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Rapid synthesis of UiO-66 by means of electrochemical cathode method with electrochemical detection of 2,4,6-TCP
Journal Pre-proofs Rapid Synthesis of UiO-66 by means of Electrochemical Cathode Method with Electrochemical Detection of 2,4,6-TCP Ting Zhang, Jin-Zhi Wei, Xiao-Jun Sun, Xue-Jing Zhao, Hong-liang Tang, Han Yan, Feng-Ming Zhang PII: DOI: Reference:
S1387-7003(19)31069-X https://doi.org/10.1016/j.inoche.2019.107671 INOCHE 107671
To appear in:
Inorganic Chemistry Communications
Received Date: Revised Date: Accepted Date:
22 October 2019 3 November 2019 5 November 2019
Please cite this article as: T. Zhang, J-Z. Wei, X-J. Sun, X-J. Zhao, H-l. Tang, H. Yan, F-M. Zhang, Rapid Synthesis of UiO-66 by means of Electrochemical Cathode Method with Electrochemical Detection of 2,4,6TCP, Inorganic Chemistry Communications (2019), doi: https://doi.org/10.1016/j.inoche.2019.107671
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Rapid Synthesis of UiO-66 by means of Electrochemical Cathode
Method
with
Electrochemical
Detection
of
2,4,6-TCP Ting Zhang, Jin-Zhi Wei*,[email protected], Xiao-Jun Sun, Xue-Jing Zhao, Hong-liang Tang, Han Yan and Feng-Ming Zhang*,[email protected] Key Laboratory of Green Chemical Engineering and Technology of College of Heilongjiang Province, College of Chemical and Environmental Engineering, Harbin University of Science and Technology, Harbin 150040, P. R. China. *Corresponding
authors.
Graphical abstract Highlights UiO-66 material was synthesized rapidly and in large quantities by electrochemical cathode synthesis at room temperature for the first time. The synthesized material was prepared into UiO-66-CPE for electrochemical detection of 2,4,6-TCP. UiO-66-CPE has good detection performance for 2,4,6-TCP, and the detection limit is as low as 6.49 × 10-9 M. UiO-66-CPE has good stability and can be used repeatedly.
Abstract Electrochemical cathode methods were used to rapidly synthesize metal-organic frameworks (MOFs) UiO-66 and applied to electrochemical detection of 2,4,6-trichlorophenol (2,4,6-TCP). The effects of reaction voltage, time and temperature on the rapid synthesis of UiO-66 by means of electrochemical cathode method were systematically studied. It was confirmed that the UiO-66 synthesized by this method had small particle size with the diameter of 60 nm. Moreover, the UiO-66’s performance in electrochemical detection of 2,4,6-TCP was studied. The effect of the content for UiO-66 in the electrode, the types of electrolyte solution, and
the pH value of the electrolyte solution on the electrochemical detection of 2,4,6-TCP were systematically investigated. The minimum detection limit of this experiment could reach 6.49 × 10-9 M (1.29 μg/L), which is significantly lower than the one specified by the national standard: 10 μg/L in drinking water. The limit of detection concentration is significantly lower than that of UiO-66-CPE prepared by conventional hydrothermal methods. Furthermore, in addition to 2,4-dichlorophenol (2,4-DCP) and phenol, some common cations and anions had only weak effect on the signals of 2,4,6-TCP with signal change less by 10%. This strategy provides specificity and sensitivity approach for the detection of 2,4,6-TCP and has promising applications in the water analysis field. Keywords: Electrochemical Cathode Method; UiO-66; Carbon paste electrode; Electrochemical Detection; 2,4,6-TCP
Introduction Metal-organic frameworks (MOFs) are one of the most popular materials studied by researchers in recent years. Due to their porous structure, large specific surface area and diverse structures [1-3], MOFs have been widely used in gas storage and separation [4,5], catalysis [6-8], electrochemical energy storage [9], adsorption [10], drug loading [11-13] and sensing [14-17]. So far, the synthesis methods of MOFs reported in the literature mainly focused on hydrothermal and solvothermal methods [18-20]. However, by using the above-mentioned methods, MOFs usually suffer defects such as high energy consumption, long time in synthesis and low yield [21], which limit their application in industry. Therefore, it is important to find a MOFs synthesis method which is rapid, high-yielded and with good reproducibility under mild conditions. The electrochemical synthesis method was first proposed in the field of MOFs synthesis by BASF in 2005. According to different synthesis mechanisms [22], the electrochemical synthesis methods have been divided into two types: anode synthesis and cathode synthesis. The reaction mechanism of the former is that the metal ions
generated by the anodic dissolutions self-assembled with the organic linkers in the solution to form a MOFs material [23]. Different from the above-mentioned method, the latter is performed to get the metal source by adding metal salts (nitrate, chlorate, etc.). Some oxoacidates (NO3-, ClO4-, etc.) [24] form an alkaline gradient near the cathode, promoting deprotonation of the organic linkers so that the organic linkers and metal ions self-assemble to generate MOFs on the surface of the cathode [25]. This method has many advantages, such as short time in synthesis, mild reaction conditions, flexible deposition substrate and easy film formation on the electrode surface. Therefore, it has been widely concerned by researchers in recent years [26]. 2,4,6-TCP is widely used as a fungicide, preservative and defoliant in the organic synthesis, paper making, printing and dyeing and dyeing industries [27-32]. It can do great harm to the health and may also result in the pollution of the water environment by being inhaled, ingestedor absorbed through skin [33]. Therefore, for the purpose of environmental protection and human health safety, it is very necessary to develop sensitive, rapid and simple analytical methods to identify and quantify 2,4,6-TCP in environmental
samples.
High-performance
liquid
chromatography
[34],
spectrophotometry [35] and gas chromatography mass spectrometry [36,37] were used as traditional methods to detect 2,4,6-TCP with limited utility due to their defects such as being time-consuming and inability to be monitored in real time. Compared with the conventional analytical method, electrochemical sensors have been widely used in clinical medicine, biochemistry and environmental monitoring thanks to their advantages such as high sensitivity, short time in response and easy operation [32,38]. Successful application of the electrochemical detection technology for 2,4,6-TCP has been reported on various modified electrodes [31,39,40]. Xu et al [41] studied microwave-assisted covalent modification of graphene nanosheets with hydroxypropyl-b-cyclodextrin and its electrochemical detection of 2,4,6-TCP etc organic pollutants. Zhu et al [42] synthesis of a bromocresol purple/graphene composite and its application in electrochemical determination of 2,4,6-TCP. Zheng et al [43] prepared a kind of HS-b-cyclodextrin/gold nanoparticles composites
modified indium tin oxide electrode for highly sensitive detection of 2,4,6-TCP. However, the above electrode materials are difficult to be used to detect actual water samples because of its stability and structural characteristics. The emergence of MOFs provides new ideas for the detection and treatment of environmental pollutants. UiO-66 is one of a series of materials with high stability in MOFs materials due to its good performance in hydrothermal stability and chemical stability [44-47]. However, it has not been reported that the electrochemical detection of 2,4,6-TCP by UiO-66. In this work, we used electrochemical cathode synthesis to rapidly synthesize UiO-66 materials. The synthesized materials were characterized by powder X-ray diffraction (PXRD), Fourier Transforms Infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and N2 adsorption-desorption isotherm. Constant voltage studies were carried out, and the reaction conditions were optimized to synthesize UiO-66, which had very tiny particle size of only 60 nm. The synthetic material was made into a UiO-66-carbon paste electrode (UiO-66-CPE) to study its performance in detecting of 2,4,6-TCP. The UiO-66-CPE was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). In addition, differential pulse voltammetry (DPV) was employed to determine the linear range and detection limit of 2,4,6-TCP. It was found that the synthesis of UiO-66 by means of electrochemical cathode method had an absolute advantage in the electrochemical detection of 2,4,6-TCP, with detection limit as low as at 6.49 × 10-9 M. The synthesized UiO-66-CPE showed good performance in stability and strong anti-interference ability, and could be repeatedly used.
Results and discussion Characterization of UiO-66 During the process of electrochemical cathode synthesis of UiO-66, several important conditions need to be taken into account, such as voltage, temperature and reaction time. Voltage being an important factor in electrochemical cathode synthesis
[48], so a series of different reaction voltages were first studied. The products of the electrolytic cell with different reaction voltage were analyzed by XRD and the results are shown in Fig. 1a. The reaction time was controlled to be 5 h, the temperature was 50 °C, and the molar ratio of ZrCl4 to H2BDC was 1:1. As the reaction voltage gradually increased, the peak position of the synthesized material matched well with that of the simulated UiO-66, indicating that the synthesized material was the expected UiO-66. When the voltage was 2 V, the synthesized material did not show a characteristic peak that coincided with the standard. When the reaction voltage became greater or equal to 6 V, the peak position of the synthetic material was completely identical to the one of the simulated UiO-66 and the degree of crystallites became high. We performed SEM measures on synthetic materials of different voltages, as shown in Fig. 1b. When the reaction voltage was 2 V, the synthetic material had no fixed morphology. As the reaction voltage gradually increased, the synthetic material deviated little by little from the block shape, and the crystal form became increasingly better and more even, presenting a spherical shape. The particle diameter grew more uniform with an average of around 60 nm. Therefore, 6 V reaction voltages were chosen for subsequent experiments. Compared with traditional hydrothermal synthesis method, one of the most outstanding advantages of the electrochemical method is shorter time in synthesis [49]. Thus, the effect of reaction time on the structure was studied. During the experiment, the reaction voltage was controlled to be 6 V and the reaction temperature was 50 °C. The experimental results of the influence of the reaction time on the synthesis of UiO-66 are shown in Fig. S1a. When the reaction time was 2.5 h, white precipitates began to form in the cathode. The longer reaction time, the more white precipitates would be produced in the cathode and solution. When the reaction time reached 5 h, the characteristic peak value of the synthetic material coincided with the standard one. In the next experiment, 5 h was chosen as the optimum reaction time. The morphology of the synthesized material at different time was studied (Fig. S1b). The crystallites of the synthetic material were getting better as the reaction time extended.
