Polymerization of graphene oxide nanosheet by using of aminoclay: Electrocatalytic activity of its platinum nanohybrids

This study describes the polymerization of graphene oxide (GO) nanosheet to reduced‐GO‐aminoclay (RGC) by covalent functionalization of chemically reactive epoxy groups on the basal planes of GO with amine groups of magnesium phyllosilicate clay (known as aminoclay). The resulting RGC sheets were characterized and applied to support platinum nanostructures at toluene/water interface. Pt nanoparticles (NPs) with diameters about several nanometers were adhered to RGC sheets by chemical reduction of [PtCl₂(cod)] (cod = cis,cis‐1,5‐cyclooctadiene) complex. Catalytic activity of Pt NPs thin films were investigated in the methanol oxidation reaction. Cyclic voltammetry results exhibit that the Pt/reduced‐GO (RGO) and Pt/RGC thin films showed improved catalytic activity in methanol oxidation reaction in comparison to other Pt NPs thin films, demonstrating that the prepared Pt/RGO and Pt/RGC thin films are promising catalysts for direct methanol fuel cell.     

Simultaneous Determination of Nitrophenol Isomers Based on β‐Cyclodextrin Functionalized Reduced Graphene Oxide

β‐CD modified reduced graphene oxide (RGO) sheets have been prepared and characterized by TEM, AFM, IR, EIS and CVs. In comparison with bare glass carbon electrode (GCE) and RGO modified GCE, CD‐RGO/GCE showed much higher peak currents to the reduction of nitrophenol isomers (NPs), attributed to the larger specific surface area of RGO and high quantities of host–guest recognition sites. Three pairs of redox peaks are observed on the CVs of CD‐RGO for p‐NP (0.3 V), o‐NP (?0.2 V) and m‐NP (0.05 V), separating well with each other. Under the optimized condition, the anodic peak currents were linear over ranges around 1–10 mg dm^?3 for p‐NP, 1–9 mg dm^?3 for o‐NP and 1–6 mg dm^?3 for m‐NP, with the detection limits of 0.05 mg dm^?3, 0.02 mg dm^?3 and 0.1 mg dm^?3, respectively. Thus, the CD‐RGO is expected to be a promising sensor material for detecting trace NPs in waste water.     

Photocatalytically Renewable Micro‐electrochemical Sensor for Real‐Time Monitoring of Cells

Electrode fouling and passivation is a substantial and inevitable limitation in electrochemical biosensing, and it is a great challenge to efficiently remove the contaminant without changing the surface structure and electrochemical performance. Herein, we propose a versatile and efficient strategy based on photocatalytic cleaning to construct renewable electrochemical sensors for cell analysis. This kind of sensor was fabricated by controllable assembly of reduced graphene oxide (RGO) and TiO₂ to form a sandwiching RGO@TiO₂ structure, followed by deposition of Au nanoparticles (NPs) onto the RGO shell. The Au NPs‐RGO composite shell provides high electrochemical performance. Meanwhile, the encapsulated TiO₂ ensures an excellent photocatalytic cleaning property. Application of this renewable microsensor for detection of nitric oxide (NO) release from cells demonstrates the great potential of this strategy in electrode regeneration and biosensing.     

Dispersion of Reduced Graphene Oxide in Multiple Solvents with an Imidazolium‐Modified Hexa‐peri‐hexabenzocoronene

An imidazolium‐modified hexa‐peri‐hexabenzocoronene derivative (HBC‐C₁₁‐MIM[Cl^?]) was designed and synthesized as a stabilizer to fabricate reduced graphene oxide (RGO). The resulting RGO/HBC‐C₁₁‐MIM[Cl^?] hybrid shows excellent dispersivity (5.0 mg mL^?1) and stability in water. RGO/HBC‐C₁₁‐MIM[Cl^?] was comprehensively characterized by using atomic force microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, thermogravimetric analysis, and Raman spectroscopy, thus revealing that one HBC‐C₁₁‐MIM[Cl^?] group can stabilize about 178 carbon atoms on the graphene sheets. The obtained hybrid film exhibits a high conductivity of 286 S m^?1. Furthermore, the HBC‐C₁₁‐MIM[Cl^?]‐modified RGO sheets can be readily dispersed in polar organic solvents upon exchange of the hydrophilic Cl^? ions for hydrophobic bis(trifluoromethylsulfonyl) amide (NTf₂^?) ions.     

