acs.iecr.7b00167

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Study of thermal, electrical and photocatalytic activity of Iron complex doped polypyrrole and polythiophene nanocomposites Syed Kazim Moosvi, kowsar majid shah, and Tabassum Ara Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b00167 • Publication Date (Web): 29 Mar 2017 Downloaded from http://pubs.acs.org on March 30, 2017

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Industrial & Engineering Chemistry Research

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Study of thermal, electrical and photocatalytic activity of Iron complex doped polypyrrole and polythiophene nanocomposites Syed Kazim Moosvia, Kowsar Majida*, Tabassum Araa a

Department of Chemistry, National Institute of Technology Srinagar-190 006, J & K, India *Corresponding author: [email protected], phone: 09796123801

Abstract: Nanocomposites of polypyrrole (PPY) and polythiophene (PTP) were prepared with [Fe(TEMED)(H2O)(CN)3].H2O photoadduct via the oxidative chemical polymerisation method. The morphology and structure of photoadduct and nanocomposites were studied by XRD, SEM and FTIR. Thermal and electrical properties of nanocomposites were found to be significantly improved in comparison to pristine polymers. The photocatalytic activities of samples were studied by monitoring the degradation of Methyl orange (MO), Methylene blue (MB), Rhodamine B (RhB) and Eosin Gelblich (EG) dyes under irradiation, using a UV-Vis spectrophotometer. The samples were found to exhibit promising photocatalytic activities against dye degradation under light illumination. Results also showed attenuation in photodegradation of the MO dye by the disodium ethylenediaminetetraacetate dihydrate (EDTA-Na2;C10H14N2Na2O8.2H2O) (hole scavenger) and tert-butyl alcohol (C4H10O) (radical

scavenger). This clearly indicated the generation of reactive oxygen species (ROS) in the photocatalytic activity. The synthesized nanocomposite systems were also explored for the treatment of dye industry effluents in waste water. Key words: Conducting polymers, Nanocomposites, electrical study, photocatalytic activity

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Introduction In the recent past, there has been an increased contamination of surface and ground water. Organic dyes which are non-biodegradable and highly toxic to aquatic creatures are main sources of contamination to the environment 1. Methyl Orange (MO) is a simple azo dye having IUPAC name Sodium 4-{[4-(dimethylamino)phenyl]diazenyl}benzene-1-sulfonate and molecular formula C14H14N3NaO3S. Its uses are for a range of different fields, such as textile, printing, pharmaceutical and research laboratories. It can enter the human body through skin and has been reported to cause damage of lung tissues, increase heart rate and induce vomiting 2. MO has also mutagenic properties. Thus, it is an important concern to remove MO dye from contaminated water so as to maintain the ecological balance and facilitate the natural water recycling. The structure of MO dye is shown in Fig. 1. Thus the damage caused by organic dye pollution to environment and humans, demands the use of photocatalyst to degrade organic compounds in contaminated air or water or to convert them into harmless chemicals. From last few decades, several methods like coagulation, reverse osmosis and the adsorbents have been extensively studied to remove organic dye such as Rhodamine B (RhB), Methylene blue (MB) dye from the waste water 3. Among them, the heterogeneous photocatalytic degradation is an economical and easy way to degrade these organic pollutants into some less lethal form. The organic/inorganic nanocomposites have been recently known as promising photocatalysts for the degradation of harmful organic dye under light illumination 4. Among various conductive polymers, polypyrrole (PPY) and polythiophene (PTP) are the most promising conductive polymers due to their good conductivity, electrochemical reversibility, high polarizability and the ease of preparation through chemical or electrochemical routes

5-8

. These polymers have been studied the most for many practical

applications such as sensors, electrical/electrochemical applications, photocatalytic activity,



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and environment remediation 9. There are several reports focussed on photocatalytic activity of nanocomposites of PPY and PTP with metal oxides

10 - 15

. However, the photocatalytic

activity of nanocomposites of conducting polymers with transition metal complexes (TMCs) has not been explored so much. TMCs are known to show good catalytic activity and nanocomposites of conducting polymers with transition metal complexes can prove as good candidates for photocatalytic activity. Many TMCs are good at harnessing light energy and are attractive for solar energy conversion and storage due to their spectral properties, long lifetimes of their excited states and the ease with which they undergo oxidation and reduction reactions 16.Recently our research group has reported the photocatalytic activity of such type of nanocomposites and they have been found to exhibit not only good photocatalytic activity but also many other interesting properties such as enhanced electrical properties and high thermal stabilities 16 - 20. In this direction, we have chosen tetramethylethylenediamine (TEMED) complex of Fe as filler and it is expected that the combination of this complex with polypyrrole (PPY) and polythiophene (PTP) matrices would improve the structural, optical, electrical and thermal properties, which results to numerous applications in nano-electronics, catalytic properties, rechargeable batteries and electrochemical systems. To the best of our knowledge, the photocatalytic degradation of Methyl orange (MO), methylene blue (MB), Rhodamine B (RhB), and Eosin Gelblich (EG) dyes over the synthesized PPY and PTP nanocomposite systems as photocatalyst has not been reported so far. The present work deals the synthesis of nanocomposites of PPY and PTP by oxidative chemical polymerization. The photocatalytic degradation of MO dye and other dyes have been studied over the surface of the prepared nanocomposites under light illumination. From results the degradation of MO dye has occurred efficiently. In addition to MO dye degradation, some other dyes (Methylene blue, Rhodamine-B and Eosin Gelblich) were also found to be efficiently degraded by the


