Manipulating Polyaniline Fibrous Networks by Doping Tetra-Î²

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Manipulating polyaniline fibrous networks by doping tetra-#carboxyphthalocyanine cobalt (II) for remarkably enhanced ammonia sensing Hao Wu, Zhimin Chen, Jialin Zhang, Feng Wu, Chunying He, Zhiyu Ren, and Yiqun Wu Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.7b03645 • Publication Date (Web): 20 Oct 2017 Downloaded from http://pubs.acs.org on October 24, 2017

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Chemistry of Materials

Manipulating polyaniline fibrous networks by doping tetra-βcarboxyphthalocyanine cobalt (II) for remarkably enhanced ammonia sensing Hao Wu,† Zhimin Chen,*,† Jialin Zhang,† Feng Wu,† Chunying He,† Zhiyu Ren† and Yiqun Wu*,†,‡ † Key Laboratory of Functional Inorganic Material Chemistry (Ministry of Education of China), School of Chemistry and Materials Science, Heilongjiang University, 74# Xuefu Road, Nangang District, Harbin 150080, People’s Republic of China; ‡ Shanghai Institutes of Optics and Fine Mechanics, Chinese Academy of Sciences, 390# Qinghe Road, Jiading District, Shanghai 201800, People’s Republic of China. ABSTRACT: Manipulating the morphology and protonic acid doping of polyaniline (PANI) is significant for optimizing its NH3-sensing. Herein, tetra-β-carboxyphthalocyanine cobalt (II) (TcPcCo) acted as the dopant and structure-directing agent simultaneously to fabricate the uniform fibrous network-like PANI (PANI-TcPcCo hybrids) by a one-step polymerization at low temperature. During the reaction process, the protonic acid groups in TcPcCo not only induced the aniline monomers polymerizing into one-dimensional nanofibers (consist of both solid and hollow cylinders) with abundant tiny protuberances on the surface, but also successfully doped into PANI. The resulting PANI-TcPcCo hybrids displayed the enhancement in terms of the good conductivity, the large gas adsorption capacity, and the unobstructed channels for the electron and gas transport. The central metal atoms of TcPcCo presents the strong and selective affinity to NH3. Meanwhile, the deep-seated conversion of PANI’s molecular structure after exposure in NH3 could occur due to the presence of TcPcCo. Thus, the PANI-2.5TcPcCo sensor showed the excellent NH3-sensing performance at room temperature, including an ultra-high and fast response (802.7 % and ~17.0 s for 100 ppm NH3), a very low detection limit of 10 ppb (about 5,000 parts of human olfaction limit of detection, 55 ppm), and superior NH3-sensing stability and selectivity. The strategy developed here provides a reliable and valid way to synthesize functional PANI-based hybrids with unique morphology and appropriate doping, which is able to be extended to other areas.

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INTRODUCTION Ammonia (NH3), as one of the colorless and stimulating odour gas, not only is detrimental to our health but also endangers environment and ecosystem over the long term.1-4 However, it is widely used in the processing of food, fertilizer production, refrigeration systems and chemicals products, and thus its global production exceeds 100 million tonnes per year.5,6 Owing to the lowdensity and volatile properties of NH3, the affected area is fairly large once a NH3 leakage occurs.7 Exposure to NH3 at extremely low concentrations (about 50 ppm in air) may cause respiratory tract irritation or acute poisoning; while, at higher concentrations, it may even lead to skin disease, lung disease and permanent blindness.8 Therefore, sensitive and easily available materials for detection and quantification of the poisonous NH3 at room temperature are critically needed to prevent adverse effects. Semiconducting metal oxides (SMOs), as the traditional NH3-sensing materials, have been deeply investigated.9-

Recent significant progress demonstrated that some SMO-based NH3 sensors were able to operate at room temperature,13-15 however, the lower sensitivity and poor selectivity of them still need to be further improved for practical applications. In addition, a variety of novel materials were also developed to construct high-performance NH3 sensors, such as organic semiconductors,16-19 conductive polymers,20-22 metal-organic frameworks,5 carbon nanotubes,23,24 and graphene,3,25-27 etc. Among them, polyaniline (PANI) with the unique conjugated polymeric structure shows many advantages in NH3-sensing, including room-temperature operability, low production costs, and adjustable conductivity based on a change in the oxidation state.28 However, the sensitivity, recovery speed, and selectivity of pristine PANI towards NH3 still remain to be improved. In order to overcome the inherent shortcomings of PANI and strengthen its gas-sensing performance, one of the primary and efficient approaches is regulating its conductivity by chemical doping/dedoping. More specifi-

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cally, the common dopants for PANI are various protonic acids.29 The electronic conductivity of PANI can be tuned by the unique reversible protonation/deprotonation in chemical structure, from the undoped semiconducting (emeraldine base, EB) or insulator (pernigraniline or leucoemeraldine, LM) to the fully doped conducting salt (emeraldine salt, ES).30-32 Thus, the appropriate doping of PANI is beneficial for accelerating the speed of electron transport, resulting in a rapid response and recovery. Previous studies have been validated that the gas-sensing performance of acid-doped PANI is severely influenced by changing the chemical nature, and doping PANI also created more active sites.33,34 Additionally, conveniently regulating the morphology and structure of PANI (e. g. nanosheets,20 nanotubes,35 and nanowires,36 etc.) is also highly desirable, since the nanostructured PANI has high surface-to-volume ratios for more activity sites exposed on the surface, which contributes to the large gas adsorption capacity and the high sensitivity. And more notably, the one-dimensional (1D) structure also offers the unhindered electron transport channel for a rapid response and recovery. Up to now, various strategies have been used to prepare PANI 1D nanomaterials.37-43 Although the hardtemplate synthesis is particularly effective and powerful among these methods, the performances of resulting PANI materials are generally limited by the template, and the preparation and removal of the hard-template are rather tedious. Instead, if the doping agents could help control the aggregation morphology of aniline (An) monomers, the manipulating of PANI’s conductivity and structure should be simultaneously achieved.44,45 Potential dopants for PANI, including sulfuric acid, β-naphthalene sulfonic acid, etc,46,47 have been shown the effect on regulating PANI’s morphology and structure. Unfortunately, these dopants aren’t conducive to enhance the selectivity and sensitivity of PANI, as they have no gas-sensing characteristics. Metal phthalocyanines (MPcs) are among the most important gas-sensing materials,16,48 which can work at room temperature with transitory response time, fast recovery rate and good selectivity, arising from their unique conjugated 18π-electron structure and highly active central metal atoms. More important, the outer ring of MPcs could be easily tailored with –COOH or –SO3H groups. This offers the opportunity for optimizing and enhancing the NH3-sensing performance of PANI by using substituted MPcs as dopants. On the one hand, the protonic acid groups in substituted MPcs could induce the An monomers polymerizing into nanostructure, resulting in the large gas adsorption capacity compared with pristine bulk PANI. On the other hand, as dopants, the substituted MPcs favor for the interchain charge transport of PANI due to the presence of protonic acid, and thus greatly enhancing the conductivity. Meanwhile, the central metal atoms of MPcs also provide a lot of active sites for selective NH3 adsorption. Apparently, the NH3-sensing performance of substituted MPc/PANI hybrids will be greatly improved.

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Based on the above considerations, in this work, tetraβ-carboxyphthalocyanine cobalt (II) doped PANI (PANITcPcCo) was successfully prepared. The –COOH groups of TcPcCo, act as proton dopants, made each TcPcCo molecule link with the An monomer by the acid-base interaction. The forming An-TcPcCo salt, serving as the “components”, further assembled and polymerized to form 1D nanostructure. The effect of the TcPcCo concentration on the morphology, conductivity, and gassensing performance of PANI-TcPcCo hybrids was investigated. In particular, the PANI-2.5TcPcCo hybrid with the highest surface area and conductivity, exhibited an extremely high gas response of 802.7 % for 100 ppm NH3 with a fast response time of 17.0 s, and a very low detection limit of 10 ppb. Furthermore, the stability and selectivity were examined and the NH3-sensing mechanism has also been discussed in detail.

