Next Article in Journal
An Overview of the Latest Advances in the Catalytic Synthesis of Glycerol Carbonate
Previous Article in Journal
Eucalyptol, an All-Purpose Product
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Catalysts
Volume 12
Issue 1
10.3390/catal12010049
catalysts-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Electrocatalytic Properties of a BaTiO3/MWCNT Composite for Citric Acid Detection

by
Siraprapa Pitiphattharabun
1,2,
Nicha Sato
1,
Gasidit Panomsuwan
1,3 and
Oratai Jongprateep
1,3,*
1
Department of Materials Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand
2
Program of Sustainable Energy and Resources Engineering, Faculty of Engineering, Kasetsart University, Bangkok 10900, Thailand
3
International Collaborative Education Program for Materials Technology, Education, and Research (ICE-Matter), ASEAN University Network/Southeast Asia Engineering Education Development Network (AUN/SEED-Net), Bangkok 10330, Thailand
*
Author to whom correspondence should be addressed.
Catalysts 2022, 12(1), 49; https://doi.org/10.3390/catal12010049
Submission received: 23 November 2021 / Revised: 27 December 2021 / Accepted: 29 December 2021 / Published: 2 January 2022
(This article belongs to the Section Electrocatalysis)
Browse Figures
Versions Notes

Abstract

:
Although barium titanate (BaTiO3) shows prominent dielectric properties for fabricating electronic devices, its utilization in electrochemical applications is limited. Thus, this study examined the potential of a BaTiO3-based composite in the detection of a food additive, i.e., citric acid. First, a submicron-scale BaTiO3 powder was synthesized using the solution combustion method. Then, a BaTiO3/multiwalled carbon nanotube (MWCNT) composite was hydrothermally synthesized at BaTiO3:MWCNT mass ratios of 1:1 and 2:1. This composite was used as a working electrode in a nonenzymatic sensor to evaluate its electrocatalytic activity. Cyclic voltammetric measurements revealed that the BaTiO3/MWCNT composite (2:1) exhibited the highest electrocatalytic activity. Reduction reactions were observed at applied voltages of approximately 0.02 and −0.67 V, whereas oxidation reactions were detected at −0.65 and 0.47 V. With acceptable sensitivity, decent selectivity, and fair stability, the BaTiO3/MWCNT composite (2:1) showed good potential for citric acid detection.

1. Introduction

Citric acid is a soluble organic substance naturally found in citrus fruits. In the human body, it acts as an antioxidant as well as a buffering and mineral delivery agent and participates in the glycolytic process. Moreover, it inhibits the growth of calcium oxalate and calcium phosphate stones, preventing urolithiasis and other kidney diseases. However, high concentrations of citric acid cause the erosion, softening, and damage of the tooth enamel [1,2]. According to Fiume et al., the safe threshold level of citric acid in human blood is ~0.13 mM. In addition to its natural functions, citric acid is used as a dietary supplement, as well as a food additive for preservation and flavor enhancement. Furthermore, it is used in cosmetics and medicine; however, severe skin irritation and breathing difficulties have been reported after using cosmetic products that contain high-concentration citric acid [3].
Based on this discussion, the detection of citric acid is essential, which can be achieved using several techniques, including high-performance liquid chromatography (HPLC) and capillary electrophoresis [4,5]. However, because of the requirements of high-cost instruments and experienced operators, these techniques are unsuitable for point-of-care testing applications. Furthermore, colorimetry, visible–near-infrared spectroscopy, and fluorescence spectroscopy have been used for citric acid detection [6,7,8]. However, colorimetry is unsuitable for detecting colorless samples [9]. In the presence of interference in the sample, a high noise signal may be detected in spectroscopic techniques. Alternatively, nonenzymatic electrochemical sensing techniques exhibit good simplicity, sensitivity, selectivity, reusability, and stability and thus can be used for the quantitative detection of citric acid [10]. The electrochemical activity and performance of electrochemical sensors are often evaluated using cyclic voltammetry (CV) because of its simplicity, fast operation, low cost, and capability to analyze both organic and inorganic analytes [11,12].
Barium titanate (BaTiO3) is a perovskite with unique piezoelectric, ferroelectric, and dielectric properties [13,14]. It generally comprises tetragonal and cubic phases; cubic BaTiO3 exhibits paraelectric properties with a low dielectric constant, whereas tetragonal BaTiO3 shows ferroelectric properties with a high dielectric constant [15]. BaTiO3 has been widely used for fabricating microelectronic and optoelectronic devices such as actuators, capacitors, ferroelectric random-access memories, transducers, and electro-optic modulators [16,17]. However, although BaTiO3 exhibits high stability and good electrocatalytic activity, its application in electrochemical sensing has been limited compared with dielectric applications [18].
BaTiO3 can be synthesized using different methods such as solid-state reaction, coprecipitation, sol–gel, and spray pyrolysis techniques [19,20,21,22]. According to Ashiri and Clabel et al., BaTiO3 synthesis using the solid-state reaction technique involves the milling process and requires a high temperature and a prolonged processing time [23,24]. Additionally, the sol–gel and coprecipitation techniques can afford good-quality powders. However, sol–gel reactions such as hydrolysis or polymerization generally require a long completion time. For the coprecipitation technique, an acid or a base is employed to control pH, possibly resulting in chemical residues. BaTiO3 synthesis using the spray pyrolysis technique involves expensive equipment [25,26]. Jongprateep et al. and Khort et al. proposed the solution combustion method as a simple, low-cost, low-energy-consumptive, and robust method for preparing BaTiO3 [27,28].
The electrocatalytic performance of oxides can be generally enhanced by adding Pt and its alloys; however, the high cost, low abundance, and toxicity associated with Pt and its alloys hinder their usage. Alternatively, carbonaceous materials, including graphene oxide (GO) and carbon nanotubes (CNTs), present low cost, high abundance, high stability, large surface-to-volume ratio, and enhanced electron-transfer ability; hence, they are a great alternative to Pt and its alloy to improve the electrocatalytic activity of electrochemical sensing materials [29,30,31,32].
Because of the high electrocatalytic performance of metal–oxide/multiwalled CNT (MWCNT) composites, they have been used as electrodes and studied extensively. Yusoff et al. observed clear micropores in a Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) perovskite/MWCNT composite [33]. This composite achieved a higher specific surface area (SSA) than that of the pure BSCF perovskite and exhibited enhanced electrocatalytic oxygen reduction, which was attributed to the ability of MWCNTs to promote electron transfer and provide short-distance transportation between the ionic mass and charge. Chen et al. assessed the efficiency of BaTiO3/reduced GO (rGO) composites to enhance the performance of screen-printed carbon electrodes, obtaining a high current response when detecting ractopamine, a food additive with antibacterial properties used in the preservation of meat products [34].
This work aimed at exploring the potential of a BaTiO3/MWCNT composite as a citric acid sensor by investigating its electrocatalytic activities in the presence of citric acid. The chemical composition, microstructure, SSA, and optical characteristics of the BaTiO3 powder prepared using the solution combustion method were also examined.

