Surface Functionalization Of Graphene Research Articles

Graphene-Based Photodynamic Therapy and Overcoming Cancer Resistance Mechanisms: A Comprehensive Review.

Photodynamic therapy (PDT) is a non-invasive therapy that has made significant progress in treating different diseases, including cancer, by utilizing new nanotechnology products such as graphene and its derivatives. Graphene-based materials have large surface area and photothermal effects thereby making them suitable candidates for PDT or photo-active drug carriers. The remarkable photophysical properties of graphene derivates facilitate the efficient generation of reactive oxygen species (ROS) upon light irradiation, which destroys cancer cells. Surface functionalization of graphene and its materials can also enhance their biocompatibility and anticancer activity. The paper delves into the distinct roles played by graphene-based materials in PDT such as photosensitizers (PS) and drug carriers while at the same time considers how these materials could be used to circumvent cancer resistance. This will provide readers with an extensive discussion of various pathways contributing to PDT inefficiency. Consequently, this comprehensive review underscores the vital roles that graphene and its derivatives may play in emerging PDT strategies for cancer treatment and other medical purposes. With a better comprehension of the current state of research and the existing challenges, the integration of graphene-based materials in PDT holds great promise for developing targeted, effective, and personalized cancer treatments.

Effect of the Surface Functionalization of Graphene and MWCNT on the Thermodynamic, Mechanical and Electrical Properties of the Graphene/MWCNT-PVDF Nanocomposites.

The nanocomposites of poly(vinylidene fluoride) (PVDF) with pristine graphene nanoflakes (GNF) and a multi-wall carbon nanotube (MWCNT) were prepared by the solution casting method. Additionally, the GNF and MWCNT were functionalized by acid treatment, and nanocomposites of the acid-treated MWCNT/GNF and PVDF were prepared in the same method. The effect of the acid treatment of MWCNT and GNF on the mechanical, thermal and thermo-oxidative stability and the thermal conductivity of the MWCNT/GNF-PVDF nanocomposites was evaluated, and the results were compared with the untreated MWCNT/GNF-PVDF nanocomposites. In both cases, the amount of GNF and MWCNT was varied to observe and compare their thermal and mechanical properties. The functionalization of the GNF or MWCNT resulted in the change in the crystallization and melting behavior of the nanocomposites, as confirmed by the differential scanning calorimetry analysis. The addition of the functionalized GNF/MWCNT led to the improved thermal stability of the PVDF nanocomposites compared to that of the non-functionalized GNF/MWCNT-PVDF nanocomposites. The thermal and electrical conductivity of the functionalized and non-functionalized GNF/MWCNT-PVDF composites were also measured and compared. The functional groups, crystal structure, microstructure and morphology of the nanocomposites were characterized by Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively.

Electronic properties and quantum transport in functionalized graphene Sierpinski-carpet fractals

Recent progress in the controllable functionalization of graphene surfaces enables the experimental realization of complex functionalized graphene nanostructures, such as Sierpinski carpet (SC) fractals. Herein, we model the SC fractals formed by hydrogen and fluorine functionalized patterns on graphene surfaces, namely, H-SC and F-SC, respectively. We then reveal their electronic properties and quantum transport features. From the calculated results of the total and local densities of state, we find that states in H-SC and F-SC have two characteristics: (i) low-energy states inside about $|E/t|\ensuremath{\le}1$ (with $t$ as the nearest-neighbor hopping) are localized inside free graphene regions due to the insulating properties of functionalized graphene regions and (ii) high-energy states in F-SC have two special energy ranges including $\ensuremath{-}2.3<E/t<\ensuremath{-}1.9$ with localized holes only inside free graphene areas and $3<E/t<3.7$ with localized electrons only inside fluorinated graphene areas. The two characteristics are further verified by the real-space distributions of normalized probability density. We analyze the fractal dimension of their quantum conductance spectra and find that conductance fluctuations in these structures follow the Hausdorff dimension. We calculate their optical conductivity and find that several additional conductivity peaks appear in high-energy ranges due to the adsorbed H or F atoms.

A Multicomponent Polymer-Metal-Enzyme System as Electrochemical Biosensor for H2O2 Detection.

