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Article

Bi2S3/rGO Composite Based Electrochemical Sensor for Ascorbic Acid Detection

1
Institute for New Energy Materials & Low-Carbon Technologies, School of Materials Science and Engineering, Tianjin University of Technology, Tianjin 300384, China
2
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, China
3
Plasma-Surface Interaction Chemistry (ChIPS), Research Institute for Materials Science and Engineering, University of Mons, 20 Place du Parc, 7000 Mons, Belgium
*
Author to whom correspondence should be addressed.
Submission received: 2 June 2021 / Revised: 9 July 2021 / Accepted: 18 July 2021 / Published: 23 July 2021
(This article belongs to the Special Issue Chemical Sensors for Bio-Medical and Environmental Applications)

Abstract

:
The engineering of an efficient electrochemical sensor based on a bismuth sulfide/reduced graphene oxide (Bi2S3/rGO) composite to detect ascorbic acid (AA) is reported. The Bi2S3 nanorods/rGO composite was synthesized using a facile hydrothermal method. By varying the amount of graphene oxide (GO) added to the synthesis, the morphology and size of Bi2S3 nanorods anchored on the surface of rGO can be tuned. Compared to a bare glassy carbon electrode (GCE), the GCE modified with Bi2S3/rGO composite presented enhanced electrochemical performance, which was attributed to the optimal electron transport between the rGO support and the loaded Bi2S3 as well as to an increase in the number of active catalytic sites. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis of Bi2S3/rGO/GCE demonstrate that the active Bi2S3/rGO layer on GCE plays an important role in the electrochemical behavior of the sensor. In particular, the Bi2S3/rGO/GCE sensor shows a wide detecting range (5.0–1200 μM), low detection limit (2.9 µM), good sensitivity (268.8 μA mM−1 cm−2), and sufficient recovery values (97.1–101.6%) for the detection of ascorbic acid.

1. Introduction

Ascorbic acid (AA), as an essential biological molecule in the human blood, is indispensable for various physiological and metabolic activities. Therefore, it is important to develop facile and sensitive techniques to accurately determine amounts of AA for application in the pharmaceutical, chemical, cosmetic, and food sectors. Compared with traditional analysis methods, such as fluorimetry [1], colorimetry [2], voltammetry [3,4], flow injection analyses [5], spectrophotometry [6], and liquid chromatography [7], the electrochemical detection of AA is considered to be a simple low-cost method owing to its easy operation, high sensitivity and low detection limit [8,9]. However, the direct oxidation of AA on bare electrodes results in electrode surface fouling, high overvoltage, low sensitivity, poor reproducibility, and high interference with other biomolecules [10]. Therefore, it is important to choose an appropriate active material to modify glassy carbon electrodes (GCE) improving their selectivity and sensitivity towards an accurate AA determination.
Following the development of nanomaterials in electrochemical sensors, various materials such as organic redox mediators [11], nanoparticles [12], polymers [13], carbon nanotubes [14], and graphene [15] have been used as redox-active sites to modify the standard electrode surface, reducing the activation energy barrier of the electrochemical reaction and speeding up the electron transfer process [16]. Recently, bismuth sulfide (Bi2S3) has attracted much attention as the electrochemically active material in gas sensors, photoresponsive devices, and solar cells due to its unique electronic and optical properties [17,18,19,20,21]. However, the poor intrinsic conductivity and easy agglomeration of Bi2S3 nanoparticles result in low sensitivity and narrow linear range in electrochemical detection limiting its practical applications [22]. Up to now, various strategies have been proposed to improve the electrochemical properties of Bi2S3. Graphene (GO) has been reported to be an ideal substrate material for the development of optimal nanocomposite sensing materials due to its surface properties and electronic transport properties [23,24]. Luo et al. reported on Cu/graphene nanocomposites as active layer for non-enzymatic glucose sensors, with good stability and selectivity [25]. Guo et al. [26] used MoS2-rGO/ITO composites as active materials in electrochemical sensors to simultaneously detect uric acid (UA) and dopamine (DA). Yan et al. [27] synthesized rGO/Bi2S3 nanocomposites using thioacetamide as the sulfur source, and used these nanocomposites as the active layers with remarkable increases in the selectivity and sensitivity of the DA sensor.
In this work we describe a facile-yet-efficient strategy to engineer the structure of Bi2S3 nanostructures. The correlation among graphene content, Bi2S3 structure and electrochemical characteristics is evaluated. In addition, the Bi2S3/rGO modified glassy carbon electrode (GCE) is validated as active layer in electrochemical sensors for ascorbic acid (AA) detection. The fabricated Bi2S3/rGO/GCE as AA sensor presented a wide linear detection range, high sensitivity and good selectivity in the presence of various interfering compounds in aqueous phosphate buffer solutions. This work provided an additional step for improving the electrocatalytic activity of transition metal chalcogenides and expanding their applications in the field of electrochemical sensing.