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synthesised PPY and PTP nanocomposites under irradiation. These results demonstrate that the synthesised nanocomposites have a potential viability for using as an effective photocatalyst under light irradiation. The synthesized nanocomposite systems were explored for the treatment of dye industry effluents in waste water. 2. Experimental 2.1. Chemicals Materials used in this work were pyrrole, thiophene, anhydrous ferric chloride, chloroform, potassium ferricyanide and tetramethylethylenediamine (TEMED). Pyrrole and thiophene monomer were purified by simple distillation. All the chemicals used in the experimental work were of analytical grade. Distilled deionised water was used throughout this work. 2.2. Physical measurements UV-Vis absorption spectrum was obtained on double beam spectrophotometer (PG instruments T80). FTIR analysis was done in the form of KBr Pellets using Perkin Elmer RX–1, FTIR spectrophotometer by mixing the powder with dry KBr. Irradiation was done with Osram UV photolamp. SEM analysis was carried out by using Hitachi FE –SEM, Model S – 3600N. XRD pattern was obtained on PW 3050 base diffractometer, operating with Cu-Kα radiations (λ = 1.54060Å). Dielectric study was carried out using Agilent 4285 A precision LCR meter at room temperature in the frequency range of 20Hz - 1MHz. For this purpose the powder was pressed into circular pellets of diameter 10 mm and thickness 2.35 mm. Silver paint was applied on both sides of the pellet and air dried to have good ohmic contact. 2.3. Synthesis of nanophotoadduct



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The synthesis of photoadduct was carried out by irradiating an equimolar mixture of K3[Fe(CN)6] and TEMED using Osram photolamp. The mixture was irradiated for half an hour in the dark and was then concentrated on water bath and cooled to room temperature. The greenish colored product obtained was then re-crystallized for purification and was subjected to various spectroscopic and surface characterizations. The reduction of photoadduct to nanosize was done by ball milling using 30 zirconium balls of 5 mm size for 10 hours at 450 rpm. The reduction to nanosize was confirmed from XRD. 2.4. Synthesise of PPY/photoadduct nanocomposite The nanocomposite of PPY with photoadduct was synthesised via oxidative chemical polymerisation method using FeCl3as oxidant. The synthesis was carried out in non-aqueous medium (Chloroform). In a typical experiment, 0.055M FeCl3 in 180 mL of chloroform was added drop wise to the stirred solution of 0.022M (in 70 mL chloroform) of distilled pyrrole monomer containing one gram of homogenised nanophotoadduct. The mixture was kept on stirring for 24 hours. After 24 hours, product was filtered and washed several times with methanol in order to remove oligomers and impurities. The black powder was then dried at room temperature. 2.5. Synthesis of PTP/photoadduct nanocomposite: To the stirring solution of 0.35 M thiophene monomer (in 70 mL of CHCl3), one gram of synthesized nano sized photoadduct was homogenized in it. To this mixture, 0.30 M solution of FeCl3 in 180 ml of CHCl3 as oxidant was added and was kept on stirring for 24 hours. After 24 hours stirring, black colored precipitate of composite obtained was filtered and washed with methanol repeatedly. The final product was then dried in oven at 20- 30 ⁰C. An illustration for the formation of nanophotoadduct and nanocomposite is shown in scheme I.


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Scheme I 3. Results and discussions 3.1. CHNS analysis: Based on the observed percentage of C, H, N i.e. 36.9%, 5%, 23.8% against the calculated percentage of 37.2%, 5.8%, 24.1% respectively, the empirical formula assigned to the synthesized nano sized photoadduct was found to be [Fe(TEMED)(H2O)(CN)3].H2O. This was also supported by FTIR and thermal analysis. 3.2. UV -Visible characterization: The UV-Vis spectra of aqueous solution of K3[Fe(CN)6] and TEMED recorded before and after irradiation are depicted in Fig. 2.(a and b) respectively. Before irradiation (Fig.2. (a)), the UV-Visible spectrum shows presence of two peaks at 235 nm and 445 nm which are assigned to charge transfer transitions18. However, after irradiation both peaks undergo red shift to 240 nm and 454 nm as shown in Fig.2.(b). This spectral change due to irradiation indicates perturbation in the energy levels of transition metal complex due to incorporation of TEMED ligand, indicating successful synthesis of photoadduct 19. The UV-Visible spectra of PPY and PTP nanocomposites are shown in Fig.2(c & d) respectively. The UV –Vis spectra of PPY shows a major absorption peak at 409 nm 18. The 6 ACS Paragon Plus Environment


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UV-Vis spectra of PTP show absorption bands at 287 nm and 410 nm 19. However, in case of nanocomposites, the characteristic peaks are shifted to higher wavelength region. The observed shifts thus indicate interaction of PPY and PTP matrices with photoadduct. A classical Tauc method was employed to estimate the band gap of PPY and PTP nanocomposites according to the following equation: αhν = A[hν – Eg]n where hν is energy of photon, α is absorption coefficient, Eg is the band gap energy , A is the absorption constants for indirect transitions, n is the index and depends on the characteristics of the transition in a semiconductor. It possesses discrete values viz. 1/2, 3/2, 2 and 3 for direct allowed, direct forbidden, indirect allowed and indirect forbidden transitions. From the plot of (αhν)n vs hν, a linear fit has been obtained for n=2. The band gap of PPY and PTP nanocomposites (Fig. 2.(e and f)) are calculated to be 2.35, and 2.6 eV, respectively. They are less than pure PPY and PTP

