Variations in Surface Morphologies, Properties and Electrochemical

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Variations in Surface Morphologies, Properties and Electrochemical Responses to Nitro-analyte by Controlled Electropolymerization of Thiophene Derivatives Silan Bai, Qiong Hu, Qiang Zeng, Min Wang, and Lishi Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b00554 • Publication Date (Web): 17 Mar 2018 Downloaded from http://pubs.acs.org on March 18, 2018

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ACS Applied Materials & Interfaces

Variations in Surface Morphologies, Properties and Electrochemical Responses to Nitro-analyte by Controlled Electropolymerization of Thiophene Derivatives Silan Bai, Qiong Hu, Qiang Zeng, Min Wang*, Lishi Wang* School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510641, People's Republic of China *Corresponding author Email: [email protected] [email protected] Keywords: Conjugated microporous polymer, Electropolymerization, Surface morphology, Electrochemical reduction, Metronidazole Abstract Herein, we reported the fabrication of conjugated microporous polymer (CMP) films based on three thiophene derivatives using a one-step templateless electropolymerization in dichloromethane without any surfactants. The formation of hydrophilic or hydrophobic films with specific morphology is a comprehensive result of the polymerization sites in each monomer,

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ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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the polymerization rate and the gas bubble produced in situ during the polymerization process, which can be easily controlled by the experimental conditions, such as electropolymerization method, electrolyte and “trace water” existed in the organic solvent. Moreover, the electrochemical reduction of metronidazole as prototypical nitro-analyte at CMP-modified glassy carbon (GC) electrode shows remarkably increased current response compared to non-modified GC electrode. The process is demonstrated to be typical adsorption controlled, and the hydrophobic surface of the electrode coating film is more favorable to the absorption thus reduction of metronidazole. This work provide a new perspective and a breakthrough point for the application of CMPs in the electrochemical sensors. 1. Introduction In the past decade, microporous or porous organic materials have attracted attention because of their inherent porosity and high surface area. Design and synthesis of microporous materials with various functions have generated enormous interest as potentially suitable candidates for various applications, such as gas capture,1-3 drug delivery,4,5 catalysis,6-8 electric energy storage9 and sensors.10-12 Conjugated microporous polymers (CMPs), which are a class of amorphous porous organic polymers, are generally obtained by copolymerization of a variety of monomers, such as , alkyne-, thiophene-, and metalloporphyrin-based compounds.13 Chemical reactions for synthesizing polymers, including Suzuki or Sonogashira-Hagihara cross-coupling reaction,14-16 Yamamoto reaction,17,18 oxidative coupling,19 heat treatment,20 have been extensively studied. However, chemical methods seem to have many inconveniences for their further applications. For example, it is difficult to obtain thin films or layers and polymerization usually requires some expensive


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catalysts. Electropolymerization has been proven to be an especially useful method for the preparation of CMP films.21,22 In particularly, the one-step templateless electropolymerization are extremely interesting as the dimensions of cross-linked polymer network films can be easily controlled by electrochemical process and the monomer used.23 For CMPs prepared by chemical methods, the internal micropore is the key characterization to be investigated and there are two methods commonly used. One is transmission electron microscopy (TEM), which is used to observe the nanostructure of material and the other is the Brunauer-Emmett-Teller (BET) surface areas, calculated by gas sorption experiments. As the electropolymerization of CMPs is easily controlled, the influence of the film thickness on CMP’s properties are additionally studied in recent years.24,25 However, little attention has been paid to the surface morphology. Guittard et al26 reported the electropolymerization of five thienothiophene derivatives, where the electrochemical parameters are extremely important in the control of surface morphology and result in hydrophilic/hydrophobic surface. Meanwhile, conducting polymer films, which are electroposited by thiophene-,27 pyrrole-,28 and carbazole-based29 monomers possess excellent electrochromic properties. Scherf et al also reported the electrochemical reduction of nitroaromatic analyte on the glassy carbon (GC) electrode modified carbazole-30 and thiophene-based31 CMP film. The good conductivity and high surface area indicate that CMPs are credible candidate for the modified materials of the electrochemical sensor. Therefore, it is important to understand the factors influenced morphology and corresponding properties of the film surface where the electron-transfer occurs. In our work, CMP films are generated from three multifunctional thiophene-based monomers by one-step templateless electropolymerization without any surfactants. Each film display specific surface morphology by controlling electropolymerization process. We discussed the factors


