Nanocomposite material in the trace and simultaneous electrochemical detection of As(III) and As(V)

Melody Lalhruaitluangi; Ricky Lalawmpuia; Diwakar Tiwari; Rama Dubey

doi:10.4491/eer.2024.663

Environ Eng Res > Volume 30(5); 2025 > Article

Lalhruaitluangi, Lalawmpuia, Tiwari, and Dubey: Nanocomposite material in the trace and simultaneous electrochemical detection of As(III) and As(V)

Research

Environmental Engineering Research 2025; 30(5): 240663.

Published online: February 27, 2025

DOI: https://doi.org/10.4491/eer.2024.663

Nanocomposite material in the trace and simultaneous electrochemical detection of As(III) and As(V)

Melody Lalhruaitluangi¹, Ricky Lalawmpuia¹, Diwakar Tiwari^1,^†

, Rama Dubey²

¹Department of Chemistry, School of Physical Sciences, Mizoram University, Aizawl-796004, India

²Defence Research Laboratory, Post Bag No 02, Tezpur, Assam-784001, India

^†Corresponding author: E-mail: diw_tiwari@yahoo.com, Tel: +91-9862323015, ORCID: 0000-0002-9177-9704

Received November 27, 2024 Revised February 11, 2025 Accepted February 26, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Arsenic contamination in groundwater is severely impacting millions in North Eastern India, causing significant health issues. This communication discusses the use of a novel material for simultaneously detecting As(III) and As(V) at very low concentrations to address monitoring and safety concerns. Butter fruit (Persea americana) synthesized the silver nanoparticles (AgNP). These nanoparticles are then embedded directly into silane-functionalized bentonite to produce AgNP@TBNT. Several analytical methods characterize amicably the material and are utilized in fabricating the thin film glassy carbon electrode. An enhanced electroactive surface area and accelerated electron transfer processes are observed from the scan rate and EIS studies when compared with an unmodified glassy carbon electrode (GCE). Extensive parametric studies are conducted to optimize analyte detection, focusing on factors including pH, preconcentrated time, and potential, as well as the presence of ions that could interfere. The produced calibration graph for detecting As(III) and As(V) is quite satisfactory showing quite promising low limit of detection of (LOD) of 0.037 and 0.087 μgL⁻¹ for As(III) and As(V), respectively. Further, the AgNP@TBNT fabricated electrode is fairly stable, reasonable self-life and detects efficiently arsenic in river water samples.

Keywords: Fabrication of electrode, Mechanism of detection, Nanocomposite material, Real water implications, Self-life electrode, Simultaneous detection

Graphical Abstract

Keywords: Fabrication of electrode, Mechanism of detection, Nanocomposite material, Real water implications, Self-life electrode, Simultaneous detection

1 Introduction

Arsenic is the second most toxic element present on the earth’s layer and poses a serious threat to human health and other living organisms [1,2]. It is a pollutant that can enter the environment from both natural and man-made sources [3] and the accumulation of arsenic in sedimentary rocks, volcanic rocks, and soils [4] is responsible for the release of arsenic into the environment. Moreover, mining, smelting, burning of coal, petroleum extraction, arsenic-containing pesticides, weed killers, insect repellents, phosphate fertilizers, and timber preservatives [5–7] are the potential anthropogenic sources of arsenic contamination. Human hazardous arsenic consumption is primarily caused by taking water or food that is contaminated with arsenic. The World Health Organisation (WHO) has established a recommended maximum amount of 0.01 mgL⁻¹ for arsenic in groundwater [8].

However, the groundwater in different parts of the world contains much higher levels of arsenic, and the population living around is widely consuming the contaminated water and showing severe health concerns, including the potential arsenic poisoning of hyperkeratosis [9,10]. A rough estimate indicated that more than 250 million people in developing countries, such as India, Bangladesh, China, and Mexico, are at potential risk of arsenic poisoning [11]. This imparted renewed concerns to safeguard living beings and protect the terrestrial environment for greater public health concerns [12,13].

Although the analytical techniques viz., AAS (atomic absorption spectroscopy), atomic emission spectroscopy (AES), chromatography, hydride generation AAS, ICP-MS (inductively coupled plasma mass-spectroscopy), laser-induced breakdown spectroscopy (LIBS), etc. are efficient enough to detect arsenic at low levels [14–18], however; these detection systems are having inherent drawbacks such as the high instrument cost, sophisticated instrumentation and off-site detection. Therefore, the search for robust, miniaturized devices for efficient on-site detection is inevitable. The electrochemical devices are efficient and found promising over several other detection systems [19]. However, the efficiency and selectivity of the electrochemical devices are one of the key challenges to meet the real implications. The role of advanced and engineered materials found impetus in the detection systems and opened newer areas of research for device development.

