Template assisted synthesis and assembly of nanoparticles 3

Chapter Chapter PANi/Ag2S nanocomposites Silver sulfide Ag2S is a compound semiconductor of great interest due to its intrinsic properties with a narrow band gap and good chemical stability. It has already been used for manufacturing optical and electronic devices, such as photovoltaic cells, photo conductors, IR detectors, and ion selective electrodes (ISE).1, Ag2S was also reported to be used as a superionic conductor.3 In this study, we are interested in using in-situ decomposition of precursor to prepare Ag2S nanoparticles in polymer matrix for ISE application. In order to avoid aggregation, nanocomposites constituting the nanoparticles homogeneously distributed in a suitable matrix are commonly prepared for practical applications. In the literature, Ag2S nanocomposites have been reported within some polymeric matrices. For example, Kumar et al successfully synthesized Ag2S nanoparticles in polyvinyl alcohol (PVA)4, while Akamatsu and co-workers prepared Ag2S/nylon 11 composite film by using a thermal relaxation technique.5 Qian et al prepared Ag2S/PVP nanocomposite using an in-situ reaction with CS2 as the sulfide source at room temperature and ambient pressure.6 Ag2S nanoparticles with uniform size distribution have also been prepared within Nafion7 membrane and polyacrylamide8. In this Chapter, we have chosen to use polyaniline (PANi) emeraldine salt as the matrix. PANi is a conjugative polymer that has attracted considerable attention due to its simple synthesis, good environmental stability, and adequate level of electrical 79 Chapter conductivity. There are two kinds of structures within the backbone of PANi: quinonoid ring and benzenoid ring (as shown in Figure 3.1). The electronic properties of PANi can be reversibly controlled changing the ratio of these two structures. Thus, PANi will serve as a conducting matrix when the PANi/Ag2S nanocomposite film is used as ISE. As summarized in Chapter 1, there are several approaches to synthesize nanocomposites. Our approach is based on the use of a molecular precursor, MTB (M = Ag, Pb, Cd), which has been well-established in our research group to decompose at room temperature or under mild conditions to form metal sulfide nanoparticles.9 We have already established the interplay between activating agent (e.g. amine) and stabilizing agent (e.g. TOPO) in controlling the size and shape of these metal sulfide nanoparticles10. By adapting this synthesis route for the preparation of nanocomposites, we could achieve two main advantages. Firstly, by using a molecular precursor, we eliminate the problem associated with different solubilities of the two starting salts as well as the matrix. Secondly, since the molecular precursor can mix well in the matrix and the nanoparticles are formed in situ, we eliminate the use of surfactant and also the need for subsequent transfer of nanoparticles into the polymer matrix. This is particularly useful as the left-over surfactant has been found to affect charge transfer of the prepared composites.11, 12 The major problems of differential diffusion and inhomogenity encountered in most of the reported preparation are thus overcome in our approach. As reported, amine also acted as a capping agent in this precursor decomposition. Thus it is expected that the –NH– in benzenoid rings of PANi can serve as the 80 Chapter capping agent for the nanoparticles formation. The capping function is through the interactions between N atoms in the benzenoid ring and metal atoms in Ag2S nanoparticles. Thus, when AgTB were decomposed at room temperature in the PANi solution, the morphology and size distribution of the nanoparticles formed are expected to be affected by the relative amount of reagents present. Thus, in Section 3.1, we will first characterize the nanocomposites formed with varying amount of reagents. We will then investigate in Section 3.2 resultant changes in PANi, particularly the –N= and –NH– functional groups, when Ag2S nanoparticles are formed. Finally, the applications of these nanocomposites as ISE are studied in Section 3.3. 