2D Metal-Organic Frameworks: Properties, Synthesis, and Applications in Electrochemical and Optical Biosensors.

Two-dimensional (2D) nanomaterials like graphene, layered double hydroxides, etc., have received increasing attention owing to their unique properties imparted by their 2D structure. The newest member in this family is based on metal-organic frameworks (MOFs), which have been long known for their exceptional physicochemical properties-high surface area, tunable pore size, catalytic properties, etc., to list a few. 2D MOFs are promising materials for various applications as they combine the exciting properties of 2D materials and MOFs. Recently, they have been extensively used in biosensors by virtue of their enormous surface area and abundant, accessible active sites. In this review, we provide a synopsis of the recent progress in the field of 2D MOFs for sensor applications. Initially, the properties and synthesis techniques of 2D MOFs are briefly outlined with examples. Further, electrochemical and optical biosensors based on 2D MOFs are summarized, and the associated challenges are outlined.

Laser-Assisted Scalable Pore Fabrication in Graphene Membranes for Blue-Energy Generation.

The osmotic energy from a salinity gradient (i. e. blue energy) is identified as a promising non-intermittent renewable energy source for a sustainable technology. However, this membrane-based technology is facing major limitations for large-scale viability, primarily due to the poor membrane performance. An atomically thin 2D nanoporous material with high surface charge density resolves the bottleneck and leads to a new class of membrane material the salinity gradient energy. Although 2D nanoporous membranes show extremely high performance in terms of energy generation through the single pore, the fabrication and technical challenges such as ion concentration polarization make the nanoporous membrane a non-viable solution. On the other hand, the mesoporous and micro porous structures in the 2D membrane result in improved energy generation with very low fabrication complexity. In the present work, we report femtosecond (fs) laser-assisted scalable fabrication of µm to mm size pores on Graphene membrane for blue energy generation for the first time. A remarkable osmotic power in the order of µW has been achieved using mm size pores, which is about six orders of magnitudes higher compared to nanoporous membranes, which is mainly due to the diffusion-osmosis driven large ionic flux. Our work paves the way towards fs laser-assisted scalable pore creation in the 2D membrane for large-scale osmotic power generation.

A novel, highly sensitive electrochemical 1,4-dioxane sensor based on reduced graphene oxide-curcumin nanocomposite.

1,4-Dioxane is a carcinogenic, non-biodegradable, organic water pollutant which is used as a solvent in various industries. It is also formed as an undesired by-product in the cosmetic and pharmaceutical industry. Given its carcinogenicity and ability to pollute, it is desirable to develop a sensitive and selective sensor to detect it in drinking water and other water bodies. Current works on this sensor are very few and involve complex metal oxide composite systems. A sensitive electrochemical sensor for 1,4-dioxane was developed by modifying a glassy carbon electrode (GCE) with a reduced graphene oxide-curcumin (rGO-CM) nanocomposite synthesized by a simple solution approach. The prepared rGO-CM was characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) Spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, and Scanning Electron Microscopy (SEM). The rGO-CM/GCE sensor was employed for the detection of 1,4-dioxane in the range of 0.1-100 µM. Although, the detection range is narrower compared to reported literature, the sensitivity obtained for the proposed sensor is far superior. Moreover, the limit of detection (0.13 µM) is lower than the dioxane detection target defined by the World Health Organization (0.56 µM). The proposed rGO-CM/GCE also showed excellent stability and good recovery values in real sample (tap water and drinking water) analysis.

Design and development of an automated experimental setup for ion transport measurements.

The ion transport measurements using various ion-exchange membranes (IEMs) face several challenges, including controllability, reproducibility, reliability, and accuracy. This is due to the manual filling of the solutions in two different reservoirs in a typical diffusion cell experiment with a random flow rate, which results in the diffusion through the IEM even before turning on the data acquisition system as reported so far. Here, we report the design and development of an automated experimental setup for ion transport measurements using IEMs. The experimental setup has been calibrated and validated by performing ion transport measurements using a standard nanoporous polycarbonate membrane. We hope that the present work will provide a standard tool for realizing reliable ion transport measurements using ion-exchange membranes and can be extended to study other membranes of various pore densities, shapes, and sizes.

