-IR characterization). 2.5 The glassy carbon electrode modification 2.3 T he synthesis BEA type nano‑sized zeolite The GCE electrode was modified by the drop cast method. The beta nanozeolite (BEA) synthesis was adapted from the procedure described by Larlus et al. [51]. The synthesis Initially, stock solutions (5 mg/mL) of BEA/APTMS/GA and GO were prepared in ethanol, followed by 30 min soni- gel was prepared by dissolving 0.56 g of aluminum isopro- poxide in 37.0 g of tetraethylammonium hydroxide solution cation for effective dispersion of the solid materials. The modifier BEA/APTMS/GA/GO solution was prepared by (TEAOH, 20%) under magnetic stirring for 1 h, followed by the addition of 6.05 g of Cab-o-sil. The precursor gel was mixing the suspensions obtained in a 1:1 proportion BEA/ APTMS/GA:GO immediately after sonication to mini- stirred and aged overnight at room temperature. Afterward, the gel was transferred to steel autoclaves with 120 mL Tef- mize precipitation and concomitantly achieve reproducible preparations. A 1.5% Nafion (NF) solution was also pre- lon liners, and the syntheses performed under autogenous conditions for 5 days at 140 °C. The nanocrystals were pared by diluting the 5% concentrated commercial solution in ultrapure water. Before modification, the GCE surface cooled to room temperature, recovered by centrifugation 13,400×g (Hitachi Koki Himac CR22N High-Speed Refrig- was polished using 0.3 µM alumina in a polishing pad, fol- lowed by sonication in ethanol and ultrapure water for 5 min erated Centrifuge), washed with deionized water until reach- ing pH < 8, and dried at 80 °C for 12 h. The as synthetized each, respectively, for the elimination of polishing residues. The casting process consisted of dropping with use of a material was then calcinated at 600 °C for 9 h to remove 1 3 Journal of Applied Electrochemistry micropipette two layers of 2 µL each of BEA/APTMS/GA/ 3 Results and discussion GO solution (sonicated for 1 min right before pipetting), 5 min wait for ethanol evaporation, followed by a final 2 µL 3.1 BPE cyclic voltammetry at bare and modified layer of NF solution. The NF solvent evaporation was per- GCE formed in open air and room temperature for 30 min. The obtained modified electrode is hereafter denominated GCE/ The search for a more sensitive electrode consisted in com- BEA/APTMS/GA/GO/NF. Other GCE modifications using parative experiments using CV to study the oxidation of BPE as modie fi rs NF, BEA/NF, BEA/APTMS/NF, BEA/APTMS/ at bare GCE and at a series of modified electrodes: BEA and GA/NF, GO/NF, GO/APTMS, GO/APTMS/GA, GO/BEA/ BEA derivatives only; GO only; GO derivatives; and finally, NF, and GO/BEA/APTMS/NF were performed following the BEA and BEA derivatives mixtures with GO. Figure 2 the same procedure. shows the oxidative part of CVs curves arising from 50 µM BPE in 0.1 M phosphate buffer solution (pH 5) for some of the modified electrodes in comparison with bare GCE. To 2.6 Electrochemical tests illustrate the analyte oxidation current despite background, the baselines (only buffer) were subtracted from the ana- The electrochemical characterization of the sensor was made lyte’s measurements and only the oxidative scan presented by use of cyclic voltammetry (CV) and differential pulse (see Supplementary Info, Fig. S3, to check the raw data full voltammetry (DPV). The CV voltammograms were recorded voltammograms). Oxidation peaks are noted in all curves, in a potential range from − 0.3 to 1.0 V using a scan rate of and the absence of reduction peaks (not shown) indicated −1 50 mVs . The supporting electrolyte initially used was a that the process was irreversible (see Fig. S3). The results 0.1 M sodium phosphate buffer solution, pH 5. A typical are similar to what is known for the analogous bisphenols experiment was performed as follows: 20 mL of 50 µM BPE BPA [, , 10, 53, 54], BPF [, 12, 13], and TBrBPA [, 55, 56]. solution in phosphate buffer was poured into the voltammet- Figure 2 highlights the results for the bare GCE in com- ric cell. Before measurements, nitrogen gas was purged into parison with GCE covered with BEA/APTMS/GA/NF, the solution for 5 min, and the atmosphere was kept under GO/NF, GO/BEA/APTMS/GA/NF, and GO/APTMS/GA/ nitrogen flow throughout the measurements to avoid oxygen NF. Lower anodic peak current intensity (I ) was noted for gas dissolution. The pH dependence was studied using Brit- modified BEA based electrode in absence of GO. However, ton–Robinson buffer to reduce the influence of supporting GCE/GO/NF presented an increase of I , and the electrode electrolyte on current values, as it can cover a broad range GCE/BEA/APTMS/GA/GO/NF had a remarkable increase of pH values. Prior to DPV measurements, the freshly made electrode was submitted to 20 CV’s cycles in phosphate buffer, pH 5, to verify its stabilization (reproducible base- lines). Following, 15 mL of various concentrations of ana- lyte solutions were added into the cell. A pre-conditioning step before DPV measurement was performed, in which the solution was purged with nitrogen gas while under vigorous stirring at an applied potential of 0.5 V for 90 s. The DPV recording proceeded in static state with no further purging. The increment potential, pulse period, pulse amplitude, and pulse width were adjusted at 0.075 mV, 0.4 s, 0.05 V, and 0.075 s, respectively. All measurements were performed in triplicate for statistical mean. 2.6.1 Recovery tests Tap water from Liverpool John Moores University was col- lect in a 200 mL glass container, filtered using 45 µm filters and stored at 4 °C for further analysis. Measurements were Fig. 2 The CV curves of 50  µM BPE solutions in 0.1  M phosphate buffer solution (pH 5) at bare or modified GCE electrodes (only performed using DPV optimized parameters. Recovery tests −1 oxidative scan shown). Scan rate: 50 mVs , under N atmosphere. carried out using the standard addition method with concen- Background was first recorded in the absence of analyte and sub- trations within the linear range obtained for the analytical tracted from the respective voltammograms. (see Fig. S3 for the calibration. respective unsubtracted full voltammograms) 1 3 Journal of Applied Electrochemistry of around seven folds higher than the bare GCE. All compo- potential measurements. The as-synthetized zeolites pre- nents of the GCE/BEA/APTMS/GA/GO/NF electrode were sented negative zeta potentials, while APTMS functional- tested separately, and none by itself gave a similar I to the ized zeolites showed slight positive potentials, and impor- BEA/APTMS/GA/GO/NF modified electrode. Intermediate tantly, the cross-linked materials showed potentials that were electrodes of the constituent parts gave analogous or slightly substantially more positive. The GCE/BEA/APTMS/GO/NF higher I in comparison to the bare GCE electrode (Fig. did not show much improvement on BPE oxidation; how- S3). To evaluate whether the functional groups arising from ever, the GCE/BEA/APTMS/GA/GO/NF electrode exceeded APTMS and GA would lead to higher I in the absence of expectations. Thus, it suggests that the zeolite electrostatic zeolite, the functionalization of GO with both reagents was surface features play a determinate role on analyte determi- carried out. Despite significant peak shift, the maximum cur - nation, and this could not be achieved by solely functional- rent was not much different than that found for the bare elec- izing GO. It appears that a more positively charged zeolite trode (Fig. 2), and significantly lower than unmodified GO, surface results in more favorable electrode interaction with which indicated that the addition of APTMS and GA to GO analyte. A balance between GO and nanozeolite specific had a negative influence on the electrode sensitivity.It is rea- electrostatic features is necessary, and only achieved after sonable to attribute the increased current output to a coactive using the GA based material, with surfaces more positively interaction between the coating components, which led to a charged. more favorable BPE interaction with the electrode surface. Additionally, the modified