3.1 Synthesis and Characterization of PANi/Ag2S nanocomposites The synthetic procedure of PANi/Ag2S nanocomposites is shown schematically in Figure 3.1, with the details already described in Section 2.4.2. PANi/NMP H N N Benzenoid ring AgTB precursor N N Quinonoid ring H Propylamine 2hours, RT PANi/Ag2S nanocomposites Figure 3.1. Schematic diagram showing the synthesis procedure of PANi/Ag2S nanocomposites (including the structure of PANi). 81 Chapter PANi and the AgTB precursor were prepared following the procedures detailed in Section 2.3 and 2.4. Gel Permeation Chromatography (GPC) measurement was used to characterize the molecular weight and polydispersity of PANi prepared. The average molecular weight (Mw) of PANi dissolved in N-methylpyrrolidinone (NMP) was determined to be 50,900 with polydispersity index (PDI) = 1.33. A series of homogeneous PANi/Ag2S nanocomposites were prepared at room temperature by varying the relative amount of PANi and AgTB. The feed amounts of the various reagents for Samples to in increasing Ag weight percentage are stated in Table 2.1 of Chapter 2. Typically, the concentration of PANi in NMP was fixed at 0.01 mol L-1 while the amount of AgTB added was varied to achieve the desired molar ratios of AgTB : PANi. The number of moles of propylamine used was kept similar to AgTB. All Ag2S nanoparticles were formed in situ within PANi matrix and these as-prepared nanocomposites were characterized without further size selection and purification. Sample Sample Ag2S 14-0072 20 30 40 50 60 2θ Figure 3.2. Representative XRD patterns of PANi/Ag2S nanocomposites (shown here for Samples and 4) compared with Ag2S standard pattern obtained from the database. Figure 3.2 showed the representative XRD pattern of the as-synthesized 82 Chapter PANi/Ag2S nanocomposites. All the diffraction peaks corresponded to the diffraction planes of the monoclinic Ag2S phase (JCPDS 14-0072 Acanthite), which confirmed the formation of Ag2S nanoparticles inside polyaniline. Representative TEM and HRTEM images of the PANi/Ag2S nanocomposites are shown in Figure 3.3. In this sample, the silver sulfide nanoparticles (black spots) were uniform and spherical, with an average particle diameter 6.1 ± 2.0 nm. There was no aggregation of the Ag2S particles, which confirmed the capping function of PANi as we proposed. In addition, we found that Ag2S nanoparticles were located mainly within the polymeric regions (grey part), which suggested good interaction between PANi matrix and the silver sulfide nanoparticles. The interaction between silver sulfide nanoparticles and PANi matrix will be further discussed in the next section. The HRTEM image showed clear lattice fringes with 2.82Å spacing, corresponding to the ( 12) plane crystal lattice of Ag2S particles. 10nm Figure 3.3. Representative TEM and HRTEM images of the PANi/Ag2S nanocomposites (Sample 1). Figure 3.4 showed the TEM images of PANi/Ag2S prepared using different AgTB 83 Chapter feed ratio, with the size distribution of the Ag2S nanoparticles depicted with histograms respectively It is noted that when [PANi]/[AgTB] ratio approached 1:3 and above, the aggregation of Ag2S particles became severe. For the smaller size and dispersed samples, our preparation gives a reasonable improvement in terms of uniformity compared to Ag2S particles synthesized within polyvinylpyrrolidone (particles diameter: 8-10 nm,6 elliptical or Y-shape particles ~200×400 nm13), polyvinyl alcohol (particles ~25 nm by sonochemical irradiation4, large particles 80120 nm by hydrothermal14) and biopolymer-sago starch (two main size-classes of 9.5 ± 3.6 and 27.2 ± 9.8 nm)15. Indeed, the size distribution