Nanomaterials have garnered increased attention in recent times for their potential in sensor development [20]. Single polypyrrole nanowire (PpyNW) functionalized with gold nanoparticles (AuNPs) utilized to detect the As(III) in water samples utilizing the voltammetric investigations involving anodic stripping in which the device shows a sensitivity of 0.8417 μgL⁻¹ with a detection limit of 0.37 μgL⁻¹ for As(III) [21]. Similarly, a multi-walled carbon nanotube decorated with Au(NPs) modifies the GCE and shows an enhanced ability to detect As(III) ions. The linear sweep voltammetry (LSV) as well as the square wave voltammetry (SWV) techniques achieves the optimal accumulation time of 240 seconds for LSV and 120 seconds for SWV. Further, the LSV and SWV measure a very low detection limit of 0.6 μgL⁻¹ and 0.10 μgL⁻¹, respectively, for As(III) utilizing the fabricated electrode which shows the gold nanoparticles provide a greater surface area and a higher current density, which enhances the sensitivity of the fabricated electrode [22]. The Ag(NPs) occupy the gold electrode and are employed for the detection of As(III) which shows a distinct reductive peak of As(III) in the cyclic voltammetric analysis and provides a reasonably good calibration line within a wide range of arsenic concentrations 6.45 × 10³ μgL⁻¹ to 2.58 × 10³ μgL⁻¹ with the detection limit of 0.179 × 10³ μgL⁻¹ [23]. The composite material precursors of Ag(NPs) and graphene oxide (GO) modify the glassy carbon electrode (GCE) surface that detects efficiently the As(III) in an aqueous medium and the results reveal that the Ag(NPs)-GO shows nearly 3 times enhanced sensitivity compared to the GO film alone in the anodic stripping analysis, as a result, the Ag(NPs)-GO achieves the detection limit of 0.24 × 10⁻¹ nM for As(III) and shows high stability [24].

Green synthesis gains greater interest in synthesizing nanomaterials or their corresponding nanocomposites due to their abundance, low cost, and environment benign [25]. The potential phytochemicals (viz., alkaloids, tannins, terpenoids, flavonoids, polyphenols, glycosides) of plants readily reduce and stabilize the precursors ions (viz., Ag, Au, Pt, Fe, Ti, etc.) [26]. Further, the plant extracts provide precise control of nanoparticle synthesis, allowing the well-defined sizes and morphologies in a one-step synthesis method. Other studies reported the synthesis of Au(NPs) utilizing the Persea americana (Butter fruit/Avocado) leaf extract in which, the Au(NPs) decorates the silane-grafted bentonite and modify the glassy carbon electrodes to detect efficiently the Pb(II) and the fabricated electrodes show a detection limit of 8.1 × 10⁻² μgL⁻¹ for Pb(II) [27]. However, green synthesis shows problems, including low yields, variable particle sizes, complicated extraction methods, and seasonal and regional variations of raw materials. Research shows that the level of bioactive compounds in plant leaves fluctuate considerably throughout the growing season [28]. Furthermore, the age of leaves significantly influences their chemical composition, with older leaves often exhibiting diminished concentrations of specific compounds as a result of the senescence process [29]. Therefore, optimizing the leaf extracts in synthesis of shape, size and yield of nanoparticles.

The clay materials offer unique features like chemical and thermal stability, ease of ion exchange, and the available hydroxyl group active sites, which play a crucial role as primary substrate material for introducing the inorganic and organic molecules to obtain the composite materials [30]. Therefore, the clay-modified electrodes (CLME) show interest in device development for detecting various heavy metals in aqueous medium [31–33]. Bentonite is a naturally occurring hydrated aluminosilicate mineral, primarily composed of smectite. It consists of tetrahedral silicates and octahedral aluminium hydroxide (Si₂O₅ and Al₂(OH)₄), which form a layered structure in a 2:1 ratio, and the charge of the three-sheet layer (unit cell) varies between 0.5 and 1.2 [34]. Bentonite is a porous material with a high surface area that provides enhanced catalytic properties, cation exchangeability, and thermal and chemical stability [35]. Au(NP) decorated bentonite (Au-bt) fabricates the GCE and detects efficiently As(III) at neutral (pH 7.0) conditions. The electrode shows a low detection limit of 12.9 μgL⁻¹ for As(III) [36]. Further, the use of siloxane functionalized bentonite decorated with Ag(NPs) (Ag(NP)/TCOD/BNT) measures efficiently the Pb(II) and Cd(II) simultaneously using ASV with the detection limit of 0.79 μgL⁻¹ and 0.88 μgL⁻¹ for Cd(II), and Pb(II), respectively and further reveal that the nanomaterials provide stable and reproducible sensing devices with enhanced shelf life [37]. Electrochemical detection of As(V) is cumbersome because of applying a very low negative potential to accumulate As(V) on the electrode surface to overcome the high energy barrier for its reduction. However, at excessively negative potentials, hydrogen evolution occur, leading to hydrogen adsorption on the electrode surface, that inhibits the deposition of As(0) [38]. Therefore, a chemical reduction of As(V) to As(III) followed by the electrochemical detection of As(III) detects primarily the As(V) in aqueous medium. A scanty of the studies reveal the direct detection of arsenate (As(V)), or on the simultaneous detection of (As(III)) and arsenate (As(V)) [9,39,40].