Highly Selective and Active Pd‐In/three‐dimensional Graphene with Special Structure for Electroreduction CO2 to Formate

Electrocatalytic reduction of CO₂ to formate on carbon based electrodes is known to suffer from low electrochemical reaction activity and product selectivity. Pd/three‐dimensional graphene (Pd/3D‐RGO), In/3D‐RGO and Pd‐In/3D‐RGO for the electrochemical reduction of CO₂ were prepared by a mild method that combines chemical and hydrothermal. The metal/3D‐graphenes (metal/3D‐RGO) were characterized by scanning electron microscopy, X‐ray diffraction, transmission electron microscopy and X‐ray photoelectron spectroscopy (XPS). Cyclic voltammetry and the ion chromatography were performed to investigate the electrochemical performance of the metal/3D‐RGO. The morphology and dispersion of metal/3D‐RGO are 3D structure with amount of interconnected pores with metal NPs loading on the fold. And the Pd_0.5‐In_0.5/3D‐RGO show excellent surface performance with well dispersion and smallest particle size (12.8 nm). XPS reveal that binding energy of Pd (In) NPs is shifted to negative energy, for the metal lose electrons in metal and combine with C, which is demonstrated in the HNO₃ experiment. The peak potential of Pd_0.5‐In_0.5/3D‐RGO is −0.70 V (vs. Ag/AgCl), which is more positive than In_1.0/3D‐RGO (−0.73 V) and Pd_1.0/3D‐RGO (−1.2 V). The highest faradaic efficiency (85.3 %) happens in Pd_0.5‐In_0.5/3D‐RGO at −1.6 V vs. Ag/AgCl. In these experiments, the special structure that metal NPs combine with C and the bimetal NPs give a direction to convert CO₂ to formate.     

Optical and Magnetic Properties of Conjugate Structures of PbSe Quantum Dots and γ‐Fe2O3 Nanoparticles

An investigation of the optical and magnetic properties of a unique hydrogen‐linked conjugate nanostructure, comprised of superparamagnetic γ‐Fe₂O₃ nanoparticles (NPs) and near‐infrared PbSe nanocrystal quantum dot (NQD) chromophores, is reported. The results show retention of the NQDs’ emission quantum efficiency and radiative lifetime, and only a small red shift of its band energy, upon conjugation to the dielectric surroundings of γ‐Fe₂O₃ NPs. The study also shows the sustainability of the superparamagnetism of the NPs after conjugation, with only a slight decrease of the ferromagnetic–superparamagnetic transition temperature with respect to that of the individual NPs. Thus, the conjugate nanostructure can be considered as a useful medical platform when PbSe NQDs act as fluorescent tags, while the γ‐Fe₂O₃ NPs are used as a vehicle driven by an external magnetic field for targeted delivery of tags or drugs.     

Synthesis of PNIPAM polymer brushes on reduced graphene oxide based on click chemistry and RAFT polymerization

Preparation and characterization of poly(N‐isopropylacrylamide) (PNIPAM) polymer brushes on the surfaces of reduced graphene oxide (RGO) sheets based on click chemistry and reversible addition‐fragmentation chain transfer (RAFT) polymerization was reported. RGO sheets prepared by thermal reduction were modified by diazonium salt of propargyl p‐aminobenzoate, and alkyne‐functionalized RGO sheets were obtained. RAFT chain transfer agent (CTA) was grafted to the surfaces of RGO sheets by click reaction. PNIPAM on RGO sheets was prepared by RAFT polymerization. Fourier transform‐infrared spectroscopy, thermogravimetric analysis, X‐ray photoelectron spectroscopy, and transmission electron microscopy (TEM) results all demonstrated that RAFT CTA and PNIPAM were successfully produced on the surfaces of RGO sheets. Nanosized PNIPAM domains on RGO sheets were observed on TEM. Micro‐DSC result indicated that in aqueous solution PNIPAM on RGO sheets presented a lower critical solution temperature at 33.2 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Iron Oxide Nanoparticles: Biosynthesis,Magnetic Behavior,Cytotoxic Effect

Iron oxide nanoparticles have attracted much attention because of their superparamagnetic properties and their potential applications in many fields such as magnetic storage devices, catalysis, sensors, superparamagnetic relaxometry (SPMR), and high-sensitivity biomolecule magnetic resonance imaging (MRI) for medical diagnosis and therapeutics. In this study, iron oxide nanoparticles (Fe₂O₃ NPs) have been synthesized using a taranjabin (camelthorn or persian manna) aqueous solution. The synthesized Fe₂O₃ NPs were identified through powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), field energy scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDX), vibrating-sample magnetometer (VSM) and Raman technics. The results show that the nanoparticles have a hexagonal structure with 20 to 60 nm in size. The cytotoxic effect of the synthesized nanoparticles has been tested upon application against lung cancer cell (A549) lines. It was found that there is no cytotoxic activity at lower concentrations of 200 μg/mL. The ability of the synthesized nanoparticles for lead removal in wastewaters was tested. Results show that highest concentration of adsorbent (50 mg/L) has maximum removal efficiency (96.73 %). So, synthesized Fe₂O₃ NPs can be a good candidate to use as heavy metals cleaner from contaminated waters.     

