Prashant Tripathi

High yield synthesis of electrolyte heating assisted electrochemically exfoliated graphene for electromagnetic interference shielding applications

Herein, we demonstrate a facile one pot synthesis of graphene nanosheets by electrochemical exfoliation of graphite. In the present study, we report a significant increase in the yield of graphene by electrolyte heating assisted electrochemical exfoliation method. The obtained results of heating assisted electrochemically exfoliated graphene (utilizing H2SO4 + KOH + DW) synthesis clearly exhibit that the yield increases ∼4.5 times i.e. from ∼17% (room temperature) to ∼77% (at 80 °C). A plausible mechanism for the enhanced yield based on lattice expansion and vibration of intercalated ions has been put forward and discussed in details. The quality of graphene was examined by Raman, XPS, FTIR, AFM, SEM, TEM/HRTEM and TGA techniques. The Raman as well as morphogenesis results confirm the quality of the graphene nanosheets. We have used this graphene as electromagnetic interference shielding material where a comparatively large quantity of graphene is required. This graphene exhibits enhanced shielding effectiveness (46 dB at 1 mm thickness of stacked graphene sheets in frequency region 12.4 to 18 GHz) as compared to conventional electromagnetic interference shielding materials, which is greater than the recommended limit (∼30 dB) for techno-commercial applications. Thus the present work is suggestive for future studies on enhancement of yield of high quality graphene by proposed method and the use of synthesized graphene in electromagnetic interference shielding and other possible applications.

High Per formance and Flexible Supercapacitors based on Carbonized Bamboo Fibers for Wide Temperature Applications

High performance carbonized bamboo fibers were synthesized for a wide range of temperature dependent energy storage applications. The structural and electrochemical properties of the carbonized bamboo fibers were studied for flexible supercapacitor applications. The galvanostatic charge-discharge studies on carbonized fibers exhibited specific capacity of ~510F/g at 0.4 A/g with energy density of 54 Wh/kg. Interestingly, the carbonized bamboo fibers displayed excellent charge storage stability without any appreciable degradation in charge storage capacity over 5,000 charge-discharge cycles. The symmetrical supercapacitor device fabricated using these carbonized bamboo fibers exhibited an areal capacitance of ~1.55 F/cm2 at room temperature. In addition to high charge storage capacity and cyclic stability, the device showed excellent flexibility without any degradation to charge storage capacity on bending the electrode. The performance of the supercapacitor device exhibited ~65% improvement at 70 °C compare to that at 10 °C. Our studies suggest that carbonized bamboo fibers are promising candidates for stable, high performance and flexible supercapacitor devices.

High-Performance Flexible Supercapacitors obtained via Recycled Jute: Bio-Waste to Energy Storage Approach

In search of affordable, flexible, lightweight, efficient and stable supercapacitors, metal oxides have been shown to provide high charge storage capacity but with poor cyclic stability due to structural damage occurring during the redox process. Here, we develop an efficient flexible supercapacitor obtained by carbonizing abundantly available and recyclable jute. The active material was synthesized from jute by a facile hydrothermal method and its electrochemical performance was further enhanced by chemical activation. Specific capacitance of 408 F/g at 1 mV/s using CV and 185 F/g at 500 mA/g using charge-discharge measurements with excellent flexibility (~100% retention in charge storage capacity on bending) were observed. The cyclic stability test confirmed no loss in the charge storage capacity of the electrode even after 5,000 charge-discharge measurements. In addition, a supercapacitor device fabricated using this carbonized jute showed promising specific capacitance of about 51 F/g, and improvement of over 60% in the charge storage capacity on increasing temperature from 5 to 75 °C. Based on these results, we propose that recycled jute should be considered for fabrication of high-performance flexible energy storage devices at extremely low cost.

New emerging radially aligned carbon nano tubes comprised carbon hollow cylinder as an excellent absorber for electromagnetic environmental pollution

Herein, we demonstrated the synthesis of a hollow cylinder with a new architecture of up to several centimeters in diameter and several centimeters long and having ∼100 μm wall thickness. The hollow carbon cylinder was formed by radially aligned CNTs. These CNTs were grown on ferrocene derived Fe nanoparticles deposited throughout the inner wall of the quartz growth tube. This new ingenious carbon architecture was grown by a customized spray pyrolysis method. Furthermore, we also synthesized such carbon hollow cylinders using different precursor concentrations (ferrocene:benzene), different phases and microstructures to evaluate their EMI shielding effectiveness. The structural and microstructural characterizations of these hollow carbon cylinders comprising radially aligned CNTs were examined through various techniques, including XRD, Raman, FTIR, XPS, SEM, TEM, and HRTEM spectroscopy. Furthermore, the magnetic measurements (M–H) were performed for such structures to probe the magnetic properties of these carbon hollow cylinders for different concentrations. Furthermore, the EMI shielding through different concentrations of Fe bearing CNTs were explored in detail for tailoring the desired shielding effectiveness value for possible potential applications. Hence, our synthesis method provides a unique architecture for promising next generation building blocks in the form of carbon hollow cylinders made up of radially aligned CNTs over the conventional randomly oriented CNTs. This could be directly used to make it as a co-axial cover for electrical cables to protect them from EMI pollutants.

