Microwave-assisted rapid synthesis of nitrogen-enriched amphibious carbon quantum dots for sensitive detection of ROS and multiple other applications

Carbon quantum dots (CQDs) have gained tremendous attention due to their pertinence in diverse application fields. Herein, we report the application of nitrogen-doped CQDs (N-CQDs) for the sensitive detection of reactive oxygen species (ROS) in vitro. The N-CQDs were synthesized via a rapid, one-pot, cost-effective and environmentally friendly approach, and exhibited amphibious solubility in solvents with a wide range of relative polarities from 1 to 0.4. Spectroscopic and microscopic techniques were used to accomplish the functional, morphological, and optical characterization of these nanoparticles. The as-synthesized luminous N-CQDs reproducibly demonstrated an average size distribution with a diameter of 5-6 nm. Their suitability for multiple other applications, such as metal sensing, confidential information inscription, hosting on cellulose materials with long-standing stability, designing polysaccharide molds flashing bright fluorescence, fingerprint imprinting, and in vitro bioimaging has also been exhibited. The plausible mechanism of peroxide induced fluorescence quenching of CQDs is presented. Treatment of human neuroblastoma cells SH-SY5Y with 1000 μg mL^-1 N-CQDs demonstrated excellent (∼100%) cell viability. An empirical relation between fluorescent intensity of N-CQDs as a function of the concentration of oxidants inside single-cells has been established for the first time.

Dual-channel P-type ternary DNTT–graphene barristor

P-type ternary switch devices are crucial elements for the practical implementation of complementary ternary circuits. This report demonstrates a p-type ternary device showing three distinct electrical output states with controllable threshold voltage values using a dual-channel dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]-thiophene–graphene barristor structure. To obtain transfer characteristics with distinctively separated ternary states, novel structures called contact-resistive and contact-doping layers were developed. The feasibility of a complementary standard ternary inverter design around 1 V was demonstrated using the experimentally calibrated ternary device model.

Waste derived approach towards wealthy fluorescent N-doped graphene quantum dots for cell imaging and H2O2 sensing applications

Herein, we report the synthesis of a highly fluorescent nitrogen doped graphene quantum dots (N-GQDs) from waste precursors such as melamine sponge and arjuna bark via a microwave treatment and its functional and morphological characterization using various spectroscopy techniques such as optical, FTIR, XPS and TEM. The as-prepared aqueous N-GQD (dia. 2-3 nm) was used for the bio-imaging application using breast carcinoma cell line (MDA-MB-231) as a model, and the locations of all cells in the cytoplasm as well as nuclei were observed to stain brightly in blue fluorescent color successfully. In addition to that, the aqueous N-GQD showed fluorescence quenching behavior in the presence of hydrogen peroxide, which was exploited to sense H₂O₂, a probable toxin generated in the diseased cells. Importantly, the cell cytotoxicity was measured and found to be non-toxic (70% survival) to the MDA-MB-231 cells even at very high concentration (∼1.8 mg/ml) of the synthesized N-GQD. This study revealing excellent biocompatibility and imaging of the model cancer cells, and sensing of H₂O₂ by fluorescent quenching, indicates potential in-vivo cell culture applications of the prepared fluorescent N-GQD.

Phosphorous grafted chitosan functionalized graphene oxide based nanocomposite as novel flame retardant

We report synthesis of phosphorous grafted chitosan functionalized graphene oxide (GO) based nanocomposite (PCG) as a highly potent flame retardant (FR). PCG coated cloth (PCGC) sample on exposure to flame...

Red-fluorescent graphene quantum dots from guava leaf as a turn-off probe for sensing aqueous Hg(ii)

In this work, we have prepared red-fluorescent graphene quantum dots and utilized as a highly selective and sensitive fluorescence turn-off probe for detection of the toxic metal ion Hg²⁺ from guava leaf extract.

Novel approach towards the synthesis of highly efficient flame retardant electrode and oil/organic solvent absorber

We have developed a facile one pot process to synthesize an ultra-light functionalized spongy graphene (FSG). This is the first approach to use carbon based flame retardant spongy material as an electrode to build completely flame retardant supercapacitor (FRS) also as an oil/organic solvent absorber. The fully FRS concept has created by the compilation of as-prepared FSG with flame retardant separator and electrolyte. As-prepared FSG contained high amount of phosphorus and nitrogen functional groups, which makes it potent flame retardant electrochemical material, to use it as an efficient FR electrode. Flame test of FSG revealed that it doesn't catch fire for ∼1500 s. Also, FSG was able to sustain flame retardancy at a temperature as high as 1500 °C for continuous exposure of ∼300 s. FSG used as an electrode for symmetric capacitor possessing maximum specific capacitance of 494.3 F g^-1 at a current density 1 A g^-1. Corresponding high energy density and power density values are 55.6 Wh kg^-1 and 1799 W kg^-1. It shows cycling stability of 86.1% after 5000 cycles at current density of 10 A g^-1. The electrochemical property of FSG was also confirmed using three electrode system. Flame retardant FSG material was also used for the absorption and recovery of oil and organic solvents. FSG has high oil and organic solvent sorption capacity in the range of 40-70 g/g, also can be reused for minimum 10 cycles. Such approach has great significance for multifunctional graphene based nanocomposites will open the new window for large-scale applications.