When the synthesis time was 4 h, the synthetic material appeared spherical and condensed at the same time. The synthetic materials showed uniformly dispersed small spherical shape with an average particle diameter of around 60 nm when the reaction time was extended to 5 h. Compared with other methods, one of the advantages of the electrochemical synthesis method was that the reaction conditions were mild and the reaction temperature was low [50]. Therefore, the influence of the reaction temperature on the electrochemical synthesis of UiO-66 was discussed in this experiment and the results are shown in Fig. 2a. The reaction voltage was controlled to be 6 V and the reaction time was 5 h. It can be clearly seen that the UiO-66 material can be synthesized when the reaction is carried out at room temperature, and the morphology of the product does not change significantly as the reaction temperature increases. The UiO-66 synthesized at different temperatures was also subject to SEM test and the results are shown in Fig. 2b. As the temperature rose, the morphology of UiO-66 did not change significantly, and crystals with good morphology could be synthesized at room temperature. The yield of UiO-66 synthesized by means of electrochemical cathode method at 5 hours was 73.27%, which was higher than that of 58% obtained by hydrothermal synthesis. In summary, thanks to its advantages such as short time in reaction, mild reaction conditions and high yields, electrochemical cathode synthesis is expected to achieve large-scale production. In order to further confirm the structure of the synthesized UiO-66, FT-IR tests were performed and the results are shown in Fig. 3a. The absorption peak appearing at 1655 cm-1 was caused by the stretching vibration of the carbon-oxygen double bond (C=O) in the carboxyl group, and the absorption peak caused by the asymmetric stretching vibration of COO- appeared at 1569 cm-1. The absorption peak addressed at 1388 cm-1 was assigned to symmetric stretching vibration of COO- from ligands. In addition, the characteristic peak of the carboxyl group is red shifted from 1685 cm-1 to 1655 cm-1, which may be due to the substitution of the zirconium oxygen cluster for H on the carboxyl group.
In summary, the optimized conditions for electrochemical cathode synthesis of UiO-66 with high crystallites are room temperature condition, 6 V as applied voltage, and 5 h as reaction time. The results confirm that electrochemically synthesized UiO-66 under the optimized condition possesses apparent merits such as high crystallites, uniform morphology and high porosity. UiO-66 synthesized under optimized conditions were chosen to make UiO-66-CPE for subsequent electrochemical detection of 2,4,6-TCP. The specific surface area is an important parameter in measuring the adsorption performance of the material. Therefore, the pore structure properties of UiO-66 at 77 K were determined by N2 adsorption-desorption isotherm measurement. As shown in Fig. 3b, the electrochemical synthesis sample of UiO-66 was a typical type Ⅱ adsorption isotherm [51]. Moreover, the quantitative calculation showed that the Brunauer–Emmett–Teller (BET) surface area of the UiO-66 was 1110.72 m2/g, much higher than that of UiO-66 resulting from hydrothermal synthesis, which offered a specific interface for the adsorption of 2,4,6-TCP. Optimization of sensor preparation and detection conditions Electrochemical CV response signals for UiO-66 contents (0, 5, 10, 15, 20, 25 and 30 wt%) in the carbon paste were tested and the experimental results are shown in Fig. 4a. The oxidation peak current value showed a tendency which rose first and then fell as the content of UiO-66 increased. It is apparent that the electron transfer rate of the electrode material changed after the addition of some UiO-66 and the mass ratio of UiO-66 in the carbon paste electrode was 15%, generating the maximum response current to 2,4,6-TCP. The reasons may be that UiO-66 had a large specific surface area and increased the adsorption amount of 2,4,6-TCP on the electrode. In addition, the conjugation effect of UiO-66 and 2,4,6-TCP also enhanced the electrochemical response of the modified electrode to 2,4,6-TCP. However, the poor conductivity of UiO-66 determined that excessive addition would reduce the conductivity of the modified electrode and affect the electrochemical detection performance of 2,4,6-TCP.
Meanwhile, the UiO-66-CPE was characterized by EIS using [Fe (CN) 6]3−/4− as the electrochemical redox probes. Generally, the semicircle part at higher frequencies corresponded to the electron transfer-limited process, and its diameter was equal to the electron transfer resistance (Rct), which controlled the electron transfer kinetics of the redox probe at the electrode interface. Fig. 4b shows the Nyquist diagrams of different electrodes in 5.0 mM [Fe (CN) 6]3−/4− solution containing 0.1 M KCl. In the high frequency region, a well-defined minimum semicircle was observed at UiO-66-CPE (15 wt%) with a Rct of 2437 Ω, which is lower than the other electrodes with different ratios of UiO-66 (Table S1). This might be attributed to the formation of the conjugated system between carboxyl group and benzene ring in UiO-66 structure, which enhanced electron transfer efficiency. This is consistent with the CV phenomenon, so UiO-66-CPE (15 wt%) was chosen for subsequent experiments. The electrolyte solution can eliminate the migration current generated by the migration movement of the ions to be measured in the solution under the electric field, reduce the electrical resistance of the solution, enhance the conductivity of the solution, and improve the accuracy of the measurement [52]. Therefore, the effects of different electrolyte solutions on the electrochemical detection of 2,4,6-TCP were investigated, including PBS, NaCl, K2SO4, KNO3 and Na2SO4. The above-mentioned electrolyte solution concentration was 0.1 mM, and the experimental results are shown in Fig. S2a. When the electrolyte solution was PBS, the oxidation peak current value of 2,4,6-TCP was significantly higher than that of other electrolyte solutions reaching as high as 127 uA. Therefore, PBS was chosen as an electrolyte solution for electrochemical detection for the subsequent experiment. The effect of scan rate on electrochemical detection of 2,4,6-TCP was also explored. Fig. S2b shows CV of 1 mM 2,4,6-TCP at UiO-66-CPE with different scan rates. It is obvious shown that the oxidation peak currents values rose with the increase of the scan rate (v). The relationship between I p,a and the v are shown in the inset. The oxidation peak current values (I p,a) increased linearly with the scan rate (v) within the range of 25 - 350 mV/s, and the linear relationship can be expressed as: I p,a
(uA) = 27.613 × v + 3.1966 (R2 = 0.9962). Meanwhile, with the increase of scanning rate, the oxidation peak potential (E p,a) is slightly shifted positive. It is indicated that the oxidation of 2,4,6-TCP on UiO-66-CPE was a typical adsorption control process of electrode [53]. The effect of pH values on the CV response of 2,4,6-TCP at the UiO-66-CPE was studied. CV of UiO-66-CPE in 0.1 M PBS with 1 mM 2,4,6-TCP were examined over a potential range from 0.2 to 1.2 V in different pH values range from 4.0 to 9.0 at the scan rate of 200 mV/s, the results are shown in Fig. 5a. As the pH value of the solution increased, the oxidation peak current value of 2,4,6-TCP showed a tendency which rose first and then fell. The maximum current of 2,4,6-TCP was achieved at pH value 7.0. A decrease in the oxidation peak current value was observed at pH value 9.0. This phenomenon could be attributed to the higher concentration of hydroxyl anion, which may replace 2,4,6-TCP molecule and go into the adsorption sites of the UiO-66-CPE surface. Meanwhile, the oxidation peak potential value (E
p,a)
of
2,4,6-TCP gradually shifted from 0.932 V to 0.609 V, as shown in Fig. 5b. With the pH value increased from 4 to 9, the oxidation peak potential value (E
p,a)
shifted
towards negative potential direction. Especially, a matched linear relationship was observed between the E
p,a
and pH (E
p,a
= 1.123 - 0.057 × pH, R2 = 0.9906). This
phenomenon could be explained by the fact that proton was present in the electron transfer process [54]. Considering the oxidation peak current value of the modified electrode for the determination of 2,4,6-TCP, the PBS at pH value 7.0 was chosen for the subsequent analytical experiments. In order to compare the electrochemical cathode synthesis method with the traditional hydrothermal, which one prepared UiO-66-CPE has better electrochemical detection effect on 2,4,6-TCP, CV of two electrodes was measured 2,4,6-TCP solution of different concentrations and the results are shown in Fig. 6a and b. Under the same concentration of 2,4,6-TCP conditions, the oxidation peak current value of the electrode prepared by the electrochemical cathode method is significantly higher than that of the UiO-66 electrode synthesized by hydrothermal method and the latter
can only measure 2,4,6-TCP with a concentration higher than 1 × 10-3 mM. The analysis may be due to the fact that the BET specific surface area of UiO-66 prepared by means of electrochemical cathode method was larger than that of UiO-66 synthesized by means of hydrothermal method, so that more 2,4,6-TCP were adsorbed on the surface. Thus, it can be concluded that UiO-66-CPE prepared by means of electrochemical cathode synthesis has an obvious superiority in the electrochemical detection of 2,4,6-TCP. The performance of UiO-66-CPE Compared with the conventional CV process, the DPV mode yields better signal-to-background characteristics. Besides, the peaks of DPV were sharper and clearly defined with a lower concentration of the analysis. Thus, the determination of 2,4,6-TCP was carried out by DPV obtained by scanning the potential in the range from 0.2 to 1.0 V. After the background current dropped to a steady value, the 2,4,6-TCP solution was added to the 0.1 M PBS (pH 7.0). As can be seen from Fig. 6c and d, the oxidation peak currents values increased linearly with 2,4,6-TCP concentrations in the range of 10-500 (1 × 10-3 uM). The linear regression equation can be expressed as I p, a (uA) = 22 × C (uM) + 3.793 (R2 = 0.9955). A detection limit (LOD) of 6.49 × 10-9 M was calculated according to (S/N = 3) criteria. The sensitivities of this electrochemical detection in the linear range were calculated to be 22 uA/uM. Reproducibility was determined by measuring 30 repeated experiments on a single electrode in 0.1 mM 2,4,6-TCP. The relative standard deviation of the 2,4,6-TCP peak current value was 10.2% and the result is shown in Fig. S3a. The stability of the UiO-66-CPE was determined by immersing it in PBS (0.1 M), and the results are shown in Fig. S3b. The framework of UiO-66 immersed in PBS buffer solution for 72 h did not collapse, and the crystal form of the material did not change, indicating that UiO-66-CPE had good stability. To study the specificity of the UiO-66-CPE for 2,4,6-TCP, various common
interfering substances including 2, 4-DCP, phenol, 4-nitrophenol (PNP), K+, Mg2+ and Cd2+ were detected in 0.1 M PBS containing 0.1 mM 2,4,6-TCP. As seen in the Table S2, except for 2, 4-DCP and phenol, the peak current value of 2,4,6-TCP was not affected by other substances, and the change of peak current value was less than 10%. Although 2,4,6-TCP, 2,4-DCP and phenol had response signal in the potential range of 0-1.2 V, 2,4,6-TCP was more susceptible to oxidation because its acidity was stronger than that of 2, 4-DCP and phenol. The result was shown in Figs S3c and Fig S3d. The response peak current value of 2,4,6-TCP was highest and these three substances could be better distinguished due to their response peak potentials were different. Thus, UiO-66-CPE prepared by means of electrochemical cathode method had better selectivity for 2,4,6-TCP and does not need to be deliberately separated before testing. Electrochemical behavior of UiO-66-CPE The UiO-66 was prepared as a UiO-66-CPE to investigate its response to 2,4,6-TCP. Fig. 7 is a CV of a pure graphite electrode and a UiO-66-CPE in a 1 mM 2,4,6-TCP PBS (pH 7.0). The UiO-66-CPE has a better electrochemical response to 2,4,6-TCP at an oxidation peak potential value of 0.7 V compared with a carbon paste electrode. Firstly, since the UiO-66-CPE made of UiO-66 has a higher specific surface area, 2,4,6-TCP is more easily enriched on the UiO-66-CPE. Secondly, the electron transfer efficiency is improved due to the formation of a conjugated system between the carboxyl and the benzene ring in the UiO-66 structure. Meanwhile, when 2,4,6-TCP enters the pore of UiO-66, its benzene ring structure easily forms a larger π-π conjugated system with the organic linkers of UiO-66. This conjugated system promotes the transfer of electrons between the organic linkers of UiO-66 and 2,4,6-TCP. Thirdly, the defects on the zirconium oxide cluster play a certain role in the reduction with 2,4,6-TCP. Real samples analysis The tap water and the river water were served as actual samples to assess the
practical application of UiO-66-CPE in the process of detecting 2,4,6-TCP. 2,4,6-TCP was not found in real water samples. The reason may be that the 2,4,6-TCP in the real water sample is lower than the detection limit of UiO-66-CPE. The standard addition method had been proved to be an effective and reliable method for the trace analysis. Considering that the concentration of the 2,4,6-TCP in the real water sample is low, a certain amount of 2,4,6-TCP is added to a certain volume of real water sample. Thereafter, the results of measuring the amount of 2,4,6-TCP by the DPV technique are shown in Table 1. The recovery rate is 98%-106%, indicating that UiO-66-CPE can accurately determine the trace amount of 2,4,6-TCP in the actual sample. 4. Conclusions In summary, the electrochemical cathode method was used to rapidly synthesize UiO-66 material at room temperature under the applied voltage of 6 V for 5 h. A UiO-66-CPE for electrochemical detection of 2,4,6-TCP was prepared. It is concluded that UiO-66-CPE (15 wt%) has the best detection effect on 2,4,6-TCP in PBS at pH value 7.0, and its oxidation peak current value is proportional to the scan rate. The UiO-66-CPE has a good detection effect on 2,4,6-TCP due to the strong adsorption capacity of UiO-66, excellent electron transfer efficiency and electro catalytic activity of the unsaturated metal coordination center. The electrode has the advantages of low detection limit, high sensitivity, good reproducibility, good stability and strong anti-interference ability for the detection of 2,4,6-TCP. The production process is simple and no complicated equipment will be required. It provides a new method for the electrochemical detection of small molecular organics in MOFs materials. Acknowledgments This work was financially supported by NSFC (No. 21676066), Joint Guidance Project of Provincial Natural Science Foundation（No. LH2019B026）and the special fund for scientific and technological innovation talents of Harbin Science and Technology Bureau (No. 2017RAQXJ057).
