Honey John

Synthesis of reduced graphene oxide–ZnO hybrid with enhanced optical limiting properties

Reduced graphene oxide–ZnO (rGO–ZnO) is synthesized by in situ growth of ZnO on the surface of graphene oxide (GO) by facile solution methods; namely, a solution precipitation method and a hydrothermal method. The characterization shows that GO is reduced and exfoliated to graphene sheets and ZnO is partially covered by graphene layers. A formation mechanism of rGO–ZnO hybrid proposed is well suited to the experimental results. Structural analysis indicates that the graphene possesses a greater extent of π-conjugation in the hydrothermally prepared rGO–ZnO hybrid. These hybrids exhibit an intense and broad absorption in the visible region, in addition to the sharp UV absorption peak. These rGO–ZnO hybrids also show fluorescence quenching properties. The nonlinear absorption coefficient and optical limiting properties of rGO–ZnO hybrid is evaluated using an open aperture Z-scan technique. More interestingly, we found that there is a 15 times enhancement in the nonlinear absorption coefficient of the rGO–ZnO hybrid compared to the bare ZnO. The hybrid shows excellent optical limiting properties compared to its individual counterparts, implying the usability of these hybrids in optoelectronics.

Optical limiting studies of ZnO nanotops and its polymer nanocomposite films

In the present work, we have investigated the optical limiting property of zinc oxide (ZnO) nanotop colloids and nanocomposite films of polymer-ZnO nanotops, using Z-scan technique. ZnO nanotops are prepared using two different capping agents. Films of polymethyl methacrylate-ZnO nanotop composite are fabricated for two concentrations of ZnO using spin coating technique. On exposing the nanocolloids to a pulsed nanosecond laser, the two photon absorption coefficient is enhanced with increase in applied fluence and particle size. The efficiency of limiting is found to be enhanced for the composite films, opening a way towards optoelectronic device fabrication.

Phenylenediamine functionalized reduced graphene oxide/polyaniline hybrid: synthesis, characterization, improved conductivity and photocurrent generation

Phenylenediamine functionalized reduced graphene oxide (GONH2) is designed and synthesized for the preparation of a polyaniline/reduced graphene oxide hybrid having better interactions than that of the unfunctionalized graphite oxide/polyaniline hybrid. Hybrids are synthesized by the in situ polymerization of aniline in the presence of GONH2. Defects generated in GONH2 during functionalization are repaired during hybrid formation. Due to the presence of free amino groups in GONH2, it will participate in the polymerization of aniline and covalent bonds will be formed between polyaniline and GONH2, resulting in the increased room temperature conductivity and photocurrent generation compared to pure polyaniline and polyaniline/graphite oxide hybrid synthesized in the same experimental conditions. Significant reduction and exfoliation of graphite oxide after functionalization with phenylenediamine, formation of direct conducting pathways by covalent connections and the photoinduced electron transfer between polyaniline and GONH2 plays a major role for the improved electrical conductivity and photocurrent generation.

Polyaniline and polypyrrole with PVC content for effective EMI shielding

Conducting polymers are characterized by attractive features like high anticorrosion property, controlled conductivity, high temperature resistance, low cost and ease of bulk preparation. These properties make conducting polymers as good shielding materials for electromagnetic interference. Poly aniline and polypyrrole with different proportion of PVC are prepared and studied at the S-band microwave frequencies. Dielectric parameters such as dielectric constant, dielectric loss, conductivity and S-parameters are evaluated. Suitability of these materials for EMI shielding is discussed.

Core-shell nanostructures of covalently grafted polyaniline multi-walled carbon nanotube hybrids for improved optical limiting

Polyaniline multi-walled carbon nanotube (MWCNT) hybrids are synthesized by the in situ polymerization of aniline in the presence of phenylenediamine-functionalized MWCNTs. Along with the aniline monomer, the aniline moiety on the surface of phenylenediamine-functionalized MWCNTs also participates in the polymerization and acts as a covalent bridge between the polyaniline and the MWCNT. The photoluminescence quenching in the hybrid, due to the electron transfer between the polyaniline and the MWCNT, and the resulting improvement in optical limiting are also discussed. The large nonlinear absorption coefficient with the low-limiting threshold of the hybrids compared to polyaniline is attributed to the combined nonlinear optical (NLO) mechanisms and the photo-induced electron transfer interactions.