2. Materials and Methods

2.1. Reagents

GO was prepared using graphite powder by the modified Hummers method [28]. Thiourea, thioacetamide (TAA), Na2S2O3, Na2S∙9H2O, and bismuth nitrate [Bi (NO3)3∙5H2O] were obtained from Shanghai Chemical Reagent Company (Shanghai, China). Disodium hydrogen phosphate (Na2HPO4), sodium dihydrogen phosphate (NaH2PO4), ascorbic acid (AA), and interferents were provided by Aladdin Reagent Co., Ltd. (Shanghai, China). The phosphate buffer (PBS, 0.1 M) was prepared by mixing Na2HPO4·2H2O and Na2HPO4·2H2O. The pH of PBS was adjusted with HCl or NaOH. All chemicals were of analytical grade. Deionized water was used throughout the experiments.

2.2. Instruments

The morphology and crystal structure of the samples were determined by Environmental scanning electron microscope with a field emission gun (ESEM, Quanta FEG 250, Hillsboro, OR, USA) and transmission electron microscopy (TEM, Talos F 200 X, Waltham, MA, USA). The crystal phase structure and composition of Bi2S3 in the composite were analyzed by X-ray diffractometer (XRD, D/Max2500pc, Akishima-shi, Tokyo, Japan), Raman spectroscopy (Horiba Evolution, Minami-ku, Kyoto, Japan), and X-ray photoelectron spectra (XPS, ESCALAB250Xi, Waltham, MA, USA). The molecular structure and chemical composition of graphene materials were determined by Fourier transform infrared spectrometer (FT-IR, Perkin Elmer, Waltham, MA, USA). Electrochemical studies were measured by CHI 660E electrochemical analyser (Shanghai Chenhua Instrument Co., Ltd., Shanghai, China) using a conventional three-electrode system.

2.3. Synthesis of Bi2S3/rGO Nanocomposites

Bi2S3 samples were synthesized with different sulfur sources to determine the the sulfur source leading to nanostructures with best sensor activity. As shown in Figure S1 Bi2S3 the sample prepared with thiourea has a higher current response. This may be attributed to the higher specific surface area and presence of more active sites on Bi2S3 nanostructures prepared with thiourea which can improve the electrochemical performance of the working electrode by accelerating electron transfer, compared with nanostructures synthesized with other sulfur sources.
Synthesis procedure: the GO was sonicated for 2 h in deionized water to form a solution of 1 mg mL−1. Then, different amounts of Bi (NO3)3∙5H2O were added to the GO solution and stirred for 30 min (solution A). Based on the weight ratio of Bi (NO3)3∙5H2O:GO, the nanocomposites were named Bi2S3/rGO-1 (4:1), Bi2S3/rGO-2 (2:1), Bi2S3/rGO-3 (1:1) and Bi2S3/rGO-4 (1:2), respectively. The thiourea was dissolved in 10 mL deionized water (solution B), Bi (NO3)3∙5H2O and thiourea in a molar ratio of 1:10. Next, solution B was slowly added into solution A with continuous stirring for 20 min. The resulting mixture was transferred into 100 mL Teflon lined stainless steel autoclave, sealed, and heated at 180 °C for 12 h in an electric oven, and the brownish-black products were centrifuged (at 7000 rpm for 5 min) and washed five times with deionized water and alcohol. Finally, the obtained Bi2S3/rGO products were dried for 5 h in a vacuum oven at 60 °C.