of our prepared Ag2S nanoparticles in PANi (refer to Table 3.1: 6.1 ± 2.0 nm and 5.7 ± 1.2 nm) is comparable to those Ag2S particles reported in the literatures: Ag2S formed within polyacrylamide (size controlled from 43.8 ± 1.7 to 81.4 ± 14.8 nm)8, prepared by micro-heating in Nylon 11 (4.8 ± 1.3 nm)5 and in Nafion membrane film (10.5 ± 2.2 nm)7. Using the Debye-Scherrer equation16, D=kλ/(βcosθ), the sizes of Ag2S particles could also be estimated from XRD (Figure 3.2). The average diameters deduced from both XRD and TEM results are thus compared in Table 3.1. Generally, the sizes of Ag2S particles increase with an increase in the amount of Ag precursor used in the synthesis. Histograms were plot on the basis of counting more than 100 particles in corresponding TEM images. 84 Chapter a Fraction % 20 10 0 b 10 15 20 25 15 20 25 30 35 25 30 35 Diameter nm 30 35 Fraction % 30 15 0 10 Diameter nm c Fraction % 40 20 0 10 15 20 Diameter nm 85 Chapter b d 12 Fraction% 0 10 15 20 25 30 35 40 Diameter nm Figure 3.4. TEM images and histograms showing the size distribution of PANi/Ag2S nanocomposites prepared with different AgTB feed ratio, (a) Sample 1, (b) Sample 2, (c) Sample 3, and (d) Sample 4. (Refer to Table 3.1 for sample details). Table 3.1. Silver content expected from feed ratios compared to those obtained from EA and TGA, together with the average diameter of silver sulfide nanoparticles in PANi matrix estimated from XRD and TEM analysis. Average particle Expected Ag Ag content from Ag content from diameter (nm) content from # EA (wt %) TGA (wt %) feed ratio (wt %) XRD TEM Sample 25% 27.61 34.8 ~9 6.1±2.0 Sample 32% 33.42 34.2 ~9 5.7±1.2 Sample 35% 39.56 47.0 ~11 7-12* Sample 38% 42.42 57.2 ~23 6-28* # Ag content is calculated from the residual weight% at 600°C (see text on page 87-88). * Figure 3.4 showed the polydispersity of Ag2S particle size in Samples and 4. Table 3.1 also showed the expected, EA and TGA experimental results for the silver content in PANi/Ag2S nanocomposites. The EA results, however, suggested a silver content that is higher than expected from the feed ratio. During the centrifugation and purification steps, we found that the discarded washings and supernatants after centrifugation were blue in color, which indicates the loss of PANi in final composites. Thus, higher Ag content in EA is observed as a result of the good solubility of PANi in NMP TGA analyses were performed to further confirm the loading percentage of 86 Chapter nanoparticles in the PANi/Ag2S nanocomposites. Figure 3.5 showed the TGA curves of PANi, AgTB and PANi/Ag2S nanocomposites for comparison. The AgTB precursor was found to decompose quite neatly at 200°C, giving a remaining weight of 52.7%. This remaining weight corresponded well with Ag2S% in the molecular precursor (expected: 50.6%), and was found to be stable between temperatures of 300°C to 600°C. Continual heating to 1000°C under N2 gave a residue that has a shiny metallic color, which suggests silver sulfide was partially decomposed to silver metal. Sample Sample Sample Sample PANi AgTB 100 80 Wt% 65% 60 54% 52.7% 40% 39.3% 40 20 0% 0 200 400 600 800 1000 o Temperature C Figure 3.5. TGA curves of PANi, AgTB and PANi/Ag2S nanocomposites prepared with different AgTB feed ratios. For the PANi sample, TGA showed an initial ~ 5% weight loss at ~ 100°C due to moisture trapped in the sample. A gradual weight loss is further observed between 100°C to 300°C (13%), probably due to the removal of trapped NMP solvent. Similar weight loss (4%-8%) is also observed in most of the PANi/Ag2S samples prepared from NMP. Finally, the PANi sample was found to completely decompose with no 87 Chapter residue left at ~550°C. Comparing with the stability observed between 300°C and 600°C for AgTB, it is thus reasonable for us to assign the residual weight% at 600°C in the PANi/Ag2S samples to the embedded