Herein, an Au nanoparticles-polydopamine-poly acrylic acid-graphene (Au NPs-PDA-PAA-graphene) multicomponent nanohybrid is fabricated by surface functionalization of graphene alongside extensive in-situ growth of Au nanoparticles. The as-obtained nanocomposite possesses good hydrophilicity, excellent biocompatibility and high biomolecules loading capacity, which acts as an ideal platform for enzyme modification. Considering this fact, Horseradish peroxidase is expressively immobilized upon Au NPs-PDA-PAA-graphene surface, in order to lay the foundations of a biosensor that is majorly based on enzymatic activity. The biosensor exhibits higher sensitivity towards the determination of H2O2 with linearity ranging from 0.1 μm upto 20 mm, and the limit of detection going down to 0.02 μm. Encouraged by its acceptable electrocatalytic performance, this multicomponent system can also be easily employed for carrying out the real-time tracking of H2O2 coming out of Macrophage cells. Therefore, this work designs an extraordinarily updated platform for biosensing related applications, and also presents a reliable platform for the direct detection of H2O2 in vivo and in vitro, which show great potential in bioelectroanalytical chemistry, cellular biology, and pathophysiology.

Surface Functionalization of Graphene‐Based Materials: Biological Behavior, Toxicology, and Safe‐By‐Design Aspects (Adv. Biology 9/2021)

Graphene Based Materials In article 2100637, Guo and co-workers review the surface functionalization of graphene based materials (GBMs) through the lenses of nanotoxicity and safe-by-design, discuss the computational tools that can predict the interaction of GBMs behavior with their toxicity, and provide a concise framing of current knowledge and key features of GBMs to be controlled for safe and sustainable applications.

Metal-Free Antibacterial Additives Based on Graphene Materials and Salicylic Acid: From the Bench to Fabric Applications.

The custom functionalization of a graphene surface allows access to engineered nanomaterials with improved colloidal stability and tailored specific properties, which are available to be employed in a wide range of applications ranging from materials to life science. The high surface area and their intrinsic physical and biological properties make reduced graphene oxide and graphene oxide unique materials for the custom functionalization with bioactive molecules by exploiting different surface chemistries. In this work, preparation (on the gram scale) of reduced graphene oxide and graphene oxide derivatives functionalized with the well-known antibacterial agent salicylic acid is reported. The salicylic acid functionalities offered a stable colloidal dispersion and, in addition, homogeneous absorption on a sample of textile manufacture (i.e., cotton fabrics), as shown by a Raman spectroscopy study, thus providing nanoengineered materials with significant antibacterial activity toward different strains of microorganisms. Surprisingly, graphene surface functionalization also ensured resistance to detergent washing treatments as verified on a model system using the quartz crystal microbalance technique. Therefore, our findings paved the way for the development of antibacterial additives for cotton fabrics in the absence of metal components, thus limiting undesirable side effects.

Exfoliation and Noncovalent Functionalization of Graphene Surface with Poly-N-Vinyl-2-Pyrrolidone by In Situ Polymerization.

Heteroatom functionalization on a graphene surface can endow the physical and structural properties of graphene. Here, a one-step in situ polymerization method was used for the noncovalent functionalization of a graphene surface with poly-N-vinyl-2-pyrrolidone (PNVP) and the exfoliation of graphite into graphene sheets. The obtained graphene/poly-N-vinyl pyrrolidone (GPNVP) composite was thoroughly characterized. The surface morphology of GPNVP was observed using field emission scanning electron microscopy and high-resolution transmission electron microscopy. Raman spectroscopy and X-ray diffraction studies were carried out to check for the exfoliation of graphite into graphene sheets. Thermogravimetric analysis was performed to calculate the amount of PNVP on the graphene surface in the GPNVP composite. The successful formation of the GPNVP composite and functionalization of the graphene surface was confirmed by various studies. The cyclic voltammetry measurement at different scan rates (5–500 mV/s) and electrochemical impedance spectroscopy study of the GPNVP composite were performed in the typical three-electrode system. The GPNVP composite has excellent rate capability with the capacitive property. This study demonstrates the one-pot preparation of exfoliation and functionalization of a graphene surface with the heterocyclic polymer PNVP; the resulting GPNVP composite will be an ideal candidate for various electrochemical applications.