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influencing the morphology and resulting in surface hydrophilicity/hydrophobicity, such as monomers, electropolymerization method, electrolyte and “trace water”. The thin polymer films also show remarkably increased electrochemical response to nitro compounds, represented by metronidazole. We demonstrated that the hydrophobic surface of electrode coating is more conductive to the reduction of the nitro-analyte. 2. Experimental Section 2.1 Materials The

monomers,

3,3'-bithiophene

(BT),

1,3,5-tri(thiophen-2-yl)benzene

(TTB),

tris(4-(thiophen-2-yl)phenyl)amine (TTPA) were purchased from TCI Company (Shanghai, China).

Tetrabutylammonium

perchlorate

(Bu4NClO4)

and

tetrabutylammonium

hexafluorophosphate (Bu4NPF6) were obtained from Aladdin (Shanghai, China). Anhydrous dichloromethane was purchased from J&K Chemical (Beijing, China). Metronidazole was purchased from Macklin Biochemical Co. Ltd (Shanghai, China). Britton-Robinson (BR) buffer solutions was prepared by mixing 0.04 mol dm-3 of phosphoric acid, boric acid and acetic acid, and then adjusted to pH = 10 using 0.2 mol dm-3 of NaOH solution. All reagents were used without further purification. 2.2 Electropolymerization


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Scheme 1. Monomers Used in This Work As shown in Scheme1, three thiophene derivatives were tested as monomers: 3,3'-bithiophene

(BT),

1,3,5-tri(thiophen-2-yl)benzene

(TTB),

tris(4-(thiophen-2-yl)phenyl)amine (TTPA). All of the electropolymerization experiments were performed on a CHI660E electrochemical workstation (Chenhua, Shanghai, China) using three-electrode system. The 5 mL dichloromethane solution containing 5 mmol dm-3 monomers and 0.1 mol dm-3 supporting electrolyte are added to a glass electrochemical cell. Glassy carbon electrode (GCE, for electrochemical properties), glass carbon sheet (GCS, for roughness), and scanning electron microscopy (SEM) electrode (SEME, for polymer characterization) were used as working electrodes (WE), in combination with a platinum counter electrode (CE) and an Ag/Ag+ electrode as the reference electrode (RE). In order to study the growth of polymer membranes, chronoamperometry (CA) and cyclic voltammetry (CV) are used. Necessarily, two different deposition methods used the same working potential (Ew) that is slightly less than that of the monomer oxidation potential: -Cyclic voltammetry from −0.7 V to the working potential at a scan rate of 20 mV s-1 and using different number of scans (1, 3 and 5 scans);


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-Chronoamperometry at the working potential of each monomer and using different imposed time (5, 10, 25, 50 and 75 s). After deposition, the films were washed twice with dichloromethane and slowly dried. In particular, the corresponding polymers for BT, TTB and TTPA are indicated as PBT, PTTB and PTTPA in the following sections, respectively. 2.3 Surface Characterization The surface morphology of the substrates was characterized using a field emission scanning electron microscope (FE-SEM; Zeiss Ultra55, Germany). Transmission electron microscopy (TEM) were conducted on JEOL-2100F microscope (Japan). The apparent contact angles (θw) were measured using a OCA40 microscope (Germany) by taking the tangent at the triple point contact line with 2 µL water droplet. The AFM images, mean arithmetic (Ra) and quadratic (Rq) roughness were obtained with an atomic force microscope (AFM; Bruker Multimode 8, Germany) operated in the tapping mode. 2.4 Electrochemical Detection of metronidazole For the determination of metronidazole, a GCE modified with the electropolymerized film was used as the working electrode, platinum as counter electrode and a saturated calomel electrode as the reference electrode. The reduction peak potential was measured by cyclic voltammetry and differential pulse voltammetry (DPV) recorded from -1.1 V to -0.4 V with a 200 µmol dm-3 metronidazole in BR (pH 10) buffer solution. 3. Results and Discussion 3.1 Electrochemical Characterization


