Controlled Covalent Functionalization of Thermally Reduced Graphene Oxide To Generate Defined Bifunctional 2D Nanomaterials

Covalent functionalization of 1D and 2D sp2-carbon nanoallotropes - twelve years of progress (2011-2023)

Carbon nanoallotropes have attracted significant attention in the field of materials science due to their unique combination of physicochemical and biological properties, with numerous applications. One-dimensional (1D) and two-dimensional (2D) sp2-carbon nanoallotropes, such as carbon nanohorns (CNHs), carbon nanotubes (CNTs), and graphene, have emerged as prominent candidates for a variety of technological advancements. To fully exploit their exceptional characteristics, the covalent functionalization of these nanostructures may alleviate the problems with the processing and final performance. This route of the carbon nanoallotrope functionalization is based on a covalent attachment of functional groups or molecules (via linkers of various strengths) to their surfaces, enabling precise control over physical, chemical, biological, and electronic properties. Such an approach opens up new avenues for tailoring the nanoallotrope characteristics, such as solubility/dispersibility, reactivity, and interactions with other materials. Over more than the last decade, significant progress has been made in the covalent functionalization of both 1D and 2D sp2-carbon nanoallotropes, paving the way for diverse applications in the nanoelectronics, energy storage, sensing, and biomedical fields. In this comprehensive review, we provide state-of-the-art advancements and achievements in the covalent functionalization of 1D and 2D sp2-carbon nanoallotropes during the past dozen years. We aim to highlight the key strategies, methodologies, and breakthroughs that have significantly contributed to this field. Eventually, we discuss the implications of those advancements and explore the opportunities for future research and applications.

Electrochemical biosensing based on folic acid-triazine-grafted reduced graphene oxide: a highly selective breast cancer cell sensor

Based on the results of this research, a new electrochemical sensor has been developed to detect human breast cancer cells (MCF-7). A folic acid (FA)-functionalized triazine-grafted reduced graphene oxide (RGOTrz) was used as the modifier of a glassy carbon electrode (GCE) for application as the sensing element. The composition of the resulting FA-RGOTrz/GCE was investigated using XRD (X-ray diffraction), FT-IR (Fourier-transform infrared) spectroscopy, SEM (scanning electron microscopy) and UV-vis spectroscopy studies. CV (cyclic voltammetry) and EIS (electrochemical impedance spectroscopy) techniques were also used to characterize the electrochemical proficiency of the new electrode. Further, MCF-7 cancer cells were examined in solutions of phosphate buffer and [Fe(CN)6]3-/4- as a suitable supporting electrolyte and a useful probe, respectively. The FA-RGOTrz/GCE provides a suitable substrate to reversible redox reactions and provides good electrochemical signals after binding to cancer cells. DPV (differential pulse voltammetry) results indicated that the binding of folate receptor (FR) in the MCF-7 cell to the RGOTrz-modified electrode, in the presence of [Fe(CN)6]3-/4-, reduced folic acid, diminished electron transfer and collapsed the current signal. During the measured flow, a detection limit of 50 human breast cancer cells per milliliter was obtained. The FA-RGOTrz/GCE, with its unique structural design, significantly increases the electron transfer and electrochemical activity towards the detection of MCF-7 cells. This FA-RGOTrz/GCE sensor, due to its special structure, shows high sensitivity to FR in MCF-7 cells and excellent, reliable and satisfactory performance and a great promise for use in industries and medical field.

Functionalized Fullerene for Inhibition of SARS-CoV-2 Variants

As virus outbreaks continue to pose a challenge, a nonspecific viral inhibitor can provide significant benefits, especially against respiratory viruses. Polyglycerol sulfates recently emerge as promising agents that mediate interactions between cells and viruses through electrostatics, leading to virus inhibition. Similarly, hydrophobic C₆₀ fullerene can prevent virus infection via interactions with hydrophobic cavities of surface proteins. Here, two strategies are combined to inhibit infection of SARS-CoV-2 variants in vitro. Effective inhibitory concentrations in the millimolar range highlight the significance of bare fullerene's hydrophobic moiety and electrostatic interactions of polysulfates with surface proteins of SARS-CoV-2. Furthermore, microscale thermophoresis measurements support that fullerene linear polyglycerol sulfates interact with the SARS-CoV-2 virus via its spike protein, and highlight importance of electrostatic interactions within it. All-atom molecular dynamics simulations reveal that the fullerene binding site is situated close to the receptor binding domain, within 4 nm of polyglycerol sulfate binding sites, feasibly allowing both portions of the material to interact simultaneously.

