Synthesis and Mechanism of Spherical Ag-doped Polypyrrole Assisted by Complexing Agents

Highly dispersed Ag-doped Polypyrrole (PPy) spherical composites can be efficiently synthesized via oxidative polymerization of pyrrole with FeCl3 in an aqueous Ag+-containing solution in the presence of trisodium citrate, followed by concentrated ammonia treatment. However, the formation mechanisms involved in how to control the shape and how to get the metallic Ag0 need further investigation. In order to elucidate the formation mechanisms, the intermediates in different reaction stage were collected and investigated. Combining the experimental phenomenon and the structure characterization of the samples, it was found that citrate ions make a role of complexing Ag+ to produce [Ag3(C6H5O7)n+1]3n− complexes in the early reaction stage, then mainly play a role of steric stabilizer of AgCl micelles and are responsible for the shape tailoring of PPy composite as well as the reduction of Ag+ in the process of ammonia treatment. Evidently, negative-charged AgCl micelles become the main nucleation sites of pyrrole polymerization through the electrostatic attraction between the negative and positive ions. Concentrated ammonia is adopted to eliminate AgCl cores from the precursor of Ag-doped PPy composites obtained by chemical redox reaction and provides an accelerated reaction condition for reduction of Ag+ by reductants (citrate ion or pyrrole monomer). Ag-containing micelles induction method is a facial chemical method to obtain uniform Ag-doped composites and can be broadened to design other Ag-containing functional materials.


Introduction
Silver, one of the noble metals, owns excellent conductivity of heat and electricity, relatively low cost and fair stability in the ambient environment. In recent years, Ag nanostructures were widely investigated for their unique optical, electrical and chemical properties [1][2][3] in various fields including catalysts [4][5][6], optical devices [7], optoelectronic devices [8], Surface Enhanced Raman Scattering (SERS) [9], therapeutic agent, etc. [10][11][12][13]. Hence, Ag nanostructures with different shapes (eg. nanowires [14,15], nanospheres [15,16] and different sizes (eg. Nanometer [17], micrometer [14] were designed separately or composed with other materials. In most cases, Ag nanostructures are applied by incorporating with functional material to enhance some special properties of these materials [4, 5, 7-9, 12, 18-20]. For example, Ag@SiO 2 or Ag@ZnO 2 core-shell catalysts were prepared by reducing AgNO 3 impregnated on the surface of SiO 2 or ZnO powder and a good Diesel Particulate Matter (DPM) oxidation activity is obtained because of the presence of Ag 0 on the catalyst surfaces [4]. As an antibacterial agent, Ag@Bi 2 O 3 nanocomposites were prepared by chemically precipitating Ag species on the surface of Bi 2 O 3 nanospheres and displayed improved antibacterial ability in comparison with single component Bi 2 O 3 nanospheres [10]. TiO 2 is a popular functional material for its hydrophilic and depolluting properties. In order to improve TiO 2 photocatalytic activity, Ag-doped TiO 2 are also produced by impregnating to TiO 2 solid nanomaterials in AgNO 3 solution [20]. However, through impregnation or chemically deposition method, Ag species often tend to accumulate on the surface which a liquid can reach and is usually less in the interior of the materials, which is benefit to the interface reactions aimed on the surface of the materials.
In electrochemical application, Ag is also widely studied to dope the less-conductive active materials (MnO 2 [18,19], graphene [22], LiMn 2 O 4 [23], PPy [12,24,25,27,28] 1 3 to improve their electrochemical performance. In this case, the uniform distribution of Ag in the composite becomes very essential. Hence, in order to achieve the aim of uniform distribution of Ag in composite, different preparation methods and different preparation routes have been adopted [4,12,[15][16][17][18][19][20][21][22][23] and chemical synthesis method is considered to be a more effective and easier way to modify the morphology and performance of the materials [18,19,24,25,27,28]. Among of this, One-step in-situ synthesis of Ag-incorporated composite is very popular [12,18,19,22,23,[28][29][30]. Therefore, PPy@Ag shell-core nanostructures were prepared by one-step interfacial polymerization for a dopamine biosensor [29]. Spherical interlaced PPy/ PAA/Ag composites, in which Ag nanoparticles attach onto the granules of polymer, were synthesized by chemical polymerization technique for supercapacitor [25]. a hybrid of polypyrrole (PPy), silver amalgam (AgHg) and natural biomineralization hydroxyapatite (BioHAP) was designed for glucose detection [26]. Recently, we reported Ag-doped submicron materials (Ag-doped MnO 2 [18], Ag-PPy [12]) prepared by micelle-inducing chemical solution techniques. In our works, spherical structures are successfully synthesized and Ag species uniformly distribute in MnO 2 or PPy matrix, showing an improved electrochemical performance for supercapacitor. Pitifully, we didn't clearly elucidate the formation mechanism of spherical Ag-incorporated PPy or spherical Ag-doped MnO 2 except for reasonable reasoning in literatures [12,18]. Here, we synthesized spherical Ag-doped PPy composites via oxidative polymerization of pyrrole with FeCl 3 in an aqueous Ag + -containing solution assisted by trisodium citrate. The procedures of spherical Ag-doped PPy composites were studied in details and the formation mechanisms of spherical composites which included the role of all the materials and how to control spherical shape were also elucidated.