electrode did not show any Overall, Fig. 2 shows that the modified zeolite combined fouling caused by the deposition of BPE oxidation products; with GO was required for increased BPE electrooxidation. phenomena that is commonly reported in bare or modified Some reasonable understanding as to the causes of these electrodes for the analysis of BPs [, , , , , , 15, 19, 22, 27, 28, observations can be made based on the chemistry of modi- 30, 31], resulting from the deposition of oxidation products fied zeolites. It is clear that the nanozeolite functional sur - hindering further analyte oxidation. This is usually an effect face groups have a crucial role on the sensor electrochemi- observed after multiple voltammetry cycles, and it was not cal performance, consistent with previous reports of very observed for the number of cycles performed at the same complex processes occurring where functional groups were electrode in this study. included to improve the analyte interaction with the elec- Electrochemical behaviors of BPE at GCE/BEA/APTMS/ trode and concomitantly the quantification [, , , , 19, 20, GA/GO/NF with different scan rates (ν) were further investi - 22, 23, 57]. Based on our previous experience of zeolites gated. Figure 3A shows the CV curves obtained. Figure 3B functionalization [32], where alkoxysilane functionalization shows that the oxidation peak current increased linearly with −1 was performed, followed by glutaraldehyde cross-linking, scan rate in the range from 10 to 1000 m Vs , indicating zeolitic surface electrostatic changes were observed by zeta that the oxidation of BPE at GCE/BEA/APTMS/GA/GO/ Fig. 3 A Cyclic voltammograms of 50  µM BPE at GCE/BEA/ tively. Inset: Curves a–c. B Dependence of the oxidation peak cur- APTMS/GA/GO/NF with different scan rates. Curves (a–h) are rent (I ) on the scan rate. C Dependence of the oxidation peak current −1 obtained at 10, 20, 50, 100, 200, 300, 500, and 1000 mVs , respec- potential (E ) on the natural logarithm of scan rate (ν) 1 3 Journal of Applied Electrochemistry NF electrode was an adsorption-controlled process [58]. The regression equation were expressed as I = (0.0202 ± 0.0003) −1 ν + (1.57 ± 0.06) (µA, mVs , R = 0.997). Figure 3C shows the relationship between the peak poten- tial (E ) and the natural logarithm of scan rate ν. It can be observed that the anodic peak potential E changed line- arly versus ln(ν) with a linear regression equation of E = −1 (0.024 ± 0.001)ln(ν) + (0.598 ± 0.006) (V, mVs , R = 0.988) −1 in the range of 10 to 1000 mVs . For a totally irreversible electrode process, the relationship between the potential (E ) and scan rate (ν) is expressed as reported by Laviron [58]: E = E + (RT∕nF) ln RTk ∕nF +(RT∕nF) ln () p 0 s Where α is transfer coefficient, k is standard rate constant of the reaction, n is the electron transfer number, ν is the scan rate, E is the formal redox potential, R is the gas con- stant, T is the absolute temperature, and F is the Faraday −1 −1 constant (T = 294 K, R = 8.314 JK  mol , and F = 96,485 −1 Cmol ). According to the slope of the plot of E versus ln(ν), the value of αn was calculated to be 1.05. Generally, α is assumed to be 0.50 in a totally irreversible electrode process. This allowed the inference that the electron transfer number (n) for oxidation of bisphenol E was around 2. 3.2 pH dependence of BPE at GCE/GO/BEA/APTMS/ GA/NF The effect of pH on the electrochemical responses of BPE at GCE/GO/BEA/APTMS/GA/NF was studied over the pH range of 2.0–9.0 using Britton–Robinson buffer (Fig.  4A). As the process was adsorption-controlled, 90 s magnetic stirring was employed before measurements to guarantee Fig. 4 A The CV curves of 50 µM BPE in different pH values (Brit- diffusion to the electrode surface and reproducible amounts ton–Robinson buffer) at GCE/GO/BEA/APTMS/GA/NF electrode. of BPE at the electrode surface for the voltammetric cycles. Background was first recorded in the absence of analyte and sub- −1 The oxidation currents were very similar at pH values 2.0, tracted from the respective voltammograms. Scan rate 100  mVs, N atmosphere. B Dependence of the pH on the oxidation peak current 3.0, 5.0, and 7.0, slightly lower for pH 6.0 and considerable potential (E ) lower for pH values 4.0, 8.0, and 9.0. The pKa of BPE lies in the basic range (9.81–10.42 [59]), however, our observa- BPA behaved differently at the GCE/GO/BEA/APTMS/GA/ tions do not follow any trend. This behavior was different to that reported for BPA [24], where a maximum was observed NF electrode. Based on the low variation in peak current intensity at pH 5 and 2 for BPE, we reasoned to use pH 5 for at pH 8.0 using a GCE electrode decorated with magnetic nanoparticles and reduced graphene oxide. As no similar the continuation of the studies, and used phosphate buffer solution as carried out through the modification screening. studies to the best of our knowledge have been reported for BPE, we measured the behavior of BPA at the GCE/GO/ Further, the peak potential shifted negatively with the increase of pH value. The relationship between E and pH BEA/APTMS/GA/NF electrode for comparison. Interest- ingly, results diverge from the reported [24], with a maxi- is shown in Fig.  4B for BPE, and obeys the equation E = (− 0.0590 ± 0.003)pH + (1.00 ± 0.02) (V, R = 0.979). mum at pH 2.0, moderate oxidation current reduction at pH 3.0, and slightly lower current (compared with pH 3.0) for A slope of about − 59.0 mV per pH unit was close to the theoretical value of − 57.6 mV/pH. This indicated that an the pH values from 4.0 to 9.0 (Fig. S4 for BPA CV curves). This indicated the influence of the electrode composition on equal number of electrons and protons were involved in this electrochemical reaction [, , , , 18, 24, 27–29], therefore, the the pH dependence. Clearly, though, the bisphenol structure influenced the interaction with the electrode, as BPE and electrooxidation of BPE at GCE/GO/BEA/APTMS/GA/NF 1 3 Journal of Applied Electrochemistry for 90 s for the DPV measurements. The DPV parameters were also tested for optimization, and the highest current was measured when increment potential, pulse period, pulse amplitude, and pulse width were adjusted to 0.075 mV, 0.4 s, 0.05 V, and 0.075 s, respectively. Under the optimized con- Fig. 5 Proposed electrochemical reaction of BPE ditions, DPV of a series of BPE concentrations were col- lected, as shown in Fig. 6A. A linear relationship between was a two-electron and two-proton process, as the number of oxidation current (I ) and BPE concentration (C ) was p BPE electrons were estimated to be two in the previous section. obtained over the range of 0.07 and 4.81 μM (Fig. 6B), and The proposed electrochemical reaction equation of BPE is the regression equation was expressed as I = (0.52 ± 0.01) shown in Fig. 5. C + (0.011 ± 0.001) (µA, μM) with a correlation coeffi- BPE cient of 0.995. The limit of detection (LOD) was estimated 3.3 Insights of the electrode surface to be 0.056 μM (S/N = 3). For means of comparison, BPA was also tested and a linear regression was obtained for a Figure S5 shows the SEM images of the bare GCE elec- linear range of 0.2–4.00 μM, which obeyed the equation I trode (Fig. S5A) in comparison with the modified electrode = (1.00 ± 0.04)C + (0.170 ± 0.007) (µA, μM, R = 0.991)) BPA before (GCE/GO/BEA/APTMS/GA) (Fig. S5B) and after and LOD = 0.19 μM (S/N = 3) (See Fig. S6 for DPV curves NF coating (Fig. S5C). A flat surface was observed for the and linear regression fitting). The optimized conditions for bare GCE, while agglomerates were evident at the modified the two bisphenols were the same indicating that the elec- electrode. The aggregates are caused by the interaction of the trode was not selective toward bisphenols of similar struc- modifier components, BEA/APTMS/GA and GO, and may ture; although a lower LOD was obtained for BPE. In the give rise to the synergistic effect discussed before, where the work reported by Lu et al. using a MOF/tyrosinase biosensor disposition of the modifiers benefits the electrostatic adsorp- (2016) [45], the LOD for BPE was 0.015 μM, in a linear tion of