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The monomers were first polymerized by multicycled cyclic voltammetry in anhydrous dichloromethane containing 0.1 mol dm-3 of Bu4NClO4 at a scan rate of 20 mV s-1. The potential range of the polymerization has a significant effect on the formation of polymers and their surface morphologies. Taking TTB as an example, the high potential called working potential (Ew) is related to the production of the polymer, while the low potential affects the surface morphology (Figure 1). The Ew should be slightly less than the oxidation potential (Eox) of the monomer. Comparison of Figure 1A, B and D shows that the amount of polymer deposited are quite different with scanning from -0.7 V to different high potential. When Ew = 2.5 V, which is higher than the Eox of TTB (2.2 V), the overoxidation of conducting polymers takes place, resulting in the degradation of PTTB. When Ew (1.6 V) is too low, the monomer is difficult to oxidize, which restricted the formation of the oligomer and following polymerization (Figure 1D). A large amount of polymer can be obtained only when Ew (2.0 V) is slightly less than the Eox (Figure 1B). When changing the low potential, the amount of polymer tubes deposited on the electrode remains practically the same, but the number of the top-open tubes changes (Figure 1B and C). When the low potential is -0.7 V, the number is almost 100%. Similar effect of the potential range were observed for TTPA and BT. As the Eox of TTPA and BT are 2.0 V and 2.3 V, Ew used for TTPA and BT are determined as 1.9 V and 2.1 V, respectively. The potential range from -0.7 V to Ew are used in following experiments.


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Figure 1. SEM images of PTTB electrodeposited by cyclic voltammetry (three scans at 20 mV s-1) at different potential ranges: (A) -0.7 - 2.5 V; (B) -0.7 - 2.0 V; (C) 0 - 2.0 V; (D) -0.7 - 1.6 V in 0.1 mol dm-3 Bu4NClO4/dichloromethane. The initial five cycles of the CV are displayed in Figure 2. With TTPA, the current rises gradually with the increase of scan cycles, suggesting the quickly growth of the polymer on the electrode throughout the electropolymerization (Figure 2A). However, the amount of polymers deposited after five cycles is much less than the expectation. The possible reason is the instability of PTTPA, which can be supported by the phenomenon that the color of the electroposition solution containing 5 mmol dm-3 TTPA changed from the nearly colorless to pale yellow, final to bright yellow during the electropolymerization. With PTTPA generating on the electrode, the polymers are easy to collapse and then dissolve into the solution. For TTB and BT, the current shown in the initial five CV cycles does not significantly increase (Figure 2B and C). Moreover, the current falls down when exceeding electrodeposition of five cycles due to the poorer conductivity caused by the increase in thickness of polymer film. Note that, a very slight reductive peak at about -0.4 V is observed during the electropolymerization of PTTB. This peak, according to the report, can be attributed to the decomposition of acidic water in organic solution,


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which lead to the formation of H2 gas bubble and resulting porous structure.26 Hence, on the premise of suitable thickness of the polymer film, TTB seems to be the favorite monomer concerning the stability and plasticity of polymers.