Toxicity of Graphene: An Update.

Graphene possesses wider biomedical applications including drug delivery, photothermal ablation of tumors, biosensors, and also in the disease diagnosis. The accidental or intentional exposure of the environment including plants, ecosystem, and humans toward graphene is gradually increasing. Therefore, graphene toxicity becomes a critical issue to be addressed despite their diverse applications in multiple fields. In this situation, the scientific community as well as the general public must get awareness about the toxicity of graphene. This article, therefore, reviews the investigations on graphene toxicity. This review reveals the toxicity of graphene in vitro, in vivo models along with the environmental toxicity. The advantages of graphene toxicity in bacterial cells and cancer cells were also reviewed.

Magnetic field assisted high capacity durable Li-ion battery using magnetic α-Fe2O3 nanoparticles decorated expired drug derived N-doped carbon anode.

We have synthesized a novel ferromagnetic material by coating α-Fe2O3 nanoparticles with N-doped carbon matrix using a simple combustion method. Expired paracetamol drugs are used as nitrogen and carbon source. This α-Fe2O3/NC shows ferromagnetic property due to the incorporation of oxygen defects. When used as the Li-ion battery anode, α-Fe2O3/NC shows higher capacity compared to commercial α-Fe2O3 due to the occurrence of both intercalation and conversion reaction. Further, application of magnetic field at the anode of the freshly assembled cell at the first charge-discharge cycle, results in ~two-fold enhancement in specific capacity. For the cycled cell also, increase in the capacity from 80 mAh. g-1 to 150 mAh. g-1 at 5 A. g-1 is observed during the application of magnetic field at the 501st charging cycle. This improved performance is attributed to the field-dependent enhancement of diffusion and convection due to the magnetohydrodynamic effect. Further, application of the magnetic field at 1001st, 1501st and 1751st charging cycles shows improved LIB performance. We can show that not only the magnetic field, magnetic properties of the anode α-Fe2O3/NC also play a crucial role in influencing the battery performance. Moreover, utilization of expired drug helps in dramatically reducing pollution caused by its disposal.

In situ nitrogen-doped, defect-induced carbon nanotubes as an efficient anode for sodium-ion batteries.

The incorporation of heteroatoms and defects in carbonaceous material is a well-known approach to improve the electrochemical performance of the anode in a sodium-ion battery (NIB). However, previous works aimed to use either heteroatom-doped or defect-enriched carbon material. The present work focuses on nitrogen-doped, defect-induced surface-modified carbon nanotubes (MN-BCNT) having the synergy of both the effects to improve the electrochemical performance of the NIB. Initially, in situ nitrogen-doped CNTs were grown using a scalable, cost-effective and green synthesis technique. In situ nitrogen doping introduces lattice defects resulting in bamboo-shaped CNTs. The defects were further enriched by opening the ends of the tubes and also by shortening them. This structure demonstrates the high capacity of 278 mA h g-1 at a current density of 50 mA g-1, which is more than double compared to conventional CNTs. The improved performance of MN-BCNT is attributed to the improved electrical conductivity due to nitrogen doping and the availability of significant active sites as a result of tube shortening. Moreover, the designed structure shows good cyclic stability at 200 mA g-1 accompanied with excellent rate capability.

Optimizing metal-support interphase for efficient fuel cell oxygen reduction reaction catalyst.