2. Results and Discussion

2.1. Phase Identification and Elemental Analysis of Synthesized Powder

The XRD pattern of the synthesized BaTiO3 powder (Figure 1) revealed the presence of the cubic phase of BaTiO3 (JCPDS No. 01-074-1964). The peak observed in the range of 43°–48° could be an indicator of the BaTiO3 phase. A single peak corresponding to the (200) plane indicated the cubic BaTiO3 phase, whereas a peak splitting into the (002) and (200) planes suggested the tetragonal BaTiO3 phase [35]. The XRD pattern revealed only a single peak of the (200) plane, indicating cubic-structured BaTiO3 (Figure 1).
The Rietveld refinement was performed to gain additional insights into the structural information of the synthesized BaTiO3 powder. The structural refinement revealed that the diffraction pattern of BaTiO3 powder fitted well (χ2 = 1.65) with the cubic BaTiO3 pattern in the crystallography open database (COD ID 1507757, space group Pm-3m) (Figure 2) [36,37]. The results showed that the refined lattice parameters a, b, and c were equal to 4.0014 Å.
The cubic and tetragonal phases of BaTiO3 with distinct properties have been reported. According to Thanki et al., cubic BaTiO3 shows better electrical conductivity than that of tetragonal BaTiO3 [38]. Moreover, many studies have reported the potential of cubic BaTiO3 in sensor applications. According to Petrovic et al., pseudocubic La-doped BaTiO3 shows greater performance in gas sensing than that the tetragonal phase [39]. Chaudhari et al. reported the potential of nanocubic BaTiO3 in the detection of liquid petroleum gas [40]. Based on the cubic structure, the synthesized BaTiO3 powder may show the desirable sensing performance.
In addition to the BaTiO3 peaks, the XRD pattern revealed a low-intensity peak assigned to barium carbonate (JCPDS No. 01-071-2394), whose formation can be associated with a chemical reaction between barium from the initial reagent and carbon from CO2 or the combustion fuel. Khort et al. reported the formation of BaCO3 via the reaction between barium oxide (decomposed from barium nitrate) and CO2, whereas Jongprateep and Tanmee observed the formation of BaCO3 via the reaction between barium oxide and carbon from glycine [27,41].
The semiquantitative analysis of the BaCO3 secondary phase was performed using Klug’s equation, achieving the BaCO3 content of 5.23 wt.%. Moreover, the quantitative analysis performed using the X’Pert HighScore Plus program indicated a comparable result of 5 wt.% BaCO3 (Figure 3). A minimal content of BaCO3 should not have considerable detrimental effects on the catalysis. Moreover, previous studies have reported that the presence of BaCO3 could even enhance the catalytic process. According to Hong et al., the deposition of BaCO3 on a La0.6Sr0.4Co0.2Fe0.8O3−δ perovskite afforded synergistic electrocatalytic activity [42]. Cao et al. reported that the presence of the BaCO3 impurity phase in BaTiO3 and LaFeO3 yielded enhanced active sites, which contributed to the improved performance of ethanol sensing [43].
Energy-dispersive X-ray spectroscopy (EDS) was performed to analyze the elemental composition of the synthesized powder. The elemental mapping and EDS spectra of the BaTiO3 powder revealed that it was composed of barium (Ba), titanium (Ti), and oxygen (O). The atomic contents of Ba and Ti were 29.92 at.% and 26.96 at.%, respectively. To confirm the formation of BaTiO3, the atomic ratio of Ba:Ti must be close to 1:1 [44,45,46]. The elemental analysis of the BaTiO3 powder showed a Ba:Ti atomic ratio of 1.1:1, showing the presence of BaTiO3 as the primary phase. As shown in Figure 4.

2.2. Morphology of BaTiO3 Powder

The SEM images of BaTiO3 revealed irregular and cubic-shaped particles with a nonuniform particle size distribution (Figure 5a). The micrographs also revealed agglomeration among the particles. The average particle size and agglomerate size were 1.05 ± 0.51 and 3.42 ± 1.91 µm, respectively. According to Gao et al. and Khort et al., the agglomeration of the powder synthesized using the solution combustion method was triggered by the prolonged combustion period and high temperatures during the combustion and calcination processes [47,48].
SEM was also used to examine the BaTiO3/MWCNT composite. The results revealed that the agglomerated BaTiO3 particles were nonuniformly deposited in the MWCNT clusters (Figure 5b,c).

2.3. Specific Surface Area

The BET technique was used to determine the SSA of BaTiO3. A large SSA provides several active sites for reactions, enhancing the catalytic activity and performance [49]. The SSA of the synthesized BaTiO3 powder was low (4.25 m2/g), possibly attributed to the agglomeration of the BaTiO3 particles, as revealed by SEM observations (Figure 5a). The SSA of MWCNTs was 315.28 m2/g, suggesting additional active sites for reactions and enhanced electron transfer. Therefore, compared with pure BaTiO3, the BaTiO3/MWCNT composites potentially demonstrate superior electrocatalytic activity.

