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 two-dimensional 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-structure-property 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.

Magnetic transitions in graphene derivatives

The magnetic transitions in graphene oxide （GO） have been investigated experimentally. Micron-sized GO flakes exhibit dominant diamagnetism accompanied by weak ferromagnetism at room temperature. However, when the lateral dimensions of GO flakes are reduced from micron-size to nano-size, a clear transition from dominant diamagnetism to ferromagnetism is observed. After reducing the GO chemically or thermally, the dominant magnetic properties are not altered markedly except for the gradual enhancement of ferromagnetic components. In contrast, at 2 K, significant paramagnetism is present in both the micron-sized and nano-sized GO sheets. The effects of different functional groups on magnetic transitions in graphene derivatives have been further investigated using on hydroxyl-, carboxyl-, amino- and thiol- functionalized graphene. The results reveal that significant diamagnetism with weak ferromagnetism is present at room temperature in all of these functionalized graphene derivatives and the ability of different functional groups to introduce magnetic moments follows the order -SH 〉 --OH 〉 -COOH, -NH2. Notably, at 5 K, diamagnetism, paramagnetism and ferromagnetism coexist in thiol-, hydroxyl- and carboxyl-functionalized graphene, while amino-graphene exhibits dominant paramagnetism, analogous to the low-temperature magnetism in GO. These results indicate that diamagnetism, paramagnetism and ferromagnetism can coexist in graphene derivatives and magnetic transitions among the three states can be achieved which depend on edge states, vacancies, chemical doping and the attached functional groups. The results obtained may help settle the current controversy about the magnetism of graphene-related materials.

A review on the current research on microwave processing techniques applied to graphene-based supercapacitor electrodes:An emerging approach beyond conventional heating

The various methods for microwave processing of materials exhibit numerous advantages,such as short processing times,high yield,expanded reaction conditions,high reproducibility,and high purity of products.Microwave-assisted synthesis strategies have been widely adopted for the preparation of highperformance graphene-based materials for supercapacitor electrodes.Metal oxides,mixed metal oxides,metal hydroxides,layered double hydroxides,carbon nanotubes and conducting polymers are some of the main materials which have been added to graphene derivatives for advanced composite/hybrid electrodes.This review article first provides a brief introduction and an overview of microwave heating and its advantages for processing graphene-based electrode materials.After that,a systematic survey of recently published research on microwave irradiation-assisted processing is presented,focusing on:(i)transformation of graphite/graphite oxide into graphene/graphene oxide by exfoliation and reduction;(ii)formation of graphene derivatives in various liquid and gaseous media;(iii)modification of graphene derivatives with various metal oxides/hydroxides,carbon nanotubes,and conducting polymers for use in supercapacitors.Major challenges and future perspectives for microwave-assisted processing of graphene-based materials for cutting-edge supercapacitor electrode applications are also summarized in the conclusion.

Temperature-induced resistance transition behaviors of melamine sponge composites wrapped with different graphene oxide derivatives

Temperature-re s ponsive resistance transition behaviors of the melamine sponges wrapped with different graphene oxide derivatives(i.e.nanoribbon,wide-ribbon and sheet)were investigated.Melamine sponge composites coated by three types of GO derivatives were prepared by a simple dip-coating approach.All these composites show good mechanical flexibility and reliability(almost unchanged compressive stress at 70%strain after 100 cycles),high hydrophobicity(water contact angle>120°),excellent flame resistance(self-extinguishing)and structural stability even after burning,which was used to construct the resistance-based fire alarm/warning sensor.Notably,the different resistance response behaviors of such sensors are strongly dependent on the GO size and network formed on the MF skeleton surface.Typically,at a fixed high temperature of~350℃,the three fire alarm sensors show different response time(to trigger the alarm light)of 6.3,8.4 and 11.1 s for nanoribbon,wide-ribbon and sheet at the same concentration,respectively.The structural observation and chemical analysis demonstrated that the discrepancy of temperature-responsive resistance transition behaviors of various GO derivatives was strongly determined by their different thermal reduction degrees during the high-tempe rature or flame treating process.This work offers a design and development for construction of smart fire alarm device for potential fire prevention and safety applications.

Chemical Self-Assembly of Graphene Sheets

Chemically derived and noncovalently functionalized graphene sheets(GS)were found to self-assemble onto patterned gold structures via electrostatic interactions between the functional groups and the gold surfaces.This afforded regular arrays of single graphene sheets on large substrates,which were characterized by scanning electron microscopy(SEM),Auger microscopy imaging,and Raman spectroscopy.This represents the fi rst time that self-assembly has been used to produce on-substrate and fully-suspended graphene electrical devices.Molecular coatings on the GS were removed by high current“electrical annealing”,which restored the high electrical conductance and Dirac point of the GS.Molecular sensors for highly sensitive gas detection using the self-assembled GS devices are demonstrated.

One-step co-electrodeposition of graphene oxide doped poly(hydroxymethylated-3,4-ethylenedioxythiophene) film and its electrochemical studies of indole-3-acetic acid

A novel graphene oxide （GO） doped poly（hydroxymethylated-3,4-ethylenedioxythiophene） （PEDOTM） film has been achieved via one-step co-electrodeposition and utilized for electrochemical studies of indole-3-acetic acid （IAA）. The incorporation of GO into PEDOTM film facilitated the electrocatalytic activity and exhibited a favorable interaction between the PEDOTM/GO film and the phytohormone during the oxidation of IAA. Under optimized conditions, differential pulse voltammetry and square wave voltammetry were used for the quantitative analysis of IAA, respectively, each exhibiting a wide linearity range from 0.6 μmol L-1 to 10 μmol L-1 and 0.05 μmol L-1 to 40 μmol L-1, good sensitivity with a low detection Iimit of 0.087 μmol L-1 and 0.033μmol L T, respectively, as well as good stability. With the notable advantages of a green, sensitive method, expeditious response and facile operation, the as-prepared PEDOTM/GO organic-inorganic composite film provides a promising platform for electrochemical studies of IAA.

The utilization of carbon-based nanomaterials in bone tissue regeneration and engineering:Respective featured applications and future prospects

In recent years,with advancements in bone tissue regeneration and engineering technologies,carbon-based nanomaterials(CNMs)have progressively demonstrated advantages in the therapies of critical bone defects and related diseases that conventional substances fail to develop,such as excellent mechanical properties,large specific surface,tunable surface characteristics,and superior biocompatibility.More importantly,carbon-based nanomaterials with efficient cell proliferation and osteogenic differentiation could have a significant impact on bone tissue regeneration.In this paper,we have reviewed the characteristic applications of extraordinary types of carbon-based nanomaterials(fullerene,carbon dots,carbon nanotubes,as well as graphene and its derivatives)in bone tissue regeneration and engineering based on their structural properties,with a view to presenting their unique advantages,applications,and current directions of development as specifically and comprehensively as possible.