BPE and the electron transfer, including an increase range of 0.05–3.0 μM, which is of similar sensitivity to the of the electrode surface area. Thorough characterization of electrode in this work. The observed differences regarding BEA and BEA functionalized derivatives were previously BPE and BPA electrode sensitivity and behavior was also reported [32], however, as the materials used in this work in line with previous observations of the substituent group consisted of new batches, XRD, SEM, and FT-IR characteri- properties (electron acceptor or electron donor) on the bis- zation data is presented in the Supplementary Information phenol framework having strong influence on the electrode (Fig. S1), which are consistent with the previously reported performance. Although the electrochemical determination of data. FT-IR data (Fig. S2) provided evidence for the effec- BPE is not vastly reported, the analytical performance of the tive functionalization of GO. Bands at wavelengths between presented sensor was comparable to other graphene oxide or −1 1000 and 1200  cm , were assigned to the C − N, Si − O − Si, zeolite material-based sensors reported in the literature for and Si − O − C bonds of the aminopropyl groups, as well the determination of BPA, what is pertinent considering that −1 as the N − H broad band at aproximately 3200  cm [52]. both BP’s have shown similar behavior in this work. Linear −1 Furthermore, bands in the region 1350–1750  cm were ranges and LOD are summarized in Table 1. It can be seen assigned to the bending mode of CH − R − CH and methyl that the presented sensor displays a comparable linear range group − CH of glutaraldehyde, as well as the C = O stretch- with an acceptable detection limit. ing mode [, 32, 52]. 3.5 Interference, repeatability, and stability 3.4 Differential pulse voltammetric determination In order to check the robustness of the methodology, an Differential pulse voltammetry (DPV) was chosen to check interference assay was performed using 4-chlorophenol the analytical performance of the electrode toward BPE. (CP), BPA, BPF, TBrBPA, and duroquinone (DQ). For this, A non-systematic optimization was performed to check the I of 2 μM BPE was compared with the I of 2 μM BPE p p the influence of parameters such as accumulation time and in solutions containing the same concentration of the pos- potential. Potentials from 0 to 0.5 V where checked at a sible interfering chemical. Figure 7A presents the relative I fixed time (60 s) with magnetic stirring, and no significant percentage recovery of the isolated BPE (100%) within the peak current increase was observed. However, the current mixtures. Among the tested compounds, only BPA showed a depended on accumulation time. An interval from 0 to 180 s substantial interference of around 40%. Nevertheless, it can was tested, and an increase was observed for the first 90 s be pointed out that a 100% interference would be expected and no increase was observed over longer periods. Based on if BPE and BPA had no specific interactions each with the these tests, an accumulation potential of 0.5 V was applied electrode surface as they oxidize at the same voltage (within 1 3 Journal of Applied Electrochemistry error). The analytical equations obtained (DPV calibration of BPE and BPA, Fig.  6B and Figure S6B, respectively) showed different slopes, 0.52 ± 0.01 (BPE) and 1.00 ± 0.04 (BPA), which numerically showed differences in the rate current/concentration that can be attributed to the interaction between analyte and electrode. To verify electrode repeatability and stability, two differ - ent GCE electrodes were coated on same day under the same conditions, and used to measure 2 μM BPE solutions on the day of preparation, and after 3 and 7 days, Fig. 7B. Repeat- ability was analyzed considering the percentage difference between consecutive measurements on the same day for one electrode, which were found to be lower than 3%. Good sta- bility was also verified, as the electrodes did not significantly present higher or lower current output in the seven-day time interval tested, with lower and maximum relative I within all measurements showing less than 10% difference. It is fair to point out that after measurements the electrodes were simply rinsed with distilled water, dried with a nitrogen flush and stored at room temperature in a closed container. 3.6 Application to analysis To validate the method proposed, the standard addition method was employed, and recoveries ranging from 91 to 109% were obtained, with residual standard deviation up to 6%, Table 2. The recovery tests indicate that the proposed method is suitable for BPE determination. Fig. 6 A The DPV curves for different BPE concentration (C ): a BPE 4 Conclusion − 0.07, b − 0.20, c − 0.33, d − 0.46, e − 0.71, f − 1.19, g − 2.09, h − 3.10, I − 4.00, and j − 4.81  µM. B Linear regression for the cali- In summary, it has been demonstrated that the modification bration C versus anodic peak current (I ). The increment poten- BPE p tial, pulse period, pulse amplitude, and pulse width were adjusted at of GCE with BEA/APTMS/GA/GO/NF nanocomposite was 0.075 mV, 0.4 s, 0.05 V, and 0.075 s, respectively effective for the highly sensitive determination of BPE. The Table 1 Comparison of the Sensor Bisphenol Linear range/μM Detection Refs analytical performance of limit/μM this work electrode with other electrochemical sensors GO-poly(NPBimBr)/GCE BPA 0.2–10.0 0.017 [20] graphene oxide/nanozeolite SiO /GO/AgNP/GCE BPA 0.1–2.6 0.127 [21] based for the determination of GO/APTES–MIP/GCE BPA 0.006–0.1 and 0.2–20 0.003 [22] BPE and BPA RGO/M-GCE BPA 0.01–200 0.004 [26] ZnTsPc/f-GN/GCE BPA 0.05–4.0 0.02 [23] ZrO (20%)/Nano-ZSM-5/GCE BPA 0.006–600.0 0.003 [44] PDMS@SNCM/ITO BPA 1–100 0.23 [31] α-MoO /CPE BPA 0.03–1.6 0.015 [30] CuMOFs-Tyr-Chi/GCE BPE 0.05–3.0 0.015 [45] BPA 0.05–3.0 0.013 ITO modified with A-G-GO BPA 5–1000 5 [46] BPE 10–1000 10 GCE/BEA/APTMS/GA/NF BPE 0.07–4.8 0.056 This work BPA 0.2–4.0 0.19 1 3 Journal of Applied Electrochemistry Table 2 Tap water analysis and recovery tests of BPE oxidation at GCE/GO/BEA/APTMS/GA/NF electrode Samples C added/µM C found/µM RSD/% Recovery/% BPE BPE Tap water 0 0 – – 0.483 0.530 1.46 91.12 1.049 1.050 2.82 99.99 1.557 1.570 3.63 99.14 2.026 2.080 2.31 97.41 interference toward CP, DQ, BPF and TBrBPA. Despite BPE and BPA having very similar peak potential dependence of pH, the current response diverged, which was in agreement with the observation of a higher response for BPE deter- mination compared to BPA using the optimized analytical method proposed. These differences can be hypothesized as response to BPs structural differences, what leads to spe- cific interactions between analytes and electrode surface and may be influenced by the observed surface agglomerates. The results suggest that the functionalized nanozeolite/gra- phene-based electrode is a potential platform for bisphenols determination. Supplementary Information The online version contains supplemen- tary material available at https://doi. or g/10. 1007/ s10800- 023- 01875-2 . Author contributions AJF, JGN and AHM wrote the main manuscript text; AHM and HTN carried out experiments and prepared figures. All authors reviewed the manuscript. Funding This research project was financially supported by São Paulo Research Foundation (FAPESP) in the form of graduate fellowship Fig. 7 A Interference test for BPE determination in the presence of (Grant Nos: 2016/24303-0 and 2018/21483-3). We would like to BPA, BPF, TBrBPA, DQ, and CP. DPV measurements under the opti- thank Paul Gibbons and Patrick Byrne (Liverpool John Moores Uni- mized conditions were employed to detect 2 µM of BPE only, or the versity) for the assistance with SEM images, and general assistance, same amount of BPE in the presence of 2 µM of the tested interfering respectively. compound. Relative anodic current (I ) was calculated considering the assay with no interfering as 100%. B Repeatability and stability Declarations tests for BPE determination using two different electrodes. Measure- ments performed at the day of preparation, after 3  days, and after Conflict of interest The authors declare no competing interests. 