Ag2S nanoparticles. Hence, the silver content was worked out as such for these samples as shown in Table 3.1. These values tend to be higher estimates compared with the value expected from feed ratio, as some small amounts of PANi which is interacted with Ag2S nanoparticles may be left at 600°C. Comparing the various PANi/Ag2S decomposition curves, we found that the decomposition onset temperatures of nanocomposites were moving to the right (i.e. higher temperature) generally with an increase in the Ag content. This suggests that there are probably some interactions between the Ag2S particles and PANi. We will investigate the effects of Ag2S particles formation on the backbone of PANi by XPS, UV-vis and other spectroscopic methods in the next section. 3.2 Effects of Ag2S nanoparticles formation in PANi matrix In order to further understand the chemical environment of silver sulfide in PANi matrix, XPS analysis was performed on all the samples. The C 1s, N 1s, S 2p, Ag 3d XPS peaks were shown in Figures 3.6-3.9. The wide scan spectra are presented in Appendix 1A while details of numerical fitted peak areas are given in Appendix 1B. The FWHM of all XPS peaks are restrained within 1.2 to 1.8 during peak fitting. Figure 3.6 showed the C 1s XPS peaks of PANi and PANi/Ag2S nanocomposites. Similar to the pristine PANi, the C 1s profile for most of the PANi/Ag2S samples can be fitted with two components except Sample 4. The component located at 284.7 eV 88 Chapter literature, however, on the study of polymer/Ag2S nanocomposite as solid-state ISE. In this case, our synthesized PANi/Ag2S nanocomposites were used as silver ISE, with the Ag2S nanoparticles acting as ion recognition sites and PANi working as the solid contact. Spin-coating was used to prepare a homogeneous nanocomposite film onto ITO electrodes (details in Chapter 2). The spin-coated film thickness could be determined from AFM topography on scratches purposely performed on the film surface using tweezers. Representative AFM images with section analysis are presented in Appendix 1C. In most of the following investigation, Sample was used to prepare the ISE films from NMP solution. For testing the ISE films on the effect of silver percentage in composites film, Samples 2, and were utilized also. SEM was used to characterization the morphology of the PANi/Ag2S composites film. Figure 3.13a shows a typical SEM image of PANi/Ag2S film which was deposited onto ITO glass. It is clear that the silver sulfide nanoparticles were well dispersed in the PANi matrix. However, compared with TEM results, the particle sizes were much bigger and size distribution of Ag2S was much broader. This may be caused by the casting procedure, as some Ag2S particles will self-aggregate due to the surface tension of particles. In order to verify the durability of such ISE films, used composite films were washed and soaked in distilled water to deplete away the trapped Ag ions (detailed procedure in Section 2.4.3). Repeat SEM analysis (Figure 3.13b) suggested that though some big particles formed (200-500 nm), there is no significant change in the average sizes of particles. Those big particles observed in used film are formed by the precipitation of excess silver ions with chloride ions (trapped during the PANi polymerization). Such precipitation is often observed in 102 Chapter Ag/AgCl electrode in high silver concentration and should not affect the performance of ISE. b a Figure 3.13. Representative SEM image of PANi/Ag2S nanocomposites film deposited on ITO (a) original electrode, (b) used electrode. When the PANi/Ag2S nanocomposite films are used as ISE, silver ions pass through between the test solution and the film, the distribution of silver ions between the two phases thus develops a potential which is dependent on the silver ion concentration in the sample solutions. The experimental cell can be represented as: ITO | PANi/Ag2S nanocomposites film electrode | test solution (0.1M KNO3(aq)) | Ag/AgCl reference electrode The potential of the above cell is given by E = C + 2.303 RT log α Ag + F (1.1) where the cell constant “C” can be taken as the sum of the potentials at the PANi/Ag2S nanocomposite electrode, the Ag/AgCl reference electrode, the liquidjunction potential between the test solution and the reference electrode, and the potential across the membrane when the silver ion activity in the test solution is unity. 