Molecular Transformation, Diffusion, and Assembling into Three

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Molecular Transformation, Diffusion and Assembling into Threedimensional Freestanding Tube Arrays via a Triphasic Reaction Tuo Ji, Long Chen, Liwen Mu, and Jiahua Zhu Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b03418 • Publication Date (Web): 17 Oct 2016 Downloaded from http://pubs.acs.org on October 18, 2016

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Molecular Transformation, Diffusion and Assembling into Three-dimensional Freestanding Tube Arrays via a Triphasic Reaction Tuo Ji, Long Chen, Liwen Mu and Jiahua Zhu*

Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, OH 44325 USA

ACS Paragon Plus Environment

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Abstract Converting nitrobenzene to freestanding polyaniline tube arrays has been successfully carried out in a “Water-oil-water” triphasic reaction system, where catalytic reduction of nitrobenzene to aniline and aniline polymerization reactions were synergistically integrated. With optimized control over molecular diffusion and reaction at separate solid/liquid and liquid/liquid interfaces, polyaniline nanostructures could be synthesized with different morphologies. Paired molecular diffusion and reaction rate is revealed as the dominating factor that determines the feasibility of reaction system to produce patterned array structure. Slow molecular diffusion leads to a better ordered 3D assembling structure. This work demonstrates a new approach to control 3D assembling structures with integrated control on diffusion and reaction across multiple liquid/liquid interfaces.

KEYWORDS: polyaniline tube arrays, diffusion, interfacial reaction, polymerization, catalytic reduction


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1. INTRODUCITON Nitroaromatics have been listed as top organic pollutants by the United State Environmental Protection Agency.1 Nitroaromatics remain in water stream and soil for a long time with negligible degradation and thus cause harmful effects to agricultural plants, animals and human beings.2 It is well accepted that catalytic reduction of nitro-group into amino-group3, 4 is the most economic and eco-friendly approach that converts harmful nitroaromatics into valuable chemicals those can be used as intermediate to synthesize analgesic, antipyretic drugs and ideal reducing agent for photographic developer and dye industry.5-7 Nitrobenzene, one member from the nitroaromatics family, can be catalytically reduced to aniline that has been widely used as monomer to synthesize conductive polyaniline (PANI).8-11 Over past decades, the structure and morphology control of PANI including nanoparticle, nanofiber, nanotube, hollow sphere, hollow tube, three-dimensional (3-D) crystals,12-16 has resulted enormous promising applications in various emerging fields such as energy harvesting and storage,17-19 electromagnetic wave shielding,20 sensing21, 22 and etc. One dimensional conductive polymer hollow structures, especially polyaniline, have attracted great interests due to its large surface-to-volume ratio and unprecedented physicochemical properties along the longitudinal direction.23-25 Most of the existing research efforts are devoted to synthesize individual PANI hollow tube structures. For example, rectangular-shaped PANI hollow tube was synthesized with the assistance of carbon nanosphere26 or crystals27 as template. PANI nanotubes were also synthesized by using different templates such as poly(L-lactase) fiber,28 thin glass tubes29 and amphiphilic micelle.30 Template seems necessary to obtain the hollow tube structure, while the template itself is often not desirable in practical applications. To remove the template, corrosive chemicals or intensive heat


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treatment process needs to be involved while it often causes either structural damage or property degradation of PANI. Therefore, it remains a great challenge to manufacture free-standing tube array structures without templates. Even more challenging is to pattern PANI tubes into arrayed structure that is expected to boost its physicochemical properties and enable its convenient integration with electronic, photoelectronic and sensing devices. Liquid/liquid interface has been recognized as an ideal confined environment to control the dimension of nanostructures.31 In general, interfacial assembly is driven by the drop in the total free energy of the system brought about by the reduction in the organic/water surface area. As the two solutions are immiscible, the sum of the surface tension between the solid and the organic and the solid and the aqueous phase is lower than the surface tension between the two liquids.32 For example, Wigner crystal conformation,33 liquid-like metal film34 and other unique structures could be produced by liquid/liquid interfacial assembly. The situation becomes more complicated when chemical reaction occurs at the liquid/liquid interface since molecular diffusion, reaction and assembling occur at the same time and the control on overall process is very difficult. Even though, previous research has demonstrated a few successful examples that utilizes interfacial reaction to synthesize dimensional nanostructures. For example, Huang et al. synthesized PANI nanofibers via interfacial polymerization at “oil-water” interface12 and afterwards other 1-D polyaniline structures such as nanoneedles35 and nanorods36 were synthesized by other researchers. Using a similar method, our group recently reported the synthesis of superhydrophobic polyaniline hollow spheres with mesoporous brain-like convexfold shell textures.37 In fact, interfacial method has been demonstrated as an effective approach to synthesize 0-D,37, 38 1-D35, 36 and 2-D39 nanostructures, while it has been rarely reported to build 3-D structures while chemical reactions occurs during assembling.