Figure 2. Cyclic voltammogram (five scans at 20 mV s-1) of the three monomers: (A) TTPA; (B) TTB; (C) BT in 0.1 mol dm-3 Bu4NClO4/dichloromethane. 3.2 Surface Morphology The SEM images of monomers for different number of polymerization scans are given in Figure 3. It is obvious that a large number of polymer tubes are fabricated and the extremely rough surfaces can be observed for PTTB, PBT and PTTPA, despite their morphologies are quite different. These differences may be due to the monomer structures, the number of the polymerization sites in each monomer and the steric hindrance during polymerization. As BT is small but possess double polymerization sites in a thiophene group, its polymerization is less limited, resulting in the long and cross-overlapping tubes. TTPA is large as well as more complex and flexible in structure, which induces a high steric hindrance during polymerization. Thus, PTTPA represents long rods after one scan and trends to large-size hollow vesicles as the number of deposition scans increases. TTB, by contrast, has middle size and relatively stable structure, therefore, its polymerization is more organized, which favors the formation of nanotubes. Moreover, when the number of deposition scans increases, similar shape of nanotube, slight growth in diameter as well as great increase in the thickness of tube wall, are observed.


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Figure 3. SEM images of the polymers electrodeposited by cyclic voltammetry, with the red line for the boundaries from left to right are polymerization 1 scan, 3 scans and 5 scans at 20 mV s-1 in 0.1 mol dm-3 Bu4NClO4/dichloromethane. To better understand the factors influenced the polymer growth, electropolymerization is also carried out using chronoamperometry at the Ew with different imposed time (Figure 4). For all of three monomers, nanoseeds are formed in the first instance of the electrodeposition. It is noting that the morphologies of the initial formed polymers are similar to that of tubes fabricated by CV after one scan, while the growth of the nanoseeds is very different. For PTTB, the diameters and the heights of the surface structures increase significantly with the t increasing. Meanwhile, the wall thickness of PTTB tubes maintains almost constant but the number of the open-top tubes regularly decreases. The number is about 90% for t = 5 and10 s, 25% for t = 25 s, and 0% for t = 75 s. Figure 4 also shows the similar granular morphology for PBT and PTTPA.


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The difference between them lie in the structural evolution process. For PBT, gradual growth and uniform distribution are observed. By contrast, for PTTPA, the surface morphology suddenly changed from original rods to cauliflower-like pellets with messy distribution after t = 25 s.

Figure 4. SEM images of the polymers electrodeposited by chronoamperometry using different imposed time (5, 10, 25 and 75 s) in 0.1 mol dm-3 Bu4NClO4/dichloromethane. The surface roughness (Ra and Rq) and the apparent contact angles for water (θw) of the “smooth” polymers are shown in Table S1. The Young's angles of the three polymers are less than 90°, indicating that the three polymers are inherently hydrophilic. However, the dates


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presented in Table 1 suggest that the surface morphology and property can be controlled by changing the electropolymerization method. The θw of each polymer with CV is greater than that obtained with CA. Taking PBT as an example, the difference in θw is nearly 70°, indicating the surface property transforms from strong hydrophobicity to strong hydrophilicity as changing the electropolymerization method from CV to CA. In general, tightly connected tubes and more rough structure can be obtained by CV, which contributes to prevent water droplets from permeating into the film. In contrast, the trend from “rough” to “smooth”, as well as the constant hydrophilicity are observed when using CA, due to the disappearance of the tubular structure and the arrangement of the structural units are relatively loose. Table 1. Apparent Contact Angles and Roughness of the Polymers Structure Obtained by Cyclic voltammetry (CV) and Chronoamperometry (CA), in Dichloromethane (Bu4NClO4 as Electrolyte) deposition Polymer

Ra [nm]

Rq [nm]

CV 1scan

342

368

120.0

CV 3scans

351

405

104.0

CV 5scans

369

449

98.1

CA 5s

27

36

87.3

CA 10s

142

167

84.1

CA 25s

224

273

85.9

CA 50s

243

303

93.5

CA 75s

326

429

84.1

CV 1scan

318

455

112.5

θw [deg]

conditions PTTB

PBT


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PTTPA

CV 3scans

473

562

110.6

CV 5scans

516

654

120.5

CA 5s

3

4

61.8

CA 10s

23

40

56.9

CA 25s

65

119

46.8

CA 50s

354

498

49.6

CA 75s

524

630

58.0

CV 1scan

20

34

91.8

CV 3scans

305

416

96.0

CV 5scans

413

563

100.5

CA 5s

4

11

84.2

CA 10s

7

12

77.1

CA 25s

8

10

64.7

CA 50s

50

82

78.1

CA 75s

135

247

75.7

3.3 Influence of Solution Composition It is reported that counterions from the supporting electrolyte act as dopants in the conducting polymers during their formation, which is referred to as electrochemical doping.32 This process inevitably instigated the change in the surface morphology and accompanying properties of the polymers. Another common supporting electrolyte, tetrabutylammonium hexafluorophosphate (Bu4NPF6), was studied to investigate its effect on the surface morphology and properties.