Nanoporous Activated Carbon Functionalized Graphene Sensors for Selective Detection of Ethanol

Graphene surface functionalization enables the facile detection of low concentration volatile organic compounds (VOCs). Herein, activated carbon functionalization of chemical vapour deposition (CVD) graphene is shown to enhance ethanol gas sensing in CVD graphene by three orders of magnitude. The presence of activated carbon was confirmed via Helium Ion Microscopy, and Raman spectroscopy and porosity were confirmed via Transmission Electron Microscopy (TEM). Unlike CVD graphene, the activated carbon functionalized graphene field effect transistor (aCF-GFET) had a sensitivity of 50 ppb with performance improving with increase in temperature. The extreme activated carbon-induced sensitivity is attributed to the catalytic activity and oxidation of the adsorbed ethanol molecules, consequently inducing higher graphene-ethanol charge transfer and Van der Waals bonding. The dependence of this charge transfer on the applied tuning voltage was investigated using the charge neutrality point disparity (CNPD) method, which shows an increase in CNPD values with increasing concentration, confirming the activated carbon-induced oxidation of adsorbed ethanol molecules.

A Facile Method for the Non-Covalent Amine Functionalization of Carbon-Based Surfaces for Use in Biosensor Development.

Affinity biosensors based on graphene field-effect transistor (GFET) or resistor designs require the utilization of graphene’s exceptional electrical properties. Therefore, it is critical when designing these sensors, that the electrical properties of graphene are maintained throughout the functionalization process. To that end, non-covalent functionalization may be preferred over covalent modification. Drop-cast 1,5-diaminonaphthalene (DAN) was investigated as a quick and simple method for the non-covalent amine functionalization of carbon-based surfaces such as graphene, for use in biosensor development. In this work, multiple graphene surfaces were functionalized with DAN via a drop-cast method, leading to amine moieties, available for subsequent attachment to receptor molecules. Successful modification of graphene with DAN via a drop-cast method was confirmed using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and real-time resistance measurements. Successful attachment of receptor molecules also confirmed using the aforementioned techniques. Furthermore, an investigation into the effect of sequential wash steps which are required in biosensor manufacture, on the presence of the DAN layer, confirmed that the functional layer was not removed, even after multiple solvent exposures. Drop-cast DAN is thus, a viable fast and robust method for the amine functionalization of graphene surfaces for use in biosensor development.

Effect of graphene surface functionalization on the oxygen reduction reaction in alkaline media

Two types of few-layer graphene structures with different degrees of doping with nitrogen and with close surface concentrations of carbonyl groups were synthesized using the electrochemical exfoliation of graphite in the cathodic plasma mode. As for the concentrations of oxygen-containing functional groups and doping nitrogen atoms, pyridine N atoms make a dominating contribution to the electrocatalysis of oxygen reduction reaction on the synthesized structures.

In situ single-step reduction of bromine-intercalated graphite to covalently brominated and alkylated/brominated graphene

Abstract

RGO/GO Nanosheets in Tribology: From the State of the Art to the Future Prospective

In the last few decades, in the lubricant industry, the request for new performing additives has been becoming imperative. In this scenario, control at the nanoscale can be the key factor for the improvement of more efficient nanolubricants. Herein, after a discussion about the nanoparticles’ four main lubrication mechanisms, considerable attention is devoted to the usage of reduced graphene oxide/graphene oxide (rGO/GO) nanosheets in tribology. Moreover, graphene surface functionalization is reviewed, also including unexplored results in the field of lubrication. As far as the literature is concerned, it can be postulated that rGO/GO nanosheets can reduce wear and friction. Wear reduction is obtained by deposition and film formation, while friction reduction is related more to the shear and lamination of the sheets on the contacting surfaces. Nevertheless, the two phenomena are interrelated and work in sync. In this context, it is of high importance to form a homogenous suspension for a continuous nanosheet supply after deposition and shearing. The focus of this review was placed on the main issues still to be overcome, e.g., the literature results in rationalization; dispersion stability enhancement; and finding the optimum concentration in the delicate balance of different components. Possible solutions for their efficient overcoming are eventually reported.

Chitosan-Functionalized Graphene Nanocomposite Films: Interfacial Interplay and Biological Activity.

Graphene oxide (GO) has recently captured tremendous attention, but only few functionalized graphene derivatives were used as fillers, and insightful studies dealing with the thermal, mechanical, and biological effects of graphene surface functionalization are currently missing in the literature. Herein, reduced graphene oxide (rGO), phosphorylated graphene oxide (PGO), and trimethylsilylated graphene oxide (SiMe3GO) were prepared by the post-modification of GO. The electrostatic interactions of these fillers with chitosan afforded colloidal solutions that provide, after water evaporation, transparent and flexible chitosan-modified graphene films. All reinforced chitosan–graphene films displayed improved mechanical, thermal, and antibacterial (S. aureus, E. coli) properties compared to native chitosan films. Hemolysis, intracellular catalase activity, and hemoglobin oxidation were also observed for these materials. This study shows that graphene functionalization provides a handle for tuning the properties of graphene-reinforced nanocomposite films and customizing their functionalities.

