水溶液体系中氧化石墨烯的γ射线辐射还原

石墨烯是一种碳原子以二维蜂窝状晶格结构构成的单片层材料,由于其具有优异的电传导性、力学性能和热传导性近年来受到广泛关注.本文采用γ射线辐射技术分别处理水溶液和对苯二胺(PPD)水溶液中的氧化石墨烯(GO),得到辐照还原氧化石墨烯(RGO)和胺基化修饰的还原氧化石墨烯(RGON).通过傅里叶变换红外(FTIR)光谱、X射线光电子能谱(XPS)、拉曼(Raman)光谱、X射线衍射(XRD)和热失重分析(TGA)等表征分析产物的化学结构和元素组成;通过四探针测试仪和接触角测量仪研究产物的导电性能和亲水性.实验结果表明,在水溶液及PPD水溶液中γ射线辐射均可高效还原GO,还原后得到的RGO和RGON电导率均显著增大.PPD的胺基在辐射还原过程中还可以修饰到石墨烯的表面,因此RGON的亲水性比RGO好,但胺基的存在会干扰石墨烯表面π电子的传导,导致其电导率下降.     

Hyperbranched polytriazine grafted reduced graphene oxide and its application

In this article, cyanuric chloride (CC) and hexamethylenediamine (HMD) as raw material, the grafting of hyperbranched polytriazine onto reduced graphene oxide surface (HBP‐RGO) was achieved by the repeated nucleophilic substitution between chlorine groups of CC and amino groups of HMD, respectively. The Fourier transform infrared, X‐ray photoelectron spectroscopic, Raman, transmission electron microscopic, thermogravimetric, and atomic force microscopic analysis showed that HBP‐RGO had been successfully prepared and the HBP had a dendritic structure on the surface of RGO. And then, the HBP‐RGO was added into polystyrene (PS) and the HBP‐RGO/PS composite was prepared by solution mixing. The micro‐morphology, thermal stability, and electrical conductivity of RGO/PS and HBP‐RGO/PS composites were characterized and compared. The scanning electron microscopic analysis showed that the HBP‐RGO can uniformly disperse in PS. Meanwhile, the HBP‐RGO/PS composite showed good thermal stability and electrical conductivity, the percolation threshold of the composites is low as 0.32 vol %. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2132–2140     

Preparation of porous polyimide/in‐situ reduced graphene oxide composite films for electromagnetic interference shielding

Herein we report an easy and efficient approach to prepare lightweight porous polyimide (PI)/reduced graphene oxide (RGO) composite films. First, porous poly (amic acid) (PAA)/graphene oxide (GO) composite films were prepared via non‐solvent induced phase separation (NIPS) process. Afterwards PAA was converted into PI through thermal imidization and simultaneously GO dispersed in PAA matrix was in situ thermally reduced to RGO. The GO undergoing the same thermal treatment process as thermal imidization was characterized with thermogravimetric analysis, Raman spectra, X‐ray photoelectron spectroscopy and X‐ray diffraction to demonstrate that GO was in situ reduced during thermal imidization process. The resultant porous PI/RGO composite film (500‐µm thickness), which was prepared from pristine PAA/GO composite with 8 wt% GO, exhibited effective electrical conductivity of 0.015 S m^?1 and excellent specific shielding efficiency value of 693 dB cm² g^?1. In addition, the thermal stability of the porous PI/RGO composite films was also dramatically enhanced. Compared with that of porous PI film, the 5% weight loss temperature of the composite film mentioned above was improved from 525°C to 538°C. Moreover, tensile test showed that the composite film mentioned above possessed a tensile strength of 6.97 MPa and Young's modulus of 545 MPa, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation of a poly(methyl methacrylate)-reduced graphene oxide composite with enhanced properties by a solution blending method