Experimental
Ag-incorporated PPy spherical composites were prepared by the same route recorded in reference [12]. Pyrrole (Py) monomer, silver nitrate (AgNO 3 ), trisodium citrate(C 6 H 5 Na 3 O 7 ⋅ H 2 O) and ferric trichloride (FeCl 3 ) were used as the starting materials. The synthesis procedure of Ag-incorporated PPy composites can be divided into the following three steps.
Step 1: 50 mL of a 0.07 mol L −1 trisodium citrate solution was dropped slowly into 200 mL of the colorless solution containing 0.015 mol pyrrole monomer and 0.0012 mol AgNO 3 at 0-2 °C and then stirred for 15 min. White color appears initially when the droplets of trisodium citrate solution touch the surface of the solution and then vanishes gradually. A milk-like solution was obtained finally after stirring; step2: 50 mL of 1.0 mol L −1 ferric chloride solution was added dropwise to trigger the polymerization of pyrrole. In order to adjust the growth of PPy chains, the feeding speed of ferric chloride solution was controlled very slowly. With the increase of the reaction time, the color of the solution changes from white to light green, dark green and finally black. The polymerization reaction was taken under constant stirring condition for approximately 10 h. After polymerization, the black solid particles were collected by filtering the solution and completely washed with deionized water. The collected black solid powder is the precursor of spherical Ag-doped composite (coded as Ag/PPy-1); Step 3: the collected solid particles (Ag/PPy-1) were put into aqueous concentrated ammonia solution and stirred for 10 min and then collected by filtration. This process was repeated twice and finally the solid residue was washed with deionized water or ethanol. The designed spherical Ag-incorporated PPy composite (codes as Ag/PPy-2) was obtained by filtering the residue followed by drying it in a vacuum oven at 80 °C for 12 h.
X-ray diffraction (XRD) analysis was performed on an X-ray diffractometer (PAN Alytical X'pert Pro, CuKα anode: λ = 1.54187 Å) to investigate the crystal structure of the samples. A scanning electron microscope (SEM, FEI NovaSEM × 30) and a transmission electron microscope (TEM Hitachi600) were used to examine the morphologies and structures of the samples. X-ray photoelectron spectroscopy (XPS VG ESCALAB 200i-XL) data were recorded with a Theta Probe electron spectrometer using A Kα (hν = 1484.6 eV) radiation. Spectral deconvolution was carried using a Gaussian-broadened Lorentzian curve-fitting program, and the binding energies were corrected by the C 1s line at 284.6 eV from adventitious carbon.

