Synthesis And Characterization Of Ag@polycarbazole Nanostructures And Their Properties

Silver is metallic chemical element represented by Ag having atomic number 47. It is white, lustrous transition metal, which has the highest electrical conductivity as compared to any element and the highest thermal conductivity as compared to any metal. It has been extensively used in catalysis, electronics, photonics, photography, biological labeling, and surface-enhanced Raman scattering. Since it is excellent and efficient material, so its nanostructures were extensively and intensively fabricated as it was believed to give superior performance on transforming into nano domain. Until now, the different Ag nanostructures like nanoparticles, nanocubes, nanotriangles, nanotubes, nanobelt, nanorods and nanowires have been reported by different group from all over the world. These were prepared by different methods and many properties like SER effect, electronic, photonic, biological labeling, and properties with reference to environment were studied. However, the potential applications of nano Ag suffer from its tendency to make coalescence and alongwith its sensitive nature with reference to the environmental oxidation and corrosion. Therefore, Ag@polymer nanocomposite formation was required and since last decade, Ag was encapsulated by many types of polymers, like poly(vinylalcohol), poly(vinylpyrolidone), poly(methyl methacrylate), and poly(vinyl acetate). It was further extended for conductive polymers in order to study the electrochemical and optochemical behavior of composite materials and thus Ag-polyaniline, Ag-polythiophene and Ag-polypyrrole nano-composites were prepared. These all studies were aimed to fabricate thermally and environmentally stable product and to avoid surface touch within metal NPs, which can lead to the coalescence that is not desired for functional unit's behavior of nanomaterials in the nanodevices. Under the same objectives, our group selected polycarbazole (PCz) as a thin coating material because, it is thermally and environmentally more stable than polypyrrole (ppy), poly (thiophene) and polyaniline (PANI) and can also form coherent film on suitable substrate, which is useful to reduce the probability of surface touch within metal nanostructures. The further interest in PCz was due to its photoconductivity, electrochromic, electroluminescence, photoluminescence and electron-hole transporting properties, hence its composite would be helpful to protect the electric conductive and photoluminescent behavior of nano Ag.The Ag@PCz nanocomposite is the new material and fabrication of PCz around any nanometal was not conducted before, therefore a facile and reproducible approach was designed to achieve this nanocomposite material. We used oxidative polymerization technique to grow PCz around Ag nanostructures, and applied oxidizing agents like AgNO3, FeCl3, Cu(CH3COO-)2, [1:1 FeCl2/Cu(CH3COO-)2], and Fe (CH3COO-)3 in different solvents like ethanol, acetonitrile and chloroform. The Cu(CH3COO-)2 in acetonitrile was found as a suitable oxidizing agent amongst the above all, whose application is proved beneficial to produce uniform polymer sheath around the core Ag nanostructures without damaging the metallic core structure. The other oxidizing agents except Cu(CH3COO-)2 were also suitable for polymerization growth, but they adversely affected the core Ag nanostructure. The selection of Cu(CH3COO-)2 in acetonitrile as suitable oxidizing agent was determined by TEM and FT-IR observations. TEM showed that core material (Ag) due this oxidizing agent remained intact and uniform polymer sheath having about 5-9nm thickness was enclosing whole Ag surface. FT-IR displayed the characteristics bands related to polycarbazole, where N-H stretching and aromatic ring stretching were very prominent. Therefore, we selected Cu(CH3COO-)2 as oxidizing agent to tailor PCz around different Ag nanostructures and prepared Ag@PCz co-axial nanocables (CNCs) and Ag@PCz nanoparticles respectively.The core structure of Ag@PCz CNCs is Ag NWs, which were produced by polyol reduction method at 160℃using PVP as soft template. The polymerization of carbazole over the surface of Ag NWs was achieved by using Cu(CH3COO-)2 as an oxidizing agent. Herein the Cu2+, were absorbed by u-sonicating the Ag NWs and solution of Cu(CH3COO-)2 in acetonitrile and further adsorption occurred by centrifuging this mixture at high speed which mounted more pressure over the cations and thus more adsorption happened. In this way the Ag NWs changed into cations loaded Ag NWs, which became