Nitrogen-doped graphene: effect of graphite oxide precursors and nitrogen content on the electrochemical sensing properties

Heteroatom Codoped Graphene: The Importance of Nitrogen

Although graphene has exceptional properties, they are not enough to solve the extensive list of pressing world problems. The substitutional doping of graphene using heteroatoms is one of the preferred methods to adjust the physicochemical properties of graphene. Much effort has been made to dope graphene using a single dopant. However, in recent years, substantial efforts have been made to dope graphene using two or more dopants. This review summarizes all the hard work done to synthesize, characterize, and develop new technologies using codoped, tridoped, and quaternary doped graphene. First, I discuss a simple question that has a complicated answer: When can an atom be considered a dopant? Then, I briefly discuss the single atom doped graphene as a starting point for this review's primary objective: codoped or dual-doped graphene. I extend the discussion to include tridoped and quaternary doped graphene. I review most of the systems that have been synthesized or studied theoretically and the areas in which they have been used to develop new technologies. Finally, I discuss the challenges and prospects that will shape the future of this fascinating field. It will be shown that most of the graphene systems that have been reported involve the use of nitrogen, and much effort is needed to develop codoped graphene systems that do not rely on the stabilizing effects of nitrogen. I expect that this review will contribute to introducing more researchers to this fascinating field and enlarge the list of codoped graphene systems that have been synthesized.

Moderating cellular inflammation using 2-dimensional titanium carbide MXene and graphene variants

The effective control of microbial and metabolically derived biological toxins which negatively impact physical health remains a key challenge for the 21st century. 2-Dimensional graphene and MXene nanomaterials are relatively new additions to the field of biomedical materials with superior external surface areas suited to adsorptive remediation of biological toxins. However, relatively little is known about their physiological interactions with biological systems and, to date, no comparative biological studies have been done. This study compares titanium carbide MXene (Ti3C2Tx) in multilayered and delaminated forms with graphene variants to assess the impact of variable physical properties on cellular inflammatory response to endotoxin stimulus. No significant impact on cell metabolism or induction of inflammatory pathways leading to cell death was observed. No significant increase in markers of blood cell activation and haemolysis occurred. Whilst graphene nanoplatelets (GNP), graphene oxide (GO) and Ti3C2Tx showed insignificant antibacterial activity towards Escherichia coli, silver nanoparticle-modified GO (GO-Ag) induced bacterial cell death and at a lower dose than silver nanoparticles. All nanomaterials significantly reduced bacterial endotoxin induced THP-1 monocyte IL-8, IL-6 and TNF-α cytokine production by >99%, >99% and >80% respectively, compared to control groups. This study suggests the utility of these nanomaterials as adsorbents in blood contacting medical device applications for removal of inflammatory cytokines linked to poor outcome in patients with life-threatening infection.

Heteroatom-doped graphene as sensing materials: a mini review

Graphene is one of the astounding recent advancements in current science and one of the most encouraging materials for application in cutting-edge electronic gadgets. Graphene and its derivatives like graphene oxide and reduced graphene oxide have emerged as significant nanomaterials in the area of sensors. Furthermore, doping of graphene and its derivatives with heteroatoms (B, N, P, S, I, Br, Cl and F) alters their electronic and chemical properties which are best suited for the construction of economical sensors of practical utility. This review recapitulates the developments in graphene materials as emerging electrochemical, ultrasensitive explosive, gas, glucose and biological sensors for various molecules with greater sensitivity, selectivity and a low limit of detection. Apart from the most important turn of events, the properties and incipient utilization of the ever evolving family of heteroatom-doped graphene are also discussed. This review article encompasses a wide range of heteroatom-doped graphene materials as sensors for the detection of NH₃, NO₂, H₂O₂, heavy metal ions, dopamine, bleomycinsulphate, acetaminophen, caffeic acid, chloramphenicol and trinitrotoluene. In addition, heteroatom-doped graphene materials were also explored for sensitivity and selectivity with respect to interfering analytes present in the system. Finally, the review article concludes with future perspectives for the advancement of heteroatom-doped graphene materials.

Graphene is one of the astounding recent advancements in current science and one of the most encouraging materials for application in cutting-edge electronic gadgets.