7  days, using 2  µM BPE solutions. Relative anodic current (I ) was calculated considering Electrode 1 first day as 100% Open Access This article is licensed under a Creative Commons Attri- bution 4.0 International License, which permits use, sharing, adapta- tion, distribution and reproduction in any medium or format, as long modifier composition, showed a synergistic effect toward as you give appropriate credit to the original author(s) and the source, electrode current response compared to bare GCE. This is provide a link to the Creative Commons licence, and indicate if changes hypothesized to be related to electrostatic changes on the were made. The images or other third party material in this article are zeolite surface due to the functionalization using APTMS included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in and GA, favoring analyte adsorption, as the electrochemi- the article's Creative Commons licence and your intended use is not cal process was adsorption-controlled and involves an equal permitted by statutory regulation or exceeds the permitted use, you will number of electrons and protons. The analytical method need to obtain permission directly from the copyright holder. To view a proposed presented good detection limits and linear range, copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . which are very close to the limit and range for the only elec- trochemical sensor for BPE reported (CuMOFs-Tyr-Chi/ GCE) [45]. In addition, the electrode has shown good repro- ducibility, repeatability and storage stability, as well as low 1 3 Journal of Applied Electrochemistry 32. de Vasconcellos A, Miller AH, Aranda DAG, Nery JG (2018) References Colloids Surf, B 165:150 33. Salih FE, Achiou B, Ouammou M, Bennazha J, Ouarzane A, 1. 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Antoniazzi C, de Lima CA, Marangoni R, de Castro EG, San- tana ER, Spinelli A (2020) Microchem J 159:105528 31. Wang J, Yu J, Yu Y, Luo Z, Li G, Lin X (2023) Food Chem 405:134806 1 3 Journal of Applied Electrochemistry Authors and Affiliations 1,2,3 1 2 1 Alex H. Miller  · Huong Thi‑Thanh Nguyen  · José G. Nery  · Alistair J. Fielding 1 3 Centre for Natural Products Discovery, School of Pharmacy Present Address: Department of Chemistry, University and Biomolecular Science, Liverpool John Moores of York, Heslington, York YO10 5DD, UK University, James Parsons Building, Byrom Street, Liverpool L3 3AF, UK Physics Department, Institute of Biosciences, Letters, and Exact Sciences—IBILCE/São Paulo State University— UNESP, São José Do Rio Preto, São Paulo 15054-000, Brazil 1 3 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Applied Electrochemistry Springer Journals

Electrochemical sensor based on epoxy-functionalized BEA nanozeolite and graphene oxide modified glassy carbon electrode for bisphenol E determination

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Abstract

An epoxy-functionalized beta type nanozeolite (BEA)/graphene oxide nanocomposite modified glassy carbon electrode (GCE/BEA/APTMS/GA/GO/NF) has been created for the differential pulse voltammetric determination of bisphenol E (BPE). The modified electrode presented an enhanced current response in comparison with bare GCE. A linear dependence of anodic peak current (I ) and scan rate (ν) was observed, which showed that the electrochemical process was adsorption- controlled. Differential pulse voltammetry (DPV) was employed and optimized for the sensitive determination of BPE. Under the optimized conditions, the anodic peak current was linearly proportional to BPE concentration in the range between 0.07 and 4.81 µM, with a correlation coefficient of 0.995 and limit of detection 0.056 μM (S/N = 3). The electrode showed good repeatability and storage stability, and a low response to interfering compounds. Comparison was made to the determination of bisphenol A. To confirm the electrode analytical performance, recovery tests were performed, and deviations lower than 10% were found. The BEA zeolite-GO nanocomposite proved to be a promising sensing platform for bisphenol determination. Graphical abstract Keywords BEA nanozeolite · Graphene oxide · Bisphenol E · Bisphenol A · Electrochemistry 1 Introduction Bisphenols (BPs) are a known group of endocrine disrupting compounds with adverse effects on human health and the environment [1]. Bisphenol A (BPA), 2, 2-bis (4-hydroxy- phenyl) propane, is the most used among BPs with a wide * Alistair J. Fielding a.j.fielding@ljmu.ac.uk range of applications, such as polycarbonate plastics manufacturing, with potent endocrine-disrupting activity. Extended author information available on the last page of the article Vol.:(0123456789) 1 3 Journal of Applied Electrochemistry Bisphenol E (BPE), 1,1-bis(4-hydroxyphenyl) ethane, which They indicated that the BPs molecular structure influ- has a structure very similar to BPA (Fig. 1) is another impor- enced electrode performance. Recently, Vaghela et  al. tant industrial chemical used as monomer for the production [46] described the preparation of a electrochemical bio- of polycarbonate plastics and epoxy resins [2]. BPE has been electrode containing entrapped tyrosinase in an agarose- reported to have similar acute toxicity and estrogenic activity guar gum-graphene oxide composite cast on indium tita- to that of BPA [, , , , 2–6]. nium oxide (ITO) glass plates. The mechanism of sensing Conventional chromatography, such as liquid chromatog- involved enzymatic oxidation of bisphenols to correspond- raphy (LC) or gas chromatography (GC), sometimes com- ing o-bisphenols and subsequently their reduction on the bined with mass-spectroscopy (MS); LC–MS and GC–MS; designed bioelectrodes at a potential of 80 mV. The limit and/or UV–Vis spectroscopy are sensitive and selective of detection found for BPE was 10 µM. To our knowledge, analytical procedures for the routine determination of BPs. there are no reports of zeolitic nanocomposites applied to Disposable or simple manufactured tools have been widely BPE electrochemical determination. used for environmental analysis in the last couple of years, in The creation of electrodes using zeolite in combination which electrochemical sensors or biosensors stand as good with graphene oxide (GO) has been reported [36]. GO is options due to their wide applicability and feasibility [, , 1, known for its high electronic conductivity, relatively inert 7, 8]. Advances in the area of nanostructured materials, have electrochemistry, biocompatibility, wide potential range made possible the design of a series of different electro- and low cost [47], and can act as a reinforcement for the chemical sensors, where nanocomposites are used to deco- assembling of oxides to form stable sensing platforms rate conventional glassy carbon electrodes (GCE) or screen [48]. These properties in combination with zeolites has printed electrodes (SPE) with reported increased sensitivity led to a great increase of the sensitivity [, , 36, 49, 50]. In a and/or selectivity for the determination of BPs [, , , , , , , , , previous work, we reported the synthesis and characteriza- , 9–19]. Graphene oxide (GO) nanocomposites or hybrids tion of nanozeolites, such as beta type zeolite (BEA), and with other materials [, , , , , , 20–26] are also examples of its alkoxysilane functionalization with (3-aminopropyl) nanomaterials used for this purpose. Surfactants, dendrim- trimethoxysilane (APTMS), followed by cross-linking ers, ionic liquids, among others, are additional materials with glutaraldehyde (GA) [32]. Herein, we report the used for the preparation of electrochemical sensors for BPs application of BEA/APTMS/GA and GO decorated GCE determination [, , , , 27–31]. to bisphenol E determination. Unmodified and modified Among many different materials, micro- and nano-sized nanozeolite and GO suspensions were prepared in etha- zeolites have attracted extensive attention due to their mul- nol and used for GCE coating by a drop coating method. tifunctional properties such as small sizes, biocompatibility, Nafion (NF) polymer