Organic-Inorganic Porphyrinoid Frameworks for Biomolecule Sensing

Porphyrinoids and their analogous compounds play an important role in biosensing applications on account of their unique and versatile catalytic, coordination, photophysical, and electrochemical properties. Their remarkable arrays of properties can be finely tuned by synthetically modifying the porphyrinoid ring and varying the various structural parameters such as peripheral functionalization, metal coordination, and covalent or physical conjugation with other organic or inorganic scaffolds such as nanoparticles, metal-organic frameworks, and polymers. Porphyrinoids and their organic-inorganic conjugates are not only used as responsive materials but also utilized for the immobilization and embedding of biomolecules for applications in wearable devices, fast sensing devices, and other functional materials. The present review delineates the impact of different porphyrinoid conjugates on their physicochemical properties and their specificity as biosensors in a range of applications. The newest porphyrinoid types and their synthesis, modification, and functionalization are presented along with their advantages and performance improvements.

Heavy‐Atom Quantum Tunnelling in Spin Crossovers of Nitrenes**

We simulate two recent matrix‐isolation experiments at cryogenic temperatures, in which a nitrene undergoes spin crossover from its triplet state to a singlet state via quantum tunnelling. We detail the failure of the commonly applied weak‐coupling method (based on a linear approximation of the potentials) in describing these deep‐tunnelling reactions. The more rigorous approach of semiclassical golden‐rule instanton theory in conjunction with double‐hybrid density‐functional theory and multireference perturbation theory does, however, provide rate constants and kinetic isotope effects in good agreement with experiment. In addition, these calculations locate the optimal tunnelling pathways, which provide a molecular picture of the reaction mechanism. The reactions involve substantial heavy‐atom quantum tunnelling of carbon, nitrogen and oxygen atoms, which unexpectedly even continues to play a role at room temperature.

Integration of Nanographenes and Organic Chemistry - Toward Nanographene-based Two-Dimensional Materials

Graphene and its relatives have received considerable attention from the fields of physics and chemistry since the isolation of pristine graphene sheets. Nanographenes (NGs) are graphene fragments that are a few to tens of nanometers in diameter. Compared to graphene and its relatives, such as graphene oxides, NGs can be handled more easily, and their large π surface and oxygen functional groups on the edge allow postsynthetic modifications. The study of NGs is gradually shifting from the development of synthetic procedures to postsynthetic modification. From the structural point of view, NGs can be regarded as two-dimensional carbon polymers. Their unique structures and affinity for organic molecules make NGs excellent scaffolds for two-dimensional materials, which are now an important topic in organic and polymer chemistry. In this conceptual article, we introduce the position of NGs from the perspective of two-dimensional substances and briefly summarize both the structural features of NGs and the effects of functionalization on their physical properties. These are valuable when producing reasonable strategies for their postsynthetic modifications.

Modification of carbon-based nanomaterials by polyglycerol: recent advances and applications

Hyperbranched polymers, a subclass of dendritic polymers, mimic nature's components such as trees and nerves. Hyperbranched polyglycerol (HPG) is a hyperbranched polyether with outstanding physicochemical properties, including high water-solubility and functionality, biocompatibility, and an antifouling feature. HPG has attracted great interest in the modification of different objects, in particular carbon-based nanomaterials. In this review, recent advances in the synthesis and application of HPG to modify carbon-based nanomaterials, including graphene, carbon nanotubes, fullerene, nanodiamonds, carbon dots, and carbon fibers, are reviewed.

Modification of carbon nanomaterials by hyperbranched polyglycerol improves their properties.