Poly(methyl methacrylate) (PMMA)/graphene nanocomposites were prepared by a simple solution blending method. The glass transition temperature of the produced PMMA/graphene composite was increased by 37 °C with 1.0 wt.% RGO content, which is approximately 40% of improvement compared to that of pure PMMA. The thermal expansion coefficient (TEC) decreased by 68% with as low as 0.1 wt.% RGO loading. The electrical conductivity of the nanocomposites reached up to 0.037 S/m even with only 2.0 wt.% RGO, which increased by more than twelve orders of magnitude. The resulting nanocomposites showed that a stable colloidal suspension of graphene dispersion in organic solvent before blending with PMMA is necessary to fabricate the nanocomposites with enhanced properties.     

Enzymatically active colloidal crystal arrays

We report the construction of three-dimensional (3D) colloidal crystal arrays (CCA) and hollow colloidal crystal arrays (HCCA) derived from the self-assembly of polyelectrolytes (PE)-coated polystyrene (PS) particles and their use as models of high surface area systems to immobilize peroxidase (POD). POD molecules could infiltrate into the deep layers of CCA and HCCA through their interconnected pores and strongly adsorbed at the PE shell of the colloidal particles. And the total enzyme loading amount and bioactivities increased linearly with the thickness of the CCA till ca. 10 mum. Compared with flat substrates with the same geometrical area, CCA and HCCA exhibit much higher enzyme loading abilities (approximately 43 and 53 times respectively) and the resulting bioactivities (approximately 35 and 41 times respectively) due to their inherently higher surface area and 3D interconnected porous structures. In addition, HCCA could load approximately 30% more POD than CCA because some POD molecules could infiltrate into the interior of the hollow capsule under salt condition.     

Colloidal crystalline array of hydrogel-coated silica nanoparticles: effect of temperature and core size on photonic properties

This paper reports the fabrication of a photonic crystal made of hydrogel-coated colloidal nanoparticles, which can act as an optical sensor in visible and near-infrared region triggered by temperature. The synthetic scheme involves silanization of silica nanoparticles followed by radical-initiated precipitation polymerization forming a thermoresponsive polymer coating. These core–shell nanostructures self-assemble to produce colloidal crystalline array (CCA). The main advantages of self-assembly approach are experimental simplicity, possibility of 3D assembly and inexpensive mass production. Photon correlation spectroscopy results revealed a very interesting new phenomenon of showing a distinct break near the lower critical solution temperature along with a set of two-step curves, in the plot of mean hydrodynamic radius vs. temperature, which can be attributed to the breakage of two different types of hydrogen-bonding. The lattice parameters of these CCAs and hence their sensor properties can be effectively tuned by varying the core-size and temperature, which in turn changes the composite particle size as well as shape and hence volume fraction. In Reflectance measurements, the position of the stop-band was found to be directly proportional to the core-size, whereas the appearance of a second diffraction peak was correlated to the non-spherical nature of the nanocomposites supported by atomic force microscope images and possibly due to the existence of a second phase. The occurrence of such high-order multiple Bragg’s diffraction peak certainly opens a new door towards nanophotonic sensor devices.     

A Self‐assembled L‐Cysteine and Electrodeposited Gold Nanoparticles‐reduced Graphene Oxide Modified Electrode for Adsorptive Stripping Determination of Copper

Glassy carbon electrode (GCE) modified with L‐cysteine and gold nanoparticles‐reduced graphene oxide (AuNPs‐RGO) composite was fabricated as a novel electrochemical sensor for the determination of Cu²⁺. The AuNPs‐RGO composite was formed on GCE surface by electrodeposition. The L‐cysteine was decorated on AuNPs by self‐assembly. Physicochemical and electrochemical properties of L‐cysteine/AuNPs‐RGO/GCE were characterized by scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, Raman spectroscopy, X‐ray diffraction, cyclic voltammetry and adsorptive stripping voltammetry. The results validated that the prepared electrode had many attractive features, such as large electroactive area, good electrical conductivity and high sensitivity. Experimental conditions, including electrodeposition cycle, self‐assembly time, electrolyte pH and preconcentration time were studied and optimized. Stripping signals obtained from L‐cysteine/AuNPs‐RGO/GCE exhibited good linear relationship with Cu²⁺ concentrations in the range from 2 to 60 μg L⁻¹, with a detection limit of 0.037 μg L⁻¹. Finally, the prepared electrode was applied for the determination of Cu²⁺ in soil samples, and the results were in agreement with those obtained by inductively coupled plasma mass spectrometry.     