was used to complete the coating and high surface area, and the possibility of modulation [32] of guarantee that modifiers did not leach from the electrode their hydrophilicity and hydrophobicity on electrode sur- surface. The intensity of the oxidation peak of BPE was faces for applications of sensing [, , , 33–36] and biosensing significantly increased when using GCE/BEA/APTMS/ [, , , , , , 37–43]. An electrochemical sensor for BPA quanti- GA/GO/NF in comparison with bare GCE or other tested fication using ZrO supported Nano-ZSM-5 nanocomposite modified electrodes. This electrode was then selected for with nanomolar sensitivity has been reported recently [44], further investigation of its electrochemical properties and and used for real sample analysis. analytical performance. Although a wide range of different electrodes have been reported for BPA determination, few works have targeted BPE and/or studied its potential interference proper- ties during electrochemical analytical methods used for 2 Experimental BPs. Lu et al. [45] reported a Metal–Organic Framework (MOF)-based tyrosinase electrochemical sensor for a 2.1 Reagents series of BPs, including BPE, with nanomolar sensitivity. Aluminum isopropoxide (98%), tetraethylammonium hydroxide solution (20%), Cab-O-sil® M-5, graphene oxide (15–20 sheets, 4–10% edge-oxidized), Nafion solution (5 wt%), ethanol (99.8%), inorganic salts, glutaraldehyde solution (25%), (3-aminopropyl)trimethoxysilane (APTMS, 97%), and anhydrous dichloromethane were purchased from Sigma-Aldrich. All chemicals were used without further purification. Fig. 1 Bisphenols A and E structures 1 3 Journal of Applied Electrochemistry the organic templates. Calcinated material hereafter denoted 2.2 Instrumentation BEA. See Figure S1 for XRD patterns and SEM images. The crystallographic structure and morphology of the syn- thetized nanozeolite were determined by X-ray diffraction 2.4 BEA and GO functionalization (XRD) and scanning electron microscopy (SEM). The XRD analyses were performed with a MiniFlex II instru- The BEA was alkoxysilane surface functionalized as previ- ous reported [32]. Initially, 1 g of BEA was suspended in a ment (Rigaku, Tokyo, Japan) equipped with a rotating anode source with flat-plate Bragg–Brentano geometry and solution containing 30 mL of dichloromethane and 1 mL of APTMS, and the suspension stirred for 16  h at room a graphite monochromator, operating at 40 kV and 40 mA, with Cu Kα radiation (wavelength = 1.5418 Å). The powder temperature. The obtained material was then centrifuged (13,400×g) and washed several times with distilled water diffraction patterns were recorded in the 2θ range from 3° to −1 50°, with scanning at a goniometer rate of 2° min . SEM to remove the unreacted APTMS. The final precipitated was dried at 60 °C for 12 h, and denoted BEA/APTMS. images were recorded using a Magellan 400 L instrument (FEI Company), with deposition of a thin coating of gold Finally, the BEA/APTMS functionalized nanozeolite was cross-linked with glutaraldehyde (GA). The experiment onto the samples prior to the analyses. Surface alkoxysilane functionalization was measured using Fourier transform was performed as follows: 1 g of BEA/APTMS nanozeolite was mixed with 20 mL of a 5% glutaraldehyde solution by infrared (FT-IR). FT-IR spectra were acquired using a Perki- nElmer Frontier FT-IR spectrometer equipped with an ATR magnetic stirring for 24 h at room temperature. The GA- functionalized nanozeolite was collected by centrifugation accessory. The samples were scanned 64 times between −1 −1 4000 and 400  cm , at a resolution of 4  cm . (13,400×g) and the solid product was washed three times with distilled water, dried at room temperature, and stored All electrochemical apparatus, including electrodes, was purchased from Metrohm, Netherlands. The electrochemi- under vacuum in order to prevent oxidation. Cross-linked material denoted BEA/APTMS/GA (See Fig. S1 for FT-IR cal process was performed using Autolab potentiostat/galva- nostat equipment (PGSTAT 101), and data processed using characterization). The GO functionalization with APTMS was adapted from Lin et al. [52]. 200 mg GO was dispersed NOVA 2.1.4 software. A three-electrode cell was employed using Ag/AgCl (3  M KCl) as reference electrode and a into 50 mL toluene and sonicated for 30 min. Next, 1.3 mL of APTMS was added and the mixture refluxed under nitro- platinum wire as counter-electrode (all potentials hereafter presented follow this reference). A glassy carbon electrode gen atmosphere at 30  °C for 3  h and then at 100  °C for another 3 h. Following, the reaction product was filtered and (GCE) (3 mm diameter) was used as working electrode in its original form and after surface modification. Bare and modi- washed thrice with toluene to remove the residual APTMS. The filtrate was dried in an over at 40 °C overnight, solid fied electrode surfaces were characterized by SEM using an Inspect S50 microscope (FEI company), with deposition of product denoted GO/APTMS. The GO/APTMS was then cross-linked with glutaraldehyde in the same fashion as the a thin coating of gold onto the modified electrodes prior to the analyses. BEA/APTMS. Resulting material denoted GO/APTMS/GA (See Fig. S2 for FT-IR characterization). 2.5 The glassy carbon electrode modification 2.3 T he synthesis BEA type nano‑sized zeolite The GCE electrode was modified by the drop cast method. The beta nanozeolite (BEA) synthesis was adapted from the procedure described by Larlus et al. [51]. The synthesis Initially, stock solutions (5 mg/mL) of BEA/APTMS/GA and GO were prepared in ethanol, followed by 30 min soni- gel was prepared by dissolving 0.56 g of aluminum isopro- poxide in 37.0 g of tetraethylammonium hydroxide solution cation for effective dispersion of the solid materials. The modifier BEA/APTMS/GA/GO solution was prepared by (TEAOH, 20%) under magnetic stirring for 1 h, followed by the addition of 6.05 g of Cab-o-sil. The precursor gel was mixing the suspensions obtained in a 1:1 proportion BEA/ APTMS/GA:GO immediately after sonication to mini- stirred and aged overnight at room temperature. Afterward, the gel was transferred to steel autoclaves with 120 mL Tef- mize precipitation and concomitantly achieve reproducible preparations. A 1.5% Nafion (NF) solution was also pre- lon liners, and the syntheses performed under autogenous conditions for 5 days at 140 °C. The nanocrystals were pared by diluting the 5% concentrated commercial solution in ultrapure water. Before modification, the GCE surface cooled to room temperature, recovered by centrifugation 13,400×g (Hitachi Koki Himac CR22N High-Speed Refrig- was polished using 0.3 µM alumina in a polishing pad, fol- lowed by sonication in ethanol and ultrapure water for 5 min erated Centrifuge), washed with deionized water until reach- ing pH < 8, and dried at 80 °C for 12 h. The as synthetized each, respectively, for the elimination of polishing residues. The casting process consisted of dropping with use of a material was then calcinated at 600 °C for 9 h to remove 1 3 Journal of Applied Electrochemistry micropipette two layers of 2 µL each of BEA/APTMS/GA/ 3 Results and discussion GO solution (sonicated for 1 min right before pipetting), 5 min wait for ethanol evaporation, followed by a final 2 µL 3.1 BPE cyclic voltammetry at bare and modified layer of NF solution. The NF solvent evaporation was per- GCE formed in open air and room temperature for 30 min. The obtained modified electrode is hereafter denominated GCE/ The search for a more sensitive electrode consisted in com- BEA/APTMS/GA/GO/NF. Other GCE modifications using parative experiments using CV to study the oxidation of BPE as modie fi rs NF, BEA/NF, BEA/APTMS/NF, BEA/APTMS/ at bare GCE and at a series of modified electrodes: BEA and GA/NF, GO/NF, GO/APTMS, GO/APTMS/GA, GO/BEA/ BEA derivatives only; GO only; GO derivatives; and finally, NF, and GO/BEA/APTMS/NF were performed following the BEA and BEA derivatives mixtures with GO. Figure 2 the same procedure. shows the oxidative part of CVs curves arising from 50 µM BPE in 0.1 M phosphate buffer