The present studies utilizes the nanocomposite material AgNP@TBNT to detect As(III) and As(V) in single and simultaneous systems at trace concentrations in aqueous medium. Furthermore, parametric studies provide the mechanism at the electrode surface, and the stability with real water implications is extensively studied for the enhanced shelf life of the electrode.

2 Experimental Method

2.1. Chemicals and Instruments

The chemicals and instrumental details are included in Text S1.

2.2. Electrochemical Measurements

The modified AgNP@TBNT electrode investigates the electroanalytical properties of As(III) and As(V) working with cyclic voltammetric (CV) studies at a concentration of 1.0 mgL⁻¹ in 0.1 molL⁻¹ KCl. Moreover, the DPASV approach detects these ions in single and simultaneous systems at various concentrations that fall at a potential value of −0.8 V to 0.7 V for both As(III) and −0.3 V to 0.7 V for As(V), respectively. For the electrochemical analysis of As(III) and As(V), the DPASV uses the applied voltage values of −0.7 V and −0.9 V during the preconcentration potential along with a preconcentration duration of 60 sec and 90 sec, respectively.

2.3. Synthesis of Nanocomposite Materials

Butter fruit aqueous leaf extract synthesized the silver nanoparticles (AgNP) as depicted in Fig. 1. The collected leaves were dried at 60°C. 10g of dried leaf was added to 200 mL of purified water and heated up at 80°C for 30 mins. Following the cooling process, the solution was filtered using 11.0 μm (pore diameter) filter paper after which it was kept at room temperature. The precursor silver nitrate solution (10.0 mL of 0.001 molL⁻¹) mixes with 1 mL of freshly prepared aqueous leaf extract, and the solution mixture is stirred continuously for 50 mins at 60°C. A yellowish Ag⁰ colloidal solution appears, and the solution cools at room temperature and is utilized for further use.

The dried bentonite clay (15 g) was sieved (BSS No.325, pore size 45 microns) and mixed with 200 mL of toluene. After stirring for about half an hour, 10.0 mL of trichloro-octadecyl silane was mixed gradually while stirring. The solution mixture is refluxed day and night at 80°C, under continuous stirring. A suspension was cooled at ambient temperature and centrifuged at 3000 rpm. Ethanol washes the solid (TBNT) and dried at 60°C for 24 hrs. A polyethylene bottle stores the solid for further use. Furthermore, ethanol mixes with 10.0 g of TBNT, and under continuous stirring, 4.0 mL of freshly made silver colloidal solution is introduced and allowed to be stirred for agitation at 60°C for 24 hours. The AgNP incorporated in TBNT (AgNP@TBNT) is then collected by centrifugation (4500 rpm). Further, the 10 mL of ethanol followed by purified water washed the solid and evaporated at 50°C for about 24 hours.

2.4. GCE Modification

GCE surface was cleaned with a polishing cloth and cleaning solution (diamond and alumina solution) and then it was washed in an ultrasonic bath with purified water followed by ethyl alcohol for 5 min each. The cleaned and dried electrode is then used for surface modification using the nanocomposite material. Separately, the casting solution is prepared as: a 4.0 mL mixed solution of dimethylformamide and DW (1:1 volume per volume) dissolves 8.0 mg of nanocomposite material (AgNP@TBNT). 0.02 mL of casting solution is applied at the GC electrode surface and dried at 50°C for about 20 min in an oven. The fabricated electrode is dried at ambient temperature and it is ready for additional electrochemical applications.

3 Results and Discussion

3.1. Characterization of Nanocomposite

The ultraviolet (UV) spectrum of each leaf extract, precursor silver, and colloidal solution of silver are displayed in Fig. S1, which reveals that silver colloidal solution shows an absorbance peak Ca 415 nm. The surface plasmon resonance (SPR) occurs by mutual vibrations of free electrons in the conduction bands of silver with light waves producing a characteristic absorbance peak at 415 nm [41,42]. Additionally, the qualitative screening of leaf extract shows the presence of phenolics, saponins, triterpenoids, reducing sugars, flavonoids, etc. (Cf Table S1). These compounds primarily reduce the silver ions and also cap and stabilize the nanoparticles.

Fig. S2. depicts the FT-IR analysis of BNT, TBNT, and AgNP@TBNT. The BNT and AgNP@TBNT show additional peaks at 2924 cm⁻¹, 2862 cm⁻¹, and 1473 cm⁻¹, 1481 cm⁻¹, due to the asymmetric and symmetric stretching vibrations of C-CH₂ and scissoring oscillations of an organic aliphatic chain of grafted organic silane, respectively [43]. These results affirm the grafting of silane molecules within the BNT solid.