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Figure 5. SEM images of the PTTB electrodeposited by cyclic voltammetry using different number of scans (1, 3 and 5 scans) at 20 mV s-1 in 0.1 mol dm-3 Bu4NPF6/dichloromethane.


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Figure 6. SEM images of PTTB after electropolymerization by constant potential at various imposed time (5, 10, 25 and 75 s) in 0.1 mol dm-3 Bu4NPF6/dichloromethane. Using Bu4NPF6 as electrolyte, PTTB obtained by CV (Figure 5) shows the cauliflower-like structure after one scan cycle, and the diameter of the structure increases with the number of scans increasing. Roughness dates in Table 2 indicate that the surface morphology trends to be “smooth” and uniform after five-cycle scans. The electropolymerization by CA shown in Figure 6, displays clearly the whole evolution process of the surface morphology. The hollow nanoballs with the diameter about 200 nm are observed at t = 5 s. Then, the nanoballs grow to be cauliflower-like particles, and their size enlarge as t increases from 10 s to 75 s. It is noted that cauliflower-like surface absents porous structure, both by CV and by CA. There should be at least two parameters that give rise to this result. First, the rate of electropolymerization is much higher than that using Bu4NClO4 as electrolyte. Second, less bubbles are produced during the polymerization when using Bu4NPF6, which is confirmed by the results displayed in Figure S1. The absence of peak near -0.4 V that corresponding to H+ reduction in its CV curve, means that the production of H2 bubble is minimized during polymerization process. It is surprising that high θw are presented by both CV and CA (shown in Table 2), suggesting that the cauliflower-like structure is more beneficial to the formation of the hydrophobic surface. Table 2. Apparent Contact Angles and Roughness for PTTB Surfaces Obtained by Cyclic voltammetry (CV) and Chronoamperometry (CA), in Dichloromethane (Bu4NPF6 as Electrolyte) deposition Electrolyte

Ra [nm]

Rq [nm]

θw [deg]

373

407

104.0

conditions Bu4NPF6

CV 1scan


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CV 3scans

483

571

123.5

CV 5scans

151

191

110.4

CA 5s

22

28

118.7

CA 10s

41

60

122.8

CA 25s

68

91

116.3

CA 50s

98

127

128.5

CA 75s

135

170

106.0

Serval researchers have reported that H2 and O2 bubbles can be produced from the water in the solution during the electropolymerization process. And gas bubbles will be as the “soft template” to format regular porous and hollow surface morphology.33-35 Although the polymerization was carried out in the anhydrous dichloromethane in this work, it is certain that “trace” water existed in the solution. In an attempt to make clearer the effect of water, 0.5% water was added in the experiment. The increases in the porosity of the surface morphology is observed, no matter which electropolymerization method are applied. By CA, Figure 7 shows that gas bubbles break through the polymer tubes, resulting in fragmented porous polymer at t = 10 s; as t increases to 50 s, the top of polymer tubes begin to close. By contrast, the porous structure by CV persists at each stage (Figure S2). As displayed the PTTB in Figure 3 and Figure 4, similar morphologic difference is obtained by the two methods without addition of extra water. Those results suggest that the formation of porous structure is mainly controlled by the rate of polymerization and the


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generation of gas bubbles. As CA is carried out at high potential, the oligomers are rapidly polymerized, and simultaneously only O2 bubbles can be produced. However, using CV, the oligomers is formed only when the potential scans to a certain high potential. As a consequence, the rate of polymerization is much slower than that by CA. Thus, more porous and disordered structure is obtained by CV. Additional proof are shown in Figure S3 and Figure S4. As is stated above, H2 bubbles can be formed when using Bu4NClO4 as electrolyte, and the rate of polymerization in Bu4NPF6 solution is higher than that in Bu4NClO4. It is not surprising to obtain more porous structure when using Bu4NClO4 as electrolyte.