Effect of Doping Temperatures and Nitrogen Precursors on the Physicochemical, Optical, and Electrical Conductivity Properties of Nitrogen-Doped Reduced Graphene Oxide

The greatest challenge in graphene-based material synthesis is achieving large surface area of high conductivity. Thus, tuning physico-electrochemical properties of these materials is of paramount importance. An even greater problem is to obtain a desired dopant configuration which allows control over device sensitivity and enhanced reproducibility. In this work, substitutional doping of graphene oxide (GO) with nitrogen atoms to induce lattice–structural modification of GO resulted in nitrogen-doped reduced graphene oxide (N-rGO). The effect of doping temperatures and various nitrogen precursors on the physicochemical, optical, and conductivity properties of N-rGO is hereby reported. This was achieved by thermal treating GO with different nitrogen precursors at various doping temperatures. The lowest doping temperature (600 °C) resulted in less thermally stable N-rGO, yet with higher porosity, while the highest doping temperature (800 °C) produced the opposite results. The choice of nitrogen precursors had a significant impact on the atomic percentage of nitrogen in N-rGO. Nitrogen-rich precursor, 4-nitro-ο-phenylenediamine, provided N-rGO with favorable physicochemical properties (larger surface area of 154.02 m² g⁻¹) with an enhanced electrical conductivity (0.133 S cm⁻¹) property, making it more useful in energy storage devices. Thus, by adjusting the doping temperatures and nitrogen precursors, one can tailor various properties of N-rGO.

A novel one-pot facile economic approach for the mass synthesis of exfoliated multilayered nitrogen-doped graphene-like nanosheets: new insights into the mechanistic study

The present research focuses on providing a novel facile, cost-effective and eco-friendly method for the mass production of N-doped graphene-like nanosheets (NGLs), in order to industrially benefit the exploitation of N-doped graphene in electronics, which will lead to the remarkable prosperity of graphene-based nanoelectronics. NGLs have been synthesized through a one-pot single-step process involving hydrolysis/hydrothermal treatment of glucose under mild conditions, using cetyltrimethylammonium bromide (CTAB) and ammonia solution (NH₄OH) as the structure-directing agents. NGLs of high yield (65 wt%) and fascinating structural features, including low oxidation level, good crystalline structural order, and large laterally sized and well-exfoliated nanosheets, have been produced. The growth mechanism has been deeply investigated. The impressive chemical nature of CTAB has a synergistic effect in controlling the NGL structure. The cationic head of CTAB and anionic OH^- ions resulting from NH₄OH ionization have formed a passivating layer that played a profound role in hindering the NGL agglomeration and allowing the NGLs to grow into large lateral dimensions. Meanwhile, the polar (mainly H-bonding) and apolar (hydrophobic) interfacial interactions between the passivating layer and the graphitic network can be mainly considered responsible for the mild disturbed structural order inside the sp² crystals. On the other hand, the excessive decomposition of CTAB that is also accompanied by fair ammonia decomposition during the hydrothermal treatment resulted in plenty of hydrogen and nitrogen gases in the atmosphere. The nitrogen gas N-doped the graphitic structure and the hydrogen gas effectively deoxygenated it. Furthermore, the high evolution rate of gases throughout the synthesis system contributed to the obstruction of NGL agglomeration. These results emphasize the high yield and good quality of the synthesized NGLs, which makes such a strategy promising in trust acquisition for investors in industrial production of N-doped graphene.

A Molecular Interaction Analysis Reveals the Possible Roles of Graphene Oxide in a Glucose Biosensor

In this paper, we report the molecular docking study of graphene oxide and glucose oxidase (GOx) enzyme for a potential glucose biosensing application. The large surface area and good electrical properties have made graphene oxide as one of the best candidates for an enzyme immobilizer and transducer in the biosensing system. Our molecular docking results revealed that graphene oxide plays a role as a GOx enzyme immobilizer in the glucose biosensor system since it can spontaneously bind with GOx at specific regions separated from the active sites of glucose and not interfering or blocking the glucose sensing by GOx in an enzyme-assisted biosensor system. The strongest binding affinity of GOx-graphene oxide interaction is -11.6 kCal/mol and dominated by hydrophobic interaction. Other modes of interactions with a lower binding affinity have shown the existence of some hydrogen bonds (H-bonds). A possibility of direct sensing (interaction) model of glucose by graphene oxide (non-enzymatic sensing mechanism) was also studied in this paper, and showed a possible direct glucose sensing by graphene oxide through the H-bond interaction, even though with a much lower binding affinity of -4.2 kCal/mol. It was also found that in a direct glucose sensing mechanism, the sensing interaction can take place anywhere on the graphene oxide surface with almost similar binding affinity.

Chemistry of Graphene Derivatives: Synthesis, Applications, and Perspectives

The chemistry of graphene and its derivatives is one of the hottest topics of current material science research. The derivatisation of graphene is based on various approaches, and to date functionalization with halogens, hydrogen, various functional groups containing oxygen, sulfur, nitrogen, phosphorus, boron, and several other elements have been reported. Most of these functionalizations are based on sp³ hybridization of carbon atoms in the graphene skeleton, which means the formation of out-of-plane covalent bonds. Several elements were also reported for substitutional modification of graphene, where the carbon atoms are substituted with atoms like nitrogen, boron, and several others. From tens of functional groups, for only two of them were reported full functionalization of graphene skeleton and formation of its stoichiometric counterparts, fluorographene and hydrogenated graphene. The functionalization of graphene is crucial for most of its applications including energy storage and conversion devices, electronic and optic applications, composites, and many others.