Directed morphology engineering of 2D MoS2 nanosheets to 1D nanoscrolls with enhanced hydrogen evolution and specific capacitance.

1D-molybdenum disulfide (MoS2) nanoscrolls displayed enhanced electrochemical properties compared to 2D-MoS2 nanosheet counterparts. Rolling of nanosheets is the main fabrication route to nanoscrolls. However, owing to the conflict between chemical stability and multiple bending, the morphology transition from nanosheets to nanoscrolls is quite challenging. Herein we describe a reversible morphology transition from nanosheets to nanoscrolls by utilizing non-covalent interactions between MoS2 nanosheets and phenothiazine based organic dye. Interestingly, nanoscrolls can easily be opened back into nanosheets by destroying the non-covalent interactions with organic solvents. The prepared nanoscrolls exhibited enhanced electrochemical properties than nanosheets. Compared to nanosheets, nanoscrolls exhibited comparatively lower overpotential with a Tafel slope of 141 mV dec-1 and high specific capacitance of 1868 F g-1. Hydrogen evolution by the Volmer-Heyrovsky mechanism being superior for the nanoscrolls is envisaged by the relatively increased availability of Hads sites at MoS2 edges induced by scrolling. Whereas the high specific capacitance value of nanoscrolls is ascribed to the enhanced electrical double-layer capacitance mediated charge storage, which arises due to the synergistic effect of both scrolled structure and the electron-rich phenothiazine-based dye.

Chitin/deacetylated chitin nanocomposite film for effective adsorption of organic pollutant from aqueous solution.

Cross-linked chitin/deacetylated chitin nanocomposite films can be considered as a potential industrial adsorbent for the removal of organic pollutants for water purification. Chitin (C) and deacetylated chitin (dC) nanofibers were extracted from raw chitin and characterized using FTIR, XRD and TGA techniques. The TEM image confirmed the formation of chitin nanofibers with a diameter range of 10-45 nm. The deacetylated chitin nanofibers (DDA-46 %) having 30 nm diameter was evidenced using FESEM. Further, the C/dC nanofibers were prepared at different ratios (80/20, 70/30, 60/40 & 50/50 ratios) and cross-linked. The highest tensile strength of 40 MPa and Young's modulus of 3872 MPa was exhibited by 50/50C/dC. The DMA studies revealed that the storage modulus enhanced by 86 % for 50/50C/dC (9.06 GPa) in comparison to 80/20C/dC nanocomposite. Further, the 50/50C/dC exhibited a maximum adsorption capacity of 30.8 mg/g at pH = 4 in 30 mg/L of Methyl Orange (MO) dye within 120 min. The experimental data agreed with pseudo-second-order model indicating chemisorption process. The adsorption isotherm data was best described by Freundlich model. The nanocomposite film is an effective adsorbent that can be regenerated and recycled for five adsorption-desorption cycle.

Recent trends in industrial and academic developments of green tyre technology.

Growing natural calamities as a consequence of global warming are one of the most pondering subjects today. The exponential growth of environmental pollution due to unscientific human exploitation of natural resources is considered the prime reason for the harsh responses of nature. Researchers from various fields of industry and academia are working hard to develop and implement products/technologies that are environmentally friendly or less harmful to the ecosystem. Material researchers, specifically those working in the automobile sector are also not behind in search of green products from eco-friendly raw materials and production methods. The automobile industry is collectively responsible for around 40% of global pollution in terms of greenhouse gas emissions. Out of which around 20-30% is originating from tyre production and its end-use. In this view, tyre production from eco-friendly raw materials and technologies that have minimum hazardousness to the environment is a hot research topic today. A few products in the market with "green" tags and many are in the pipeline for the recent future. This review summarises a detailed discussion of the emerging green technologies for tyre production and depicted comprehensive data from the available literature. The paper has been drafted from a well-balanced academic and industrial point of view since the researchers from both sectors are working in harmony for a better future for green tyre technology.

Electrode materials for stretchable triboelectric nanogenerator in wearable electronics.

Stretchable Triboelectric Nanogenerators (TENGs) for wearable electronics are in significant demand in the area of self-powered energy harvesting and storage devices. Designing a suitable electrode is one of the major challenges in developing a fully wearable TENG device and requires research aimed at exploring new materials and methods to develop stretchable electrodes. This review article is dedicated to presenting recent developments in exploring new materials for flexible TENGs with special emphasis on electrode components for wearable devices. In addition, materials that can potentially deliver properties such as transparency, self-healability and water-resistance are also reviewed. Inherently stretchable materials and a combination of soft and rigid materials including polymers and their composites, inorganic and ceramic materials, 2D materials and carbonaceous nanomaterials are also addressed. Additionally, various fabrication strategies and geometrical patterning techniques employed for designing highly stretchable electrodes for wearable TENG devices are also explored. The challenges reflected in the present approaches as well as feasible suggestions for future advancements are discussed.

Graphene coupled TiO2 photocatalysts for environmental applications: A review.