A highly porous, light weight 3D sponge like graphene aerogel for electromagnetic interference shielding applications

Here we report the microwave shielding properties of a light weight three dimensional (3D) sponge like graphene aerogel (GA) derived from graphene oxide (GO). GA is a new exotic form of graphene nanosheet, which shows improved shielding features as compared to its pristine counterpart. The structural and microstructural characteristics of this new indigenous 3D sponge like graphene aerogel architecture have been probed by XRD, Raman, SEM and TEM/HRTEM. Furthermore, the porosity of this newly synthesized structure has been investigated by the Brunauer–Emmett–Teller (BET) method, which confirms the high surface area of ∼516 m2 g−1 with an average pore diameter of ∼2.5 nm. The high surface area and better porosity improve the EMI shielding effectiveness of GA. Simultaneously, the GA nanostructure also enhances the dielectric properties which provide a better alternative for EMI shielding materials as compared to GO. This engineered GA exhibits enhanced shielding effectiveness (∼20.0 dB at 0.20 g in a frequency region of 12.4 to 18.0 GHz) as compared to the conventional GO. Thus, the result of the EMI shielding of GA offers a new ingenious nanostructure which can be used as an EMI pollutant quencher for next-generation EMI shielding devices.

High-performance field emission device utilizing vertically aligned carbon nanotubes-based pillar architectures

The vertical aligned carbon nanotubes (CNTs)-based pillar architectures were created on laminated silicon oxide/silicon (SiO2/Si) wafer substrate at 775 °C by using water-assisted chemical vapor deposition under low pressure process condition. The lamination was carried out by aluminum (Al, 10.0 nm thickness) as a barrier layer and iron (Fe, 1.5 nm thickness) as a catalyst precursor layer sequentially on a silicon wafer substrate. Scanning electron microscope (SEM) images show that synthesized CNTs are vertically aligned and uniformly distributed with a high density. The CNTs have approximately 2–30 walls with an inner diameter of 3–8 nm. Raman spectrum analysis shows G-band at 1580 cm−1 and D-band at 1340 cm−1. The G-band is higher than D-band, which indicates that CNTs are highly graphitized. The field emission analysis of the CNTs revealed high field emission current density (4mA/cm2 at 1.2V/μm), low turn-on field (0.6 V/μm) and field enhancement factor (6917) with better stability and longer lifetime....

Filtration of sodium chloride from seawater using carbon hollow tube composed of carbon nanotubes

The present article deals with filtration of seawater to remove sodium chloride (NaCl) using filter made from organized structures of carbon nanotubes (CNTs). The filter consists of hollow carbon cylinder (length ~10 cm, diameter ~1 cm), which is composed of radially aligned CNTs. This carbon hollow cylinder has been synthesized by continuous spray pyrolysis of ferrocene–benzene solution in argon atmosphere. The hollow cylinder has been turned into a water filter by closing one end and keeping a small funnel at the other. Filtration of seawater (Marina Beach, Chennai, India) has been obtained both under the self pressure of seawater column in the hollow cylinder and under the difference of pressure created by enclosing the filter in a vacuum tight container. It has been found that the efficiency of filtration is about two times higher under partial vacuum (~10–2 torr) created on the filtrate (water) side. After filtration of seawater, a deposit in the inner surface of hollow cylinder has been found. This deposit has been characterized by X-ray diffraction, transmission electron microscopy and energy dispersive X-ray analysis, and it has been found that the deposit was NaCl. The filtration leads to almost complete removal of NaCl from the seawater.

Highly efficient field emission properties of radially aligned carbon nanotubes

Here, we report extraordinary field emission properties from one pot synthesized aligned carbon nanotubes endowed with related Fe nanoparticles (NPs). The CNT configuration is in the form of a carbon hollow cylinder (CHC) with CNTs radially aligned towards the CHC axis. The structure generates electron field emission properties such as an ultralow turn on field (0.35 V μm−1 at 10 μA cm−2), a low threshold field (0.41 V μm−1 at 100 μA cm−2) and a high field emission current density (7.71 mA cm−2 at 0.78 V μm−1). It also exhibits multi-fold improvement in the field enhancement factor (1.34 × 104) with highly stable current emission at 100 μA measured for 14 h. No post synthesis treatment is required for enhanced field emission characteristics. The growth related Fe NPs assist in lowering the work function and hence enhancing the field emission properties. The possibility of assembling nano-structured field emitters into macroscale architectures suggests new prospects for next generation three dimensional electron sources.

Facile Synthesis of Large Surface Area Graphene and Its Applications

In 2008, one of the most costly materials on earth was graphene which was obtained by exfoliation method, having a model area of a human hair cross section costing more than

Synthesis of reduced graphene oxide–TiO2 nanoparticle composite systems and its application in hydrogen production

1000 as of April 2008 [2]. Since then, hunger for searching low-cost, non-hazardous alternative methods for scalable production of graphene continued. Graphene’s flexible chemistry with an atomic thickness makes it superlatives in material science, an ideal candidate for countless applications. Incredibly light weight and flexible, yet 200 times stronger than steel. Highly conductive but at the same time transparent, first 2D material existing but is one million times smaller than the diameter of a single human hair. Having all these amazing properties, graphene is creating an impact in wide range of industries including in fields of electronics, EMI shielding, composites, sensing devices as well as in energy storage, biomedical devices, and many more. Application of this wonder material is restricted to our imagination only. These engineering applications necessitate accessibility of graphene on the large scale, and methods used to synthesize this are facile, cost-effective, simple, quick, and single-step process, and thus appropriate processes are essential for synthesizing it down to a single-sheet level. The quality and quantity of graphene also plays an essential role, as the occurrence of defects, structural disorders, impurities, multiple domains, grain boundaries, and wrinkles in the graphene sheet can leave an unwanted effect on its electronic and optical properties. The present chapter will be aimed at the preparation of high quality few-layer graphene on a bulk scale from graphite in an affordable, nontoxic, and easy method. The methods which will be discussed in this chapter will be mostly on microwave-assisted synthesis of graphene and electrochemical exfoliation method used in our lab as well as reported by other workers, and how these methods are advantageous over conventional exfoliation methods. Last segment of this chapter will deal with applications of graphene particularly in EMI shielding.