103 Chapter Since the measurements were carried out at a constant ionic strength of 0.1M, the junction potential was kept approximately constant. Neglecting the junction potential, and introducing standard potentials E0Ag+, Ag = 0.7991 volt, EAg/AgCl = 0.222 volt at 25oC, and 0.76 as the activity coefficient of Ag+ ion, Eq. (1.1) becomes E = 0.5771 + 0.05916 log[ Ag + ] (1.2) and the theoretical cell constant is calculated to be 0.5771 volt using the activity scale. The equilibrium potential response of PANi/Ag2S ISE vs. the standard Ag/AgCl reference electrode at different silver ion concentration is demonstrated in Figure 3.14. It is clearly shown that as the equilibrium concentration of silver ion increases, the measured potential increases linearly over a range of Ag+ ion concentrations from 10-1 to 10-8 mol/L. A slope of 63.3 mV per log [Ag+] unit and y-intercept of 579.7 mV were obtained. These values are in close agreement with those predicted by the Nernst relationship (0.5771 volt as given above). Previous study has shown that deviations from Nernstian behavior will occur if processes like diffusion or chemical reactions take place in the electrode membrane during measurement.49 It is therefore reasonable to attribute our observed slight deviation to diffusion of the chemisorbed or complexed silver sulfide nanoparticles within the PANi matrix. Controlled experiments using pure PANi film as the working electrode recorded no potential response, and thus confirmed that the potential change is due to Ag2S nanoparticles in the PANi/Ag2S nanocomposites film. The detection limit of PANi/Ag2S ISE was found to be ~10-8 mol/L, which is comparable to other reported silver ion ISEs. Since the detection limit is predominantly determined by the solubility of silver sulfide, this detection limit indicated good mobility of silver ions 104 Chapter in the matrix. 500 Potential mV 400 300 200 Detection limit 100 -log[Ag+] 10 12 14 Figure 3.14. Measured potential of PANi/Ag2S nanocomposite film coated onto ITO vs. the standard Ag/AgCl reference electrode at varying silver ion concentration (Film thickness = 240 nm). For ISE application, usability test, effect of electrode film thickness, effect of initial silver loading percentage, working pH range and interfering ion test are required to evaluate its performance. In following paragraphs, we investigated these parameters one by one. Reusability test First, we measured the potential response (increase) of the used PANi/Ag2S film when small increment of Ag+ ions was added. In this case, 20 µL Ag+ solution ([Ag+] = 3.7012 × 10-8 mol/L) was added at each step into the cell containing 100 mL 0.1 mol/L KNO3 solution as electrolyte under slow stirring. Figure 3.15 showed the response and reusability of two PANi/Ag2S electrodes with different film thickness. It is clear from the plots that good linear response could be obtained from the new as 105 Chapter well as the re-used films. The slope of the linear graphs, however, was decreasing with the number of times of re-use and is particularly significant for the film with thinner coating. This observation seems to indicate that ion recognizing sites in these nanocomposite films could not be fully recovered by washing and soaking in distilled water. However, this won’t affect the performance of PANi/Ag2S ISE because good linearity still can be obtained. 