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In this work, two independent reactions, reduction of nitrobenzene to aniline and interfacial polymerization of aniline to polyaniline, have been synergistically integrated into a “water/oil/water” triphasic reaction system. Single batch conversion of nitrobenzene to freestanding polyaniline tube arrays has been successfully achieved without using templates or substrates. Based on the reaction rate control on both catalytic nitrobenzene reduction reaction and aniline polymerization reaction, the structure of polyaniline can be well controlled. The structure formation mechanism of polyaniline tube array from this interfacial method is investigated. This approach opens up a new venue that transforms toxic pollutants to functional materials. 2. EXPERIMENTAL 2.1 Materials Nitrobenzene (>99%), ammonium persulfate (APS ≥98%), p-Toluenesulfonic acid monohydrate (PTSA ≥98%), toluene (≥99.5%), silver nitrate (AgNO3, ≥99%) were purchased from Sigma Aldrich. Sodium borohydride (NaBH4, ≥99%) was purchased from Fluka Chemical Corp. Ammonium hydroxide (NH4OH, 28~30%) was purchased from BDH Chemistry. Ethanol (99.9%) was purchased from Decon laboratories, Inc. Cotton fabric was cut from a commercially available T-Shirt (100% cotton). All reagents were used as received. Deionized water was used for all experiments. 2.2 Synthesis of Ag/Carbon (Ag/C) Catalyst The Ag/C catalyst was synthesized following our previously reported work.40 In brief, mesoporous carbon support was prepared from cotton fabric by a two-step process, carbonization in nitrogen at 800 oC and air oxidation at 370 oC. Fresh Ag(NH3)2NO3 (5.0 mM) aqueous solution was prepared by dropwise addition of 10 wt% aqueous ammonia into 20.0 mL AgNO3


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aqueous solution until the solution become pellucid. Then, Ag(NH3)2NO3 aqueous solution was mixed with ethanol (ethanol: water= 1:4, v/v) to prepare Ag precursor. In order to load Ag nanoparticles, a few pieces of carbon fabric support (2.0 g) were added into 100.0 mL Ag precursor solution and stirred at 40 ºC for 35 min. The resulting product was denoted as Ag/C. The product was filtered, rinsed with 1.0 L deionized water and finally dried at 65 ºC for 8 h. 2.3 Setup of Triphasic Reaction System The reaction system can be easily set up by placing a small glass vial (volume: 5 mL, ID: 12 mm) into a large glass vial (volume: 22 mL, ID: 23 mm). In the large vial, a whole piece of Ag/C catalyst was compressed at the bottom by the small vial and 4.0 mL NaBH4 aqueous solution (0.65 M) was added to the large vial afterwards. Then, 0.1~0.2 mL nitrobenzene was injected carefully to the bottom of large vial by using a 0.5 mL syringe. In the small vial, certain amount of APS and PTSA were dissolved in 2.0 mL H2O. Finally, 14.0 mL toluene was added slowly on top of the two aqueous phases to form a steady triphasic system at room temperature. The reaction was proceeded with up to 96 hours. Products formed at the toluene/water interface of small vial or precipitates at the bottom were collected for analysis. 2.4 Characterization The morphologies of PANI samples and Ag/C catalyst were characterized by a scanning electron microscope (SEM, JEOL-7401. Transmission electron microscopy (TEM) samples were prepared by placing a drop of sample suspended in ethanol on carbon-coated copper TEM grids and further characterized with an accelerating voltage of 120 kV. The UV-Vis spectra of PANI in ethanol were collected on a UV-1800 Shimadzu spectrophotometer. The rate of aniline generation in catalytic reduction reaction was characterized by UV-Vis spectra and calculated by measuring the peak intensity evolution at wavelength of 230 nm. The X-ray diffraction analysis