References [1] G.M. Espallargas, E. Coronado, Magnetic functionalities in MOFs: from the framework to the pore, Chem. Soc. Rev., 47 (2018) 533. [2] Y.W. Peng, M.T. Zhao, B. Chen, Z.C. Zhang, Y. Huang, F.N. Dai, Z.C. Lai, X.Y. Cui, C.L. Tan, H. Zhang, Hybridization of MOFs and COFs: A New Strategy for Construction of MOF@COF Core-Shell Hybrid Materials, Adv. Mater., 30 (2018) 1705454. [3] A. Burgun, C.J. Coghlan, D.M. Huang, W.Q. Chen, S. Horike, S. Kitagawa, J.F. Alvino, G.F. Metha, C.J. Sumby, C.J. Doonan, Mapping-Out Catalytic Processes in a Metal-Organic Framework with Single-Crystal X-ray Crystallography, Angew. Chem., Int. Ed., 56 (2017) 8412. [4] H. Li, K.C. Wang, Y.J. Sun, C.T. Lollar, J.L. Li, H.C. Zhou, Recent advances in gas storage and separation using metal-organic frameworks, Mater. Today, 21 (2018) 108. [5] D. Banerjee, C.M. Simon, S.K. Elsaidi, M. Haranczyk, P.K. Thallapally, Xenon Gas Separation and Storage Using Metal-Organic Frameworks, Thallapally, Chem, 4 (2018) 650. [6] L. Zhu, X.Q. Liu, H.L. Jiang, L.B. Sun, Metal-Organic Frameworks for Heterogeneous Basic Catalysis, Chem. Rev., 117 (2017) 8129. [7] F.M. Zhang, J.L. Sheng, Z.D. Yang, X.J. Sun, H.L. Tang, M. Lu, H. Dong, F.C. Shen, J. Liu, Y.Q. Lan, Rational Design of MOF/COF Hybrid Materials for Photocatalytic H-2 Evolution in the Presence of Sacrificial Electron Donors, Angew. Chem., Int. Ed., 57 (2018) 12106. [8] H. Xiao, W.Y. Zhang, Q.S. Yao, L.L. Huang, L.H. Chen, B. Boury, Z.W. Chen, Zn-free MOFs like MIL-53(Al) and MIL-125(Ti) for the preparation of defect-rich, ultrafine ZnO nanosheets with high photocatalytic performance, Appl. Catal., B, 244 (2019) 719. [9] L. Zhang, H.W. Liu, W. Shi, P. Cheng, Synthesis strategies and potential applications of metal-organic frameworks for electrode materials for rechargeable lithium ion batteries, Coord. Chem. Rev., 388 (2019) 293. [10] W.J. Mu, S.Z. Du, X.L. Li, Q.H. Yu, R. Hu, H.Y. Wei, Y.C. Yang, S.M. Peng, Efficient and irreversible capture of strontium ions from aqueous solution using metal-organic frameworks with ion trapping groups, Dalton Trans, 48 (2019) 3284. [11] P.P. Bag, D. Wang, Z. Chen, R. Cao, Outstanding drug loading capacity by water stable microporous MOF: a potential drug carrier, Chem. Commun., 52 (2016) 3669. [12] F.M. Zhang, H. Dong, X. Zhang, X.J. Sun, M. Liu, D.D. Yang, X. Liu, J.Z. Wei, Postsynthetic Modification of ZIF-90 for Potential Targeted Codelivery of Two Anticancer Drugs, Acs Appl. Mater.
Interfaces, 9 (2017) 27332. [13] Y. Xie, X.J. Liu, X.X. Ma, Y.F. Duan, Y.W. Yao, Q. Cai, Small Titanium-Based MOFs Prepared with the Introduction of Tetraethyl Orthosilicate and Their Potential for Use in Drug Delivery, Acs Appl. Mater. Interfaces, 10 (2018) 13325. [14] X.L. Zhang, G.L. Li, D. Wu, X.L. Li, N. Hu, J. Chen, G. Chen, Y.N. Wu, Recent progress in the design fabrication of metal-organic frameworks-based nanozymes and their applications to sensing and cancer therapy, Biosens.Bioelectron., 137 (2019) 178. [15] Y.Y. Lu, W.W. Zhan, Y. He, Y.T. Wang, X.J. Kong, Q. Kuang, Z.X. Xie, L.S. Zheng, MOF-Templated Synthesis of Porous Co3O4 Concave Nanocubes with High Specific Surface Area and Their Gas Sensing Properties, Acs Appl. Mater. Interfaces, 6 (2014) 4186. [16] K. Muller-Buschbaum, F. Beuerle, C. Feldmann, MOF based luminescence tuning and chemical/physical sensing, Microporous Mesoporous Mater., 216 (2015) 171. [17] H.Y. Li, Y.L. Wei, X.Y. Dong, S.Q. Zang, T.C.W. Mak, Novel Tb-MOF Embedded with Viologen Species for Multi-Photofunctionality: Photochromism, Photomodulated Fluorescence, and Luminescent pH Sensing, Chem Mater, 27 (2015) 1327. [18] Y.A. Li, S. Yang, Q.Y. Li, J.P. Ma, S.J. Zhang, Y.B. Dong, UiO-68-ol NMOF-Based Fluorescent Sensor for Selective Detection of HCIO and Its Application in Bioimaging, Inorg. Chem., 56 (2017) 13241. [19] Z.D. Lei, Y.C. Xue, W.Q. Chen, W.H. Qiu, Y. Zhang, S. Horike, L. Tang, MOFs-Based Heterogeneous Catalysts: New Opportunities for Energy-Related CO2 Conversion, Adv. Energy Mater., 8 (2018) 1801587. [20] V. Shrivastav, S. Sundriyal, P. Goel, H. Kaur, S.K. Tuteja, K. Vikrant, K.H. Kim, U.K. Tiwari, A. Deep, Metal-organic frameworks (MOFs) and their composites as electrodes for lithium battery applications: Novel means for alternative energy storage, Coordin. Chem. Rev., 393 (2019) 48. [21] J.Z. Wei, F.X. Gong, X.J. Sun, Y. Li, T. Zhang, X.J. Zhao, F.M. Zhang, Rapid and Low-Cost Electrochemical Synthesis of UiO-66-NH2 with Enhanced Fluorescence Detection Performance, Inorg. Chem., 58 (2019) 6742. [22] M.Y. Li, M. Dinca, On the Mechanism of MOF-5 Formation under Cathodic Bias, Chem. Mater., 27 (2015) 3203. [23] M.Y. Li, M. Dinca, Reductive Electrosynthesis of Crystalline Metal-Organic Frameworks (N), J. Am. Chem. Soc., 133 (2011) 12926. [24] N. Campagnol, E.R. Souza, D.E. De Vos, K. Binnemans, J. Fransaer, Luminescent
terbium-containing metal-organic framework films: new approaches for the electrochemical synthesis and application as detectors for explosives, Chem. Commun., 50 (2014) 12545. [25] N. Campagnol, T.R.C. Van Assche, M.Y. Li, L. Stappers, M. Dinca, J.F.M. Denayer, K. Binnemans, D.E. De Vos, J. Fransaer, On the electrochemical deposition of metal-organic frameworks, J. Mater. Chem. A, 4 (2016) 3914. [26] H.P. Liu, H.M. Wang, T.S. Chu, M.H. Yu, Y.Y. Yang, An electrodeposited lanthanide MOF thin film as a luminescent sensor for carbonate detection in aqueous solution, J. Mater. Chem. C, 2 (2014) 8683. [27] J.L. Fan, J. Zhang, C.L. Zhang, L.A. Ren, Q.Q. Shi, Adsorption of 2,4,6-trichlorophenol from aqueous solution onto activated carbon derived from loosestrife, Desalination, 267 (2011) 139. [28] S.K. Karn, M.S. Reddy, Degradation of 2,4,6-trichlorophenol by bacteria isolated from secondary sludge of a pulp and paper mill, J. Gen. Appl. Microbiol., 58 (2012) 413. [29] S. Abbasloo, Y. Xu, H.J. Chao, C2TCP: A Flexible Cellular TCP to Meet Stringent Delay Requirements, Ieee Journal on Selected Areas In Communications, 37 (2019) 918. [30] L. Sinusaite, A.M. Renner, M.B. Schuetz, A. Antuzevics, U. Rogulis, I. Grigoraviciute-Puroniene, S. Mathur, A. Zarkov, Effect of Mn doping on the low-temperature synthesis of tricalcium phosphate (TCP) polymorphs, J. Eur. Ceram. Soc., 39 (2019) 3257. [31] X.L. Zhu, K.X. Zhang, D.W. Wang, D.M. Zhang, X. Yuan, J. Qu, Electrochemical sensor based on hydroxylated carbon nanotubes/platinum nanoparticles/rhodamine B composite for simultaneous determination of 2, 4,6-trichlorophenol and 4-chlorophenol, J. Electroanal. Chem., 810 (2018) 199. [32] E. Elaiyappillai, S. Kogularasu, S.M. Chen, M. Akilarasan, C.E. Joshua, P.M. Johnson, M.A. Alin, F.M.A. Al-Hemaid, M.S. Elshikh, Sonochemically recovered silver oxide nanoparticles from the wastewater of photo film processing units as an electrode material for supercapacitor and sensing of 2, 4, 6-trichlorophenol in agricultural soil samples, Ultrason. Sonochem., 50 (2019) 255. [33] X.W. Jin, J.M. Zha, Y.P. Xu, J.P. Giesy, K.L. Richardson, Z.J. Wang, Derivation of predicted no effect concentrations (PNEC) for 2,4,6-trichlorophenol based on Chinese resident species, Chemosphere, 86 (2012) 17. [34] Q. Cheng, F. Qu, N.B. Li, H.Q. Luo, Mixed hemimicelles solid-phase extraction of chlorophenols in environmental water samples with 1-hexadecyl-3-methylimidazolium bromide-coated Fe3O4 magnetic nanoparticles with high-performance liquid chromatographic analysis, Anal. Chim. Acta, 715 (2012) 113. [35] H.H. Ji, F. Chang, X.F. Hu, W. Qin, J.W. Shen, Photocatalytic degradation of