The SEM pictures of GC surface, TBNT surface, and AgNP@TBNT-covered GC surfaces are presented in Fig. 2. (a–d). Fig. 2. (a) shows a smooth surface of GC, however, the BNT and TBNT-covered GC show heterogeneous and disordered patterns. Additionally, the material exhibits visible pores on its surface (Cf Fig.1. (b–c)). Moreover, the presence of Si molecules is visible on the bentonite clay surface and perhaps this silane is bonded to the bentonite’s terminal OH group. Fig. 2. (d) depicts the AgNP@TBNT-GC heterogeneous surface and the surface shows the presence of silver nanoparticles randomly distributed on the glassy carbon surface.

EDX elemental mapping was also performed, and the resulting data was given in Inset Fig. 2. (b–d). The EDX spectrum indicated that the BNT shows predominant peaks which comprise the following elements: Si, O, Fe, Mg, Na, and C. Similarly, the TBNT spectra show another peak of chlorine (Cl) which confirms that the attachment of silane onto the bentonite network was done successfully. In addition, the EDX spectrum of the nanomaterial exhibits a prominent peak of Ag, confirming that the material is decorated with silver nanoparticles.

Fig. 2. (e) depicts the TEM micrographs of AgNP@TBNT which clearly shows that silver nanoparticles are spherical having a mean particle diameter of 8 nanometers [Cf Fig. 2. (f)]. Additionally, the d-spacings from the lattice fringes of the silver nanoparticles are 0.20 nm [Cf Fig. 2. (g)] which refers to the (200) plane of the fcc structure of Ag [44].

The XPS spectrum of AgNP@TBNT was displayed in Fig. 2. (h), illustrating the electronic states of Ag and the elemental compositions of AgNP@TBNT. The XPS survey reveals the XPS peaks of O_1s, Fe_2p, C_1s, Ag_3d, and Si_2p, confirming the presence of silver nanoparticles in the material (Cf Fig. S3.). The Ag3d core level spectra are split into two spin-orbit components, which are identified as Ag3d_5/2 and Ag3d_3/2 at the binding energies of 368.3 and 374.1 eV, respectively which infer the presence of reduced silver in the material [45].

3.2. Electrochemical Characterization of Various Modified Electrodes

Various GCEs’ are electrochemically characterized using the standard 0.01 molL⁻¹ Fe²⁺/Fe³⁺ redox couple in 0.1 molL⁻¹ KCl at pH 6.02. Fig. S4. (a) shows the CV scan rate (20 to 150 mVs⁻¹) voltammo grams for these electrodes. Scanning at a faster rate results in higher peak currents is attributed to the redox reaction of Fe²⁺/Fe³⁺, respectively. Further, Fig. S4. (b) shows a straight-line dependency of the peak current with varying scan rates. From the slopes of these straight lines, the electroactive surface area of the GCE and AgNP@TBNT-GCE was estimated. Table S2. shows the electroactive surface region of each electrode, which infers that the modified electrodes have an electroactive surface area that is often greater than the GCE. Moreover, the electroactive surface area of AgNP@TBNT-GCE is almost two times increased compared to the unmodified GCE. The nanomaterial facilitates the electron transfer reactions at the electrode surface with enhanced electron transfer reactions enabling an increased electroactive surface area of the electrode [46].

Furthermore, 0.01 molL⁻¹ Fe²⁺/Fe³⁺ (0.1 molL⁻¹) at pH 6 is utilized for the EIS studies using the GCE, BNT GCE, TBNT GCE, and AgNP@TBNT GCE. Fig. 3. depicts the Nyquist plots (−Z_imag vs. Z_real) of each working electrode, which shows that the semicircle diameter of modified electrodes is considerably smaller than that of the GCE. The smaller circular arc shows an increased transfer of electrons and increased electrical conductivity at the modified electrode surface [47]. The Nyquist plots are simulated for possible equivalent circuits and fitted curves are displayed in Fig. 3. (Inset). For GCE, BNT, TBNT, and AgNP@TBNT, each charge transfer resistance (R_ct) values are 16.53 x 10³, 5.98 x 10³, 5.04 x 10³, and 3.22 x 10³ Ω, respectively (Table S2.). These results show that the R_ct value is significantly decreased for the AgNP@TBNT electrode compared to the GCE. The low R_ct indicates that the electrode surface facilitates faster charge transfer reactions. A previous study showed that the semicircle diameter of GO-Ag nanocomposite decreased significantly compared to the bare GCE, indicating enhanced charge transfer reactions [48].

3.3. Electrochemical Studies on the Detection of As(III) and As(V)

3.3.1. Cyclic voltammetric study

Supplementary Text S2 & Fig. S5 include As(III) and As(V) cyclic voltammetric studies.

