Amino-functionalized Graphene Research Articles

Photoluminescence enhancement of amino-functionalized graphene quantum dots in two-dimensional optical resonators.

This paper reports on the emission characteristics of amino-functionalized graphene quantum dots (af-GQDs). We employed the variable stripe length method to measure the net optical gain of af-GQDs. Photoluminescence emission was enhanced through the efficient confinement of photons using an optical resonator. The two-dimensional resonator is made up of a cholesteric liquid crystal (CLC) reflector to enable the redistribution of spontaneous emission from the af-GQDs. The proposed method was shown to increase the intensity of peak emission to more than three times that of the reference sample without a CLC reflector. The peak emission intensity of af-GQDs in the optical resonator grows exponentially with an increase in excitation energy. These results demonstrate the feasibility of two-dimensional optical amplifiers based on CLC reflectors.

Amino-functionalized graphene oxide/neutral alumina nanocomposite based solid-phase extraction coupled with ion chromatography-mass spectrometry for the determination of trace haloacetic acids in drinking water

An efficient solid-phase extraction strategy was developed for the extraction and enrichment of ten haloacetic acids from drinking water.

CNT-enhanced amino-functionalized graphene aerogel adsorbent for highly efficient removal of formaldehyde

Graphene aerogels modified using two different methods were investigated for their capacities to adsorb gaseous formaldehyde.

Binary adsorption of 17β-estradiol and bisphenol A on superparamagnetic amino-functionalized graphene oxide nanocomposites

Two types of graphene oxide (GO), namely, superparamagnetic GO (SM-GO) and chemically modified superparamagnetic amino-functionalized GO (SM-NGO), were prepared in this study. The adsorption of 17β-estradiol (E2) and bisphenol A (BPA) by the two types of GO composites was investigated. SM-NGO showed better adsorptive performance than SM-GO in adsorbing E2 and BPA. Moreover, E2 was suitably removed by both adsorbents, which indicated the stronger interaction of E2 with the composites than BPA. The performance of the sorbents was examined through pH, kinetic, and isotherm experiments. The adsorption of E2 and BPA was favorable under neutral condition. The rate-limiting step in the adsorption process was chemisorption for both adsorbents, which fit well with the pseudo-second-order kinetic model. The adsorption isotherms were described by the Langmuir model. Moreover, the theoretical maximum adsorption capacity (Qmax) of E2 by SM-NGO and SM-GO reached 106.38 and 52.91 mg g−1, respectively, and the corresponding Qmax values for BPA were 41.32 and 18.11 mg g−1. Both nanocomposites can be easily separated by a commercial magnet within a few seconds. Therefore, SM-NGO is a promising magnetic adsorbent of heterogeneous organic chemicals.

High-Purity Amino-Functionalized Graphene Quantum Dots Derived from Graphene Hydrogel

The unique properties of graphene quantum dots (GQDs) make them interesting candidate materials for innovative applications. Herein, we report a facile method to synthesize amino-functionalized graphene quantum dots (AF-GQDs) by a hydrothermal reaction. Graphene oxide (GO) was synthesized by Hummer’s method where ultra-small GO sheets were obtained by a prolonged oxidation process followed by sonication using an ultrasonic probe. Subsequently, graphene hydrogel (GH) was also obtained by a hydrothermal synthesis method. Proper care was taken during synthesis to avoid contamination from water soluble impurities, which are present in the precursor, GO solution. Following the treatment of GH in ammonia, ultra-small amino-functionalized graphene fragments (AF-GQDs) were formed, which detached from the GH to eventually disperse evenly in the water without agglomerating. This modified synthesis process enables the formation of high-purity AF-GQDs (99.14%) while avoiding time-consuming synthesis procedures. Our finding shows that AF-GQDs with sizes less than 5[Formula: see text]nm were well dispersed. A strong photoluminescence (PL) emission at [Formula: see text]410[Formula: see text]nm with 10% PL quantum yield was also observed. These AF-GQDs can be used in many bio applications in view of their low cytotoxicity and strong fluorescence that can be applied to cell imaging.

An Electrochemical pH Sensor Based on the Amino-Functionalized Graphene and Polyaniline Composite Film.