2.4. Electrocatalytic Activity

The sensing performance of MWCNTs, BaTiO3, and BaTiO3/MWCNT composites with BaTiO3:MWCNT mass ratios of 1:1 and 2:1 in the presence of citric acid was examined using CV. The BaTiO3/MWCNT composite-based electrode exhibited an oxidation peak at 0.43 V and reduction peaks at 0.02 and –0.77 V. For the BaTiO3 electrode, a reduction reaction occurred at an applied voltage of −0.83 V. Two oxidation peaks were detected at applied voltages of approximately –0.65 and 0.47 V for the BaTiO3/MWCNT composite-based electrode with BaTiO3:MWCNT mass ratios of 1:1 and 2:1, whereas two reduction peaks were detected at approximately 0.02 and −0.67 V. The BaTiO3/MWCNT composite (2:1) exhibited the highest peak current among the electrodes (Table 1).
BaTiO3 showed low electrocatalytic activity and a minor reduction peak (Figure 6). Compared with BaTiO3, BaTiO3/MWCNT composite-based electrode showed superior electrocatalytic activity based on a higher peak current. This can be attributed to the large SSA of the CNTs, which provides additional active sites for reactions and enhances electron transfer. MWCNT-based materials have been used to fabricate cocatalysts and support many catalytic applications. According to Sato et al., carbon-supported metal–oxide composites show excellent electrocatalytic performance owing to the tuned electronic states of catalysts [50]. Therefore, combining carbon materials and metal oxides can enhance the catalytic process [51,52,53]. The synergistic effects of metal oxides and large-SSA carbon-based materials on electrocatalytic activities have been reported in many studies [54,55]. A similar observation was clearly evident in this study. The BaTiO3/MWCNT composites showed excellent electrocatalytic activities based on the prominent reduction and oxidation peaks in the presence of citric acid.
Citric acid dissociates into various species during electrochemical reactions between metal and citric acid, including H2Cit−, HCit2−, and Cit3−. These species serve as initial precursors for the production of metal–citric acid complexes via redox reactions [56]. Similarly, electrochemical reactions occurring in BaTiO3/MWCNTs can be expressed as follows:
BaTiO3/MWCNTs + H2Cit− ⇋ [BaTiO3/MWCNTs][H2Cit]+ + 2e−
Because the results revealed that the BaTiO3/MWCNT composite (2:1)-based electrode showed the highest electrocatalytic activity in the detection of citric acid, this composite was selected for further electrocatalytic performance examinations.
The CV measurements of the BaTiO3/MWCNT composite (2:1) in 500 µM citric acid were conducted at scan rates of 25.0–100.0 mV/s (Figure 7a). The cyclic voltammograms exhibited two prominent peaks, corresponding to oxidation reactions at applied voltages ranging from −0.74 to −0.65 V and 0.35 to 0.47 V. The peaks corresponding to reduction reactions were observed at applied voltages ranging from −0.67 to −0.51 V and 0.02 to 0.12 V. The correlation between the peak current and scan rate or square root of the scan rate was employed to determine the mechanism involved in electrocatalytic reactions. A good linear relation (R2 > 0.75) between the peak current and scan rate suggested the presence of an adsorption-controlled reaction, whereas a good linear relation between the peak current and square root of the scan rate indicated a diffusion-controlled reaction [57].
The relation between the peak current and scan rate and between the peak current and square root of the scan rate showed good linear relations with R2 = 0.981 and 0.998, respectively (Figure 7b,c). Therefore, the mechanisms controlling the catalytic activities of the BaTiO3/MWCNT composite (2:1) in citric acid were both adsorption-controlled reactions, associated with the concentration of analytes, and diffusion-controlled reactions, associated with electron transfer in the reactions.
Generally, the relation between the current density and analyte concentration can be used to determine the sensitivity of an electrode. Herein, the sensitivity of the BaTiO3/MWCNT composite (2:1)-based electrode for citric acid detection was evaluated using a calibration curve between the reduction current density and citric acid concentration. The results showed good linearity in the citric acid concentration range of 100–10,000 µM (Figure 8), corresponding to the citrate concentration range in blood [3]. Table 2 presents the corresponding sensitivity values.
The lowest concentration that an electrode can detect at 95% level of confidence is generally referred to as the limit of detection (LOD), while the limit of quantification (LOQ) refers to the reliable lowest concentration of an analyte in detection. These values can be calculated as follows [58,59]:
LOD = 3.3σ/S
LOQ = 10σ/S,
where σ represents the standard deviation of blank and S represents the calibration curve slope at the lowest concentration range.
The LOD and LOQ of the BaTiO3/MWCNT composite (2:1)-based electrode for citric acid were 0.061 and 0.18 mM, respectively. The performance of this electrode for the detection of citric acid is listed along with those reported in other studies in Table 3. The linear range and LOD values obtained in this study were within an acceptable range when compared with those obtained in the case of other electrochemical sensors, capillary electrophoresis, HPLC, fluorescence spectroscopic, and colorimetric techniques.
The selectivity of the BaTiO3/MWCNT composite (2:1)-based electrode was examined via chronoamperometric measurements in the presence of citric acid, glutamate, nitrate, ascorbic acid, and nitrite. The electrode exhibited a prominent current signal of citric acid, demonstrating its good selectivity toward the target analyte (Figure 9).
The stability of the BaTiO3/MWCNT composite (2:1)-based electrode for citric acid detection was examined based on the peak current after repeating cycles (Figure 10). After 200 cycles, the peak current decreased by 23.31%, which was in the acceptable range for sensing materials reported by other researchers [67,68].

3. Materials and Methods

3.1. Synthesis of BaTiO3 Powder

BaTiO3 was synthesized using the solution combustion method by employing barium nitrate (Daejung, Daejung Chemicals & Metals Co., Ltd, Gyeonggi-do, Korea) and titanium dioxide (Sigma-Aldrich, Sigma-Aldrich Chemie GmbH, Steinheim, Germany) as the initial reagents and dissolving them in nitric acid (RCI Labscan, RCI Labscan Limited, Bangkok, Thailand). First, a homogeneous aqueous solution containing barium and titanium ions was prepared. Then, glycine (Daejung, Daejung Chemicals & Metals Co., Ltd., Gyeonggi-do, Korea), functioning as a combustion fuel, was added to the solution. The combustion process was initiated at 400 °C, yielding a white powder that was collected and subsequently calcined at 900 °C for 3 h (Figure 11a). The reactions involved in the solution combustion synthesis of BaTiO3 can be expressed using Equations (1) and (2).
TiO2 + 4HNO3 → Ti(NO3)4 + 2H2O
7Ti(NO3)4 + 7Ba(NO3)2 + 30C2H5NO2 → 7BaTiO3 + 36N2 + 60CO2 + 45H2O
The average yield of the solution combustion synthesis of BaTiO3 for two replicates of the synthesis process was 75.8%.

3.2. Preparation of BaTiO3/MWCNT Composite as a Working Electrode

The BaTiO3/MWCNT composite was prepared by mixing the synthesized BaTiO3 powder and MWCNTs at BaTiO3:MWCNT mass ratios of 1:1 and 2:1, followed by sonication for 30 min. The resulting mixture was dispersed in deionized water, autoclaved at 150 °C for 5 h, and dried overnight at 60 °C. The average yield of the BaTiO3/MWCNT composite for two replicates of the synthesis process was 94.2%. The as-obtained BaTiO3/MWCNT composite was dispersed in 99.9% ethanol (QRëC, Asia Chemie (Thailand) Co., Ltd., Chonburi, Thailand) at a composite:ethanol ratio of 1 mg:1 mL and sonicated for 30 min. Subsequently, 5 µL of the BaTiO3/MWCNT composite suspension was dropped onto a glassy carbon electrode (Figure 11b).