EXPERIMENTAL METHODS Reagents. Aniline (An, 99.5 % purity), oxalic acid (OA, 99 % purity) and ammonium persulfate (APS, 98 % purity) were received from Aladdin Co. LLC. Ultra-pure water (resistivity 18.2 MΩ·cm) was obtained from a Milli-Q Water System (Millipore Corp., Bedford, MA, USA) and was applied to the whole experiment process. Tetra-βcarboxyphthalocyanine cobalt (II) (TcPcCo) was synthesized by the common template reaction of 1, 2, 4Benzenetricarboxylic anhydride with anhydrous cobalt (II) chloride in the presence of ammonium molybdate tetrahydrate (the synthetic process in detail was listed in Supporting Information). All the other reagents were of analytical grade and used without further purification in this work. Preparation of PANI-TcPcCo hybrids. The PANITcPcCo hybrids were prepared by a one-step of lowtemperature polymerization. Briefly, An (1 mmol) and different amounts of TcPcCo (let the molar ratio of An and TcPcCo to reach 20: 0.5, 20: 2.5, and 20: 5.0, respectively) were dissolved in water (10 mL) under supersonic stirring for 30 min at -5 ± 0.5 °C, subsequently, a precooling aqueous solution of APS (0.5 g in 10 mL water) was poured into the reaction mixture and mixed thoroughly. Then, the mixture was left at -5 ± 0.5 °C for 8 h and the product was filtered and washed with water, methanol and ether until the filtrate was colorless. Finally, the filter-cake was dried in a vacuum oven at 80 ºC for 2 h, and the PANI-TcPcCo hybrids were achieved as blue-black powder. The PANI-TcPcCo hybrids with the molar ratio of An and TcPcCo about 20: 0.5, 20: 2.5, and 20: 5.0 were labeled as PANI-0.5TcPcCo, PANI-2.5TcPcCo and PANI5.0TcPcCo, respectively. In order to explore the mechanism of TcPcCo on the structure and properties of the PANI-TcPcCo hybrids, the PANI was fabricated using the same procedure without using TcPcCo as dopants (labeled as PANI NPs), and the PANI doped with OA (labeled as PANI-2.5OA) was prepared by the same method as PANI-2.5TcPcCo hybrid except that the TcPcCo was replaced with OA. Additionally, the PANI-2.5TcPcCo hybrid was also prepared in the


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same manner except that the polymerization temperature was converted to room temperature (28 °C) from -5 ± 0.5 °C, so that the effect of temperature on the reaction can be studied. Sensor assembling and sensing measurements. A complete description for the gold interdigitated electrodes (IDEs) and the gas sensor testing device was already reported in our previous study.49 To prepare gas sensors composed of PANI-TcPcCo hybrids, PANI NPs or PANI-2.5OA hybrids, the as-prepared PANI-TcPcCo hybrids, PANI NPs or PANI-2.5OA hybrid were dispersed in ethanol to obtain a uniform suspension of 1.0 mg mL-1 by ultrasonication for 30 min, and then approximately 50 μL of the homogeneous dispersion was sprayed on the IDEs using an airbrush tool. To remove the solvent of the sensor and improve the electrical contact between the sensing materials and the gold electrodes, the sensor devices were annealed in a vacuum oven for 2 h at 50 ºC before sensing tests. For comparison, gas sensor composed of TcPcCo was also fabricated by the same procedures except for the replacement of ethanol using acetone. A typical sensing test cycle consisted of three sequential steps. First, air flow was introduced into the sensing test chamber to record a baseline. Then, a target gas with certified concentrations was injected to register sensor signals. Finally, the sensor was recovered in air flow. A constant DC voltage of 0.5 V was applied to the electrode gap bridged by the sensing materials and all measurements were performed at 28 ± 0.5 °C with a relative humidity (RH) of 60 ± 2 %. In this study, sensitivity (S) is defined by the change of relative resistance, as follows:

S =

600, TA Instruments). The current-voltage (I−V) characteristics of the fabricated sensors were measured using a two-point probe setup via sweeping the potential between −1 to +1 V under a 0.01 V·s–1 scan rate (Keithley 4200). Contact angles (CAs) were measured on a Dataphysics OCA20 contact-angle system at ambient temperature.

RESULTS AND DISCUSSION Preparation and characterizations of the PANITcPcCo hybrids The morphology of PANI-TcPcCo hybrids sprayed on the interdigitated electrodes (IDEs) was characterized by SEM and TEM. The PANI-2.5TcPcCo hybrid shows a uniform fiber structure with an average diameter of about 200 nm, and these fibers interconnected each other to form a large network-like structure (Figure 1A). A large number of “tiny protuberances” can be observed distinctly in the high-magnification SEM image (Figure 1B) of PANI2.5TcPcCo hybrid. Meanwhile, many fibers emerge the hollow 1D structure, as evidenced by the cross-section image. The same result can be further confirmed by TEM images of PANI-2.5TcPcCo hybrid (Figure 1C and 1D). Apparently, the hollow and solid nanofibers co-exist in PANI-2.5TcPcCo hybrid. The generation of “tiny protuberances” on the surface of nanofibers is due to the accumulation of high crystallinity polymer particles. Such unique structure derived from the control of TcPcCo, can provide the larger surface area/active sites to improve gas adsorption abilities, and the interaction between the hybrid and adsorbed gas molecules.

R − R0 ∆R × 100% = g × 100% R0 R0

Where R0 is the sensor resistance in initil air flow which is used as the background and Rg is the sensor resistance after being exposed to a certain concentration of target gas. Response and recovery times are defined as the time needed for 90 % of total resistance change to target gas and air, respectively. The sensor responses to different RH were measured at 28 ± 0.5 °C, and the certain RH level was achieved by mixing the dry air and the water vapour.2,50 Characterizations. Scanning electron microscopy (SEM, S-4800, Hitachi) and transmission electron microscopy (TEM, JEM-3010, JEOL) were used to analyze the microstructure of the sample, and their operating voltages were 15 kV and 300 kV, respectively. UV/Vis (UV2550, Shimadzu), FT-IR (Nicolet 6700, Thermo Fisher Scientific), Raman (HR800, HORIBA Jobin Yvon) and Xray photoelectron (XPS, AXIS UL TRA DLD, Krayos) spectrometers were used to record the spectral data of the sample. The Brunauer-Emmett-Teller (BET) surface area of the sample was measured by nitrogen adsorptiondesorption isotherms at 77 K (ASAP 2010, Micromeritics). Thermogravimetric (TG) analysis was performed under a stream of nitrogen at a heating rate of 10 ºC min-1 (TAQ

Figure 1. The typical SEM (A and B) and TEM (C and D) images of PANI-2.5TcPcCo hybrid prepared at -5 ± 0.5 °C. As expected, TcPcCo as dopants plays a vital role in determining the formation of 1D nanostructure. It can be seen from Figure S1 that only agglomerated and irregular nanoparticles (labeled as PANI NPs) can be obtained, when PANI was synthesized using the same procedure without TcPcCo. While, the effect of the [An]/[TcPcCo] ratio on the morphology of PANI-TcPcCo hybrids is slight. On increasing the [An]/[TcPcCo] ratio from 20 : 0.5 to 20 : 5.0, the 1D nanofibers are significantly uniform, except for the slightly increasing of diameter from 180 to 240 nm (Figure 1A and Figure S2). The morphology of PANI-



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TcPcCo hybrids is also influenced by the reaction temperature. As shown in the Figure S3, when the polymerization temperature is raised to the room temperature (25 ± 0.5 °C), the PANI-2.5TcPcCo hybrid aggregates into massive structures, suggesting that the low temperature may slow the polymerization rate of An, which is advantageous for regulating the morphology of PANI by TcPcCo.

