Manufacturing N,O-carboxymethyl chitosan-reduced graphene oxide under freeze-dying for performance improvement of Li-S battery

Lithium-sulfur(Li-S) batteries can provide far higher energy density than currently commercialized lithium ion batteries, but challenges remain before it they are used in practice.One of the challenges is the shuttle effect that originates from soluble intermediates, like lithium polysulfides. To address this issue, we report a novel laminar composite, N,O-carboxymethyl chitosan-reduced graphene oxide(CC-rGO), which is manufactured via the self-assembly of CC onto GO and subsequent reduction of GO under an extreme condition of 1 Pa and-50°C. The synthesized laminar CC-rGO composite is mixed with acetylene black(AB) and coated on a commercial polypropylene(PP) membrane, resulting in a separator(CC-rGO/AB/PP) that can not only completely suppress the polysulfides penetration, but also can accelerate the lithium ion transportation, providing a Li-S battery with excellent cyclic stability and rate capability. As confirmed by theoretic simulations, this unique feature of CC-rGO is attributed to its strong repulsive interaction to polysulfide anions and its benefit for fast lithium ion transportation through the paths paved by the heteroatoms in CC.

Ag/reduced graphene oxide(RGO) nanocomposites for detection of TNT

The modified Hummers method was employed to generate graphene oxide,and Ag /reduced graphene oxide (RGO) nanocomposites were synthesized at different temperatures by using sodium citrate as the reductant. Scanning electron microscopy (SEM),transmission electron microscopy (TEM),X-ray diffraction (XRD),X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were employed to characterize the reaction products. The results indicate that RGO has been synthesized successfully,and Ag particles are distributed evenly on the surface of RGO.The RGO prepared at a reaction temperature of 120℃ shows the best surface-enhanced Raman scattering (SERS) activity.The Ag /RGO nanocomposites modified by 10^- 5 mol /L 4-aminothiophenol (PATP) successfully detect a 10^- 5 mol /L 2,4,6-trinitrotoluene (TNT) alcohol solution.

Enabling High-Performance Sodium Battery Anodes by Complete Reduction of Graphene Oxide and Cooperative In-Situ Crystallization of Ultrafine SnO_(2)Nanocrystals

The main bottleneck against industrial utilization of sodium ion batteries(SIBs)is the lack of high-capacity electrodes to rival those of the benchmark lithium ion batteries(LIBs).Here in this work,we have developed an economical method for in situ fabrication of nanocomposites made of crystalline few-layer graphene sheets loaded with ultrafine SnO_(2)nanocrystals,using short exposure of microwave to xerogel of graphene oxide(GO)and tin tetrachloride containing minute catalyzing dispersoids of chemically reduced GO(RGO).The resultant nanocomposites(SnO_(2)@MWG)enabled significantly quickened redox processes as SIB anode,which led to remarkable full anode-specific capacity reaching 538 mAh g^(−1)at 0.05 A g^(−1)(about 1.45 times of the theoretical capacity of graphite for the LIB),in addition to outstanding rate performance over prolonged charge–discharge cycling.Anodes based on the optimized SnO_(2)@MWG delivered stable performance over 2000 cycles even at a high current density of 5 A g^(−1),and capacity retention of over 70.4%was maintained at a high areal loading of 3.4 mg cm^(−2),highly desirable for high energy density SIBs to rival the current benchmark LIBs.

Reduced Graphene Oxide-Wrapped FeS_2 Composite as Anode for High-Performance Sodium-Ion Batteries

Iron disulfide is considered to be a potential anode material for sodium-ion batteries due to its high theoretical capacity. However, its applications are seriously limited by the weak conductivity and large volume change, which results in low reversible capacity and poor cycling stability.Herein, reduced graphene oxide-wrapped FeS_2(FeS_2/rGO)composite was fabricated to achieve excellent electrochemical performance via a facile two-step method. The introduction of rGO effectively improved the conductivity,BET surface area, and structural stability of the FeS_2 active material, thus endowing it with high specific capacity, good rate capability, as well as excellent cycling stability. Electrochemical measurements show that the FeS_2/rGO composite had a high initial discharge capacity of 1263.2 mAh gg^(-1) at 100 mA gg^(-1) and a high discharge capacity of 344 mAh gg^(-1) at 10 A gg^(-1), demonstrating superior rate performance. After 100 cycles at 100 mA gg^(-1),the discharge capacity remained at 609.5 mAh g^(-1), indicating the excellent cycling stability of the FeS_2/rGO electrode.