Layer-by-layer growth of attractive binary colloidal particles

We investigate the two-dimensional (2D) colloidal structures formed by oppositely charged polystyrene monolayers grown layer-by-layer, where the electrostatic forces are recruited to assist in the packing of the layers. Our results show a transition through several 2D-superlattices to more close-packed structures with increasing ionic strength. The observed geometrical packing constraints of the 2D-superlattice structures agree well with the estimated Debye screening length of the electric double layer. By tuning interaction forces between charged colloids, electrostatic interactions could enhance the template-directed self-assembly process to achieve more complex and diverse structures.     

Layer-by-Layer Self-Assembled Multilayer Films Composed of Graphene/Polyaniline Bilayers: High-Energy Electrode Materials for Supercapacitors

Multilayer assemblies of uniform ultrathin film electrodes with good electrical conductivity and very large surface areas were prepared for use as electrochemical capacitors. A layer-by-layer self-assembly approach was employed in an effort to improve the processability of highly conducting polyaniline (PANi) and chemically modified graphene. The electrochemical properties of the multilayer film (MF-) electrodes, including the sheet resistance, volumetric capacitance, and charge/discharge ratio, were determined by the morphological modification and the method used to reduce the graphene oxide (GO) to reduced graphene oxide (RGO) in the multilayer films. The PANi and GO concentrations could be modulated to control the morphology of the GO monolayer film in the multilayer assemblies. Optical ellipsometry was used to determine the thickness of the GO film in a single layer (1.32 nm), which agreed well with the literature value (～1.3 nm). Hydroiodic acid (HI), hydrazine, or pyrolysis were tested for the reduction of GO to RGO. HI was found to be the most efficient technique for reducing the GO to RGO in the multilayer assemblies while minimizing damage to the virgin state of the acid-doped PANi. Ultimately, the MF-electrode, which could be optimized by fine-tuning the nanostructure and selecting a suitable reduction method, exhibited an excellent volumetric capacitance, good cycling stability, and a rapid charge/discharge rate, which are required for supercapacitors. A MF-electrode composed of 15 PANi/RGO bilayers yielded a volumetric capacitance of 584 F/cm(3) at a current density of 3.0 A/cm(3). Although this value decreased exponentially as the current density increased, approaching a value of 170 F/cm(3) at 100 A/cm(3), this volumetric capacitance is one of the best yet reported for the other carbon-based materials. The intriguing features of the MF-electrodes composed of PANi/RGO multilayer films offer a new microdimensional design for high energy storage devices for use in small portable electronic devices.     

Photochemical incorporation of silver quantum dots in monodisperse silica colloids for photonic crystal applications.

We developed a novel method to fabricate nanocomposite monodisperse SiO2 spheres (approximately 100 nm) containing homogeneously dispersed Ag quantum dots (approximately 2 to 5 nm). The inclusion morphology is controlled through the timing of the photochemical reduction of silver ions during hydrolysis of tetraethoxysilane in a microemulsion. Depending on the timing, Ag quantum dots can be directed to different annuli within the SiO2 spheres, as well as onto the SiO2 sphere surfaces. The embedded Ag quantum dots show a plasmon resonance absorption band at 438 nm. These Ag@SiO2 particles have significant surface charge and readily self-assemble into crystalline colloidal array (CCA) photonic crystals which Bragg-diffract light in the visible region. The magnitude of the plasmon resonance absorption depends on the CCA Bragg diffraction condition. The negative dielectric constant of the silver nanoparticles may be decreasing the silica-silver nanodot composite refractive index below that of the water medium. We may be observing an analogue of the Borrmann effect previously observed in X-ray scattering, where the incident and diffracted electric field standing wave becomes localized in regions of small CCA crystal absorption.     