3.3.2. Voltammetric response of modified electrode using DPASV

A comparison of the voltammogram peaks of As(III) and As(V) (50.0 μgL⁻¹) using the GCE and AgNP@TBNT-GCE was given in Fig. 4. (a&b). The GCE shows no peak current whereas, the AgNP@TBNT-GCE shows a strong anodic peak around the applied potential of 0.06 V for As(III) and 0.16 V for As(V), respectively. A higher oxidized peak observed can be attributed to the sorption of the analyte onto the nanomaterial’s surface which seemingly oxidized at the electrode surface. This peak current was caused by vacant bentonite surface sites and the extra siloxane binding site, which is expected to produce a powerful hydrogen bond between the surface of nanomaterials and the arsenite or arsenate molecule, enhancing the electron transfer process. In another study, bentonite materials loaded with HDTMA are used for the low-level detection of both As(III) and As(V) where the detection of As(V) is done after chemically reducing to As(III) using sodium dithionite solution, showing a limit of detection of 2.04 μgL⁻¹ and 2.214 μgL⁻¹, respectively [49,50].

Further, a series of optimizations of various parameters were carried out to acquire a sufficient and increased electrochemical response which includes pH, deposition time, and deposition potential.

3.3.2.1. Effects on pH

It has been reported that the pH level of the solution is responsible for regulating the speciation of As(III) and As(V) species where As(III) exists to its neutral species of H₃AsO₃ up to pH ~ 8 [51]. However, the AgNP@TBNT electrode exhibits a charge that is positive when the pH is less than 6.5, and it carries an electrically negative charge when the pH is greater than 6.5.

Fig. 4. (c) depicts the results of pH dependence studies, which show that changing the solution pH greatly affects the peak currents for As(III) and As(V). Moreover, the oxidation peak current of As(III) exhibits distinct peak currents within pH region 1.0 – 8.0 reaching its at highest values a pH 2.0. At higher pH values, an excess of the hydroxyl ions suppresses the oxidation of As(III). Comparable results have been reported in which As(III) was detected at an extremely low pH value using the silica nanoparticles which shows lower current signal obtained at a higher pH solution is caused by the generation of hydroxyl ions at the electrode surface, as a result, these ions impede the sorption of arsenic on the surface of the electrode and decreases the anodic peak current [52].

Meanwhile, the pH effect studies on the electrochemical analysis of As(V) are performed at varied pH levels, where pH 2.5 favored the peak current of As(V). At pH ~ 2.5 As(V) exists predominantly as an H₂AsO₄⁻ species [53], and the positively charged AgNP@TBNT (Cf Fig. S6.) surface attracts the As(V) species and facilitates sorb at the solid surface. This enables enhanced oxidation of As(V) at the electrode surface. However, at pH below 2.5, the peak current steadily drops, this happens because there is a large amount of H⁺ ions preferably adsorbed at the electrode surface and reduced to generate hydrogen. A gradual increase in pH (pH > 2.5) causes a gentle decline in the oxidized peak which is mainly because of the generation of hydroxyl ions at the electrode’s outer layer. Additionally, pH > 6.5, As(V) exists predominantly as H₂AsO₄²⁻ and the negatively charged AgNP@TBNT-GCE surface repels the As(V) species thereby inhibiting the electrochemical response of As(V) beyond pH 6.5. As a result, the optimal pH for the subsequent detection of As(III) is 2.0, whereas for As(V) it is 2.5.

3.3.2.2. Effects of preconcentration conditions

The optimization of deposition potential to efficiently detect both analyte species at a concentration of 50.0 μgL⁻¹ is investigated within the potential value of −0.8 V to −1.3 V for As(III) and −0.6 V to −1.2 V for As(V) at optimized pH, and by applying a deposition time of 60 sec. Fig. 4. (d) depicts that the anodic peak current rises as the potential being applied increases, reaching its maximum value at −0.7 V for As(III) and −0.9 V for As(V). However, an additional rise in deposition potential decreases the peak current. This is because an enormous quantity of charge particles are present near the electrode surface, leading to an excessive production of hydrogen bubbles which interferes with the electron transfer process. Similar findings were observed in which the optimum potential for electrochemically detecting As(III) was set at −0.9V using a modified electrode using Chitosan-Fe(OH)₃. It was observed that with increased cathodic potential, water molecules engaged in competition with arsenic to produce H₂ gas, therefore occupying the electrode surface and decreasing the response current [54]. Therefore, the optimized potential for the electrochemical detection of these analytes was set at −0.7 V for As(III) and −0.9 V for As(V), respectively.

Similarly, an accumulation time is the duration for which the ionic species accumulate at the GCE surface. These investigations were performed at varied time intervals i.e., 30 sec to 180 sec. Fig. 4. (e) demonstrates that the oxidized current of As(III) and As(V) elevates as the deposition duration is long and achieves a maximum value at a deposition time of 60 sec and 90 sec. However, as we increase the deposition duration, a slight decline in anodic peak current is observed. Therefore, an optimal deposition time has been set as 60 sec and 90 sec for the electrochemical determination of As(III) and As(V), respectively.