4.0 first time second time third time fourth time a 3.5 3.0 ΔV/mV 2.5 2.0 1.5 1.0 0.5 0.0 4.0 b 3.5 3.0 ΔV/mV 12 16 + -11 [Ag ]x10 mol/L 20 24 28 first time second time third time fourth time fifth time 2.5 2.0 1.5 1.0 0.5 0.0 10 15 11 + [Ag ] x10- mol/L 20 25 Figure 3.15. Measured change in potential at increasing silver ion concentration (Film thickness: a = 240 nm, b = 74 nm). 106 Chapter Effect of PANi/Ag2S film thickness Figure 3.16 compared further the potential responses at sequential increments of Ag+ ions (same conditions mentioned above) using ISEs of different film thickness. It is found that the thickness of the film affects the detection sensitivity insignificantly, a decrease in the potential change is observed as the thickness of the film increased from 74 nm to 125 nm. Such a decrease is due to a reduction in the diffusion and exchange rate of silver ion in the thicker composite films (geometrical effect). It is noted that the potential response didn’t reduce as much when the film thickness was further increased from 125 nm to 240 nm. This seems to suggest that when the thickness of film is bigger than 125 nm, ion exchange has reached the diffusionlimited regime for films of this thickness and the diffusion and exchange rate is independent of film thickness. Generally it can be concluded that there is no intrinsic material properties change with different film thicknesses. 4.0 65nm 74nm 125nm 208nm 240nm 3.5 ΔV/mV 3.0 2.5 2.0 1.5 1.0 0.5 0.0 12 + 16 -11 [Ag ] x10 mol/L 20 24 28 Figure 3.16. Measured change in potential at increasing silver ion concentration using PANi/Ag2S films with different thickness. 107 Chapter Effect of initial silver loading content In the literature, some studies have showed that the concentration of primary ion will affect the shape of potential response curve due to the release of primary ions from ISE membrane to solution.58-60 We have thus repeated the above analysis by preparing ISE films from samples with different silver loading content (i.e. Samples 1, and 4). Figure 3.17 showed that there is not much change in the linear response of our measured potential. This steady increase of potential responses regardless of silver loading content suggested that there is no significant release of silver ions from the PANi/Ag2S composite films. In conclusion, the potential response has nothing to with the Ag2S loading percentage and Ag2S nanoparticles size. Sample Sample Sample 2.5 ΔV/mV 2.0 1.5 1.0 0.5 0.0 10 12 14 16 18 20 22 + -11 [Ag ] x10 mol/L Figure 3.17. Measured change in potential at increasing silver ion concentration using PANi/Ag2S films with different silver loading content. Working pH range The influence of pH value of the test solution was also examined. In Figure 3.18, the equilibrium potential measured over the pH range of 2.5 to 10 (adjusted by the 108 Chapter addition of nitric acid or sodium hydroxide solution) is presented. The potential was found to vary much less from pH to 8, hence this range may be taken as the functional (or effective) pH range of the ISE. Interestingly, we noted that the potential increases almost linearly as the pH value decreased gradually in the acidic environment. This increase indicates that PANi/Ag2S membrane not only responded to silver ions, but also towards hydrogen ions in this pH range. This implied that the PANi/Ag2S nanocomposite electrodes can also be used to detect hydrogen ions in principle, although further investigation on the selectivity towards hydrogen ions is of course needed. 250 480 460 200 440 150 400 Potential mV Potential mV 420 380 360 340 100 50 320 300 280 -50 2.5 3.0 3.5 4.0 4.5 pH 5.0 5.5 6.