18, 19

. The above results thus reveal that the absorption edges of

PPY and PTP nanocomposites lie in the visible region, so the production of electron-hole pairs can be enhanced upon light irradiation. This can result to higher photocatalytic activity. 3.3.FTIR analysis: The FTIR spectrum of photoadduct and nanocomposites of PPY and PTP have been recorded in the region 4000 - 400 cm-1 (Fig. 3(a-c). The peak assignments were made on the basis of earlier reports in literature. In the spectrum of photoadduct (Fig. 3(a)), bands assigned to ν (O-H)-coordinated water, ν (O-H) lattice water, ν (CH2), ν (CH3), δ (OH2), δ (C-H), ν(CH3– N), ν(C–N–C) of the TEMED ligand are observed in the 3521,3442, (3050- 2479), 2043, 1630, 1467,1292 &1169 cm-1 regions respectively

21

. A sharp band assigned to (C≡N)

stretching vibration of cyanide & ν (Fe-N) were observed at 2044 cm-1, 585 cm-1 respectively22. Thus the vibrational analysis of photoadduct clearly supports the formation of [Fe(TEMED)(OH2)(CN)3].H2O. 7 ACS Paragon Plus Environment

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The FTIR spectrum of PPY exhibit peaks at wavenumbers 3391 cm-1 , 1536 cm-1, 1444 cm-1 , 1297 cm-1, 1041 cm-1 , 784 cm-1 and 606 cm-1 assignable to ν (N-H), ν (C-C), ν (C=C), ν (CN), C-N in plane deformation mode, C-H, N-H in plane deformation vibration and C-H outer bending vibrations

18

. The FTIR spectrum of the Polythiophene exhibit characteristic

vibration at 2275 cm-1, 1628 cm-1, 1323 cm-1, 1204 cm-1,1111 cm-1, 787 cm-1,672 cm-1 for C-H stretching vibration band, C=C asymmetric stretching of thiophene ring, C–H bending, C=S stretching, in-plane and out of plane C-H aromatic bending vibrations of thiophene ring, C–S–C ring deformation stretching is also seen in the spectrum22. The FTIR spectrum of nanocomposites of PPY and PTP (Fig.3 (b and c) show the presence of characteristic peaks of corresponding pristine polymers and photoadduct though with some shifts, hence justifying the synthesis of nanocomposites. 3.4. XRD analysis: XRD patterns of photoadduct and nanocomposites of PPY and PTP are shown in Fig.4.(a c) respectively. The characteristic peaks in the XRD pattern of photoadduct were indexed using powder X software which depicted its monoclinic structure. PPY and PTP show amorphous hump around 2θ value of 20 - 24° and 10° respectively, indicating the amorphous nature

18, 19

. The successful synthesis of nanocomposite is justified by the

presence of characteristic peaks of photoadduct. Monoclinic structure of photoadduct is retained in the nanocomposite with almost similar lattice parameters indicating the dispersion of photoadduct in the host polymer matrices. In case of photoadduct, PPY and PTP nanocomposites, the value of calculated d spacing is in agreement with the experimental d spacing as shown in table 1.1 - 1.3 respectively. The lattice parameters obtained after refinement and volume of unit cell for photoadduct, PPY and PTP nanocomposites are depicted in table 1.4. The average crystallite size was calculated using Scherrer formula: 8 ACS Paragon Plus Environment


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D = Kλ/βCosθ where D is crystallite size and k is shape factor (0.90). The crystallite size was found to be 20 nm, 29 nm, and 24 nm for photoadduct, PPY and PTP nanocomposites respectively. 3.5. SEM micrographs: Fig.5. (a - e) shows the SEM images of PPY, PTP, photoadduct, PPY nanocomposite, and PTP nanocomposite, respectively. SEM image of photoadduct shows irregular shaped particles with porosity. PPY and PTP on the other hand depicts rough surface with lot of grooves

18, 22

. The SEM images of nanocomposites show improved microstructure. A cross

linked type network has been observed in the nanocomposites of PPY and PTP as revealed from FE-SEM. 3.6. Thermal analysis The thermograms of photoadduct, pure PPY, pure PTP, PPY nanocomposite and PTP nanocomposite are presented in Fig. 6(a - e). The thermogram of photoadduct shows three main transitions (Fig.6(a)). Initial transition begins from ambient to 365°C with an observed weight loss of 38.5% against the calculated weight loss of 39%. This can be attributed to the loss of coordinated water, lattice water and three CN moieties. Second transition in the temperature range 367-578°C occurs with small weight loss of 9.9% against the calculated weight loss of 9.7% is attributed to the loss of N2. Third transition from 582 - 886 °C with a weight loss of 32% can be attributed to the removal of two moles of C2H6 and one mole of C2H4 moieties. This is in accordance with the calculated weight loss of 31.4%. The thermogram of pure PPY shows two transitions (Fig. 6(b)). First transition starts soon after ambient temperature to 100 °C can be attributed to the loss of water molecules and unreacted monomer. The second transition starts from 165 °C and ends at 550 °C with a rapid weight loss of 100%. This can be attributed to the degradation of whole polymer chain. Thermogram of PPY nanocomposite shows three main transitions (Fig. 6(d)). Initial transition occurs from 9 ACS Paragon Plus Environment