The crystal packing of 4,7‐dichloro‐ and 4,7‐dibromobenzo[c]furazan 1‐oxide

The molecular structures of 4,7‐di­chloro­benzo­[c]­fur­azan 1‐­oxide, C₆H₂Cl₂N₂O₂, (I), and 4,7‐di­bromo­benzo­[c]­fur­azan 1‐oxide, C₆H₂Br₂N₂O₂, (II), are normal. Compound (I) occurs in two polymorphic forms. One polymorph contains one mol­ecule in the asymmetric unit, organized into two‐dimensional sheets involving intermolecular N?Cl and O?Cl inter­actions. The second polymorph has three mol­ecules in the asymmetric unit, organized into two crystallographically different two‐dimensional sheets with similar interactions. Compound (II) is isomorphous with the second polymorph of (I). The three two‐dimensional sheets in the two polymorphs comprise a set of three two‐dimensional polymorphic arrangements.     

Preparation of FePd‐RGO Bimetallic Composites with High Catalytic Activity for Formic Acid Electro‐Oxidation

FePd‐RGO composites through the growth of uniformly dispersed iron‐palladium bimetallic nanoparticles (NPs) on reduced graphene oxide (RGO) nanosheets were prepared by a two‐step method. The firstly formed Fe is used as the seed for the subsequent Pd growth. The formation of Fe NPs on RGO in the first step is performed by an in‐situ reduction reaction with the reducer ethylene glycol under oil bath at 180°C. NPs in the as‐prepared FePd‐RGO have an average particle size of 6.5 nm, and Pd is added to one side of Fe which leads to the formation of Fe‐Pd bimetallic interfaces. As compared with the commercial Pd black at the same loading, the composites have higher electro‐catalytic activity, better electrochemical stability and higher resistance to CO poisoning for formic acid electro‐oxidation.     

Mechanism of Proton Relaxation for Enzyme‐Manipulated,Multicomponent Gold–Magnetic Nanoparticle Chains

Longitudinal and transverse relaxation times of multicomponent nanoparticle (NP) chains are investigated for their potential use as multifunctional imaging agents in magnetic resonance imaging (MRI). Gold NPs (ca. 5 nm) are arranged linearly along double‐stranded DNA, creating gold NP chains. After cutting gold NP chains with restriction enzymes (EcoRI or BamHI), multicomponent NP chains are formed through a ligation reaction with enzyme‐cut, superparamagnetic NP chains. We evaluate the changes in relaxation times for different constructs of gold–iron oxide NP chains and gold–cobalt iron oxide NP chains using 300 MHz ¹H NMR. In addition, the mechanism of proton relaxation for multicomponent NP chains is examined. The results indicate that relaxation times are dependent on the one‐dimensional structure and the amount of superparamagnetic NP chains present in the multicomponent constructs. Multicomponent NP chains arranged on double‐stranded DNA provide a feasible method for fabrication of multifunctional imaging agents that improve relaxation times effectively for MRI applications.     

Application of biosynthesized palladium nanoparticles (Pd NPs) on Rosa canina fruit extract‐modified graphene oxide as heterogeneous nanocatalyst for cyanation of aryl halides

A green palladium (Pd)‐based catalyst supported on Rosa canina fruit extract‐modified graphene oxide [Pd nanoparticles (NPs)/reduced graphene oxide (RGO)‐Rosa canina] hybrid materials has been used as a recoverable and heterogeneous nanocatalyst for cyanating aryl halides using K₄[Fe (CN)₆] as the resource of cyanide. The nitriles were achieved in good to high yield, and the catalyst can be recovered and reused for up to seven cycles with no remarkable decrease in its catalytic activity.     

One-step synthesis of Pt nanoparticles/reduced graphene oxide composite with enhanced electrochemical catalytic activity

A one-step electrochemical approach for synthesis of Pt nanoparticles/reduced graphene oxide(Pt/RGO) was demonstrated.Graphene oxide(GO) and chloroplatinic acid were reduced to RGO and Pt nanoparticles(Pt NPs) simultaneously,and Pt/RGO composite was deposited on the fluorine doped SnO 2 glass during the electrochemical reduction.The Pt/RGO composite was characterized by field emission-scanning electron microscopy,Raman spectroscopy and X-ray photoelectron spectroscopy,which confirmed the reduction of GO and chloroplatinic acid and the formation of Pt/RGO composite.In comparison with Pt NPs and RGO electrodes obtained by the same method,results of cyclic voltammetry and electrochemical impedance spectroscopy measurements showed that the composite electrode had higher catalytic activity and charge transfer rate.In addition,the composite electrode had proved to have better performance in DSSCs than the Pt NPs electrode,which showed the potential application in energy conversion.     