Development of Graphene-Based Polymeric Nanocomposites: A Brief Overview

Graphene (G) and its derivatives, such as graphene oxide (GO) and reduced GO (rGO), have outstanding electrical, mechanical, thermal, optical, and electrochemical properties, owed to their 2D structure and large specific surface area. Further, their combination with polymers leads to novel nanocomposites with enhanced structural and functional properties due to synergistic effects. Such nanocomposites are becoming increasingly useful in a wide variety of fields ranging from biomedicine to the electronics and energy storage applications. In this review, a brief introduction on the aforementioned G derivatives is presented, and different strategies to develop polymeric nanocomposites are described. Several functionalization methods including covalent and non-covalent approaches to increase their interaction with polymers are summarized, and selected examples are provided. Further, applications of this type of nanocomposites in the field of energy are discussed, including lithium-ion batteries, supercapacitors, transparent conductive electrodes, counter electrodes of dye-sensitized solar cells, and active layers of organic solar cells. Finally, the challenges and future outlook for G-based polymeric nanocomposites are discussed.

Functionalized Graphene Platforms for Anticancer Drug Delivery

Two-dimensional nanomaterials are emerging as promising candidates for a wide range of biomedical applications including tissue engineering, biosensing, pathogen incapacitation, wound healing, and gene and drug delivery. Graphene, due to its high surface area, photothermal property, high loading capacity, and efficient cellular uptake, is at the forefront of these materials and plays a key role in this multidisciplinary research field. Poor water dispersibility and low functionality of graphene, however, hamper its hybridization into new nanostructures for future nanomedicine. Functionalization of graphene, either by covalent or non-covalent methods, is the most useful strategy to improve its dispersion in water and functionality as well as processability into new materials and devices. In this review, recent advances in functionalization of graphene derivatives by different (macro)molecules for future biomedical applications are reported and explained. In particular, hydrophilic functionalization of graphene and graphene oxide (GO) to improve their water dispersibility and physicochemical properties is discussed. We have focused on the anticancer drug delivery of polyfunctional graphene sheets.

Graphene-Assisted Synthesis of 2D Polyglycerols as Innovative Platforms for Multivalent Virus Interactions

2D nanomaterials have garnered widespread attention in biomedicine and bioengineering due to their unique physicochemical properties. However, poor functionality, low solubility, intrinsic toxicity, and nonspecific interactions at biointerfaces have hampered their application in vivo. Here, biocompatible polyglycerol units are crosslinked in two dimensions using a graphene-assisted strategy leading to highly functional and water-soluble polyglycerols nanosheets with 263 ± 53 nm and 2.7 ± 0.2 nm average lateral size and thickness, respectively. A single-layer hyperbranched polyglycerol containing azide functional groups is covalently conjugated to the surface of a functional graphene template through pH-sensitive linkers. Then, lateral crosslinking of polyglycerol units is carried out by loading tripropargylamine on the surface of graphene followed by lifting off this reagent for an on-face click reaction. Subsequently, the polyglycerol nanosheets are detached from the surface of graphene by slight acidification and centrifugation and is sulfated to mimic heparin sulfate proteoglycans. To highlight the impact of the two-dimensionality of the synthesized polyglycerol sulfate nanosheets at nanobiointerfaces, their efficiency with respect to herpes simplex virus type 1 and severe acute respiratory syndrome corona virus 2 inhibition is compared to their 3D nanogel analogs. Four times stronger in virus inhibition suggests that 2D polyglycerols are superior to their current 3D counterparts.

Conductive Nanofilms with Oppositely Charged Reduced Graphene Oxides as a Base for Electroactive Coatings and Sensors

We demonstrate a method for the formation of multilayers composed of reduced graphene oxide (rGO), which can be used for transparent, conducting thin films. Using the layer-by-layer (LbL) assembly of positively and negatively charged GO sheets, we could obtain thin films with highly controllable sheet resistance. The natural negative charge of graphene oxide was turned to positive by the amidation reaction. After forming the multilayer films, the graphene oxide underwent thermal reduction at temperatures above 150 °C. The (rGO+/rGO−) films were characterized by UV-Vis and scanning electron microscopy (SEM), and their conductivity was measured by the four-point method. We found that after deposition of five (rGO+/rGO−), the coating structure reached the percolation limit, and the film resistance decreased more gradually to around 20 kΩ/sq for the films obtained by eleven deposition cycles with graphene oxide reduced at 250 °C. The formation of thin films on polyimide allows the forming of new flexible conductive materials, which can find applications, e.g., in biomedicine as new electroactive, low-cost, disposable sensors.

