Kumud Malika Tripathi

Recent progress in micro-scale energy storage devices and future aspects

Recent developments in the field of energy storage materials are expected to provide sustainable solutions to the problems related to energy density and storage. The increasing energy demand for next generation portable and miniaturized electronic devices has sparked intensive interest to explore micro-scale and lightweight energy storage devices. This critical review provides an overview of the state-of-the-art recent research advances in micro-scale energy storage devices for supercapacitors (SCs), as well as their future importance in technology. Much effort has been devoted to fabricate high performance, ultrathin, planar, solid state and flexible micro-supercapacitors (MSCs) with aesthetic appeal. Nano-materials for MSCs, their fabrication techniques and performances are critically analyzed. The technical challenges and perspectives for MSCs are also discussed. The review concludes with few suggestions for future advancements in this area.

Pollutant soot of diesel engine exhaust transformed to carbon dots for multicoloured imaging of E. coli and sensing cholesterol

A convenient method for the synthesis of water soluble, fluorescent carbon dots from environmental pollutant diesel soot is described. The soot, generated from the exhaust of diesel engines as black, diesel particulate matter (DPM), is an environmental pollutant. This pollutant has been utilized as the precursor carbon source to create water soluble versions of carbon dots by chemical oxidation. The small sized water soluble carbon dots once separated display multicoloured emissions covering the green to red and extended to the near-infrared region. These have been used in imaging Escherichia coli and further used in sensing cholesterol.

Green synthesis of carbon quantum dots from lemon peel waste: applications in sensing and photocatalysis

In this work, water soluble carbon quantum dots (wsCQDs) were synthesized from lemon peel waste using a facile and cost effective hydrothermal process. As synthesized wsCQDs were 1–3 nm in size with spherical morphology and oxygen rich surface functionalities. These wsCQDs manifest excellent photoluminescence (PL) properties and exhibited quantum yield (QY) ∼14% with high aqueous stability. wsCQDs were further used to design an economic, green and highly sensitive fluorescent probe for the detection of Cr6+ ions with a detection limit of ∼73 nM. This wsCQDs based fluorescent probe could provide a simple, rapid, convenient technique for the sensitive and selective detection of Cr6+ in water purification processes. Further, wsCQDs were immobilized over electrospun TiO2 nanofibers and the photocatalytic activity for such a TiO2–wsCQDs composite was demonstrated using methylene blue (MB) dye as a model pollutant. Photocatalytic activity for the TiO2–wsCQDs composite was found to be ∼2.5 times more than that of TiO2 nanofibers. The synthesis method for wsCQDs could be easily scaled up for gram scale synthesis of carbon quantum dots.

Gram scale synthesis of green fluorescent water-soluble onion-like carbon nanoparticles from camphor and polystyrene foam

Herein, we report a cost effective and simple method for gram scale synthesis of water-soluble onion-like carbon nanoparticles (wsOCNPs) using common carbonaceous sources like camphor and polystyrene foam. The synthetic methodology involves ambient burning of these carbon rich materials under an insufficient oxygenic atmosphere. Furthermore, the oxidative treatment of carbon soot (CS) imposes dense carboxylic group functionalization over the surface of wsOCNPs. The high degree of surface functionalization imposes a self-passivated fluorescence effect along with photostability, which makes the material a potential candidate for bio-imaging purposes. Surprisingly, these wsOCNPs show exceptional excitation wavelength independent fluorescence emission properties over a wide region of the visible spectrum.

Large-scale synthesis of soluble graphitic hollow carbon nanorods with tunable photoluminescence for the selective fluorescent detection of DNA

Photoluminescent water-soluble hollow carbon nanorods were synthesized by the pyrolysis of castor oil seeds (Ricinus communis) without the use of a catalyst. Oxidation of the pyrolysed soot produced a water-soluble form of graphitic hollow carbon nanorods. These showed excitation-dependent multicoloured photoluminescent emission from the green to red region of the visible spectrum and extending to the near-infrared region. This photoluminescent behaviour was used to produce a fluorescent turn-off/turn-on sensor for the specific, sensitive and rapid determination of DNA with a detection limit of ∼1.14 nM.