2,4,6-trichlorophenol over g-C3N4 under visible light irradiation, Chem. Eng. J., 218 (2013) 183. [36] I. Limam, R.D. Limam, M. Mezni, A. Guenne, C. Madigou, M.R. Driss, T. Bouchez, L. Mazeas, Penta- and 2,4,6-tri-chlorophenol biodegradation during municipal solid waste anaerobic digestion, Ecotoxicol. Environ. Saf., 130 (2016) 270. [37] J. Regueiro, E. Becerril, C. Garcia-Jares, M. Llompart, Trace analysis of parabens, triclosan and related chlorophenols in water by headspace solid-phase microextraction with in situ derivatization and gas chromatography-tandem mass spectrometry, J. Chromatogr. A, 1216 (2009) 4693. [38] T. Zhang, L. Wang, C.W. Gao, C.Y. Zhao, Y. Wang, J.M. Wang, Hemin immobilized into metal-organic frameworks as an electrochemical biosensor for 2,4,6-trichlorophenol, Nanotechnology, 29 (2018) 074003. [39] R. Xu, J.Y. Cui, R.Z. Tang, F.T. Li, B.R. Zhang, Removal of 2,4,6-trichlorophenol by laccase immobilized on nano-copper incorporated electrospun fibrous membrane-high efficiency, stability and reusability, Chem. Eng. J., 326 (2017) 647. [40] X.L. Zhu, K.X. Zhang, N. Lu, X. Yuan, Simultaneous determination of 2,4,6-trichlorophenol and pentachlorophenol based on poly(Rhodamine B)/graphene oxide/multiwalled carbon nanotubes composite film modified electrode, Appl. Surf. Sci., 361 (2016) 72. [41] C.H. Xu, J.C. Wang, L. Wan, J.J. Lin, X.B. Wang, Microwave-assisted covalent modification of graphene nanosheets with hydroxypropyl-beta-cyclodextrin and its electrochemical detection of phenolic organic pollutants, J. Mater. Chem., 21 (2011) 10463. [42] X.L. Zhu, J.G. Liu, Z.S. Zhang, N. Lu, X. Yuan, D.M. Wu, Green synthesis of a bromocresol purple/graphene
composite
and
its
application
in
electrochemical
determination
of
2,4,6-trichlorophenol, Anal. Methods-Uk., 7 (2015) 3178. [43] X.L. Zheng, S. Liu, X.X. Hua, F.Q. Xia, D. Tian, C.L. Zhou, Highly sensitive detection of 2,4,6-trichlorophenol based on HS-beta-cyclodextrin/gold nanoparticles composites modified indium tin oxide electrode, Electrochim. Acta, 167 (2015) 372. [44] G.C. Shearer, S. Chavan, S. Bordiga, S. Svelle, U. Olsbye, K.P. Lillerud, Defect Engineering: Tuning the Porosity and Composition of the Metal-Organic Framework UiO-66 via Modulated Synthesis, Chem. Mater., 28 (2016) 3749. [45] C.A. Trickett, K.J. Gagnon, S. Lee, F. Gandara, H.B. Burgi, O.M. Yaghi, Definitive Molecular Level Characterization of Defects in UiO-66 Crystals, Angew. Chem., Int. Ed., 54 (2015) 11162. [46] M.R. DeStefano, T. Islamoglu, J.T. Hupp, O.K. Farha, Room-Temperature Synthesis of UiO-66 and Thermal Modulation of Densities of Defect Sites, Chem. Mater., 29 (2017) 1357.
[47] X.L. Liu, N.K. Demir, Z.T. Wu, K. Li, Highly Water-Stable Zirconium Metal Organic Framework UiO-66 Membranes Supported on Alumina Hollow Fibers for Desalination, J. Am. Chem. Soc, 137 (2015) 6999. [48] H. Al-Kutubi, J. Gascon, E.J.R. Sudholter, L. Rassaei, Electrosynthesis of Metal-Organic Frameworks: Challenges and Opportunities, Chemelectrochem, 2 (2015) 462. [49] N. Campagnol, T. Van Assche, T. Boudewijns, J. Denayer, K. Binnemans, D. De Vos, J. Fransaer, High pressure, high temperature electrochemical synthesis of metal-organic frameworks: films of MIL-100 (Fe) and HKUST-1 in different morphologies, J. Mater. Chem. A, 1 (2013) 5827. [50] J.Z. Wei, X.L. Wang, X.J. Sun, Y. Hou, X. Zhang, D.D. Yang, H. Dong, F.M. Zhang, Rapid and Large-Scale Synthesis of IRMOF-3 by Electrochemistry Method with Enhanced Fluorescence Detection Performance for TNP, Inorg. Chem., 57 (2018) 3818. [51] S.Y. Dong, G.C. Suo, N. Li, Z. Chen, L. Peng, Y.L. Fu, Q. Yang, T.L. Huang, A simple strategy to fabricate high sensitive 2,4-dichlorophenol electrochemical sensor based on metal organic framework Cu-3(BTC)(2), Sensor Actuat B-Chem, 222 (2016) 972. [52] Y.J. Yang, N. Ma, Z.Y. Bian, Cu-Au/rGO Nanoparticle Based Electrochemical Sensor for 4-Chlorophenol Detection, Int. J. Electrochem. Sci., 14 (2019) 4095. [53] S.Y. Dong, P.H. Zhang, H. Liu, N. Li, T.L. Huang, Direct electrochemistry and electrocatalysis of hemoglobin in composite film based on ionic liquid and NiO microspheres with different morphologies, Biosens. Bioelectron., 26 (2011) 4082. [54] Y.L. Sun, L.P. Wang, H.H. Liu, Myoglobin functioning as cytochrome P450 for biosensing of 2,4-dichlorophenol, Anal. Methods-Uk., 4 (2012) 3358.
Fig. 1 (a) XRD patterns of samples electrochemically synthesized at different voltage range in comparison with the simulated pattern of UiO-66, where a−d represent the voltages at 2, 4, 6 and 8 V, respectively. (b) SEM of samples electrochemically synthesized at different voltage range, where a-d represent the voltages at 2, 4, 6 and 8 V, respectively. Fig. 2 (a) XRD patterns of samples electrochemically synthesized at different reaction temperatures in comparison with the simulated pattern of UiO-66, where a−d represent the reaction temperatures at room temperature, 30, 40 and 50 °C, respectively. (b) SEM of samples electrochemically synthesized at different reaction temperatures, where a−d represent the reaction temperatures at room temperature, 30, 40 and 50 °C, respectively. Fig. 3 (a) FT-IR diagram of the synthetic material UiO-66 and H2BDC. (b) N2
adsorption-desorption isotherms for the UiO-66 synthesized by means of electrochemical method and hydrothermal method respectively. Fig. 4 (a) CV of UiO-66-CPE (0-30 wt%) in 0.1 M PBS (pH 7.0) containing 1.0 mM 2,4,6-TCP at 200 mV/s. (b) Nyquist diagrams of CPE and UiO-66-CPE(0-30 wt%) in 5.0 mM [Fe (CN) 6]3−/4− (1:1) solution containing 0.1 M KCl. The parameters are as follows: frequency range from 0.01 to 103 Hz; initiative potential, 0.2 V; amplitude 0.01 V and quiet time of 2 s. Fig. 5 (a) CV of 2,4,6-TCP under different pH values (b) Linear fit between pH value and spike. Fig. 6 (a) CV of UiO-66-CPE (15 wt%) synthesized by means of electrochemical cathode method in 0.1 M PBS (pH 7.0) containing 0-1.0 mM 2,4,6-TCP, 200 mV/s. (b) Hydrothermally synthesized UiO-66-CPE (15 wt%) in 0.1 M PBS (pH 7.0) containing 0-1.0 mM 2,4,6-TCP, 200 mV/s. (c) DPV curves for various concentrations of 2,4,6-TCP in the range of 10-500 (1 × 10-3 uM) in 0.1 M PBS (pH 7.0). (d) Standard curve of peak current value with 2,4,6-TCP concentration. Fig. 7 CV of UiO-66-CPE (a) (15 wt%), CPE (b) in 0.1 M PBS (pH 7.0) containing 1.0 mM 2,4,6-TCP at 200 mV/s. Scheme 1. UiO-66 was synthesized by means of electrochemical cathode method.