2.4. Sensor Fabrication

Firstly, the glassy carbon electrodes (GCEs) were carefully polished using Al2O3 powders (0.5 mm, and 0.05 µm) on a polishing cloth, successively washed with ethanol and deionized water and dried at room temperature. Next, 10 mg of Bi2S3/rGO sample was dispersed in the mixture solution containing 5.0 mL of N, N-Dimethylformamide (DMF) and 100 µL of Nafion for ultrasonic treatment for 20 min, obtaining homogeneous Bi2S3/rGO composite suspension. Then, 5.0 µL of the above Bi2S3/rGO suspension was coated on surface of the cleaned GCE, after drying in hot air for 10 min, the sensor fabricated with Bi2S3/rGO/GCE was obtained. Likewise, for comparison, the similar sensor based on rGO/GCE and Bi2S3/GCE were prepared.

3. Results

3.1. Characterization of Bi2S3/rGO

The morphology of the Bi2S3/rGO samples was characterized by SEM and TEM as shown in Figure 1. From SEM images (Figure 1a–d), it is clearly seen that well dispersed rod-like structures of Bi2S3 are formed on the surface of rGO in all Bi2S3/rGO samples. Moreover, we observed that when the weight ratio of Bi (NO3)3∙5H2O: GO decreased from 4:1 to 1:2, the average size of Bi2S3 nanorods on the rGO sheets increased by three to five times. In contrast, pure Bi2S3 samples prepared using different sulfur sources in the absence of GO (Figure S2), are highly aggregated, indicating that GO plays an important role in dispersing nanoparticles during the hydrothermal synthesis. The interaction of Bi+ with oxygen-containing groups of GO was reported to be responsible for the dispersibility of Bi2S3 nanorods [29]. It is worth noting that using an appropriate amount of GO in the solution resulted in higher interfacial contact between rGO sheets and Bi2S3 nanorods. As shown in Figure 1c, the Bi2S3 rods are wrapped around the thin rGO sheets in Bi2S3/rGO-3, this sample also presented the best electrochemical performance. From TEM images of Bi2S3/rGO-3 shown in Figure 1e,f, the diameter of Bi2S3 rods is about 50–120 nm and the length ranges from 0.4–2.3 μm. The Bi2S3 rods are mostly randomly distributed on the surface of rGO. In addition, the elemental mapping (Figure S3) further illustrates the good dispersion in the composite material, and the EDAX analysis indicates that the synthesized composite has high purity.
Figure 2a shows XRD patterns of the GO, rGO, Bi2S3, and Bi2S3/rGO composite materials. After the hydrothermal treatment in the presence of thiourea, the typical diffraction peak of GO sample at 2θ = 10.2° disappeared; and the presence of the broad peak at 23.9° corresponding to the (002) plane of rGO indicates the conversion of GO to rGO [30,31]. On the other hand, the diffraction peaks of all Bi2S3/rGO samples match with the typical peaks of Bi2S3 in the CPDS card (No. 17-0320), indicating that GO used in the synthesis promotes the crystal growth of Bi2S3. However, the intensity of the peaks of Bi2S3/rGO gradually decreased with increasing amounts of GO, which is probably due to the shielding effect of rGO on the Bi2S3 surface [32]. Moreover, no pronounced diffraction peak of rGO has been found in XRD patterns of Bi2S3/rGO composites, which can be attributed to the relatively low intensity of the rGO peak or the face-to-face stacking of Bi2S3 on both sides [33].