A simple one-step hydrothermal route towards water solubilization of carbon quantum dots from soya-nuggets for imaging applications

A simple and low-cost pyrolytic carbonization method has been performed for the easy synthesis of carbon quantum dots from soya-nuggets under an insufficient amount of oxygen. Furthermore, hydrothermal functionalization of the carbonized black material after Soxhlet purification with nitric acid leads to the formation of its quantum sized water soluble version. The hydrothermally functionalized, water soluble carbon quantum dots (wsCQDs) are highly fluorescent and self-passivated, having a quantum yield value of ∼3%, with a small range of size distribution. High photostability with high solubility makes these potential candidates for imaging purposes, and we used these for the fluorescent labeling of Escherichia coli cells.

From the traditional way of pyrolysis to tunable photoluminescent water soluble carbon nano-onions for cell imaging and selective sensing of glucose

The traditional pyrolysis of vegetable ghee leads to the fabrication of graphitic photoluminescent, water soluble carbon nano-onions (wsCNO) with tunable photoluminescence without using any metal catalyst. Simple oxidative treatment by nitric acid fabricated a high density “self-passivated” water soluble version. As-synthesized wsCNO possessed tunable photoluminescence behavior from the visible-to-near infrared region. Further small sized wsCNO separated from the bulk as-synthesized wsCNO via gel filtration achieved a highly fluorescent colored fraction, used for cell imaging (Escherichia coli and Pseudomonas putida) and selective, immediate sensing of glucose molecules based upon a simple fluorescence “turn-off”/“turn-on” technique.

Temperature dependent, shape variant synthesis of photoluminescent and biocompatible carbon nanostructures from almond husk for applications in dye removal

This work reports the synthesis of water soluble and photoluminescent carbon nanostructures (wsFCNS) from almond husk, a bio-waste. Effect of carbonization temperature on morphology of the synthesized carbon nanostructures is illustrated. Carbonization was carried out at three different temperatures ranging from 750 °C to 950 °C. Carbonization at higher temperature resulted in carbon nanodots having spherical morphology, while lower temperature resulted in rod shaped carbon nanostructures. Further, oxidative treatment of the as-synthesized carbon nanostructures imparts water solubility as well as photoluminescent properties over the visible to near infrared (NIR) regions of the electro-magnetic spectrum. The synthesized wsFCNS are non-toxic in nature and on direct interaction with erythrocytes, show less than 2% hemolysis. The synthesized wsFCNS were further explored for the adsorptive removal of p-nitrophenol (PNP), a model dye pollutant. The removal of PNP with wsFCNS follows pseudo first order adsorption kinetics. The proposed synthesis method could be easily scaled up for gram scale synthesis of various carbon nanostructures.

Isolation of water soluble carbon nanotubes with network structure possessing multipodal junctions and its magnetic property

Water soluble carbon nanotubes (wsCNTs) with network structure possessing multipodal junctions were isolated by the oxidative treatment of carbon soot (generally discarded as waste during fullerene synthesis) using dilute nitric acid as black crystalline solid. wsCNTs having multipodal junctions are highly soluble in water due to the incorporation of adequate amount of hydrophilic carboxylic acid groups. Microscopic investigation shows the presence of extensive networked wsCNTs possessing different types of junctions such as tri (“Y”, “T”), tetrapodal, pentapodal and even “H” type junctions. Furthermore these wsCNTs possessing interesting magnetic properties due to presence of multipodal junctions and defective surfacial structures, usually known as surfacial ‘defects’ on graphitic pool (sp2 hybridized carbon atoms) of nanotubes. Easy solubility along with magnetic properties makes these wsCNTs to be used as a potential probe for their use in biological and spintronic applications respectively.

Nanospheres of copper(III) 1,2-dicarbomethoxy-1,2-dithiolate and its composite with water soluble carbon nanotubes

We report here the synthesis and structural characterization of a new discrete bis-dithiolene complex, [PPh4][Cu(DMED)2] (1; DMED = 1,2-dicarbomethoxy-1,2-dithiolate), involving the reaction between a copper polysulfide precursor with activated acetylene. 1 is stable, showing a sulfur-based radical character, as observed by electronic, EPR and cyclic voltammetric studies. This complex, possessing terminal –COOCH3 groups, forms nanospheres by hydrogen bonding in a mixture of solvents containing water as one of the components. These nanospheres further aggregate with water soluble (carboxylated) carbon nanotubes (wsCNTs). These nano-composites are assisted by hydrogen bonding between the carboxylic acid groups of the wsCNTs and the peripheral –COOCH3 groups of the coordinated dithiolenes of the nanospheres, which is promoted by water molecules. Interaction between the nanospheres on wrapping with wsCNTs, in forming the nano-composites, showed a perturbed EPR signal of the sulfur radical originating from the oxidised dithiolate ligand of the discrete complex 1.