The development of cost-effective and highly-efficient electro-catalysts is essential for the advancement of proton exchange membrane fuel cells (PEMFC). We present a novel nitrogen-sulphur co-doped carbon nanotubes-few layer graphene1D-2D hybrid support formed by partially exfoliating multiwall carbon nanotubes (PECNT), to improve interface bonding to catalyst nanoparticles. Detailed Raman spectroscopy and STEM-EDS analyses demonstrate that active sites on the co-doped hybrid support ensure both uniform distribution and improved bonding of the catalyst nanoparticles to the support. Electrochemical studies show that Pt nanoparticles decorated on nitrogen-sulphur co-doped PECNT (Pt/NS-PECNT) have higher electrochemical active surface area and mass activity accompanied by low H2O2 formation and improved positive half-wave potential, as compared to those decorated on co-doped rGO-incorporated PECNT hybrid structure (Pt/NS-(rGO-PECNT)). Fuel cell measurements demonstrate a higher power density for our novel (Pt/NS-PECNT) electro-catalyst when compared to both Pt/NS-(rGO + PECNT), and commercial Pt/C electro-catalyst. We demonstrate in this work that the interconnectivity between Pt-nanoparticles and the dopant or defect sites on the support play a crucial role in enhancing the ORR activity, fuel cell performance, and durability of the catalyst.

Boron and nitrogen co-doped carbon nanosheets encapsulating nano iron as an efficient catalyst for electrochemical CO2 reduction utilizing a proton exchange membrane CO2 conversion cell.

Electrochemical carbon dioxide (CO2) reduction, ideally in an aqueous medium, accounts for the sustainable storage of energy from renewable sources in the form of chemical energy in fuels or value-added chemicals. Herein, we report boron and nitrogen co-doped carbon nanosheets encapsulating iron nanocrystals (Fe/BCNNS) as a low cost, highly efficient and precious-metal-free electrocatalyst for the electrochemical reduction of carbon dioxide to formic acid. The porous architecture of the boron and nitrogen co-doped carbon nanosheets along with the active Fe-Nx, N and B sites synergistically allow better three phase contact to enhance the electrocatalytic activity of the cell. Both half-cell as well as full cell measurements have been performed with this particular catalyst. The proton exchange membrane (PEM) CO2 conversion cell is tested under a continuous flow of CO2 gas and is demonstrated to selectively produce a high yield of formic acid due to improved interaction between the catalyst and gas molecules. The maximum yield of formic acid achieved is as high as 94% after 60 min of reaction with Fe/BCNNS as both anode and cathode catalysts. It can be anticipated that such a facile synthesis strategy and excellent electrocatalytic performance of low-cost Fe/BCNNS catalyst can be easily scaled up for industrial applications in electrochemical CO2 conversion.

Carbon nanotube bottles for incorporation, release and enhanced cytotoxic effect of cisplatin.

Carbon nanotubes (CNTs) have emerged as promising drug delivery systems particularly for cancer therapy, due to their abilities to overcome some of the challenges faced by cancer treatment, namely non-specificity, poor permeability into tumour tissues, and poor stability of anticancer drugs. Encapsulation of anticancer agents inside CNTs provides protection from external deactivating agents. However, the open ends of the CNTs leave the encapsulated drugs exposed to the environment and eventually their uncontrolled release before reaching the desired target. In this study, we report the successful encapsulation of cisplatin, a FDA-approved chemotherapeutic drug, into multi-walled carbon nanotubes and the capping at the ends with functionalised gold nanoparticles to achieve a "carbon nanotube bottle" structure. In this proof-of-concept study, these caps did not prevent the encapsulation of drug in the inner space of CNTs; on the contrary, we achieved higher drug loading inside the nanotubes in comparison with data reported in literature. In addition, we demonstrated that encapsulated cisplatin could be delivered in living cells under physiological conditions to exert its pharmacological action.

An efficient electrode material for high performance solid-state hybrid supercapacitors based on a Cu/CuO/porous carbon nanofiber/TiO2 hybrid composite.