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ambient temperature to 80 °C with a weight loss of 6% can be attributed to the loss of moisture. Second transition with a weight loss of 20% occurs from 108 – 314 °C can be due to the loss of dopant. Third transition which is steep commences from 314 °C to 940 °C with a weight loss of 61% can be attributed to the degradation of polymer chain. The thermogram of PTP (Fig.6(c)) shows 95% weight loss till 496 °C owing to the degradation of the whole polymer chain. This shows a significant thermal degradation of PTP chain. The thermogram of PTP nanocomposite (Fig.6(e)) shows three main transitions. Initial transition from ambient temperature to 180 °C with a weight loss of 20% can be attributed to the loss of moisture and oligomers. Second transition commences from 223°C to 662°C with a weight loss of 24% can be attributed to the loss of dopant. The weight loss remains steady up to 825 °C and then rapid weight loss occurs till 960 °C due to rapid degradation of PTP chain. Thus, thermal analysis in essence indicates better thermal stability of PPY and PTP nanocomposites than that of corresponding pristine polymers. The synthesised nanocomposites demonstrate enhanced thermal stability in comparison to that reported in literature 23-30 (Table 1.5). 3.7. IV characteristics: I-V characteristics of PPY and PTP nanocomposites recorded at room temperature are presented in Fig.7 (a and b), respectively. From the I-Vcurves of the nanocomposites the values of dc electrical conductivity (σ) have been calculated, using the following relation 31. σ = [(I x L) / (V x A)] where I is the current, V is the voltage, L is the thickness and A is the cross-section area of sample. The dc conductivity obtained at room temperature in case of PPY and PTP nanocomposite was found to be 9×10-5and 4 × 10-6 S cm-1respectively. The dc conductivity of pure PPY and PTP was found to be 5.4 × 10-8 and 5.38×10-7 S cm-1 respectively

18, 19

.

This indicates enhanced dc conductivity of nanocomposites than their corresponding pristine



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polymers owing to the improved microstructure of nanocomposites as is evident from SEM micrographs also. 3.8. Dielectric properties & ac - conductivity: Dielectric response of synthesised nanocomposite of PPY and PTP has been carried out by Agilent 4285A precision LCR meter as a function of frequency in the range of 20Hz-1MHz. Fig.8shows variation of real part of dielectric constant(ɛ′), imaginary part of dielectric constant (ɛ″), dielectric loss (tan δ), and ac conductivity (σac) with the frequency of applied electric field. The parameters have been calculated using following relations: ɛ′= Cpd ̸ ɛͦ A ɛ″ = ɛ′tanδ σac = 2πνɛ″ where Cp is the capacitance, d is the thickness of sample, ɛͦ is the permittivity of the free space (ɛͦ = 8.854 × 10-12F/m), and A is the effective area. Fig.8.(a) and (b) presents the variation of dielectric constant (ε̍) of PPY and PTP nanocomposites with frequency respectively. The value of dielectric constant decreases with increase in frequency. The dielectric constant of PPY and PTP nanocomposites were found to be high at lower frequency region and then slowly decrease with increase in frequency, which is considered as a normal dielectric behaviour

32

. The variation of dielectric constant with

frequency at lower frequency region can be explained on the bases of polarization effect. The polarization effect is more significant at lower frequency region as the molecules of dielectric materials get enough relaxation time to orient them in the direction of applied electric field. At higher frequency region, dielectric constant remains almost constant for both the nanocomposites. The reason is that, beyond a particular frequency of the applied electric


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field, the molecules do not get sufficient time to orient themselves in the direction of applied field

33

. The dielectric constant of nanocomposites of PPY and PTP were found to be more

than their corresponding pristine polymers. The dielectric constant of pure PPY and PTP is 5.8 × 102 and 1.5 × 102 at 100 Hz respectively ((Fig. 8.(i , j))), whereas the dielectric constant of PPY and PTP nanocomposites are 0.24 × 106 and 1.24 ×106 at the same applied frequency. This can be due to several factors such as, (i) the morphology of the polymer in the nanocomposites is changing in the presence of nanophotoadduct, (ii) the large surface area and nano-sized photoadduct creates a large interaction zone with the neighbours in the polymer nanocomposites, and (iii) the change in space charge distribution in the nanocomposites owing to the high electrical conductive nature of the nano-sized photoadduct 34

. The magnitude of dielectric constant of PTP nanocomposite is greater than that of PPY.

This can be attributed to the presence of easily polarizable sulphur in polythiophene than less polarizable nitrogen in PPY

35

. The imaginary part of dielectric constant (ε̋) also shows the

similar variation as shown in Fig. 8. (c and d) for PPY and PTP nanocomposites respectively. Variation of tan δ of PPY and PTP nanocomposites with frequency is shown in Fig. 8. (e and f) respectively. It is observed that the behaviour of tan δ shows a decreasing trend with increase in frequency. It is evident from the graph that tan δ decreases rapidly in low frequency region and slowly in the higher frequency region. This can be due to the presence of impurities, defects and the space charge formation in the interface layers of the nanomaterial. The variation of ac - conductivity at room temperature with frequency in the range of 20 Hz to 1 MHz for nanocomposites of PPY and PTP is presented in Fig.8.(g and h). As is clear from Fig.8. (g and h) the ac-conductivity remains almost constant until a certain frequency region, known as critical frequency (fc). When the frequency is greater than the critical frequency (i.e. f > fc), the ac-conductivity was observed to have strong dependence on the