Figure 7. SEM images of PTTB after electropolymerization by constant potential at various imposed time (5, 10, 25 and 50 s) in 0.1 mol dm-3 Bu4NPF6/dichloromethane + 0.5% water. 3.4 Electrochemical Detection of Metronidazole Although different porous polymers have been used as the modified materials in the electrochemical sensors, the application related to the CMPs are rare. Scherf et al reported the electrochemical reduction of 1,3,5-trinitrobenzene at the GC electrode modified with carbazole-


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and thiophene-based CMP coatings,30,31 which show remarkably increased current responses compared to non-modified GC electrode. However, their studies of the surface microstructure only focus on surface area and the film thickness, and the effect of the fine morphology and properties was not concerned.

Figure 8. Differential pulse voltammetrys for 200 µmol dm-3 metronidazole in BR (pH 10) buffer solution using PTTB/GCE in 0.1 mol dm-3 Bu4NClO4 (A) and Bu4NPF6 (B) at (a) CA at 5 s PTTB/GCE, (b) CA at 10 s PTTB/GCE, (c) CV for 1cycle PTTB/GCE, (d) bare GCE. Cyclic voltammetrys for PTTB/GCE obtained in 0.1 mol dm-3 Bu4NClO4 (C) and Bu4NPF6 (D) using


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CA at t = 5 s with different scan rates (25, 50, 75, 100, 150, 200, 250, 300, 400, 500 mV s-1), inset: the relationship between the reduction peak current and scan rate. In our experiments, PTTB, which possess hydrophilic or hydrophobic surface, were investigated to demonstrate the application potential of CMPs in the electrochemical sensors. As first step, the PTTB coating with different surface morphologies and properties were modified on the GC electrode both by CA and CV method using different supporting electrolyte. Then, these electrodes were used as the working electrode for sensing metronidazole, a prototypical nitroimidazole medicines. Differential pulse voltammetry of 200 µmol dm-3 metronidazole in BR (pH 10) buffer solution36 using PTTB-modified GC electrode and non-modified GC electrode are shown in Figure 8. The cathodic peak, attributing to the reduction of the nitro groups of metronidazole to hydroxylamine groups, is observed. Compared bare GC electrode, the reduction peak potentials at the thin PTTB film modified GC electrode shift more negatively, probably due to reduction of the conductivity. However, an enhancement of the current response is observed for the PTTB-modified electrode, which is driven by the strong charge-transfer interactions between the electron-poor structural units of nitro-analytes and the electron-rich, high surface area thiophene-based microporous polymers (Figure S5).30,31 By electropolymerization using CA method with 5s, extremely thin PTTB film is deposited on the electrode, and the highest increases in current response are obtained. With the increase of the deposition time, the conductivity of the electrode is getting worse as the polymer film grows thicker. Therefore, the reduction current is obviously reduced. When using the CV method for only one scan, the deposited film is too thick, and the reduction current even less than that obtained on the bare GC electrode. The interesting results are that the PTTB-modified electrode by using Bu4NPF6 as supporting electrolyte show higher increase of current responses, when compared with that using