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 pH Figure 3.18. Effect of pH value to the measured potential. Effect of interfering ion The selectivity of PANi/Ag2S ISE for Ag+ with respect to interfering ions such as Hg2+ was determined by a mixed solution method, i.e. the fixed interference method (FIM).61 The background concentrations of interfering ion was 5×10-4 mol/L using Hg(NO3)2 and the pH value of the solution was about 5.3. As showed in Figure 3.19, 109 Chapter Hg2+ ion gives a rather severe interference to the selectivity towards silver ions. This have been attributed to the comparable size and similar chemical characteristics between Hg2+ ion and Ag+ ion, as well as the strong affinity of Hg2+ towards the nitrogen atoms.62, 63 The results are similar to conventional ISE based on the calixarene derivatives and crown ether neutral carriers containing soft donor atoms, such as N and S atoms.64 Thus, there is no benefits of our PANi/Ag2S ISE in working with the existence of interfering Hg+ ions and further investigations are needed to improve the selectivity. 0.14 0.12 ΔV/mV 0.10 0.08 0.06 0.04 0.02 + -11 [Ag ]x10 10 12 14 16 mol/L Figure 3.19. Potential responses of the prepared PANi/Ag2S ISE in the presence of Hg2+ interfering ions. In summary, Table 3.5 presents a comparison of data obtained for this PANi/Ag2S ISE with commercial ISEs. We found that the sensitivity of our PANi/Ag2S electrode with excellent reusability is comparable to those quoted for the commercial ISEs. The detecting limit is ~10-8 mol/L while the working pH range is 5-8. The film thickness and Ag2S loading percentage not affect the potential response to silver ions, which make this PANi/Ag2S ISE easily prepared and used. The response time of the 110 Chapter PANi/Ag2S electrode, however, is longer than the commercial electrodes especially when silver ion concentration of testing sample is high. This is probably due to the difficulty of reaching equilibrium for silver ion exchange and diffusion within PANi/Ag2S nanocomposites films. Table 3.5. Comparison with reported silver ion selective electrode. PANi/Ag2S film electrode Detecting limit Linear Range Slope pH Range ~10-8 mol/L 0.1~10-7 mol/L 63.3 mV 5-8 Commercial Silver ISE Van London-pHoenix65 Italy Hanna Model# AGS1502 10-8 mol/L 10-8 mol/L -7 0.1~10 mol/L 1~10-7 mol/L ~56 mV 57 ± mV 2-8 2-8 3.4 Conclusions In conclusion, PANi/Ag2S nanocomposites have been successfully synthesized by in situ decomposition of the AgTB precursor in polymer matrix. We have found that, as long as the loading percentage of silver precursor not exceed times of PANi, monodispersed silver sulfide nanoparticles in PANi can be obtained. PANi was found not only to serve as a capping agent, but the quinonoid ring in the polymer structure also play a donor role in the decomposition of silver precursor. XPS, UV/visible absorption and FTIR results confirmed that quinonoid moieties of PANi emeraldine base has been reduced companying with the decomposition of AgTB and the formation of silver sulfide nanoparticles within the PANi matrix. 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Van London-pHoenix Company http://www.vl-pc.com/, Houston, Texas, 77081 Tel: (800) 522-7920. 117 [...]... with an area ratio of 2 :3 This fits well with reported position for Ag2S (Standard positions given in the Handbook of XPS25, Ag0: 37 4.2 & 36 8.2 eV, Ag2S 37 4.1 & 36 8.1 eV and Ag2SO4: 37 4 .3 & 36 8 .3 eV) 91 Chapter 3 a Ag 3d5/2 b Ag 3d3/2 37 6.0 37 2.0 36 8.0 36 4.0 37 6.0 Binding Energy (eV) c 37 6.0 37 2.0 36 8.0 36 4.0 Binding Energy (eV) d 37 2.0 36 8.0 Binding Energy (eV) 36 4.0 37 6.0 37 2.0 36 8.0 36 4.0 Binding Energy... peaks for (a) PANi, and nanocomposites of various AgTB feed ratio: (b) Sample 1, (c) Sample 2, (d) Sample 3, and (e) Sample 4 In Figure 3. 8, typical spectra for Ag 3d3/2 and 3d5/2 peaks are shown There was no shift in the peak profile and binding energy while the Ag content was increased in the series of nanocomposites prepared The Ag 3d3/2 and 3d5/2 peaks were fitted at 37 4.1 eV and 36 8.1 eV respectively,... 