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applied frequency. The ac-conductivity of any dielectric material is the summation of two components and can be expressed by the following equation σac = σdc + ωε̋ The first component of the equation is σdc which arises due to the ionic or electronic conductivity. The value of the second component in the equation strongly depends on the extent of polarization of charges and the accumulated interfacial charges known as MaxwellWagner-Sillars (MWS) effect 36. Nanocomposites of PPY and PTP were observed to exhibit higher ac - conductivities than their corresponding pristine polymers (PPY and PTP). The ac - conductivity of pure PPY and PTP (Fig.8. (k & l)) is 0.89×103 S/m and 1.2× 104 S/m at 105 Hz, respectively. However, in case of nanocomposites of PPY and PTP, the ac-conductivity at 105 Hz is 3.6 × 108 and 5.7× 109 S/m respectively. This improvement in ac-conductivity for nanocomposites of PPY and PTP can be attributed to the effective dispersion of photoadduct nanoparticles in the polymer matrix (shown in SEM images). This favors better electronic transport 37. The ac-conductivity of PTP nanocomposite is higher than PPY nanocomposite, it can be explained on the basis of (i) Elliot’s Barrier hopping model, according to which σac = nπ2NNpεω(Rω)6/24, where n is the number of polarons involved in the hopping process, NNp is proportional to the square of concentration of states and Rω is the hopping distance 38. Thus lesser the particle size, more the hopping distance and hence higher will be the acconductivity (ii) more polarisation of S in thiophene unit of PTP than N in pyrrole unit of PPY. Also, these nanocomposites show superior dielectric constant and ac - conductivity to the other already reported composite/nanocomposite systems 27, 28, 35, 39-43 (Table 1.6). 3.9. Photocatalytic activity: The photocatalytic activity of synthesized PPY and PTP nanocomposites were explored through degradation studies of Methyl orange (MO) and several other dyes under 470 W


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Mercury/ Xenon arc lamp over the wavelength range of 250 – 580 nm. The distance between the lamp and the sample was about 12 cm. The intensity of the light near the sample was about 260 mW cm-2. A 0.4g sample of synthesized PPY and PTP nanocomposites were suspended into the 50 ppm aqueous solution of MO (200mL).The change in absorption spectra of MO dye by the synthesized nanocomposites of PPY and PTP for different time intervals were recorded and are presented in Fig.9.(a and b) respectively. Generally, the adsorption/desorption equilibrium is an important preliminary step in the photocatalytic degradation process. Therefore, prior to irradiation, the MO dye solution was magnetically stirred in the dark for 30 min to ensure the establishment of the adsorption/desorption equilibrium. As can be seen in the Figure 9, the decrease in intensity of characteristic peak of MO dye around 500 nm indicates the degradation of MO dye by the nanocomposites of PPY and PTP. The MO dye degradation plots of PPY and PTP nanocomposites are shown in Fig. 9 (c and d) respectively. In order to investigate the propensity of synthesized PPY and PTP nanocomposite for a wider scope of dye degradation, we attempted the photocatalytic degradation of Methylene Blue (MB), Rhodamine B (RhB) and Eosin Gelblich (EG) dyes using the MO standardized dye degradation protocol. The concentrations of MB, RhB and EG dye solutions at different time intervals in presence of synthesized nanocomposites were determined from their absorbance’s corresponding to their λmax of 650, 540 and 515 nm respectively using double beam spectrophotometer (PG instruments T80). The % degradation of dye is calculated as

% Degradation =

େబ ିେ౪

× 100

େబ



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where C0 is the initial concentration of dye before illumination and Ct after time t. The nanocomposite of PPY shows 98% of MO dye degradation in just 100 minutes. Nanocomposite of PTP shows 80% degradation after two hours (Fig.9.(c and d)). The pristine polymers (PPY and PTP) cause 24% and 15% degradation of MO dye after 2 hours respectively

18, 19

. This indicates the enhanced photocatalytic activity of nanocomposites in

comparison to pristine polymers. The enhanced photocatalytic activity of nanocomposites in comparison to pristine polymers can be attributed to the enhancement of the rapid separation efficiency of photoinduced electrons and holes through the interaction between photoadduct nanoparticles and polymer matrices 44. This leads to a higher concentration of electron/hole pair on the surface of a nanocomposites and hence enhancing the photocatalytic activity. The photocatalytic activity begins with the generation of electron/hole pair. These electrons and holes react with the dissolved oxygen molecules and water. This leads to the formation of reactive superoxide radical anions and hydroxyl radicals. These radicals are known to be the strong oxidising agents, to decompose the dye

45

. This can act as a mediator of interfacial

charge transfer, thus leading to high separation rate of photo induced charge carriers. Kinetics of the photodegradation rates of MO dye in presence of PPY and PTP nanocomposites was also calculated as presented in Fig.9 (e and f), respectively. The photodegradation rates fit a first-order model, that is, ln(Ct/C0) = -kobst, where C0 and Ct are the concentration of MO dye at time 0 and t, respectively . The kobs is the observed pseudo first-order rate constant and t is the reaction time. The values of kobs for nanocomposite of PPY and PTP are 2.9×10-2 and 4.9×10-3 respectively. The mechanism of photocatalytic activity of synthesized nanocomposites was proposed from the results of a parallel experiment involving the photodegradation of the MO dye in presence of radical and hole scavengers

like

disodium

ethylenediaminetetraacetate

dihydrate

(EDTA-

Na2;C10H14N2Na2O8.2H2O) (hole scavenger) and tert-butyl alcohol (C4H10O) (radical 15 ACS Paragon Plus Environment

