Functionalized Graphene Surfaces Research Articles

Molecular insights into H3O+/Fe2+ sieving on functionalized graphene surface: The role of the ionic microstructures caused by different oxygen groups

In this study, we utilize a series of molecular dynamics simulations to explore the effects of microstructures of H3O+ and Fe2+ ions on their transport and sieving behavior on a functionalized graphene surface. The functionalization of the surface is modified by varying the epoxy group (i.e., xepoxy = epoxy/(epoxy + hydroxyl)) from 0 to 60 %. Results demonstrate that significantly high ion density, relative to the bulk, occurs within the range from the solid surface to the first valley of Fe2+, which is defined as the transport region (0 to 6.7–10.3 Å). For xepoxy values in 0–20 and 40–60 %, the high number of hydrogen bonds (H-bonds) between interfacial groups (namely, hydroxyl and epoxy groups) and H3O+ results in a high H3O+ density in the interfacial contact layer, subsequently leading to a high Fe2+ density in the subcontact layer. Conversely, xepoxy value of 30 % results in a relatively high H3O+ density and the lowest Fe2+ density in the subcontact layer. A detailed examination of the hydration microstructure reveals that the larger effective hydration radius induces the higher diffusion coefficient of H3O+ and Fe2+, which occurs because the larger effective hydration radius, which corresponding to weaker hydration ability, allows the easier exchange of hydrated water in the second hydration shell with non-hydrated water, thereby increasing the ion diffusion coefficient. High H3O+ permeability is shown to arise from the combined effect of interfacial H-bond structures and the large effective hydration radius. Additionally, the H-bond structure and ionic hydration microstructure drive high selectivity due to the induced high-density and effective hydration ratios, respectively. Notably, a xepoxy value of 30 % offers relatively high H3O+permeability and the highest H3O+/Fe2+ selectivity, making it the optimal choice for separating H3O+ from Fe2+.

Formaldehyde interactions with oxygen- and nitrogen-functionalized carbonaceous surfaces in the presence of moisture: Computational approach vs experimental results

Theoretical studies of physical adsorption of formaldehyde and water (through a hydrogen bond formation), as well as chemisorption of formaldehyde (through a covalent CC bond formation) on the functionalized graphene surfaces were carried out. Various functional groups that are likely to exist at graphene surface edges, including hydroxyl, amine, carboxyl, amide, pyrrole, pyridine, lactam and imide groups were considered as interacting with HCHO. In the case of physical adsorption, hydroxyl, amine and amide groups showed the highest affinity towards formaldehyde, and lactam, carboxyl and hydroxyl groups towards water with stabilization energies in the range of 7.8–8.2 kcal mol−1 and 8.2–9.9 kcal mol−1 for formaldehyde and water, respectively. This effect was magnified when additional hydroxyl group(s), capable of forming hydrogen bonds with a specific target group, were present in its vicinity. For more than 50% configurations, physical adsorption favors water molecules. However, chemisorption of formaldehyde also occurred on surface functionalized with hydroxyl groups at room temperature since the electron rich graphene π-electron system initiated CHCHO-Cgraphene bond formation. This process requires overstepping the energy barrier of merely ca. 2.5 kcal mol−1 which means that it easily occurs at room temperature without an external catalyst. The opposite (desorption) reaction could not proceed as the energy barrier exceeded 30 kcal mol−1. Similar reaction, less energetically favorable though, was shown to take place in the case of amine functionality.

Chemical gradients on graphene via direct mechanochemical cleavage of atoms from chemically functionalized graphene surfaces.

Manipulating the surface chemistry of graphene is critical to many applications that are achievable by chemical functionalization. Specifically, tailoring the spatial distribution of functional groups offers more opportunities to explore functionality using continuous changes in surface energy. To this end, careful consideration is required to demonstrate the chemical gradient on graphene surfaces, and it is necessary to develop a technique to pattern the spatial distribution of functional groups. Here, we demonstrate the tailoring of a chemical gradient through direct mechanochemical cleavage of atoms from chemically functionalized graphene surfaces via an atomic force microscope. Additionally, we define the surface characteristics of the fabricated sample by using lateral force microscopy revealing the materials' intrinsic properties at the nanoscale. Furthermore, we perform the cleaning process of the obtained lateral force images by using a machine learning method of truncated singular value decomposition. This work provides a useful technique for many applications utilizing continuous changes in the surface energy of graphene.