3.3. Characterization

X-ray diffraction (XRD; X’Pert, Philips, PANalytical B.V., Almelo, Netherlands) was performed for phase identification via 2θ scanning from 20° to 80° with a step size of 0.02°. Moreover, the XRD pattern was used to examine the secondary phase based on Klug’s equation [69,70]:
W e i g h t   f r a c t i o n =   ( I mix I pure ) A mix A pure −   ( I mix I pure )   ( A pure − A mix )  
where Imix and Ipure denote the integrated intensities of the secondary and pure phases, respectively, and Amix and Apure denote the corresponding mass absorption coefficients for the Cu Kα radiation, respectively (Amix and Apure are 253.22 and 256.65 cm2/g) [36]. To confirm the results obtained using Klug’s equation, the content of the secondary phase was also examined using the X’Pert HighScore Plus program version 3.0.
The XRD pattern of the synthesized powder was also used to conduct the Rietveld refinement on the FullProf Suite program version 7.40.
The morphology of the synthesized powder was characterized using scanning electron microscopy (SEM; Hitachi, SU3500, Hitachi High-Technologies Corporation, Tokyo, Japan). The SSA of the BaTiO3 and MWCNT powders was examined using a surface area analyzer (Micrometrics, 3Flex, Micromeritics Instrument Corporation, Norcross, Georgia) using the Brunauer–Emmett–Teller (BET) technique. Before measuring the N2 adsorption–desorption at 77 K, the powder was degassed at 200 °C for 3 h.
CV measurements were performed using a potentiostat (VSP, BioLogic, BioLogic Science Instruments Ltd., Seyssinet-Pariset, France) to evaluate the electrocatalytic activity of the BaTiO3/MWCNT powder in a citric acid solution. To determine the peak current, the measurements were replicated for at least five cycles. Ag/AgCl, Pt, and the BaTiO3/MWCNT composite were used as the reference, auxiliary, and working electrodes, respectively. The applied voltage ranged from −1.4 to 1.4 V (Figure 12).

4. Conclusions

BaTiO3 powder with average particle sizes of 1.05 ± 0.51 µm was successfully synthesized using the solution combustion method. BaTiO3/MWCNT composites at BaTiO3:MWCNT mass ratios of 1:1 and 2:1 were prepared as BaTiO3/MWCNT composite-based electrodes for citric acid detection. In the presence of citric acid, both BaTiO3/MWCNT composite (1:1)- and BaTiO3/MWCNT composite (2:1)-based electrodes underwent reduction reactions at 0.02 and −0.67 V. Oxidation reactions at −0.65 and 0.47 V were also observed. The BaTiO3/MWCNT composite (2:1)-based electrode achieved the highest performance in citric acid detection, with sensitivities of 0.00059 and 0.000068 µA µM−1 mm−2 in citric concentration ranges of 100–1000 and 1000–10,000 μM, respectively. The LOD of the BaTiO3/MWCNT composite (2:1)-based electrode was 0.061 mM. Owing to the good electrocatalytic performance, including an acceptable sensitivity, LOD, selectivity, and stability, BaTiO3/MWCNT composites demonstrated great potential for applications in citric acid detection.

Author Contributions

Conceptualization, S.P., N.S. and O.J.; methodology, S.P. and N.S.; software, S.P.; validation, O.J. and G.P.; formal analysis, S.P. and O.J.; investigation, O.J. and G.P.; resources, O.J. and G.P.; data curation, S.P. and O.J.; writing—original draft preparation, S.P. and O.J.; writing—review and editing, O.J. and G.P.; visualization, O.J.; supervision, O.J.; project administration, O.J.; funding acquisition, O.J. and G.P. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Kasetsart University Research and Development Institute (KURDI) and ASEAN University Network/Southeast Asia Engineering Education Development Network (AUN/SEED-Net).

Data Availability Statement

Data sharing is not applicable to this article.