Scheme 1. A schematic illustration of the synthesis procedure for PANI-TcPcCo hybrids. To further investigate the formation mechanism, the morphology evolution of PANI-2.5TcPcCo hybrid with the polymerization time was investigated in detail. Obviously, after 10 min polymerization, a large number of scattered and small blocks clearly emerge (Figure S4A). When the polymerization time is extended to 60 min, PANI2.5TcPcCo hybrid with rod-like structure can be observed (Figure S4B). Then, the rods gradually lengthen, interlace with each other, and form a nanofiber network structure until the polymerization time reaches 8 hours (Figure S4C-E). Meanwhile, the PANI-2.5TcPcCo hybrid obtained at this time exhibits the best conductivity, leading to the faster charge transfer (Figure S5). However, the fiber length of PANI-2.5TcPcCo hybrid no longer increases, even if the polymerization time is increased to 16 hours (Figure S4F). Companied with the prolongation of the polymerization time, the color of PANI-2.5TcPcCo hybrid gradually changes from brown yellow to blue-black (insets in Figure S4), also confirming that the structure of PANI-2.5TcPcCo hybrid has undergone significant changes. Taking into account the above factors, a possible formation process for 1D PANI-TcPcCo hybrids is proposed in the Scheme 1. At the beginning, the –COOH groups of TcPcCo and the amino group of An could be linked together, forming an An-TcPcCo salt based on the acid-base interaction.32 These salts, serving as the “components”, spontaneously gather to form small micelles in solution.46 Subsequently, the polymerization process could occur on the surface of these micelles with the addition of APS.51 Owing to the rigid molecule of PANI, the micelles tends to fuse and assemble each other along the direction of the polymer molecular chain, as the reaction time increases.52 Meanwhile, some An-TcPcCo salts may fill into the mi-

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celles, eventually leading to the hollow and solid nanofibers co-exist in PANI-TcPcCo hybrids simultaneously. In order to prove the successful doping of TcPcCo into PANI, UV-Vis, FT-IR and Raman spectra were used to analyze the composition of PANI-TcPcCo hybrids. The UV-Vis spectra corresponding to TcPcCo, PANI NPs and PANI-TcPcCo hybrids dissolved in NMP are shown in Figure 2A, compared with the PANI NPs, the characteristic Q-band of TcPcCo (667 nm) is obviously observed in the PANI-TcPcCo hybrids, and the absorption intensity increases with the increase of TcPcCo content (Figure S6). Meanwhile, this new absorption peak appears at about 11 nm red shift.53,54 Similar evidence can be observed by the typical FT-IR spectra (Figure 2B). Besides the typical vibrations of PANI NPs at 1498 and 1577 cm−1 (C–N and C=C stretching mode of vibration for the quinonoid and benzenoid),55 two distinct new peaks (1733 and 1374 cm−1 assigned to C=O and C–O of –COOH, respectively) derived from TcPcCo appear in the FT-IR spectrum of PANI-2.5TcPcCo hybrid and undergo a certain red shift (35 and 41 nm).56-58 Further evidence can be observed from the Raman spectra (Figure S8).59 When TcPcCo doped into PANI, the most typical peak of TcPcCo at 1547 and 1620 cm-1 (pyrrole stretching and benzene stretching60,61) shift to 1521 and 1587 cm−1. The shift of corresponding peaks is attributed to the acid-base interaction between TcPcCo and PANI, indicating that TcPcCo and PANI can be linked together. In addition, the FT-IR and Raman spectra of PANI-0.5TcPcCo and PANI-5.0TcPcCo hybrids were also obtained, in which the characteristic peaks are the same as that of PANI-2.5TcPcCo hybrid, except that the intensity of the peaks changes with the doping amount of TcPcCo (Figure S7 and S8).

Figure 2. (A) UV-Vis spectra and (B) FT-IR spectra of TcPcCo, PANI NPs, and PANI-2.5TcPcCo hybrid; (C) N2 adsorption-desorption isotherms and pore-size distribution curves (the inset) of the PANI NPs and PANI2.5TcPcCo hybrid; (D) I-V curves of TcPcCo, PANI NPs and PANI-0.5TcPcCo hybrid. The thermal stability of TcPcCo, PANI NPs and the PANI-TcPcCo hybrids were measured by TG analysis under a N2 atmosphere presented in Figure S9. Compared


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with TcPcCo, TG curves of the PANI-TcPcCo hybrids are similar to that of PANI NPs, except a slower weight loss in the whole range of heating due to the good thermal stability of TcPcCo. This suggests that the doping of TcPcCo does not destroy the molecular-chain structure of PANI. The changes in morphology, transforming from NPs to nanofibers, also leads to the enhanced of surface area, as evidenced by the N2 adsorption-desorption isotherms measurement. As shown in Figure 2C, the surface area of PANI-2.5TcPcCo hybrid is about 47.64 m2 g-1, which is about 1.5 times that of the PANI NPs (30.72 m2 g-1), and the BET pore size reduces to 35.06 nm from 42.35 nm. Notably, the surface area of PANI-2.5TcPcCo hybrid is the biggest among all the samples (Figure S10), indicating that the size and morphology of the PANI-2.5TcPcCo hybrid prepared under this ratio condition (the molar ratio of An and TcPcCo) is the most desirable, which can bring the enhanced gas adsorption capacity for high sensitivity. Additionally, the resulting current-voltage (I–V) curves of TcPcCo, PANI NPs and the PANI-TcPcCo hybrids reveal that the PANI-TcPcCo hybrids are in good electrical contact with the sensor substrate, and the resistance of PANI2.5TcPcCo hybrids is lower than that of TcPcCo, PANI NPs and other PANI-TcPcCo hybrids (Figure 2D and Figure S11). Consequently, the appropriate TcPcCo doping can promote the interchain charge transport of PANI.

Figure 3. The survey XPS spectra of TcPcCo, PANI NPs and PANI-2.5TcPcCo hybrid; the inset images of (a) and (b) are the high-resolution C 1s and N 1s XPS spectra of TcPcCo, PANI NPs and PANI-2.5TcPcCo hybrid, respectively. The relationship between TcPcCo and PANI molecular chain was explored further by XPS measurements. Besides C 1s, N 1s and O 1s peaks, Co 2p, S 2s and S 2p peaks appear in the survey spectrum of PANI-2.5TcPcCo hybrid (Figure 3), resulting from TcPcCo doped and the use of APS during the polymerization.62 The C 1s and N 1s XPS of PANI NPs can be deconvoluted into five Gaussian peaks located at about 284.6 (C–C), 286.0 (C–N), 398.8 (−N=), 399.5 (−NH–) and 401.4 eV (−N+=),63,64 respectively. When TcPcCo combined with PANI, the peaks corresponding to 285.8 eV (C–OH) of TcPcCo disappeared as well as a new peak situated at 286.9 eV emerges, and the C 1s peaks of

TcPcCo situated at 288.9 eV (C=O) shifts to 289.0 eV, indicating that the –COOH groups of TcPcCo doped into PANI by electrostatic action (the inset image of (a) in Figure 3).59 Compared with the N 1s spectrum of PANI NPs, the pyrrole nitrogen (400.1 eV) can be observed in the PANI-2.5TcPcCo hybrid,65 which issues from the doping of TcPcCo. In addition, the protonated nitrogen (−N+=) is clearly shown at 401.3 eV, showing its doped state (the inset image of (b) in Figure 3).66 All of these evidences further suggest that TcPcCo is successfully introduced into PANI-2.5TcPcCo hybrid based on acid-base interaction. NH3-sensing properties of the PANI-TcPcCo hybrids