Table 1 Detection of 2,4,6-TCP by UiO-66-CPE in real samples
Samples
River water
Tap water
Add 2,4,6-TCP Found (µM) (µM)
2,4,6-TCP Recovery (%)
1
50
53
106%
2
100
103
103%
3
150
157
104.7%
1
50
49
98%
2
100
102
102%
3
150
143
95.3%
S1387-7003(19)31069-X https://doi.org/10.1016/j.inoche.2019.107671 INOCHE 107671
To appear in:
Inorganic Chemistry Communications
Received Date: Revised Date: Accepted Date:
22 October 2019 3 November 2019 5 November 2019
Please cite this article as: T. Zhang, J-Z. Wei, X-J. Sun, X-J. Zhao, H-l. Tang, H. Yan, F-M. Zhang, Rapid Synthesis of UiO-66 by means of Electrochemical Cathode Method with Electrochemical Detection of 2,4,6TCP, Inorganic Chemistry Communications (2019), doi: https://doi.org/10.1016/j.inoche.2019.107671
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Rapid Synthesis of UiO-66 by means of Electrochemical Cathode
Method
with
Electrochemical
Detection
of
2,4,6-TCP Ting Zhang, Jin-Zhi Wei*,[email protected], Xiao-Jun Sun, Xue-Jing Zhao, Hong-liang Tang, Han Yan and Feng-Ming Zhang*,[email protected] Key Laboratory of Green Chemical Engineering and Technology of College of Heilongjiang Province, College of Chemical and Environmental Engineering, Harbin University of Science and Technology, Harbin 150040, P. R. China. *Corresponding
authors.
Graphical abstract Highlights UiO-66 material was synthesized rapidly and in large quantities by electrochemical cathode synthesis at room temperature for the first time. The synthesized material was prepared into UiO-66-CPE for electrochemical detection of 2,4,6-TCP. UiO-66-CPE has good detection performance for 2,4,6-TCP, and the detection limit is as low as 6.49 × 10-9 M. UiO-66-CPE has good stability and can be used repeatedly.
Abstract Electrochemical cathode methods were used to rapidly synthesize metal-organic frameworks (MOFs) UiO-66 and applied to electrochemical detection of 2,4,6-trichlorophenol (2,4,6-TCP). The effects of reaction voltage, time and temperature on the rapid synthesis of UiO-66 by means of electrochemical cathode method were systematically studied. It was confirmed that the UiO-66 synthesized by this method had small particle size with the diameter of 60 nm. Moreover, the UiO-66’s performance in electrochemical detection of 2,4,6-TCP was studied. The effect of the content for UiO-66 in the electrode, the types of electrolyte solution, and
the pH value of the electrolyte solution on the electrochemical detection of 2,4,6-TCP were systematically investigated. The minimum detection limit of this experiment could reach 6.49 × 10-9 M (1.29 μg/L), which is significantly lower than the one specified by the national standard: 10 μg/L in drinking water. The limit of detection concentration is significantly lower than that of UiO-66-CPE prepared by conventional hydrothermal methods. Furthermore, in addition to 2,4-dichlorophenol (2,4-DCP) and phenol, some common cations and anions had only weak effect on the signals of 2,4,6-TCP with signal change less by 10%. This strategy provides specificity and sensitivity approach for the detection of 2,4,6-TCP and has promising applications in the water analysis field. Keywords: Electrochemical Cathode Method; UiO-66; Carbon paste electrode; Electrochemical Detection; 2,4,6-TCP
Introduction Metal-organic frameworks (MOFs) are one of the most popular materials studied by researchers in recent years. Due to their porous structure, large specific surface area and diverse structures [1-3], MOFs have been widely used in gas storage and separation [4,5], catalysis [6-8], electrochemical energy storage [9], adsorption [10], drug loading [11-13] and sensing [14-17]. So far, the synthesis methods of MOFs reported in the literature mainly focused on hydrothermal and solvothermal methods [18-20]. However, by using the above-mentioned methods, MOFs usually suffer defects such as high energy consumption, long time in synthesis and low yield [21], which limit their application in industry. Therefore, it is important to find a MOFs synthesis method which is rapid, high-yielded and with good reproducibility under mild conditions. The electrochemical synthesis method was first proposed in the field of MOFs synthesis by BASF in 2005. According to different synthesis mechanisms [22], the electrochemical synthesis methods have been divided into two types: anode synthesis and cathode synthesis. The reaction mechanism of the former is that the metal ions
generated by the anodic dissolutions self-assembled with the organic linkers in the solution to form a MOFs material [23]. Different from the above-mentioned method, the latter is performed to get the metal source by adding metal salts (nitrate, chlorate, etc.). Some oxoacidates (NO3-, ClO4-, etc.) [24] form an alkaline gradient near the cathode, promoting deprotonation of the organic linkers so that the organic linkers and metal ions self-assemble to generate MOFs on the surface of the cathode [25]. This method has many advantages, such as short time in synthesis, mild reaction conditions, flexible deposition substrate and easy film formation on the electrode surface. Therefore, it has been widely concerned by researchers in recent years [26]. 2,4,6-TCP is widely used as a fungicide, preservative and defoliant in the organic synthesis, paper making, printing and dyeing and dyeing industries [27-32]. It can do great harm to the health and may also result in the pollution of the water environment by being inhaled, ingestedor absorbed through skin [33]. Therefore, for the purpose of environmental protection and human health safety, it is very necessary to develop sensitive, rapid and simple analytical methods to identify and quantify 2,4,6-TCP in environmental
samples.
High-performance
liquid
chromatography
[34],
spectrophotometry [35] and gas chromatography mass spectrometry [36,37] were used as traditional methods to detect 2,4,6-TCP with limited utility due to their defects such as being time-consuming and inability to be monitored in real time. Compared with the conventional analytical method, electrochemical sensors have been widely used in clinical medicine, biochemistry and environmental monitoring thanks to their advantages such as high sensitivity, short time in response and easy operation [32,38]. Successful application of the electrochemical detection technology for 2,4,6-TCP has been reported on various modified electrodes [31,39,40]. Xu et al [41] studied microwave-assisted covalent modification of graphene nanosheets with hydroxypropyl-b-cyclodextrin and its electrochemical detection of 2,4,6-TCP etc organic pollutants. Zhu et al [42] synthesis of a bromocresol purple/graphene composite and its application in electrochemical determination of 2,4,6-TCP. Zheng et al [43] prepared a kind of HS-b-cyclodextrin/gold nanoparticles composites
modified indium tin oxide electrode for highly sensitive detection of 2,4,6-TCP. However, the above electrode materials are difficult to be used to detect actual water samples because of its stability and structural characteristics. The emergence of MOFs provides new ideas for the detection and treatment of environmental pollutants. UiO-66 is one of a series of materials with high stability in MOFs materials due to its good performance in hydrothermal stability and chemical stability [44-47]. However, it has not been reported that the electrochemical detection of 2,4,6-TCP by UiO-66. In this work, we used electrochemical cathode synthesis to rapidly synthesize UiO-66 materials. The synthesized materials were characterized by powder X-ray diffraction (PXRD), Fourier Transforms Infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and N2 adsorption-desorption isotherm. Constant voltage studies were carried out, and the reaction conditions were optimized to synthesize UiO-66, which had very tiny particle size of only 60 nm. The synthetic material was made into a UiO-66-carbon paste electrode (UiO-66-CPE) to study its performance in detecting of 2,4,6-TCP. The UiO-66-CPE was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). In addition, differential pulse voltammetry (DPV) was employed to determine the linear range and detection limit of 2,4,6-TCP. It was found that the synthesis of UiO-66 by means of electrochemical cathode method had an absolute advantage in the electrochemical detection of 2,4,6-TCP, with detection limit as low as at 6.49 × 10-9 M. The synthesized UiO-66-CPE showed good performance in stability and strong anti-interference ability, and could be repeatedly used.
Results and discussion Characterization of UiO-66 During the process of electrochemical cathode synthesis of UiO-66, several important conditions need to be taken into account, such as voltage, temperature and reaction time. Voltage being an important factor in electrochemical cathode synthesis
[48], so a series of different reaction voltages were first studied. The products of the electrolytic cell with different reaction voltage were analyzed by XRD and the results are shown in Fig. 1a. The reaction time was controlled to be 5 h, the temperature was 50 °C, and the molar ratio of ZrCl4 to H2BDC was 1:1. As the reaction voltage gradually increased, the peak position of the synthesized material matched well with that of the simulated UiO-66, indicating that the synthesized material was the expected UiO-66. When the voltage was 2 V, the synthesized material did not show a characteristic peak that coincided with the standard. When the reaction voltage became greater or equal to 6 V, the peak position of the synthetic material was completely identical to the one of the simulated UiO-66 and the degree of crystallites became high. We performed SEM measures on synthetic materials of different voltages, as shown in Fig. 1b. When the reaction voltage was 2 V, the synthetic material had no fixed morphology. As the reaction voltage gradually increased, the synthetic material deviated little by little from the block shape, and the crystal form became increasingly better and more even, presenting a spherical shape. The particle diameter grew more uniform with an average of around 60 nm. Therefore, 6 V reaction voltages were chosen for subsequent experiments. Compared with traditional hydrothermal synthesis method, one of the most outstanding advantages of the electrochemical method is shorter time in synthesis [49]. Thus, the effect of reaction time on the structure was studied. During the experiment, the reaction voltage was controlled to be 6 V and the reaction temperature was 50 °C. The experimental results of the influence of the reaction time on the synthesis of UiO-66 are shown in Fig. S1a. When the reaction time was 2.5 h, white precipitates began to form in the cathode. The longer reaction time, the more white precipitates would be produced in the cathode and solution. When the reaction time reached 5 h, the characteristic peak value of the synthetic material coincided with the standard one. In the next experiment, 5 h was chosen as the optimum reaction time. The morphology of the synthesized material at different time was studied (Fig. S1b). The crystallites of the synthetic material were getting better as the reaction time extended.