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scavenger)

45-47

. The results of the controlled experiment showed attenuation of

photodegradation of the MO dye by synthesized nanocomposites in presence of these additives (Fig.10. (a, b, c)). This clearly indicated the generation of reactive oxygen species (ROS) in the photocatalytic activity of the synthesized nanocomposites. The absorption of a photon with sufficient energy is the necessary condition for the photochemical reaction to occur at the photocatalytic surface. Upon absorption of photon by nanocomposite, electronhole pairs are generated. The resulting electron - hole pairs migrate to the surface of nanocomposite and retort with H2O or OH- to form OH· or can directly oxidize adsorbed species. The electrons from the conduction band react with the adsorbed molecular oxygen to form superoxide radicle (O2-·) ions. The radical’s thus generated disrupt the conjugation in the organic dye and hence degrade it (Scheme II). The similar photocatalytic mechanism of photoadduct based nanocomposite of PPY was also recently reported by our research group16.

Scheme II



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The degradation studies of MB, RhB and EG dye using the synthesized PPY and PTP nano composites were in a similar trend to that of MO dye degradation suggesting the similarity in the photocatalytic activity. The obtained photocatalytic data depicted in Fig.11.A.(a, b, c) shows the dye degradation plots of MB, RhB and EG dyes respectively using synthesized PPY nanocomposite. The percentage of dye degradation from the photocatalytic data analysis was calculated to be 90 and 81 % for MB and RhB in a span of 120 minutes respectively over synthesized PPY nanocomposite. However for EG dye 96% degradation was achieved only in 70 minutes over the synthesized PPY nanocomposite. The dye degradation plots of MB, RhB and EG dyes using PTP nanocomposite are depicted in Fig. 11.B.(d, e, f), respectively. The photocatalytic data analysis of the PTP nanocomposite revealed 65, 62 and 86 % dye degradation in case of MB, RhB, and EG dyes respectively in 120 minutes. Thus the dye degradation study data is suggestive of a promising photocatalytic activity of synthesized PPY and PTP nanocomposites under the light irradiation condition. Furthermore, the nanocomposites of PPY were seen to be relatively better towards the degradation of studied dyes than corresponding PTP nanocomposites. This can be corroborated with the comparatively smaller band gap in case of PPY than that of PTP nanocomposites. The robustness towards dye degradation was established through kinetic profiles of the photocatalytic degradation of MB, RhB and EG dyes respectively over the synthesized PPY and PTP nanocomposites. The observed kinetic data depicted a linear correlation of the ln(Ct/C0) versus time which got fitted to a pseudo first-order reaction kinetic model for all the selected dyes and is as shown in Fig.11.(C, D). The observed rate constants (kobs) for the photocatalytic degradation of MB, RhB, and EG dyes with the PPY and PTP nanocomposites, were seen to be relatively of higher value in case of PPY than PTP nanocomposites. The calculated rate constants for selected dyes at 25 °C in presence of PPY


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and PTP nanocomposites are: i) MB = 1.8 ×10-2, 9.8 ×10-3 ii) RhB = 1 .3 ×10-2, 8.1×10-3 and iii) EG = 4.7 × 10-2, 1.96×10-2 respectively. The photocatalytic dye degradation results of our studied systems encouraged us to explore the synthesized PPY and PTP nanocomposite systems towards the possible effluent treatment in the form of waste water from fabric dying industry for a real time application. We attempted the photocatalytic degradation of various dye industry effluents using synthesized PPY and PTP nanocomposite systems. It was observed that the PPY and PTP nanocomposite systems could successfully degrade the different effluents under different time intervals. The photo degradation studies of Turquoise blue, commercial fabric dye degradation with time in presence of PPY and PTP nanocomposite has been documented as a representative example. It was observed that PPY nanocomposite degrades 90% of Turquoise blue dye in 60 minutes while as 85% degradation of the Turquoise blue dye could be achieved in 90 minutes over PTP nanocomposite (Fig. 12.(a, b)). Thus the synthesized PPY and PTP nanocomposite systems can be proposed as materials with effective photocatalytic degradation ability towards dye industry effluents in waste water. 4. Conclusion Photoadduct and nanocomposites of PPY and PTP were successfully synthesized via an oxidative chemical polymerization method. The synthesized materials were characterized through the structural and elemental analysis. The experimental data revealed that the structural, thermal and dielectric properties got improved significantly on the inclusion of photoadduct in polymer matrices. The photocatalytic activities of synthesized materials were explored for methyl orange, methylene blue, Rhodamine-B and Eosin Gelblich dye degradation. The photocatalytic activity of the synthesised nanocomposites against methyl orange dye was found to be via production of reactive oxygen species. The nanocomposites were found to exhibit good photocatalytic activity towards several dye degradations under 18 ACS Paragon Plus Environment


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light illumination.The synthesized PPY and PTP nanocomposite systems were seen to degrade the dye industry effluents under different time intervals which can be utilized for the interesting application of real waste water treatment. Acknowledgement The authors are thankful to SAIF Chandigarh, SAIF STIC Kochi, and NIT Hamirpurfor providing the instrumentation facilities. Conflict of interest: There is no conflict of interest among the contributing authors and the institute where the present work has been carried out. References 1.