Polyaniline/graphene nanocomposite: Effect of the graphene functionalization with a long-chain fatty acid

Polyaniline (PANI)/graphene nanocomposites are expected to be useful in several applications, such as supercapacitors, sensors, corrosion protection, and photocatalysis. The performance of the nanocomposite depended on the interaction between graphene and PANI and the good distribution of the nanomaterial in the polymer matrix. This study investigated the effect of graphene surface modification with a long-chain fatty acid on the nature of the interactions of PANI/graphene nanocomposites. Myristic acid, a long-chain fatty acid with a 13-carbon backbone, was added to the graphene surface to improve the interaction and distribution of the graphene nanoplatelets in the PANI matrix. An innovative mechanochemical route was applied to functionalize the graphene surface with the fatty acid by ball milling. Nanocomposites were prepared through the in situ synthesis of PANI on pristine and functionalized graphene surfaces. The bare and composite materials were characterized by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, ultraviolet–visible–near infrared spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Summarily, noncovalent graphene functionalization was successfully achieved. The results indicated that the functionalized graphene acted as a template for the uniform growth of PANI. It was concluded that the nature of the interactions with PANI was different for graphene (π–π stacking) and functionalized graphene (electrostatic and hydrophobic attraction). The characterization performed showed that the graphene surface modification allowed the production of a nanocomposite with a uniform distribution, better graphene incorporation, and good electronic properties. We concluded that this nanocomposite is suitable for applications that use redox PANI properties, such as sensors and anticorrosive coatings.

Chemiluminescence of a Functionalized Graphene Surface

To analyze the modification of the functionalized surface of graphene by protein molecules, a chemiluminescent enzyme-linked immunosorbent assay based method was proposed. Using the example of functionalized graphene (FG) purification, the possibilities of chemiluminescent control of the state of its surface are shown. Methods for purifying FG from protein molecules with the restoration of the ability to resorb protein molecules are discussed. It has been shown that the FG surface can be cleaned from sorbed proteins, and a biosensor can be designed again based on such purified graphene, including with a different specificity. Therefore, the graphene sensor can be used repeatedly. Keywords: functionalized graphene, 1-pyrenemethylamine hydrochloride, cyclic voltammetry, chemiluminescence, monoclonal antibodies, biosensors

Хемилюминесценция функционализированной поверхности графена

To analyze the modification of the functionalized surface of graphene by protein molecules, a chemiluminescent enzyme immunoassay method was proposed. Using the example of functionalized graphene (FG) purification, the possibilities of chemiluminescent control of the state of its surface are shown. Methods for purifying FG from protein molecules with the restoration of the ability to resorb protein molecules are discussed. It has been shown that the FG surface can be cleaned from sorbed proteins, and a biosensor can be designed again based on such purified graphene, including with a different specificity. Therefore, the graphene sensor can be used repeatedly.

Investigation of the Morphology and Electrical Properties of Graphene Used in the Development of Biosensors for Detection of Influenza Viruses.

In this study, we discuss the mechanisms behind changes in the conductivity, low-frequency noise, and surface morphology of biosensor chips based on graphene films on SiC substrates during the main stages of the creation of biosensors for detecting influenza viruses. The formation of phenylamine groups and a change in graphene nano-arrangement during functionalization causes an increase in defectiveness and conductivity. Functionalization leads to the formation of large hexagonal honeycomb-like defects up to 500 nm, the concentration of which is affected by the number of bilayer or multilayer inclusions in graphene. The chips fabricated allowed us to detect the influenza viruses in a concentration range of 10−16 g/mL to 10−10 g/mL in PBS (phosphate buffered saline). Atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed that these defects are responsible for the inhomogeneous aggregation of antibodies and influenza viruses over the functionalized graphene surface. Non-uniform aggregation is responsible for a weak non-linear logarithmic dependence of the biosensor response versus the virus concentration in PBS. This feature of graphene nano-arrangement affects the reliability of detection of extremely low virus concentrations at the early stages of disease.