When the synthesis time was 4 h, the synthetic material appeared spherical and condensed at the same time. The synthetic materials showed uniformly dispersed small spherical shape with an average particle diameter of around 60 nm when the reaction time was extended to 5 h. Compared with other methods, one of the advantages of the electrochemical synthesis method was that the reaction conditions were mild and the reaction temperature was low [50]. Therefore, the influence of the reaction temperature on the electrochemical synthesis of UiO-66 was discussed in this experiment and the results are shown in Fig. 2a. The reaction voltage was controlled to be 6 V and the reaction time was 5 h. It can be clearly seen that the UiO-66 material can be synthesized when the reaction is carried out at room temperature, and the morphology of the product does not change significantly as the reaction temperature increases. The UiO-66 synthesized at different temperatures was also subject to SEM test and the results are shown in Fig. 2b. As the temperature rose, the morphology of UiO-66 did not change significantly, and crystals with good morphology could be synthesized at room temperature. The yield of UiO-66 synthesized by means of electrochemical cathode method at 5 hours was 73.27%, which was higher than that of 58% obtained by hydrothermal synthesis. In summary, thanks to its advantages such as short time in reaction, mild reaction conditions and high yields, electrochemical cathode synthesis is expected to achieve large-scale production. In order to further confirm the structure of the synthesized UiO-66, FT-IR tests were performed and the results are shown in Fig. 3a. The absorption peak appearing at 1655 cm-1 was caused by the stretching vibration of the carbon-oxygen double bond (C=O) in the carboxyl group, and the absorption peak caused by the asymmetric stretching vibration of COO- appeared at 1569 cm-1. The absorption peak addressed at 1388 cm-1 was assigned to symmetric stretching vibration of COO- from ligands. In addition, the characteristic peak of the carboxyl group is red shifted from 1685 cm-1 to 1655 cm-1, which may be due to the substitution of the zirconium oxygen cluster for H on the carboxyl group.
In summary, the optimized conditions for electrochemical cathode synthesis of UiO-66 with high crystallites are room temperature condition, 6 V as applied voltage, and 5 h as reaction time. The results confirm that electrochemically synthesized UiO-66 under the optimized condition possesses apparent merits such as high crystallites, uniform morphology and high porosity. UiO-66 synthesized under optimized conditions were chosen to make UiO-66-CPE for subsequent electrochemical detection of 2,4,6-TCP. The specific surface area is an important parameter in measuring the adsorption performance of the material. Therefore, the pore structure properties of UiO-66 at 77 K were determined by N2 adsorption-desorption isotherm measurement. As shown in Fig. 3b, the electrochemical synthesis sample of UiO-66 was a typical type Ⅱ adsorption isotherm [51]. Moreover, the quantitative calculation showed that the Brunauer–Emmett–Teller (BET) surface area of the UiO-66 was 1110.72 m2/g, much higher than that of UiO-66 resulting from hydrothermal synthesis, which offered a specific interface for the adsorption of 2,4,6-TCP. Optimization of sensor preparation and detection conditions Electrochemical CV response signals for UiO-66 contents (0, 5, 10, 15, 20, 25 and 30 wt%) in the carbon paste were tested and the experimental results are shown in Fig. 4a. The oxidation peak current value showed a tendency which rose first and then fell as the content of UiO-66 increased. It is apparent that the electron transfer rate of the electrode material changed after the addition of some UiO-66 and the mass ratio of UiO-66 in the carbon paste electrode was 15%, generating the maximum response current to 2,4,6-TCP. The reasons may be that UiO-66 had a large specific surface area and increased the adsorption amount of 2,4,6-TCP on the electrode. In addition, the conjugation effect of UiO-66 and 2,4,6-TCP also enhanced the electrochemical response of the modified electrode to 2,4,6-TCP. However, the poor conductivity of UiO-66 determined that excessive addition would reduce the conductivity of the modified electrode and affect the electrochemical detection performance of 2,4,6-TCP.
Meanwhile, the UiO-66-CPE was characterized by EIS using [Fe (CN) 6]3−/4− as the electrochemical redox probes. Generally, the semicircle part at higher frequencies corresponded to the electron transfer-limited process, and its diameter was equal to the electron transfer resistance (Rct), which controlled the electron transfer kinetics of the redox probe at the electrode interface. Fig. 4b shows the Nyquist diagrams of different electrodes in 5.0 mM [Fe (CN) 6]3−/4− solution containing 0.1 M KCl. In the high frequency region, a well-defined minimum semicircle was observed at UiO-66-CPE (15 wt%) with a Rct of 2437 Ω, which is lower than the other electrodes with different ratios of UiO-66 (Table S1). This might be attributed to the formation of the conjugated system between carboxyl group and benzene ring in UiO-66 structure, which enhanced electron transfer efficiency. This is consistent with the CV phenomenon, so UiO-66-CPE (15 wt%) was chosen for subsequent experiments. The electrolyte solution can eliminate the migration current generated by the migration movement of the ions to be measured in the solution under the electric field, reduce the electrical resistance of the solution, enhance the conductivity of the solution, and improve the accuracy of the measurement [52]. Therefore, the effects of different electrolyte solutions on the electrochemical detection of 2,4,6-TCP were investigated, including PBS, NaCl, K2SO4, KNO3 and Na2SO4. The above-mentioned electrolyte solution concentration was 0.1 mM, and the experimental results are shown in Fig. S2a. When the electrolyte solution was PBS, the oxidation peak current value of 2,4,6-TCP was significantly higher than that of other electrolyte solutions reaching as high as 127 uA. Therefore, PBS was chosen as an electrolyte solution for electrochemical detection for the subsequent experiment. The effect of scan rate on electrochemical detection of 2,4,6-TCP was also explored. Fig. S2b shows CV of 1 mM 2,4,6-TCP at UiO-66-CPE with different scan rates. It is obvious shown that the oxidation peak currents values rose with the increase of the scan rate (v). The relationship between I p,a and the v are shown in the inset. The oxidation peak current values (I p,a) increased linearly with the scan rate (v) within the range of 25 - 350 mV/s, and the linear relationship can be expressed as: I p,a
(uA) = 27.613 × v + 3.1966 (R2 = 0.9962). Meanwhile, with the increase of scanning rate, the oxidation peak potential (E p,a) is slightly shifted positive. It is indicated that the oxidation of 2,4,6-TCP on UiO-66-CPE was a typical adsorption control process of electrode [53]. The effect of pH values on the CV response of 2,4,6-TCP at the UiO-66-CPE was studied. CV of UiO-66-CPE in 0.1 M PBS with 1 mM 2,4,6-TCP were examined over a potential range from 0.2 to 1.2 V in different pH values range from 4.0 to 9.0 at the scan rate of 200 mV/s, the results are shown in Fig. 5a. As the pH value of the solution increased, the oxidation peak current value of 2,4,6-TCP showed a tendency which rose first and then fell. The maximum current of 2,4,6-TCP was achieved at pH value 7.0. A decrease in the oxidation peak current value was observed at pH value 9.0. This phenomenon could be attributed to the higher concentration of hydroxyl anion, which may replace 2,4,6-TCP molecule and go into the adsorption sites of the UiO-66-CPE surface. Meanwhile, the oxidation peak potential value (E
p,a)
of
2,4,6-TCP gradually shifted from 0.932 V to 0.609 V, as shown in Fig. 5b. With the pH value increased from 4 to 9, the oxidation peak potential value (E
p,a)
shifted
towards negative potential direction. Especially, a matched linear relationship was observed between the E
p,a
and pH (E
p,a
= 1.123 - 0.057 × pH, R2 = 0.9906). This
phenomenon could be explained by the fact that proton was present in the electron transfer process [54]. Considering the oxidation peak current value of the modified electrode for the determination of 2,4,6-TCP, the PBS at pH value 7.0 was chosen for the subsequent analytical experiments. In order to compare the electrochemical cathode synthesis method with the traditional hydrothermal, which one prepared UiO-66-CPE has better electrochemical detection effect on 2,4,6-TCP, CV of two electrodes was measured 2,4,6-TCP solution of different concentrations and the results are shown in Fig. 6a and b. Under the same concentration of 2,4,6-TCP conditions, the oxidation peak current value of the electrode prepared by the electrochemical cathode method is significantly higher than that of the UiO-66 electrode synthesized by hydrothermal method and the latter
can only measure 2,4,6-TCP with a concentration higher than 1 × 10-3 mM. The analysis may be due to the fact that the BET specific surface area of UiO-66 prepared by means of electrochemical cathode method was larger than that of UiO-66 synthesized by means of hydrothermal method, so that more 2,4,6-TCP were adsorbed on the surface. Thus, it can be concluded that UiO-66-CPE prepared by means of electrochemical cathode synthesis has an obvious superiority in the electrochemical detection of 2,4,6-TCP. The performance of UiO-66-CPE Compared with the conventional CV process, the DPV mode yields better signal-to-background characteristics. Besides, the peaks of DPV were sharper and clearly defined with a lower concentration of the analysis. Thus, the determination of 2,4,6-TCP was carried out by DPV obtained by scanning the potential in the range from 0.2 to 1.0 V. After the background current dropped to a steady value, the 2,4,6-TCP solution was added to the 0.1 M PBS (pH 7.0). As can be seen from Fig. 6c and d, the oxidation peak currents values increased linearly with 2,4,6-TCP concentrations in the range of 10-500 (1 × 10-3 uM). The linear regression equation can be expressed as I p, a (uA) = 22 × C (uM) + 3.793 (R2 = 0.9955). A detection limit (LOD) of 6.49 × 10-9 M was calculated according to (S/N = 3) criteria. The sensitivities of this electrochemical detection in the linear range were calculated to be 22 uA/uM. Reproducibility was determined by measuring 30 repeated experiments on a single electrode in 0.1 mM 2,4,6-TCP. The relative standard deviation of the 2,4,6-TCP peak current value was 10.2% and the result is shown in Fig. S3a. The stability of the UiO-66-CPE was determined by immersing it in PBS (0.1 M), and the results are shown in Fig. S3b. The framework of UiO-66 immersed in PBS buffer solution for 72 h did not collapse, and the crystal form of the material did not change, indicating that UiO-66-CPE had good stability. To study the specificity of the UiO-66-CPE for 2,4,6-TCP, various common
interfering substances including 2, 4-DCP, phenol, 4-nitrophenol (PNP), K+, Mg2+ and Cd2+ were detected in 0.1 M PBS containing 0.1 mM 2,4,6-TCP. As seen in the Table S2, except for 2, 4-DCP and phenol, the peak current value of 2,4,6-TCP was not affected by other substances, and the change of peak current value was less than 10%. Although 2,4,6-TCP, 2,4-DCP and phenol had response signal in the potential range of 0-1.2 V, 2,4,6-TCP was more susceptible to oxidation because its acidity was stronger than that of 2, 4-DCP and phenol. The result was shown in Figs S3c and Fig S3d. The response peak current value of 2,4,6-TCP was highest and these three substances could be better distinguished due to their response peak potentials were different. Thus, UiO-66-CPE prepared by means of electrochemical cathode method had better selectivity for 2,4,6-TCP and does not need to be deliberately separated before testing. Electrochemical behavior of UiO-66-CPE The UiO-66 was prepared as a UiO-66-CPE to investigate its response to 2,4,6-TCP. Fig. 7 is a CV of a pure graphite electrode and a UiO-66-CPE in a 1 mM 2,4,6-TCP PBS (pH 7.0). The UiO-66-CPE has a better electrochemical response to 2,4,6-TCP at an oxidation peak potential value of 0.7 V compared with a carbon paste electrode. Firstly, since the UiO-66-CPE made of UiO-66 has a higher specific surface area, 2,4,6-TCP is more easily enriched on the UiO-66-CPE. Secondly, the electron transfer efficiency is improved due to the formation of a conjugated system between the carboxyl and the benzene ring in the UiO-66 structure. Meanwhile, when 2,4,6-TCP enters the pore of UiO-66, its benzene ring structure easily forms a larger π-π conjugated system with the organic linkers of UiO-66. This conjugated system promotes the transfer of electrons between the organic linkers of UiO-66 and 2,4,6-TCP. Thirdly, the defects on the zirconium oxide cluster play a certain role in the reduction with 2,4,6-TCP. Real samples analysis The tap water and the river water were served as actual samples to assess the
practical application of UiO-66-CPE in the process of detecting 2,4,6-TCP. 2,4,6-TCP was not found in real water samples. The reason may be that the 2,4,6-TCP in the real water sample is lower than the detection limit of UiO-66-CPE. The standard addition method had been proved to be an effective and reliable method for the trace analysis. Considering that the concentration of the 2,4,6-TCP in the real water sample is low, a certain amount of 2,4,6-TCP is added to a certain volume of real water sample. Thereafter, the results of measuring the amount of 2,4,6-TCP by the DPV technique are shown in Table 1. The recovery rate is 98%-106%, indicating that UiO-66-CPE can accurately determine the trace amount of 2,4,6-TCP in the actual sample. 4. Conclusions In summary, the electrochemical cathode method was used to rapidly synthesize UiO-66 material at room temperature under the applied voltage of 6 V for 5 h. A UiO-66-CPE for electrochemical detection of 2,4,6-TCP was prepared. It is concluded that UiO-66-CPE (15 wt%) has the best detection effect on 2,4,6-TCP in PBS at pH value 7.0, and its oxidation peak current value is proportional to the scan rate. The UiO-66-CPE has a good detection effect on 2,4,6-TCP due to the strong adsorption capacity of UiO-66, excellent electron transfer efficiency and electro catalytic activity of the unsaturated metal coordination center. The electrode has the advantages of low detection limit, high sensitivity, good reproducibility, good stability and strong anti-interference ability for the detection of 2,4,6-TCP. The production process is simple and no complicated equipment will be required. It provides a new method for the electrochemical detection of small molecular organics in MOFs materials. Acknowledgments This work was financially supported by NSFC (No. 21676066), Joint Guidance Project of Provincial Natural Science Foundation（No. LH2019B026）and the special fund for scientific and technological innovation talents of Harbin Science and Technology Bureau (No. 2017RAQXJ057).