Results and Discussion
In the initial stage of the synthesis process, Ag + species are mixed with pyrrole. They can coexist together in reasonable short time because the weak oxidation ability to Pyrrole polymerization. Trisodium citrate is popular for the reduction and complexation for noble metal (eg. Ag or Au) [29,[31][32][33]. In step 1, when citrate ions is dropped into the Ag + -containing solution, white color appears because Ag 3 C 6 H 5 O 7 is formed according to the following reaction: Silver citrate is a white substance. It has a very limited solubility in water (the maximum concentration of silver ions in saturated solution of silver citrate in water is ca. 2.8 × 10 -3 mol L −1 [34]. According to the amounts of the starting materials, the actual concentration of Ag + in solution is 4.8 × 10 -3 mol L −1 , larger than the value of the maximum concentration of silver ions in a saturated aqueous solution. Hence, the precipitation of white Ag 3 C 6 H 5 O 7 will occur. However, no white solid appeared on the bottom of the reactor at the end of the step 1, indicating that the size of the obtained white powder is very small and reasonably stable in solution. It should thank to the existence of adequate citrate ions in reaction system. Compared to Ag ions (0.0012 mol), the number of citrate ions (0.0035 mol) which was afforded in solution is too adequate for the reaction (1). Hence, the surplus citrate ions will further react with silver citrate according to the following reaction [32]: The obtained [Ag 3 (C 6 H 5 O 7 ) n+1 ] 3n− complex ions are negative charged micelles, which are reasonably stable in solution. Till up to the step 1, the role of trisodium citrate should be the producer of negative-charged micelles, which can directionally induce the adsorption of cations (such as Fe 3+ , the oxidant for pyrrole polymerization) around the micelles. The overall reaction for reaction 1 and reaction 2 can be written as the following reaction: The reaction (3) is reversible, depending on the concentrations of the involved species. Even though the complexation of citrate ions with Ag ions is predominant in this stage, the redox reaction between Ag + and citrate ions may occur according to the following reaction 4: However, considering the mild reductive ability of citrate [33], this redox reaction rate is slow in present system and can be ignored in the initial synthesis stage. That is to say, at the end of the step 1, the reaction (3) is in a state of dynamically equilibrium in solution and C 6 H 5 O 7 3− ions mainly serve as steric stabilizer of Ag + -containing micelles.
In step 1, another reaction also exists in theory which is the reaction of the redox reaction of Ag + with pyrrole (reaction 5). However, the rate of this redox is also very low and the Ag-PPy nanoparticles was often obtained in condition of enough reaction time (several days [31], hence, reaction 5 can be disregarded in stage of step 1.
In step 2, a FeCl 3 solution was added dropwise to the system obtained by step 1, two kinds of reactions will occur in no doubt. As a strong oxidant, ferric ions will initiate the redox polymerization of pyrrole monomer as the following reaction: During Py polymerization, pyrrole initially loses one electron to be oxidized and then be followed by dimerization, aromation, oxidation of the dimer and finally realized the growth of PPy chains [30,35]. However, except for polymerization, the other reaction, almost simultaneously or even preferentially, is the reaction of chloride ions (Cl − ) with Ag + to produce AgCl when a droplet of FeCl 3 solution is dropped into the solution containing Ag + and pyrrole monomer (see reaction 7). With the increasing Cl − ions, AgCl will continue to combine with Cl − and become AgCl x+1 x− complexes (reaction 8).
AgCl is also an insoluble white substance. The maximum concentration of Ag + in a saturated solution of AgCl in water is ca. 1.3 × 10 -5 mol L −1 ( this value can further decrease when the water is substituted to other organic solvent) [16], much lower than that of Ag + concentration of Ag 3 C 6 H 5 O 7 saturated aqueous solution. Hence, when FeCl 3 is introduced into the solution obtained in step 1, evidently, the reverse reaction of reaction (3) will occur because of the competition of the reaction (7) and (8). In this case, the negative charged [AgCl x+1 ] x− complex and the negative charged [Ag 3 (C 6 H 5 O 7 ) n+1 ] 3n− complex coexist in the solution and they both have the ability of adsorbing positive charge Fe 3+ from the solution because of the electrostatic attraction of the negative and positive ions. Hence, the polymerization of Py will preferentially occur on the surfaces of negative charged complex micelles, which become the nucleation sites of PPy polymerization. In order to verify this speculation, the black solid product from step 2 was collected by filtration and washed completely with deionized water for several times until the filtrate was clear and colorless. The black solid powder (named PPy-Ag-1) was obtained after drying the washed residue in a vacuum oven.
The color of the obtained powder indicates that PPy was obtained successfully because only PPy is black among the possible products. The powder X-ray diffraction (XRD) patterns were applied to detect the crystal structure of the sample. The XRD patterns of PPy-Ag-1 shown in Fig. 1 7) preferentially take place in solution system and hence, negative charged [AgCl x+1 ] x− complexes surely become the main micelles for induction nucleation of PPy in step 2. From the XRD patterns, it is failure to distinguish the PPy structure because it is amorphous (the XRD patterns of PPy is also shown in Fig. 1 for comparison). In spite that Agincorporated PPy has been successfully produced [12], however, metallic Ag, which is supposed to be obtained through the reaction (4) and (5) in step 2, is not visible in PPy-Ag-1 sample according to the results of XRD tests.