Nonspherical Metal-Based Nanoarchitectures: Synthesis and Impact of Size, Shape, and Composition on Their Biological Activity

Metal-based nanoentities, apart from being indispensable research tools, have found extensive use in the industrial and biomedical arena. Because their biological impacts are governed by factors such as size, shape, and composition, such issues must be taken into account when these materials are incorporated into multi-component ensembles for clinical applications. The size and shape (rods, wires, sheets, tubes, and cages) of metallic nanostructures influence cell viability by virtue of their varied geometry and physicochemical interactions with mammalian cell membranes. The anisotropic properties of nonspherical metal-based nanoarchitectures render them exciting candidates for biomedical applications. Here, the size-, shape-, and composition-dependent properties of nonspherical metal-based nanoarchitectures are reviewed in the context of their potential applications in cancer diagnostics and therapeutics, as well as, in regenerative medicine. Strategies for the synthesis of nonspherical metal-based nanoarchitectures and their cytotoxicity and immunological profiles are also comprehensively appraised.

Chiral Graphene Hybrid Materials: Structures, Properties, and Chiral Applications

Chirality has become an important research subject. The research areas associated with chirality are under substantial development. Meanwhile, graphene is a rapidly growing star material and has hard-wired into diverse disciplines. Rational combination of graphene and chirality undoubtedly creates unprecedented functional materials and may also lead to great findings. This hypothesis has been clearly justified by the sizable number of studies. Unfortunately, there has not been any previous review paper summarizing the scattered studies and advancements on this topic so far. This overview paper attempts to review the progress made in chiral materials developed from graphene and their derivatives, with the hope of providing a systemic knowledge about the construction of chiral graphenes and chiral applications thereof. Recently emerging directions, existing challenges, and future perspectives are also presented. It is hoped this paper will arouse more interest and promote further faster progress in these significant research areas.

Graphene Sheets with Defined Dual Functionalities for the Strong SARS-CoV-2 Interactions

Search of new strategies for the inhibition of respiratory viruses is one of the urgent health challenges worldwide, as most of the current therapeutic agents and treatments are inefficient. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a pandemic and has taken lives of approximately two million people to date. Even though various vaccines are currently under development, virus, and especially its spike glycoprotein can mutate, which highlights a need for a broad-spectrum inhibitor. In this work, inhibition of SARS-CoV-2 by graphene platforms with precise dual sulfate/alkyl functionalities is investigated. A series of graphene derivatives with different lengths of aliphatic chains is synthesized and is investigated for their ability to inhibit SARS-CoV-2 and feline coronavirus. Graphene derivatives with long alkyl chains (>C9) inhibit coronavirus replication by virtue of disrupting viral envelope. The ability of these graphene platforms to rupture viruses is visualized by atomic force microscopy and cryogenic electron microscopy. A large concentration window (10 to 100-fold) where graphene platforms display strongly antiviral activity against native SARS-CoV-2 without significant toxicity against human cells is found. In this concentration range, the synthesized graphene platforms inhibit the infection of enveloped viruses efficiently, opening new therapeutic and metaphylactic avenues against SARS-CoV-2.

Graphene Sheets with Defined Dual Functionalities for the Strong SARS-CoV-2 Interactions

Search of new strategies for the inhibition of respiratory viruses is one of the urgent health challenges worldwide, as most of the current therapeutic agents and treatments are inefficient. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused a pandemic and has taken lives of approximately two million people to date. Even though various vaccines are currently under development, virus, and especially its spike glycoprotein can mutate, which highlights a need for a broad-spectrum inhibitor. In this work, inhibition of SARS-CoV-2 by graphene platforms with precise dual sulfate/alkyl functionalities is investigated. A series of graphene derivatives with different lengths of aliphatic chains is synthesized and is investigated for their ability to inhibit SARS-CoV-2 and feline coronavirus. Graphene derivatives with long alkyl chains (>C9) inhibit coronavirus replication by virtue of disrupting viral envelope. The ability of these graphene platforms to rupture viruses is visualized by atomic force microscopy and cryogenic electron microscopy. A large concentration window (10 to 100-fold) where graphene platforms display strongly antiviral activity against native SARS-CoV-2 without significant toxicity against human cells is found. In this concentration range, the synthesized graphene platforms inhibit the infection of enveloped viruses efficiently, opening new therapeutic and metaphylactic avenues against SARS-CoV-2.