Nanostructured photocatalysts have always offered opportunities to solve issues concerned with the environmental challenges caused by rapid urbanization and industrialization. These materials, due to their tunable physicochemical characteristics, are capable of providing a clean and sustainable ecosystem to humanity. One of the current thriving research focuses of visible-light-driven photocatalysts is on the nanocomposites of titanium dioxide (TiO2) with carbon nanostructures, especially graphene. Coupling TiO2 with graphene has proven more active by photocatalysis than TiO2 alone. It is generally considered that graphene sheets act as an electron acceptor facilitating the transfer and separation of photogenerated electrons during TiO2 excitation, thereby reducing electron-hole recombination. This study briefly reviews the fundamental mechanism and interfacial charge-transfer dynamics in TiO2/graphene nanocomposites. Design strategies of various graphene-based hybrids are highlighted along with some specialized synthetic routes adopted to attain preferred properties. Importantly, the enhancing interfacial charge transfer of photogenerated e¯CB through the graphene layers by morphology orientation of TiO2, predominated exposure of their high energy crystal facets, defect engineering, enhancing catalytic sites in graphene, constructing dedicated architectures, tuning the nanomaterial dimensionality at the interface, and employing the synergism adopted through various modifications, are systematically compiled. Portraying the significance of these photocatalytic hybrids in environmental remediation, important applications including air and water purification, self-cleaning surfaces, H2 production, and CO2 reduction to desired fuels, are addressed.

Rolling and unrolling of graphene sheets via in situ generation of superparamagnetic iron oxide nanoparticles.

This manuscript reports a novel method for the automatic rolling and unrolling of reduced graphene oxide sheets using in situ generated superparamagnetic iron oxide nanoparticles. The graphene oxide synthesized through a low temperature modified hydrothermal method is subjected to hydrothermal reduction to obtain reduced graphene oxide (rGO). The as-prepared rGO was subjected to a second level of hydrothermal reduction in the presence of in situ generated superparamagnetic iron oxide nanoparticles, which led to the formation of graphene nanoscrolls decorated with superparamagnetic iron oxide nanoparticles. The nanoscrolls are unrolled to produce rGO sheets when the iron oxide nanoparticles are washed with hydrochloric acid. The repeatability of nanoscroll formation was examined by repeating the hydrothermal reaction for the in situ generation of superparamagnetic iron oxide nanoparticles in the presence of opened up rGO sheets. This reaction again made the rGO sheets scrolled. A blank reaction was also carried out without iron oxide particles to confirm the necessity of Fe3O4 in nanoscroll formation.

Reduced graphene oxide-ZnO self-assembled films: tailoring the visible light photoconductivity by the intrinsic defect states in ZnO.

ZnO is a wide direct bandgap semiconductor; its absorption can be tuned to the visible spectral region by controlling the intrinsic defect levels. Combining graphene with ZnO can improve its performance by photo-induced charge separation by ZnO and electronic transport through graphene. When reduced graphene oxide-ZnO is prepared by a hydrothermal method, the photophysical studies indicate that oxygen vacancy defect states are healed out by diffusion of oxygen from GO to ZnO during its reduction. Because of the passivation of oxygen vacancies, the visible light photoconductivity of the hybrid is depleted, compared to pure ZnO. In order to overcome this reduction in photocurrent, a photoelectrode is fabricated by layer-by-layer (LBL) self-assembly of ZnO and reduced graphene oxide. The multilayer films are fabricated by the electrostatic LBL self-assembly technique using negatively charged poly(sodium 4-styrene sulfonate)-reduced graphene oxide (PSS-rGO) and positively charged polyacrylamide-ZnO (PAM-ZnO) as building blocks. The multilayer films fabricated by this technique will be highly interpenetrating; it will enhance the interaction between the ZnO and rGO perpendicular to the electrode surface. Upon illumination under bias voltage defect assisted excitation occurs in ZnO and the photogenerated charge carriers can transfer to graphene. The electron transferred to graphene sheets can recombine in two ways; either it can recombine with the holes in the valence band of ZnO in its bilayer or the ZnO in the next bilayer. This type of tunnelling of electrons from graphene to the successive bilayers will result in efficient charge transfer. This transfer and propagation of electron will enhance as the number of bilayers increases, which in turn improve the photocurrent of the multilayer films. Therefore this self-assembly technique is an effective approach to fabricate semiconductor-graphene films with excellent conductivity.

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.

Defect engineering in ZnO nanocones for visible photoconductivity and nonlinear absorption.

Nanostructured ZnO is a promising material for optoelectronic and nonlinear optical applications because of the flexibility of band gap engineering by means of various defect states present in it. Employing the time-correlated single photon counting photoluminescence technique, the correlation between defect levels and optoelectronic and nonlinear optical properties of ZnO is explored in this work. By a facile solution method, ZnO nanocones with a dominating preferential orientation along energetically less favorable, oxygen terminated (10̄11) facets were synthesized using a passivating capping agent. Photoluminescence spectra demonstrate that the as-grown samples have both oxygen and zinc vacancies, and after calcination in air oxygen vacancies vanish, but zinc vacancies are enhanced. Photoconductivity of the samples reduces significantly upon calcination, confirming the reduction in oxygen vacancies. However, the samples exhibit a significant enhancement in the nonlinear optical absorption coefficient upon calcination, indicating that the effective two-photon absorption causing the nonlinear optical behaviour originates from zinc vacancies. These results illustrate the vast possibilities of band gap engineering in intrinsic ZnO for future optoelectronic applications.

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.