XPS spectra were obtained in order to elucidate both the elemental components and chemical state of the elements of the samples. Figure 2a show the survey scan spectra of PPy-Ag-1 sample and pure PPy. New peaks at ca. 370 eV, attributing to Ag 3d binding energy, were observed significantly in PPy-Ag-1 spectrum, suggesting the present of Ag species in the sample. This result is in accordance with the XRD measurement. However, the high-resolution Ag 3d spectrum of PPy-Ag-1shown in Fig. 2b, indicates that the Ag 3d5/2 is at 368.25 eV while the Ag 3d3/2 is 374.25 eV, which is apparently corresponding to Ag 0 electronic state [12,17,36]. It is inconceivable that the information of Ag + is absent in XPS spectra. The contradiction between the XPS tests and the XRD tests can be considered from the difference between their individual detection mechanisms. The XPS test preferentially detects the element information from the thinner surface (2-10 nm) and the X-ray in XRD test can penetrate to the micron depth of the sample and catch the element information. Meanwhile, the detection limit of the XPS test (0.1-1 at. %) is much lower than that of the XRD test (~ 2%) [37,38]. If the hypothesis of micelle-inducing nucleation of PPy is correct, the insoluble AgCls must be covered by PPy and locate in the center of the PPy-Ag-1. Hence, the information of Ag + species is failure to be detected by XPS because of the long distance of AgCl to the surface of the sample. The loss of the Ag 0 species in XRD tests may be due to its low quantity in PPy-Ag-1, indicating that the reaction (4) and (5) take place at a very low reaction rate.
In order to verify the hypothesis of micelle-induction nucleation, PPy-Ag-1 sample as well as pure PPy (without AgNO 3 in solution) was obtained for comparison at the stage of step 2. Their morphologies were observed by Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and shown in Fig. 3. A bright spot in the center of the PPy-Ag-1 particle (Fig. 3c) can be clearly observed, suggesting that the obtained PPy-Ag-1 is a heterogeneous structure compared to pure PPy particles. The TEM image of PPy-Ag-1 furtherly confirms the core-shell structure of PPy-Ag-1. Obviously, the core of PPy-Ag-1 is AgCl nanograins which have been detected by the XRD tests. The morphology measurements of PPy-Ag-1 verify the function of micelle-induction for tailoring Intensity/(a.u.) However, the AgCl-containing PPy-Ag-1 is not the desired product. In order to get pure Ag-doped PPy composite, AgCl nanograins have to be eliminated from the PPy-Ag-1. In step 3, ammonia was applied to treat the PPy-Ag-1 powders for several times and then the residue was collected by filtration and washed completely with deionized water followed by drying in a vacuum condition. The obtained powder was coded as PPy-Ag-2. The XRD patterns of PPy-Ag-2 was collected and shown in Fig. 4. It is very interesting that several strong diffraction peaks which are completely different from that of AgCl appear at 2θ = 38.1 0 , 44.3 0 , 64.5 0 , and 77.3 0 , corresponding to the (111), (200), (220) and (311) planes of face-centered cubic structure of silver (JCPDS 04-0783) [11,14]. This result indicates that AgCl has been removed from the PPy-Ag-1 sample and a larger amount of Ag 0 is produced after treating PPy-Ag-1with concentrated ammonia. Figure 5 presents the images of the morphology of PPy-Ag-2. After treatment by concentrated ammonia, the spherical particles of PPy-Ag-1 remain spherical morphology (Fig. 5a) and the cores located in the powder disappear. The TEM image of the obtained PPy-Ag-2 spherical structure is hollow, evidently verifying that AgCl nanograins located in the center of the PPy-Ag-1 is successfully etched by ammonia. So, the following reaction is supposed to occur in the third step:

/degree
In strong basic solution of ammonia, AgCl will react with ammonia to produce water soluble [Ag(NH 3 ) 2 ] + complex and is dissolved into the water from the insoluble PPy matrix. Fig. 3 SEM images (a, c) and TEM images (b, d) of PPy (a, b) and PPy-Ag-1 (c, d) 20 30 Though the reaction (9) reasonably gives the elucidation of AgCl how to eliminate from the powder, another interesting phenomenon should not be ignored. Different from the PPy-Ag-1 sample, Ag 0 is obviously detected by XRD measurement, indicating that the larger number of Ag 0 is produced by ammonia treatment. The increase of Ag 0 in PPy-Ag composite is surely due to the reduction of Ag + ions which are incorporated in the composite matrix. Except for Ag reduction due to light irradiation or other unidentified factors, the Ag 3 C 6 H 5 O 7 is the species which can be firstly considered because it provides not only Ag + ions, but also C 6 H 5 O 7 3− , the reductant of Ag + . In fact, for PPy-Ag-1, Ag 3 C 6 H 5 O 7 is inevitably inlayed into the composite matrix for the complexion of C 6 H 5 O 7 3− with Ag + . As described before, citrate ion is a mild reductant for Ag + and in order to accelerate the reduction reaction, heat-treatment techniques are often applied [32,39]. This condition doesn't be afforded to realize the redox reaction in our study. However, it is reported that the rate of citrate reduction of Ag + depends on the pH value of the reaction and higher pH can promote the reductive ability of citrate [31]. Hence, the increase of Ag 0 in PPy-Ag composite after ammonia treatment may be due to the occurrence of the reaction (4) because the pH value of concentrated ammonia is very high. Based on the above discussion, concentrated ammonia plays two main roles in system. One function of ammonia is dissolving AgCl to remove the micelle template. The other is accelerating the citrate reduction of Ag + . As for citrate ions, they play roles of Ag + reservoir in the form of [Ag 3 (C 6 H 5 O 7 ) n+1 ] 3n− as well as the reductant of Ag + . Except for this, they are also responsible for the spherical structure of PPy-Ag composite [12]. The function of citrate will be elucidated in more details in the following study.