Acknowledgments

The authors would like to express their sincere gratitude to Kasetsart University Research and Development Institute (KURDI) and ASEAN University Network/Southeast Asia Engineering Education Development Network (AUN/SEED-Net) for financial support. The Department of Materials Engineering, Faculty of Engineering, Kasetsart University, is also acknowledged for equipment support. Valuable suggestions and discussion from Ratchatee Techapiesancharoenkij, Maythee Saisriyoot, and Chatchawal Wongchoosuk are highly appreciated.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Tang, H.; Gao, T.; Luo, Z. An electrochemical approach for the determination of the fruit juice freshness using carbon paste electrode modified with ZnO nanorods. Int. J. Electrochem. Sci. 2020, 15, 2766–2775. [Google Scholar] [CrossRef]
  2. Brima, E.I.; Abbas, A.M. Determination of citric acid in soft drinks, juice drinks and energy drinks using titration. Int. J. Chem. Stud. 2014, 1, 30–34. [Google Scholar]
  3. Fiume, M.M.; Heldreth, B.A.; Bergfeld, W.F.; Belsito, D.V.; Hill, R.A.; Klaassen, C.D.; Liebler, D.C.; Marks, J.G., Jr.; Shank, R.C.; Slaga, T.J.; et al. Safety assessment of citric Acid, inorganic citrate salts, and alkyl citrate esters as used in cosmetics. Int. J. Toxicol. 2014, 33, 16S–46S. [Google Scholar] [CrossRef]
  4. Scherer, R.; Rybka, A.C.P.; Ballus, C.A.; Meinhart, A.D.; Filho, J.T.; Godoy, H.T. Validation of HPLC method for simultaneous determination of main organic acid in fruits and juices. Food Chem. 2012, 135, 150–154. [Google Scholar] [CrossRef] [Green Version]
  5. Izco, J.M.; Tormo, M.; Jiménez-Flores, R. Rapid simultaneous determination of organic acids, free amino acids, and lactose in cheese by capillary electrophoresis. J. Dairy Sci. 2002, 85, 2122–2129. [Google Scholar] [CrossRef] [Green Version]
  6. Leininger, E.; Katz, S. Fluorometric method for determination of citric acid. Anal. Chem. 1949, 21, 810–813. [Google Scholar] [CrossRef]
  7. Cen, H.; Bao, Y.; He, Y.; Sun, D.W. Visible and near infrared spectroscopy for rapid detection of citric and tartaric acids in orange juice. J. Food Eng. 2007, 82, 253–260. [Google Scholar] [CrossRef]
  8. Pucher, G.W.; Sherman, C.C.; Vickery, H.B. A method to determine small amounts of citric acid in biological material. J. Biol. Chem. 1936, 113, 235–245. [Google Scholar] [CrossRef]
  9. Pashchenko, O.; Shelby, T.; Banerjee, T.; Santra, S. A comparison of optical, electrochemical, magnetic, and colorimetric point-of-care biosensors for infectious disease diagnosis. ACS Infect. Dis. 2018, 4, 1162–1178. [Google Scholar] [CrossRef] [PubMed]
  10. Detpisuttitham, W.; Phanthong, C.; Ngamchana, S.; Rijiravanich, P.; Surareungchai, W. Electrochemical detection of salicylic acid in pickled fruit/vegetable and juice. J. Anal. Test. 2020, 4, 291–297. [Google Scholar] [CrossRef]
  11. Sandford, C.; Edwards, M.A.; Klunder, K.J.; Hickey, D.P.; Li, M.; Barman, K.; Sigman, M.S.; White, H.S.; Minteer, S.D. A synthetic chemist’s guide to electroanalytical tools for studying reaction mechanisms. Chem. Sci. 2019, 10, 6404–6422. [Google Scholar] [CrossRef] [Green Version]
  12. Pisoschi, A.M.; Danet, A.F.; Kalinowski, S. Ascorbic acid determination in commercial fruit juice samples by cyclic voltammetry. J. Autom. Methods Manag. Chem. 2008, 2008, 937651. [Google Scholar] [CrossRef] [Green Version]
  13. Ismail, F.A.; Osman, R.A.M.; Idris, M.S.; Hambali, N.A.M.A. Structure and electrical characteristics of BaTiO3 and Ba0.99Er0.01TiO3 ceramic. Solid State Phenom. 2018, 280, 127–133. [Google Scholar] [CrossRef]
  14. Zhao, X.; Liu, W.; Chen, W.; Li, S. Preparation and properties of BaTiO3 ceramics from the fine ceramic powder. Ceram. Int. 2015, 41, S111–S116. [Google Scholar] [CrossRef]
  15. Yoon, D.H. Tetragonality of barium titanate powder for a ceramic capacitor application. J. Ceram. Process. Res. 2006, 7, 343–354. [Google Scholar]
  16. Cai, W.; Fu, C.; Gao, J.; Guo, Q.; Deng, X.; Zhang, C. Preparation and optical properties of barium titanate thin films. Phys. B 2011, 406, 3583–3587. [Google Scholar] [CrossRef]
  17. Petraru, A.; Schubert, J.; Schmid, M.; Buchal, C. Ferroelectric BaTiO3 thin-film optical waveguide modulators. Appl. Phys. Lett. 2002, 81, 1375–1377. [Google Scholar] [CrossRef] [Green Version]
  18. Soderznik, K.Z.; Fabrega, C.; Ramirez, F.H.; Prades, J.D.; Ceh, M. BaTiO3 based nanostructures for humidity sensing applications. Proceedings 2019, 15, 9. [Google Scholar] [CrossRef] [Green Version]
  19. Hasbullah, N.N.; Jew, L.O.; Chyi, J.L.Y.; Kien, C.S.; Talib, Z.A. Synthesis of BaTiO3 nanoparticles via hydrothermal method. Solid State Phenom. 2017, 268, 172–176. [Google Scholar] [CrossRef]
  20. Simon-Seveyrat, L.S.; Hajjaji, A.; Emziane, Y.; Guiffard, B.; Guyomar, D. Re-investigation of synthesis of BaTiO3 by conventional solid-state reaction and oxalate coprecipitation route for piezoelectric applications. Ceram. Int. 2007, 33, 35–40. [Google Scholar] [CrossRef]
  21. Kavian, R.; Saidi, A. Sol-gel derived BaTiO3 nanopowders. J. Alloy. Comp. 2009, 468, 528–532. [Google Scholar] [CrossRef]
  22. Gryteselv, M. Novel Synthesis Method of BaTiO3-Nanoparticles—Synthesis of BaTiO3-Nanoparticles by Spray-Pyrolysis of TiO2-Nanoparticles Dispersed in Ba(NO3)2-Solution. Master’s Thesis, Norwegian University of Science and Technology (NTNU), Trondheim, Norway, June 2016. [Google Scholar]
  23. Clabel, H.J.L.; Awan, I.T.; Pinto, A.H.; Nogueira, I.C.; Bezzon, V.D.N.; Leite, E.R.; Balogh, D.T.; Mastelaro, V.R.; Ferreira, S.O.; Marega, M., Jr. Insights on the mechanism of solid state reaction between TiO2 and BaCO3 to produce BaTiO3 powders: The role of calcination, milling, and mixing solvent. Ceram. Int. 2020, 46, 2987–3001. [Google Scholar] [CrossRef]
  24. Ashiri, R. On the solid-state formation of BaTiO3 nanocrystals from mechanically activated BaCO3 and TiO2 powders: Innovative mechanochemical processing, the mechanism involved, and phase and nanostructure evolutions. RSC Adv. 2016, 6, 17138–17150. [Google Scholar] [CrossRef]