Edge-Functionalized Nanographenes

Nanographenes (NGs) have recently emerged as new carbon materials. Their nanoscale size results in a size-dependent quantum confinement effect, opening the band gap by a few eV. This energy gap allows NGs to be applied as optical materials. This property has attracted researchers across multiple scientific fields. The photophysical properties of NGs can be manipulated by introducing organic groups onto their basal planes and/or into their edges. In addition, the integration of organic functional groups into NGs results in NG-based hybrid materials. These features make the post-synthetic modification of NGs an active research area. As obtainable information on chemically functionalized NGs is limited owing to their nonstoichiometry and structural uncertainty, their structural characterization requires a combination of multiple spectroscopic methods. Therefore, information on the characterization procedures of recently published chemically functionalized NGs is of value for advancing the field of NG-based hybrid materials. The present review focuses on the structural characterization of chemically functionalized NGs. It is hoped that this review will help to advance this field.

Chemically Functionalized Two-Dimensional Carbon Materials

Nanographenes (NGs), also known as graphene quantum dots, have recently been developed as nanoscale graphene fragments. These nanocarbon species can be excited with UV light and emit light from the UV-to-visible region. This photoemission has received great attraction across multiple scientific fields. NGs can be produced by cutting off carbon sources or fusing small organic molecules to grow graphitic structures. Furthermore, the organic synthesis of NGs has been intensely studied. Recently, the number of research papers on postsynthetic modification of NGs has gradually increased. Installed organic groups can tune the properties of NGs and provide new functionalities, opening the door for the development of sophisticated carbon-based functional materials. This review sheds light on recent progress in the postsynthetic modification of NGs and provides a brief summary of their production methods.

Metal-Assisted and Solvent-Mediated Synthesis of Two-Dimensional Triazine Structures on Gram Scale

Covalent triazine frameworks are an emerging material class that have shown promising performance for a range of applications. In this work, we report on a metal-assisted and solvent-mediated reaction between calcium carbide and cyanuric chloride, as cheap and commercially available precursors, to synthesize two-dimensional triazine structures (2DTSs). The reaction between the solvent, dimethylformamide, and cyanuric chloride was promoted by calcium carbide and resulted in dimethylamino-s-triazine intermediates, which in turn undergo nucleophilic substitutions. This reaction was directed into two dimensions by calcium ions derived from calcium carbide and induced the formation of 2DTSs. The role of calcium ions to direct the two-dimensionality of the final structure was simulated using DFT and further proven by synthesizing molecular intermediates. The water content of the reaction medium was found to be a crucial factor that affected the structure of the products dramatically. While 2DTSs were obtained under anhydrous conditions, a mixture of graphitic material/2DTSs or only graphitic material (GM) was obtained in aqueous solutions. Due to the straightforward and gram-scale synthesis of 2DTSs, as well as their photothermal and photodynamic properties, they are promising materials for a wide range of future applications, including bacteria and virus incapacitation.

Self-degrading graphene sheets for tumor therapy

Low biodegradability of graphene derivatives and related health risks are the main limiting factors for their in vivo biomedical applications. Here, we present the synthesis of enzyme-functionalized graphene sheets with self-degrading properties under physiological conditions and their applications in tumor therapy. The synergistic enzyme cascade glucose oxidase and myeloperoxidase are covalently conjugated to the surface of graphene sheets and two-dimensional (2D) platforms are obtained that can produce sodium hypochlorite from glucose. The enzyme-functionalized graphene sheets with up to 289 nm average size are degraded into small pieces (≤40 nm) by incubation under physiological conditions for 24 h. Biodegradable graphene sheets are further loaded with doxorubicin and their ability for tumor therapy is evaluated in vitro and in vivo. The laser-triggered release of doxorubicin in combination with the enzymatic activity of the functionalized graphene sheets results in a synergistic antitumor activity. Taking advantage of their neutrophil-like activity, fast biodegradability, high photo- and chemotherapeutic effects, the novel two-dimensional nanoplatforms can be used for tumor therapeutic applications.

