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Shiv Nadar University

Abstract Grapes (Vitis vinifera) extract was explored as a "green reducing agent" for the preparation of reduced graphene oxide (RGO) from graphene oxide (GO). The effect of reduction time on physical, chemical and optical properties of the RGO was also investigated. Synthesized RGO samples exhibited excellent activity as an adsorbent for the removal of organic dye. Proposed synthesis is environmental friendly, cost effective and promising for the large scale production of RGO. © 2015 Elsevier B.V.

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Physics

(SoNS) School of Natural Sciences

Materials Letters

Grape extract assisted green synthesis of reduced graphene oxide for water treatment application

Proper bonding technique is investigated to achieve leakage-free surface-driven capillary flow in polymethylmethacrylate (PMMA) microfluidic devices. SU-8-based silicon stamp is fabricated by maskless lithography. This stamp is used to produce PMMA microchannel structure by hot embossing lithography. A direct bonding technique is mainly employed for leakage-free sealing inside PMMA microfluidic devices. The effect of surface wettability on surface-driven capillary flow is also investigated in PMMA microfluidic devices. The separation of polystyrene microparticles in PMMA laboratory-on-a-chip systems is investigated with the reduction of separation time by air dielectric barrier discharge (DBD) plasma processing of channel surfaces. This study is useful to fabricate the microfluidic laboratory-on-a-chip systems and to understand the surface-driven capillary flow. © 2015 World Scientific Publishing Company.

Surface Review and Letters

Experimental studies of surface-driven capillary flow in PMMA microfluidic devices prepared by direct bonding technique and passive separation of microparticles in microfluidic laboratory-on-a-chip systems

Due to the fact that much of the world's best solar resources are inversely correlated with population centers, significant motivation exists for developing technology which can deliver reliable and autonomous conversion of sunlight into electricity. Thermoelectric generators are gaining incremental ground in this area since they do not require moving parts and work well in remote locations. Thermoelectric materials have been extensively used in space satellites, automobiles, and, more recently, in solar thermal applications as power generators, known as solar thermoelectric generators (STEG). STEG systems are gaining significant interest in both concentrated and non-concentrated systems and have been employed in hybrid configurations with solar thermal and photovoltaic systems. In this article, the key developments in the field of thermoelectric materials and on-going research work on STEG design conducted by various researchers to date are critically reviewed. Finally, we highlight the strategic research directions being undertaken to make highly efficient thermoelectric materials for developing a cost-effective STEG system, which could serve to bring this technology towards commercial readiness. This journal is © the Partner Organisations 2014.

Fulltext

RSC Advances

Recent advances in thermoelectric materials and solar thermoelectric generators-a critical review

Lack of control on the chirality or diameter of single-wall carbon nanotubes (SWCNTs) during synthesis is a major impediment in the path of their widespread commercialization. We demonstrate that the humble technique of catalytic chemical vapor deposition of methane, without any sophisticated catalyst preparation, can provide significant control on the diameter of the synthesized SWCNTs. The catalyst used is a solid solution of the bimetals Fe-Mo or Co-Mo in MgO. The radial breathing modes (RBMs) in the Raman spectra of SWCNTs were used to find out the diameters. Kataura plot along with RBMs was used to study the chirality of the tubes. High concentration of the catalysts (Co:Mo:MgO = 1:0.5:15 and Fe:Mo:MgO = 1:0.5:30) resulted in high yields. However, most of these carbonaceous materials were impurities. Reducing the concentration not only improved the purity and crystallinity (I D /I G ratio ∼0.1), but most importantly reduced the diameter spread of the SWCNTs. Majority of the SWCNTs grown using the low concentration catalysts (Co:Mo:MgO = 1:0.5:300 and Fe:Mo:MgO = 1:0.5:200) were estimated to have diameters lying between 1.13 and 1.65 nm. This narrowing of diameter spread happened for both Fe and Co catalyst systems and depended only on the concentration of the catalyst. © 2014 Elsevier B.V. All rights reserved.

Applied Surface Science

Diameter control of single wall carbon nanotubes synthesized using chemical vapor deposition

With a rapidly growing population, development of new materials, techniques and devices which can provide safe potable water continues to be one of the major research emphases of the scientific community. While the development of new metal oxide catalysts is progressing, albeit at a slower pace, the concurrent and rapid development of high surface area catalyst supports such as graphene and its functionalised derivatives has provided unprecedented promise in the development of multifunctional catalysts. Recent works have shown that metal oxide/graphene composites can perform multiple roles including (but not limited to): photocatalysts, adsorbents and antimicrobial agents making them an effective agent against all major water pollutants including organic molecules, heavy metal ions and water borne pathogens, respectively. This article presents a comprehensive review on the application of metal oxide/graphene composites in water treatment and their role as photocatalyst, adsorbent and disinfectant in water remediation. Through this review, we discuss the current state of the art in metal oxide/graphene composites for water purification and also provide a comprehensive analysis of the nature of interaction of these composites with various types of pollutants which dictates their photocatalytic, adsorptive and antimicrobial activities. The review concludes with a summary on the role of graphene based materials in removal of pollutants from water and some proposed strategies for designing of highly efficient multifunctional metal oxide/graphene composites for water remediation. A brief perspective on the challenges and new directions in the area is also provided for researchers interested in designing advanced water treatment strategies using graphene based advanced materials. © 2013 The Royal Society of Chemistry.