Figure 4. (A) The NH3-sensing responses of TcPcCo, PANI NPs, PANI-0.5TcPcCo, PANI-2.5TcPcCo and PANI5.0TcPcCo sensors upon exposure to 5, 10, and 20 ppm NH3; (B) response of the PANI-2.5TcPcCo sensor upon exposure to various NH3 concentrations; (C) the relationships of the response of the PANI-2.5TcPcCo sensor to various NH3 concentration; (D) the response and recovery time of PANI-2.5TcPcCo sensor to various NH3 concentration; (E) ten sensing cycles of PANI-2.5TcPcCo sensor to 50 ppm and 100 ppm NH3; (F) the reproducibility characteristic of the PANI-2.5TcPcCo sensor to 50 ppm and 100 ppm NH3 at different durations. The NH3-sensing performances of the PANI-TcPcCo hybrids and control samples (TcPcCo and PANI NPs) were analyzed in detail. As shown in Figure 4A and Table S1, the response intensities of all the sensors increase as the concentration of NH3 increases, which is consistent with the characteristics of P-type semiconductors.6,29 The TcPcCo sensor, as described above, exhibits the transitory response and fast recovery, but accompanied with the weakest response intensity; and the PANI NPs sensor also



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displays poor NH3-sensing performance in term of the response rate, the recovery rate, and the response intensity. By contrast, the PANI-TcPcCo sensors availably overcome these disadvantages. The obtained PANI-2.5TcPcCo sensor exhibits the gas response of 802.7 % for 100 ppm NH3 with the response of 17.0 s and recovery of 5 min, which is the highest response and the fastest response speed among all sensors. Meanwhile, the roomtemperature sensing responses of PANI-2.5TcPcCo sensors with different polymerization times towards 100 ppm NH3 were also been studied (Figure S12). The gas response of PANI-2.5TcPcCo sensor, obtained after the polymerization of 8 h, is the highest. The NH3-sensing properties of PANI-2.5TcPcCo sensor were further studied in detail as shown in Figure 4B-F. Fourteen cycles were successively recorded at room temperature, corresponding to NH3 concentrations from 50 ppb to 250 ppm (Figure 4B). Obviously, the PANI-2.5TcPcCo sensor exhibits a rapid and reversible response for NH3, even at low concentration detection (50 ppb). The relationship of the response of PANI-2.5TcPcCo sensor to the concentration of NH3 shows two good linear responses (Figure 4C and Table S2), 24.88 % per ppm NH3 for concentrations ranging from 0.05 to 5 ppm, 6.48 % per ppm NH3 for concentrations ranging from 10 to 200 ppm, and the lowest theoretically detection limit (S/N = 3) for NH3 is approximately 10 ppb. The response and recovery time of PANI-2.5TcPcCo sensor also shows the expected trends, that is, faster response time and slower recovery time with increased in NH3 concentrations (Figure 4D). The good NH3-sensing performance of PANI-2.5TcPcCo hybrid is superior to, in most respects, the similar conductive polymer-based materials (Table S3) or other materials (Table S4) that are applied at room temperature. The reproducibility and long-term stability of PANI2.5TcPcCo sensor have also been investigated, which is significant for practical applications. It is apparent that, after ten cycles of continuous testing towards 50 and 100 ppm NH3 (Figure 4E), there is no significant difference (relative error < 2.0 % for ten cycles) in the responses of PANI-2.5TcPcCo sensor. After storage in air at room temperature for 60 days, the response of PANI-2.5TcPcCo sensor to 50 and 100 ppm NH3 slightly decreased by 8.50 and 8.00 %, respectively (Figure 4F). The superior stability stems from the uniform fibrous network-like structure (Figure 1) and the rigidity of the PANI molecular chain,52 which means that the PANI-2.5TcPcCo hybrid is not susceptible to the unknown contaminants in the air and can be used directly without the need for additional protection. Moreover, the high gas selectivity is also vital for gas sensor to apply in the complex and changing environment. The selectivity of TcPcCo, PANI NPs, and PANI2.5TcPcCo sensors to the representative gases in air and volatile organic compounds (VOCs) at room temperature is shown in Figure 5A. Herein, except for NH3 and three gases (diaethylamin, triethylamine and pyridine) with similar structure and electron-donating nature in 200 ppm, the concentration of other gases is 10000 ppm. Owing to the protonation/deprotonation interaction with

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NH3, the PNAI NPs sensor shows certain ability of distinguishing NH3 from the other gases;35,67 while, the significantly improved selectivity of PANI-2.5TcPcCo sensor to NH3 is driven by the TcPcCo, which will be discussed in the mechanism section.68,69 Additionally, the relationship of environmental humidity and response of TcPcCo, PANI NPs and PANI-2.5TcPcCo sensors to 200 ppm NH3 was also investigated. As shown in Figure 5B and Figure S13, the humidity has an obvious impact on TcPcCo and PANI NPs sensors due to their hydrophilic property (the inset image in Figure S13);50,70,71 while, the response of the PANI-2.5TcPcCo sensor is almost unchanged in a wide RH range (0 % to 70 %), because the formation of rough surfaces leads to the network-like PANI-2.5TcPcCo hybrid forms a certain hydrophobic capacity with a water CA of about 125.4°(the inset image in Figure 5B).1,72 These results indicate that the PANI2.5TcPcCo hybrid offers superior sensing stability, selectivity and enhanced humidity tolerance, and hold great potential for practical applications.

Figure 5. (A) Cross-sensitivities of TcPcCo, PANI NPs and PANI-2.5TcPcCo sensors to various gases at room temperature; DEA = diaethylamin, TEA = triethylamine, PY = pyridine, MeOH = methanol, EtOH = ethanol, DMK = acetone, DCM = dichloromethane, TCM = trichloromethane, CTC = carbon tetrachloride, PhH = benzene, Tol = toluene, THF = tetrahydrofuran, MA = Methyl Aldehyde, DEE = diethyl ether, and EA = ethyl acetate; (B) response of the PANI-2.5TcPcCo sensor by varying RH from 0 % to 90 % (the concentration of NH3 is 200 ppm) and the water contact angle of PANI-2.5TcPcCo hybrid (the inset image). The enhanced NH3-sensing properties of PANI-TcPcCo hybrids are attributed to the doping PANI with TcPcCo, which can be summarized as the following three points:


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For one thing, with the aid of TcPcCo, PANI tends to assemble/polymerize into interconnected nanofiber network structure with abundant “tiny protuberances” on the surface, not the common, aggregated nanoparticles. Such hierarchical structure results in a greater surface area, and more contact sites with gas molecules, which is beneficial to the adsorption of gas molecules and improving the sensitivity. Besides, the –COOH groups of TcPcCo, which acts as proton dopants, greatly improve the interchain charge transport of PANI, thereby enhancing the conductivity of PANI-TcPcCo hybrids. Generally, the higher the electrical conductivity of the materials, the faster the carriers diffusion and transmission speed. When the gas molecules come in contact with the conductive PANI-TcPcCo hybrids, the resulting carriers can transfer high-efficiently, and ultimately lead to a fast response/recovery speed. Most importantly, the high-active center metal atoms of TcPcCo could enhance the adsorption capacity, and improve the selectivity and sensitivity of PANI-TcPcCo hybrids due to their strong interaction with the NH3 molecules. NH3-sensing mechanism of the PANI-TcPcCo sensors The remarkably NH3-sensing performance of the PANITcPcCo hybrids is derived from the synergistic effect of TcPcCo and PANI. Generally, in the air, oxygen molecules spontaneously and rapidly adsorb on the center metal atoms of TcPcCo in fully doped PANI-TcPcCo hybrids, and capture electrons forming adsorbed oxygen species (O2-).68 When the PANI-TcPcCo hybrids are exposed to NH3 flow, the following two processes occur at the same time (as described in Scheme 2). On one hand, NH3 reacts with the pre-chemisorbed O2-,73,74 and releases a large number of electrons as indicated in the following equation: 4NH3 (g) + 3O2− (ads) → 2N2 (g) + 6H2O (g) + 6e−. For P-type semiconductors, this process can lead to reduced charge carriers in PANI-TcPcCo hybrids, in accord with the charge-transfer model of gas-sensing.75,76 On the other hand, when exposed to NH3 flow, the PANI also changes from fully doped conducting salt (ES) to the undoped semiconducting (EB), based on the unique reversible protonation/deprotonation in structure.30,31,36 Moreover, the electrons released from O2- can inject into the PANI molecular chain, and further promote the more deep-seated conversion of PANI from the semiconducting (EB) to insulator (LM), with consequent dramatic increase in resistance.

Scheme 2. A schematic illustration of the gas-sensing mechanism of PANI-TcPcCo sensors upon interaction with NH3. To verify the above mechanism, the structural evolution of PANI-TcPcCo hybrids and the reference sample PANI-2.5OA hybrids (PANI doped with OA) is tracked. Compared with the UV-Vis spectra of PANI-2.5OA, besides the blue shift assigned to the conversion of PANI from ES to EB, a significant reduced intensity can be observed in that of PANI-2.5TcPcCo hybrids after exposure to NH3 (as shown in Figure S14). These results indicate that PANI in PANI-TcPcCo hybrids has undergone the change from ES to EB, and further to LM.77 Such PANI’s structure conversion can be also confirmed by XPS measurement. As shown in Figure S15 and Table S5, after exposure to NH3, the content of protonated nitrogen (−N+=) in PANI-2.5TcPcCo and PANI-2.5OA hybrids is significantly reduced, which resulted from the dedoping reaction of PANI.62,78 However, relative to the slight change in PANI-2.5OA hybrid, a remarkable enhancement in −NH– content appears in N 1s XPS spectrum of PANI-2.5TcPcCo hybrid, which demonstrates that the reduction of the internal quinone ring structure of the PANI and the occurrence of internal reduction process.77 Additionally, the peak intensity of O2- (531.5 eV) becomes weakened in O 1s XPS spectrum of PANI-2.5TcPcCo hybrid (Figure S15C), implying that the redox reaction occurs between adsorbed oxygen (O2-) and NH3.79,80 Consequently, though the PANI-2.5OA hybrid exhibits the similar morphology, surface area and electrical conductivity to PANI-2.5TcPcCo hybrid, the NH3-sensing properties of PANI-2.5OA sensor are far less than that of PANI-2.5TcPcCo hybrid, especially in terms of the selectivity (Figure S16 and S17). Apparently, TcPcCo as doping agent not only regulates the morphology of PANI, but more promotes the conversion of PANI in configuration, which makes PANI-TcPcCo hybrids emerge the high sensitivity and good selectivity towards NH3.

CONCLUSIONS In summary, the interconnected network-like PANITcPcCo hybrids, made up of both solid and hollow 1D nanofibers, were successfully synthesized by a one-step low-temperature polymerization reaction. TcPcCo not only works as dopants to expedite the charge transport of PANI between the molecular chains, but also induces the aniline (An) monomers polymerizing into 1D nanostructure. Owing to the more exposed active sites for O2− and NH3 adsorbing, the fast orientational transmission of electrons, and loose network-like structure for gas diffusion, the PANI-TcPcCo hybrid exhibits enhanced NH3-sensing performance at room temperature. Compared with the reported NH3 sensors, the PANI-2.5TcPcCo sensor shows an ultra-high sensing sensitivity (802.7 % to 100 ppm NH3), a fast response speed (~ 17.0 s to 100 ppm NH3), and a very low detection limit (10 ppb). More importantly, with the aid of TcPcCo, the PANI-2.5TcPcCo sensor exhibits superior stability, reproducibility and selectivity towards NH3. Therefore,



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this work provides a valid pathway to design scalable, highly efficient PANI-based gas-sensing materials via a simple TcPcCo doping strategy; thereby regulating the morphology and structure, enhancing the conductivity and producing more active sites, which can be further extended to the preparation of other nanostructured conductive polymers for application in sensors, catalysis, supercapacitors, fuel/solar cells, adsorbents, and so on.

ASSOCIATED CONTENT Supporting Information This material is available free of charge via the Internet at http://pubs.acs.org. Experimental details, additional structural and compositional characterizations, and comparison of NH3-sensing performance.

AUTHOR INFORMATION Corresponding Author * Z. M. Chen. E-mail: [email protected]. * Y. Q. Wu. E-mail: [email protected].

Author Contributions The work presented here was carried out in collaboration between all authors. Z. M. Chen and Y. Q. Wu conceived and designed the experiments. H. Wu performed the syntheses of PANI-TcPcCo hybrids and conducted the NH3-sensing measurements. J. L. Zhang and F. Wu carried out the preparation and purification of TcPcCo. Y. Q. Wu and C. Y. He executed the chemical and physical characterizations and gave helpful discussion. Z. Y. Ren, Z. M. Chen and H. Wu wrote the original draft of the manuscript.

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT We gratefully acknowledge the support by the National Natural Science Foundation of China (21573062 and 51002046), the Natural Science Foundation for the Returned Overseas Scholars of Heilongjiang Province of China (LC2012C02), the Fundamental Research Funds for the Heilongjiang Universitiy of Heilongjiang Province of China (HDJCCX-201606 and HDRCCX-2016Z02) and the Science Fund for Distinguished Young Scholar of Heilongjiang University (JCL201501).

REFERENCES (1) Luo, W.; Zhao, T.; Li, Y. H.; Wei, J.; Xu, P. C.; Li, X. X.; Wang, Y. W.; Zhang, W. Q.; Elzatahry, A. A.; Alghamdi, A.; Deng, Y. H.; Wang, L. J.; Jiang, W.; Liu, Y.; Kong, B.; Zhao, D. Y. A Micelle Fusion-Aggregation Assembly Approach to Mesoporous Carbon Materials with Rich Active Sites for Ultrasensitive Ammonia Sensing. J. Am. Chem. Soc. 2016, 138, 12586-12595. (2) Duy, L. T.; Trung, T. Q.; Dang, V. Q.; Hwang, B. U.; Siddiqui, S.; Son, I. Y.; Yoon, S. K.; Chung, D. J.; Lee, N. E. Flexible Transparent Reduced Graphene Oxide Sensor Coupled with Organic Dye Molecules for Rapid Dual-Mode Ammonia Gas Detection. Adv. Funct. Mater. 2016, 26, 4329-4338. (3) Duy, L. T.; Kim, D. J.; Trung, T. Q.; Dang, V. Q.; Kim, B. Y.; Moon, H. K.; Lee, N. E. High Performance Three-Dimensional