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of Ag/C was carried out with a Bruker AXS D8 Discover diffractometer with GADDS (General Area Detector Diffraction System) operating with a Cu-K α radiation source filtered with a graphite monochromator (λ = 1.541 Å). The Ag nanoparticle loading was determined by thermogravimetric analysis (TGA, TA instrument Q500) in air from 20 to 700 ºC with a heating rate of 10 ºC/min. Brunaure–Emmet–Teller (BET) surface area analysis of samples was performed using a TriStar II 3020 surface analyzer (Micromeritics Instrument Corp., USA) by N2 adsorption–desorption isotherms at 77 K. The CO2 adsorption isotherm was used to combine with N2 adsorption isotherm by using DFT method for analyzing the pore size distribution. 3. RESULTS AND DISCUSSION

Figure 1. (a) Schematic illustration of the integrated reduction reaction and interfacial polymerization in a triphasic liquid system. I: external aqueous phase where nitrobenzene was reduced to aniline via catalytic reaction over Ag/C catalyst. II: toluene phase in charge of aniline diffusion from phase I to the interface of phase II/III. III: internal aqueous phase dissolving APS and PTSA that provides reactive interface with phase II for aniline polymerization. (b) top-view of the polymerized thin film floating at the interface of phase II/III. (c) side-view of the thin film clearly shows arrayed tube structure. (d) TEM image focusing on one single tube.


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The function of each phase (I, II and III) and the roles of the two interfaces (I/II and II/III) in the synthetic path are detailed as follow. The reaction system design and reprehensive reactions in the system is schematically illustrated in Figure 1(a). The system composes of three liquid phases, I, II and III. Phase I and III are both aqueous phases, which was separated by an organic phase II-toluene. In the external phase I, nitrobenzene is reduced to aniline by Ag/C catalyst with the presence of sodium borohydride. It is worth mentioning that the solubility of nitrobenzene in water is poor and thus only limited amount of nitrobenzene is dissolved. Thus, the majority of nitrobenzene remains as droplet in phase I. When the reaction proceeds, the nitrobenzene will be continuously consumed and dissolved to participate the reduction reaction. Then, the resulting aniline molecules start to migrate to phase II and afterwards diffuse to phase II/III interface where aniline monomer is polymerized into ordered tube array structures. The involved reactions in this process are presented in Scheme 1.

Scheme 1. Chemical reactions occurred in the triphasic system. Chemical reduction of nitrobenzene to aniline in Phase I and aniline polymerization at the interface of Phase II/III.


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Using “water/oil” interfacial polymerization method to synthesize individual polyaniline nanofibers has been well investigated.12, 35, 36 In such process, the diffusion of aniline monomer from organic phase to reaction interface is very fast and difficult to control. The polymerization reaction occurs immediately once aniline monomer diffuses through the interface. The fast reaction rate leaves no room for structural assembly at interface and therefore the polymerized product diffuses through the interface and dispersed in the entire aqueous phase. Through the catalytic reduction reaction in phase I, the aniline monomer could be continuously supplied with a controlled rate. A slowed feeding rate allows more time for structural transformation and polymerization at the interface rather than in the bulk phase. By tuning the feeding rate and polymerizing rate at separate interfaces, freestanding tubular array pattern of PANI could be synthesized without using template or substrate. Figure 1(b) provides the surface morphology of synthesized thin film facing to phase II (flat surface was observed on the film facing to phase III) indicating a well patterned tube array structure with tube size of 0.86±0.24 µm. Focusing on the surface of the thin film, the tube array structure is much more obvious from a side view of the film, Figure 1(c). The thickness of polyaniline film is about 5.7 µm based on a statistical analysis on over 100 samples. The tube structure is further confirmed by TEM in Figure 1(d). It is observed that the interior space of the microtube shows funnel-shaped structure. In the triphasic reaction system, the conversion of nitrobenzene to polyaniline relies on the two reactions, reduction reaction in phase I and polymerization reaction at phase II/III interface. These two reactions proceed independently and the polyaniline structural control relies on a synergistic coupling of the two reactions. In other words, the reaction rate of these two reactions needs to be in good match that allows a continuous slow feeding of aniline to phase II/III interface.


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Figure 2. (a) SEM of Ag/C showing its fabric structure, inset shows a XRD spectra of Ag/C. (b) TEM of Ag/C, inset gives the Ag particle size distribution. (c) N2 adsorption–desorption isotherm of Ag/C at 77 K, inset table provides the BET surface area, pore volume and average pore diameter, (d) DFT pore size distributions of Ag/C.