4.1% 2.6% 39 9.5 39 8 .3 401.4 86.4% 8.7% 4.9% 39 9.5 39 8.4 401.6 85.8% 11.5% 2.7% Relative area ratio –NH– to –N= –NH– to N+ 1 - 3. 2 7.6 22.7 19.0 9.9 17.6 7.5 31 .8 90 Chapter 3 a N 1s b –N– N+ –N= 402.0 39 9.0 39 6.0 Binding Energy (eV) 402.0 39 9.0 39 6.0 Binding Energy (eV) d c 402.0 39 9.0 39 6.0 Binding Energy (eV) 402.0 39 9.0 39 6.0 Binding Energy (eV) e 402.0 39 9.0 39 6.0 Binding Energy (eV) Figure 3. 7 N 1s... literature17, 23 A definite trend among the relative amounts of –NH– and –N+– species, however, was not shown by the series of PANi/Ag2S samples prepared Table 3. 2 Fitted components for the N 1s XPS peaks for PANi and the various PANi/Ag2S samples PANi Sample 1 Sample 2 Sample 3 Sample 4 Peak position (eV) and area % –NH– –N= N+ 39 9.4 39 8 .3 50.5% 49.5% 39 9.5 39 8.4 400.6 69.4% 21.5% 9.1% 39 9.5 39 8.0 401.0 93. 2%... 1650 1594 1500 138 2 130 8 1161 1145 829 Assignments C=O stretching band C=C stretching of N=Q=N C=C stretching of N-B-N C-N stretching in QBQ C-N stretching of secondary aromatic amine C-H and aliphatic C-N stretching36 C-H in plane bending of N=Q=N, Q=N+H-B, B–NH+–B38 aromatic 1,4 C-H out of plane bending From Figure 3. 11, it is clear that the pristine PANi exhibited two bands at 1594 and 1500 cm-1 respectively... groups of the amide byproduct which could have capped onto the surface of the Ag2S nanoparticles 98 Chapter 3 In summary, the XPS, UV/visible absorption and FTIR results confirmed that –N= of PANi emeraldine base is reduced companying with the decomposition of AgTB and the formation of silver sulfide nanoparticles within the PANi matrix In Figure 3. 12, the photoluminescence (PL) spectra of PANi and PANi/Ag2S... Transmittance% 1650 d c 1594 138 2 130 8 1161 2000 1800 1600 1400 b 1145 1500 1200 Wavenumber cm 1000 a 829 800 600 -1 Figure 3. 11 FTIR spectra of (a) pristine PANi, (f) Ag2S nanoparticles, and (b-e) PANi/Ag2S nanocomposites with different AgTB feed ratio: (b) Sample 1, (c) Sample 2, (d) Sample 3, and (e) Sample 4 97 Chapter 3 Table 3. 4 Assignments for FTIR transmission bands for PANi and PANi/Ag2S nanocomposites... 1.9 9.2% 8.6 6.2 ( 83. 7%) (16 .3% ) 161.6 1 63. 6 Sample 2 1.4 1.8 9.2% 7.7 6.0 (77.6%) (22.4%) 161.6 1 63. 5 Sample 3 1.8 6.0% 7.8 5.9 (76.0%) (24.0%) 161.5 1 63. 4 Sample 4 1.9 4.8% 8.4 6 .3 (79.9%) (20.1%) PANi 7.7% 8 * S 2p XPS peak excluding the area of sulfate component at ~168.6 eV (see text) # Bulk C/N ratio obtained from elemental analysis 93 Chapter 3 a SA: S 2p3/2 SA: S 2p1/2 SB: S 2p3/2 SB: S 2p1/2... Peak I q ~2eV Peak II b Scheme 3. 1 Schematic energy level diagram of PANi emeraldine base .34 95 Chapter 3 0min 25mins 65mins 93mins 130 mins 160mins 190mins 220mins 250mins 270mins 290mins 30 5mins 0.5 Absorbance 0.4 0 .3 0.2 0.1 0.0 30 0 400 500 600 700 800 Wavelength (nm) Figure 3. 10 UV-vis spectra of the reaction mixture at different time (sample feed ratios follow those of Sample 1) Similar decrease... investigation on the selectivity towards hydrogen ions is of course needed 250 480 460 200 440 150 400 Potential mV Potential mV 420 38 0 36 0 34 0 100 50 32 0 0 30 0 280 -50 2.5 3. 0 3. 5 4.0 4.5 pH 5.0 5.5 6.0 6 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 pH Figure 3. 18 Effect of pH value to the measured potential Effect of interfering ion The selectivity of PANi/Ag2S ISE for Ag+ with respect to interfering ions . (eV) 37 6.0 37 2.0 36 8.0 36 4.0 d Binding Energy (eV) 37 6.0 37 2.0 36 8.0 36 4.0 c Binding Energy (eV) 37 6.0 37 2.0 36 8.0 36 4.0 37 6.0 37 2.0 36 8.0 36 4.0 Binding Energy (eV) 92 Chapter 3 component. XPS 25 , Ag 0 : 37 4.2 & 36 8.2 eV, Ag 2 S 37 4.1 & 36 8.1 eV and Ag 2 SO 4 : 37 4 .3 & 36 8 .3 eV). Binding Energy (eV) 402.0 39 9.0 39 6.0 a Binding Energy (eV) 402.0 39 9.0 39 6.0 b Binding. 402.0 39 9.0 39 6.0 c Binding Energy (eV) 402.0 39 9.0 39 6.0 e 402.0 39 9.0 39 6.0 d Binding Energy (eV) – N – N 1s – N= N + 91 Chapter 3 a Ag 3d 5/2 Ag 3d 3/ 2 b Figure 3. 8. Ag 3d