From Nano Scale Silver Particles to Metallic Bulk Sizes: Increase of Silver Ion Reduction Rate in Chitosan:AgNO3 Polymer electrolyte Mediated by Titanium Dioxide Filler

Synthesis of silver ion conducting polymer composites and its optical, electrical and 13 morphological properties were conducted. In the study various amounts of titanium dioxide (TiO2) 14 was added to the chitosan:silver nitrate (CS:AgNt) system. The appearance of SPR peak for CS:AgNt 15 system and CS:AgNt doped with 1 wt.% TiO2 and disappearance of SPR peak for the system 16 incorporated with 5 wt.% TiO2 reveals the formation of silver particle from nano scales to bulk 17 metallic sizes. The optical microscope images reveal the formation of silver particles with bulk 18 metallic sizes at 5 wt.% TiO2 filler . The SEM images show silver particles with small sizes for 19 CS:AgNt and CS:AgNt incorporated with 1 wt.% TiO2. To make sure the reduction process of silver 20 ions to metallic silver particles the impedance spectroscopy has been carried out. The decrease of 21 dielectric constant and DC conductivity at high TiO2 concentration was correlated with the results 22 of UV-vis and morphological achievments. Shifting of tanδ loss peak towards the lower frequency 23 side at 5 wt.% TiO2 is an evident for the decrease in conductivity. The results of the present work 24 reveals that silver ion conducting polymer electrolytes mediated by TiO2 filler are not suitable for 25 electrochemical device application. Distinct peaks become visible in Mi spectra whereas no peaks 26 can be seen in dielectric loss spectra. 27

fuel cells [5,6]. Moreover, the removal of mercury from solutions and the adsorption kinetics of 48 mercuric ions (Hg 2+ ) by chitosan were reported in literature [7]. Recently, it was reported that silver 49 polymer electrolytes comprising silver salts dissolved in a polar polymer such as poly (2-ethyl-2-50 oxazoline) (POZ), poly (vinylpyrrolidone) (PVP) or poly (ethylene oxide) (PEO) matrix have attracted 51 much attention for their application in solid state facilitated transport membranes. These silver SPEs 52 have many advantages, including high separation performance, simple operation and low energy 53 consumption [8][9][10][11]. The performance of the separation of olefin/paraffin mixtures by facilitated 54 transport membranes containing silver salts is a promising alternative to energy-intensive distillation 55 processes and as a consequence has attracted considerable interest [12]. It is well reported that lone 56 pair electrons on atoms of functional groups of polar polymers are responsible for complexation with 57 as well as reduction of silver ions [13][14][15][16][17]. A number of approaches have been proposed to solve the 58 state-of-the-art problems of ion-conducting polymers. Among them, nanocomposite fabrication is the 59 newest one [18]. It was confirmed that the incorporation of inorganic fillers such as SiO2, α-Al2O3,

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AlBr3, TiO2 and ZnO into polymer electrolytes can enhance the mechanical stability and increase the 61 conductivity due to higher polymer chain mobility and thus a faster cation diffusion [19,20]. The 62 noticeable data results of the present work reveals that the process of reduction of silver ions to 63 nanoparticles in silver ion conducting polymer electrolyte membranes is a considerable challenging 64 facing the purification and separation technologies using polymer membranes incorporated with 65 silver ions. The data results of the present work shows that silver particles from nano scale to metallic 66 bulk sizes occurred when a high amounts of TiO2 filler has been added to the chitosan:AgNt  Chitosan from crab shells (≥75% deacetylated, average molecular weight 1.1× 10 5 , procured from 73 Sigma), silver nitrate (AgNO3) and Titanium dioxide (TiO2, size < 100 nm) were purchased from 74 sigma Aldrich. Acetic acid (1%) was prepared using glacial acetic acid solution that then used as a

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The nanaparticle formation was evidenced by the Uv-Visible spectra of the prepared films were 90 recorded using a Jasco V-570, Uv-Vis-NIR spectrophotometer (Jasco SLM-468, Japan) in the

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It is clear that at 1 wt.% of TiO2, the intensity of SPR peak greatly enhanced whereas at 5 wt. % of TiO2 104 the SPR peak disappeared. This can be related to the reduction of a huge amount of silver ions to 105 silver particles in the former case. For the latter case, coagulation of silver nanoparticles was occurred, behavior of the metal nanoparticles as well as the dielectric behavior of the host materials [24,25]. It 115 is interesting to notice that the broad LSPR peaks than the sharper ones can be due to the larger size

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Electrical studies may give more insights into the reduction of silver ions to metallic silver Here, Co is the vacuum capacitance and given by εoA/t, where εo is a permittivity of free space and is

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To gain understanding of the relaxation processes, tanδ was plotted as a function of frequency for all 215 the samples as the tanδ shape in the Figure 6 can be interpreted on the basis of Koops 216 phenomenological model [40]. According to this model, loss tangent increases with an increase in 217 frequency, and shows it's maximum value at particular frequencies for different temperatures 218 because the ohmic component of current increases more rapidly than its capacitive component. At   The dielectric response caused by ion relaxation has been studied using the reciprocal quantity within it [44]. Distinguishable peaks are appeared in Mi spectra while these peaks are obscured in 240 dielectric loss spectra (see Fig. 5). Previous studies confirmed that the dielectric loss (ɛ'') parameter 241 always affected by an ohmic conduction (DC conductivity) [6,35]. Consequently, the dielectric loss 242 peaks are hidden in dielectric loss spectra as depicted in Figure 5 and almost clearly appeared in Mi 243 spectra (see Figure 8). From Figure 8, the distinguishable peaks in M″ spectra can also be observed

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The main conclusion of this work is that silver particles from nano scales to bulk metallic sizes 325 can be fabricated in silver ion conducting chitiosan based electrolytes mediated by different 326 concentration of TiO2 filler. The optical microscope appearances reveal the formation of silver 327 particles with bulk metallic sizes at 5 wt.% TiO2 filler and percolation paths among silver particles 328 can clearly be observed. To confirm the reduction of silver ions to metallic silver particles electrical 329 impedance spectroscopy has been carried out. The decrease of dielectric constant at high TiO2