Since feeding rate and polymerization rate are the dominant impact factors for successful structure control, each factor in the reaction system is investigated to generate a better understanding on the reaction and assembling processes. Firstly, the feeding rate of aniline can be controlled via the catalytic reduction reaction in phase I, i.e. by changing initial reactant concentration (nitrobenzene) and catalyst amount. As shown in Figure 2(a), the cotton fabric morphology was remained even after the carbonization, oxidation and Ag doping processes. The Ag/C catalyst was compressed at the bottom of the large vial as a whole piece. It is worth mentioning that remaining the whole piece of catalyst is important in this study. Crashed catalyst powder is readily to transfer from phase I to phase II carried by generated hydrogen bubbles


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during reaction. TGA, XRD and TEM techniques were employed to characterize the catalyst. TGA results (Figure S1, SI) quantifies the specific Ag loadings of 1.2 wt% in Ag/C. From XRD results in the inset of Figure 2(a), the diffraction peaks at 38.1, 44.3, 64.4 and 77.4o are indexed to the (111), (200), (220) and (311) crystal planes of Ag0 (JCPDS #4-783).41 It clearly reveals that the silver precursor has been successfully reduced to crystallized Ag nanoparticles. These results confirm that the oxygenated functional groups on the carbon support are responsible for the reduction of silver precursor to Ag nanoparticles as well as their uniform distribution. TEM micrograph in Figure 2(b) reveals the well distributed Ag nanoparticles on the carbon support. The inset of Figure 2(b) summarized the statistical particle size distribution analysed from more than 500 Ag particles. The mean particle size is 3.5 ±0.9 nm in Ag/C. The small particle size and good dispersion ensure good catalytic activity of Ag/C for the reduction of nitrobenzene. Additionally, N2 adsorption-desorption isotherm was conducted at 77 K to characterize the pore structure and surface area of the Ag/C, Figure 2(c). Ag/C presents typical type IV isotherm with enlarged H4 hysteresis loop, which confirms the presence of mesopores.42 The surface area of Ag/C is 621.1 m2/g. In order to access the micropore information, CO2 adsorption-desorption isotherm was further performed at 273 K. The CO2 adsorption isotherm was then combined with N2 adsorption isotherm by using DFT method in MicroActive software. Pore size distribution and pore volume were then analysed as shown in Figure 2(d). This results indicate that the micropores contribute a large portion of total pore volume.


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Figure 3. UV-Vis spectra of (a) aniline and nitrobenzene, (b) aniline at different concentrations. The inset is linear curve relating aniline concentration and peak intensity at 230 nm.

The determination of aniline concentration is based on a UV-Vis spectral method and the results are provided in Figure 3. The nitrobenzene shows a characteristic absorbance band at 270 nm. After adding Ag/C catalyst and NaBH4 into nitrobenzene solution, the peak at 270 nm disappeared and two new peaks at 230 and 280 nm appeared after one minute, Figure 3(a). These two newly generated peaks are characteristic absorbance bands of aniline.43 Nitrobenzene exists as a droplet in Phase I and its solubility in water is 1.9 mg/mL. The disappearance of nitrobenzene absorbance band indicates that the nitrobenzene was immediately reacted to form aniline. In other words, the catalytic reaction rate is faster than the dissolution rate of nitrobenzene in water. In order to quantify the aniline amount, different concentrations of aniline solutions were prepared from 1.4 to 24.4 ppm for constructing a standard liner curve that relates the aniline concentration and UV-Vis peak intensity at 230 nm. The peak intensity at 230 and 280 nm increases with increasing aniline concentration, Figure 3(b). To avoid the possible interference with the nitrobenzene, the peak intensity at 230 nm was chosen to correlate the aniline concentration. For the aniline concentration ranging from 1.4 to 24.4 ppm, a highly linear


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curve was obtained with R2 value of 0.999 (inset of Figure 3b). In order to study the effect of aniline feeding rate on the polyaniline morphology, three different concentrations of Ag/C catalyst were added in phase I and the change of aniline concentration was continuously monitored for three hours, Figure S2 in SI.

Figure 4. (a) The change of aniline concentration in phase I with reaction time by using different amount of Ag/C catalyst, this reaction is scaled up by a factor of 10 for precisely monitoring aniline concentration. Surface morphology of polyaniline film at phase II/III interface by using (b) 0.33 and (c) 0.67 g (Ag/C)/mL (nitrobenzene). (d) morphology of polyaniline nanofiber deposited at the bottom of phase III by using 1.0 g/mL catalyst.