Switching of absorptive nonlinearity from reverse saturation to saturation in polymer-ZnO nanotop composite films

We report an interesting switchover of optical nonlinearity from Reverse Saturable Absorption (RSA) to Saturable Absorption (SA) in polymer-Zinc Oxide (ZnO) nanotop composite films, investigated using the Z-scan technique. The nanocomposites have been prepared by in situ polymerization of the monomer in which ZnO nanotops are dispersed with the help of a dispersing agent. The films exhibit RSA for lower concentrations of ZnO nanotops, which changes to SA on increasing the loading concentration, irrespective of the monomer and dispersing agent used. These versatile films are good candidates for applications such as ultrafast optical switching and optical limiting.

Enhanced optical limiting in polystyrene–ZnO nanotop composite films

In this work we investigate the optical limiting property of polystyrene-zinc-oxide (ZnO) nanotop composite films, using an open aperture Z-scan technique. The nanocomposites are prepared for different loading concentrations of ZnO and are fabricated using spin and dip coating techniques. On exposing the films to a pulsed nanosecond laser at 532 nm, the nonlinear absorption (NLA) coefficient is found to be greater for spin-coated films compared to dip-coated films. The measured NLA coefficient is found to be enhanced with an increase in loading concentration of ZnO in the monomer for both spin- and dip-coated films.

Studies on the microwave conductivity of polyaniline- polyvinyl chloride composites

Abstract Polyaniline/polyvinyl chloride semi-interpenetrating polymer networks were prepared by the chemical oxidative polymerisation of aniline using ammonium persulphate as initiator in the presence of emulsion-grade polyvinyl chloride. The polymerisation was carried out for about 4 h at room temperature. It was then dried under different conditions (room temperature drying, vacuum drying and oven drying). The dielectric properties such as dielectric constant, conductivity, dielectric loss, dielectric heating coefficient and loss tangent were measured using the cavity perturbation technique. Cavity operating at S band was used for the study. The dielectric properties were found to depend on both the frequency and the composition of the mix (polyaniline-polyvinyl chloride).

Photoinduced electron transfer, improved nonlinear optical properties and photocurrent generation in polyaniline-graphite oxide hybrid

Synergetic improvement in the optical limiting behaviour, as well as in the photocurrent generation, is observed when polyaniline is hybridized with graphite oxide (GO) by a simple in situ polymerization method. The noncovalent functionalization of polyaniline by GO is mainly by π-π interactions, hence the electronic structure of GO is maintained and crystallinity is restored in the hybrid. The hybrid material is fully characterized and the effect of the proportion of GO in the hybrid for the improvement in properties as compared to polyaniline is also studied. The nonlinear optical properties of the hybrid are studied by open aperture Z scan technique at 532 nm, in the nanosecond excitation domain. The photocurrent measurements of the films made by spin coating are also reported. The photoluminescence of polyaniline is significantly quenched in the hybrid, indicating light induced charge separation and electron transfer from polyaniline to GO, thereby improving the photocurrent generation and optical limiting behaviour.

Enhanced photocatalytic activity of polyaniline through noncovalent functionalization with graphite oxide

Photocatalytic activities of polyaniline-graphite oxide (GO) hybrids are studied by considering the degradation of methylene blue (MB) under UV and visible illumination. Photocatalytic activity of the hybrid P1G2 (aniline to GO ratio 1:2) is significantly high (10 times) compared to pristine polyaniline under UV irradiation. The hybrid also shows 83% photodegradation of MB under low intensity visible light. The enhanced photocatalytic activity of the hybrid can be attributed to the synergetic effect between polyaniline and GO, which promoted the adsorption of the dye and migration efficiency of photogenerated electron–hole pair. A possible mechanism for the hybrid to act as a photocatalyst is proposed based on experimental evidence. The hybrids can be easily regenerated from the suspension and show fairly good cycling stability also. This is the first report on the visible light photodegradation of MB by polyaniline-GO hybrids.