References [1] G.M. Espallargas, E. Coronado, Magnetic functionalities in MOFs: from the framework to the pore, Chem. Soc. Rev., 47 (2018) 533. [2] Y.W. Peng, M.T. Zhao, B. Chen, Z.C. Zhang, Y. Huang, F.N. Dai, Z.C. Lai, X.Y. Cui, C.L. Tan, H. Zhang, Hybridization of MOFs and COFs: A New Strategy for Construction of MOF@COF Core-Shell Hybrid Materials, Adv. Mater., 30 (2018) 1705454. [3] A. Burgun, C.J. Coghlan, D.M. Huang, W.Q. Chen, S. Horike, S. Kitagawa, J.F. Alvino, G.F. Metha, C.J. Sumby, C.J. Doonan, Mapping-Out Catalytic Processes in a Metal-Organic Framework with Single-Crystal X-ray Crystallography, Angew. Chem., Int. Ed., 56 (2017) 8412. [4] H. Li, K.C. Wang, Y.J. Sun, C.T. Lollar, J.L. Li, H.C. Zhou, Recent advances in gas storage and separation using metal-organic frameworks, Mater. Today, 21 (2018) 108. [5] D. Banerjee, C.M. Simon, S.K. Elsaidi, M. Haranczyk, P.K. Thallapally, Xenon Gas Separation and Storage Using Metal-Organic Frameworks, Thallapally, Chem, 4 (2018) 650. [6] L. Zhu, X.Q. Liu, H.L. Jiang, L.B. Sun, Metal-Organic Frameworks for Heterogeneous Basic Catalysis, Chem. Rev., 117 (2017) 8129. [7] F.M. Zhang, J.L. Sheng, Z.D. Yang, X.J. Sun, H.L. Tang, M. Lu, H. Dong, F.C. Shen, J. Liu, Y.Q. Lan, Rational Design of MOF/COF Hybrid Materials for Photocatalytic H-2 Evolution in the Presence of Sacrificial Electron Donors, Angew. Chem., Int. Ed., 57 (2018) 12106. [8] H. Xiao, W.Y. Zhang, Q.S. Yao, L.L. Huang, L.H. Chen, B. Boury, Z.W. Chen, Zn-free MOFs like MIL-53(Al) and MIL-125(Ti) for the preparation of defect-rich, ultrafine ZnO nanosheets with high photocatalytic performance, Appl. Catal., B, 244 (2019) 719. [9] L. Zhang, H.W. Liu, W. Shi, P. Cheng, Synthesis strategies and potential applications of metal-organic frameworks for electrode materials for rechargeable lithium ion batteries, Coord. Chem. Rev., 388 (2019) 293. [10] W.J. Mu, S.Z. Du, X.L. Li, Q.H. Yu, R. Hu, H.Y. Wei, Y.C. Yang, S.M. Peng, Efficient and irreversible capture of strontium ions from aqueous solution using metal-organic frameworks with ion trapping groups, Dalton Trans, 48 (2019) 3284. [11] P.P. Bag, D. Wang, Z. Chen, R. Cao, Outstanding drug loading capacity by water stable microporous MOF: a potential drug carrier, Chem. Commun., 52 (2016) 3669. [12] F.M. Zhang, H. Dong, X. Zhang, X.J. Sun, M. Liu, D.D. Yang, X. Liu, J.Z. Wei, Postsynthetic Modification of ZIF-90 for Potential Targeted Codelivery of Two Anticancer Drugs, Acs Appl. Mater.
Interfaces, 9 (2017) 27332. [13] Y. Xie, X.J. Liu, X.X. Ma, Y.F. Duan, Y.W. Yao, Q. Cai, Small Titanium-Based MOFs Prepared with the Introduction of Tetraethyl Orthosilicate and Their Potential for Use in Drug Delivery, Acs Appl. Mater. Interfaces, 10 (2018) 13325. [14] X.L. Zhang, G.L. Li, D. Wu, X.L. Li, N. Hu, J. Chen, G. Chen, Y.N. Wu, Recent progress in the design fabrication of metal-organic frameworks-based nanozymes and their applications to sensing and cancer therapy, Biosens.Bioelectron., 137 (2019) 178. [15] Y.Y. Lu, W.W. Zhan, Y. He, Y.T. Wang, X.J. Kong, Q. Kuang, Z.X. Xie, L.S. Zheng, MOF-Templated Synthesis of Porous Co3O4 Concave Nanocubes with High Specific Surface Area and Their Gas Sensing Properties, Acs Appl. Mater. Interfaces, 6 (2014) 4186. [16] K. Muller-Buschbaum, F. Beuerle, C. Feldmann, MOF based luminescence tuning and chemical/physical sensing, Microporous Mesoporous Mater., 216 (2015) 171. [17] H.Y. Li, Y.L. Wei, X.Y. Dong, S.Q. Zang, T.C.W. Mak, Novel Tb-MOF Embedded with Viologen Species for Multi-Photofunctionality: Photochromism, Photomodulated Fluorescence, and Luminescent pH Sensing, Chem Mater, 27 (2015) 1327. [18] Y.A. Li, S. Yang, Q.Y. Li, J.P. Ma, S.J. Zhang, Y.B. Dong, UiO-68-ol NMOF-Based Fluorescent Sensor for Selective Detection of HCIO and Its Application in Bioimaging, Inorg. Chem., 56 (2017) 13241. [19] Z.D. Lei, Y.C. Xue, W.Q. Chen, W.H. Qiu, Y. Zhang, S. Horike, L. Tang, MOFs-Based Heterogeneous Catalysts: New Opportunities for Energy-Related CO2 Conversion, Adv. Energy Mater., 8 (2018) 1801587. [20] V. Shrivastav, S. Sundriyal, P. Goel, H. Kaur, S.K. Tuteja, K. Vikrant, K.H. Kim, U.K. Tiwari, A. Deep, Metal-organic frameworks (MOFs) and their composites as electrodes for lithium battery applications: Novel means for alternative energy storage, Coordin. Chem. Rev., 393 (2019) 48. [21] J.Z. Wei, F.X. Gong, X.J. Sun, Y. Li, T. Zhang, X.J. Zhao, F.M. Zhang, Rapid and Low-Cost Electrochemical Synthesis of UiO-66-NH2 with Enhanced Fluorescence Detection Performance, Inorg. Chem., 58 (2019) 6742. [22] M.Y. Li, M. Dinca, On the Mechanism of MOF-5 Formation under Cathodic Bias, Chem. Mater., 27 (2015) 3203. [23] M.Y. Li, M. Dinca, Reductive Electrosynthesis of Crystalline Metal-Organic Frameworks (N), J. Am. Chem. Soc., 133 (2011) 12926. [24] N. Campagnol, E.R. Souza, D.E. De Vos, K. Binnemans, J. Fransaer, Luminescent
terbium-containing metal-organic framework films: new approaches for the electrochemical synthesis and application as detectors for explosives, Chem. Commun., 50 (2014) 12545. [25] N. Campagnol, T.R.C. Van Assche, M.Y. Li, L. Stappers, M. Dinca, J.F.M. Denayer, K. Binnemans, D.E. De Vos, J. Fransaer, On the electrochemical deposition of metal-organic frameworks, J. Mater. Chem. A, 4 (2016) 3914. [26] H.P. Liu, H.M. Wang, T.S. Chu, M.H. Yu, Y.Y. Yang, An electrodeposited lanthanide MOF thin film as a luminescent sensor for carbonate detection in aqueous solution, J. Mater. Chem. C, 2 (2014) 8683. [27] J.L. Fan, J. Zhang, C.L. Zhang, L.A. Ren, Q.Q. Shi, Adsorption of 2,4,6-trichlorophenol from aqueous solution onto activated carbon derived from loosestrife, Desalination, 267 (2011) 139. [28] S.K. Karn, M.S. Reddy, Degradation of 2,4,6-trichlorophenol by bacteria isolated from secondary sludge of a pulp and paper mill, J. Gen. Appl. Microbiol., 58 (2012) 413. [29] S. Abbasloo, Y. Xu, H.J. Chao, C2TCP: A Flexible Cellular TCP to Meet Stringent Delay Requirements, Ieee Journal on Selected Areas In Communications, 37 (2019) 918. [30] L. Sinusaite, A.M. Renner, M.B. Schuetz, A. Antuzevics, U. Rogulis, I. Grigoraviciute-Puroniene, S. Mathur, A. Zarkov, Effect of Mn doping on the low-temperature synthesis of tricalcium phosphate (TCP) polymorphs, J. Eur. Ceram. Soc., 39 (2019) 3257. [31] X.L. Zhu, K.X. Zhang, D.W. Wang, D.M. Zhang, X. Yuan, J. Qu, Electrochemical sensor based on hydroxylated carbon nanotubes/platinum nanoparticles/rhodamine B composite for simultaneous determination of 2, 4,6-trichlorophenol and 4-chlorophenol, J. Electroanal. Chem., 810 (2018) 199. [32] E. Elaiyappillai, S. Kogularasu, S.M. Chen, M. Akilarasan, C.E. Joshua, P.M. Johnson, M.A. Alin, F.M.A. Al-Hemaid, M.S. Elshikh, Sonochemically recovered silver oxide nanoparticles from the wastewater of photo film processing units as an electrode material for supercapacitor and sensing of 2, 4, 6-trichlorophenol in agricultural soil samples, Ultrason. Sonochem., 50 (2019) 255. [33] X.W. Jin, J.M. Zha, Y.P. Xu, J.P. Giesy, K.L. Richardson, Z.J. Wang, Derivation of predicted no effect concentrations (PNEC) for 2,4,6-trichlorophenol based on Chinese resident species, Chemosphere, 86 (2012) 17. [34] Q. Cheng, F. Qu, N.B. Li, H.Q. Luo, Mixed hemimicelles solid-phase extraction of chlorophenols in environmental water samples with 1-hexadecyl-3-methylimidazolium bromide-coated Fe3O4 magnetic nanoparticles with high-performance liquid chromatographic analysis, Anal. Chim. Acta, 715 (2012) 113. [35] H.H. Ji, F. Chang, X.F. Hu, W. Qin, J.W. Shen, Photocatalytic degradation of