Based on the spectral results, aniline concentration gradually goes up with increasing catalyst loading and extending reaction time, Figure 4(a). Apparently, the reaction rate is faster in the first hour and then slows down afterwards. Larger aniline concentration allows faster


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aniline diffusion to reactive interface. By using 0.33 and 0.67 g/mL catalyst, free standing PANI films could be obtained with different surface morphologies, i.e. “spiny mace”-like tube-on-tube structure with 0.33 g/mL catalyst and well-patterned tube array structure by using 0.67 g/mL catalyst, Figure 4(b&c). By increasing catalyst amount to 1.0 g/mL, polyaniline nanofibers were formed which diffuses into phase III rather than staying at phase II/III interface, Figure 4(d). Another factor is the initial amount of reactant. Figure S3 in SI shows the morphology of polyaniline film with different initial nitrobenzene. However, the initial amount of nitrobenzene in phase I has negligible effect on the film morphology. Thus, the critical role of aniline feeding rate on PANI structure control is the amount of catalysts amount.

Figure 5. Effect of doping acid PTSA concentration in phase III on the final product morphology. Reaction condition: Catalyst: 0.1 g, volume of nitrobenzene: 0.15 mL, [APS]=0.12 M, [PTSA]: (a) 0.8 M (b) 1.0 M (c) 1.3 M and (d) 1.6 M.


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Besides the feeding rate of catalysts control in the phase I, the interfacial polymerization reaction was also investigated by changing the concentration of oxidant APS and doping acid PTSA in phase III. During reaction, PTSA served as both doping acid and surfactant, which has been demonstrated essential component to PANI morphology control.44 While APS determine the polymerization rate of monomer at the interface of phase II/III. Once the aniline monomer entered this interface and contact with PTSA and APS, polymerization reaction occurred immediately. As shown in the Figure 5, the PTSA concentration affects the size of polyaniline tube. At low concentration, the mean size of tube is 2.2 µm with smooth surface, Figure 5(a). Further increase of PTSA brings smaller size of tube formed around the large tube, and the mean size goes down to 1.5 µm, Figure 5(b). The tube size of 1.3 M and 1.6 M sample is 0.75 and 0.68 µm, respectively. It reveals that the more surfactant allows the smaller tube formation. Nevertheless, excessive PTSA molecules cause the break of polyaniline film and form nanosized polyaniline structure. Similarly, the concentration of APS has effects on the regularity of polyaniline tube array, Figure S4 in SI. Optimal APS concentration is conducive of tube structure. A mixture of solid fiber and particles were observed by further increasing APS concentration to 0.14 M, Figure S4(d).


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Figure 6. PANI film structural evolution at different reaction time: (a) 16 h, (b) 24 h, (c) 48 h, (d) 60 h, (e) 72 h and (f) 96 h. (g-j) schematic illustration from PANI film to PANI tube array. To better understand the tube array formation process, PANI structure evolution with reaction time is presented in Figure 6. Initially, aniline monomer was firstly polymerized to form an emeraldine base thin film at the interface, Figure 6(a). The thin film was doped by PTSA and changed its color from blue to green as evidenced by UV-Vis results, Figure S5 in SI. Sulfate group in PTSA preferred to form a strong interaction with N-H group in polyaniline and exposed tolyl group outwards. With reaction proceeds, the edge area of the doped thin film began to exfoliate and curled up towards the toluene phase with the assistance of surface tension driven by the hydrophobic group (tolyl group) in PTSA, Figure 6(b). Therefore, curly film would be pushed inward and bowl-shaped morphology was formed, Figure 6(c&d). Due to the existence of PTSA inside the “bowl”, the diameter of “bowl” would decrease and finally reach to a balanced condition with stabilized tube structure, Figure 6(e). The continuous feeding of aniline allows its favorable growth along the axial direction following the lowest energy path. As a result, wellpatterned freestanding tube array structure could be obtained, Figure 6(f). In a word, PTSA


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prompted the exfoliated of polyaniline films at the interface and curling up the films to ordered tube array structures. The schematic representation of the structural evolution process is also provided in Figure 6(g-j). 4. CONCLUSIONS In summary, this work demonstrates a new path to synthesize freestanding PANI tube array by using nitrobenzene as starting material. Coupled reduction and interfacial polymerization reactions were successfully integrated in a triphasic “water-oil-water” reaction system, where reaction and diffusion are synergistically controlled to allow directional growth of polyaniline at oil/water interface. Slow diffusion of aniline to reactive interface is experimentally demonstrated as the key to successful structure control. Optimized coupling of reactions and reactant diffusion across interfaces in the triphasic system opens up the window of material selection for structure control and functionality design in advanced materials. ASSOCIATED CONTENT Supporting Information. TGA results of Ag/C, the detailed UV-Vis results during the reaction and more SEM images of polyaniline are provided as supporting information. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * J. Zhu. E-Mail: [email protected]. Tel: 1-(330)972-6859. Notes The authors declare no competing financial interest.


