Effect of oxidants and dopant on morphology, crystallinity and optical absorbance of nano structural polyindole

Abstract

We prepared the nanostructural polyindoles S1, S2, S3 and S4 (Pinds) by chemical oxidative route using anhydrous Iron (III) chloride (ferric chloride - FeCl3) and (NH4)2S2O8 (ammonium persulfate - APS) as oxidants and H2O2 (Hydrogen peroxide) as a dopant. The Pind samples are characterized by FTIR, UV–vis and XRD spectroscopy. The morphology of said samples has been examined by electron microscopy, SEM and TEM. The FTIR spectrographs enriched with bands show various bond absorptions which give the identity of Pind. The UV–vis spectra of S1 shows the absorption peaks in both regions, UV and visible. Using an oxidant as APS, the sample S2 spectra show the absence of an absorption peak in the visible region. The use of APS as oxidant gives the bathochromic and hyperchromic shift for UV absorption peak in case of S2 compare to S1, and also on the spectra of S2 there is bathochromic and hyperchromic shift in IR region which may be effect of APS as oxidant while polymerization. Hypsochromic shift is observed for samples S3 and S4, at both π - π* band and n- π* band with the use of dopants while synthesizing. Decrease in particle size (<100 nm) of S2 compared with S1 examined by SEM images (surface morphology). Small sized particles are observed in sample S3 compared to sample S1 with the use of H2O2 as dopant. The SEM image of S4 shows the presence of aggregation of particles up to some extent so that sheet- like structure is observed. Presence of Cl- in polymer matrix ensured by 4.64 wt% Cl on EDAX of S1, presence of SO2 - or SO3 - or SO4 - in polymer matrix ensured by 13.1 wt% oxygen and 2.89 wt% sulphur on EDAX of S2. Presence of Cl- in the polymer matrix is confirmed by EDAX of S3 and presence of SO2 - or SO3 - or SO4 - in the polymer matrix is confirmed by EDAX of S4. Increase in crystalline nature, formation of nano crystallites and removal of nanowires structure revealed by the XRD pattern of S2 due to APS as an oxidant. Nanoparticles surrounded by polymer nanowires are shown by the TEM image of S1. Nano crystallites embed spherical particles (>100 nm) as shown by the TEM image of S2. Small sized particles are observed in sample S3 (Pind/FeCl3/H2O2) compared to sample S1. In the present study we tried to find how the nature of oxidant affects the morphology, crystallinity and optical absorbance of Pind.