A Cu/CuO/porous carbon nanofiber/TiO2 (Cu/CuO/PCNF/TiO2) composite uniformly covered with TiO2 nanoparticles was synthesized by electrospinning and a simple hydrothermal technique. The synthesized composite exhibits a unique morphology and excellent supercapacitive performance, including both electric double layer and pseudo-capacitance behavior. Electrochemical measurements were performed by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The highest specific capacitance value of 530 F g-1 at a current density of 1.5 A g-1 was obtained for the Cu/CuO/PCNF/TiO2 composite electrode in a three-electrode configuration. The solid-state hybrid supercapacitor (SSHSC) fabricated based on this composite exhibits a high specific capacitance value of 330 F g-1 at a current density of 1 A g-1 with 78.8% capacitance retention for up to 10,000 cycles. At the same time, a high energy density of 45.83 Wh kg-1 at a power density of 1.27 kW kg-1 was also realized. The developed electrode material provides new insight into ways to enhance the electrochemical properties of solid-state supercapacitors, based on the synergistic effect of porous carbon nanofibers, metal and metal oxide nanoparticles, which together open up new opportunities for energy storage and conversion applications.

Green synthesis of nitrogen-doped self-assembled porous carbon-metal oxide composite towards energy and environmental applications.

Increasing environmental pollution, shortage of efficient energy conversion and storage devices and the depletion of fossil fuels have triggered the research community to look for advanced multifunctional materials suitable for different energy-related applications. Herein, we have discussed a novel and facile synthesis mechanism of such a carbon-based nanocomposite along with its energy and environmental applications. In this present work, nitrogen-doped carbon self-assembled into ordered mesoporous structure has been synthesized via an economical and environment-friendly route and its pore generating mechanism depending on the hydrogen bonding interaction has been highlighted. Incorporation of metal oxide nanoparticles in the porous carbon network has significantly improved CO2 adsorption and lithium storage capacity along with an improvement in the catalytic activity towards Oxygen Reduction Reaction (ORR). Thus our present study unveils a multifunctional material that can be used in three different fields without further modifications.

Magnesium oxide modified nitrogen-doped porous carbon composite as an efficient candidate for high pressure carbon dioxide capture and methane storage.

In this particular work, a simple, cost-effective and single step process to synthesize magnesium oxide modified nitrogen doped porous carbon (MgO/NMC) by thermal decomposition technique has been elaborated and its high-pressure performance as CO2 and CH4 gas adsorbent is demonstrated. The uniformly distributed porous network in the samples was identified from the morphological studies by FESEM and TEM. Elemental analysis and XPS studies were carried out to understand the Mg and N contents. It has been observed that MgO/NMC shows appreciably high CO2 (30 mmol g-1 at 20 bar and 25 °C) as well as CH4 (12 mmol g-1 at 30 bar and 25 °C) adsorption capacity. The surface modification of the samples (caused by the presence of MgO nanoparticles) along with high surface area and good porosity containing interconnected macro-/ meso-/ micropores synergistically improves the adsorption capacity. In addition, high nitrogen content in the nanocomposite enhances the number of basic adsorption sites thereby increasing the gas adsorption capacity. The effect of concentration of MgO on gas adsorption capacities has also been investigated from the adsorption isotherms. The moderate heat of adsorption, as well as good recyclability and selectivity at high pressure, shows that MgO modified nitrogen doped porous carbon composite can be a promising candidate for both CO2 capture and CH4 storage.

Multi-walled carbon nanotube-induced inhalation toxicity: Recognizing nano bis-demethoxy curcumin analog as an ameliorating candidate.

Human beings and ecosystems are being possibly exposed to CNTs, as there is a rise in global production rate of carbon nanotubes (CNTs). This may affect the health of humans and increases the environmental risk. We have already reported the pulmonary toxicity due to the inhalation of MWCNTs. We claim that a compound with anti-inflammatory and antioxidant activity may ameliorate the CNT-induced toxic effect. With this view, we have investigated the ameliorative effect of intravenously-administered nano bis-demethoxy curcumin analog (NBDMCA) against MWCNTs-induced inhalation toxicity by examining the lung histopathology for inflammatory cell dynamics, pulmonary remodeling and estimating the inflammatory biomarkers in the broncho-alveolar lavage fluid. We observed that NBDMCA could ameliorate the injury as evidenced by the decline in the levels of markers of inflammation, cell damage, and the histopathological changes induced by MWCNTs. We conclude that NBDMCA may be used to reduce the risk of MWCNTs-induced inhalation toxicity.