3.3.2.3. Determination of LOD from the calibration curve

The AgNP@TBNT-GCE detects the As(III) and As(V) at previously optimal settings under the DPASV measurements. Fig. 5. (a&c) show the DPASV voltammograms of As(III) and As(V). These results infer that the oxidized current rises as the concentration of analyte rises (0 to 70.0 μgL⁻¹ for As(III) and 0.0 to 100.0 for As(V)). Moreover, a good straight line between the analyte concentrations and the peak current is observed. The corresponding calibration curve was drawn and is expressed as y (μA) = 0.2454 μgL⁻¹ +13.743 (R² = 0.994) for As(III) [Cf Fig. 5. (b)] and y (μA) = 0.1048 μgL⁻¹ + 10.61 (R² = 0.992) for As(V) [Cf Fig. 5. (d)]. The LOD and LOQ are calculated utilizing and , where M represents the mean and Sd represents the standard deviation, based on 5 repeated DPASV readings. As a result, the calculated LOD and LOQ are 0.037 μgL⁻¹ and 0.124 μgL⁻¹ for As(III) and 0.087 μgL⁻¹ and 0.291 μgL⁻¹ for As(V), separately. A comparison of the AgNP@TBNT-GCE with other materials in the detection of As(III) and As(V) at specified physico-chemical conditions are shown in Table1. According to the results, the AgNP@TBNT shows reasonably low detection limit for detecting the As(III) and As(V) in aqueous medium. The nanomaterial’s low LOD can be attributed to the material showing an extensive electroactive surface region with low charge transfer resistance. Further, the porous and functionalized nanomaterial efficiently facilitates the sorption of As(III) and As(V), which undergoes seemingly oxidation and produces an enhanced oxidative current [35].

3.3.2.4. Stability of the fabricated electrode

The DPASV method determines the stability and repeatability of the fabricated electrode. One important and necessary quality of a sensor is that it must be able to maintain high stability measurement response over repeated measurements and the shelf-life of the electrode. In this study, the stability of the synthesized AgNP@TBNT electrode is investigated at concentrations of 10.0 μgL⁻¹ As(III) and 30.0 μgL⁻¹ As(V) for prolonged and repeated operations. This experiment is performed five times at varied time intervals. Once after completing the detection process, the electrode is rinsed with plenty of DW and evaporated at ambient temperature for the next procedure. Tables S4 and S5 show the percentage relative standard deviation (%RSD), obtained from 5 repetitive runs. The %RSD for As(III) and As(V) lies below 3%. Additionally, the anodic peak current response remains within 98% for As(III) and 93% for As(V) of its initial peak current even after 48 hrs of repeated use. The results indicate that AgNP@TBNT is stable at the surface and the fabricated electrode shows enhanced self-life in detecting As(III) and As(V) in a liquid media.

3.3.2.5. Influence on the existence of interfering ions

Multiple interfering ions assess the productivity of the material in detecting As(III) and As(V). 10 times more concentrated (i.e., 500.0 μgL⁻¹) of each ion namely calcium(II), chromium(VI), nickel( II), manganese(II), magnesium(II), copper(II), iron(III), lead(II), phosphate, nitrate, and fluoride determines the electrochemical analysis of As(III) and As(V). As we can see in Fig. 5. (c), these ions do not have substantial interference with the oxidized current of As(III). Similarly, the As(V) peak current was unaffected by these ions except Pb(II) [Cf Fig. 5. (d)]. This interference is caused by the transfer of electrons from Pb(0) to Pb(II) that took place around the applied potential since the concentration of Pb is five times higher than As(V). It was reported previously that lead(II) significantly interferes with the detection of arsenic using the microfabricated gold ultramicroelectrode array (Au-UMEA) [55]. These results infer that the AgNP@TBNT possesses an excellent susceptibility as well as high specificity for detecting As(III) and As(V), which could have practical applications in the trace detection of these elements.

3.3.3. Detection of As(III) and As(V) simultaneously

3.3.3.1. Concentration studies

The AgNP@TBNT-GCE can detect both the As(III) and As(V) simultaneously in a liquid medium using DPASV techniques under optimized experimental parameters. The analyte concentrations are increased from 1.0 μgL⁻¹ to 25.0 μgL⁻¹ in 0.1 molL⁻¹ KCl at pH 3. The best deposition potential and deposition duration are 1.0 V and 60 sec, respectively. Fig. 6. (a) depicts the DPASV response for concurrent detection of As(III) and As(V). We can see these two analytes are spatially separated with different oxidation potentials and hence, clear oxidized peaks for As(III) and As(V) are identified that occur at potentials of −0.01 V and 0.20 V, respectively. Fig. 6. (b) illustrates that the concentration studies display straight lines with varying analyte concentrations and the corresponding calibration equation for the As(III) and As(V) as represented by the equations y (μA) = 0.2005 μgL⁻¹ + 4.2236 (R² of 0.985) and y (μA) = 0.1837 μgL⁻¹ + 4.2515 (R² of 0.991). More importantly, the LOD values for As(III) and As(V) employing AgNP@TBNT-GCE are 0.045 μgL⁻¹ and 0.049 μgL⁻¹, respectively. Notably, this LOD measurement is significantly lower than the total allowable arsenic in drinking water (10.0 μgL⁻¹). The electrochemical device using AgNP@TBNT modified electrode detects efficiently the As(III) and As(V) simultaneously even at trace level hence, shows promising in detecting these two species in the aqueous medium. An earlier study shows SPE modified with [Ru(bpy)₃]²⁺-GO was capable of detecting both As(III) and As(V) simultaneously, both the oxidation of As(0) to As(III) and the oxidation of As(III) to As(V) appeared in the DPV, which displayed two peaks at 0.48 and 0.86 V, respectively and the developed sensor showed linear performance with a detection limit of 4.7 μgL⁻¹ and 9.5 μgL⁻¹ for As(III) and As(V), respectively [65]. Using the square wave voltammetry, one could detect As(III) and As(V) employing a nanohybrid electrode made of Eu-MGO/Au@MWCNT displaying low LOD of As(III) and As(V) was 0.27 μgL⁻¹ and 0.99 μgL⁻¹, respectively [66]. It has been reported that the cathodic preconcentration of electron-insulating As(0) on Au and Pt electrodes is increased through the chemical reduction of As(III) and As(V) by electrogenerated hydrogen and further observed that the Au electrode exhibits enhanced sensitivity to the rapid LSASV oxidation of preconcentrated As(0) to As(III) and subsequently to As(V), with detection limits of 0.1 μgL⁻¹ for As(III) and 2.2 μgL⁻¹ for As(V) [67]. Therefore, the AgNP@TBNT-GCE has a promising sensing platform for detecting As(III) and As(V) simultaneously at trace amounts and is useful for developing the miniaturized device.