A general photonic crystal sensing motif: creatinine in bodily fluids

We developed a new sensing motif for the detection and quantification of creatinine, which is an important small molecule marker of renal dysfunction. This novel sensor motif is based on our intelligent polymerized crystalline colloidal array (IPCCA) materials, in which a three-dimensional crystalline colloidal array (CCA) of monodisperse, highly charged polystyrene latex particles are polymerized within lightly cross-linked polyacrylamide hydrogels. These composite hydrogels are photonic crystals in which the embedded CCA diffracts visible light and appears intensely colored. Volume phase transitions of the hydrogel cause changes in the CCA lattice spacings which change the diffracted wavelength of light. We functionalized the hydrogel with two coupled recognition modules, a creatinine deiminase (CD) enzyme and a 2-nitrophenol (2NPh) titrating group. Creatinine within the gel is rapidly hydrolyzed by the CD enzyme in a reaction which releases OH(-). This elevates the steady-state pH within the hydrogel as compared to the exterior solution. In response, the 2NPh is deprotonated. The increased solubility of the phenolate species as compared to that of the neutral phenols causes a hydrogel swelling which red-shifts the IPCCA diffraction. This photonic crystal IPCCA senses physiologically relevant creatinine levels, with a detection limit of 6 microM, at physiological pH and salinity. This sensor also determines physiological levels of creatinine in human blood serum samples. This sensing technology platform is quite general. It may be used to fabricate photonic crystal sensors for any species for which there exists an enzyme which catalyzes it to release H(+) or OH(-).     

P(HEMA-co-AM)胶体晶体膜的制备及其性能

将聚苯乙烯胶体晶体嵌入丙烯酰胺(AM)与甲基丙烯酸羟乙酯(HEMA)的交联共聚膜中,制备了共聚物P(AM-co-HEMA)胶体晶体膜.研究了单体配比及交联剂N,N'-亚甲基双(丙烯酰胺)(MBA)对胶体晶体膜的光子带隙峰位置、拉伸强度和断裂伸长率的影响.结果表明:当n(HEMA)/n(AM)≤2.33时,光子带隙峰较明...     

Graphene‐Assisted Room‐Temperature Synthesis of 2D Nanostructured Hybrid Electrode Materials: Dramatic Acceleration of the Formation Rate of 2D Metal Oxide Nanoplates Induced by Reduced Graphene Oxide Nanosheets

A new prompt room temperature synthetic route to 2D nanostructured metal oxide–graphene‐hybrid electrode materials can be developed by the application of colloidal reduced graphene oxide (RGO) nanosheets as an efficient reaction accelerator for the synthesis of δ‐MnO₂ 2D nanoplates. Whereas the synthesis of the 2D nanostructured δ‐MnO₂ at room temperature requires treating divalent manganese compounds with persulfate ions for at least 24 h, the addition of RGO nanosheet causes a dramatic shortening of synthesis time to 1 h, underscoring its effectiveness for the promotion of the formation of 2D nanostructured metal oxide. To the best of our knowledge, this is the first example of the accelerated synthesis of 2D nanostructured hybrid material induced by the RGO nanosheets. The observed acceleration of nanoplate formation upon the addition of RGO nanosheets is attributable to the enhancement of the oxidizing power of persulfate ions, the increase of the solubility of precursor MnCO₃, and the promoted crystal growth of δ‐MnO₂ 2D nanoplates. The resulting hybridization between RGO nanosheets and δ‐MnO₂ nanoplates is quite powerful not only in increasing the surface area of manganese oxide nanoplate but also in enhancing its electrochemical activity. Of prime importance is that the present δ‐MnO₂–RGO nanocomposites show much superior electrode performance over most of 2D nanostructured manganate systems including a similar porous assembly of RGO and layered MnO₂ nanosheets. This result underscores that the present RGO‐assisted solution‐based synthesis can provide a prompt and scalable method to produce nanostructured hybrid electrode materials.     