Conventional glass-based pH sensors are usually fragile and space consuming. Herein, a miniature electrochemical pH sensor based on amino-functionalized graphene fragments and polyaniline (NH2-G/PANI) composite film is developed via simply one-pot electrochemical polymerization on the ITO-coated glass substrates. Cyclic Voltammetry (CV), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM), X-ray Photoelectron Spectroscopy (XPS), and Raman Spectra are involved to confirm the successful synthesis and to characterize the properties of the NH2-G/PANI composite film. The developed electrochemical pH sensor presents fast response, high sensitivity (51.1 mV/pH) and wide detection range when applied to PBS solutions of pH values from 1 to 11. The robust reproducibility and good stability of the developed pH sensors are investigated as well. Compared to the conventional glass-based pH meters, the NH2-G/PANI composite film-based pH sensor could be a promising contender for the flexible and miniaturized pH-sensing devices.

Amino-modification and successive electrochemical reduction of graphene oxide for highly sensitive electrochemical detection of trace Pb2+

Both synthesis method and heteroatom doping could tailor graphene properties and promise its practical application. Here, a facile electrolytic route was developed to prepare amino-functionalized graphene, which could be directly used to build chemical sensor electrode. In this method, graphene oxide (GO) was electrolyzed in ethylenediamine aqueous solution to induce ammonization and electrochemical reduction successively. The unique chemical structure of ammoniated reduced GO (AErGO) strongly increased the chelation between electrode surface and Pb2+, and provided plenty active sites for electrochemical redox. Therefore, AErGO exhibits good electrical conductivity and high electrocatalytic activities, which ensures high selectivity, low detection limit (0.0924 μg L−1 at S/N = 3) and ultra wide linear range (0.5–350 μg L−1) during the Pb2+ detection. This simple and effective route can also be extended in the preparation of S-doping or S, N-dual doping graphene materials with potential applications in chemical sensor, electrochemical catalysis, and energy conversion or storage.

Theoretical design and experimental synthesis of counter electrode for dye-sensitized solar cells: Amino-functionalized graphene

For some specific catalytic reaction, how to construct active sites on two dimensional materials is of great scientific significance. Dye-sensitized solar cells (DSCs) can be viewed as one representative photovoltaics because in which liquid electrolyte with triiodide/iodide (I3−/I−) as redox couples are involved. In this study, amino-functionalized graphene (AFG) has been designed according to theoretically analyzing iodine reduction reaction (IRR) processes and rationally screening the volcanic plot. Then, such AFG has been successfully synthesized by a simple hydrothermal method and shows high electrocatalytic activity towards IRR when serving as counter electrode in DSCs. Finally, a high conversion efficiency of 7.39% by AFG-based DSCs was obtained, which is close to that using Pt as counter electrode.

Amino-functionalized graphene quantum dots based ratiometric fluorescent nanosensor for ultrasensitive and highly selective recognition of horseradish peroxidase

Herein, a ratiometric fluorescent nanosensor for ultrasensitive and highly selective recognition of horseradish peroxidase (HRP) was reported for the first time, by employing amino-functionalized graphene quantum dots (af-GQDs) as the reference fluorophore and 2,3-diaminophenazine (DAP) as the specific response signal. DAP was the oxidation product of o-phenylenediamine (OPD) that acted as the cosubstrate of HRP. Upon the addition of HRP, OPD could be catalytically oxidized to DAP, then the fluorescence intensity corresponding to DAP at 553nm increased dramatically with a simultaneous fluorescence quenching of af-GQDs at 440nm, resulting in a ratiometric fluorescent nanosensor toward HRP. This ratiometric fluorescent nanosensor exhibited a broad linear range and excellent sensitivity toward HRP detection. The fluorescence intensity ratio of DAP to af-GQDs linearly increased with the increasing of HRP concentration in the range of 2 fM–800 fM (0.02μUmL−1–8μUmL−1) with a detection limit down to 0.21 fM (2.1nUmL−1). The present ratiometric fluorescent nanosensor also showed excellent selectivity for HRP over some amino acids, nucleotides, and other heme-containing proteins. The enzymatic activity of HRP was further evaluated by quantitatively calculating the enzymatic velocity and Michaelis−Menten kinetic parameter.

High-Capacity Molecular Scale Conversion Anode Enabled by Hybridizing Cluster-Type Framework of High Loading with Amino-Functionalized Graphene.

Exploring high-capacity anodes with multielectron reaction, sufficient charge/mass transfer, and suppressed volume expansion is highly desired. The open frameworks consisting of independent structure units, which possess conversion reaction potentiality, can meet these demands and show advantages over routine insertion-type open frameworks with at most one-electron transfer or conversion materials with compact ligand linkage. Here, we report a class of electrochemically stable cluster-like polyoxometalates (POMs) as such open framework anodes. Their high loading and low solubility are enabled by Al- or Si-driven polymerization and hybridization with positively charged graphene, which immobilizes polyanions of POMs and improves their electric contact. Al-based POM composite (NAM-EDAG) for Li-storage achieves a high reversible capacity above 1000 mAh g(-1) and tolerates a long-term cycling with more than 1100 cycles and a current density up to 20 A g(-1). A six-electron conversion reaction occurring at molecular scale and the consequent optimized distribution of products benefiting from original open framework are also responsible for the high electroactivity. POM-based open frameworks give inspiration for exploring advanced, less soluble (or insoluble) framework materials made up of electroactive molecule or cluster moieties for Li- and Na-storage.