Page 8 of 11

Chemical Sensor Platform Using Reduced Graphene Oxide Formed on High Aspect-Ratio Micro-Pillars. Adv. Funct. Mater. 2015, 25, 883-890. (4) Yu, X. F.; Li, Y. C.; Cheng, J. B.; Liu, Z. B.; Li, Q. Z.; Li, W. Z.; Yang, X.; Xiao, B. Monolayer Ti2CO2: A Promising Candidate for NH3 Sensor or Capturer with High Sensitivity and Selectivity. ACS Appl. Mater. Interfaces 2015, 7, 13707-13713. (5) Travlou, N. A.; Singh, K.; Rodriguez-Castellon, E.; Bandosz, T. J. Cu-BTC MOF-Graphene-Based Hybrid Materials as Low Concentration Ammonia Sensors. J. Mater. Chem. A 2015, 3, 11417-11429. (6) Liang, X. H.; Chen, Z. M.; Wu, H.; Guo, L. X.; He, C. Y.; Wang, B.; Wu, Y. Q. Enhanced NH3-Sensing Behavior of 2,9,16,23-Tetrakis(2,2,3,3-tetrafluoropropoxy) Metal(II) Phthalocyanine/Multi-walled Carbon Nanotube Hybrids: An Investigation of the Effects of Central Metals. Carbon 2014, 80, 268-278. (7) Liu, X.; Chen, N.; Han, B. Q.; Xiao, X. C.; Chen, G.; Djerdj, I.; Wang, Y. D. Nanoparticle Cluster Gas Sensor: Pt Activated SnO2 Nanoparticles for NH3 Detection with Ultrahigh Sensitivity. Nanoscale 2015, 7, 14872-14880. (8) Wang, J.; Yang, P.; Wei, X. W. High-Performance, RoomTemperature, and No-Humidity-Impact Ammonia Sensor Based on Heterogeneous Nickel Oxide and Zinc Oxide Nanocrystals. ACS. Appl. Mater. Interfaces 2015, 7, 3816-3824. (9) Kannan, P. K.; Late, D. J.; Morgan, H.; Rout, C. S. Recent Developments in 2D Layered Inorganic Nanomaterials for Sensing. Nanoscale 2015, 7, 13293-13312. (10) Nayak, A. K.; Ghosh, R.; Santra, S.; Guha, P. K.; Pradhan, D. Hierarchical Nanostructured WO3-SnO2 for Selective Sensing of Volatile Organic Compounds. Nanoscale 2015, 7, 12460-12473. (11) Ryu, S. R.; Ram, S. D. G.; Cho, H. D.; Lee, D. J.; Kang, T. W.; Woo, Y. Single ZnO Nanocactus Gas Sensor Formed by Etching of ZnO Nanorod. Nanoscale 2015, 7, 11115-11122. (12) Zhang, G.; Liu, H. J.; Qu, J. H.; Li, J. H. Two-Dimensional Layered MoS2: Rational Design, Properties and Electrochemical Applications. Energy Environ. Sci. 2016, 9, 1190. (13) Choi, S. J.; Choi, C.; Kim, S. J.; Cho, H. J.; Hakim, M.; Jeon, S.; Kim, I. D. Highly Efficient Electronic Sensitization of NonOxidized Graphene Flakes on Controlled Pore-Loaded WO3 Nanofibers for Selective Detection of H2S Molecules. Sci. Rep. 2015, 5, 8067. (14) Xu, K.; Li, N.; Zeng, D. W.; Tian, S. Q.; Zhang, S. S.; Hu, D.; Xie, C. S. Interface Bonds Determined Gas-Sensing of SnO2SnS2 Hybrids to Ammonia at Room Temperature. ACS. Appl. Mater. Interfaces 2015, 7, 11359-11368. (15) Meng, H.; Yang, W.; Ding, K.; Feng, L.; Guan, Y. F. Cu2O Nanorods Modified by Reduced Graphene Oxide for NH3Sensing at Room Temperature. J. Mater. Chem. A 2015, 3, 11741181. (16) Zhang, C. C.; Chen, P. L.; Hu, W. P. Organic Field-Effect Transistor-Based Gas Sensors. Chem. Soc. Rev. 2015, 44, 20872107. (17) Mirza, M.; Wang, J. W.; Li, D. X.; Arabi, S. A.; Jiang, C. Novel Top-Contact Monolayer Pentacene-Based Thin-Film Transistor for Ammonia Gas Detection. ACS Appl. Mater. Interfaces 2014, 6, 5679-5684. (18) Huang, W. G.; Besar, K.; LeCover, R.; Rule, A. M.; Breysse, P. N.; Katz, H. E. Highly Sensitive NH3 Detection Based on Organic Field-Effect Transistors with Tris(pentafluorophenyl) borane as Receptor. J. Am. Chem. Soc. 2012, 134, 14650-14653. (19) Chen, Y. L.; Li, D. P.; Yuan, N.; Gao, J.; Gu, R. M.; Lu, G. F.; Bouvet, M. Tuning the Semiconducting Nature of Bis(phthalocyaninato) Holmium Complexes via Peripheral Substituents. J. Mater. Chem. 2012, 22, 22142-22149. (20) Han, J.; Song, G. P.; Guo, R. Nanostructure-Based LeafLike Polyaniline in the Presence of an Amphiphilic Triblock Copolymer. Adv. Mater. 2007, 19, 2993-2999.


Page 9 of 11

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


(21) Rai, P; Yoon, J. W; Jeong, H. M; Hwang, S. J; Kwak, C. H; Lee, J. H. Design of Highly Sensitive and Selective Au@NiO YolkShell Nanoreactors for Gas Sensor Applications. Nanoscale 2014, 6, 8292-8299. (22) Jiang, T. T.; Wang, Z. J.; Li, Z. Y.; Wang, W.; Xu, X. R.; Liu, X. C.; Wang, J. F.; Wang, C. Synergic Effect Within N-Type Inorganic-P-Type Organic Nano-Hybrids in Gas Sensors. J. Mater. Chem. C 2013, 1, 3017-3025. (23) Mirica, K. A.; Weis, J. G.; Schnorr, J. M.; Esser, B.; Swager, T. M. Mechanical Drawing of Gas Sensors on Paper. Angew. Chem. Int. Ed. 2012, 51, 10740-10745. (24) Cui, S. M.; Pu, H. H.; Mattson, E. C.; Lu, G. H.; Mao, S.; Weinert, M.; Hirschmugl, C. J.; Gajdardziska-Josifovska, M.; Chen, J. H. Ag Nanocrystal as a Promoter for Carbon NanotubeBased Room-Temperature Gas Sensors. Nanoscale 2012, 4, 58875894. (25) Wu, J.; Tao, K.; Miao, J. M.; Norford, L. K. Improved Selectivity and Sensitivity of Gas Sensing Using a 3D Reduced Graphene Oxide Hydrogel with an Integrated Microheater. ACS Appl. Mater. Interfaces 2015, 7, 27502-27510. (26) Zhang, R. Y.; Alecrim, V.; Hummelgard, M.; Andres, B.; Forsberg, S.; Andersson, M.; Olin, H. Thermally Reduced KaolinGraphene Oxide Nanocomposites for Gas Sensing. Sci. Rep. 2015, 5, 7676. (27) Ghosh, R.; Midya, A.; Santra, S.; Ray, S. K.; Guha, P. K. Chemically Reduced Graphene Oxide for Ammonia Detection at Room Temperature. ACS. Appl. Mater. Interfaces 2013, 5, 75997603. (28) Zhang, Y. X.; Kim, J. J.; Chen, D.; Tuller, H. L.; Rutledge, G. C. Electrospun Polyaniline Fibers as Highly Sensitive Room Temperature Chemiresistive Sensors for Ammonia and Nitrogen Dioxide Gases. Adv. Funct. Mater. 2014, 24, 4005-4014. (29) Chatterjee, K.; Dhara, P.; Ganguly, S.; Kargupta, K.; Banerjee, D. Morphology dependent ammonia sensing with 5sulfosalicylic acid doped nanostructured polyaniline synthesized by several routes Sens. Actuators, B 2013, 181, 544-550. (30) Lange, U.; Roznyatouskaya, N. V.; Mirsky, V. M. Conducting Polymers in Chemical Sensors and Arrays. Anal. Chim. Acta 2008, 614, 1-26. (31) Fratoddi, I.; Venditti, I.; Cametti, C.; Russo, M. V. Chemiresistive Polyaniline-Based Gas Sensors: A Mini Review. Sens. Actuators, B 2015, 220, 534-548. (32) Zhang, Z. M.; Wan, M. X.; Wei, Y. Highly Crystalline Polyaniline Nanostructures Doped with Dicarboxylic Acids. Adv. Funct. Mater. 2006, 16, 1100-1104. (33) Raut, B. T.; Godse, P. R.; Pawar, S. G.; Chougule, M. A.; Bandgar, D. K.; Patil, V. B. Novel Method for Fabrication of Polyaniline-CdS Sensor for H2S Gas Detection. Measurement 2012, 45, 94-100. (34) Taylor, K. K.; Cole, C. V.; Berry, B. C.; Tito, V. Use of Tanninsulfonic Acid in the Synthesis of Water-Dispersible Polyaniline. J. Appl. Polym. Sci. 2007, 103, 2113-2119. (35) Wan, P. B.; Wen, X. M.; Sun, C. Z.; Chandran, B. K.; Zhang, H.; Sun, X. M.; Chen, X. D. Flexible Transparent Films Based on Nanocomposite Networks of Polyaniline and Carbon Nanotubes for High-Performance Gas Sensing. Small 2015, 11, 5409-5415. (36) Bai, S. L.; Sun, C. Z.; Wan, P. B.; Wang, C.; Luo, R. X.; Li, Y. P.; Liu, J. F.; Sun, X. M. Transparent Conducting Films of Hierarchically Nanostructured Polyaniline Networks on Flexible Substrates for High-Performance Gas Sensors. Small 2015, 11, 306-310. (37) Silva, R.; Voiry, D.; Chhowalla, M.; Asefa, T. Efficient Metal-Free Electrocatalysts for Oxygen Reduction: PolyanilineDerived N- and O- Doped Mesoporous Carbons. J. Am. Chem. Soc. 2013, 135, 7823-7826.