Improvement on adsorption of amino-carboxy-functionalized graphene: A first-principles study

Different graphene surfaces have been proposed for modifying drug delivery of mesalazine as drug model. The adsorption of the drug on pristine graphene and functionalized graphene with amino group and amino-carboxyl groups were analyzed at the level of the functional density theory (DFT). Conclusive results were observed regarding the advantage of using the functionalized graphene surface with amino-carboxyl groups due to its greater stability in the adsorption energy compared to the lower energies obtained for pristine and amine functionalized graphene. The major changes in adsorption can be attributed to the changes in HOMO-LUMO orbitals of mesalazine specie at basic pH, and the decreased gap between valence-conduction bands on the bi-functionalized graphene DOS spectrum that facilitate the interactions between the drug and graphene surface.

Grafting of Lanthanum Complexes on a Functionalized Graphene Surface: Theoretical Investigation on Ethylene and 1,3-Butadiene Homo- and Co-Polymerization.

In this contribution, we describe the use of graphene as an efficient catalyst support and the role it plays in increasing the Lewis acidity of the supported metal complexes. By a density functional theory study, we show that the [La(N(SiMe3 )2 )3 ] complex can be easily grafted on graphene-OH and -COOH functionalized surfaces. Two stable mono-grafted compounds, (gO)-[La(N(SiMe3 )2 )2 ] and (gOO)-[La(N(SiMe3 )2 )2 ], are formed, behaving as stronger Lewis acids than the previously reported silica grafted analogues. To study the role of the graphene support in catalysis, we also computed the catalytic activity of the alkylated (gO)-[La(CH3 )2 ] and (gOO)-[La(CH3 )2 ] complexes in the ethylene and 1,3-butadiene homo- and co-polymerization reactions. Both compounds are efficient catalysts for the homo-polymerization of the ethylene and 1,3-butadiene. For the 1,3-butadiene homo-polymerization, the stereoselectivity outcome of the reaction differs according to the grafting site. The results computed for the co-polymerization reaction, finally, show that the high stability of the allylic products leads to the formation of block copolymers.

Functionalized Graphene Surfaces for Selective Gas Sensing.

Environmental monitoring through gas sensors is paramount for the safety and security of industrial workers and for ecological protection. Graphene is among the most promising materials considered for next-generation gas sensing due to its properties such as mechanical strength and flexibility, high surface-to-volume ratio, large conductivity, and low electrical noise. While gas sensors based on graphene devices have already demonstrated high sensitivity, one of the most important figures of merit, selectivity, remains a challenge. In the past few years, however, surface functionalization emerged as a potential route to achieve selectivity. This review surveys the recent advances in the fabrication and characterization of graphene and reduced graphene oxide gas sensors chemically functionalized with aromatic molecules and polymers with the goal of improving selectivity toward specific gases as well as overall sensor performance.

Nickel nanoflakes on 4-Amino-4H-1,2,4-triazole/graphene for sustainable hydrogen evolution in acid and alkaline media

The development of highly active and stable non-noble-metal-based electrocatalysts for the sustainable hydrogen production by hydrogen evolution reaction (HER) in water-splitting cells is now vitally needed. Herein, we design a facile strategy to fabricate the nickel nanoflakes onto 4-Amino-4H-1,2,4-triazole (ATz) functionalized graphene surface through the amidation reaction (Ni/ATz-G) via wet-chemical method. For the development of nickel nanoflakes, nitrogen atoms of ATz which grafted onto graphene sheets are coordinated to nickel atoms initially, and then the formation of nickel nanoflakes is proceeded via epitaxial film growth. Several instrumental characterizations confirm that the nickel nanoflakes are in the Ni(OH)2 form. The as prepared catalyst exhibits remarkable electrocatalytic activity towards the HER while it requires only 48 and 58 mV overpotential to gain current density at 10 mA cm−2 in alkaline and acidic media, respectively. Also it shows improved kinetics and higher stability in both media which makes it a promising catalyst for practical application. The coordination in between nitrogen and nickel nanoflakes and the amidation between ATz and graphene (Ni-N-C system) play a key role in not only intrinsic catalytic activity for HER but also high stability through better grafting of nickel nanoflakes active sites onto the graphene.

