Abstract

1. Composite materials based on carbon nanotubes and poly o-phenylenediamineM. Baibarac*, I. Baltog, I. Smaranda, M.Scocioreanu, I. Gontia, T. Velula, L. Mihut Abstract The chemical polymerization of o-phenylenediamine (OPD) on single-walled carbon nanotubes (SWCNTs) in the presence of phosphomolybdic acid (H3PMo12O40 xH2O) has been studied by surface enhanced resonant Raman scattering (SERRS) spectroscopy. One demonstrates that an organic–inorganic hybrid composite of the type poly(o-phenylenediamine)/polyoxometallate-functionalized SWCNTs is produced by the chemical interaction between polyoxometallate-functionalized SWCNTs and poly(ophenylenediamine) (POPD) doped with [H2PMo12O40] ions. According to TEM investigations, a result of the chemical interaction of SWCNT with H3PMo12O40 xH2O is the formation into the composite mass of tube fragments of shorter length, which behave like closed shell fullerenes since and for these the Raman fingerprint is given by lines situated at 240–275 and 1450–1472 cm-1. The chemical polymerization of OPD on SWCNTs achieved in the absence of H3PMo12O40 xH2O leads to a covalent functionalization of the wall side of the tubes, which is revealed in Raman spectra at the excitation wavelength of 514 nm by an enhancement of the lines associated with the tangential vibrational modes of SWCNTs. Using FTIR spectroscopy, significant hindrance steric effects are evidenced in the POPD/polyoxometallate- functionalized SWCNT composite. Fig.3.FTIR spectra of SWCNTSs (curve 1a), H3PMo12O40xH2O(curve3a),polyoxometallate- functionalized SWCNTs (curve 2a) and the polyoxometallate-functionalized SWCNTs sample interacted with a 1 M NH4OH solution (4a). Experimental Fig. 4. SERS spectra recorded at λexc = 514 nm of the SWCNTs in their initial state (a1,a2), POPD covalently functionalized SWCNTs (b1,b2) and POPD (c1). ☛The chemical interaction of SWCNTs with H3PMo12O40 xH2O was studied using the mixture of the two constituents in the weight ratios of 0.1/5 and 0.01/5. After the interaction of the two constituents, a washing with water was carried out to eliminate un-reacted H3PMo12O40. The final product obtained by a drying until constant mass corresponds to SWCNTs doped with anions of H3PMo12O40. Solutions of SWCNTs doped with anions of H3PMo12O40 in CH3CN of 0.1% concentration were used to prepare films deposited on the rough Au support to be studied by SERS spectroscopy. The chemical synthesis of the hybrid material POPD/polyoxometallate-functionalized SWCNTs was carried out by direct addition of 1 g OPD to 5 g H3PMo12O40 + 0.1 g SWCNT or 5 g H3PMo12O40 + 0.01 g SWCNTs.In the absence of H3PMo12O40, the chemical polymerization of OPD was carried out according to the method was reported ,which involves the use of 0.09 g OPD dissolved in 20 ml of water and 2.34 ml of 0.71 M ferric chloride. To obtain the POPD/ SWNTs composites. Finally, both POPD and the POPD/SWCNTs composites were washed several times with water and dried in vacuum at 50oC for 24 h. For SERS studies were used films deposited onto rough Au supports . They were obtained from were obtained by the evaporation of the solvent using solutions of POPD and POPD/SWCNTs in CH3CN of 0.1% concentration , ☛Raman spectra were recorded at room temperature in a backscattering geometry under excitation wavelengths of 514.5 and 676.4 nm with a Jobin Yvon T64000 Raman spectrophotometer . ☛ FTIR spectra were obtained in the 400–4000 cm-1 range with a 4 cm-1 resolution, using a FTIR Bruker spectrophotometer, Vertex 70 model.  Fig. 5. HRTEM picture of POPD covalent functionalized SWCNTs. Fig. 7. SERS spectra recorded at λexc =647nm of SWCNT (curve a), the composite based on SWCNTs functionalized with POPD doped with [H2PMo12O40]- ions and tube fragments of shorter length like closed shell fullerenes functionalized with POPD (curve b) and POPD (curve c). Results and Discussions Fig. 6. SERS spectra recorded at λexc = 514 nm of the SWCNTs functionalized with POPD doped with [H2PMo12O40] - ions obtained by the chemical polymerization of 1g ODP + 5g H3PMo12O40 xH2O in the presence of 0.1g (a1, a2) and 0.01 g SWCNT (b1, b2). SWCNT functionalized with POPD doped with [H2PMo12O40]- ions.: ☛ CONCLUSIONS This paper reports new results obtained by surface enhanced Raman scattering (SERS) studies on the chemical polymerization of OPD in the presence of SWCNTs and H3PMo12O40 xH2O. The following results may be highlighted: (i) the chemical interaction of SWCNTs with H3PMo12O40 xH2O leads to the formation of the polyoxometallate-functionalized SWCNTs; (ii) the chemical polymerization of OPD in the presence of FeCl3 and SWCNTs leads to POPD covalently functionalized SWCNTs composite characterized by a significant increase in intensity of the Raman lines with maximum at 1536 and 1565 cm-1; this behavior permits to conclude that a functionalization of the side-wall of the tubes with polymer took place; (iii) the chemical polymerization of OPD in the presence of SWCNTs and H3PMo12O40 xH2O leads to the formation of an organic–inorganic hybrid composite of the type SWCNTs functionalized with POPD doped with [H2PMo12O40]- ions and tube fragments of shorter length like closed shell fullerenes functionalized with POPD; (iv) the SERS spectrum of tube fragments of shorter length like closed shell fullerenes functionalized with POPD, is characterized by new Raman lines situated at ca. 240– 275 and 1450–1472 cm-1 . Fig. 1. SERS spectra recorded at  exc=514 nm of films of SWCNTs in their initial state (curve 1), polyoxometallate-functionalized SWCNTs obtained from the chemical interaction between 0.1 g SWCNTs + 5 g H3PMo12O40 xH2O (curve 2) and 0.01 g SWCNT + 5 g H3PMo12O40 xH2O (curve 3). Curve 4 shows the Raman spectrum of the polyoxometallate-functionalized SWCNT sample interacted with 1M NH4OH solution. Fig.2. SERS specra at  exc=647 nm of films of SWCNTs in their initial state (a, curve black) and polyoxometallate-functionalized SWCNTs obtained fromthe chemical interaction of 0.1g SWCNTs+5gH3PMo12O40xH2O(curve red) and 0.01g SWCNTs+5gH3PMo12O40xH2O (curve green).The curve blue (c) shows the Raman spectrum of poly-oxometallate-functionalized SWCNTs sample interacted with 1M NH4OH