Figure 2b shows the typical Raman spectra of GO, Bi2S3, and Bi2S3/rGO-3 in the range of 150–2000 cm−1. The low-intensity feature at 239 cm−1 and the peak at 974 cm−1 observed for pure Bi2S3 correspond to the Ag optical phonon modes and surface phonon modes [34]. Similar peaks of pure Bi2S3 and GO can be observed in the spectra recorded on the Bi2S3/rGO-3 sample, indicating that rGO and Bi2S3 are present in Bi2S3/rGO. The typical G band and D band of Bi2S3/rGO and GO are attributed to the E2g phonon of sp2 carbon atoms and the A1g (breathing mode) of sp3 vibrations resulting from surface defects and the structural disorder of GO, respectively [35]. The intensity ratio (ID/IG) of Bi2S3/rGO is higher than that of GO because of the increasing sp2 domains from the reduction of GO during the hydrothermal process [36]. The Raman spectra proved the structural integrity of Bi2S3/rGO composites.
The chemical composition of the samples was evaluated by X-ray photoelectron spectroscopy. Figure 3a shows the XPS survey spectra recorded on the surface of Bi2S3 and Bi2S3/rGO-3 samples. The presence of C, Bi, S, and O elements is confirmed. Compared with the pristine Bi2S3 sample, the intensities of C and O peaks are relatively higher in Bi2S3/rGO-3, suggesting the presence of rGO [37]. Figure 3b shows the XPS spectra of Bi 4f photoelectrons, in pure Bi2S3, the two intense peaks can be associated with Bi 4f7/2 and Bi 4f5/2 doublet with a spin-orbit splitting of 5.3 eV. The Bi 4f doublet with components at 158.2 and 163.5 eV can be observed in the Bi2S3/rGO-3 sample, as well as two low intensity peaks centered at 159.1 and 164.3 eV belonging to Bi-O bond, suggesting the Bi3+ ions interaction with rGO [38,39]. The Bi-O associated doublet peak is also observed in the pure Bi2S3 sample indicating that a low amount of oxygen reacted with surface Bi ions. Moreover, the S 2p3/2 and S 2p1/2 doublet peaks centered at 161.1 and 162.2 eV indicate that S2− as the primary valence state occurs in Bi2S3/rGO-3 [40]. Figure 3c shows three components of C1s centered at 284.8, 285.9, and 288.9eV corresponding to the C=C, C–O–C, and O–C=O carbon chemical environments, respectively, indicating the residual oxygen functional groups on the surface of rGO [41]. Besides, the corresponding O 1s core-level spectrum of the Bi2S3/rGO-3 sample (Figure 3d) is well reproduced with three components: the peak at the lowest binding energy can be assigned to Bi-O species, and the peaks centered at 531.8 and 533.6 eV are attributed to C=O and O–C=O bonding environments, respectively [42]. Therefore, from the XPS analysis, we can suggest that Bi2S3 nanorods interact with reduced graphene via the formation of Bi-O bonds, although surface oxidation forming Bi-O bonds cannot be discarded.
FTIR spectroscopy was used to study graphene oxide and Bi2S3/rGO functional groups (Figure 4). The broad absorption band centered at 3425 cm−1 is assigned to the stretching vibration of -OH groups from adsorbed water molecules [43]. The characteristic peaks ascribed to C=O, C=C, C–O–C, and C–O functional groups were located at 1711 cm−1, 1564 cm−1, 1165 cm−1, and 1051cm−1, respectively [44,45]. Compared with GO, it is clearly seen that the intensities of the corresponding absorption peaks of Bi2S3/rGO sample decreased, indicating the conversion of GO to rGO during the hydrothermal process, in agreement with the Raman results.