A glassy carbon electrode modified with amino-functionalized graphene oxide and molecularly imprinted polymer for electrochemical sensing of bisphenol A

The main aim of the work was to develop an efficient strategy for preparing molecularly imprinted polymers (MIPs) on the surface of graphene oxide (GO) sheets. Amine functionalization of GO was accomplished by a facile and efficient procedure with 3-aminopropyltriethoxysilane (APTES). Then, the template was immobilized onto amino-functionalized GO in order to improve the recognition ability of MIP-based sensors. Also, prior to polymerization, ethylene glycol dimethacrylate was grafted onto the APTES coated graphene oxide sheets by the Michael addition reaction. In this way, many homogeneous imprinting sites were formed on the GO sheets. The resulting composite was placed on a glassy carbon electrode (GCE) which then was used for determination of bisphenol A (BPA) by electrochemical technique. The composite of amino-functionalized GO and MIP (GO/APTES–MIP) was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and energy dispersive X-ray spectroscopy. The electrochemical behaviors of the sensors were investigated by cyclic voltammetry and differential pulse voltammetry (DPV) techniques. Compared with non-imprinted polymer, the DPV current response of MIP sensor is about 4.6 times larger. Under the optimized conditions, GO/APTES–MIP sensor displays two linear ranges (from 0.006 to 0.1 μM and 0.2 to 20 μM) for determination of BPA, and the detection limit is 0.003 μM (at an S/N ratio of 3). The MIP-based sensor was applied to the in-situ determination of BPA in milk and mineralised water without any pre-treatment and matrix interfering effects.

Preparation and characterization of magnetic fluorescent microspheres for delivery of kaempferol

This study focused on the preparation and characterization of magnetic fluorescent microspheres (MFMs) for delivery of kaempferol. Magnetic microspheres were prepared by miniemulsion polymerization in the presence of Fe3O4 ferrofluids and kaempferol, and then, the microspheres were modified with amino-functionalized graphene quantum dots through chemically bonding. The properties of as-obtained MFMs were characterized by Fourier-transform infrared spectrum, transmission electron microscopy, thermogravimetric analysis and vibration sample magnetometry and X-ray fluorescence spectrometry. It was found that the superparamagnetic microspheres had ultrafine size (below 120 nm), high saturation magnetization of 32.48 emu/g, and significant fluorescence. Then, MFMs were used as a carrier to delivery of kaempferol, and the results indicated that they had a favourable release property for kaempferol. Finally, by incorporating the MFMs with Hela cells, they could efficiently induce inhibitory effect on Hela cells.

Preparation of amino-functionalized graphene oxide by Hoffman rearrangement and its performances on polyacrylate coating latex

Amino-functionalized graphene oxide (NGO) was prepared by Hoffman rearrangement where carboxyl group was replaced directly by amino group instead of using long-chain containing amino group. The chemical structure of NGO was studied by FT-IR, UV–vis, Raman, XPS and TGA. NGO was incorporated into polyacrylate latex (PA) by blending to prepare PA/NGO composite. The dispersibility of NGO in PA latex was significantly influenced by pH values. When the pH value was higher than 6, NGO uniformly dispersed in PA. The mechanical properties of the PA/NGO film were relayed on the pH. The break strength of the film was increased from ∼2 MPa to ∼5 MPa but the elongation at break decreased from 475% to 258% compared with those of PA film. The glass transition temperature (Tg) of PA/NGO film increased by 3.48 °C. For the sake of comparison, the mechanical properties and Tg of a similar composite but with bare graphene oxide (PA/GO) are presented.