Preparation of Reduced Graphene Oxide/MnO Composite and Its Electromagnetic Wave Absorption Performance

The composite containing reduced graphene oxide and MnO nanoparticles (RGO/MnO) has been prepared via a one step pyrolysis method. The MnO nanoparticles were uniformly dispersed on the surface of RGO nanosheets forming MnO/RGO composite. The composite displays a maximum absorption of ‒38.9 dB at 13.5 GHz and the bandwidth of reflection loss corresponding to –10 dB can reach 4.9 GHz (from 11.5 to 16.4 GHz) with a coating layer thickness of only 2 mm. Therefore, the obtained RGO/MnO composite a perfect lightweight and high-performance electromagnetic wave absorbent.

     

Understanding Self-assembly,Colloidal Behavior and Rheological Properties of Graphene Derivatives for High-performance Supercapacitor Fabrication

Graphene derivatives, such as graphene oxide(GO) and reduced graphene oxide(RGO), have been widely used as promising twodimensional nanoscale building blocks due to their fascinating properties, cost-effective production, and good processability. Understanding the intrinsic self-assembling, colloidal, and rheological features of graphene derivatives is of critical importance to establish the formation-structureproperty relationship of graphene-based materials. This article reviews recent progresses in our studies of these interesting properties of graphene derivatives for developing high performance supercapacitors. The content is organized to include characteristics of the dispersions of graphene derivatives, self-assembly of nanosheets from liquid medium, colloidal behavior, rheological properties of the dispersions, processing methods based on the properties, and performance of the fabricated supercapacitors. GO and RGO nanosheets are proved to form different types of assembled structures with unique morphologies, such as ultrathin layer-by-layer films, porous aggregates, and nanoscrolls. The unique rheological properties of GO dispersions and hydrogels, feasible for both the traditional wet-processing and newly-developed technology like three-dimensional printing, are highlighted for their potential in structural manipulation and scalable fabrication of graphene-based devices. The research devoted to up-grading the performance of supercapacitors is presented in some details, which could be applicable for fabricating other graphene-based energy storage devices. Some challenges and perspectives in our point of view are given in the last part of this feature article.     

Constructing 2D Sandwich-like MOF/MXene Heterostructures for Durable and Fast Aqueous Zinc-Ion Batteries

Two-dimensional metal–organic frameworks (2D MOFs) can be used as the cathodes for high-performance zinc-ion battery due to their large one-dimensional channels. However, the conventionally poor electrical conductivity and low structural stability hinder their advances. Herein, we report an alternately stacked MOF/MX heterostructure, exhibiting the 2D sandwich-like structure with abundant active sites, improved electrical conductivity and exceptional structural stability. Ex situ characterizations and theoretical calculations reveal a reversible intercalation mechanism of zinc ions and high electrical conductivity in the 2D heterostructure. Electrochemical tests confirm excellent Zn²⁺ migration kinetics and ideal pseudocapacitive behaviors. As a consequence, Cu-HHTP/MX shows a superior rate performance (260.1 mAh g⁻¹ at 0.1 A g⁻¹ and 173.1 mAh g⁻¹ at 4 A g⁻¹) and long-term cycling stability of 92.5 % capacity retention over 1000 cycles at 4 A g⁻¹.     