2,4,6-trichlorophenol over g-C3N4 under visible light irradiation, Chem. Eng. J., 218 (2013) 183. [36] I. Limam, R.D. Limam, M. Mezni, A. Guenne, C. Madigou, M.R. Driss, T. Bouchez, L. Mazeas, Penta- and 2,4,6-tri-chlorophenol biodegradation during municipal solid waste anaerobic digestion, Ecotoxicol. Environ. Saf., 130 (2016) 270. [37] J. Regueiro, E. Becerril, C. Garcia-Jares, M. Llompart, Trace analysis of parabens, triclosan and related chlorophenols in water by headspace solid-phase microextraction with in situ derivatization and gas chromatography-tandem mass spectrometry, J. Chromatogr. A, 1216 (2009) 4693. [38] T. Zhang, L. Wang, C.W. Gao, C.Y. Zhao, Y. Wang, J.M. Wang, Hemin immobilized into metal-organic frameworks as an electrochemical biosensor for 2,4,6-trichlorophenol, Nanotechnology, 29 (2018) 074003. [39] R. Xu, J.Y. Cui, R.Z. Tang, F.T. Li, B.R. Zhang, Removal of 2,4,6-trichlorophenol by laccase immobilized on nano-copper incorporated electrospun fibrous membrane-high efficiency, stability and reusability, Chem. Eng. J., 326 (2017) 647. [40] X.L. Zhu, K.X. Zhang, N. Lu, X. Yuan, Simultaneous determination of 2,4,6-trichlorophenol and pentachlorophenol based on poly(Rhodamine B)/graphene oxide/multiwalled carbon nanotubes composite film modified electrode, Appl. Surf. Sci., 361 (2016) 72. [41] C.H. Xu, J.C. Wang, L. Wan, J.J. Lin, X.B. Wang, Microwave-assisted covalent modification of graphene nanosheets with hydroxypropyl-beta-cyclodextrin and its electrochemical detection of phenolic organic pollutants, J. Mater. Chem., 21 (2011) 10463. [42] X.L. Zhu, J.G. Liu, Z.S. Zhang, N. Lu, X. Yuan, D.M. Wu, Green synthesis of a bromocresol purple/graphene
composite
and
its
application
in
electrochemical
determination
of
2,4,6-trichlorophenol, Anal. Methods-Uk., 7 (2015) 3178. [43] X.L. Zheng, S. Liu, X.X. Hua, F.Q. Xia, D. Tian, C.L. Zhou, Highly sensitive detection of 2,4,6-trichlorophenol based on HS-beta-cyclodextrin/gold nanoparticles composites modified indium tin oxide electrode, Electrochim. Acta, 167 (2015) 372. [44] G.C. Shearer, S. Chavan, S. Bordiga, S. Svelle, U. Olsbye, K.P. Lillerud, Defect Engineering: Tuning the Porosity and Composition of the Metal-Organic Framework UiO-66 via Modulated Synthesis, Chem. Mater., 28 (2016) 3749. [45] C.A. Trickett, K.J. Gagnon, S. Lee, F. Gandara, H.B. Burgi, O.M. Yaghi, Definitive Molecular Level Characterization of Defects in UiO-66 Crystals, Angew. Chem., Int. Ed., 54 (2015) 11162. [46] M.R. DeStefano, T. Islamoglu, J.T. Hupp, O.K. Farha, Room-Temperature Synthesis of UiO-66 and Thermal Modulation of Densities of Defect Sites, Chem. Mater., 29 (2017) 1357.
[47] X.L. Liu, N.K. Demir, Z.T. Wu, K. Li, Highly Water-Stable Zirconium Metal Organic Framework UiO-66 Membranes Supported on Alumina Hollow Fibers for Desalination, J. Am. Chem. Soc, 137 (2015) 6999. [48] H. Al-Kutubi, J. Gascon, E.J.R. Sudholter, L. Rassaei, Electrosynthesis of Metal-Organic Frameworks: Challenges and Opportunities, Chemelectrochem, 2 (2015) 462. [49] N. Campagnol, T. Van Assche, T. Boudewijns, J. Denayer, K. Binnemans, D. De Vos, J. Fransaer, High pressure, high temperature electrochemical synthesis of metal-organic frameworks: films of MIL-100 (Fe) and HKUST-1 in different morphologies, J. Mater. Chem. A, 1 (2013) 5827. [50] J.Z. Wei, X.L. Wang, X.J. Sun, Y. Hou, X. Zhang, D.D. Yang, H. Dong, F.M. Zhang, Rapid and Large-Scale Synthesis of IRMOF-3 by Electrochemistry Method with Enhanced Fluorescence Detection Performance for TNP, Inorg. Chem., 57 (2018) 3818. [51] S.Y. Dong, G.C. Suo, N. Li, Z. Chen, L. Peng, Y.L. Fu, Q. Yang, T.L. Huang, A simple strategy to fabricate high sensitive 2,4-dichlorophenol electrochemical sensor based on metal organic framework Cu-3(BTC)(2), Sensor Actuat B-Chem, 222 (2016) 972. [52] Y.J. Yang, N. Ma, Z.Y. Bian, Cu-Au/rGO Nanoparticle Based Electrochemical Sensor for 4-Chlorophenol Detection, Int. J. Electrochem. Sci., 14 (2019) 4095. [53] S.Y. Dong, P.H. Zhang, H. Liu, N. Li, T.L. Huang, Direct electrochemistry and electrocatalysis of hemoglobin in composite film based on ionic liquid and NiO microspheres with different morphologies, Biosens. Bioelectron., 26 (2011) 4082. [54] Y.L. Sun, L.P. Wang, H.H. Liu, Myoglobin functioning as cytochrome P450 for biosensing of 2,4-dichlorophenol, Anal. Methods-Uk., 4 (2012) 3358.
Fig. 1 (a) XRD patterns of samples electrochemically synthesized at different voltage range in comparison with the simulated pattern of UiO-66, where a−d represent the voltages at 2, 4, 6 and 8 V, respectively. (b) SEM of samples electrochemically synthesized at different voltage range, where a-d represent the voltages at 2, 4, 6 and 8 V, respectively. Fig. 2 (a) XRD patterns of samples electrochemically synthesized at different reaction temperatures in comparison with the simulated pattern of UiO-66, where a−d represent the reaction temperatures at room temperature, 30, 40 and 50 °C, respectively. (b) SEM of samples electrochemically synthesized at different reaction temperatures, where a−d represent the reaction temperatures at room temperature, 30, 40 and 50 °C, respectively. Fig. 3 (a) FT-IR diagram of the synthetic material UiO-66 and H2BDC. (b) N2
adsorption-desorption isotherms for the UiO-66 synthesized by means of electrochemical method and hydrothermal method respectively. Fig. 4 (a) CV of UiO-66-CPE (0-30 wt%) in 0.1 M PBS (pH 7.0) containing 1.0 mM 2,4,6-TCP at 200 mV/s. (b) Nyquist diagrams of CPE and UiO-66-CPE(0-30 wt%) in 5.0 mM [Fe (CN) 6]3−/4− (1:1) solution containing 0.1 M KCl. The parameters are as follows: frequency range from 0.01 to 103 Hz; initiative potential, 0.2 V; amplitude 0.01 V and quiet time of 2 s. Fig. 5 (a) CV of 2,4,6-TCP under different pH values (b) Linear fit between pH value and spike. Fig. 6 (a) CV of UiO-66-CPE (15 wt%) synthesized by means of electrochemical cathode method in 0.1 M PBS (pH 7.0) containing 0-1.0 mM 2,4,6-TCP, 200 mV/s. (b) Hydrothermally synthesized UiO-66-CPE (15 wt%) in 0.1 M PBS (pH 7.0) containing 0-1.0 mM 2,4,6-TCP, 200 mV/s. (c) DPV curves for various concentrations of 2,4,6-TCP in the range of 10-500 (1 × 10-3 uM) in 0.1 M PBS (pH 7.0). (d) Standard curve of peak current value with 2,4,6-TCP concentration. Fig. 7 CV of UiO-66-CPE (a) (15 wt%), CPE (b) in 0.1 M PBS (pH 7.0) containing 1.0 mM 2,4,6-TCP at 200 mV/s. Scheme 1. UiO-66 was synthesized by means of electrochemical cathode method.
Table 1 Detection of 2,4,6-TCP by UiO-66-CPE in real samples
Samples
River water
Tap water
Add 2,4,6-TCP Found (µM) (µM)
2,4,6-TCP Recovery (%)
1
50
53
106%
2
100
103
103%
3
150
157
104.7%
1
50
49
98%
2
100
102
102%
3
150
143
95.3%