solution (pH 5) for some of the modified electrodes in comparison with bare GCE. To 2.6 Electrochemical tests illustrate the analyte oxidation current despite background, the baselines (only buffer) were subtracted from the ana- The electrochemical characterization of the sensor was made lyte’s measurements and only the oxidative scan presented by use of cyclic voltammetry (CV) and differential pulse (see Supplementary Info, Fig. S3, to check the raw data full voltammetry (DPV). The CV voltammograms were recorded voltammograms). Oxidation peaks are noted in all curves, in a potential range from − 0.3 to 1.0 V using a scan rate of and the absence of reduction peaks (not shown) indicated −1 50 mVs . The supporting electrolyte initially used was a that the process was irreversible (see Fig. S3). The results 0.1 M sodium phosphate buffer solution, pH 5. A typical are similar to what is known for the analogous bisphenols experiment was performed as follows: 20 mL of 50 µM BPE BPA [, , 10, 53, 54], BPF [, 12, 13], and TBrBPA [, 55, 56]. solution in phosphate buffer was poured into the voltammet- Figure 2 highlights the results for the bare GCE in com- ric cell. Before measurements, nitrogen gas was purged into parison with GCE covered with BEA/APTMS/GA/NF, the solution for 5 min, and the atmosphere was kept under GO/NF, GO/BEA/APTMS/GA/NF, and GO/APTMS/GA/ nitrogen flow throughout the measurements to avoid oxygen NF. Lower anodic peak current intensity (I ) was noted for gas dissolution. The pH dependence was studied using Brit- modified BEA based electrode in absence of GO. However, ton–Robinson buffer to reduce the influence of supporting GCE/GO/NF presented an increase of I , and the electrode electrolyte on current values, as it can cover a broad range GCE/BEA/APTMS/GA/GO/NF had a remarkable increase of pH values. Prior to DPV measurements, the freshly made electrode was submitted to 20 CV’s cycles in phosphate buffer, pH 5, to verify its stabilization (reproducible base- lines). Following, 15 mL of various concentrations of ana- lyte solutions were added into the cell. A pre-conditioning step before DPV measurement was performed, in which the solution was purged with nitrogen gas while under vigorous stirring at an applied potential of 0.5 V for 90 s. The DPV recording proceeded in static state with no further purging. The increment potential, pulse period, pulse amplitude, and pulse width were adjusted at 0.075 mV, 0.4 s, 0.05 V, and 0.075 s, respectively. All measurements were performed in triplicate for statistical mean. 2.6.1 Recovery tests Tap water from Liverpool John Moores University was col- lect in a 200 mL glass container, filtered using 45 µm filters and stored at 4 °C for further analysis. Measurements were Fig. 2 The CV curves of 50  µM BPE solutions in 0.1  M phosphate buffer solution (pH 5) at bare or modified GCE electrodes (only performed using DPV optimized parameters. Recovery tests −1 oxidative scan shown). Scan rate: 50 mVs , under N atmosphere. carried out using the standard addition method with concen- Background was first recorded in the absence of analyte and sub- trations within the linear range obtained for the analytical tracted from the respective voltammograms. (see Fig. S3 for the calibration. respective unsubtracted full voltammograms) 1 3 Journal of Applied Electrochemistry of around seven folds higher than the bare GCE. All compo- potential measurements. The as-synthetized zeolites pre- nents of the GCE/BEA/APTMS/GA/GO/NF electrode were sented negative zeta potentials, while APTMS functional- tested separately, and none by itself gave a similar I to the ized zeolites showed slight positive potentials, and impor- BEA/APTMS/GA/GO/NF modified electrode. Intermediate tantly, the cross-linked materials showed potentials that were electrodes of the constituent parts gave analogous or slightly substantially more positive. The GCE/BEA/APTMS/GO/NF higher I in comparison to the bare GCE electrode (Fig. did not show much improvement on BPE oxidation; how- S3). To evaluate whether the functional groups arising from ever, the GCE/BEA/APTMS/GA/GO/NF electrode exceeded APTMS and GA would lead to higher I in the absence of expectations. Thus, it suggests that the zeolite electrostatic zeolite, the functionalization of GO with both reagents was surface features play a determinate role on analyte determi- carried out. Despite significant peak shift, the maximum cur - nation, and this could not be achieved by solely functional- rent was not much different than that found for the bare elec- izing GO. It appears that a more positively charged zeolite trode (Fig. 2), and significantly lower than unmodified GO, surface results in more favorable electrode interaction with which indicated that the addition of APTMS and GA to GO analyte. A balance between GO and nanozeolite specific had a negative influence on the electrode sensitivity.It is rea- electrostatic features is necessary, and only achieved after sonable to attribute the increased current output to a coactive using the GA based material, with surfaces more positively interaction between the coating components, which led to a charged. more favorable BPE interaction with the electrode surface. Additionally, the modified electrode did not show any Overall, Fig. 2 shows that the modified zeolite combined fouling caused by the deposition of BPE oxidation products; with GO was required for increased BPE electrooxidation. phenomena that is commonly reported in bare or modified Some reasonable understanding as to the causes of these electrodes for the analysis of BPs [, , , , , , 15, 19, 22, 27, 28, observations can be made based on the chemistry of modi- 30, 31], resulting from the deposition of oxidation products fied zeolites. It is clear that the nanozeolite functional sur - hindering further analyte oxidation. This is usually an effect face groups have a crucial role on the sensor electrochemi- observed after multiple voltammetry cycles, and it was not cal performance, consistent with previous reports of very observed for the number of cycles performed at the same complex processes occurring where functional groups were electrode in this study. included to improve the analyte interaction with the elec- Electrochemical behaviors of BPE at GCE/BEA/APTMS/ trode and concomitantly the quantification [, , , , 19, 20, GA/GO/NF with different scan rates (ν) were further investi - 22, 23, 57]. Based on our previous experience of zeolites gated. Figure 3A shows the CV curves obtained. Figure 3B functionalization [32], where alkoxysilane functionalization shows that the oxidation peak current increased linearly with −1 was performed, followed by glutaraldehyde cross-linking, scan rate in the range from 10 to 1000 m Vs , indicating zeolitic surface electrostatic changes were observed by zeta that the oxidation of BPE at GCE/BEA/APTMS/GA/GO/ Fig. 3 A Cyclic voltammograms of 50  µM BPE at GCE/BEA/ tively. Inset: Curves a–c. B Dependence of the oxidation peak cur- APTMS/GA/GO/NF with different scan rates. Curves (a–h) are rent (I ) on the scan rate. C Dependence of the oxidation peak current −1 obtained at 10, 20, 50, 100, 200, 300, 500, and 1000 mVs , respec- potential (E ) on the natural logarithm of scan rate (ν) 1 3 Journal of Applied Electrochemistry NF electrode was an adsorption-controlled process [58]. The regression equation were expressed as I = (0.0202 ± 0.0003) −1 ν + (1.57 ± 0.06) (µA, mVs , R = 0.997). Figure 3C shows the relationship between the peak poten- tial (E ) and the natural logarithm of scan rate ν. It can be observed that the anodic peak potential E changed line- arly versus ln(ν) with a linear regression equation of E = −1 (0.024 ± 0.001)ln(ν) + (0.598 ± 0.006) (V, mVs , R = 0.988) −1 in the range of 10 to 1000 mVs . For a totally irreversible electrode process, the relationship between the potential (E ) and scan rate (ν) is expressed as reported by Laviron [58]: E = E + (RT∕nF) ln RTk ∕nF +(RT∕nF) ln () p 0 s Where α is transfer coefficient, k is standard rate constant of the reaction, n is the electron transfer number, ν is the scan rate, E is the formal redox potential, R is the gas con- stant, T is the absolute temperature, and F is the Faraday −1 −1 constant (T = 294 K, R = 8.314 JK  mol , and F = 96,485 −1 Cmol ). According to the slope of the plot of E versus ln(ν), the value of αn was calculated to be 1.05. Generally, α is assumed to be 0.50 in a totally irreversible electrode process. This allowed the inference that the electron transfer number (n) for oxidation of bisphenol E was around 2. 