Controlled assembly of superparamagnetic iron oxide nanoparticles on electrospun PU nanofibrous membrane: A novel heat-generating substrate for magnetic hyperthermia application

A facile method of fabricating novel heat-generating membranes composed of electrospun polyurethane (PU) nanofibers decorated with superparamagnetic iron oxide nanoparticles (NPs) is reported. Electrospinning was used to produce polymeric nanofibrous matrix, whereas polyol immersion technique allowed in situ assembly of well-dispersed Fe₃O₄ NPs on the nanofibrous membranes without any surfactant, and without sensitizing and stabilizing reagent. The assembly phenomena can be explained by the hydrogen-bonding interactions between the amide groups in the PU matrix and the hydroxyl groups capped on the surface of the Fe₃O₄ NPs. The prepared nanocomposite fibers showed acceptable magnetization value of 33.12 emu/g, after measuring the magnetic hysteresis loops using SQUID. Moreover, the inductive heating property of electrospun magnetic nanofibrous membranes under an alternating current (AC) magnetic field was investigated. We observed a progressive increase in the heating rate with the increase in the amount of magnetic Fe₃O₄ NPs in/on the membranes. The present electrospun magnetic nanofibrous membrane may be a potential candidate as a novel heat-generating substrate for localized hyperthermia cancer therapy.     

Three‐Dimensional Fe2N@C Microspheres Grown on Reduced Graphite Oxide for Lithium‐Ion Batteries and the Li Storage Mechanism

Nanostructured iron compounds as lithium‐ion‐battery anode material have attracted considerable attention with respect to improved electrochemical energy storage and excellent specific capacity, so lots of iron‐based composites have been developed. Herein, a novel composite composed of three‐dimensional Fe₂N@C microspheres grown on reduced graphite oxide (denoted as Fe₂N@C‐RGO) has been synthesized through a simple and effective technique assisted by a hydrothermal and subsequent heating treatment process. As the anode material for lithium‐ion batteries, the synthetic Fe₂N@C‐RGO displayed excellent Li⁺‐ion storage performance with a considerable initial capacity of 847 mAh g^?1, a superior cycle stability (a specific discharge capacity of 760 mAh g^?1 remained after the 100th cycle), and an improved rate‐capability performance compared with those of the pure Fe₂N and Fe₂N‐RGO nanostructures. The good performance should be attributed to the existence of RGO layers that can facilitate to enhance the conductivity and shorten the lithium‐ion diffusion path; in addition, the carbon layer on the surface of Fe₂N can avert the structure decay caused by the volume change during the lithiation/delithiation process. Moreover, in situ X‐ray absorption fine‐structure analysis demonstrated that the excellent performance can be attributed to the lack of any obvious change in the coordination geometry of Fe₂N@C‐RGO during the charge/discharge processes.     

Electrochemical Biosensor Utilizing Supramolecular Association of Enzyme on Sol−gel Matrix Embedded Gold Nanoparticles Supported Reduced Graphene Oxide−cyclodextrin Nanocomposite

Herein we present β‐cyclodextrin (CD)‐functionalized reduced graphene oxide (RGO) nanosheets supported on silicate sol‐gel matrix‐embedded gold nanoparticles (Au NPs) modified electrode as a new affinity binding nanocomposite. The modified electrode is fabricated through layer‐by‐layer drop casting followed by immobilization of chemically modified enzyme conjugate (horse radish peroxidase (HRP)?adamantane carboxylic acid (ADA)). This affinity system is based on the supramolecular association between CDs and HRP?ADA and is mimicking the biological avidin?biotin interactions. CDs‐functionalized RGO (RGO?CD) functions as a macrocyclic host to form stable supramolecular inclusion complexes with enzyme conjugate. Besides Au NPs improve the interfacial interaction with RGO?CD nanosheets, and thus exhibit synergistic electrocatalytic effect toward H₂O₂ reduction in the presence of 1 mM hydroquinone.     

