Amine-functionalized Graphene Oxide Research Articles

Gold nanoclusters decorated amine-functionalized graphene oxide nanosheets for capture, oxidative stress, and photothermal destruction of bacteria

Gold nanoclusters decorated amine-functionalized graphene oxide (Au-GO-NH2) nanosheets were designed as a highly efficient visible light active antibacterial agent. This assembled nanosheet is positively charged and of high specific surface area that captures bacteria through physical adsorption and electrostatic interaction. Under visible light irradiation, this photoactive nanosheet concurrently generates massive heat and produces substantial reactive oxygen species to inactivate bacteria. In comparison with bare gold nanoclusters and amine-functionalized graphene oxides, this nanosheet appears an enhanced antibacterial activity >5-fold towards Gram-postive and Gram-negative bacteria. Moreover, a nanosheet modified silicone surface was employed as a model of implant devices, which showed superior antibacterial efficacy against bacterial colonization in vitro. This work demonstrates that the assembled nanosheet is a promising novel strategy in the construction of next generation antimicrobial agent for synergistic bacterial capture, oxidative stress, and photothermal ablation in the biomedical and environmental fields.

Microfluidic-Based Electrochemical Immunosensing of Ferritin.

Ferritin is a clinically important biomarker which reflects the state of iron in the body and is directly involved with anemia. Current methods available for ferritin estimation are generally not portable or they do not provide a fast response. To combat these issues, an attempt was made for lab-on-a-chip-based electrochemical detection of ferritin, developed with an integrated electrochemically active screen-printed electrode (SPE), combining nanotechnology, microfluidics, and electrochemistry. The SPE surface was modified with amine-functionalized graphene oxide to facilitate the binding of ferritin antibodies on the electrode surface. The functionalized SPE was embedded in the microfluidic flow cell with a simple magnetic clamping mechanism to allow continuous electrochemical detection of ferritin. Ferritin detection was accomplished via cyclic voltammetry with a dynamic linear range from 7.81 to 500 ng·mL−1 and an LOD of 0.413 ng·mL−1. The sensor performance was verified with spiked human serum samples. Furthermore, the sensor was validated by comparing its response with the response of the conventional ELISA method. The current method of microfluidic flow cell-based electrochemical ferritin detection demonstrated promising sensitivity and selectivity. This confirmed the plausibility of using the reported technique in point-of-care testing applications at a much faster rate than conventional techniques.

Sulfonated poly(ether ether ketone)/amine-functionalized graphene oxide hybrid membrane with various chain lengths for vanadium redox flow battery: A comparative study

In this paper, a series of sulfonated poly(ether ether ketone) (SPEEK) hybrid membranes containing aliphatic amine-functionalized graphene oxide nanofillers as the interface modifiers, reacted with primary amine (NH2-GO), ethylenediamine (EDA-GO) and 1,6-hexanediamine (HMD-GO), respectively, have been fabricated via a simple solution-casting method. Three hybrid membranes (S/NH2-GO, S/EDA-GO, and S/HMD-GO) demonstrate much higher physicochemical property than that of pristine SPEEK and Nafion 117, which is originated from the varied interfacial interaction and the surface architecture behavior. A superior ion selectivity of S/EDA-GO-1 (24.8 × 103 S min cm−3), S/HMD-GO-2 (24.6 × 103 S min cm−3) and S/NH2-GO-2 (20.4 × 103 S min cm−3) to pristine SPEEK (4.3 × 103 S min cm−3) and Nafion 117 membrane (4.0 × 103 S min cm−3) is shown. At the current density of 50 mA cm−2, S/EDA-GO-1 hybrid membrane gives the highest energy efficiency than that of S/NH2-GO-2 and S/HMD-GO-2, endowing an excellent charge capacity retention during 100 cycles. The varied interfacial structure state originated from the introduced EDA-GO and HMD-GO nanofillers provide the different proton conductivity and vanadium ion permeability. This present work provides a guidance for developing high-performance PEMs through the regulated interfacial structure via the moderate chain length.

Nanotailoring of thermoplastic polyurethane by amine functionalized graphene oxide: Effect of different amine modifier on final properties

Thermo-mechanical properties of amine functionalized graphene oxides filled polyurethane (PU) nanocomposites have been investigated in this work. Graphene oxide (GO) was functionalized with p-phenylenediamine (PPD), hexamethylene diamine (HMD) and liquid NH3 separately to check the interaction with the PU matrix. In-situ solution polymerization technique has been adopted for the preparation of nanocomposites. The functionalization of GO with PPD, HMD, and NH3 was proved by Fourier transform infrared spectroscopy (FTIR), Raman Spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–visible spectroscopy. Furthermore, grafting of PU onto the functionalized GO surface has been confirmed from the FTIR and TGA analysis, and the filler dispersion is shown in the respective FESEM and TEM micrographs. With the incorporation of just 0.1 wt% amine functionalized GO, thermal and mechanical properties improve significantly, and the surface becomes more hydrophobic compared to GO filled nanocomposites. Maximum improvement in properties was observed with PPD functionalized GO (GO-PPD) filled PU nanocomposites. At 0.1 wt% loading of GO-PPD, tensile strength, and Young's modulus increases by 378% and 145%, respectively. In addition to these, maximum degradation temperature also increases by 13 °C, which is more than double compared to 0.1 wt% GO filled nanocomposite. Resilience behavior of PU also improves significantly with the addition of amine functionalized GO.

Heat tolerant epoxy-amine functionalized graphene oxide composites for insulation applications

Heat tolerant polymers are in much demand in electrical, structural, and electronic packaging applications. This article reports on a comparison of epoxy composites reinforced with graphene oxide (GO) and amine-functionalized GO (AGO) on their dielectric properties and adhesive strength in the temperature range of 30–110 °C. GO was synthesized using the modified Hummers method and functionalized with amine functional group using hexamethylenediamine (HMDA) and confirmed by Raman spectroscopy. Various filler concentrations (0.2–0.6 wt.%) of GO/AGO epoxy nanocomposites were prepared using the solution blending method and analyzed using a dynamic mechanical analyzer (DMA), impedance spectroscopy, and the single lap shear (SLS) test. Studies showed AGO reinforced epoxy composites outperforming than neat epoxy and GO-epoxy composites for all the compositions. The optimum concentration of AGO was found to be 0.4 wt.% based on its relative permittivity, dielectric loss and retention of adhesive strength up to 90 °C. The percentage of cohesive area on the fractured surface of SLS tested AGO was ∼1.4 and ∼3 times better than that of GO-epoxy and neat epoxy, respectively. The higher strength retention of AGO-epoxy nanocomposites is suitable for high-temperature insulation applications as adhesive coatings.

Application of eco-friendly multifunctional porous graphene oxide for adsorptive sequestration of chromium in aqueous solution.

Graphene oxide (GO) was functionalized using two silanes ((3-aminopropyl)-triethoxysilane and (3-mercaptopropyl)-triethoxysilane) to obtain, separately, the eco-friendly amine-functionalized GO (GONH) and thiol-functionalized GO (GOSH). Both silanes were also used together to obtain the amine-thiol dual-functionalized GO (GOSN). Various physicochemical characterizations were obtained including spectra from using Fourier-transform infrared (FTIR) spectrometer, thermogravimetric analyzer, and X-ray diffractometer. The adsorbents were used for a comparative study of Cr adsorption from aqueous solution. The obtained data were fitted to pseudo-first order (PFO) and pseudo-second order (PSO) models, the homogeneous fractal pseudo-second order (FPSO), and the Weber-Morris intraparticle diffusion (IPD) kinetics models. Model parameters of the Langmuir and Freundlich adsorption isotherm models, as well as the thermodynamics, were calculated. Characterization results showed successful functionalizations. The GONH, GOSH, and GOSN exhibited alkaline, acidic, and neutral pH, respectively, in water. Amine and thiol functional groups were observed in the new adsorbents, as well as reduced orderliness. The adsorbents had higher density per unit weight and better thermal stability than pristine GO. Equilibrium Cr adsorption was attained within 60min for all adsorbents. The PSO and FPSO described the rate data better. The Cr adsorption decreased as solution pH increased; optimum adsorption was recorded at pH 2. Equilibrium adsorption data fitted the Langmuir adsorption isotherm model for the GONH, while it fitted the Freundlich for both GOSH and GOSN. The adsorption process was theoretically exothermic process that was spontaneous processes. The Cr adsorption capacities of these adsorbents are 114, 89.6, and 173mg/g for GONH, GOSH, and GOSN, respectively, and these were better than several reported graphene-based adsorbents and suggest the potential of these adsorbents for water treatment. PRACTITIONER POINTS: Graphene oxide was mono and dual-functionalized with amine and thiol groups for Cr adsorption. The adsorption capacities of these adsorbents were better than several earlier reported. These adsorbents may be used for real contaminated water treatment.

Graphene oxide based functionalized chitosan polyelectrolyte nanocomposite for targeted and pH responsive drug delivery

Graphene oxide (GO) was first modified to amine functionalized GO (AGO) and acts as a cationic polyelectrolyte. Chitosan (CS) was conjugated with folic acid (FA) through N, N´ -Dicyclohexylcarbodiimide coupling to form FA-CS. After this, itaconic acid and acrylic acid monomers are grafted to the hydroxyl group of CS using ethyleneglycol dimethacrylate as cross linker and potassium peroxydisulfate as an initiator to generate –COOH functional groups and forming chemically modified chitosan (CMCS). Further doxorubicin (DOX) loaded into the FA-CMCS/AGO through π-π stacking interactions. The resulting nanocomposite was characterized by FTIR, SEM, TEM, Raman, AFM, DLS and ZP. The drug loading capacity was as high as 95.0% and the drug release rate at pH 5.3 was significantly higher than that under physiological conditions of pH 7.4. Cell viability of L929, HeLa and MCF7 cells was studied. The studies suggest the drug carrier has potential clinical applications for anticancer drug delivery.

Development of π–π Interaction-Induced Functionalized Graphene Oxide on Mechanical and Anticorrosive Properties of Reinforced Polyurethane Composites

In this study, three types of amine-functionalized graphene oxide (f-GO) have been synthesized and their polyurethane (PU) composites have been fabricated. Mechanical properties and the anticorrosion performance of as-prepared composites were thoroughly investigated. The amine groups (two aliphatic groups and one aromatic group) on GO influenced the dispersion of the fillers and the properties of the composites. Among the f-GO series, GO functionalized with 2-naphthyl amine (2NA-GO) indicated higher mechanical properties and corrosion resistance than other PU composites. Specifically, the incorporation of 0.5 wt % of 2NA-GO in the PU matrix showed a 2.2 times higher tensile modulus than the neat PU and the highest protection efficiency of 99.94%. This synergetic effect of 2NA-GO was due to the aromatic structure and relatively low molecular weight of 2NA. The aromatic structure developed π–π interfacial interactions between the amine group and phenyl groups of the hard segments in the PU backbone. Furthermore, the lower molecular weight contributed to the uniform dispersion of the filler. Based on the results, molecular structure and molecular weight could be a critical factor in designing the f-GO to improve the mechanical and corrosion properties of PU composites. Additionally, this fact can be contributed to PU industries, which require a high anticorrosion performance as well as enhanced mechanical properties.

Amine Functionalized Graphene Oxide Stabilized Pickering Emulsion for Highly Efficient Knoevenagel Condensation in Aqueous Medium

A Pickering emulsion catalytic system was developed using amphiphilic amine-functionalized graphene oxide (GO-NH2) for a Knoevenagel condensation in aqueous medium instead of organic solvent. The properties of GO-NH2 and the Pickering emulsion stabilized by GO-NH2 were characterized by Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), organic elemental analysis (OEA), contact angle (CA), Brunauer–Emmett–Teller surface area, and optical microscopy. The results indicated that the properties of the as-prepared Pickering emulsion system, such as droplet density, size, and distribution, were greatly affected by the amount of GO-NH2 and the oil–water ratio, which were closely related to the catalytic performance for Knoevenagel condensation reactions. Furthermore, this Pickering emulsion system for the Knoevenagel condensation in an aqueous medium exhibited a much higher catalytic activity than those of GO-NH2 in organic solvents under the same reaction conditions. The reaction rate constant (k) in the Pickering emulsion system was calculated to be 0.043 min−1 at 50 °C. The enhanced activity of the Pickering emulsion was mainly attributed to large interfaces between GO-NH2 and reactants in the emulsion, and the clear confinement effect. Furthermore, GO-NH2 remained stable for preparing Pickering emulsion systems after recycling in six runs, exhibiting its good reusability. A novel Pickering emulsion catalytic system was developed using amphiphilic amine functionalized graphene oxide (GO-NH2) for Knoevenagel condensation in aqueous medium instead of organic solvents. It exhibited excellent catalytic performance in the reaction.

Preparation of a Pickering emulsion by modification of an amine-functionalized graphene oxide surface with organosilane: efficient catalyst for the Knoevenagel condensation of malononitrile with aldehydes at mild temperature

In this study, a series of Pickering emulsions for catalysis of Knoevenagel condensations of malononitrile with aldehydes were prepared by surface modification of amine-functionalized graphene oxide (GO-NH2) with trimethoxymethylsilane (MTMS).

Amino functionalized ZIF-90@GO/MDEA nanofluid: As a new class of multi-hybrid systems to enhance the performance of amine solutions in CO2 absorption

Global climate change has enforced a critical action to mitigate carbon emissions. In this study, a novel procedure was investigated by addition of amine-functionalized graphene oxide into mehyldiethanolamine (MDEA) to improve the CO2 absorption capacity. The nanocomposite EDA@ZIF-90@GO was prepared by incorporation of (3-Aminopropyl) triethoxysilane (APTES) onto the graphene oxide surface and consequently functionalization of as-prepared nanostructure with ZIF-90 as well as ethylenediamine (EDA). This reagent was utilized because of various functional groups, high surface area, and potential surface modification. The stability of nanofluid was measured by zeta potential analysis. Firstly, we studied the nanoparticle loading using MDEA based nanofluid containing different dosages of GO to reach the optimal concentration. The results revealed an absorption enhancement of 9.1% and 10.4% for dosages of 0.1 wt% and 0.2 wt%, respectively. Then, after the addition of 0.1 wt% EDA@ZIF-90@GO to amine solution, the CO2 absorption was enhanced up to 23%. Different partial pressure and temperatures were employed and the results showed that the temperature has a negative effect on the performance of the system, while increasing the CO2 partial pressure led to an increase in absorption capacity rate. Thermal gravimetric analysis (TGA) confirmed the reusability of the nanofluid due to the high temperature needed for the decomposition of functional groups. Thermal conductivity and convective heat transfer coefficient were improved after addition of the nanoparticles into the base fluid.

Enhanced proton conductivity of sulfonated poly(ether ether ketone) membranes at elevated temperature by incorporating (3-aminopropyl)triethoxysilane-grafted graphene oxide

Making inexpensive proton exchange membrane with high proton conductivity for the proton exchange membrane fuel cell (PEMFC) is still a challenging problem. Graphene oxide (GO) nanoparticles grafted with (3-amino-propyl) triethoxy silane (APTES) were prepared and then incorporated into sulfonated poly(ether ether ketone) (SPEEK) matrix by solution casting to make the composite proton exchange membrane. The obtained nanoparticles and composite membranes were characterized by XRD, FT-IR, Raman, TGA, SEM, and UTM. GO treated with the silane coupling agent improved the dispersion stability and compatibility of GO in SPEEK, which decreased the agglomeration of GO nanoparticles in the SPEEK membrane. The prepared nanocomposite membranes exhibited better water retention properties and proton conductivity. The proton conductivity of the SPEEK membrane with 2 wt% amine functionalized GO (AGO) reached 11.32 mS/cm at 120 °C, which was 2.45-times higher than that of the pristine SPEEK membrane. The reason was that AGO nanoparticles disperse uniformly in the SPEEK membranes, which provides new channels for proton transfer. The potential application of this composite membrane in the PEMFC was indicated.

Influence of amine functionalized graphene oxide on mechanical and thermal properties of epoxy matrix composites

A new approach for synthesized amine functionalized graphene oxide (AFGO) was used by diethylenetriamine as a reducing or functionalizing agent. The purpose of this work is to determine the effect of AFGO on the mechanical and thermal properties of epoxy nanocomposites. In addition, the optimization of various weight percentages of AFGO was carried out. Physical and chemical characterizations were also reported to determine the effects of AFGO. The structure and morphology of the AFGO nanosheets were confirmed by fourier transform infrared spectroscopy, energy dispersive spectroscopy, X-ray diffraction analysis, and field emission scanning electron microscopy. Successful formation of amide bonds through graphene oxide (GO) sheet functionalization was proved by characterizations. Solution blending, as a simple method, was used for composite formation. The mechanical and thermal properties of the epoxy/AFGO composites were assessed. There was increment in tensile strength by 67%, flexural strength by 51%, and impact strength by 152% at 0.3 wt% loading of AFGO in epoxy composites. Similarly, the increment in hardness was also observed from 0.1 to 0.3 wt% of AFGO loading. The glass transition temperature of epoxy/AFGO nanocomposites effectively improved from 88.4 to 97.3 °C. The thermal stability of epoxy/AFGO nanocomposite increased from 351 to 358 °C.

Fabrication of pH-sensitive thin-film nanocomposite nanofiltration membranes with enhanced performance by incorporating amine-functionalized graphene oxide

To determine the influence of positively charged graphene-based nanofillers on the nanofiltration (NF) performance as well as strengthen the nanofiller stability in a polypiperazine-amide (PPA) matrix, graphene oxide (GO) was first modified with ethylenediamine (EDA) and polyethylenimine (PEI) to obtain two kinds of aminated graphene oxide (AGO) nanofillers with a positive charge. The characterization results of AGO nanofillers indicated that EDA and PEI were successfully grafted onto GO via amide bonds without destroying the original GO structure. Then, novel thin film nanocomposite (TFN) NF membranes were fabricated by incorporating AGO nanofillers into the PPA skin layer using the interfacial polymerization (IP) method. With the addition of 60 ppm GO-EDA or 40 ppm GO-PEI, the TFN-GO-EDA-60 and TFN-GO-PEI-40 NF membranes showed optimal individual permselectivities ascribed to the formation of thinner, smoother and stronger hydrophilic nanocomposite skin layers. While retaining a rejection level of sodium sulfate >98%, the water fluxes of TFN-GO-EDA-60 and TFN-GO-PEI-40 membranes reached 59.6 and 62.1 L·m−2·h−1, corresponding to 154.4 and 160.9%, respectively, of that of the TFC-blank membrane. Furthermore, both the TFN-GO-EDA-60 and TFN-GO-PEI-40 NF membranes exhibited excellent anti-fouling capabilities, chlorine resistances as well as mechanical stabilities compared with TFC-blank membrane. However, their anti-fouling performance and salt rejection varied with the solution pH due to the positively charged AGO nanofillers. Moreover, GO-PEI demonstrated a greater potential for enhancing the performance of TFN NF membranes compared with that of GO-EDA.

Fabrication of amine functionalized graphene oxide – AgNPs nanocomposite with improved dispersibility for reduction of 4-nitrophenol

In the present work, graphene oxide (GO) was synthesized through modified Hummer's method and the covalent functionalization of GO was achieved via amino moiety using N,N′-dicyclohexylcarbodiimide (DCC) as coupling agent and ethylenediamine (EDA) & 1,3-diaminopropane (DAP) as amino precursors. The amino functionalized GO served as nucleation and growth sites for silver nanoparticles. These two amino functionalized graphene oxide-AgNPs were compared based on the chain length of the alkyl-diamine and metal loading capacity. Further, these two nanocomposites were characterized using FTIR, UV, Raman, XPS and TEM analyses. We reported that these alkyl-diamine-functionalized graphene oxides had superior dispersibility in different polar solvents with reduced agglomeration of Ag nanoparticles and had control over the size of Ag nanoparticles in the range of 5–10 nm. The catalytic efficiency of these two types of amine functionalized GO-AgNPs nanocomposite were assessed based on the reduction of 4-nitrophenol. The reduction outcomes revealed that the kobs value for DAP functionalized AgNPs (7.548 × 10−4 s−1) was comparatively superior than GO-EDA-AgNPs (3.345 × 10−4 s−1) due to the variation in chain length. Optimization of parameters like [substrate], [NaBH4] and catalyst load was also investigated and found to possess influence on kobs values.

Amine-functionalized graphene oxide nanosheets (AFGONs): an efficient bifunctional catalyst for selective formation of 1,4-dihydropyridines, acridinediones and polyhydroquinolines.

We report here selective formation of functionalized 1,4-dihydropyridines (DHP), acridinediones and polyhydroquinolines in high yields using amine-functionalized graphene oxide nanosheets (AFGONs) as the bifunctional catalyst. The method overcomes the limitations of previous protocols affording a mixture of DHP and pyridine derivatives using graphene oxide as the catalyst. The mild reaction conditions are found compatible with a wide range of functional groups. It is presumed that a cooperative effect between the acidic and basic functionalities present in AFGONs may have exerted high catalytic efficiency as well as prevented further oxidation to pyridine derivatives. A plausible mechanism is proposed on the basis of some control experiments. The reactions can be scaled up conveniently, and the catalyst can be recycled for five consecutive runs without loss of its activity.

Aminated Graphene Oxide as a Potential New Therapy for Colorectal Cancer.

Nanotechnology-based drug delivery systems for cancer therapy are the topic of interest for many researchers and scientists. Graphene oxide (GO) and its derivates are among the most extensively studied delivery systems of this type. The increased surface area, elevated loading capacity, and aptitude for surface functionalization together with the ability to induce reactive oxygen species make GO a promising tool for the development of novel anticancer therapies. Moreover, GO nanoparticles not only function as effective drug carriers but also have the potential to exert their own inhibitory effects on tumour cells. Recent results show that the functionalization of GO with different functional groups, namely, with amine groups, leads to increased reactivity of the nanoparticles. The last steers different hypotheses for the mechanisms through which this functionalization of GO could potentially lead to improved anticancer capacity. In this research, we have evaluated the potential of amine-functionalized graphene oxide nanoparticles (GO-NH2) as new molecules for colorectal cancer therapy. For the purpose, we have assessed the impact of aminated graphene oxide (GO) sheets on the viability of colon cancer cells, their potential to generate ROS, and their potential to influence cellular proliferation and survival. In order to elucidate their mechanism of action on the cellular systems, we have probed their genotoxic and cytostatic properties and compared them to pristine GO. Our results revealed that both GO samples (pristine and aminated) were composed of few-layer sheets with different particle sizes, zeta potential, and surface characteristics. Furthermore, we have detected increased cyto- and genotoxicity of the aminated GO nanoparticles following 24-hour exposure on Colon 26 cells. The last leads us to conclude that exposure of cancer cells to GO, namely, aminated GO, can significantly contribute to cancer cell killing by enhancing the cytotoxicity effect exerted through the induction of ROS, subsequent DNA damage, and apoptosis.

Efficacy of ultra-low loading of amine functionalized graphene oxide into glycidol-terminated polyurethane for high-performance composite material

In this work, the effect of amine functionalization of graphene oxide on the physicomechanical properties of glycidol-terminated polyurethane (GPU) nanocomposites was studied. p-phenylenediamine (PPD) functionalized GO (GO-PPD) was used for the fabrication of nanocomposites with GPU by an in-situ polymerization method. Covalent functionalization of GO was confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Filler content of the nanocomposites was varied from 0.05 wt% to 0.2 wt% and found the best result at 0.10 wt% loading. With the incorporation of just 0.10 wt% GO-PPD, tensile strength of glycidol terminated polyurethane (GPU) was increased by 123%, Young's modulus was found to increase by 158% and elongation at break was increased by 27%. The maximum improvement in thermal stability as observed from thermogravimetric analysis (TGA) was about 16 °C. The experimental result obtained with 0.10 wt% loading of GO-PPD was compared with the same loading of GO and found that GO-PPD provides better improvement in both the thermal and mechanical properties of GPU compared to GO at the similar loading. Ultra-low loading of modified GO has a tremendous influence in physicomechanical properties of polyurethane nanocomposites. Structure-morphology relationship was established through field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM).

Ultrasound-assisted amine functionalized graphene oxide for enhanced CO2 adsorption

The present study discusses a novel ultrasound promoted amination technique to functionalize graphene oxide (GO) for CO2 adsorption. Graphene oxide was synthesized following the modified Hummer’s method. The developed functionalization technique integrates the advantages of low-frequency ultrasonic physical activation with the chemical functionalization using tetraethylenepentamine (TEPA). Acoustic treatment exfoliates the clusters of graphene oxide and enhances the surface area for the subsequent amine functionalization and CO2 adsorption. Changes in textural properties, surface functionalities, thermal stability, and elemental compositions were examined before and after activation of graphene oxide. The characterization results revealed substantial increment of N content, from 0.08 in pristine to 4.84% in functionalized GO and the subsequent reduction in surface area from 289 to 198 m2/g in the functionalized GO, indicating attachment of TEPA to GO structure. CO2 adsorption experiments were conducted under diluted CO2 with the partial pressure of 0.10 atm. at 338 K and the results revealed that ultrasonic-TEPA activated GO possessed enhanced adsorption capacity of 1.2 mmol g−1 over pristine GO. While pristine GO could only achieve the maximum adsorption capacity of 0.3 mmol g−1 at 303 K. Besides, the sonochemically modified adsorbent showed stable cyclic adsorption-regeneration performance with only 1% reduction in adsorption capacity after 10 cycles. Finally, the effectiveness of the developed physicochemical activation technique was determined by comparing its adsorption capacity with the adsorbents found from literature.

Design and Exploration of Catalytic Activity of Two-Dimensional Surface-Engineered Graphene Oxide Nanosheets in the Transannulation of N-Heterocyclic Aldehydes or Ketones with Alkylamines.

In this work, pharmaceutically and biologically important compounds containing imidazo[1,5-a]pyridine nuclei have been synthesized via transannulation of N-heteroaryl aldehydes or ketones with alkylamines using a graphene oxide-supported copper catalyst. The nanocatalyst was fabricated by the covalent immobilization of 4-aminoantipyrine onto an amine-functionalized graphene oxide nanosupport followed by its metallation with copper acetate. Structural analysis by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction demonstrates that the two-dimensional sheet-like structure of graphene oxide is maintained even after the chemical modifications, whereas XPS revealed crucial information related to elemental composition and surface electronic states of the metal present in the catalyst. Apart from this, Fourier transform infrared spectroscopy helped in identifying the degree of oxidation and the presence of oxygenated groups in graphene oxide nanocomposites. As a heterogeneous catalyst, this graphene oxide-supported copper complex showed moderate to good catalytic activity in the C(sp3)–H bond activation/amination of a variety of substrates. This superior catalytic performance originated from the unique 2-dimensional structure of graphene oxide-based material which provided space between graphitic overlayers due to appropriate positioning of metal on their basal planes, decreasing the diffusion resistances of reactant surfaces, thus making it function as a nanoreactor. More importantly, this nanomaterial could be recovered easily and reused repeatedly by simple washing without chemical treatment with no appreciable loss in its catalytic activity, showing good potential for increasing the overall turnover number of this synthetically useful catalyst.