Performance of Partially Exfoliated Nitrogen-Doped Carbon Nanotubes Wrapped with Hierarchical Porous Carbon in Electrolytes.

The preparation of highly conductive, high-surface-area, heteroatom-doped, porous carbon nanocomposite materials with enhanced electrochemical performance for sustainable energy-storage technologies, such as supercapacitors, is challenging. Herein, a route for the large-scale synthesis of nitrogen-doped porous carbon wrapped partially exfoliated carbon nanotubes (N-PPECNTs) with an interconnected hierarchical porous structure, as an advanced electrode material that can realize several potential applications for energy storage, is presented. Polypyrrole conductive polymer acts as both nitrogen and carbon sources that contribute to the pseudocapacitance. Partially exfoliated carbon nanotubes (PECNTs) provide a high specific surface area for ion and charge transportation and act as a conductive matrix. The derived porous N-PPECNT displays a nitrogen content of 6.95 at %, with a specific surface area of 2050 m2 g-1 , and pore volume of 1.13 cm3 g-1 . N-PPECNTs, as an electrode material for supercapacitors, exhibit an excellent specific capacitance of 781 F g-1 at 2 A g-1 , with a high cycling stability of 95.3 % over 10 000 cycles. Furthermore, the symmetric supercapacitor exhibits remarkable energy densities as high as 172.8, 62.7, and 53.55 Wh kg-1 in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([BMIM][TFSI]), organic, and aqueous electrolytes, respectively. Also, biocompatible hydrogel and polymer gel electrolyte based, stable, flexible supercapacitors with excellent electrochemical performance could be demonstrated.

High-performance Platinum-free oxygen reduction reaction and hydrogen oxidation reaction catalyst in polymer electrolyte membrane fuel cell.

The integration of polymer electrolyte membrane fuel cell (PEMFC) stack into vehicles necessitates the replacement of high-priced platinum (Pt)-based electrocatalyst, which contributes to about 45% of the cost of the stack. The implementation of high-performance and durable Pt metal-free catalyst for both oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) could significantly enable large-scale commercialization of fuel cell-powered vehicles. Towards this goal, a simple, scalable, single-step synthesis method was adopted to develop palladium-cobalt alloy supported on nitrogen-doped reduced graphene oxide (Pd3Co/NG) nanocomposite. Rotating ring-disk electrode (RRDE) studies for the electrochemical activity towards ORR indicates that ORR proceeds via nearly four-electron mechanism. Besides, the mass activity of Pd3Co/NG shows an enhancement of 1.6 times compared to that of Pd/NG. The full fuel cell measurements were carried out using Pd3Co/NG at the anode, cathode in conjunction with Pt/C and simultaneously at both anode and cathode. A maximum power density of 68 mW/cm2 is accomplished from the simultaneous use of Pd3Co/NG as both anode and cathode electrocatalyst with individual loading of 0.5 mg/cm2 at 60 °C without any backpressure. To the best of our knowledge, the present study is the first of its kind of a fully non-Pt based PEM full cell.

Synergistic Role of Electrolyte and Binder for Enhanced Electrochemical Storage for Sodium-Ion Battery.

Sodium-ion batteries are promising futuristic large-scale energy-storage devices because of the abundance and low cost of sodium. However, the development and commercialization of the sodium-ion battery solely depends on the use of high-capacity electrode materials. Among the various metal oxides, SnO2 has a high theoretical specific capacity for sodium-ion battery. However, the enormous volume expansion and low electrical conductivity of SnO2 hinder its capability to reach the predicted theoretical value. Although different nanostructured designs of electrode materials like SnO2 nanocomposites have been studied, the effects of other cell components like electrolyte and binder on the specific capacity and cyclic stability are yet to be understood. In the present study, we have investigated the synergistic effect of electrolyte and binder on the performance enhancement of SnO2 supported on the intertwined network structure of reduced graphene oxide partially open multiwalled carbon nanotube hybrid as anode in sodium-ion battery. Our result shows that sodium carboxyl methyl cellulose and ethylene carbonate/diethyl carbonate as the electrolyte solvent offers a high specific capacity of 688 mAh g-1 and a satisfactory cyclic stability for 500 cycles. This is about 56% enhancement in specific capacity compared to the use of poly(vinylidene fluoride) binder and propylene carbonate as the electrolyte solvent. The present study provides a better understanding of the synergistic role of electrolyte and binder for the development of metal-oxide-based electrode materials for the advancement of the commercialization of sodium-ion battery.