3.2. Formation Mechanism of Bi2S3/rGO

Based on the above analyses, the overall synthetic procedure of Bi2S3/rGO and the electrochemical sensing process for Ascorbic Acid (AA) can be seen in Scheme 1. First, the positively charged Bi3+ ions absorb the negatively charged oxygen-containing functional groups of GO sheets via electrostatic interaction [46], while the thiourea added as the sulfur source and reducing agent hydrolyzes to S2− ions at high temperature. The interaction between Bi3+ and S2− ions generates Bi2S3 nucleii which grow into Bi2S3 nanorods on the surface of the rGO to form Bi2S3/rGO composites [47]. The electrocatalytic response of AA at Bi2S3/rGO/GCE is performed in 0.1 M PBS (pH = 7.0). The oxidation process of AA with a two-electron and two-proton electro-oxidation process leads to dehydroascorbic acid formation followed by its electrochemical sensing [48].

3.3. Bi2S3/rGO Electrochemical Evaluation

The electrochemical behavior of the different modified electrodes was evaluated via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using ferro/ferricyanide as the redox probe. From Figure 5a, it can be seen that compared with bare GCE, Bi2S3/GCE, and rGO/GCE, the Bi2S3/rGO/GCE shows a dramatic enhancement of the peak current, indicating that Bi2S3/rGO as the active layer plays a vital role for electron transfer behavior. Moreover, Bi2S3/rGO-3/GCE presents the optimal current response in 0.1 M KCl using 5 mM [Fe (CN)6]3−/4 within the potential range of −0.2 to 0.8 V. The electrochemical impedance spectroscopy (EIS) Nyquist plots obtained for different modified electrodes are presented in Figure 5b,c. The straight line of Bi2S3/rGO has the steepest slope in the lower frequency area, suggesting that the synthesized Bi2S3/rGO composites have the minimum diffusion resistance. According to the Nyquist plots’ semicircle evaluating the interfacial charge transfer resistance (Rct), the Bi2S3/rGO-3/GCE has a lower electron transfer resistance than that of the bare GCE and the Bi2S3/GCE [49,50]. This phenomenon can be associated with the introduction of Bi2S3 nanorods improving electron transfer capability. Compared to the Bi2S3/rGO-1/GCE, the Bi2S3/rGO-2/GCE and the Bi2S3/rGO-4/GCE, Bi2S3/rGO-3/GCE have better conductivity (Figure 5c). According to the obtained results, the interfacial charge transfer resistance of the Bi2S3/rGO composites decreases in sequence along with the increase in the amount of GO added to the synthesis. This can be attributed to the graphene that facilitates the transport of electrons and ions. However, adding high amounts of GO increased the composite resistance, which is likely related to the morphology of the Bi2S3 nanorods. The longer length of the nanorods increases the distance between rGO nanosheets retarding facile electron transport [45]. Hence, the Bi2S3/rGO-3 was chosen in the following experiments.
In order to investigate the electrocatalytic response of the different modified electrodes in the detection of AA, differential pulse voltammetry (DPV) was carried out in 0.1 M PBS (pH = 7.0) containing 5 mM AA at a scan rate of 100 mV s−1 (Figure 6). The rate of electro-oxidation on the AA was varied at different modified electrodes, the peak potential of the AA oxidation was 0.492, 0.556, 0.188, and 0.224 V for the bare GCE, Bi2S3/GCE, rGO/GCE, and Bi2S3/rGO-3/GCE, respectively. The Bi2S3/GCE showed a weak oxidation peak due to the electric blocking effect produced by the semiconductor’s presence over the electrode surface. The Bi2S3/rGO-3/GCE showed an exceptional current response at 0.225 V, and the superior electrochemical performance of Bi2S3/rGO-3/GCE can be attributed to the synergetic combination of the nanocrystalline Bi2S3 with the GO [51]. Therefore, it is suggested that Bi2S3 and rGO improve the materials’ electrical conductivity and catalytic activity synergistically.

3.4. Optimization of Detection Conditions

3.4.1. Effect of Solution pH

To evaluate the pH effect on the response to the electrochemical behavior of AA on the Bi2S3/rGO-3/GCE, analyses were carried out in the pH range from 3.0 to 8.0. As shown in Figure 7a, the oxidation peak potential (EP) shifts towards greater negative potential for increasing pH values, indicating that the electro-oxidation process is pH-dependent and protons take part in the electrode reaction [52,53]. The oxidation peak current of AA increases steadily as the pH changes from 3.0 to 4.0 (Figure 7b); however, further increasing the pH value from 4.0 to 8.0, the anode peak current tends to decrease. The high analytical signal for AA is observed at pH 4.0. The dependence of the AA peak potential on pH can be expressed by Equation (1):
EP (V) = −0.0484 pH + 0.714, (R2 = 0.998)
In Figure 7c, the slope is a Nernstian value of −0.0484 V/pH, which indicates the participation of electron and proton involving in the process of AA on the Bi2S3/rGO-3/GCE surface [54].

3.4.2. Effect of Scan Rate

The AA oxidation reaction kinetics of Bi2S3/rGO-3/GCE was studied by CVs at a scan rate range of 20–100 mV s−1. As shown in Figure 8a, the peak current response increases with the increase in scan rate and the peak potential shifts to the positive side. Furthermore, the linear relationship between the oxidation peak current (IP) and the square roots of scan rates can be seen in Figure 8b, and the linear regression equation was described as follows:
IP (A) = 9.85 v1/2 + 25.64 (v in mV s−1), R2 = 0.994
The oxidation peak currents are well proportional to the square roots of the scan rates, which indicates that the oxidation reaction of AA is a typical diffusion-controlled process [55].

