Nitrogen-doped Graphene Oxide Nanosheets Research Articles

Pink photoluminescent nitrogen-doped graphene oxide nanosheets from Juniperus squamata roots and their cytotoxic potential against human cervical cancer cells (HeLa cells) and Plasmodium falciparum an agent of malaria: A green approach

In this paper, we reported a green synthesis of nitrogen-doped graphene oxide nanosheets (N-GONSs) from Juniperus squamata roots along with its cytotoxic potential against HeLa cells, human cervical cancer cells and Plasmodium falciparum, a causative agent of malaria in humans. The water-soluble and high fluorescent N-GONSs were synthesized by hydrothermal process using Juniperus squamata roots and ethylenediaminetetraacetic acid (EDTA), as carbon and nitrogen sources without any chemical modification. The X-ray photoelectron spectroscopy (XPS) analysis confirmed that the N-GONSs were mainly composed of carbon, oxygen and nitrogen. The synthesized N-GONSs showed pink luminescence behavior under the short wavelength at 250 nm. The viabilities of the HeLa cancer cells for N-GONSs were 76.47%, 43.98%, and 20.55% after 24 h and 48 h, and 72 h, respectively, at the concentration of 50 μg/mL. Also, N-GONSs showed moderate antimalarial activity with IC50 PF3D7 45 μg/mL. Furthermore, they were also nontoxic to VERO cells (C 1008; monkey kidney epithelial cells) up to a concentration of 100 μg/mL. The present study reflected that the N-GONSs show potential cytotoxicity against HeLa cells and Plasmodium falciparum.

Ab initio study of N-doped graphene oxide (NDGO) as a promising anode material for Li-ion rechargeable battery

ABSTRACT Since high capacity small rechargeable ion storage batteries are greatly required due to the increasing development of mobile technologies, search for new types of electrode materials with superior electrochemical properties are being explored. From its synthesis, graphene and its derivatives have been hypothesised as potential candidates for the anode material for Li-ion batteries (LIB) for their excellent electronic properties. In this work, first-principles simulation has been performed to investigate structural, electronic, adsorption and electrochemical properties of LIB where three different nitrogen-doped graphene oxide nanosheets (NDGO), with one, two and three oxygen atoms, have been chosen as anode materials with density functional theory using GGA-PBE functional. Our electrode materials predict superior structural stability without significant structural deformation. We have found that the Li+ ions are adsorbed on the electrode materials with favourable adsorption energy of 2.68 eV. The theoretical specific capacity has been found to be 1150 mAh/g which is three times higher than conventional bulk graphite. Moreover, during the lithiation process, the open-circuit voltage is found to be of 2.19 V which is benign for suppressing the dendrites formation. Our investigations provide an indication to develop better anode materials with high structural stability and high-capacity Li-ion batteries.

Mechanistic aspects for the removal of Congo red dye from aqueous media through adsorption over N-doped graphene oxide nanoadsorbents prepared from graphite flakes and powders

This work reports the mechanistic models responsible for the adsorptive removal of Congo red (CR) dye molecules by nitrogen-doped graphene oxide nanosheets (NGO) prepared via a one-pot modified Hummer's method using either graphite powder (to form NGOp) or graphite flakes (to form NGOf) as starting materials. The microstructural properties, surface chemistry and thermal stability of the produced NGO adsorbents were ascertained using a range of characterization techniques. The effects of adsorbent dosage, CR dye initial concentration, contact time and solution pH on the removal of CR dye were studied. The NGO adsorption process was highly dependent on initial dye concentration, contact time, adsorbent dosage, pH, NGO surface area and nanosheet size. The NGOp nanoadsorbents exhibited excellent selectivity towards the removal of CR dye molecules than NGOf. NGOp adsorbents achieved maximum removal efficiency of 98–99% at a pH of 2 compared to NGOf that achieved 96–98%. The adsorption kinetics and isotherms for CR dye on the NGO adsorbents were well fitted to the pseudo second-order kinetic model. The Langmuir isotherm model indicated that the adsorption behavior occurred via chemisorption and in a homogeneous monolayer on the surface of NGO. Our findings suggest that the adsorption mechanism involved was due to electrostatic interactions between the negatively charged (oxygen-containing) and positively charged (nitrogen-containing) groups on the NGO adsorbents and the positively charged (amino and cationic azo-linkages) and negatively charged (sulfonic (SO3−)) groups on the anionic CR dye molecules. The electrostatic interactions between oxygen and nitrogen containing functional groups present on the NGO surface and functional moieties of CR molecules are necessary for the enhancement of CR adsorption over NGO surface (based on the existing pH dependence). NGOp nanosheets have shown to have higher removal potential and adsorption capacity toward CR dye compared to undoped GO and NGOf adsorbents. In particular, this work indicates that NGOp can serve as good adsorbents in the removal of anionic dyes in wastewater treatment processes.

Facile Synthesis of Nitrogen Doped Graphene Oxide from Graphite Flakes and Powders: A Comparison of Their Surface Chemistry

Nitrogen-doped graphene oxide (NGO) nanosheets were prepared via a facile one-pot modified Hummer's approach at low temperatures using graphite powder and flakes as starting materials in the presence of a nitrogen precursor. It was found that the morphology, structure, composition and surface chemistry of the NGO nanosheets depended on the nature of the graphite precursor used. GO nanosheets doped with nitrogen atoms exhibited a unique structure with few thin layers and wrinkled sheets, high porosity and structural defects. NGO sheets made from graphite powder (NGOp) exhibited excellent thermal stability and remarkably high surface area (up to 240.53 m2 ·g-1) compared to NGO sheets made from graphite flakes (NGOf) which degraded at low temperatures and had an average surface area of 24.70 m2 ·g-1. NGOf sheets had a size range of 850 to 2200 nm while NGOp sheets demonstrated obviously small sizes (460-1600 nm) even when exposed to different pH conditions. The NGO nanosheets exhibited negatively charged surfaces in a wide pH range (1 to 12) and were found to be stable above pH 6. In addition, graphite flakes were found to be more suitable for the production of NGO as they produced high N-doping levels (0.65 to 1.29 at.%) compared to graphite powders (0.30 to 0.35 at.%). This study further demonstrates that by adjusting the amount of N source in the host GO, one can tailor its thermal stability, surface morphology, surface chemistry and surface area.