Functionalized nanographene sheets with high antiviral activity through synergistic electrostatic and hydrophobic interactions

As resistance to traditional drugs emerges for treatment of virus infections, the need for new methods for virus inhibition increases. Graphene derivatives with large surface areas have shown strong activity against different viruses. However, the inability of current synthetic protocols to accurately manipulate the structure of graphene sheets in order to control their antiviral activity remains a major challenge. In this work, a series of graphene derivatives with defined polyglycerol sulfate and fatty amine functionalities have been synthesized and their interactions with herpes simplex virus type 1 (HSV-1) are investigated. While electrostatic interactions between polyglycerol sulfate and virus particles trigger the binding of graphene to virus, alkyl chains induce a high antiviral activity by secondary hydrophobic interactions. Among graphene sheets with a broad range of alkyl chains, (C3-C18), the C12-functionalized sheets showed the highest antiviral activity, indicating the optimum synergistic effect between electrostatic and hydrophobic interactions, but this derivative was toxic against the Vero cell line. In contrast, sheets functionalized with C6- and C9-alkyl chains showed low toxicity against Vero cells and a synergistic inhibition of HSV-1. This study shows that antiviral agents against HSV-1 can be obtained by controlled and stepwise functionalization of graphene sheets and may be developed into antiviral agents for future biomedical applications.

Graphite and Graphene Fairy Circles: A Bottom-Up Approach for the Formation of Nanocorrals

A convenient covalent functionalization approach and nanopatterning method of graphite and graphene is developed. In contrast to expectations, electrochemically activated dediazotization of a mixture of two aryl diazonium compounds in aqueous media leads to a spatially inhomogeneous functionalization of graphitic surfaces, creating covalently modified surfaces with quasi-uniform spaced islands of pristine graphite or graphene, coined nanocorrals. Cyclic voltammetry and chronoamperometry approaches are compared. The average diameter (45-130 nm) and surface density (20-125 corrals/μm²) of these nanocorrals are tunable. These chemically modified nanostructured graphitic (CMNG) surfaces are characterized by atomic force microscopy, scanning tunneling microscopy, Raman spectroscopy and microscopy, and X-ray photoelectron spectroscopy. Mechanisms leading to the formation of these CMNG surfaces are discussed. The potential of these surfaces to investigate supramolecular self-assembly and on-surface reactions under nanoconfinement conditions is demonstrated.

Thermoresponsive Amphiphilic Functionalization of Thermally Reduced Graphene Oxide to Study Graphene/Bacteria Hydrophobic Interactions

An understanding of the interactions of 2D nanomaterials with pathogens is of vital importance to developing and controlling their antimicrobial properties. In this work, the interaction of functionalized graphene with tunable hydrophobicity and bacteria is investigated. Poly(ethylene glycol)- block-(poly- N-isopropylacrylamide) copolymer (PEG- b-PNIPAM) with the triazine joint point was attached to the graphene surface by a nitrene [2 + 1] cycloaddition reaction. By thermally switching between hydrophobic and hydrophilic states, functionalized graphene sheets were able to bind to bacteria. Bacteria were eventually disrupted when the functionality was switched to the hydrophobic state. On the basis of measuring the different microscopy methods and a live/dead viability assay, it was found that Escherichia coli ( E. coli) bacteria are more susceptible to hydrophobic interactions than B. cereus bacteria, under the same conditions. Our investigations confirm that hydrophobic interaction is one of the main driving forces at the presented graphene/bacteria interfaces and promotes the antibacterial activity of graphene derivatives significantly.

Scalable Production of Nanographene and Doping via Nondestructive Covalent Functionalization

A new method for top-down, one-pot, gram-scale production of high quality nanographene by incubating graphite in a dilute sodium hypochlorite solution at only 40 °C is reported here. The produced sheets have only 4 at% oxygen content, comparable with nanographene grown by chemical vapor deposition. The nanographene sheets are covalently functionalized using a nondestructive nitrene [2+1] cycloaddition reaction that preserves their π-conjugated system. Statistical analyses of Raman spectroscopy and X-ray photoelectron spectroscopy indicate a low number of sp³ carbon atoms on the order of 2% before and 4% after covalent functionalization. The nanographene sheets are significantly more conductive than conventionally prepared nanographene oxide, and conductivity further increases after covalent functionalization. The observed doping effects and theoretical studies suggest sp² hybridization for the carbon atoms involved in the [2+1] cycloaddition reaction leading to preservation of the π-conjugated system and enhancing conductivity via n-type doping through the bridging N-atom. These methods are easily scalable, which opens the door to a mild and efficient process to produce high quality nanographenes and covalently functionalize them while retaining or improving their physicochemical properties.