Role of graphene/metal oxide composites as photocatalysts, adsorbents and disinfectants in water treatment: A review

We report an investigation into the magnetic and electronic properties of partially hydrogenated vertically aligned few layers graphene (FLG) synthesized by microwave plasma enhanced chemical vapor deposition. The FLG samples are hydrogenated at different substrate temperatures to alter the degree of hydrogenation and their depth profile. The unique morphology of the structure gives rise to a unique geometry in which graphane/graphone is supported by graphene layers in the bulk, which is very different from other widely studied structures such as one-dimensional nanoribbons. Synchrotron based x-ray absorption fine structure spectroscopy measurements have been used to investigate the electronic structure and the underlying hydrogenation mechanism responsible for the magnetic properties. While ferromagnetic interactions seem to be predominant, the presence of antiferromagnetic interaction was also observed. Free spins available via the conversion of sp 2 to sp 3 hybridized structures, and the possibility of unpaired electrons from defects induced upon hydrogenation are thought to be likely mechanisms for the observed ferromagnetic orders.

Scientific Reports

Graphene supported graphone/graphane bilayer nanostructure material for spintronics

The capillary flow in SU8 based microfluidic devices fabricated in SF-100 by lithographic technique has been recorded and analysed in this report. Leakage free microfluidic flow is achieved by indirect bonding between polymethyl methacrylate (PMMA) coated glass lid surface and SU8 channel substrate during hard baking. The working liquids are dyed ethylene glycol, dyed ethanol, dyed isopropyl alcohol (IPA) and dyed liquid mixture (water and IPA). The capillary flow of dyed ethylene glycol is found to be slower in each device due to higher viscosity and lower surface wettability as compared to other working liquids. Square SU8 micropillar arrays (80 μm and 120 μm of side lengths) are fabricated on the glass bottom wall surface of SU8 based microchannel. The capillary flow of any particular working liquid is observed to be faster through the square micropillars of smaller side length due to their lower surface area to volume ratio in the device. Also, the capillary flow of polar liquids is found to be faster on the microchannel surface of higher polar component of surface free energy. The above results are highly significant to control the speed of capillary flow in lab-on-a-chip systems. © 2012 Elsevier Ltd.

International Journal of Adhesion and Adhesives

Effects of liquid viscosity, surface wettability and channel geometry on capillary flow in SU8 based microfluidic devices

Vertically aligned few layered graphene (FLGs) nanoflakes were synthesized by microwave plasma deposition for various time durations ranging from 30 to 600 s to yield graphene films of varying morphology, microstructure and areal/edge density. Their intrinsic electrochemical properties were explored using Fe(CN)6 3-/4- and Ru(NH3)6 3+/2+ redox species. All the FLG electrodes demonstrate fast electron transfer kinetics with near ideal ΔEp values of 60-65 mV. Using a relationship between electron transfer rate and edge plane density, an estimation of the edge plane density was carried out which revealed a moderation of edge plane density with increase in growth time. The pristine FLGs also possess excellent electrocatalytic activity towards oxygen reduction reaction (ORR) in alkaline solutions. This ORR activity can be further enhanced by exposing the pristine FLGs to nitrogen electron cyclotron resonance plasma. The metal free N-doped FLGs exhibit much higher electrocatalytic activity towards ORR than pristine FLGs with higher durability and selectivity than Pt-based catalysts. The excellent electrochemical performance of N-doped FLGs is explained in terms of enhanced edge plane exposure, high content of pyridinic nitrogen and an increase in the electronic density of states. © 2013 Springer-Verlag Berlin Heidelberg.

Journal of Solid State Electrochemistry

Electrochemical and oxygen reduction properties of pristine and nitrogen-doped few layered graphene nanoflakes (FLGs)

In this paper a modified design of a solar Parabolic Trough Thermoelectric Receiver (PTTR) tube is presented and its technical feasibility is evaluated theoretically. The innovative driving concept is its cylindrical tri-segmented receiver tube coupled with a thermoelectric generator (TEG). The system is analyzed numerically for a set of operation and design parameters and the results are discussed. This work opens up a promising option which has the potential to improve the conversion of solar thermal energy into electricity through parabolic trough system. We also explored the possibility of multi-component energy conversion using the modified structure. © 2013 IEEE.

Proceedings of the 2013 International Conference on Green Computing, Communication and Conservation of Energy, ICGCE 2013

An innovative design of a tri-segmented parabolic trough solar thermoelectric receiver tube for multi-component energy conversion

Vertically aligned few-layered graphene (FLG) nanoflakes were synthesized on bare silicon (Si) substrates by a microwave plasma enhanced chemical vapor deposition method. In situ nitrogen (N2) plasma treatment was carried out using electron cyclotron resonance plasma, resulting in various nitrogen functionalities being grafted to the FLG surface. Compared with pristine FLGs, the N2 plasma-treated FLGs showed significant improvement in field emission characteristics by lowering the turn-on field (defined at 10 ?A/cm 2) from 1.94 to 1.0 V/?m. Accordingly, the field emission current increased from 17 ?A/cm2 at 2.16 V/?m for pristine FLGs to about 103 ?A/cm2 at 1.45 V/?m for N-doped FLGs. Furthermore, N-doped FLG samples retained 94% of the starting current over a period of 10?000 s, during which the fluctuations were of the order of ±10.7% only. The field emission behavior of pristine and N2 plasma-treated FLGs is explained in terms of change in the effective microstructure as well as a reduction in the work function as probed by X-ray photoelectron valence band spectroscopy. © 2011 American Chemical Society.