activated and facilitated carbazole polymerization, around their surface. The as-synthesized Ag@PCz CNCs were characterized by SEM, TEM, HR-TEM, EDS, FT-IR, and Raman measurements. The SEM scanned the surface of Ag NWs and Ag CNCs and revealed that on polymer coating the smooth surface of Ag NWs transformed into rough one. Similarly, the TEM and HR-TEM clearly displayed the two contrast phases, where light phase was attributed to PCz and dark phase was attributed to core NWs. From the HR-TEM the polymer thickness was measured about 5 to 8nm. The EDS coupled with HR-TEM was applied on the edge of nanocables and it showed that surface of nanocables was constituted by 50-60% carbon material. Later on FT-IR and Raman characterized this carbon material as PCz, which was reconfirmed by comparing the FT-IR of pure PCz synthesized under the same conditions.The interfacial study conducted by XPS demonstrated that polymerization growth has not been affected the binding energy of Ag surface atoms and the existence of small molecules was also indicated. The XRD indexed the dominant material as silver.In the end, optical, thermal and dispersion behavior of as-synthesized material was evaluated. The optical behavior was explored by UV-Vis and PL spectroscopy. According to the UV the transverse SPR of Ag was dominant over longitudinal SPR, while the PL showed that Ag CNCs has combined the luminescence of pure metal and PCz, and displayed emissions from violet to green region. Thermal stability of pure polymer and composite polymer was conducted by TGA, which revealed that PCz in both form contain the impurity of small molecule which may be due to the solvent, oxidizing agent or polymer small molecules. However the polymer weight loss occurred from 300℃to 800℃, which expressed the PCz as thermally stable material. Finally, zeta potential measured the dispersion stability of CNCs comparative to pure Ag NWs and copper loaded Ag NWs. The pure Ag NWs showed negative charge on its surface which decreased on mixing with copper cations, but on polymer coating the negative charge on surface of Ag NWs further increased that is due to the increase in electron density shared by polymer. The increase in negative charge on Ag nanosurface is responsible for strong electrostatic repulsion, which in return is responsible for more dispersion stability. The increase in dispersion stability is highly significant to align nanocables in particular direction to measure the an-isotropic properties of material conventionally.With reference to Ag@PCz nanoparticles, which were another part of our work, the core structure is monodisperse silver nanoparticles and these nanoparticles were synthesized by microwave polyol reduction method at 120℃and 200W microwave energy. The fabrication of PCz shell around Ag nanoparticles and their characterization was carried out using same approach as it was described in case of CNCs, but interfacial study and novel optical behavior expressed by Ag@PCz nanoparticles was systemically carried out. XPS calculation of binding energy by the same machine was found less as compared to the binding energy of Ag NWs and to the standard binding energy of Ag, which on polymer coating became normalized. This observation revealed that surface atoms in nanoparticles are more labile as compared to the surface atoms of Ag NWs. Therefore, the composite formation in particles is more important as compared to the NWs. In case of optical properties, the SPR and PL of Ag nanoparticles, cations loaded Ag nanoparticles and polymer encapsulated Ag nanoparticles were determined. The SPR and PL behavior of Ag nanoparticles were found opposing to each other on cations loading and polymer encapsulation. The SPR of Ag nanoparticles increased when cations were loaded and decreased when polymer was grown, while PL of Ag nanoparticles decreased when cations were loaded and increased when polymer was grown. Furthermore, the PL of Ag@PCz nanoparticles was a combined expression of polymer and particles. The photoluminescence behavior of Ag@PCz is very important to use this material to avoid UV light or to convert UV light into visible light to increase the visibility. The potential application of this material is suggested to use in window pane to convert UV light coming from sun into visible light and in cosmetics to protect skin from UV light.In this way our whole study reported the facile strategy to make Ag@PCz nanocomposite, optimization to get monodisperse core nanostructures, effect of enclosing polymer on surface atom of substrate, dispersion stability, SPR and PL behavior of nano Ag.