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Bu4NClO4. There are probably two parameters that can explain these differences. First, the polymer films obtained by Bu4NPF6 possess higher conductivity than those by Bu4NClO4. Second, more hydrophobic surface are obtained when using Bu4NPF6, which is contribute to the absorption of the nitroimidazole analytes on the CMPs-electrode surface. To understand more information about the mechanism of reduction process, the electrochemical behavior of metronidazole on the hydrophilic/hydrophobic electrode surface obtained by CA at t = 5 s was explored at different scan rates. Figure 8C and D show the cyclic voltammograms of 200 µmol dm-3 metronidazole in BR (pH 10) buffer solution with scan rates from 25 to 500 mV s-1, and the linear relationship eqation are I (µA) = -0.03763ν (mV s-1) 6.0198 (R2 = 0.9911) and I (µA) = -0.02705ν (mV s-1) - 3.3519 (R2 = 0.9906), respectively. These results indicate that the metronidazole molecules form the adsorption layer on both hydrophobic and hydrophilic films surface, and the electron-transfer process are both adsorption controlled.

4. Conclusions

In the research, one-step electropolymerization to obtain conjugated microporous polymer films were achieved by using thiophene-based monomers without any surfactants or templates. CMP films generated under different experimental conditions possess different surface morphologies. Firstly, using Bu4NClO4 as supporting electrolyte, rough structure and hydrophobic surface are obtained by using CV method, whereas wide difference in roughness while constant hydrophilicity for surface morphologies were observed by using CA method. Secondly, using Bu4NPF6 as supporting electrolyte, the hydrophobic polymeric surface are formed no matter what polymerization method are used. Finally, the formation of porous structure is due


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to gas bubble produced during the electropolymerization, which seem to decrease the hydrophobicity of polymer surface. The as prepared CMPs were proved to be the good electrode modified materials by sensing metronidazole as a prototypical nitro-analyte. The enhancement of the current response by up to one order of magnitude for the best modified polymer is achieved. The electrochemical reductions of this nitroimidazole medicine are found to be typical adsorption controlled processes, and the hydrophobic surface of the electrode coating is favorable to the absorption thus reduction of the analyte. The subsequent works will be focused on the preparation of CMPs composite electrode materials with higher conductivity and surperhydrophobic surface, thus encouraging their applications in self-cleaning electrochemical sensors for physiological fluids.

Associated Content Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Young’s angles (θY) and roughness for the “smooth” polymers (Table S1); Cyclic voltammogram (five scans at 20 mV s-1 from -0.7 to 2.0 V) of the TTB using 0.1 mol dm-3 Bu4NPF6 and Bu4NClO4 as electrolyte in dichloromethane (Figure S1); SEM images of the PTTB electrodeposited by cyclic voltammetry using different number of scans (1, 3 and 5 scans) at 20 mV s-1 in 0.1 mol dm-3 Bu4NPF6/dichloromethane + 0.5% water (Figure S2); SEM images of the PTTB electrodeposited by cyclic voltammetry using different number of scans (1, 3 and 5 scans) at 20 mV s-1 in 0.1 mol dm-3 Bu4NClO4/dichloromethane + 0.5% water (Figure S3); SEM images of PTTB after electropolymerization by chronoamperometry at various imposed time (5,


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10, 25 and 75 s) in 0.1 mol dm-3 Bu4NClO4/ dichloromethane + 0.5% water (Figure S4); TEM images of PTTB after electropolymerization by cyclic voltammetry using 5 scans at 20 mV s-1 in 0.1 mol dm-3 Bu4NPF6/dichloromethane (Figure S5). Author information Corresponding Authors *E-mail: [email protected] (Min Wang) *E-mail: [email protected] (Lishi Wang) Notes The authors declare no competing financial interest. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Grant Nos. 21475046, 21427809, and 21645004). We also acknowledge the State Key Laboratory of Pulp and Paper Engineering (201623) and Fundamental Research Funds for the Central Universities (No. 2015ZP028, 2017MS094). References (1) Wang, W.; Zhou, M.; Yuan, D. Carbon Dioxide Capture in Amorphous Porous Organic Polymers. J. Mater. Chem. A 2017, 5,1334-1347. (2) Zeng, Y.; Zou, R.; Zhao, Y. Covalent Organic Frameworks for CO2 Capture. Adv. Mater. 2016, 28, 2855-2873.


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Graphical abstract


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Variations in Surface Morphologies, Properties and Electrochemical

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