In order to further explore the function of citrate in spherical Ag-incorporated PPy composite, Ag-doped PPy particles were prepared in solution without citrate ions for comparison. The solid powders without treated by ammonia are collected and named as PPy-Ag-1'. PPy-Ag-2' represents the product washed by ammonia. The TEM image of PPy-Ag-1' shown in Fig. 6a clearly reveals that the AgCl cores exist in the obtained samples and the hollows are left in PPy-Ag-2' powder ( Fig. 6b) after treating the sample PPy-Ag-1' with concentrated ammonia, indicating the evident induction nucleation of AgCl micelles for Py polymerization in the condition of the absence of citrate ions. Unfortunately, in the absence of citrate ions, the obtained PPy-Ag-1' grains aggregate together and the shape of the powder is not a single sphere. Moreover, there often exists more than one AgCl nucleus in the large PPy-Ag powder, suggesting the weak steric affection of AgCl micelles. The single spherical composite obtained from the system containing citrate ions indicates that citrate ions improve the effect of steric stabilization of AgCl micelles and the shape of the product can be tailored by changing the molar ratio of Ag + to citrate ion [12].
The XRD patterns of PPy-Ag-1' and PPy-Ag-2' which are obtained in the solution without citrate ions are recorded and shown in Fig. 7. The result is the same to that of samples obtained from the solution containing citrate ions. Before washed by ammonia, the sample named PPy-Ag-1' contains AgCl and has no visible metallic Ag 0 . After treated by concentrated ammonia, Ag 0 is visible in PPy-Ag-2' sample, indicating that a base intensifies the reduction reaction of Ag + to produce Ag 0 , which should correspond to the reaction (5). That is to say, there are some amounts of invisible Ag + and unoxidized Pyrrole in the PPy-Ag-1 ' matrix and the inlayed Ag + species will react with pyrrole monomer to produce Ag 0 in high pH condition. The reaction (5) may also exist in process of PPy-Ag-2 preparation.
The XPS Ag 3d spectra of Ag-doped PPy composite prepared in absence of citrate ions is compared to that of Agdoped PPy composite obtained in condition of containing citrate ions. As shown in Fig. 8, there is no obvious difference between them, indicating that Ag-doped PPy composite can be successfully synthesized whether the citrate ions exist or not. Even though this, the Ag content of PPy-Ag-2, synthesize from the solution containing citrate ions is 0.93 at. %, is higher than that of PPy-Ag-2'(0.73 at.%) obtained from the solution in absence of citrate ions. The increase of Ag content in sample reveals that citrate ion can more efficiently lock Ag + into solid PPy matrix because of the formation of Ag 3 C 6 H 5 O 7 micelle in solution. Hence, the reaction (4) and (5) are both responsible for the increase of the amount of Ag 0 in PPy-Ag-2.