Silica‐Protection‐Assisted Encapsulation of Cu2O Nanocubes into a Metal–Organic Framework (ZIF‐8) To Provide a Composite Catalyst

The integration of metal/metal oxide nanoparticles (NPs) into metal–organic frameworks (MOFs) to form composite materials has attracted great interest due to the broad range of applications. However, to date, it has not been possible to encapsulate metastable NPs with high catalytic activity into MOFs, due to their instability during the preparation process. For the first time, we have successfully developed a template protection–sacrifice (TPS) method to encapsulate metastable NPs such as Cu₂O into MOFs. SiO₂ was used as both a protective shell for Cu₂O nanocubes and a sacrificial template for forming a yolk–shell structure. The obtained Cu₂O@ZIF‐8 composite exhibits excellent cycle stability in the catalytic hydrogenation of 4‐nitrophenol with high activity. This is the first report of a Cu₂O@MOF‐type composite material. The TPS method provides an efficient strategy for encapsulating unstable active metal/metal oxide NPs into MOFs or maybe other porous materials.     

Effect of addition of iron on morphology and catalytic activity of PdCu nanoalloy thin film as catalyst in Sonogashira coupling reaction

Palladium‐supported catalysts are complex assemblies with a challenging preparation. Minor changes in their preparation conditions can affect the activity, selectivity and lifetime of these catalysts. PdCuFe nanoparticle (NP) thin films were supported on reduced graphene oxide (RGO) by the reduction of the organometallic complex [PdCl_2‌(cod)] (cod = cis ,cis ‐1,5‐cyclooctadiene), and [Cu(acac)₂] and [Fe(acac)₃] (acac = acetylacetonate) complexes at a toluene–water interface. We have investigated the application of the liquid–liquid interface method for preparing ultrathin films of catalysts and have evaluated the catalytic activity of the prepared NPs for the Sonogashira coupling reaction in micelle media. Also, we have investigated the effect of the addition of iron on the morphology, size and catalytic activity of PdCu/RGO NPs. Our study shows that both of the prepared catalysts (PdCu/RGO and PdCuFe/RGO) are efficient and recoverable catalysts for the Sonogashira carbon–carbon coupling reaction. This method has advantages compared to other routes, such as short reaction times, high to excellent yields, facile and low‐cost method for the preparation of the catalysts, and easy separation and reusability of the catalysts.     

Functionalization of Reduced Graphite Oxide Sheets with a Zwitterionic Surfactant

Films of a few layers in thickness of reduced graphite oxide (RGO) sheets functionalized by the zwitterionic surfactant N‐dodecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propanesulfonate (DDPS) are obtained by using the Langmuir–Blodgett method. The quality of the RGO sheets is checked by analyzing the degrees of reduction and defect repair by means of X‐ray photoelectron spectroscopy, atomic force microscopy (AFM), field‐emission scanning electron microscopy (SEM), micro‐Raman spectroscopy, and electrical conductivity measurements. A modified Hummers method is used to obtain highly oxidized graphite oxide (GO) together with a centrifugation‐based method to improve the quality of GO. The GO samples are reduced by hydrazine or vitamin C. Functionalization of RGO with the zwitterionic surfactant improves the degrees of reduction and defect repair of the two reducing agents and significantly increases the electrical conductivity of paperlike films compared with those prepared from unfunctionalized RGO.     

Engineered mesoporous ionic‐modified γ‐Fe2O3@hydroxyapatite decorated with palladium nanoparticles and its catalytic properties in water

A new mesoporous organic–inorganic nanocomposite was formulated and then used as stabilizer and support for the preparation of palladium nanoparticles (Pd NPs). The properties and structure of Pd NPs immobilized on prepared 1,4‐diazabicyclo[2.2.2]octane (DABCO) chemically tagged on mesoporous γ‐Fe₂O₃@hydroxyapatite (ionic modified (IM)‐MHA) were investigated using various techniques. The synergistic effects of the combined properties of MHA, DABCO and Pd NPs, and catalytic activity of γ‐Fe₂O₃@hydroxyapatite‐DABCO‐Pd (IM‐MHA‐Pd) were investigated for the Heck cross‐coupling reaction in aqueous media. The appropriate surface area and pore size of mesoporous IM‐MHA nanocomposite can provide a favourable hard template for immobilization of Pd NPs. The loading level of Pd in the nanocatalyst was 0.51 mmol g^?1. DABCO bonded to the MHA surface acts as a Pd NP stabilizer and can also lead to colloidal stability of the nanocomposite in aqueous solution. The results reveal that IM‐MHA‐Pd is highly efficient for coupling reactions of a wide range of aryl halides with olefins under green conditions. The superparamagnetic nature of the nanocomposite means that the catalyst to be easily separated from solution through magnetic decantation, and the catalytic activity of the recycled IM‐MHA‐Pd showed almost no appreciable loss even after six consecutive runs.