Development of a nitrogen-doped 2D material for tribological applications in the boundary-lubrication regime.

The present paper describes a facile synthesis method for nitrogen-doped reduced graphene oxide (N-rGO) and the application of N-rGO as an effective additive for improving the tribological properties of base oil. N-rGO has been characterized by different characterization techniques such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. N-rGO-based nanolubricants are prepared and their tribological properties are studied using a four-ball tester. The nanolubricants show excellent stability over a period of six months and a significant decrease in coefficient of friction (25%) for small amounts of N-rGO (3 mg/L). The improvement in tribological properties can be attributed to the sliding mechanism of N-rGO accompanied by the high mechanical strength of graphene. Further, the nanolubricant is prepared at large scale (700 liter) and field trials are carried out at one NTPC thermal plant in India. The implementation of the nanolubricant in an induced draft (ID) fan results in the remarkable decrease in the power consumption.

Towards Intravenous Drug Delivery: Augmenting the Stability and Dispersity of Bis-Demethoxy Curcumin Analog by Bottom-Up Strategy.

Intravenous route is the best strategy to accomplish fastest and highest delivery of drugs. Hydrophobic drugs like curcumin and its analog exhibit disadvantages like low bioavailability, poor absorption and rapid precipitation on intravenous delivery, all leading to its poor therapeutic value. These can be by-passed by enhancing the dispersity, stability and decreasing the size of the drug by nanotization. Thus, with an intention to deliver bis-demethoxy curcumin analog via intravenous route, we have studied the effect of DMSO, ethanol and acetone on the size, size distribution, stability and yield and identified the best solvent in terms of smallest size, narrow size distribution, more stability and high yield of nano bis-demethoxy curcumin analog (NBDMCA). NBDMCA prepared using DMSO showed the lowest mean particle size cum polydispersity index and highest zeta potential when compared to ethanol and acetone. Hence the DMSO based formulation can provide prolonged action and better efficacy at minimal doses. Thus, the DMSO based NBDMCA can emerge as an ideal therapeutic tool for human use.

Spontaneous and specific myogenic differentiation of human mesenchymal stem cells on polyethylene glycol-linked multi-walled carbon nanotube films for skeletal muscle engineering.

This study explored the influence of polyethylene glycol-linked multi-walled carbon nanotube (PEG-CNT) films on skeletal myogenic differentiation of human mesenchymal stem cells (hMSCs). PEG-CNT films were prepared with nanoscale surface roughness, orderly arrangement of PEG-CNTs, high hydrophilicity and high mechanical strength. Notably, PEG-CNT films alone could direct the skeletal myogenic differentiation of hMSCs in the absence of myogenic induction factors. The quantitative real-time polymerase chain reaction (RT-PCR) showed that the non-induced hMSCs plated on the PEG-CNT films, compared to the negative control, presented significant up-regulation of general myogenic markers including early commitment markers of myoblast differentiation protein-1 (MyoD) and desmin, as well as a late phase marker of myosin heavy chain-2 (MHC). Corresponding protein analysis by immunoblot assays corroborated these results. Skeletal muscle-specific markers, fast skeletal troponin-C (TnC) and ryanodine receptor-1 (Ryr) were also significantly increased in the non-induced hMSCs on PEG-CNT films by RT-PCR. For these cells, the commitment to specific skeletal myoblasts was further proved by the absence of enhanced adipogenic, chondrogenic and osteogenic markers. This study elucidated that PEG-CNT films supported a dedicated differentiation of hMSCs into a skeletal myogenic lineage and can work as a promising material towards skeletal muscle injury repair.