(38) Zhao, Y.; Liu, J.; Hu, Y.; Cheng, H. H.; Hu, C. G.; Jiang, C. C.; Jiang, L.; Cao, A. Y.; Qu, L. T. Highly Compression-Tolerant Supercapacitor Based on Polypyrrole-mediated Graphene Foam Electrodes. Adv. Mater. 2013, 25, 591-595. (39) Chen, S. G.; Wei, Z. D.; Qi, X. Q.; Dong, L. C.; Guo, Y. G.; Wan, L. J.; Shao, Z. G.; Li, L. Nanostructured PolyanilineDecorated Pt/C@PANI Core-Shell Catalyst with Enhanced Durability and Activity. J. Am. Chem. Soc. 2012, 134, 13252-13255. (40) Huang, X. L.; Hu, N. T.; Gao, R. G.; Yu, Y.; Wang, Y. Y.; Yang, Z.; Kong, E. S. W.; Wei, H.; Zhang, Y. F. Reduced Graphene Oxide-Polyaniline Hybrid: Preparation, Characterization and Its Applications for Ammonia Gas Sensing. J. Mater. Chem. 2012, 22, 22488-22495. (41) Khalid, M.; Acuna, J. J. S.; Tumelero, M. A.; Fischer, J. A.; Zoldan, V. C.; Pasa, A. A. Sulfonated Porphyrin Doped Polyaniline Nanotubes and Nanofibers: Synthesis and Characterization. J. Mater. Chem. 2012, 22, 11340-11346. (42) Xue, M. A. Q.; Li, F. W.; Zhu, J.; Song, H.; Zhang, M. N.; Cao, T. B. Structure-Based Enhanced Capacitance: In Situ Growth of Highly Ordered Polyaniline Nanorods on Reduced Graphene Oxide Patterns. Adv. Funct. Mater. 2012, 22, 1284-1290. (43) Shi, L.; Liang, R. P.; Qiu, J. D. Controllable Deposition of Platinum Nanoparticles on Polyaniline-Functionalized Carbon Nanotubes. J. Mater. Chem. 2012, 22, 17196-17203. (44) Zhang, J. T.; Zhao, Z. H.; Xia, Z. H.; Dai, L. M. A MetalFree Bifunctional Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions. Nat. Nanotechnol. 2015, 10, 444-452. (45) Wang, Y. Q.; Shi, Y.; Pan, L. J.; Ding, Y.; Zhao, Y.; Li, Y.; Shi, Y.; Yu, G. H. Dopant-Enabled Supramolecular Approach for Controlled Synthesis of Nanostructured Conductive Polymer Hydrogels. Nano Lett. 2015, 15, 7736-7741. (46) Zhang, Z. M.; Wei, Z. X.; Wan, M. X. Nanostructures of Polyaniline Doped with Inorganic Acids. Macromolecules 2002, 35, 5937-5942. (47) Wei, Z. X.; Zhang, Z. M.; Wan, M. X. Formation Mechanism of Self-Assembled Polyaniline Micro/Nanotubes. Langmuir 2002, 18, 917-921. (48) Shaymurat, T.; Tang, Q. X.; Tong, Y. H.; Dong, L.; Liu, Y. C. Gas Dielectric Transistor of CuPc Single Crystalline Nanowire for SO2 Detection Down to Sub-ppm Levels at Room Temperature. Adv. Mater. 2013, 25, 2269-2273. (49) Wu, H.; Chen, Z. M.; Zhang, J. L.; Wu, F.; He, C. Y.; Wang, B.; Wu, Y. Q.; Ren, Z. Y. Stably Dispersed Carbon Nanotubes Covalently Bonded to Phthalocyanine Cobalt( II ) for ppbLevel H2S Sensing at Room Temperature, J. Mater. Chem. A 2016, 4, 1096-1104. (50) Sizun, T.; Bouvet, M.; Suisse, J. M. Humidity Effect on Ammonia Sensing Properties of Substituted and Unsubstituted Cobalt Phthalocyanines. Talanta 2012, 97, 318-324. (51) Wei, Z. X.; Wan, M. X. Hollow Microspheres of Polyaniline Synthesized with an Aniline Emulsion Template. Adv. Mater. 2002, 14, 1314-1317. (52) Wei, Z. X.; Zhang, L. J.; Yu, M.; Yang, Y. S.; Wan, M. X. Self-Assembling Sub-Micrometer-Sized Tube Junctions and Dendrites of Conducting Polymers. Adv. Mater. 2003, 15, 13821385. (53) Xu, D. M.; Guan, M. Y.; Xu, Q. H.; Guo, Y. Multilayer Films of Layered Double Hydroxide/Polyaniline and Their Ammonia Sensing Behavior. J. Hazard. Mater. 2013, 262, 64-70. (54) Talwar, V.; Singh, O.; Singh, R. C. ZnO Assisted Polyaniline Nanofibers and Its Application as Ammonia Gas Sensor. Sens. Actuators, B 2014, 191, 276-282. (55) Li, X.; Gao, Y.; Gong, J.; Zhang, L.; Qu, L. Y. Polyaniline/Ag Composite Nanotubes Prepared Through UV Rays Irradiation via Fiber Template Approach and Their NH3 Gas Sensitivity. J. Phys. Chem. C 2009, 113, 69-73.