Optimization and analysis of pyrene-maltose functionalized graphene surfaces for Con A detection

Utilizing the non-covalent π-π stacking of pyrene functionalized molecules onto graphene surfaces has achieved great success in the detection of various bio-objects, while the fundamental investigations on surface modifications stills remain rarely exploited. Here, we report the nano and atomic scale analysis of the π-π stacking functionalized graphene surface regarding to its surface topography, molecular self-assembly as well as process optimizations. The ‘amphipathic’ molecule, pyrene-maltose, is used for the non-covalent functionalization of graphene and systematical analysis is performed to understand the influence of different solvents on the molecular surface arrangement. Atomic force microscopy (AFM) and spectroscopy analysis indicate the successful formation of pyrene-maltose layer on graphene surface and it is further confirmed by scanning tunneling microscopy, depicting the self-assembled and densely packed pyrene-maltose layer that give distinguished and ordered diamond-shape lattice as compared to triangular lattice in pristine graphene. We also demonstrated that the interfacial adhesion forces between the AFM probe and the functionalized surfaces allow the detection of the lectin protein Concavalin A through selective absorption. This work provides essential evidence of the π-π interactions between pyrene molecules and graphene, and the AFM based adhesion measurement also has the potential to be employed in a variety of bio-detection applications.

A molecular dynamics modelling adsorption study of Cu and Ag nanoparticles on pristine and functionalized graphene surfaces

The overuse of antibiotics has led to the flourishment of antibiotic-resistant bacteria and consequently to the need to develop new, more efficient pharmacological compounds. It is well known that graphene oxide (GO) doped with metallic particles exhibits broad-spectrum antimicrobial activity. In addition, in order to improve the pharmacokinetic behavior of these compounds and their solubility in biological media, polyethylene glycol (PEG) is attached to the graphene surface. Among the different available characterization techniques, molecular dynamics simulations (MD) deserve special attention, as they allow the study of different materials from a molecular point of view. In this work, MD simulations of the adsorption of small Ag and Cu clusters on pristine graphene and PEGylated graphene oxide (GO_PEG) surfaces were carried out. The results are presented in terms of adsorption energies, mean equilibrium distances between nanoparticles and graphene surfaces, radial distribution functions and diffusion coefficients of the metallic nanoclusters. These preliminary results show that PEGylation of the surface is critical to strengthen the interaction between the surfaces and the metallic clusters, which, in turn, is a key factor for improving the efficacy of these compounds.

Real-time PCR for direct aptamer quantification on functionalized graphene surfaces

In this study, we develop a real-time PCR strategy to directly detect and quantify DNA aptamers on functionalized graphene surfaces using a Staphylococcus aureus aptamer (SA20) as demonstration case. We show that real-time PCR allowed aptamer quantification in the range of 0.05 fg to 2.5 ng. Using this quantitative technique, it was possible to determine that graphene functionalization with amino modified SA20 (preceded by a graphene surface modification with thionine) was much more efficient than the process using SA20 with a pyrene modification. We also demonstrated that the functionalization methods investigated were selective to graphene as compared to bare silicon dioxide surfaces. The precise quantification of aptamers immobilized on graphene surface was performed for the first time by molecular biology techniques, introducing a novel methodology of wide application.

Adsorption mechanism of ferrocene molecule on pristine and functionalized graphene