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ACKNOWLEDGEMENTS Acknowledgement is made to the Donors of the American Chemical Society Petroleum Research Fund (#55570-DNI10) for support of this research. Partial support from start-up fund of The University of Akron is also acknowledged. REFERENCES 1.

Ji, T.; Chen, L.; Mu, L.; Yuan, R.; Knoblauch, M.; Bao, F. S.; Zhu, J., In-situ reduction of Ag nanoparticles on oxygenated mesoporous carbon fabric: Exceptional catalyst for nitroaromatics reduction. Appl. Catal., B 2016, 182, 306-315.

2.

Narayanan, K. B.; Sakthivel, N., Heterogeneous catalytic reduction of anthropogenic pollutant, 4-nitrophenol by silver-bionanocomposite using cylindrocladium floridanum. Bioresour. Technol. 2011, 102, (22), 10737-10740.

3.

Huang, X.; Liao, X.; Shi, B., Synthesis of highly active and reusable supported gold nanoparticles and their catalytic applications to 4-nitrophenol reduction. Green Chem. 2011, 13, (10), 2801-2805.

4.

Li, H.; Han, L.; Cooper-White, J.; Kim, I., Palladium nanoparticles decorated carbon nanotubes: facile synthesis and their applications as highly efficient catalysts for the reduction of 4-nitrophenol. Green Chem. 2012, 14, (3), 586-591.

5.

Vaidya, M. J.; Kulkarni, S. M.; Chaudhari, R. V., Synthesis of p-aminophenol by catalytic hydrogenation of p-nitrophenol. Org. Process Res. Dev. 2003, 7, (2), 202-208.

6.

Rode, C. V.; Vaidya, M. J.; Jaganathan, R.; Chaudhari, R. V., Hydrogenation of nitrobenzene to p-aminophenol in a four-phase reactor: reaction kinetics and mass transfer effects. Chem. Eng. Sci. 2001, 56, (4), 1299-1304.

7.

An, Q.; Yu, M.; Zhang, Y.; Ma, W.; Guo, J.; Wang, C., Fe3O4@ Carbon microsphere supported Ag–Au bimetallic nanocrystals with the enhanced catalytic activity and selectivity for the reduction of nitroaromatic compounds. J. Phys. Chem. C 2012, 116, (42), 2243222440.

8.

Hu, Y.; Tao, K.; Wu, C.; Zhou, C.; Yin, H.; Zhou, S., Size-Controlled Synthesis of Highly Stable and Active Pd@ SiO2 Core–Shell Nanocatalysts for Hydrogenation of Nitrobenzene. J. Phys. Chem. C 2013, 117, (17), 8974-8982.


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9.

Saini, P.; Choudhary, V.; Vijayan, N.; Kotnala, R., Improved electromagnetic interference shielding response of poly (aniline)-coated fabrics containing dielectric and magnetic nanoparticles. J. Phys. Chem. C 2012, 116, (24), 13403-13412.