According to the above process analysis, the formation of spherical Ag-doped polypyrrole via oxidative polymerization of pyrrole with FeCl 3 in an aqueous Ag + -containing solution in the presence of trisodium citrate are clear. As Ag + complexing agent, C 6 H 5 O 7 3− species complex Ag + and form soluble Ag complexes (the reaction 1 and 2). The reversible equilibrium of the reaction 3 will adjust the free Ag + concentration in solution. The reduction of Ag + by C 6 H 5 O 7 3− species is slow but can occur at reasonable condition. When FeCl 3 species add to the solution, the redox polymerization of pyrrole monomer occurs quickly for the strong oxidation of Fe 3+ ions (the reaction 6). Meanwhile, chloride ions (Cl − ) from FeCl 3 will react with free Ag + to produce AgCl ( the reaction 7) and make the reversible reaction of the reaction 3 occur. With the increase of FeCl 3 in solution, pyrrole monomer continues to be oxidized to form PPy and AgCl will continue combine with the increasing Cl − ions and become negative charged AgCl x+1 x− micelles (the reaction 8). The negative charged AgCl micelles will play the active sites of PPy crystallization growth and make the PPy spherical. When the size of AgCl is enough large, it can be clearly detected (Fig. 6). Sometimes, it is invisible for its too small size [12]. The complexion of C 6 H 5 O 7 3− species with Ag + can adjust the amount of free Ag + in solution as well as the particle dispersion of PPy (Fig. 3). With the increase of reaction time, Ag + combined with C 6 H 5 O 7 3− will dissolute and be combined with Cl − for the stronger complexing ability of Cl − compared to C 6 H 5 O 7 3− . A dynamic balance will occur. Hence, insoluble AgCl and Ag 3 C 6 H 5 O 7 are expected to coexist in PPy matrix. It is normal the AgCl can be detected in water-washed PPy sample ( Fig. 4 and Fig. 7). In order to 10  remove the AgCl or Ag 3 C 6 H 5 O 7 , ammonia was used to wash the obtained sample. It is obvious that the black cores in spherical sample disappear because of the reaction 9. During the reaction, a portion of Ag + will transferred to metallic Ag due to light irradiation or other unidentified factors. Agdoped PPy or MnO 2 have been successfully obtained [12,18]. However, when C 6 H 5 O 7 3− species are used to complex Ag + , the content of Ag in PPy is little higher than that of no C 6 H 5 O 7 3− species. It may be the reason that Ag 3 C 6 H 5 O 7 nanoparticle coexist in PPy matrix and the improved reduction ability of C 6 H 5 O 7 3− species make more Ag + reduce to Ag 0 in alkali condition. The whole formation mechanism of spherical Ag-doped PPy assisted by complexing agents can be illustrated by the flow chart shown in Fig. 9. When all the starting material including citrate ions are mixed together, negative charged [Ag 3 (C 6 H 5 O 7 ) n+1 ] 3n− complexes are produced and became the active site of PPy nucleation. Once FeCl 3 is added, FeCl 3 will quickly oxidize Py to form PPy and produce AgCl and negative charged AgCl x+1 x− micelles which also induce the nucleation of PPy. Both negative charged micelles make an important role of single spherical PPy formation and the inlayer of Ag + in PPy matrix. Strong base ammonia takes part in the removing of insoluble AgCl particles and produce a basic condition for the reduction of Ag + by C 6 H 5 O 7 3− species. As a result, uniform Ag-doped single spherical PPy particles are formed.

Conclusions
Spherical Ag-doped PPy composites were synthesized firstly using chemical redox reaction in solution containing pyrrole monomer, AgNO 3 , trisodium citrate and FeCl 3 and then treating the solid product with ammonia. In order to elucidate the formation mechanisms of Ag doping and spherical shape of PPy, the intermediates in different reaction stage were collected and characterized with XRD measurement, SEM and TEM microscopy and XPS scanning spectrum. The experimental phenomenon and the physical characterization of the samples collected in different reaction stage indicate that citrate ions make a role of complexing Ag + to produce [Ag 3 (C 6 H 5 O 7 ) n+1 ] 3n− complexes in the initial reaction stage, then [Ag 3 (C 6 H 5 O 7 ) n+1 ] 3n− complexes act as a reservoir of Ag + . In the following reaction stage, citrate ions also play a role of a steric stabilizer of AgCl micelles in whole reaction and are responsible for the shape tailoring of PPy composites as well as the reduction of Ag + . Evidently, negative-charged AgCl micelles induce nucleation of pyrrole polymerization through electrostatic attraction of the negative and positive ions and become the core of spherical Agdoped PPy composites. Concentrated ammonia efficiently eliminates AgCl micelles from the solid residue obtained from chemical redox reaction and provides an accelerated reaction condition for reduction of Ag + by reductants (citrate ion or pyrrole monomer). Ag-containing micelles induction method is a facial chemical method to obtain uniform Agdoped composites and can be broadened to design other Agcontaining functional materials.
Funding This study was funded by authors themselves.