  25. Varshney, G.; Kanel, S.R.; Kempisty, D.; Varshney, V.; Agrawal, A.; Sahle-Demessie, E.; Varma, R.S.; Nadagouda, M.N. Nanoscale TiO2 films and their application in remediation of organic pollutants. Coord. Chem. Rev. 2016, 1, 43–64. [Google Scholar] [CrossRef]
  26. Movlee, K.; Ganjali, M.R.; Norouzi, P.; Neri, G. Iron-based nanomaterials/graphene composites for advanced electrochemical sensor. Nanomaterials 2017, 7, 406. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  27. Khort, A.A.; Podbolotov, K.B. Preparation of BaTiO3 nanopowders by the solution combustion method. Ceram. Int. 2016, 42, 15343–15348. [Google Scholar] [CrossRef]
  28. Jongprateep, O.; Tanmee, K. Effect of fuel concentrations and calcination temperature on the particle sizes of YBa2Cu3O7-x superconductors synthesized by the solution combustion technique. J. Austr. Ceram. Soc. 2012, 48, 80–84. [Google Scholar]
  29. Hwang, H.S.; Jeong, J.W.; Kim, Y.A.; Chang, M. Carbon nanomaterials as versatile platforms for biosensing applications. Micromachines 2020, 11, 814. [Google Scholar] [CrossRef]
  30. Bai, W.; Raghavendra, A.; Podila, R.; Brown, J.M. Defect density in multiwalled carbon nanotubes influences ovalbumin adsorption and promotes macrophage activation and CD4+ T-cell proliferation. Int. J. Nanomed. 2016, 11, 4357–4371. [Google Scholar]
  31. Wang, C.; Yang, F.; Gao, L.; Xu, S.; Fan, L.; Guo, T.; Liu, Y.; Zhou, L.; Zhang, Y. AuPt nanoparticles clusters on MWCNTs with enhanced electrocatalytic activity for methanol oxidation. Catalysts 2018, 8, 669. [Google Scholar] [CrossRef] [Green Version]
  32. Kwon, W.; Kim, J.M.; Rhee, S.W. Electrocatalytic carbonaceous materials for counter electrodes in dye-sensitized solar cells. J. Mater. Chem. A 2013, 1, 3202–3215. [Google Scholar] [CrossRef]
  33. Yusoff, F.; Mohamed, N.; Aziz, A.; Ghani, S.A. Electrocatalytic reduction of oxygen at perovskite (BSCF)-MWCNT composite electrodes. Mater. Sci. Appl. 2014, 5, 199–211. [Google Scholar] [CrossRef] [Green Version]
  34. Muthumariyappan, A.; Rajaji, U.; Chen, S.M.; Baskaran, N.; Chen, T.W.; Jothi Ramalingam, R.J. Sonochemical synthesis of perovskite-type barium titanate nanoparticles decorated on reduced graphene oxide nanosheets as an effective electrode material for the rapid determination of ractopamine in meat samples. Ultrason. Sonochem. 2019, 56, 318–326. [Google Scholar] [CrossRef] [PubMed]
  35. Vittayakorn, N. Synthesis and dielectric properties of bismuth doped barium titanate (BaTiO3) ceramics. NU Sci. J. 2007, 3, 119–125. [Google Scholar]
  36. Ma, Z.; Li, G.; Sun, B.; He, L.; Gao, W.; Sun, Q.; Liu, Q.; Lou, X. Enhanced electric-field-induced strain in 0.7Bi(1-x)SmxFeO3-0.3BaTiO3 lead-free ceramics. J. Mater. Sci. 2020, 55, 8134–8144. [Google Scholar] [CrossRef]
  37. Mansuri, A.; Mishra, A. Structure evolution of BaTiO3 on Co doping: X-ray diffraction and raman study. J. Phys. Conf. Ser. 2016, 755, 012018. [Google Scholar] [CrossRef]
  38. Thanki, A.A.; Goyal, R.K. Study on effect of cubic- and tetragonal phased BaTiO3 on the electrical and thermal properties of polymeric nanocomposites. Mater. Chem. Phys. 2016, 183, 447–456. [Google Scholar] [CrossRef]
  39. Petrovic, M.M.V.; Radojkovic, A.; Bobic, J.D.; Dzunuzovic, A.; Ilic, N.; Stojanovic, B.D. Sensing properties of barium titanate nanoceramics tailored by doping and microstructure control. J. Mater. Sci. 2019, 54, 6038–6052. [Google Scholar] [CrossRef]
  40. Chaudhari, G.N.; Bambole, D.R.; Bodade, A.B. Structural and gas sensing behavior of nanocrystalline BaTiO3 based liquid petroleum gas sensors. Vacuum 2006, 81, 251–256. [Google Scholar] [CrossRef]
  41. Jongprateep, O.; Khondnakhon, T.; Palomas, J. Composition-microstructure-property relationships in BaTiO3 with Mg addition. Key Eng. Mater. 2015, 659, 58–63. [Google Scholar] [CrossRef]
  42. Hong, T.; Brinkman, K.S.; Xia, C. Barium carbonate nanoparticles as Synergistic catalysts for the oxygen reduction reaction on La0.6Sr0.4Co0.2Fe0.8O3−δ Solid-oxide fuel cell cathodes. ChemElectroChem 2016, 3, 805–813. [Google Scholar] [CrossRef]
  43. Cao, E.; Feng, Y.; Guo, Z.; Wang, H.; Song, G.; Zhang, Y.; Hao, W.; Sun, L.; Nie, Z. Ethanol sensing characteristics of (La,Ba)(Fe,Ti)O3 nanoparticles with impurity phases of BaTiO3 and BaCO3. J. Sol-Gel Sci. Technol. 2020, 96, 431–440. [Google Scholar] [CrossRef]
  44. Li, B.; Shang, W.; Hu, Z.; Zhang, N. Template-free fabrication of pure single-crystalline BaTiO3 nano-wires by molten salt synthesis technique. Ceram. Int. 2014, 40, 73–80. [Google Scholar] [CrossRef]
  45. Su, S.; Zuo, R.; Lv, D.; Fu, J. Synthesis and characterization of (001) oriented BaTiO3 platelets through a topochemical conversion. Powder Technol. 2012, 217, 11–15. [Google Scholar] [CrossRef]
  46. Dutta, P.D.; Roy, M.; Maiti, N.; Tyagi, A.K. Phase evolution in sonochemically synthesized Fe3+ doped BaTiO3 nanocrystallites: Structural, magnetic and ferroelectric characterisation. Phys. Chem. Chem. Phys. 2016, 18, 9758–9769. [Google Scholar] [CrossRef] [PubMed]
  47. Gao, Y.; Ma, J.; Meng, F.; Wang, W.; Li, Z. Solution-combusted nanosized Ni-Al2O3 catalyst for slurry CO methanation: Effects of alkali/alkaline earth metal chlorides. J. Mater. Sci. 2020, 55, 16510–16521. [Google Scholar] [CrossRef]
  48. Khort, A.; Podbolotov, K.; Serrano-García, R.; Gun’ko, Y. One-step solution combustion synthesis of pure Ni nanopowders with enhanced coercivity: The fuel effect. J. Solid State Chem. 2017, 253, 270–276. [Google Scholar] [CrossRef]
  49. Kim, D.; Zhang, K.; Cho, M.; Kang, Y.M. Critical design factors for kinetically favorable P-based compounds toward alloying with Na ions for high-power sodium-ion batteries. Energy Environ. Sci. 2019, 12, 1326–1333. [Google Scholar] [CrossRef]
  50. Sato, Y.; Kitano, S.; Kowalski, D.; Aoki, Y.; Fujiwara, N.; Ioroi, T.; Habazaki, H. Spinel-type metal oxide nanoparticles supported on platelet-type carbon nanofibers as a bifunctional catalyst for oxygen evolution reaction and oxygen reduction reaction. Electrochemistry 2020, 88, 566–573. [Google Scholar] [CrossRef]