The adsorption behavior and stable geometries of ferrocene molecule on pristine, oxygen and hydroxyl functionalized graphene surfaces are investigated by using first principle density functional calculations based on the PBE-D2 method, which uses GGA-PBE functional with the incorporation of van der Waals (VDW) forces. Our calculations reveal that on all graphene substrates (pristine, oxygen and hydroxyl functionalized), the ferrocene molecule adsorbed with its molecular axis parallel to the surface. Oxygen and hydroxyl functionalized graphene systems have higher adsorption energies, higher charge transfer values and shorter adsorption heights as compared to the pristine graphene. It is concluded that sandwich type π-π interaction along with the van der Waals forces plays a major role in these adsorptions. The physisorption of ferrocene molecule is supported by the optimized geometrical parameters, adsorption energies and electronic properties. As the activity of a catalyst relies on the controlled adsorption of molecules onto surfaces, we therefore anticipate that these calculations can play an important role in the investigation of catalytic behavior of a catalyst based on the combined systems of graphene and ferrocene molecule. These findings offer more detail investigation of the ferrocene molecule/molecules on different types of graphene surfaces, and we hope that these calculations can open a new way for the upcoming work on other molecules of the metallocene family.

Density functional theory study of adsorption properties of non-carbon, carbon and functionalized graphene surfaces towards the zinc and lead atoms

In the current study, we Investigated the adsorption properties of zinc (Zn) and lead (Pb) atoms on the surface of carbonic and non-carbonic graphene using Density functional theory calculations. The procedure for this research can be divided into two sections. First, we calculated the adsorption value of single zinc and lead atoms with such non-carbonic graphene-like structures as Boron-Nitride (BN), Aluminum-Nitride (AlN), Gallium-Nitride (GaN), Silicon-Carbide (SiC), and Silicene. We found that the silicene was more powerful to detect the stated heavy metal atoms compared with others. The calculated adsorption values between the single zinc and lead atoms with silicene monolayer sheet were equal to −0.90 eV and −3.80 eV, respectively. We also used electron transfer calculations after adsorbing the stated heavy metal atoms and found that the calculated charge transfer was equal to 0.42 and 0.12 electrons for Silicene/Pb and Silicene/Zn complex, respectively. The density of states (DOS) results demonstrated that a strong hybridization could occur between the Pb atom and the silicene graphene. Then, we performed DFT calculations to determine the interaction energy between the mentioned metal atoms with pristine carbonic graphene. We found that the interaction in graphene/Zn (−0.09 eV) and graphene/Pb (−0.45 eV) was so weak, especially for graphene and zinc. To overcome this issue, we first activated the surface of graphene by carboxyl and hydroxide group. The interaction energy values between the zinc and lead atoms with graphene-COOH were approximately −0.18 eV and −1.01 eV, respectively, which showed improvements in the adsorption energy. Then, we approached the mentioned metal atoms on the surface of OH-decorated graphene and demonstrated that the interaction energy between the single zinc and lead atoms with graphene-OH were about −0.78 eV and −3.33 eV. In other words, it improved by 755% and 623% compared with graphene/Zn and graphene/Pb, respectively. The strong adsorption between the hydroxyl group and the stated metals atom caused the OH group to be isolated from the graphene surface and become an individual molecule.

In situ immobilized palladium nanoparticles (Pd NPs) on fritillaria imperialis flower extract-modified graphene and their catalytic activity for reduction of 4-nitrophenol

Abstract In this study, a complete green synthesis method to reduced graphene oxide-Pd nanoparticles hybrid by applying extract of Fritillaria imperialis flower as both stabilizing and reducing agent was reported. Fritillaria imperialis flower extract reduce graphene oxide and adsorb on the reduced graphene oxide surface. Moreover, the surface adsorbed Fritillaria imperialis flower extract can more in situ reduce Pd ions to Pd nanoparticles and stabilize them. The physicochemical and structure properties of the produced nanohybrid were examined in detail by X-ray diffraction (XRD), UV–vis spectroscopy, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), wavelength-dispersive X-ray spectroscopy (WDX), inductively coupled plasma (ICP) and X-ray photoelectron spectroscopy (XPS). The obtained results showed that Pd nanoparticles uniformly distributed on the functionalized graphene surface. The catalytic efficiency of the resulting heterogeneous nanocatalyst (Pd NPs/FGO) was evaluated at room temperature for the 4-nitrophenol (4-NP) reduction in an environmental friendly medium. The enhanced catalytic activity observed with our nanocatalyst is attributed to the graphene surface's coated by biopolymers of Fritillaria imperialis flower extract which stabilizes and attracting the aryl nitro substrates adjacent to the catalytic sites which in turn facilitates the reduction of nitro groups. The catalyst was recycled by centrifugation and reapplied several times without any significant catalytic activity loss.