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List of Figure and Table captions: Fig.1: Structure of methyl orange (MO) dye Fig.2: UV-Visible spectra of : aqueous solution of K3[Fe(CN)6] and tetramethylethylenediamine (TEMED) (a) before irradiation and (b) after irradiation (c) UV-Vis spectra of PPY nanocomposite,(d) UV-Vis spectra of PTP nanocomposite,(e & f) Tauc plot of PPY and PTP nanocomposites respectively. Fig.3: FTIR spectra of (a) nanophotoadduct, (b) PPY nanocomposite, and (c) PTP nanocomposite. Fig. 4: XRD of (a) nanophotoadduct (b) PPY nanocomposite, and (c) PTP nanocomposite. Fig.5: SEM micrographs of (a) PPY, (b) PTP, (c) Photoadduct, (d) PPY nanocomposite, and (e) PTP nanocomposite. Fig.6: TGA of (a) nanophotoadduct, (b) PPY, (c) PTP, (d) PPY nanocomposite, and (e) PTP nanocomposite. Fig.7: I-V characteristics of (a) PPY nanocomposite, and (b) PTP nanocomposite. Fig.8: Variation of (a, b) real permittivity (c, d) imaginary permittivity (e, f) tangential loss and (g, h) acconductivity with frequency of PPY and PTP nanocomposites respectively, and (i,j) variation of real permittivity, (k,l) ac-conductivity with frequency of pure PPY and PTP respectively. Fig.9: UV-Visible spectra of (a) MO dye degradation with time in presence of PPY nanocomposite (b) MO dye degradation with time in presence of PTP nanocomposite, Plot of decrease in dye concentration Ct/C0 with time in presence of (c) PPY nanocomposite during irradiation (d) PTP nanocomposite during irradiation, linear fitting of photocatalytic activity data of (e) PPY nanocomposite, (f) PTP nanocomposite. Fig.10: Bar graphs showing the time dependent MO dye photo-decoloration efficiency of

(a) PPY

nanocomposite, (b and c) Photo-decoloration analysis showing the protective effect of disodium ethylenediaminetetraacetate dihydrate (EDTA-Na2;C10H14N2Na2O8.2H2O) (hole scavenger) and tert-butyl alcohol (C4H10O) (radical scavenger) on the MO dye in presence of PPY/photoadduct nanocomposite. Fig.11: (A) plot of Ct/C0 of (a) RhB, (b), MB, and (c) EG dye with time in presence of PPY nanocomposite, (B) plot of Ct/C0 of (d) RhB, (e) MB, and (f) EG in presence of PTP nanocomposite. (C) Linear fitting of the



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photocatalytic data of (g) MB, (h) RhB and (i) EG dye in presence of PPY nanocomposite and, (D) Linear fitting of the photocatalytic data of (j) MB, (k) RhB, and (l) EG dye in presence of PTP nanocomposite. Fig. 12: UV-Visible spectra of Turquoise blue dye degradation with time in presence of (a) PPY nanocomposite (b) PTP nanocomposite. Scheme 1: Synthetic procedure of nanophotoadduct and nanocomposite. Scheme II: Proposed mechanism of dye degradation Table 1.1: Parameters evaluated from XRD of nanophotoadduct of potassium hexacyanoferrate(III) with tetramethylethylenediamine. Table 1.2: Parameters evaluated from XRD data of nanocomposite of PPY with nanophotoadduct of potassium hexacyanoferrate(III) with tetramethylethylenediamine. Table 1.3: Parameters evaluated from XRD data of nanocomposite of PTP with nanophotoadduct of potassium hexacyanoferrate(III) with tetramethylethylenediamine. Table 1.4: Lattice parameters, crystallite size and unit cell volume of nanophotoadduct, PPY and PTP nanocomposites. Table 1.5: Comparison of thermal decomposition at 600 °C of synthesised nanocomposites to that reported in the literature Table 1.6: Comparison of the dielectric constant and ac-conductivity of as prepared samples to that reported in the literature


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Figures

Fig.1: Structure of methyl orange (MO) dye.

Fig.2: UV-Visible spectra of : aqueous solution of K3[Fe(CN)6] and tetramethylethylenediamine (TEMED) (a) before irradiation and (b) after irradiation (c) UV-Vis spectra of PPY nanocomposite, (d)UV-Vis spectra of PTP nanocomposite, (e & f) Tauc plot of PPY and PTP nanocomposites respectively.



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Fig.3: FTIR spectra of (a) nanophotoadduct, (b) PPY nanocomposite and (c) PTP nanocomposite.

Fig 4: XRD of (a) nanophotoadduct (b) PPY nanocomposite (c) PTP nanocomposite.

Fig.5: SEM micrographs of (a) PPY (b) PTP (c) photoadduct (b) PPY nanocomposite (c) PTP nanocomposite.


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Fig.6: TGA of (a) nanophotoadduct, (b) PPY, (c) PTP, (d) PPY nanocomposite, and (e) PTP nanocomposite.

Fig.7: I-V characteristics of (a) PPY nanocomposite (b) PTP nanocomposite.



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Fig.8: Variation of (a, b) real permittivity (c, d) imaginary permittivity (e, f) tangential loss and (g, h) acconductivity with frequency of PPY and PTP nanocomposites respectively, and (i,j) variation of real permittivity, (k,l) ac-conductivity with frequency of pure PPY and PTP respectively.