  51. Liu, Y.; Zhang, J.; Cheng, Y.; Jiang, S.P. Effect of carbon nanotubes on direct electron transfer and electrocatalytic activity of immobilized glucose oxidase. ACS Omega 2018, 3, 667–676. [Google Scholar] [CrossRef]
  52. Ferrara, M.; Melchionna, M.; Fornasiero, P.; Bevilacqua, M. The role of structured carbon in downsized transition metal-based electrocatalysts toward a green nitrogen fixation. Catalysts 2021, 11, 1529. [Google Scholar] [CrossRef]
  53. Dey, S.; Dhal, G.C.; Mohan, D.; Prasad, R. Advances in transition metal oxide catalysts for carbon monoxide oxidation: A review. Adv. Compos. Hybrid Mater. 2019, 2, 626–656. [Google Scholar] [CrossRef]
  54. Poolakkandy, R.R.; Menamparambath, M.M. Transition metal oxide based non-enzymatic electrochemical sensors: An arising approach for the meticulous detection of neurotransmitter biomarkers. Electrochem. Sci. Adv. 2021, 1, e2000024. [Google Scholar] [CrossRef]
  55. Fayemi, O.E.; Adekunle, A.S.; Ebenso, E.E. Metal oxide nanoparticles/multi-walled carbon nanotube nanocomposite modified electrode for the detection of dopamine: Comparative electrochemical study. J. Biosens. Bioelectron. 2015, 6, 1000190. [Google Scholar] [CrossRef]
  56. Kim, M.J.; Choe, S.; Kim, H.C.; Cho, S.K.; Kim, S.K.; Kim, J.J. Electrochemical behavior of citric acid and its influence on Cu electrodeposition for damascence metallization. J. Electrochem. Soc. 2015, 162, D354–D359. [Google Scholar] [CrossRef] [Green Version]
  57. Fotouhi, L.; Fathollahzadeh, M.; Heravi, M.M. Electrochemical behavior and voltametric determination of sulfaguanidine at a glassy carbon electrode modified with a multi-walled carbon nanotube. Int. J. Electrochem. Sci. 2012, 7, 3919–3928. [Google Scholar]
  58. Wu, Y.; Deng, P.; Tian, Y.; Feng, J.; Xiao, J.; Li, J.; Liu, J.; Li, G.; He, Q. Simultaneous and sensitive determination of ascorbic acid, dopamine and uric acid via an electrochemical sensor based on PVP-graphene composite. J. Nanobiotechnol. 2020, 18, 112. [Google Scholar] [CrossRef]
  59. Maddipatla, D.; Saeed, T.S.; Narakathu, B.B.; Obare, S.O.; Atashbar, M.Z. Incorporating a novel hexaazatriphenylene derivative to a flexible screen-printed electrochemical sensor for copper ion detection in water samples. IEEE Sens. J. 2020, 20, 12582–12591. [Google Scholar] [CrossRef]
  60. Saavedra, L.; García, A.; Barbas, C. Development and validation of a capillary electrophoresis method for direct measurement of isocitric, citric, tartaric and malic acids as adulteration markers in orange juice. J. Chromatogr. A 2000, 881, 395–401. [Google Scholar] [CrossRef]
  61. López, E.F.; Gómez, E.F. Simultaneous determination of the major organic acids, sugars, glycerol, and ethanol by HPLC in grape musts and white wines. J. Chromatogr. Sci. 1996, 34, 254–257. [Google Scholar] [CrossRef] [Green Version]
  62. Cunha, S.C.; Ferreira, I.M.P.L.V.O.; Fernandes, J.O.; Faria, M.A.; Beatriz, M.; Oliveira, P.P.; Ferreira, M.A. Determination of lactic, acetic, succinic, and citric acids in table olives by HPLC/UV. J. Liq. Chrom. Relat. 2001, 24, 1029–1038. [Google Scholar] [CrossRef]
  63. Zhang, Y.; Zhao, Y.; Zhou, A.; Qu, Q.; Zhang, X.; Song, B.; Liu, K.; Xiong, R.; Huang, C. “Turn-on” ratiometric fluorescent probe: Naked-eye detection of acidic pH and citric acid (CA) by using fluorescence spectrum and its application in real food samples and zebrafish. Spectrochim. Acta A Mol. Biomol. Spectrosc. 2021, 261, 120014. [Google Scholar] [CrossRef] [PubMed]
  64. Terazawa, K.; Takatori, T. An enzymic colorimetry of citric acid with pyruvate oxidase. Jpn. J. Clin. Chem. 1984, 13, 53–57. [Google Scholar]
  65. Do Nascimento, R.F.; Selva, T.M.G.; Ribeiro, W.F.; Belian, M.F.; Angnes, L.; do Nascimento, V.B. Flow-injection electrochemical determination of citric acid using a cobalt(II)-phthalocyanine modified carbon paste electrode. Talanta 2013, 105, 354–359. [Google Scholar] [CrossRef] [PubMed]
  66. Awasthi, S.; Srivastava, A.; Singla, M.L. Voltammetric determination of citric acid and quinine hydrochloride using polypyrrole-pentacyanonitrosylferrate/platinum electrode. Synth. Met. 2011, 161, 1707–1712. [Google Scholar] [CrossRef]
  67. Selvam, S.P.; Chinnadayyala, S.R.; Cho, S.; Yun, K. Differential pulse voltametric electrochemical sensor for the detection of etidronic acid in pharmaceutical samples by using rGO-Ag@SiO2/Au PCB. J. Nanomater. 2020, 10, 1368. [Google Scholar] [CrossRef] [PubMed]
  68. Keerthi, M.; Boopathy, G.; Chen, S.M.; Chen, T.W.; Rwei, S.P.; Liu, X. An efficient electrochemical sensor based on Ag nanoparticle decorated MnO2/reduced graphene oxide ternary nanocomposite for detection of acetaminophen in human urine sample. Int. J. Electrochem. Sci. 2019, 14, 346–358. [Google Scholar] [CrossRef]
  69. Pecharsky, V.K.; Zavalij, P.Y. Fundamentals of Powder Diffraction and Structural Characterization of Materials, 1st ed.; Springer: New York, NY, USA, 2005; pp. 384–388. [Google Scholar]
  70. Jongprateep, O.; Palomas, J. Effects of Mg addition and sintering temperatures on chemical compositions, microstructures, densities and dielectric properties of strontium titanate. Ceram. Int. 2015, 41, S63–S68. [Google Scholar] [CrossRef]
Catalysts 12 00049 g001 550
Figure 1. XRD patterns of the BaTiO3 powder synthesized using the solution combustion method.
Figure 1. XRD patterns of the BaTiO3 powder synthesized using the solution combustion method.
Catalysts 12 00049 g001
Catalysts 12 00049 g002 550
Figure 2. Rietveld refinement analysis of the BaTiO3 powder.
Figure 2. Rietveld refinement analysis of the BaTiO3 powder.
Catalysts 12 00049 g002
Catalysts 12 00049 g003 550
Figure 3. (a) Quantitative analysis and (b) peak matching of the BaTiO3 powder using the X’Pert HighScore Plus program.
Figure 3. (a) Quantitative analysis and (b) peak matching of the BaTiO3 powder using the X’Pert HighScore Plus program.
Catalysts 12 00049 g003
Catalysts 12 00049 g004 550
Figure 4. Energy-dispersive X-ray spectroscopy (EDS) results of BaTiO3 (a) SEM image of mapping area, (b) EDS spectra, and elemental mapping of (c) barium (Ba), (d) titanium (Ti), and (e) oxygen (O).
Figure 4. Energy-dispersive X-ray spectroscopy (EDS) results of BaTiO3 (a) SEM image of mapping area, (b) EDS spectra, and elemental mapping of (c) barium (Ba), (d) titanium (Ti), and (e) oxygen (O).