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

(56) Zhao, P.; Song, Y. N.; Dong, S.; Niu, L. H.; Zhang, F. S. Synthesis, Photophysical and Photochemical Properties of Amphiphilic Carboxyl Phthalocyanine Oligomers. Dalton Trans. 2009, 32, 6327-6334. (57) Vallejo, W.; Diaz-Uribe, C.; Cantillo, A. Methylene Blue Photocatalytic Degradation Under Visible Irradiation on TiO2 Thin Films Sensitized with Cu and Zn TetracarboxyPhthalocyanines. J. Photoch. Photobio. A 2015, 299, 80-86. (58) Li, Z. H.; Zhou, X. C.; Shi, J. Y.; Zou, X. B.; Huang, X. W.; Tahir, H. E.; Holmes, M. Fast Response Ammonia Sensor Based on Porous Thin Film of Polyaniline/Sulfonated Nickel Phthalocyanine Composites. Sens. Actuators, B 2016, 226, 553562. (59) Wang, H. L.; Hao, Q. L.; Yang, X. J.; Lu, L. D.; Wang, X. Effect of Graphene Oxide on the Properties of Its Composite with Polyaniline. ACS Appl. Mater.Interfaces 2010, 2, 821-828. (60) Markovic, M. G.; Matisons, J. G.; Cervini, R.; Simon, G. P.; Fredericks, P. M. Synthesis of New Polyaniline/Nanotube Composites Using Ultrasonically Initiated Emulsion Polymerization. Chem. Mater. 2006, 18, 6258-6265. (61) Shaibat, M. A.; Casabianca, L. B.; Siberio-Perez, D. Y.; Matzger, A. J.; Ishii, Y. Distinguishing Polymorphs of the Semiconducting Pigment Copper Phthalocyanine by Solid-State NMR and Raman Spectroscopy. J. Phys. Chem. B 2010, 114, 44004406. (62) Tang, S. J.; Wang, A. T.; Lin, S. Y.; Huang, K. Y.; Yang, C. C.; Yeh, J. M.; Chiu, K. C. Polymerization of Aniline Under Various Concentrations of APS and HCl. Polymer Journal 2011, 43, 667-675. (63) Zhu, Y.; Hu, D.; Wan, M. X.; Jiang, L.; Wei; Y. Conducting and Superhydrophobic Rambutan-like Hollow Spheres of Polyaniline. Adv. Mater. 2007, 19, 2092-2096. (64) Feng, X. M.; Li, R. M.; Ma, Y. W.; Chen, R. F.; Shi, N. E.; Fan, Q. L.; Huang, W. One-Step Electrochemical Synthesis of Graphene/Polyaniline Composite Film and Its Applications. Adv. Funct. Mater. 2011, 21, 2989-2996. (65) Lu, W.; Li, N.; Chen, W.; Yao, Y. The Role of Multiwalled Carbon Nanotubes in Enhancing the Catalytic Activity of Cobalt Tetraaminophthalocyanine for Oxidation of Conjugated Dyes. Carbon 2009, 47, 3337-3345. (66) Wu, Q.; Xu, Y. X.; Yao, Z. Y.; Liu, A. R.; Shi, G. Q. Supercapacitors Based on Flexible Graphene/Polyaniline Nanofiber Composite Films. ACS Nano 2010, 4, 1963-1970. (67) Guo, Y. L.; Wang, T.; Chen, F. H.; Sun, X. M.; Li, X. F.; Yu, Z. Z.; Wan, P. B.; Chen, X. D. Hierarchical Graphene-Polyaniline Nanocomposite Films for High-Performance Flexible Electronic Gas Sensors. Nanoscale 2016, 8, 12073-12080. (68) Bohrer, F. I.; Colesniuc, C. N.; Park, J.; Ruidiaz, M. E.; Schuller, I. K.; Kummel, A. C. Comparative Gas Sensing in Cobalt, Nickel, Copper, Zinc, and Metal-Free Phthalocyanine Chemiresistors. J. Am. Chem. Soc. 2009, 131, 478-485. (69) Wang, B.; Chen, Z. M.; Zuo, X.; Wu, Y. Q.; He, C. Y.; Wang, X. L.; Li, Z. Comparative NH3-Sensing in Palladium, Nickle and Cobalt Tetra-(tert-butyl)-5,10,15,20-tetraazaporphyrin Spin-Coating Films. Sens. Actuators, B 2011, 160, 1-6. (70) Xiao, C. M.; Si, L. X.; Liu, Y. M.; Guan, G. Q.; Wu, D. H.; Wang. Z. D.; Hao, X. G. Ultrastable Coaxial Cable-Like Superhydrophobic Mesh with Self-Adaption Effect: Facile Synthesis and Oil/Water Separation Application. J. Mater. Chem. A 2016, 4, 8080-8090. (71) Sizun, T.; Patois, T.; Bouvet, M.; Lakard, B. Microstructured Electrodeposited Polypyrrole-Phthalocyanine Hybrid Material, from Morphology to Ammonia Sensing. J. Mater. Chem. 2012, 22, 25246-25253. (72) Yuan, R. X.; Wang, H. Y.; Ji, T.; Mu, L. W.; Chen, L.; Zhu, Y. J.; Zhu, J. H. Superhydrophobic Polyaniline Hollow Spheres

Page 10 of 11

with Mesoporous Brain-Like Convex-Fold Shell Textures. J. Mater. Chem. A 2015, 3, 19299-19303. (73) Shafiei, M.; Hoshyargar, F.; Lipton-Duffin, J.; Piloto, C.; Motta, N.; O'Mullane, A. P. Conversion of N-Type CuTCNQ into P-Type Nitrogen-Doped CuO and the Implication for RoomTemperature Gas Sensing. J. Phys. Chem. C 2015, 119, 2220822216. (74) Du, N.; Zhang, H.; Chen, B. D.; Ma, X. Y.; Liu, Z. H.; Wu, J. B.; Yang, D. R. Porous Indium Oxide Nanotubes: Layer-byLayer Assembly on Carbon-Nanotube Templates and Application for Room-Temperature NH3 Gas Sensors. Adv. Mater. 2007, 19, 1641-1645. (75) Zhao, J. J.; Buldum, A.; Han, J.; Lu, J. P. Gas Molecule Adsorption in Carbon Nanotubes and Nanotube Bundles. Nanotechnology 2002, 13, 195-200. (76) Tran, N. L.; Bohrer, F. I.; Trogler, W. C.; Kummel, A. C. A Density Functional Theory Study of the Correlation Between Analyte Basicity, Znpc Adsorption Strength, and Sensor Response. J. Chem. Phys. 2009, 130, 204307. (77) Kang, E. T.; Neoh, K. G.; Tan, K. L. Polyaniline: A Polymer with Many Interesting Intrinsic Redox States. Prog. Polym. Sci. 1998, 23, 277-324. (78) Ding, H. J.; Wan, M. X.; Wei, Y. Controlling the Diameter of Polyaniline Nanofibers by Adjusting the Oxidant Redox Potential. Adv. Mater. 2007, 19, 465-469. (79) Xu, S.; Gao, J.; Wang, L. L.; Kan, K.; Xie, Y.; Shen, P. K.; Li, L.; Shi, K. Y. Role of the Heterojunctions in In2O3-Composite SnO2 Nanorod Sensors and Their Remarkable Gas-Sensing Performance for NOx at Room Temperature. Nanoscale 2015, 7, 14643-14651. (80) Wang, Y. T.; Lu, Y. Y.; Zhan, W. W.; Xie, Z. X.; Kuang, Q.; Zheng, L. S. Synthesis of Porous Cu2O/CuO Cages Using CuBased Metal-Organic Frame Works as Templates and Their GasSensing Properties. J. Mater. Chem. A 2015, 3, 12796-12803.


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Manipulating Polyaniline Fibrous Networks by Doping Tetra-Î²

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