Directly grafting graphene oxide onto carbon fiber and the effect on the mechanical properties of carbon fiber composites

Amino-functionalized graphene oxide (GO-NH2) was directly grafted onto carbon fiber surface by covalent bonding in an attempt to improve the mechanical properties of carbon fiber composites. The effect of surface modification on the properties of carbon fiber and the resulting carbon fiber composites was investigated by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and interfacial shear strength (IFSS). As revealed by Fourier transform infrared spectroscopy (FT-IR), GO-NH2 was successfully grafted on the carbon fiber surface. From dynamic contact angle analysis (DCAT) and XPS values, such GO-NH2 grafted carbon fiber exhibited significant improvements in surface energy and functional groups of the carbon fiber surface, which lead to an increase of 36.4% in the IFSS of its composites. Such hierarchical reinforcement shows great potential for enhancing interfacial properties in carbon fiber-reinforced composites.

Enhancing the cycling stability of Na-ion batteries by bonding SnS2ultrafine nanocrystals on amino-functionalized graphene hybrid nanosheets

An integrated composite tin sulfide bonded on an amino-functionalized graphene as a novel anode material for NIBs is reported. Tight contact with SnS2nanocrystals and discharge products on the amino-functionalized graphene interface results in excellent electrochemical performance.

Study on the adsorption of Hg(ii) by one-pot synthesis of amino-functionalized graphene oxide decorated with a Fe3O4microsphere nanocomposite

An easy one-pot solvothermal strategy approach has been reported on the preparation of ethylenediamine (EDA) decorated with magnetite/graphene oxide (EDA–Fe3O4/GO) nanocomposites and employed as a recyclable adsorbent for Hg(ii) in aqueous solution.

Colossal magnetoresistance in amino-functionalized graphene quantum dots at room temperature: manifestation of weak anti-localization and doorway to spintronics.

In this work, we have demonstrated the signatures of localized surface distortions and disorders in functionalized graphene quantum dots (fGQD) and consequences in magneto-transport under weak field regime (∼1 Tesla) at room temperature. Observed positive colossal magnetoresistance (MR) and its suppression is primarily explained by weak anti-localization phenomenon where competitive valley (inter and intra) dependent scattering takes place at room temperature under low magnetic field; analogous to low mobility disordered graphene samples. Furthermore, using ab-initio analysis we show that sub-lattice sensitive spin-polarized ground state exists in the GQD as a result of pz orbital asymmetry in GQD carbon atoms with amino functional groups. This spin polarized ground state is believed to help the weak anti-localization dependent magneto transport by generating more disorder and strain in a GQD lattice under applied magnetic field and lays the premise for future graphene quantum dot based spintronic applications.

Interfacial engineering with amino-functionalized graphene for efficient perovskite solar cells

In pursuit of reducing the surface trap states of perovskite as well as enhancing the hole control of dopant-free spiro-OMeTAD, an amino-rich graphene (NGs) was introduced via a facial solution method as an interlayer at the perovskite/HTM interface.

High-performance strain sensors based on functionalized graphene nanoplates for damage monitoring

A high-performance piezoresistive strain sensor can be used to monitor the deformation and damage in the structural composites. We developed the sensors with high sensitivity by structuring a 3D graphene network into an epoxy matrix. One-pot synthesis of amino-functionalized graphene nanoplates (f-GnP) was realized from graphite oxide and polyether amine, so that the dispersion of graphene in epoxy was well improved. The f-GnP/epoxy composite with lower percolation threshold, i.e. ∼1.31 vol%, exhibited relatively high gauge factor of ∼45 and Young's modulus of ∼2.2 GPa. Importantly, the studied sensor with f-GnP network structure could help to detect the initiation and accumulation of damage in the structure materials under tensile loading. The normalized electrical resistance change (ΔR/Ro) of the composite sensor initially almost increased linearly, then shown nonlinear drift and irregular ladder-shaped growth with the appearance of irreversible damage and deformation. These results suggest that the graphene/epoxy piezoresistive sensors show promising applications for the damage monitoring of structural materials in the field of aerospace.

Pie-like electrode design for high-energy density lithium–sulfur batteries

Owing to the overwhelming advantage in energy density, lithium–sulfur (Li–S) battery is a promising next-generation electrochemical energy storage system. Despite many efforts in pursuing long cycle life, relatively little emphasis has been placed on increasing the areal energy density. Herein, we have designed and developed a ‘pie' structured electrode, which provides an excellent balance between gravimetric and areal energy densities. Combining lotus root-like multichannel carbon nanofibers ‘filling' and amino-functionalized graphene ‘crust', the free-standing paper electrode (S mass loading: 3.6 mg cm−2) delivers high specific capacity of 1,314 mAh g−1 (4.7 mAh cm−2) at 0.1 C (0.6 mA cm−2) accompanied with good cycling stability. Moreover, the areal capacity can be further boosted to more than 8 mAh cm−2 by stacking three layers of paper electrodes with S mass loading of 10.8 mg cm−2.