One-Pot Synthesis of Sulfur and Nitrogen Co-Functionalized Graphene Material using Deep Eutectic Solvents for Supercapacitors

A green approach to the synthesis of sulfur and nitrogen co-functionalized reduced graphene oxide (SN-rGO) is presented; it involves the reduction of graphene oxide (GO) using a deep eutectic solvent (DES) as chemical reducing agent and dopant. For the first time, a DES of choline chloride and sodium sulfide comprising cheap and safe components is introduced, and is both highly effective and reusable as a reducing agent for the production of SN-rGO. The DES is utilized as a solvent as well as reducing agent and dopant to generate SN-rGO. This DES is highly efficient in removing oxygen functionalities from GO and for subsequent sulfur and nitrogen functionalization for high energy-storage efficiency. The reduction ability of this DES is confirmed with five consecutive cycles, which adds to its sustainability and recyclability in the development of energy-storage devices. SN-rGO exhibits a high specific capacitance of 509 F g^-1 at 1 A g^-1 , which corresponds to high energy and power densities of 57.3 Wh kg^-1 and 1804.7 W kg^-1 , respectively. This simple and green method for direct reduction of GO with sulfur and nitrogen functionalization on the graphene surface can provide cost-effective bulk production of a nanocarbon template for energy storage applications.

Deep Eutectic Solvent Functionalized Graphene Composite as an Extremely High Potency Flame Retardant

We report a simple and green approach to develop the deep eutectic solvent functionalized graphene derivative as an effective flame retardant. The deep eutectic solvent functionalized graphene oxide (DESGO) was synthesized by introducing nitrogen-supported phosphorus functional groups on the surface of graphene derivative via a deep eutectic solvent, which is prepared by the treatment of monosodium dihydrogen orthophosphate and choline chloride. Subsequently, the resultant DESGO material is characterized by X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The as prepared DESGO solution coated cloth piece was sustaining its initial shape and size by releasing a little amount of smoke at the early stage without catching fire for more than 540 s (9 min), whereas the pristine cloth is totally burned out within 10 s, leaving small amounts of black mass. This simple method of directly functionalized deep eutectic solvent on a graphene oxide surface can be a common process for the cost-effective bulk production of a nano carbon template for extremely high potency, nontoxic flame retardant applications.

Fast synthesis of high-quality reduced graphene oxide at room temperature under light exposure

An approach of presenting new reducing reagents, sodium-benzophenone (Na-B) or Na-B in the presence of the hydrazine (Na-B-H) system under light exposure could produce rGOs with/without N-doping at room temperature in both the solution phase and on a solid substrate. Benzophenone activated those solutions acting as a photosensitizer under light. It was assumed that the newly generated radical anions with electrons from Na-B under light can reduce GO to rGO sheets (rGONa-B1). In addition, the Na-B-H system can allow a higher degree of reduction with the doping of nitrogen atoms by the introduction of hydrazine to produce radical anions and electrons with a sodium hydrazide complex, which helps decrease the sheet resistance of the as-made rGONa-B-H2. The excellent properties (very low oxygen content (C/O ∼16.2), and low sheet resistance (∼130 Ω square(-1))) of the rGOs were confirmed by XPS, XRD, IR, Raman spectroscopy, TGA, wettability, and sheet resistance measurements. High-quality rGO films on flexible substrates could be prepared by directly immersing the GO films in these solutions for several minutes.

Highly hydrophilic and insulating fluorinated reduced graphene oxide

A facile method for the synthesis of highly fluorinated reduced graphene oxide from graphene oxide using BF3-OEt2 solution and alkylthiol/alkylamine on the Gram scale has been described using a detailed mechanism. The maximum fluorination was as high as 38 wt% and the fluorinated reduced graphene oxide produced has great wettability and high insulating properties.

Highly sensitive and selective gas sensor using hydrophilic and hydrophobic graphenes

New hydrophilic 2D graphene oxide (GO) nanosheets with various oxygen functional groups were employed to maintain high sensitivity in highly unfavorable environments (extremely high humidity, strong acidic or basic). Novel one-headed polymer optical fiber sensor arrays using hydrophilic GO and hydrophobic reduced graphene oxide (rGO) were carefully designed, leading to the selective sensing of volatile organic gases for the first time. The two physically different surfaces of GO and rGO could provide the sensing ability to distinguish between tetrahydrofuran (THF) and dichloromethane (MC), respectively, which is the most challenging issue in the area of gas sensors. The eco-friendly physical properties of GO allowed for faster sensing and higher sensitivity when compared to previous results for rGO even under extreme environments of over 90% humidity, making it the best choice for an environmentally friendly gas sensor.

Highly air-stable phosphorus-doped n-type graphene field-effect transistors

Phosphorus-doped double-layered graphene field-effect transistors (PDGFETs) show much stronger air-stable n-type behavior than nitrogen-doped double-layered graphene FETs (NDGFETs), even under an oxygen atmosphere, due to strong nucleophilicity, which may lead to real applications for air-stable n-type graphene channels.

Dual functions of highly potent graphene derivative-poly-L-lysine composites to inhibit bacteria and support human cells

Dual-function poly(L-lysine) (PLL) composites that function as antibacterial agents and promote the growth of human cell culture have been sought by researchers for a long period. In this paper, we report the preparation of new graphene derivative-PLL composites via electrostatic interactions and covalent bonding between graphene derivatives and PLL. The resulting composites were characterized by infrared spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The novel dual function of PLL composites, specifically antibacterial activity and biocompatibility with human cells [human adipose-derived stem cells and non-small-cell lung carcinoma cells (A549)], was carefully investigated. Graphene-DS-PLL composites composed of 4-carboxylic acid benzene diazonium salt (DS) generated more anionic carboxylic acid groups to bind to cationic PLLs, forming the most potent antibacterial agent among PLL and PLL composites with high biocompatibility with human cell culture. This dual functionality can be used to inhibit bacterial growth while enhancing human cell growth.