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Fig.9: UV-Visible spectra of (a) MO dye degradation with time in presence of PPY nanocomposite (b) in presence of PTP nanocomposite (c) Plot of decrease in dye concentration Ct/C0 with time in presence of (c) PPY nanocomposite during irradiation (d) PTP nanocomposite during irradiation, linear fitting of photocatalytic activity data of (e) PPY nanocomposite (f) PTP nanocomposite.

Fig. 10. Bar graphs showing the time dependent MO dye photo-decoloration efficiency (a) PPY nanocomposite, (b and c) Photo-decoloration analysis shows the protective effect of disodium ethylenediaminetetraacetate dihydrate (EDTA-Na2;C10H14N2Na2O8.2H2O) (hole scavenger) and tert-butyl alcohol (C4H10O) (radical scavenger) on the MO dye in presence of PPY/photoadduct nanocomposite



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Fig.11. (A) plot of Ct/C0 of (a) RhB (b), MB, and (c) EG dyes with time in presence of PPY nanocomposite,(B) plot of Ct/C0 of (d)RhB, (e) MB, and (f) EG dyes with time in presence of PTP nanocomposite. (C) Linear fitting of the photocatalytic data of (g) MB, (h) RhB, and (i) EG dye in presence of PPY nanocomposite and, (D) Linear fitting of the photocatalytic data of (j) MB, (k) RhB, and (l) EG dye in presence of PTP nanocomposite.

Fig.12: UV-Visible spectra of Turquoise blue dye degradation with time in presence of (a) PPY nanocomposite (b) PTP nanocomposite.


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Table 1.1. Parameters evaluated from XRD of nanophotoadduct of potassium hexacyanoferrate(III) and tetramethylethylenediamine. h

k

l

Theta(obs)

d(exp)

d(cal)

-2

2

0

10.83989

4.09977

4.10341

-2

2

1

11.26467

3.94691

3.94498

0

3

0

12.89153

3.45533

3.45855

3

2

1

16.19232

2.76400

2.75922

2

3

1

16.89566

2.65202

2.65439

1

0

3

17.99863

2.49430

2.49389

-6

1

0

20.61300

2.18906

2.19061

5

3

0

21.29363

2.12215

2.12130

7

0

3

24.94593

1.82709

1.82653

6

1

2

25.49545

1.79024

1.78987

Table 1.2. Parameters evaluated from XRD data of nanocomposite of PPY with nanophotoadduct of potassium hexacyanoferrate(III) and tetramethylethylenediamine. h

k

l

Theta (obs)

d(exp)

d(cal)

2

1

1

10.73918

4.11945

4.12684

-3

0

2

12.54742

3.53517

3.53267

3

2

1

15.46847

2.88126

2.87956

-1

0

3

16.11547

2.76875

2.76828

4

1

2

20.42457

2.20340

2.20197

5

3

0

21.39928

2.10762

2.10909

Table 1.3. Parameters evaluated from XRD data of nanocomposite of PTP with nanophotoadduct of potassium hexacyanoferrate(III) and tetramethylethylenediamine. h

k

l

Theta(obs)

d(exp)

d(cal)

-3

3

0

16.34377

2.72031

2.72031

0

5

0

21.77992

2.06652

2.06652

4

1

3

25.17053

1.80407

1.80407



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Page 36 of 36

Table 1.4. Lattice parameters, cell volume and crystallite size of nanophotoadduct, PPY and PTP nanocomposites. System

Crystal Structure

Nanophotoadduct

Monoclinic

Unit cell parameters a = 14.03088, b = 10.38899, c = 8.35752, α = γ = 90.3 , β = 107.1

Cell volume

Crystallite Size (nm)

1164.34766

20

PPY nanocomposite Monoclinic

a = 14.02205, b = 10.37283, c = 8.37433, α = γ = 89.9, β = 106.5 1167.87 29 PTP nanocomposite Monoclinic a = 14.03088, b = 10.38899, c = 1164.39 8.35752, α = γ = 90, β = 107.1 25 Table 1.5. Comparison of thermal decomposition at 600 °C of synthesized PPY and PTP nanocomposites to that reported in the literature. System Thermal decomposition (600 °C) References PPY/ Triglycinesulfate composite 90% [23] PPY–BaFe12O19 nanocomposite 60% [24] PPY–Mn doped Fe(III) oxide 68% [25] nanocomposite PPY–clay composite 65% [26] PPY/TiO2 nanocomposite 70% [27] PTP/SnO2 nanocomposites 45% [28] PTP/CdS nanocomposite 60.55% [29] PTP/graphene oxide nanocomposite 80% [30] PPY/photoadduct nanocomposite 38% PTP/photoadduct nanocomposite 43% Table 1.6. Comparison of the dielectric constant and ac-conductivity of synthesized PPY and PTP nanocomposites to the other already reported composite/nanocomposite systems. System PPY/TiO2 nanocomposite PTP/SnO2 PTP/MWCNT PPY/[Co(EDTA)NH3Cl]. H2O Nanocomposite PPY/Ag nanocomposite PPY/ZnO composite PPY-Cu Nanocomposite PTP/CoO Composites PPY/photoadduct nanocomposite PTP/photoadduct nanocomposite

Dielectric constant(100KHz) 140 29 14 0.5×102

ac-conductivity(S/m) at 100KHz 8×10-2 107 3.3×107

References

900 102 230 1.7 × 102

2 ×10-1 (S/m) 10-1 -

[41] [42] [43] [44]

1.8×103

3.6×109

3×103

5.8×109

[27] [28] [36] [40]


acs.iecr.7b00167

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