3.5. Analytical Sensing Performance

Differential pulse voltammograms (DPVs) of the Bi2S3/rGO-3/GCE for AA in the PBS solution was studied, and the obtained DPV profiles are presented in Figure 9a. The peak current increases linearly with the concentration ranging from 5 µM to 1200 µM (Figure 9b) and can be described by the corresponding Equation (3):
Ip (µA) = 0.01898 C (µM) − 0.2550 (µA) (R = 0.996)
From this data, the detection limit of the Bi2S3/rGO-3/GCE is 2.94 µM (S/N = 3) for the electrochemical detection of AA, and a sensitivity of 268.84 µA mM−1 cm−2 was determined. Comparison of the analytical results of the Bi2S3/rGO-3/GCE and reported results for ascorbic acid sensors are summarized in Table 1. From this table, the electrocatalytic activity of the Bi2S3/rGO-3/GCE sensor is comparable or better than for recently reported studies using other materials.

3.6. Reproducibility and Stability

The reproducibility and stability of the Bi2S3/rGO-3/GCE were examined in 0.1 M PBS (pH = 7), adding a fixed amount of AA (1 mM) (Figure 10). In five independently prepared electrode tests, the relative standard deviation (RSD) obtained of the peak current was 6.25%, which is within acceptable levels. Moreover, the current response of Bi2S3/rGO-3/GCE was 96.4% of its initial current value after twenty DPV tests, which implies adequate operational stability.

3.7. Interference Effect

The selectivity of the target analyte is a significant property for a biosensor. The interference experiments were carried out by successive addition of 200 µM AA and 200 µM interfering species (glucose, carbamide, clycine, K+, Na+, Mg2+, Zn2+, dopamine (DA), and uric acid (UA)) in 0.1 mM PBS (pH = 7.0). The measured effects of different interferents along with AA are shown in Figure 11. As shown in this figure, all these organic and inorganic species did not show any significant fluctuation in the determination of AA. The current response was obviously enhanced when 200 µM AA was added again. These results indicate that Bi2S3/rGO-3/GCE has high sensitivity and selectivity to AA in the presence of other organic molecules and ions normally found in food and biological samples.

3.8. AA Analytical Application

The applicability of Bi2S3/rGO-3/GCE was further examined using vitamin C tablets. Experiments were performed with the standard addition method [62] and recoveries in the range of 97.14–101.55% were obtained (Table 2). The good recovery values for AA indicate the feasible application of the Bi2S3/rGO-3/GCE electrode for the AA determination in real samples.

4. Conclusions

In summary, using a one-pot synthesis method Bi2S3/rGO composites were successfully synthesized. The obtained Bi2S3/rGO composites were used as the sensor active layer significantly improving the GCE performance in detecting AA. The size of the Bi2S3 rods can be controlled by adjusting the amount of GO in the synthesis, and the synergistic effect between rGO sheets and Bi2S3 nanorods has an essential effect on the electrochemical performance. The suitably sized nanorods of Bi2S3 anchored on rGO as an electrochemical sensor to detect AA show excellent sensitivity, good selectivity and stability, as well as good reproducibility and a detection limit of 2.94 µM. Moreover, using Bi2S3/rGO/GCE as a sensor to detect an actual sample containing AA, a good recovery (97.1% to 101.55%) was observed. The research method described in this work opens new avenues for optimizing novel materials to be used as the active layer in electrochemical detection.

Supplementary Materials

The following are available online at https://0-www-mdpi-com.brum.beds.ac.uk/article/10.3390/chemosensors9080190/s1, Figure S1: Cyclic voltammetry curves of Bi2S3 modified glassy carbon electrodes prepared using different sulfur sources, Figure S2: SEM images of Bi2S3 prepared using different sulfur sources, Figure S3: Bi2S3/rGO-3 Element mapping image and the EDAX spectrum.