A density functional theory study on the carbon defect in a graphene nano-flake surface promoting hydrogenation

The functionalization of graphene surfaces by covalent bonds has attracted much attention. Hydrogenated graphene exhibits ferromagnetism, and the degree of hydrogenation on the graphene surface allows for tuning the band gap. In this study, to elucidate the effect of defects in graphene hydrogenation, we investigated defective graphene wherein one carbon atom was removed from the central region of graphene nano-flake, by density functional theory. Hydrogenation of a graphene nano-flake by electrophilic addition in the gas phase is an exothermic reaction only when defects exist. The activation energy of defective graphene nano-flake hydrogenation is approximately 25 kcal mol−1 lower than that of the normal graphene one due to the involvement of the defect in surface distortion and transition state stabilization. The results obtained suggest that the hydrogenation of a graphene surface can be controlled by carbon defect.

First principles study on the functionalization of graphene with Fe catalyst for the detection of CO2: Effect of catalyst clustering

The surface functionalization of graphene plays an important role in the development of graphene-based sensors for gas detection and removal. Here, we report the effect of decoration of graphene with Fe catalyst, as either scattered adatoms (Feadatoms@G) or clustered (Fecluster@G) on the detection of CO2 gas molecule and its influence on the structural, adsorption, electronic and magnetic properties of graphene using the spin-polarized density functional theory (DFT). The results show that the adsorption of scattered Fe-adatoms and Fe4-cluster on graphene would break the degeneracy of spin-up and spin-down states, resulting in ferromagnetic adsorption-bed for the detection of CO2 molecules. The magnetic moment of Feadatoms@G remains the same for all concentration of CO2, while the magnetic moment of Fecluster@G decreases from 10.03 µB to 4 µB by increasing the concentration of CO2 from one to four molecules. It is found that the scattered Fe-adatoms on graphene have the higher tendency to adsorb more CO2 molecules than that of the cluster with the same number of Fe atoms, whereas Fe4-cluster on graphene detects CO2 molecules using magnetism. Our results have indeed a direct application to fabricate solid-state and magnetic-based gas sensors using graphene to detect CO2 gas molecules.

Effects of surface functionalization on thermal and mechanical properties of graphene/polyethylene glycol composite phase change materials

Polyethylene glycol (PEG)-based composite phase change materials (PCMs) are widely employed as energy storage materials in the industries of energy, microelectronics and aerospace due to their excellent thermal and mechanical properties. From the view point of molecular, the effects of graphene functionalization on the thermal and mechanical properties of composites PCMs during phase transition are studied in this paper. It is shown by the results obtained from simulations that the functionalization of graphene surface can decrease the thermal resistance at the PEG-graphene interfaces considerably, and increase the phase change temperature and isobaric heat capacity as well. In terms of mechanical properties, it was found that the Young's modulus and shear modulus of composite PCMs decreased after functionalization, and the not obvious difference was available between the effects of different functionalization on mechanical properties. The present findings provide a better understanding of the thermomechanical mechanism of graphene/PEG composite PCMs and effective guidance for improving their thermophysical properties.

Janus Graphene: Scalable Self-Assembly and Solution-Phase Orthogonal Functionalization.

Orthogonal functionalization of 2D materials by selective assembly at interfaces provides opportunities to create new materials with transformative properties. Challenges remain in realizing controllable, scalable surface-selective, and orthogonal functionalization. Herein, dynamic covalent assembly is reported that directs the functionalization of graphene surfaces at liquid-liquid interfaces. This process allows facile addition and segregation of chemical functionalities to impart Janus characteristics to graphenes. Specifically, dynamic covalent functionalization is accomplished via Meisenheimer complexes produced by reactions of primary amines with pendant dinitroaromatics attached to graphenes. Janus graphenes are demonstrated to be powerful surfactants that organize at water/organic, water/fluorocarbon, and organic/fluorocarbon liquid interfaces. This approach provides general access to the creation of diverse surfactant materials and promising building blocks for 2D materials.

Stabilization of 2D graphene, functionalized graphene, and Ti2CO2 (MXene) in super-critical CO2: a molecular dynamics study.