3.3.3.2. Real water implication

Chite river water is collected from Aizawl, Mizoram, and filtered via Whatman filter paper and the water is subjected to various physicochemical analyses using a pH meter and multiparameter photometer, TOC analyzer, and AAS. Table S6. contains various parametric evaluations of river water, which shows that water contains very low contents of Ni, Al, nitrate, phosphate sulphate, etc. However, the river water sample contains high calcium(II) and magnesium(II) concentrations. Also, the TOC results show that water contains a considerable amount of organic and inorganic carbons.

The As(III) and As(V) spikes the collected river water containing known analyte concentrations (1.0 μgL⁻¹ to 20.0 μgL⁻¹) at 6.0, which is close to the natural water pH. The DPASV experiments are performed under previously optimized conditions. Fig. S7. (a) displays the DPASV results using the AgNP@TBNT-GCE. The DPASV results again show two distinct anodic peaks of As(III) and As(V) that are well-separated for these two ions. However, the closure scrutiny of the results indicate that the oxidative peak currents of these two ions are relatively less compared to the purified water data at pH 3.0. Further, Fig. S7. (b) shows that the oxidation peak current has a strong linear performance with varying concentrations. Table 2. shows a comparison of the actual concentration and spiked concentration of As(III) and As(V), along with recovered analytes from the spiked concentration. These results show that the AgNP@TBNT-GCE recovers a very high percentage of As(III) and As(V) in Chite river samples which range from 94.8% to 101.09% and 97.7% to 104.5%. These findings demonstrate that the AgNP@TBNT is a potential material in device development that is capable of simultaneously detecting As(III) and As(V) at low levels.

3.3.3.3. Influence on the existence of interfering ions

In presence of various interfering ions investigates the selectivity of AgNP@TBNT-GCE for detecting the As(III) and As(V) simultaneously. Five interfering ions, namely Fe(III), Cu(II), Pb(II), Cl⁻, and Fare added at 10-fold concentrations (i.e., 150.0 μgL⁻¹) to the analyte concentrations. Fig. 6. (c) depicts the results and suggests that these ions are not significantly affecting the anodic peak current. The addition of copper and lead affects slightly the electrochemical analysis of As(III) and As(V). Oxidation of lead ions that occurs in the same applied potential creates this interference [Fig.6. (c) Inset]. However, the Cu(II) may be, perhaps, co-deposited with arsenic to form the Cu₃As₂ at the electrode surface which is consistent with previous studies that showed significant interference of Cu(II) in the electrochemical detection of As(III) in water using gold nanoparticle-modified electrodes [68].

4 Conclusions

A novel nanomaterial material (AgNP@TBNT) fabricates the glassy carbon electrode for detecting As(III) and As(V) both in single and simultaneous at trace levels. The SEM/TEM shows the heterogeneous and porous surface morphologies of the material. The Ag is present in its reduced state and spatially distributed on the composite material of silane grafted bentonite. In comparison to the GCE, the AgNP@TBNT fabricated electrode shows a nearly two-fold increase in the activity of the electrode surface and a notably lower R_ct. The electrochemical detection of As(III) and As(V) shows a very low detection limit of 0.037 μgL⁻¹ and 0.087 μgL⁻¹, respectively. Furthermore, the application of AgNP@TBNT shows fair applicability in river water, and their recovery percentages range from 94.8% to 101.09% for As(III) and from 97.7% to 104.5% for As(V). The occurrence of Fe(III), Cu(II), Pb(II), Cl⁻, and F⁻ affects insignificantly the detection of both As(III) and As(V). The AgNP@TBNT electrode shows high reproducibility and stability for repeated applications. The fabricated electrode exhibits promise in the development of miniaturized devices.