10. Zhang, X.; Goux, W. J.; Manohar, S. K., Synthesis of polyaniline nanofibers by “nanofiber seeding”. J. Am. Chem. Soc. 2004, 126, (14), 4502-4503. 11. Zhang, X.; Manohar, S. K., Narrow pore-diameter polypyrrole nanotubes. J. Am. Chem. Soc. 2005, 127, (41), 14156-14157. 12. Huang, J.; Virji, S.; Weiller, B. H.; Kaner, R. B., Polyaniline nanofibers: facile synthesis and chemical sensors. J. Am. Chem. Soc. 2003, 125, (2), 314-315. 13. Baba, A.; Knoll, W., Electrochemical growth of dendritic conducting polymer networks. Adv. Mater. 2003, 15, (12), 1015-1019. 14. Wu, D. C.; Xu, F.; Sun, B.; Fu, R. W.; He, H. K.; Matyjaszewski, K., Design and Preparation of Porous Polymers. Chem. Rev. 2012, 112, (7), 3959-4015. 15. Zhang, T.; Huang, X.; Asefa, T., Nanostructured polymers with high surface area using inorganic templates for the efficient extraction of anionic dyes from solutions. Chem. Commun. 2015, 51, (89), 16135-16138. 16. Tao, Y.; Li, J.; Xie, A.; Li, S.; Chen, P.; Ni, L.; Shen, Y., Supramolecular self-assembly of three-dimensional polyaniline and polypyrrole crystals. Chem. Commun. 2014, 50, (84), 12757-12760. 17. Kwon, Y. S.; Lim, J.; Yun, H.-J.; Kim, Y.-H.; Park, T., A diketopyrrolopyrrole-containing hole transporting conjugated polymer for use in efficient stable organic–inorganic hybrid solar cells based on a perovskite. Energy Environ. Sci. 2014, 7, (4), 1454-1460. 18. Vonlanthen, D.; Lazarev, P.; See, K. A.; Wudl, F.; Heeger, A. J., A Stable PolyanilineBenzoquinone-Hydroquinone Supercapacitor. Adv. Mater. 2014, 26, (30), 5095-5100. 19. Zhou, M.; Li, W.; Gu, T.; Wang, K.; Cheng, S.; Jiang, K., A sulfonated polyaniline with high density and high rate Na-storage performances as a flexible organic cathode for sodium ion batteries. Chem. Commun. 2015, 51, (76), 14354-14356. 20. Gupta, T. K.; Singh, B. P.; Mathur, R. B.; Dhakate, S. R., Multi-walled carbon nanotubegraphene-polyaniline multiphase nanocomposite with superior electromagnetic shielding effectiveness. Nanoscale 2014, 6, (2), 842-851.


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Page 20 of 23

21. Knopfmacher, O.; Hammock, M. L.; Appleton, A. L.; Schwartz, G.; Mei, J.; Lei, T.; Pei, J.; Bao, Z., Highly stable organic polymer field-effect transistor sensor for selective detection in the marine environment. Nat. Commun. 2014, 5. 22. Al-Mashat, L.; Shin, K.; Kalantar-Zadeh, K.; Plessis, J. D.; Han, S. H.; Kojima, R. W.; Kaner, R. B.; Li, D.; Gou, X.; Ippolito, S. J., Graphene/polyaniline nanocomposite for hydrogen sensing. J. Phys. Chem. C 2010, 114, (39), 16168-16173. 23. Lebedev, N.; Trammell, S. A.; Tsoi, S.; Spano, A.; Kim, J. H.; Xu, J.; Twigg, M. E.; Schnur, J. M., Increasing efficiency of photoelectronic conversion by encapsulation of photosynthetic reaction center proteins in arrayed carbon nanotube electrode. Langmuir 2008, !24, (16), 8871-8876. 24. Liu, J.; Song, K.; van Aken, P. A.; Maier, J.; Yu, Y., Self-Supported Li4Ti5O12–C Nanotube Arrays as High-Rate and Long-Life Anode Materials for Flexible Li-Ion Batteries. Nano Lett. 2014, 14, (5), 2597-2603. 25. Liu, Z.; Zhang, X.; Poyraz, S.; Surwade, S. P.; Manohar, S. K., Oxidative template for conducting polymer nanoclips. J. Am. Chem. Soc. 2010, 132, (38), 13158-13159. 26. Chen, Y.; Zhu, H.; Liu, Y., Preparation of activated rectangular polyaniline-based carbon tubes and their application in hydrogen adsorption. Int. J. Hydrogen Energy 2011, 36, (18), 11738-11745. 27. Xia, H.; Tao, X., In situ crystals as templates to fabricate rectangular shaped hollow polyaniline tubes and their application in drug release. J. Mater. Chem. 2011, 21, (8), 24632465. 28. Dong, H.; Prasad, S.; Nyame, V.; Jones, W. E., Sub-micrometer Conducting Polyaniline Tubes Prepared from Polymer Fiber Templates. Chem. Mater. 2004, 16, (3), 371-373. 29. Gao, Y.; Yao, S.; Gong, J.; Qu, L., Preparation of Polyaniline Nanotubes via “Thin Glass Tubes Template” Approach and its Gas Response. Macromol. Rapid Commun. 2007, 28, (3), 286-291. 30. Anilkumar, P.; Jayakannan, M., Divergent Nanostructures from Identical Ingredients: Unique Amphiphilic Micelle Template for Polyaniline Nanofibers, Tubes, Rods, and Spheres. Macromolecules 2008, 41, (20), 7706-7715. 31. Benjamin, I., Reaction Dynamics at Liquid Interfaces. Annu. Rev. Phys. Chem. 2015, 66, 165-188.