3.2 pH dependence of BPE at GCE/GO/BEA/APTMS/ GA/NF The effect of pH on the electrochemical responses of BPE at GCE/GO/BEA/APTMS/GA/NF was studied over the pH range of 2.0–9.0 using Britton–Robinson buffer (Fig.  4A). As the process was adsorption-controlled, 90 s magnetic stirring was employed before measurements to guarantee Fig. 4 A The CV curves of 50 µM BPE in different pH values (Brit- diffusion to the electrode surface and reproducible amounts ton–Robinson buffer) at GCE/GO/BEA/APTMS/GA/NF electrode. of BPE at the electrode surface for the voltammetric cycles. Background was first recorded in the absence of analyte and sub- −1 The oxidation currents were very similar at pH values 2.0, tracted from the respective voltammograms. Scan rate 100  mVs, N atmosphere. B Dependence of the pH on the oxidation peak current 3.0, 5.0, and 7.0, slightly lower for pH 6.0 and considerable potential (E ) lower for pH values 4.0, 8.0, and 9.0. The pKa of BPE lies in the basic range (9.81–10.42 [59]), however, our observa- BPA behaved differently at the GCE/GO/BEA/APTMS/GA/ tions do not follow any trend. This behavior was different to that reported for BPA [24], where a maximum was observed NF electrode. Based on the low variation in peak current intensity at pH 5 and 2 for BPE, we reasoned to use pH 5 for at pH 8.0 using a GCE electrode decorated with magnetic nanoparticles and reduced graphene oxide. As no similar the continuation of the studies, and used phosphate buffer solution as carried out through the modification screening. studies to the best of our knowledge have been reported for BPE, we measured the behavior of BPA at the GCE/GO/ Further, the peak potential shifted negatively with the increase of pH value. The relationship between E and pH BEA/APTMS/GA/NF electrode for comparison. Interest- ingly, results diverge from the reported [24], with a maxi- is shown in Fig.  4B for BPE, and obeys the equation E = (− 0.0590 ± 0.003)pH + (1.00 ± 0.02) (V, R = 0.979). mum at pH 2.0, moderate oxidation current reduction at pH 3.0, and slightly lower current (compared with pH 3.0) for A slope of about − 59.0 mV per pH unit was close to the theoretical value of − 57.6 mV/pH. This indicated that an the pH values from 4.0 to 9.0 (Fig. S4 for BPA CV curves). This indicated the influence of the electrode composition on equal number of electrons and protons were involved in this electrochemical reaction [, , , , 18, 24, 27–29], therefore, the the pH dependence. Clearly, though, the bisphenol structure influenced the interaction with the electrode, as BPE and electrooxidation of BPE at GCE/GO/BEA/APTMS/GA/NF 1 3 Journal of Applied Electrochemistry for 90 s for the DPV measurements. The DPV parameters were also tested for optimization, and the highest current was measured when increment potential, pulse period, pulse amplitude, and pulse width were adjusted to 0.075 mV, 0.4 s, 0.05 V, and 0.075 s, respectively. Under the optimized con- Fig. 5 Proposed electrochemical reaction of BPE ditions, DPV of a series of BPE concentrations were col- lected, as shown in Fig. 6A. A linear relationship between was a two-electron and two-proton process, as the number of oxidation current (I ) and BPE concentration (C ) was p BPE electrons were estimated to be two in the previous section. obtained over the range of 0.07 and 4.81 μM (Fig. 6B), and The proposed electrochemical reaction equation of BPE is the regression equation was expressed as I = (0.52 ± 0.01) shown in Fig. 5. C + (0.011 ± 0.001) (µA, μM) with a correlation coeffi- BPE cient of 0.995. The limit of detection (LOD) was estimated 3.3 Insights of the electrode surface to be 0.056 μM (S/N = 3). For means of comparison, BPA was also tested and a linear regression was obtained for a Figure S5 shows the SEM images of the bare GCE elec- linear range of 0.2–4.00 μM, which obeyed the equation I trode (Fig. S5A) in comparison with the modified electrode = (1.00 ± 0.04)C + (0.170 ± 0.007) (µA, μM, R = 0.991)) BPA before (GCE/GO/BEA/APTMS/GA) (Fig. S5B) and after and LOD = 0.19 μM (S/N = 3) (See Fig. S6 for DPV curves NF coating (Fig. S5C). A flat surface was observed for the and linear regression fitting). The optimized conditions for bare GCE, while agglomerates were evident at the modified the two bisphenols were the same indicating that the elec- electrode. The aggregates are caused by the interaction of the trode was not selective toward bisphenols of similar struc- modifier components, BEA/APTMS/GA and GO, and may ture; although a lower LOD was obtained for BPE. In the give rise to the synergistic effect discussed before, where the work reported by Lu et al. using a MOF/tyrosinase biosensor disposition of the modifiers benefits the electrostatic adsorp- (2016) [45], the LOD for BPE was 0.015 μM, in a linear tion of BPE and the electron transfer, including an increase range of 0.05–3.0 μM, which is of similar sensitivity to the of the electrode surface area. Thorough characterization of electrode in this work. The observed differences regarding BEA and BEA functionalized derivatives were previously BPE and BPA electrode sensitivity and behavior was also reported [32], however, as the materials used in this work in line with previous observations of the substituent group consisted of new batches, XRD, SEM, and FT-IR characteri- properties (electron acceptor or electron donor) on the bis- zation data is presented in the Supplementary Information phenol framework having strong influence on the electrode (Fig. S1), which are consistent with the previously reported performance. Although the electrochemical determination of data. FT-IR data (Fig. S2) provided evidence for the effec- BPE is not vastly reported, the analytical performance of the tive functionalization of GO. Bands at wavelengths between presented sensor was comparable to other graphene oxide or −1 1000 and 1200  cm , were assigned to the C − N, Si − O − Si, zeolite material-based sensors reported in the literature for and Si − O − C bonds of the aminopropyl groups, as well the determination of BPA, what is pertinent considering that −1 as the N − H broad band at aproximately 3200  cm [52]. both BP’s have shown similar behavior in this work. Linear −1 Furthermore, bands in the region 1350–1750  cm were ranges and LOD are summarized in Table 1. It can be seen assigned to the bending mode of CH − R − CH and methyl that the presented sensor displays a comparable linear range group − CH of glutaraldehyde, as well as the C = O stretch- with an acceptable detection limit. ing mode [, 32, 52]. 