The stabilization of nanoparticles is a main concern to produce an efficient nanofluid. Here, we carry out Molecular Dynamics (MD) modeling to evaluate the stabilization of 2D graphene, oxygen- and hydrogen-functionalized graphene, and Ti2CO2 MXene nano-sheets in carbon dioxide (CO2) liquid under supercritical conditions. The rheological properties (i.e., viscosity and self-diffusion) of the nanofluids with the corresponding nano-sheets are also calculated. The results show that pristine graphene aggregates in the liquid and the adsorbed CO2 molecules on the graphene surfaces could not provide enough repulsive forces to avoid their aggregation. The stabilization of graphene is improved by surface functionalization of graphene with oxygen and hydrogen functional groups. This is because, first, the presence of the corresponding surface groups can alter the electrostatic forces of the graphene nano-sheets and, second, a larger number of CO2 molecules attracted by the functionalized nano-sheets can provide additional repulsive forces between the nano-sheets. The results demonstrate that Ti2CO2 MXene nano-sheets aggregate severely although they are covered by oxygen surface terminations and attract more CO2 molecules than the pristine graphene. This is attributed to the strong interlayer coupling between the MXene nano-sheets so that the electrostatic repulsion of the MXene surfaces could not overcome the interlayer coupling. Based on our results, the stabilization of the corresponding 2D nano-sheets in CO2 liquid is in the order: oxygen-functionalized graphene > hydrogen-functionalized graphene > pristine graphene > Ti2CO2 MXene. The calculation of the rheological properties of the nanofluids with different nano-sheets demonstrates that immersing the nano-sheets in the CO2 liquid affords a superior viscosity enhancement as much as possible to be dispersed in the liquid. This study expands the potential applications of these 2D materials in producing SC-CO2 based nanofluids.

Effect of graphene treated with cyclohexyl diamine by diazonium reaction on cure kinetics, mechanical, thermal, and physical properties of natural rubber/graphene nanocomposite foam

The influence of functionalization of cyclohexyl diamine onto the graphene surface via diazonium reaction on the cure kinetics as well as morphology, mechanical, thermal and physical properties of natural rubber (NR)/graphene nanocomposite foam was investigated. The surface functionalization of graphene was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis (TGA). Without an addition of blowing agent, the vulcanized NR composites containing cyclohexyl amine‐treated graphene showed not obvious different dispersion of graphene nanoplatelets than those containing untreated graphene as confirmed by transmission electron microscopy micrographs. Although the addition of untreated graphene could accelerate the sulfur vulcanization rate of NR nanocomposite foam due to the high thermal conductivity of graphene particle, and the remaining oxygen functional groups on the surface of graphene, the amines from cyclohexyl diamine on the treated graphene could react with carboxylic and epoxide group on the surface of graphene leading to a reduction of reactive oxygen functional groups on graphene surface and in turn slowed vulcanization rate. The fast vulcanization rate in untreated graphene system led to small bubble size in the NR nanocomposite foams. In contrast, the treated graphene system showed high tensile strength and low thermal expansion coefficient owing to low cell density. Finally, the defect on the graphene surface after functionalization was detected by Raman spectroscopy; this resulted in poor thermal conductivity for the treated graphene composite system. POLYM. COMPOS., 40:E1766–E1776, 2019. © 2018 Society of Plastics Engineers

Renormalization of Ionic Solvation Shells in Nanochannels.

Recently, experimental studies on selective ion transport across nanoporous membranes or through single nanochannels have unveiled interesting behaviors of dissolved ions under nanoconfinement. However, the exploration was limited by the resolution of experimental characterization. In this work, we present an atomistic simulation-based study, showing how the nanoconfinement and surface functionalization of graphene and graphene oxide nanochannels renormalize the solvation of ions (Na+, K+, Mg2+, Ca2+, Cl-). We find that the spatial distribution of dissolved ions demonstrates a layered order in nanochannels. The 1st hydration shell structures of cations are well defined in channels with width beyond ∼1.0 nm, although the rotational degree of freedom is constrained, while the 2nd hydration shells could be destructed. In the graphene oxide nanochannels, oxygen-containing functional groups can participate in the hydration shells of univalent ions but not for the divalent ions, and the valence-dependent reduction in the ionic diffusivity offers good selectivity between the divalent and univalent ions with the interlayer spacing of ∼1.0 nm, which is absent in the graphene nanochannels. With these findings, we conclude that the assessment of permeability and selectivity of ions has to take the renormalized nature of ionic solvation shells into account in the design of nanoporous membranes or nanofluidic devices for energy and environmental applications.