Catalysts 12 00049 g004
Catalysts 12 00049 g005 550
Figure 5. SEM images of (a) barium titanate (BaTiO3), (b) BaTiO3/MWCNT composite (1:1), and (c) BaTiO3/MWCNT composite (2:1).
Figure 5. SEM images of (a) barium titanate (BaTiO3), (b) BaTiO3/MWCNT composite (1:1), and (c) BaTiO3/MWCNT composite (2:1).
Catalysts 12 00049 g005
Catalysts 12 00049 g006 550
Figure 6. Cyclic voltammogram of MWCNTs, BaTiO3, BaTiO3/MWCNT composite (1:1)-based electrode, and BaTiO3/MWCNT composite (2:1)-based electrode in 500 µM citric acid at a scan rate of 100.0 mV/s.
Figure 6. Cyclic voltammogram of MWCNTs, BaTiO3, BaTiO3/MWCNT composite (1:1)-based electrode, and BaTiO3/MWCNT composite (2:1)-based electrode in 500 µM citric acid at a scan rate of 100.0 mV/s.
Catalysts 12 00049 g006
Catalysts 12 00049 g007 550
Figure 7. (a) Cyclic voltammogram of the BaTiO3/MWCNT composite (2:1)-based electrode at scan rates of 25–100.0 mV/s, (b) relation between the peak current and scan rate of reduction reactions, and (c) relation between the peak current and square root of the scan rate of reduction reactions in 500 µM citric acid.
Figure 7. (a) Cyclic voltammogram of the BaTiO3/MWCNT composite (2:1)-based electrode at scan rates of 25–100.0 mV/s, (b) relation between the peak current and scan rate of reduction reactions, and (c) relation between the peak current and square root of the scan rate of reduction reactions in 500 µM citric acid.
Catalysts 12 00049 g007
Catalysts 12 00049 g008 550
Figure 8. Current density–analyte concentration calibration curves for the BaTiO3/MWCNT composite (2:1)-based electrode in (a) 100–1000 µM and (b) 1000–10,000 µM citric acid measured at a scan rate of 100 mV/s for the reduction reaction at −0.67 V.
Figure 8. Current density–analyte concentration calibration curves for the BaTiO3/MWCNT composite (2:1)-based electrode in (a) 100–1000 µM and (b) 1000–10,000 µM citric acid measured at a scan rate of 100 mV/s for the reduction reaction at −0.67 V.
Catalysts 12 00049 g008
Catalysts 12 00049 g009 550
Figure 9. Chronoamperogram of the BaTiO3/MWCNT composite (2:1)-based electrode in 500 µM glutamate (Glu), 500 µM citric acid (CA), 500 µM nitrite, 500 µM ascorbic acid (AA), and 500 µM nitrite at an applied voltage of −0.67 V.
Figure 9. Chronoamperogram of the BaTiO3/MWCNT composite (2:1)-based electrode in 500 µM glutamate (Glu), 500 µM citric acid (CA), 500 µM nitrite, 500 µM ascorbic acid (AA), and 500 µM nitrite at an applied voltage of −0.67 V.
Catalysts 12 00049 g009
Catalysts 12 00049 g010 550
Figure 10. Peak current as a function of the number of cycles for the BaTiO3/MWCNT composite (2:1)-based electrode in 500 µM citric acid at a scan rate 100 mV/s.
Figure 10. Peak current as a function of the number of cycles for the BaTiO3/MWCNT composite (2:1)-based electrode in 500 µM citric acid at a scan rate 100 mV/s.
Catalysts 12 00049 g010
Catalysts 12 00049 g011 550
Figure 11. Schematized procedures for synthesizing the (a) BaTiO3 powder using the solution combustion method and (b) BaTiO3/MWCNT composite-based electrode.
Figure 11. Schematized procedures for synthesizing the (a) BaTiO3 powder using the solution combustion method and (b) BaTiO3/MWCNT composite-based electrode.
Catalysts 12 00049 g011
Catalysts 12 00049 g012 550
Figure 12. Experimental setup for CV measurements.
Figure 12. Experimental setup for CV measurements.
Catalysts 12 00049 g012
Table
Table 1. Peak currents of MWCNTs, BaTiO3, BaTiO3/MWCNT composite (1:1)-based electrode, and BaTiO3/MWCNT composite (2:1)-based electrode in the presence of 500 µM citric acid.
Table 1. Peak currents of MWCNTs, BaTiO3, BaTiO3/MWCNT composite (1:1)-based electrode, and BaTiO3/MWCNT composite (2:1)-based electrode in the presence of 500 µM citric acid.
SamplePeak Current (mA)
−0.83 to −0.67 V0.43 to 0.47 V−0.70 to −0.65 V0.02 V
MWCNTs0.01110.0012-0.0003
BaTiO30.0057---
BaTiO3/MWCNTs (1:1)0.01540.00160.00130.0006
BaTiO3/MWCNTs (2:1)0.00980.00570.00220.0024
Table
Table 2. Sensitivity of the BaTiO3/MWCNT composite (2:1)-based electrode in 100–10,000 µM citric acid.
Table 2. Sensitivity of the BaTiO3/MWCNT composite (2:1)-based electrode in 100–10,000 µM citric acid.
ElectrodeConcentration (µM)Equation (J)Sensitivity (µA µM−1 mm−2)R2
BaTiO3/MWCNT composite (2:1)-based electrode100–1000J = 0.00059C + 0.969125.9 × 10−40.9809
1000–10,000J = 0.000068C + 1.469386.8 × 10−50.9869
Table
Table 3. Performance of various techniques in citric acid detection.
Table 3. Performance of various techniques in citric acid detection.
Detection TechniqueSensing MaterialLinear Range (mM)LOD (mM)Ref.
Capillary electrophoresis with direct UV-2.6–91.30.0104[60]
HPLC coupled with refractive index-0.2–3.10.172[61]
HPLC/UV-1–100.51[62]
Fluorescence spectroscopyFluorescent probe based on benzoindole derivatives0.014–0.0230.002967[63]
Enzymic colorimetryCitrate lyase, oxalacerate decarboxylase, pyruvate oxidase, 4-aminoantipyrine, and peroxidase5 × 10−5–2 × 10−41.3 × 10−5[64]
Electrochemical sensor with cyclic voltammetryCo(II)-phthalocyanine0.25–150.164[65]
Electrochemical sensor with cyclic voltammetryPolypyrrole-pentacyanonitrosylferrate/Pt1–90.117[66]
Electrochemical sensor with cyclic voltammetryBaTiO3/MWCNT composite (2:1)0.1–100.061This work
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Pitiphattharabun, S.; Sato, N.; Panomsuwan, G.; Jongprateep, O. Electrocatalytic Properties of a BaTiO3/MWCNT Composite for Citric Acid Detection. Catalysts 2022, 12, 49. https://doi.org/10.3390/catal12010049

AMA Style

Pitiphattharabun S, Sato N, Panomsuwan G, Jongprateep O. Electrocatalytic Properties of a BaTiO3/MWCNT Composite for Citric Acid Detection. Catalysts. 2022; 12(1):49. https://doi.org/10.3390/catal12010049

Chicago/Turabian Style

Pitiphattharabun, Siraprapa, Nicha Sato, Gasidit Panomsuwan, and Oratai Jongprateep. 2022. "Electrocatalytic Properties of a BaTiO3/MWCNT Composite for Citric Acid Detection" Catalysts 12, no. 1: 49. https://doi.org/10.3390/catal12010049

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop