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

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

Modification of carbon nanomaterials by hyperbranched polyglycerol improves their properties.     

Experimental and computational studies of a graphene oxide barrier layer covalently functionalized with amino acids on Mg AZ13 alloy in salt medium

Magnesium alloys are promising materials for the biomedical and automobile industries. The Mg alloy''s light-weight property leads to numerous industrial applications. However, the magnesium alloy oxide layers are not stable in salt environments. Organic inhibitors and epoxy coatings fail as long term barriers in such media. Recently, carbon based functionalized materials, graphene oxides, were shown to be promising materials for improving corrosion resistance in acid and salt environments. Our research considered graphene oxide covalently functionalized with the amino acid leucine to form anticorrosion coating materials. The functionalized materials were characterized by XRD, Raman, FESEM, HRTEM, FTIR, and AFM methods. The corrosion inhibition efficiency was monitored by electrochemical methods. The novelty of the functionalized graphene oxide materials is that they are water impermeable, and thus could enhance the anticorrosion resistance in salt environments.

Leucine functionalized graphene oxide chemisorbed on a 111 surface AZ13 magnesium alloy via edge functional groups.     

Ionic-exchange immobilization of ultra-low loading palladium on a rGO electro-catalyst for high activity formic acid oxidation

A formic acid oxidation electro-catalyst with ultra-low palladium (Pd) loading was prepared via an ionic exchange method by utilizing the acidic functional groups on graphene oxide (GO). After simultaneous reduction of exchanged Pd²⁺ and residual functional groups on the GO surface, an ionic exchange reduced Pd catalyst supported on reduced GO (IE-Pd/rGO) was obtained. Three times improved formic acid oxidation mass activity compared with that of the conventional synthesized Pd/C catalyst was exhibited for the IE-Pd/rGO catalyst. More importantly, formic acid oxidation stability on the IE-Pd/rGO catalyst was remarkably improved due to synergistic effect of the strong immobilization of Pd nanoparticles and the effect of in situ doped N on the rGO support.

A formic acid oxidation electro-catalyst with ultra-low palladium (Pd) loading was prepared via an ionic exchange method by utilizing the acidic functional groups on graphene oxide (GO).     

Design,synthesis, and catalytic performance of modified graphene oxide based on a cobalt complex as a heterogenous catalyst for the preparation of aminonaphthoquinone derivatives

We are reporting a functionalized graphene oxide catalyst developed by modifying graphene oxide surface using the covalent attachment of an amino-functionalized SiO₂ sphere/cobalt complex. Silica network has special characteristics including mechanical strength, high thermal and chemical stability with good dispersion in solvents. The silica/graphene oxide mixture provides improved properties and extends the scope of application. Graphene oxide was functionalized by spherical silica with the help of hybrid silane-containing nitrogen to coordinate with Co(ii) for increasing the catalytic activity. The catalyst was characterized by Fourier Transform Infrared (FT-IR) spectroscopy, powder X-ray diffraction (XRD), Energy Dispersive X-ray (EDX), Scanning Electron Microscopy (SEM), Raman spectroscopy, and Thermal Gravimetric (TGA) analyses. The catalyst showed high catalytic activity for multi-component reactions in the synthesis of aminonaphthoquinones in ethanol solvent. The catalyst''s ability to improve the yield (96–98%), reduce the reaction time (5–8 min), and recycling ability are important benefits for the catalyst.

GO@f-SiO₂@Co is a heterogenous catalyst composed of spherical silica particles grafted on the surface of graphene oxide with ethylenediamine ligands and coordination with Co(ii). We assessed the activity of the catalyst for the synthesis of aminonaphthoquinones.     

Functional drug carriers formed by RGD-modified β-CD-HPG for the delivery of docetaxel for targeted inhibition of nasopharyngeal carcinoma cells

In this study, a drug delivery system was prepared by grafting the targeting molecule arginine-glycine-aspartic acid (RGD) onto hyperbranched polyglycerol (HPG)-modified β-cyclodextrin (β-CD-HPG) for the targeted inhibition of nasopharyngeal carcinoma (NPC) cells. The obtained β-CD-HPG-RGD with a relatively small size and low surface charge delivered docetaxel (Doc) effectively and displayed a targeting effect to human NPC HNE-1 cells, as confirmed by confocal laser scanning microscopy and flow cytometry. The in vitro drug release analysis exhibited the controlled drug release kinetics of the β-CD-HPG-RGD/Doc nanomedicine. β-CD-HPG-RGD/Doc effectively inhibited the proliferation of HNE-1 cells and promoted apoptosis. Moreover, its biocompatibility in vitro and in vivo was assessed. The results indicate that the β-CD-HPG-RGD/Doc nanomedicine has potential application in NPC targeting therapy.

A new RGD targeting drug carrier based on HPG-modified β-CD has been synthesized. This carrier showed excellent biocompatibility and targeting ability. The obtained NPs could effectively inhibit the proliferation of tumor cells.     

Direct electrodeposition of cationic pillar[6]arene-modified graphene oxide composite films and their host–guest inclusions for enhanced electrochemical performance

In the present work, electrochemically reduced graphene oxide-cationic pillar[6]arene (ErGO-CP6) composite films on glassy carbon electrodes (GCEs) were prepared directly from graphene oxide-cationic pillar[6]arene (GO-CP6) dispersions by a facile one-step pulsed electrodeposition technique. The preparation of GO-CP6 and its subsequent electrochemical reduction were confirmed by Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy (UV-vis), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), zeta potential, Raman spectroscopy, and scanning electron microscopy (SEM). SEM result reveals that ErGO-CP6 could form a homogeneous film when GO-CP6 was electrodeposited on the surface of a GCE. Furthermore, Raman and XPS results confirm the removal of oxygen-containing functional groups present on the GO-CP6 surface after electrochemical reduction. Electrochemical results reveal that ErGO-CP6 films could show much higher electrochemical response to theophylline (TP), ascorbic acid (AA), acetaminophen (APAP), and folic acid (FA) than unmodified ErGO films and bare GCE, which is considered to be the synergistic effect of the graphene (excellent electrical properties and large surface area) and CP6 molecules (high inclusion complexation and enrichment capability).

Cationic pillar[6]arene functionalized graphene films with enhanced host–guest electrochemical recognition performance were fabricated directly from GO-CP6 dispersions by a one-step pulsed electrodeposition technique.     

One-pot multicomponent synthesis of thieno[2,3-b]indoles catalyzed by a magnetic nanoparticle-supported [Urea]4[ZnCl2] deep eutectic solvent

In this study, we have developed the synthesis of thieno[2,3-b]indole dyes via a multicomponent reaction of cheap and available reagents such as sulfur, acetophenones, and indoles using a magnetic nanoparticle-supported [Urea]₄[ZnCl₂] deep eutectic solvent as a green catalyst. The synthesis of a series of diversely functionalized thieno[2,3-b]indole has been successfully performed in a one-pot reaction. Among a total of 25 compounds synthesized, there are 21 new compounds with full characterization such as FT-IR, ¹H and ¹³C NMR, HRMS (ESI). Due to the deep eutectic solvent coated surface of the magnetic nanoparticles, the catalyst could be recovered by an external magnet and reused in five consecutive runs without a considerable decrease in catalytic activity.

We have developed the synthesis of thieno[2,3-b]indole dyes via a multicomponent reaction of cheap and available reagents using a magnetic nanoparticle-supported [Urea]₄[ZnCl₂] deep eutectic solvent as a green catalyst.     

A novel surface plasmon resonance sensor based on a functionalized graphene oxide/molecular-imprinted polymer composite for chiral recognition of l-tryptophan

Herein, a novel surface plasmon resonance (SPR) sensor based on a functionalized graphene oxide (GO)/molecular-imprinted polymer composite was developed for the chiral recognition of l-tryptophan (l-Trp). The composite''s recognition element was prepared via a facile and green synthesis approach using polydopamine as both a reducer of GO and a functional monomer as well as a cross-linker for molecular imprinting. The composite was characterized via Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. After attaching the composite onto the gold surface of an SPR chip, the sensor was characterized using contact-angle measurements. The sensor exhibited excellent selectivity and chiral recognition for the template (i.e., l-Trp). Density functional theory computations showed that the difference in hydrogen bonding between the composite element and l-Trp and d-Trp played an important role in chiral recognition.

Novel SPR sensor for chiral recognition of l-tryptophan using a functionalized graphene oxide/molecularly-imprinted polymer composite as a recognition element.     

Practical scale up synthesis of carboxylic acids and their bioisosteres 5-substituted-1H-tetrazoles catalyzed by a graphene oxide-based solid acid carbocatalyst

Herein, catalytic application of a metal-free sulfonic acid functionalized reduced graphene oxide (SA-rGO) material is reported for the synthesis of both carboxylic acids and their bioisosteres, 5-substituted-1H-tetrazoles. SA-rGO as a catalytic material incorporates the intriguing properties of graphene oxide material with additional benefits of highly acidic sites due to sulfonic acid groups. The oxidation of aldehydes to carboxylic acids could be efficiently achieved using H₂O₂ as a green oxidant with high TOF values (9.06–9.89 h⁻¹). The 5-substituted-1H-tetrazoles could also be effectively synthesized with high TOF values (12.08–16.96 h⁻¹). The synthesis of 5-substituted-1H-tetrazoles was corroborated by single crystal X-ray analysis and computational calculations of the proposed reaction mechanism which correlated well with experimental findings. Both of the reactions could be performed efficiently at gram scale (10 g) using the SA-rGO catalyst. SA-rGO displays eminent reusability up to eight runs without significant decrease in its productivity. Thus, these features make SA-rGO riveting from an industrial perspective.

Scalable synthesis of carboxylic acids and their bioisosteres, 5-substituted-1H-tetrazoles, catalyzed by phenylsulfonic acid functionalized reduced graphene oxide.     

Efficient removal of crystal violet dye using EDTA/graphene oxide functionalized corncob: a novel low cost adsorbent

In this study, EDTA functionalized corncob (EDTA-corncob) and EDTA/graphene oxide functionalized corncob (EDTA-GO/corncob) were prepared using disodium ethylenediamine tetraacetic acid and the graphene oxide immersion method. EDTA-corncob and EDTA-GO/corncob were characterized by SEM and FTIR spectroscopy. On this basis, the adsorption properties of EDTA-corncob and EDTA-GO/corncob were studied with crystal violet as the adsorbate. The optimum adsorption conditions were determined by the effect of samples on the adsorption properties of crystal violet at different times, temperatures and pH, and the reusability of the samples was studied. The results showed that adsorption capacity of crystal violet on EDTA-GO/corncob was higher compared with natural corncob and EDTA-corncob. The most suitable pH value of the solution is about 6.0, the adsorption equilibrium time is 200 min. EDTA-GO/corncob can be reused eight times. This study indicated that EDTA-GO/corncob is a reusable adsorbent for rapid, low-cost, and efficient removal of dye from waste water.

In this study, crystal violet dyes were adsorbed by EDTA functionalized corncob (EDTA-corncob) and EDTA/graphene oxide functionalized corncob (EDTA-GO/corncob), which were prepared using disodium ethylenediamine tetraacetic acid and the graphene oxide immersion method.     

Highly sensitive and wearable gas sensors consisting of chemically functionalized graphene oxide assembled on cotton yarn

Highly sensitive and wearable chemical sensors for the detection of toxic gas molecules are given significant attention for a variety of applications in human health care and environmental safety. Herein, we demonstrated fiber-type gas sensors based on graphene oxide functionalized with organic molecules such as heptafluorobutylamine (HFBA), 1-(2-methoxyphenyl)piperazine (MPP), and 4-(2-keto-1-benzimidazolinyl)piperidine (KBIP) by assembling functionalized graphene oxide (FGO) on a single yarn fabric. These gas sensors of FGO on yarn exhibited extraordinarily higher sensitivity upon exposure to gas molecules than chemically reduced graphene oxide due to many active functional groups on the GO surface. Furthermore, the mechanical stability and chemical durability of the resulting gas sensors are well-maintained. Based on these results, we expected that our sensors with high sensitive and wearability will provide a good premise for wearable chemical sensors-based multidisciplinary applications.

Functionalized-graphene-oxide-based gas sensors with KBIP-GO-Y showed extremely high sensitivity (∼70%) for exposure to gas molecules compared with rGO-based sensors (∼12%) in spite of relatively low gas concentrations (8 ppm NH₃ gas).     

A new and straightforward route to synthesize novel pyrazolo[3,4-b]pyridine-5-carboxylate scaffolds from 1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles

Among many acidic catalysts, amorphous carbon-supported sulfonic acid (AC-SO₃H) has been evaluated as a new-generation solid catalyst with outstanding activity. Because of the –SO₃H groups, the surface properties of the amorphous carbon catalyst were improved, which made the catalytic activity of the amorphous carbon-supported sulfonic acid many times greater than that of sulfuric acid. The amorphous carbon-supported sulfonic acid exhibited several advantages such as low cost, non-toxicity, porosity, stability, and easily adjustable chemical surface. In this paper, we introduce a new pathway for the synthesis of pyrazolo[3,4-b]pyridine-5-carboxylate scaffolds from 1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles and aniline at room temperature under ethanol in the presence of AC-SO₃H as the catalyst. This method provided the desired products with moderate to good yields. The gram-scale synthesis of the major product was carried out with good yields (up to 80%). This strategy involves a sequential opening/closing cascade reaction. This approach presents several advantages, including room temperature conditions, short reaction time, and operational simplicity.

A new pathway for the synthesis of pyrazolo[3,4-b]pyridine-5-carboxylate scaffolds from 1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles and aniline has been developed using sulfonated amorphous carbon at room temperature.     

Convenient one-pot synthesis of 1,2,4-oxadiazoles and 2,4,6-triarylpyridines using graphene oxide (GO) as a metal-free catalyst: importance of dual catalytic activity

A convenient and efficient process for the synthesis of 3,5-disubstituted 1,2,4-oxadiazoles and 2,4,6-triarylpyridines has been described using an inexpensive, environmentally benign, metal-free heterogeneous carbocatalyst, graphene oxide (GO). GO plays a dual role of an oxidizing agent and solid acid catalyst for synthesizing 1,2,4-oxadiazoles and triarylpyridines. This dual catalytic activity of GO is due to the presence of oxygenated functional groups which are distributed on the nanosheets of graphene oxide. A broad scope of substrate applicability and good sustainability is offered in this developed protocol. The results of a few control experiments reveal a plausible mechanism and the role of GO as a catalyst was confirmed by FTIR, XRD, SEM, and HR-TEM analysis.

Graphene oxide (GO) as a metal-free catalyst for the synthesis of 1,2,4-oxadiazoles and 2,4,6-triarylpyridines under mild reaction conditions.     

Graphene oxide-catalyzed trifluoromethylation of alkynes with quinoxalinones and Langlois' reagent

The direct C–H trifluoromethylation of alkynes and quinoxalinones has been achieved using a graphene oxide/Langlois'' reagent system. This multi-component tandem reaction using graphene oxide as the catalyst and Langlois'' reagent as the robust CF₃ radical source results in the formation of olefinic C–CF₃ to access a series of 3-trifluoroalkylated quinoxalin-2(1H)-ones.

The direct C–H trifluoromethylation of alkynes and quinoxalinones using a graphene oxide/Langlois'' reagent system.     

Unusual rearrangement of imidazo[1,5-a]imidazoles and imidazo[1,2-b]pyrazoles into imidazo[1,5-a]pyrimidines and pyrazolo[1,5-a]pyrimidines

A multicomponent reaction giving easy and cheap access to a variety of bicyclic 5,5-fused hetero-rings has been developed. Then, an usual rearrangement of imidazo[1,5-a]imidazoles or imidazo[1,2-b]pyrazoles leading to bi-heterocyclic imidazo- and pyrazolo[1,5-a]pyrimidines in the presence of a specific amount of I₂ in THF at room temperature has been achieved. This new method enables the hitherto unreported synthesis of functionalized imidazo- and pyrazolo[1,5-a]pyrimidines.

A multicomponent reaction giving easy and cheap access to a variety of bicyclic 5,5-fused hetero-rings has been developed.     

Polyurethane ionomers based on amino ethers of ortho-phosphoric acid

The etherification of ortho-phosphoric acid with triethanolamine and polyoxypropylene glycol is studied. The reaction process is accompanied by the formation of hyperbranched amino ethers of ortho-phosphoric acid terminated by hydroxyl groups. A specific feature of the chemical structure of the compounds obtained is the existence of ion pairs in their structure separated in space. The reaction of the etherification of ortho-phosphoric acid with glycols becomes possible through the use of tertiary amines. The amino ethers of ortho-phosphoric acid are investigated as a polyol component for the synthesis of polyurethanes with high adhesion characteristics and strength properties. The experimental results presented allow us to relate polyurethanes obtained on the basis of ortho-phosphoric acid amino ethers to polymers of ionomeric nature.

The etherification of ortho-phosphoric acid with triethanolamine and polyoxypropylene glycol is studied.     

Degradation of chemical warfare agents over cotton fabric functionalized with UiO-66-NH2

Herein, cotton fabric was treated with an alkaline solution to increase the content of surface hydroxyl groups and then functionalized with UiO-66-NH₂, a nanoporous metal–organic framework. Instrumental analysis of the thus treated fabric revealed that its surface was covered with UiO-66-NH₂ crystals in a uniform manner. The ability of the functionalized fabric to degrade two chemical warfare agents (soman and sulfur mustard) was probed by testing its permeability to these two agents (swatch testing), and the excellent degradation performance was concluded to be well suited for a broad range of filtration and decontamination applications.

We develop a very efficient modification method of cotton fabric to be functionalized with a MOF via mercerization.     

Temperature effect on the nucleation of graphene on Cu (111)

Repeated thermal cycling by using an organic precursor is shown to be a successful technique for growing graphene on metal substrates. Having control on this process is of vital importance in producing large areas of high quality graphene with well-ordered surface characteristics, which leads us to investigate the effect of temperature on the microscopic mechanisms behind this process. Apart from being an important factor in the dissociation of the organic precursor and promoting the reactions taking place on the surface of the catalyst, temperature also plays a major role in the structure of the catalyst surface. First, we used eight thermal cycles to successfully grow graphene on the surface of Cu (111). Then, we employed Ab Initio Molecular Dynamics (AIMD) simulations to study graphene island alignment evolution at two temperatures. The results shed light on our experimental observations and those reported in the literature and point to the effectiveness of controlled thermal cycling in producing high quality graphene sheets on transition metal catalyst surfaces.

Repeated thermal cycling by using an organic precursor is shown to be a successful technique for growing graphene on metal substrates.     

Convenient construction of tetrahydrochromeno[4′,3′:2,3]indolizino[8,7-b]indoles and tetrahydroindolizino[8,7-b]indoles via one-pot domino reaction

The functionalized tetrahydrochromeno[4′,3′:2,3]indolizino[8,7-b]indoles were conveniently synthesized in high yields by one-pot domino reaction of tryptamines, alkyl propiolates and 2-aryl-3-nitro-2H-chromenes. Under similar conditions, the one-pot reaction of tryptamines, alkyl propiolates and β-nitroalkenes resulted in functionalized tetrahydroindolizino[8,7-b]indoles. The reaction mechanism involved sequential generation of β-enamino ester, Michael addition, Pictet–Spengler reaction and annulation process. The reaction showed high atomic economy and met the goals of sustainable chemistry.

The functionalized tetrahydrochromeno[4′,3′:2,3]indolizino[8,7-b]indoles were conveniently synthesized in high yields by one-pot domino reaction of tryptamines, alkyl propiolates and 2-aryl-3-nitro-2H-chromenes.     

Synthesis of oxygen functionalized carbon nanotubes and their application for selective catalytic reduction of NOx with NH3

Oxygen functionalized carbon nanotubes synthesized by surface acid treatment were used to improve the dispersion properties of active materials for catalysis. Carbon nanotubes have gained attention as a support for active materials due to their high specific surface areas (400–700 m² g⁻¹) and chemical stability. However, the lack of surface functionality causes poor dispersion of active materials on carbon nanotube supports. In this study, oxygen functional groups were prepared on the surface of carbon nanotubes as anchoring sites for decoration with catalytic nanoparticles. The oxygen functional groups were prepared through a chemical acid treatment using sulfuric acid and nitric acid, and the amount of functional groups was controlled by the reaction time. Vanadium, tungsten, and titanium oxides as catalytic materials were dispersed using an impregnation method on the synthesized carbon nanotube surfaces. Due to the high density of oxygen functional groups, the catalytic nanoparticles were well dispersed and reduced in size on the surface of the carbon nanotube supports. The selective catalytic reduction catalyst with the oxygen functionalized carbon nanotube support exhibited enhanced NO_x removal efficiency of over 90% at 350–380 °C which is the general operating temperature range of catalysis in power plants.

Oxygen functionalized carbon nanotubes synthesized by surface acid treatment were used to improve the dispersion properties of active materials for catalysis.