3.5 Interference, repeatability, and stability 3.4 Differential pulse voltammetric determination In order to check the robustness of the methodology, an Differential pulse voltammetry (DPV) was chosen to check interference assay was performed using 4-chlorophenol the analytical performance of the electrode toward BPE. (CP), BPA, BPF, TBrBPA, and duroquinone (DQ). For this, A non-systematic optimization was performed to check the I of 2 μM BPE was compared with the I of 2 μM BPE p p the influence of parameters such as accumulation time and in solutions containing the same concentration of the pos- potential. Potentials from 0 to 0.5 V where checked at a sible interfering chemical. Figure 7A presents the relative I fixed time (60 s) with magnetic stirring, and no significant percentage recovery of the isolated BPE (100%) within the peak current increase was observed. However, the current mixtures. Among the tested compounds, only BPA showed a depended on accumulation time. An interval from 0 to 180 s substantial interference of around 40%. Nevertheless, it can was tested, and an increase was observed for the first 90 s be pointed out that a 100% interference would be expected and no increase was observed over longer periods. Based on if BPE and BPA had no specific interactions each with the these tests, an accumulation potential of 0.5 V was applied electrode surface as they oxidize at the same voltage (within 1 3 Journal of Applied Electrochemistry error). The analytical equations obtained (DPV calibration of BPE and BPA, Fig.  6B and Figure S6B, respectively) showed different slopes, 0.52 ± 0.01 (BPE) and 1.00 ± 0.04 (BPA), which numerically showed differences in the rate current/concentration that can be attributed to the interaction between analyte and electrode. To verify electrode repeatability and stability, two differ - ent GCE electrodes were coated on same day under the same conditions, and used to measure 2 μM BPE solutions on the day of preparation, and after 3 and 7 days, Fig. 7B. Repeat- ability was analyzed considering the percentage difference between consecutive measurements on the same day for one electrode, which were found to be lower than 3%. Good sta- bility was also verified, as the electrodes did not significantly present higher or lower current output in the seven-day time interval tested, with lower and maximum relative I within all measurements showing less than 10% difference. It is fair to point out that after measurements the electrodes were simply rinsed with distilled water, dried with a nitrogen flush and stored at room temperature in a closed container. 3.6 Application to analysis To validate the method proposed, the standard addition method was employed, and recoveries ranging from 91 to 109% were obtained, with residual standard deviation up to 6%, Table 2. The recovery tests indicate that the proposed method is suitable for BPE determination. Fig. 6 A The DPV curves for different BPE concentration (C ): a BPE 4 Conclusion − 0.07, b − 0.20, c − 0.33, d − 0.46, e − 0.71, f − 1.19, g − 2.09, h − 3.10, I − 4.00, and j − 4.81  µM. B Linear regression for the cali- In summary, it has been demonstrated that the modification bration C versus anodic peak current (I ). The increment poten- BPE p tial, pulse period, pulse amplitude, and pulse width were adjusted at of GCE with BEA/APTMS/GA/GO/NF nanocomposite was 0.075 mV, 0.4 s, 0.05 V, and 0.075 s, respectively effective for the highly sensitive determination of BPE. The Table 1 Comparison of the Sensor Bisphenol Linear range/μM Detection Refs analytical performance of limit/μM this work electrode with other electrochemical sensors GO-poly(NPBimBr)/GCE BPA 0.2–10.0 0.017 [20] graphene oxide/nanozeolite SiO /GO/AgNP/GCE BPA 0.1–2.6 0.127 [21] based for the determination of GO/APTES–MIP/GCE BPA 0.006–0.1 and 0.2–20 0.003 [22] BPE and BPA RGO/M-GCE BPA 0.01–200 0.004 [26] ZnTsPc/f-GN/GCE BPA 0.05–4.0 0.02 [23] ZrO (20%)/Nano-ZSM-5/GCE BPA 0.006–600.0 0.003 [44] PDMS@SNCM/ITO BPA 1–100 0.23 [31] α-MoO /CPE BPA 0.03–1.6 0.015 [30] CuMOFs-Tyr-Chi/GCE BPE 0.05–3.0 0.015 [45] BPA 0.05–3.0 0.013 ITO modified with A-G-GO BPA 5–1000 5 [46] BPE 10–1000 10 GCE/BEA/APTMS/GA/NF BPE 0.07–4.8 0.056 This work BPA 0.2–4.0 0.19 1 3 Journal of Applied Electrochemistry Table 2 Tap water analysis and recovery tests of BPE oxidation at GCE/GO/BEA/APTMS/GA/NF electrode Samples C added/µM C found/µM RSD/% Recovery/% BPE BPE Tap water 0 0 – – 0.483 0.530 1.46 91.12 1.049 1.050 2.82 99.99 1.557 1.570 3.63 99.14 2.026 2.080 2.31 97.41 interference toward CP, DQ, BPF and TBrBPA. Despite BPE and BPA having very similar peak potential dependence of pH, the current response diverged, which was in agreement with the observation of a higher response for BPE deter- mination compared to BPA using the optimized analytical method proposed. These differences can be hypothesized as response to BPs structural differences, what leads to spe- cific interactions between analytes and electrode surface and may be influenced by the observed surface agglomerates. The results suggest that the functionalized nanozeolite/gra- phene-based electrode is a potential platform for bisphenols determination. Supplementary Information The online version contains supplemen- tary material available at https://doi. or g/10. 1007/ s10800- 023- 01875-2 . Author contributions AJF, JGN and AHM wrote the main manuscript text; AHM and HTN carried out experiments and prepared figures. All authors reviewed the manuscript. Funding This research project was financially supported by São Paulo Research Foundation (FAPESP) in the form of graduate fellowship Fig. 7 A Interference test for BPE determination in the presence of (Grant Nos: 2016/24303-0 and 2018/21483-3). We would like to BPA, BPF, TBrBPA, DQ, and CP. DPV measurements under the opti- thank Paul Gibbons and Patrick Byrne (Liverpool John Moores Uni- mized conditions were employed to detect 2 µM of BPE only, or the versity) for the assistance with SEM images, and general assistance, same amount of BPE in the presence of 2 µM of the tested interfering respectively. compound. Relative anodic current (I ) was calculated considering the assay with no interfering as 100%. B Repeatability and stability Declarations tests for BPE determination using two different electrodes. Measure- ments performed at the day of preparation, after 3  days, and after Conflict of interest The authors declare no competing interests. 7  days, using 2  µM BPE solutions. Relative anodic current (I ) was calculated considering Electrode 1 first day as 100% Open Access This article is licensed under a Creative Commons Attri- bution 4.0 International License, which permits use, sharing, adapta- tion, distribution and reproduction in any medium or format, as long modifier composition, showed a synergistic effect toward as you give appropriate credit to the original author(s) and the source, electrode current response compared to bare GCE. This is provide a link to the Creative Commons licence, and indicate if changes hypothesized to be related to electrostatic changes on the were made. The images or other third party material in this article are zeolite surface due to the functionalization using APTMS included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in and GA, favoring analyte adsorption, as the electrochemi- the article's Creative Commons licence and your intended use is not cal process was adsorption-controlled and involves an equal permitted by statutory regulation or exceeds the permitted use, you will number of electrons and protons. The analytical method need to obtain permission directly from the copyright holder. To view a proposed presented good detection limits and linear range, copy of this licence, visit http://cr eativ ecommons. or g/licen ses/ b y/4.0/ . which are very close to the limit and range for the only elec- trochemical sensor for BPE reported (CuMOFs-Tyr-Chi/ GCE) [45]. In addition, the electrode has shown good repro- ducibility, repeatability and storage stability, as well as low 1 3 Journal of Applied Electrochemistry 32. de Vasconcellos A, Miller AH, Aranda DAG, Nery JG (2018) References Colloids Surf, B 165:150 33. Salih FE, Achiou B, Ouammou M, Bennazha J, Ouarzane A, 1. 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Antoniazzi C, de Lima CA, Marangoni R, de Castro EG, San- tana ER, Spinelli A (2020) Microchem J 159:105528 31. Wang J, Yu J, Yu Y, Luo Z, Li G, Lin X (2023) Food Chem 405:134806 1 3 Journal of Applied Electrochemistry Authors and Affiliations 1,2,3 1 2 1 Alex H. Miller  · Huong Thi‑Thanh Nguyen  · José G. Nery  · Alistair J. Fielding 1 3 Centre for Natural Products Discovery, School of Pharmacy Present Address: Department of Chemistry, University and Biomolecular Science, Liverpool John Moores of York, Heslington, York YO10 5DD, UK University, James Parsons Building, Byrom Street, Liverpool L3 3AF, UK Physics Department, Institute of Biosciences, Letters, and Exact Sciences—IBILCE/São Paulo State University— UNESP, São José Do Rio Preto, São Paulo 15054-000, Brazil 1 3

Journal

Journal of Applied Electrochemistry – Springer Journals

Published: Mar 18, 2023

Keywords: BEA nanozeolite; Graphene oxide; Bisphenol E; Bisphenol A; Electrochemistry

References