Author Contributions

Investigation, data curation, writing—original draft, C.Q.; methodology, H.L. and S.Z.; validation, supervision, C.W. and R.S.; visualization, writing—review and editing, C.B. and G.L.; conceptualization, supervision, writing—review and editing, W.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research was partially funded by the National Natural Science Foundation of China (Nos. U1764254 and 21911530255), 111 Project, China (No. D17003), and the Open Research Fund of the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry (Jilin University, Grant No. 2021-03). C.B. thanks the Belgian Fund for Scientific Research under the FRFC contract CDR J001019. C.B. is a research associate of the National Funds for Scientific Research (FRS-FNRS, Belgium).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. SEM images of Bi2S3/rGO-1 (a), Bi2S3/rGO-2 (b), Bi2S3/rGO-3 (c), Bi2S3/rGO-4 (d); TEM images of Bi2S3/rGO-3 (e,f).
Figure 1. SEM images of Bi2S3/rGO-1 (a), Bi2S3/rGO-2 (b), Bi2S3/rGO-3 (c), Bi2S3/rGO-4 (d); TEM images of Bi2S3/rGO-3 (e,f).
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Figure 2. (a) The XRD spectra of the GO, rGO, Bi2S3, and Bi2S3/rGO; (b) Typical Raman spectra of GO, Bi2S3, and prepared Bi2S3/rGO.
Figure 2. (a) The XRD spectra of the GO, rGO, Bi2S3, and Bi2S3/rGO; (b) Typical Raman spectra of GO, Bi2S3, and prepared Bi2S3/rGO.
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Figure 3. XPS survey spectra of (a) Bi2S3, and Bi2S3/rGO-3 and core-level XPS spectra of (b) Bi 4f and S 2p, (c) C1s, (d) O1s in Bi2S3/rGO-3.
Figure 3. XPS survey spectra of (a) Bi2S3, and Bi2S3/rGO-3 and core-level XPS spectra of (b) Bi 4f and S 2p, (c) C1s, (d) O1s in Bi2S3/rGO-3.
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Figure 4. FTIR spectra of GO and Bi2S3/rGO-3 composite.
Figure 4. FTIR spectra of GO and Bi2S3/rGO-3 composite.
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Scheme 1. Proposed growth mechanism of Bi2S3/rGO and the electrochemical oxidation of AA.
Scheme 1. Proposed growth mechanism of Bi2S3/rGO and the electrochemical oxidation of AA.
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Figure 5. (a) CVs of bare GCE, Bi2S3/GCE, GO/GCE, Bi2S3/rGO-1/GCE, Bi2S3/rGO-2/GCE, Bi2S3/rGO-3/GCE, and Bi2S3/rGO-4/GCE in 0.1 M KCl containing 5 mM [Fe (CN)6]3−/4; (b) EIS of bare GCE, Bi2S3/GCE, and Bi2S3/rGO-1/GCE; (c) EIS of Bi2S3/rGO-1/GCE, Bi2S3/rGO-2/GCE, Bi2S3/rGO-3/GCE, and Bi2S3/rGO-4/GCE. The inset in (b) represents the equivalent circuit model.
Figure 5. (a) CVs of bare GCE, Bi2S3/GCE, GO/GCE, Bi2S3/rGO-1/GCE, Bi2S3/rGO-2/GCE, Bi2S3/rGO-3/GCE, and Bi2S3/rGO-4/GCE in 0.1 M KCl containing 5 mM [Fe (CN)6]3−/4; (b) EIS of bare GCE, Bi2S3/GCE, and Bi2S3/rGO-1/GCE; (c) EIS of Bi2S3/rGO-1/GCE, Bi2S3/rGO-2/GCE, Bi2S3/rGO-3/GCE, and Bi2S3/rGO-4/GCE. The inset in (b) represents the equivalent circuit model.
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Figure 6. DPVs for bare GCE, Bi2S3/GCE, rGO/GCE, and Bi2S3/rGO-3/GCE in 0.1 M PBS (pH=7.0) with AA concentrations 5 mM.
Figure 6. DPVs for bare GCE, Bi2S3/GCE, rGO/GCE, and Bi2S3/rGO-3/GCE in 0.1 M PBS (pH=7.0) with AA concentrations 5 mM.
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Figure 7. (a) CVs of Bi2S3/rGO-3/GCE in the presence of 5 mM AA comprising of various pH solutions from 3 to 8 at a scan rate of 100 mV s−1; (b) The plot of IP vs. pH value, and (c) EP vs. pH value.
Figure 7. (a) CVs of Bi2S3/rGO-3/GCE in the presence of 5 mM AA comprising of various pH solutions from 3 to 8 at a scan rate of 100 mV s−1; (b) The plot of IP vs. pH value, and (c) EP vs. pH value.