Supplementary Information

eer-2024-663-supplementary.pdf

Notes

Acknowledgments

One of the authors DT acknowledges the DRDO, Govt. of India, New Delhi providing the financial support in the form of Research Project (vide No.: DFTM/07/3600/NESTC/EWM/M/P-01/01).

Conflict-of-Interest Statement

The authors confirm that they have no conflict of interest.

Author Contributions

M.L. (Ph.D.) conducted the experiment and wrote the initial draft of the manuscript. R.L. (Ph.D.) gathered relevant literature and contributed to the rough draft of the manuscript. D.T. (Professor) developed the conceptual framework, critically reviewed the manuscript, and finalized the draft. R.D. (Scientist) offered valuable feedback and assisted in finalizing the manuscript.

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Fig. 1

Green synthesis of AgNP using butter fruit leaf extract.

Fig. 2

(a) SEM micrographs of pure GC sheet, (b) SEM micrographs of BNT-GC [Inset: EDX spectra of BNT], (c) SEM micrographs of TBNT-GC [Inset: EDX spectra of TBNT], (d) SEM micrographs of AgNP@TBNT-GC sheets [Inset: EDX spectra of AgNP@TBNT], (e) TEM micrograph AgNP@TBNT, (f) Particle size distribution histogram of AgNP@TBNT, (g) calculated d-spacing of AgNP@TBNT, and (h) XPS spectrum of Ag3d.

Fig. 3

Nyquist plots for GCE, BNT-GCE, TBNT-GCE and AgNP@TBNT-GCE.

Fig. 4

DPAS voltammogram of: (a) As(III); (b) As(V); (c) Effect on pH; Impacts on the anodic current of As(III) and As(V) in a 0.1 molL⁻¹ KCl solution of the following parameters: (d) deposition potential; and (e) deposition time using AgNP@TBNT-GCE.

Fig. 5

(a) Differential pulse anodic stripping voltammograms with AgNP@TBNT GCE at different As(III) at varied concentrations (pH = 2.0, deposition potential = −0.9 V, accumulation duration = 60 sec; (b) Anodic peak current versus As(III) concentration calibration line; (c) Differential pulse anodic stripping voltammograms with AgNP@TBNT GCE at different As(V) at varied concentrations (pH = 2.5, deposition potential = −0.9 V, accumulation duration = 90 sec; (d) Anodic peak current versus As(V) concentration calibration line; Influence on the existence of each interfering ion on peak current of: (e) As(III); and (f) As(V).

Fig. 6

(a) DPASV response of As(III) and As(V) at 1–25 μgL⁻¹ concentration range on AgNP@TBNT-GCE, (b) Calibration plots of As(III) and As(V), (c) Effect of each interfering ions on detection of 50.0 μgL⁻¹ of As(III) and As(V) in 0.1 M KCl [Inset: Bar graph representation on the effect of the interfering ions].

Table 1

Comparison of the developed material with existing material for electrochemical detection of As(III) and As(V).

Material	Analyte	Response time (s)	Supporting electrolyte	LOD (μg/L)	Reference
AgNPs/CT GCE	As(III)	120	1.0 M HNO₃	1.2	[56]
AgNPs modified gold electrode	As(III)	300	0.1 M HNO₃ (pH 1)	0.013	[23]
AgNPs/GO composite	As(III)	120	0.1 M H₂SO₄ (pH 0.7)	0.168	[57]
Ag-NP/MT nanocomposites	As(III)	60	0.1 M PBS (pH 7)	4.06	[58]
AgNP/PpyNW	As(III)	10	1 M HCl	1.5	[59]
rGO/Ag nanocomposite	As(III)	120	1 M HNO₃	0.24	[60]
AgNP-SPCNFE	As(V)	120	HCl (pH 2)	0.64	[61]
AAGA doped PDDA-PA nanocomposites	As(V)	300	AcBS (pH 4)	8.99	[62]
LCAH-modified CPE	As(V)	NR	1.0 M KCl (pH 6)	1.49	[49]
Gold microelectrode	As(V)	120	0.005 M HCl (pH 2)	0.5	[63]
PANI/MoO₃ composite/ITO	As(V)	300	PBS (pH 4)	0.15	[64]
AgNP@TBNT GCE	As(III)	60	0.1 M KCl (pH 2)	0.037	This work
AgNP@TBNT GCE	As(V)	90	0.1 M KCl (pH 2.5)	0.087	This work

Table 2

Recovery percentage of As(III) and As(V) in Chite river water.

Spiked amount of analytes (μgL⁻¹)	Found (μgL⁻¹) ± 3σ		Recovery%

	As(III)	As(V)	As(III)	As(V)
1	0.94 ± 0.06	1.03 ± 0.03	94.8	103.3
10	9.51 ± 0.49	9.77 ± 0.23	95.6	97.7
20	20.21 ± 0.21	20.8 ± 0.8	101.09	104.5