Proton-Gradient-Driven Oriented Motion of Nanodiamonds Grafted to Graphene by Dynamic Covalent Bonds.

Manipulating nanoscopic objects by external stimuli is the cornerstone of nanoscience. Here, we report the implementation of dynamic covalent chemistry in the reversible binding and directional motion of fluorescent nanodiamond particles at a functionalized graphene surface via imine linkages. The dynamic connections allow for controlling the formation and rupture of these linkages by external stimuli. By introduction of pH gradients, the nanoparticles are driven to move along the gradient due to the different rates of the imine condensation and hydrolysis in the two environments. The multivalent nature of the particle-to-surface connection ensures that particles remain attached to the surface, whereas its dynamic character allows for exchange reaction, thus leading to displacement yet bound behavior in two-dimensional space. These results open a pathway for thermodynamically controlled manipulation of objects on the nanoscale.

Polymeric Self-Assembled Monolayers Anomalously Improve Thermal Transport across Graphene/Polymer Interfaces.

Ultralow thermal conductivities of bulk polymers greatly limit their applications in areas demanding fast heat dissipation, such as flexible electronics and microelectronics. Therefore, polymeric composites incorporating highly thermally conductive filler materials (e.g., graphene and carbon nanotubes) have been produced to address the issue. However, despite some enhancement, thermal conductivities of these materials are still far below theoretical predictions, mainly due to the inefficient thermal transport across material interfaces. Here, using molecular dynamics simulations, we demonstrate that polyethylene (PE) self-assembled monolayer (SAM) functionalized graphene surfaces at a high grafting density can drastically improve interfacial thermal conduction between graphene and the matrix of poly(methyl methacrylate) (PMMA). In contrast to abrupt temperature drop across pristine graphene/PMMA interfaces, temperature field in the vicinity of a PE-grafted graphene/PMMA interface is continuous with a smoother transition and higher thermal conductance. This anomalous improvement is attributed to three factors that closely relate to the grafting density of the SAM of PE. First, the SAM with high grafting densities features highly extended chains that enhance along-chain thermal conduction. Second, the strong covalent bonding between the SAM and the graphene facilitates heat transfer at their joints. Third, the SAM and the PMMA matrix are both organic materials, leading to enhanced interfacial vibrational coupling. Molecular mechanisms underpinning these phenomena are systematically elucidated by analyzing the temperature field, density distribution, Herman's orientation factor, the vibrational density of states, cumulative correlation factor, the integrated autocorrelation of interfacial heat power, and interfacial adhesion. All results suggest the incorporation of SAMs at a high grafting density or extremely extended polymer brushes for drastically improved interfacial thermal transport between hard and soft materials toward a wide range of applications.

Functionalization of gold and graphene electrodes by p-maleimido-phenyl towards thiol-sensing systems investigated by EQCM and IR ellipsometric spectroscopy

Electrografting of gold and graphene surfaces by functional p‐(N‐maleimido)phenyl groups was performed by reduction of p‐(N‐maleimido)phenyldiazonium tetrafluoroborate. The reduction was carried out using cyclic voltammetry coupled with micro-gravimetric measurements by means of electrochemical quartz crystal microbalance (EQCM). The overall deposited mass on gold was higher than on graphene. However, the Faradaic efficiency was lower on Au (14%) compared to graphene (22%) after the first potential scan. Subsequently, the maleimide functional groups have been tested for immobilization of terminal thiols using (4-nitrobenzyl)mercaptan for the functionalized graphene surface and a cysteine-modified peptide for the functionalized gold surface. The functionalization by p‐(N‐maleimido)phenyl groups and the following thiol coupling of the particular surface was proven by infrared spectroscopic ellipsometry (IRSE). In addition, the interaction of the tetrabutylammonium and tetrafluoroborate ions present in the electrolyte with the Au and graphene electrodes was investigated by EQCM and revealed less electrostatic interaction of graphene with these ions in solution compared to the metal (Au) surface.