Bifunctional Reduced Graphene Oxide/V2O5 Composite Hydrogel: Fabrication,High Performance as Electromagnetic Wave Absorbent and Supercapacitor

Multifunctional graphene hydrogels have attracted great attention aimed at practical applications. Herein, the novel and bifunctional composite hydrogel containing reduced graphene‐oxide nanosheets (RGO) and V₂O₅ nanobelts (RGO/V₂O₅) is successfully prepared for the first time. Surprisingly, tridimensional (3D) RGO/V₂O₅ composite hydrogels cannot only be used as high‐performance electromagnetic (EM) wave absorbents; they also exhibit excellent properties suitable for supercapacitor electrodes. The composites exhibit a maximum absorption of up to ?21.5 dB. In particular, a composite hydrogel showed a bandwidth of 6.63 GHz, corresponding to a reflection loss at ?10 dB, which opens the possibility for the use of 3D graphene with other functional nanomaterials as lightweight and high‐performance EM wave absorption materials. Remarkably, the composite hydrogel is capable of delivering a high specific capacitance of about 320 F g^?1 at a current density of 1.0 A g^?1.     

A Butterfly‐Inspired Hierarchical Light‐Trapping Structure towards a High‐Performance Polarization‐Sensitive Perovskite Photodetector

Extensive applications for photodetectors have led to demand for high‐responsivity polarization‐sensitive light detection. Inspired by the elaborate architecture of butterfly Papilio paris, a 1D nanograting bonded porous 2D photonic crystal perovskite photodetector (G‐PC‐PD) using a commercial DVD master and 2D crystalline colloidal arrays template was fabricated. The coupling effect from grating diffraction and reflection of the PC stopband renders the enhanced light harvesting of G‐PC‐PD. The porous scaffold and nanoimprinting process afford a highly crystalline perovskite film. White light responsivity and detectivity of G‐PC‐PD are up to 12.67 A W^?1 and 3.22×10¹³ Jones (6～7 times that of a pristine perovskite photodetector). The highly ordered nanograting arrays of G‐PC‐PD enable polarization‐sensitive light detection with a rate of ?0.72 nA deg^?1. This hierarchical perovskite integrated nanograting and 2D PC architecture opens a new avenue to high‐performance optoelectronic devices.     

Close-packed colloidal crystalline arrays composed of polystyrene latex coated with titania nanosheets

We have demonstrated that polystyrene latex coated with titania nanosheets can be fabricated into a close-packed colloidal crystalline array, and that these coated colloidal spheres can be used to control the peak position of optical stop bands through the coating. The titania-nanosheets-coated polystyrene latex was prepared by the layer-by-layer (LBL) assembly coating process, involving alternating lamination of cationic polyelectrolytes and anionic titania nanosheets on monodisperse polystyrene latex particles. The Bragg diffraction peak of the colloidal crystalline array shifted to longer wavelengths with the coating of titania nanosheets. This red shift was caused by an increase in refractive index upon coating, as revealed by angle-resolved reflection spectra measurements. The current work suggests new possibilities for the creation of advanced colloidal crystals having tunable optical properties from tailored colloidal spheres.     

Microwave absorption studies of polyaniline nanocomposites encapsulating gold nanoparticles on the surface of reduced graphene oxide in the presence of 2-naphthalene sulfonic acid

Polyaniline nanocomposites containing gold nanoparticles (GNPs) attached to the surface of reduced graphene oxide (RGO) were chemically prepared using β-naphthalene sulfonic acid as a dopant. The synthesized composites were characterized using Fourier transform infrared spectroscopy and UV-vis spectroscopy, and their surface morphology and amended crystallinity were determined by scanning electron microscopy and X-ray diffraction, respectively. Further the elemental analysis was also performed to identify the synthesized polymer composites. Complex impedance measurements were performed on the composite samples in the form of films. Sheets prepared by conventional techniques were used to study the microwave absorption properties in the microwave range of 2–12?GHz, and the effects of sample thickness on the microwave absorption were investigated. Experimental results show that the electrical conductivity of the composites increases with increasing concentrations of added GNP-RGO without a percolation threshold.