Highly dispersed of Ni0.85Se nanoparticles on nitrogen-doped graphene oxide as efficient and durable electrocatalyst for hydrogen evolution reaction

To promote the improvement of the hydrogen evolution reaction (HER) performance, it is critical to expose as many active sites of Ni0.85Se as possible. In this study, we prepared well-dispersed Ni0.85Se nanoparticles on nitrogen-doped graphene oxide (NGO) assisted by the ethylenediamine treatment of NGO before selenylation reaction during hydrothermal process. The NGO nanosheets decorated by uniformly distributed Ni0.85Se nanoparticles was confirmed to be the optimal morphology with maximum catalytic active sites. Moreover, optimized structure control resulted in strong interaction between Ni0.85Se and NGO, which contributes to effective electron delivery, thus leading to excellent HER activity evidenced from the small overpotential of 104 mV at 10 mA cm−2, the low Tafel slope of 50.7 mV dec−1. Moreover, the catalyst exhibits outstanding stability which accelerates the electrochemical measurement. This work provides a general approach to the synthesis of highly dispersed nanoparticles grown on the two-dimensional carbon substrate materials for catalytic reactions.

Nanocomposites of sulphur-nitrogen co-doped graphene oxide nanosheets and cobalt mono carboxyphenoxy phthalocyanines for facile electrocatalysis

Nanocomposites consisting of cobalt mono carboxyphenoxy phthalocyanine (CoMCPhPc) either covalently linked to graphene oxide nanosheets (GONS), sulphur doped graphene oxide nanosheets (SDGONS), nitrogen doped graphene oxide nanosheets (NDGONS) or sulphur/nitrogen co-doped graphene oxide nanosheets (SNDGONS) or sequentially added were used to modify glassy carbon electrode. The modified electrodes were characterised using several techniques: voltammetry, X-ray photon spectroscopy and scanning electron spectroscopy before testing their activity on the detection of hydrogen peroxide at pH7. The presence of SNDGONS had a significant improvement on the currents as compared to CoMCPhPc modification alone in both sequentially added or covalently linked to MPcs. CoMCPhPc-SNDGONS(seq)-GCE and CoMCPhPc-SDGONS(linked)-GCE resulted in impressive limits of detection and catalytic rate constant values of 1.58nM and 5.44nM, 3.07×105M−1s−1 and 3.01×103M−1s−1 respectively. Gibbs energy value was determined to be −21.22kJmol−1 for CoMCPhPc-SNDGONS(linked)-GCE indicative of a facile spontaneous electroreduction reaction on the surface of this electrode.

Development of nanocomposites of phosphorus-nitrogen co-doped graphene oxide nanosheets and nanosized cobalt phthalocyanines for electrocatalysis

Conjugates of reduced phosphorus-nitrogen co-doped graphene oxide nanosheets (rPNDGONS), reduced phosphorus doped graphene oxide nanosheets (rPDGONS), reduced nitrogen doped graphene oxide nanosheets (rNDGONS), reduced pyrolised graphene oxide nanosheets (rpyGONS) with nanosized cobalt (II) phthalocyanine (CoPcNP) or cobalt tetra amino phenoxy phthalocyanine (CoTAPhPcNP) were characterised and tested for their electrocatalytic behaviour towards the detection of hydrogen peroxide. Cyclic and linear scan voltammetries, and chronoamperometry were used to evaluate the electrocatalytic nature of the designed probes. For hydrogen peroxide detection, CoPcNP-rPNDGONS-GCE oxidation gave sensitivity of 12.00mA/M, limit of detection of 4.48nM, a rate constant of 2.66×105M−1s−1, adsorption equilibrium constant of 3.7×102M−1 and Gibbs free energy −14.84kJmol−1. The lowest detection limit was obtained for CoTAPhPcNP-rPNDGONS-GCE at 1.21nM.

Electrode modification using nanocomposites of boron or nitrogen doped graphene oxide and cobalt (II) tetra aminophenoxy phthalocyanine nanoparticles

Reduced graphene oxide nanosheets (rGONS), reduced boron doped graphene oxide nanosheets (rBDGONS) and reduced nitrogen doped graphene oxide nanosheets (rNDGONS) and their composites with cobalt tetra aminophenoxy phthalocyanine nanoparticles (CoTAPhPcNP) were employed towards the detection of hydrogen peroxide. The nanomaterials were characterized by absorption spectroscopy, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, linear sweep voltammetry and cyclic voltammetry. rNDGONS showed excellent electrooxidation and electroreduction of hydrogen peroxide supported by superior surface coverage values. The inclusion of nanosized Pc significantly lowered the reduction overpotential. CoTAPhPcNP-rNDGONS-GCE gave a sensitivity of 39.30mA/M, catalytic rate constant of 1×103M−1s−1 and a detection limit of 8.2nM. An adsorption equilibrium constant and Gibbs free energy of 1.26×103M−1 and −17.69kJmol−1 respectively were observed.