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32. Booth, S. G.; Dryfe, R. A. W., Assembly of Nanoscale Objects at the Liquid/Liquid Interface. The Journal of Physical Chemistry C 2015, 119, (41), 23295-23309. 33. Leunissen, M. E.; van Blaaderen, A.; Hollingsworth, A. D.; Sullivan, M. T.; Chaikin, P. M., Electrostatics at the oil–water interface, stability, and order in emulsions and colloids. Proceedings of the National Academy of Sciences 2007, 104, (8), 2585-2590. 34. Fang, P.-P.; Chen, S.; Deng, H.; Scanlon, M. D.; Gumy, F.; Lee, H. J.; Momotenko, D.; Amstutz, V.; Cortés-Salazar, F.; Pereira, C. M.; Yang, Z.; Girault, H. H., Conductive Gold Nanoparticle Mirrors at Liquid/Liquid Interfaces. ACS Nano 2013, 7, (10), 9241-9248. 35. Huang, J.; Kaner, R. B., A general chemical route to polyaniline nanofibers. J. Am. Chem. Soc. 2004, 126, (3), 851-855. 36. Li, W.; Zhang, Q.; Chen, D.; Li, L., Study on nanofibers of polyaniline via interfacial polymerization. J. Macromol. Sci. Part A Pure Appl. Chem. 2006, 43, (11), 1815-1824. 37. Yuan, R.; Wang, H.; Ji, T.; Mu, L.; Chen, L.; Zhu, Y.; Zhu, J., Superhydrophobic polyaniline hollow spheres with mesoporous brain-like convex-fold shell textures. J. Mater. Chem. A 2015, 3, (38), 19299-19303. 38. Zhu, Y.; Hu, D.; Wan, M.; Jiang, L.; Wei, Y., Conducting and superhydrophobic rambutanlike hollow spheres of polyaniline. Adv. Mater. 2007, 19, (16), 2092. 39. Trchová, M.; Šeděnková, I.; Konyushenko, E. N.; Stejskal, J.; Holler, P.; Ćirić-Marjanović, G., Evolution of Polyaniline Nanotubes: The Oxidation of Aniline in Water. J. Phys. Chem. B 2006, 110, (19), 9461-9468. 40. Ji, T.; Chen, L.; Schmitz, M.; Bao, F. S.; Zhu, J., Hierarchical macrotube/mesopore carbon decorated with mono-dispersed Ag nanoparticles as a highly active catalyst. Green Chem. 2015, 17, (4), 2515-2523. 41. Ji, T.; Chen, L.; Mu, L.; Yuan, R.; Knoblauch, M.; Bao, F. S.; Shi, Y.; Wang, H.; Zhu, J., Green processing of plant biomass into mesoporous carbon as catalyst support. Chem. Eng. J. 2016, 295, 301-308. 42. Khalili, N. R.; Campbell, M.; Sandi, G.; Golaś, J., Production of micro-and mesoporous activated carbon from paper mill sludge: I. Effect of zinc chloride activation. Carbon 2000, 38, (14), 1905-1915.


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43. Xu, K.; Lin, W.; Wu, J.; Peng, J.; Xing, Y.; Gao, S.; Ren, Y.; Chen, M., Construction and electronic properties of carbon nanotube hybrids with conjugated cubic silsesquioxane. New J. Chem. 2015, 39, (11), 8405-8415. 44. Ji, T.; Cao, W.; Chen, L.; Mu, L.; Wang, H.; Gong, X.; Lu, X.; Zhu, J., Confined molecular motion across liquid/liquid interfaces in a triphasic reaction towards free-standing conductive polymer tube arrays. J. Mater. Chem. A 2016, 4, (17), 6290-6294.


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Table of Content Molecular Transformation, Diffusion and Assembling into Threedimensional Freestanding Tube Arrays via a Triphasic Reaction Tuo Ji, Long Chen, Liwen Mu and Jiahua Zhu*

Freestanding polyaniline tube arrays are synthesized from nitrobenzene via integrated solid/liquid and liquid/liquid reaction interfaces.


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Molecular Transformation, Diffusion, and Assembling into Three

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