Multivalent Interactions between 2D Nanomaterials and Biointerfaces

2D nanomaterials, particularly graphene, offer many fascinating physicochemical properties that have generated exciting visions of future biological applications. In order to capitalize on the potential of 2D nanomaterials in this field, a full understanding of their interactions with biointerfaces is crucial. The uptake pathways, toxicity, long-term fate of 2D nanomaterials in biological systems, and their interactions with the living systems are fundamental questions that must be understood. Here, the latest progress is summarized, with a focus on pathogen, mammalian cell, and tissue interactions. The cellular uptake pathways of graphene derivatives will be discussed, along with health risks, and interactions with membranes-including bacteria and viruses-and the role of chemical structure and modifications. Other novel 2D nanomaterials with potential biomedical applications, such as transition-metal dichalcogenides, transition-metal oxide, and black phosphorus will be discussed at the end of this review.

A facile and processable integration strategy towards Schiff-base polymer-derived carbonaceous materials with high lithium storage performance

Herein, a novel in situ concentrated-solution-induced polymerization strategy is developed towards the integration of Schiff-base networks into graphene foam with processable and moldable characteristics. This bottom-up design process endows the resultant composites with a high nitrogen content (9.6 at%) and abundant porosity and accordingly demonstrates high lithium storage properties.

Functionalized 2D nanomaterials with switchable binding to investigate graphene-bacteria interactions

Graphene and its derivatives have recently attracted much attention for sensing and deactivating pathogens. However, the mechanism of multivalent interactions at the graphene-pathogen interface is not fully understood. Since different physicochemical parameters of graphene play a role at this interface, control over graphene's structure is necessary to study the mechanism of these interactions. In this work, different graphene derivatives and also zwitterionic graphene nanomaterials (ZGNMs) were synthesized with defined exposure, in terms of polymer coverage and functionality, and isoelectric points. Then, the switchable interactions of these nanomaterials with E. coli and Bacillus cereus were investigated to study the validity of the generally proposed "trapping" and "nano-knives" mechanisms for inactivating bacteria by graphene derivatives. It was found that the antibacterial activity of graphene derivatives strongly depends on the accessible area, i.e. edges and basal plane of sheets and tightness of their agglomerations. Our data clearly confirm the authenticity of "trapping" and "nano-knives" mechanisms for the antibacterial activity of graphene sheets.

A Water-Processable and Bioactive Multivalent Graphene Nanoink for Highly Flexible Bioelectronic Films and Nanofibers

The capabilities of conductive nanomaterials to be produced in liquid form with well-defined chemical, physical, and biological properties are highly important for the construction of next-generation flexible bioelectronic devices. Although functional graphene nanomaterials can serve as attractive liquid nanoink platforms for the fabrication of bioelectronics, scalable synthesis of graphene nanoink with an integration of high colloidal stability, water processability, electrochemical activity, and especially bioactivity remains a major challenge. Here, a facile and scalable synthesis of supramolecular-functionalized multivalent graphene nanoink (mGN-ink) via [2+1] nitrene cycloaddition is reported. The mGN-ink unambiguously displays a well-defined and flat 2D morphology and shows good water processability and bioactivity. The uniquely chemical, physical, and biological properties of mGN-ink endow the constructed bioelectronic films and nanofibers with high flexibility and durability, suitable conductivity and electrochemical activity, and most importantly, good cellular compatibility and a highly efficient control of stem-cell spreading and orientation. Overall, for the first time, a water-processable and bioactive mGN-ink is developed for the design of flexible and electrochemically active bioelectronic composites and devices, which not only presents manifold possibilities for electronic-cellular applications but also establishes a new pathway for adapting macroscopic usages of graphene nanomaterials in bionic, biomedical, electronic, and even energy fields.