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Figure 8. (a) CV response of 5 MM of AA for different scan rates ranging from 20 to 100 mV s−1 at Bi2S3/rGO-3/GCE in 0.1 M PBS solution (pH = 7.0), (b) The plots of the peak current vs. square roots of scan rates ( v 1/2 ).
Figure 8. (a) CV response of 5 MM of AA for different scan rates ranging from 20 to 100 mV s−1 at Bi2S3/rGO-3/GCE in 0.1 M PBS solution (pH = 7.0), (b) The plots of the peak current vs. square roots of scan rates ( v 1/2 ).
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Figure 9. (a) DPV responses of Bi2S3/rGO-3/GCE in the presence of AA in concentrations ranging from 5 µM to 1200 µM; (b)The plot of anodic peak current versus different concentration values.
Figure 9. (a) DPV responses of Bi2S3/rGO-3/GCE in the presence of AA in concentrations ranging from 5 µM to 1200 µM; (b)The plot of anodic peak current versus different concentration values.
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Figure 10. DPVs of Bi2S3/rGO-3/GCE in 0.1 M PBS containing 1 mM AA (a) for five independently prepared electrodes, and (b) the current responses of the 1st, 10th, and 20th cycle.
Figure 10. DPVs of Bi2S3/rGO-3/GCE in 0.1 M PBS containing 1 mM AA (a) for five independently prepared electrodes, and (b) the current responses of the 1st, 10th, and 20th cycle.
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Figure 11. The amperometric response of the Bi2S3/rGO-3/GCE electrode towards the addition of 200 µM AA and various interfering compounds in 0.1 M PBS.
Figure 11. The amperometric response of the Bi2S3/rGO-3/GCE electrode towards the addition of 200 µM AA and various interfering compounds in 0.1 M PBS.
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Table 1. The performance in AA detection using Bi2S3/rGO-3/GCE, in comparison with other reported materials.
Table 1. The performance in AA detection using Bi2S3/rGO-3/GCE, in comparison with other reported materials.
Modified MaterialsLOD (μM)Linear Range (μM)Reference
(μA mM−1 cm−2)
Reference
Bi2S3/TNF-1000–10,00038[51]
GO/TmPO439100–1000[56]
NP-Cu/RGO/GCE0.090.5–30[57]
MoS2-PANI/rGO22.250–800048.2[58]
rGO/GCE4.765–2530[59]
Pd NWs/GCE0.225–900166.5[60]
PCN/ GO3.730–3000380[61]
Bi2S3/rGO2.945–1200268.84This work
Table 2. Determination of AA in vitamin C tablets (n = 3).
Table 2. Determination of AA in vitamin C tablets (n = 3).
SampleAdded (μM)Found (μM)Recovery (%)RSD (%)
Vitamin C tablets0<LOD--
200203.11101.552.25
300297.4298.261.58
400388.5797.143.04
500487.6297.422.71
RSD (%) = (Standard deviation/The average of the data obtained by repeating 3 times) × 100%.
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Qu, C.; Li, H.; Zhou, S.; Li, G.; Wang, C.; Snyders, R.; Bittencourt, C.; Li, W. Bi2S3/rGO Composite Based Electrochemical Sensor for Ascorbic Acid Detection. Chemosensors 2021, 9, 190. https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9080190

AMA Style

Qu C, Li H, Zhou S, Li G, Wang C, Snyders R, Bittencourt C, Li W. Bi2S3/rGO Composite Based Electrochemical Sensor for Ascorbic Acid Detection. Chemosensors. 2021; 9(8):190. https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9080190

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Qu, Chengling, He Li, Shuang Zhou, Guodong Li, Cheng Wang, Rony Snyders, Carla Bittencourt, and Wenjiang Li. 2021. "Bi2S3/rGO Composite Based Electrochemical Sensor for Ascorbic Acid Detection" Chemosensors 9, no. 8: 190. https://0-doi-org.brum.beds.ac.uk/10.3390/chemosensors9080190

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