Facile synthesis of graphitic C3N4 nanoporous-tube with high enhancement of visible-light photocatalytic activity

A simple and convenient method was used to synthesize a graphitic carbon nitride (g-C₃N₄) nanoporous-tube by using SiO₂ nanoparticles as pore formers. The structure of the g-C₃N₄ nanoporous-tube was characterized by the SEM and TEM images. Taking photodegradation of RhB as an example, the photocatalytic activity of the as-prepared g-C₃N₄ nanoporous-tube was investigated. It can photodegrade 90% RhB in 40 min under visible-light irradiation and obtain a k value of 0.04491 min^-1, which is 8.16 times that of bulk g-C₃N₄, 3.09 times that of tubular g-C₃N₄ and 1.48 times that of tubular g-C₃N₄-SiO₂. The significant enhancement in photocatalytic efficiency is due to the edge effect of the pores and the special structure of the tubes. In addition, the possible mechanism of photocatalytic degradation of RhB was also proposed based on the trapping experiment of active species, which indicated that the superoxide radicals ([Formula: see text]) and the holes (h ⁺) were the main reactive species in this photocatalyst. This work may open up a new idea of innovation in g-C₃N₄ structure and inspire its follow-up study.

Functionalized graphene sheets for intracellular controlled release of therapeutic agents

Since therapeutic agents target specific compartments inside the cells, their efficiency depends on their intracellular release from drug delivery systems (DDS). However, control over the intracellular release of therapeutic agents is a challenging issue and can only be achieved by governing their interactions with the DDS. In this work, polyglycerol amine- and polyglycerol sulfate-functionalized graphene sheets as positively and negatively charged 2D nanomaterials with 150 nm lateral size were used to deliver and control the release of doxorubicin (DOX) inside cells. A pH-sensitive dye was conjugated onto the surfaces of graphene sheets and used as an antenna to obtain specific signals from the acidic cell compartments. It was found that both positively and negatively charged graphene sheets undergo similar acidification processes after cellular uptake. Nevertheless, the intracellular drug release of these DOX-loaded nanomaterials was distinctly different. As an overall effect of the π-π stacking and electrostatic interactions, the release of DOX from the positively charged graphene sheets was much faster than that from their analogs with a negative surface charge. Therefore, therapeutic efficiency in the first case was much higher than that in the latter. Based on our findings, the intracellular release of drugs from the surfaces of graphene sheets can be finely tuned by manipulating their functionalities, which is of great importance in the designing of the future graphene-based nanomedicines.

Twin defects engineered Pd cocatalyst on C3N4 nanosheets for enhanced photocatalytic performance in CO2 reduction reaction

Photocatalytic conversion of CO₂ to value-added chemicals, a potential route to addressing the depletion of fossil fuels and anthropogenic climate change, is greatly limited by the low-efficient semiconductor photocatalyst. The integration of cocatalyst with light-harvesting semiconductor is a promising approach to enhancing the photocatalytic performance in CO₂ reduction reaction. The enhancement is greatly determined by the catalytic active sites on the surface of cocatalyst. Herein, we demonstrate that the photocatalytic performance in the CO₂ reduction reaction is greatly promoted by twin defects engineered Pd cocatalyst. In this work, Pd nanoicosahedrons with twin defects were in situ grown on C₃N₄ nanosheets, which effectively improve the photocatalytic performance in reduction of CO₂ to CO and CH₄ in comparison with Pd nanotetrahedrons without twin defects. It is proposed that the twin boundary (TB) terminations on the surface of Pd cocatalysts are highly catalytic active sites for CO₂ reduction reaction. Based on the proposed mechanism, the photocatalytic activity and selectivity in CO₂ reduction were further advanced through reducing the size of Pd icosahedral cocatalyst resulted from the increased surface density of TB terminations. The defect engineering on the surface of cocatalyst represents a novel route in realizing high-performance photocatalytic applications.

Controlled Covalent Functionalization of Thermally Reduced Graphene Oxide To Generate Defined Bifunctional 2D Nanomaterials

A controlled, reproducible, gram-scale method is reported for the covalent functionalization of graphene sheets by a one-pot nitrene [2+1] cycloaddition reaction under mild conditions. The reaction between commercially available 2,4,6-trichloro-1,3,5-triazine and sodium azide with thermally reduced graphene oxide (TRGO) results in defined dichlorotriazine-functionalized sheets. The different reactivities of the chlorine substituents on the functionalized graphene allow stepwise post-modification by manipulating the temperature. This new method provides unique access to defined bifunctional 2D nanomaterials, as exemplified by chiral surfaces and multifunctional hybrid architectures.