Magnetic Fe_3O_4-Reduced Graphene Oxide Nanocomposites-Based Electrochemical Biosensing

An electrochemical biosensing platform was developed based on glucose oxidase(GOx)/Fe3O4-reduced graphene oxide(Fe3O4-RGO) nanosheets loaded on the magnetic glassy carbon electrode(MGCE).With the advantages of the magnetism, conductivity and biocompatibility of the Fe3O4-RGO nanosheets, the nanocomposites could be facilely adhered to the electrode surface by magnetically controllable assembling and beneficial to achieve the direct redox reactions and electrocatalytic behaviors of GOx immobilized into the nanocomposites. The biosensor exhibited good electrocatalytic activity, high sensitivity and stability. The current response is linear over glucose concentration ranging from 0.05 to 1.5 m M with a low detection limit of0.15 μM. Meanwhile, validation of the applicability of the biosensor was carried out by determining glucose in serum samples. The proposed protocol is simple, inexpensive and convenient, which shows great potential in biosensing application.

Reduced graphene oxide-grafted bovine serum albumin/bredigite nanocomposites with high mechanical properties and excellent osteogenic bioactivity for bone tissue engineering

The optimization of the scaffolds to provide a suitable matrix and accelerate the regeneration process is vital for bone tissue engineering.However,poor mechanical and biological characteristics remain the primary challenges that must be addressed.For example,although bredigite(Br)has shown great potential for application in bone tissue engineering,it easily fails in replacement.In the present work,these challenges are addressed by reinforcing the Br matrix with nanosheets of graphene oxide(rGO)that have been reduced by bovine serum albumin(BSA)in order to enhance the mechanical properties and biological behavior.The reduction of graphene oxide by BSA improves the water stability of the nanosheets and provides an electrostatic interaction between theBSA-rGO nanosheets and theBr particles.The high thermal conductivity of theBSA-rGO nanosheets decreases the porosity of the Br by transferring heat to the core of the tablet.Furthermore,the addition of BSA-rGO nanosheets into the Br matrix enhances the adhesion of G-292 cells on the surface of the tablets.These findings suggest that the tablet consisting of BSA-rGO-reinforced Br has encouraging potential for application in bone tissue engineering.

Synthesis of Graphene Oxide (GO) by Modified Hummers Method and Its Thermal Reduction to Obtain Reduced Graphene Oxide (rGO)

Over the span of years, improvements over various synthesis methods of graphene are constantly pursued to provide safer and more effective alternatives. Though the extraction of graphene through Hummers method is one of the oldest techniques yet it is one of the most suitable methods for the formation of bulk graphene. Graphene can be obtained in the form of reduced Graphite oxide, sometimes also referred as Graphene oxide. The effectiveness of this oxidation process can be evaluated by the magnitude of carbon/oxygen ratio of the obtained graphene. Here, graphene oxide (GO) was prepared by oxidizing the purified natural flake graphite (NFG) by a modified Hummers method. The attempts have been made to synthesize GO having few layers by using a modified Hummers method where the amount of NaNO3 has been decreased, and the amount of KMnO4 is increased. The reaction has been performed in a 9:1 (by volume) mixture of H2SO4/H3PO4. This modification is successful in increasing the reaction yield and reducing the toxic gas evolution while using a varied proportion of KMnO4 and H2SO4 as those required by Hummers method. A new component of K2S2O8 has been introduced to the reaction system to maintain the pH value. Reduced graphene oxide (rGO) was thereafter extracted by thermal modification of GO. Here, GO has been used as a precursor for graphene synthesis by thermal reduction processes. The results of FTIR and Raman spectroscopy analysis show that the NFG when oxidized by strong oxidants like KMnO4 and NaNO3, introduced oxygen atoms into the graphite layers and formed bonds like C=O, C-H, COOH and C-O-C with the carbon atoms in the graphite layers. The structure and morphology of both GO and rGO were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy, Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

Three-dimensional MoS_2/reduced graphene oxide aerogel as a macroscopic visible-light photocatalyst

Photocatalysis is regarded as an ideal technology for solving the urgent environmental and energy issues that we face today.Among the reported photocatalysts,molybdenum disulfide（MoS2） is very promising for applications in hydrogen production and pollutant photodegradation.However,its lack of active sites and the difficulty of recovering catalysts in powder form have hindered its wide application.Here,we report the successful preparation of a macroscopic visible-light responsive MoS2/reduced graphene oxide（MoS2/RGO） aerogel.The obtained MoS2/RGO aerogel exhibits enhanced photocatalytic activity towards hydrogen production and photoreduction of Cr（Ⅵ） in comparison with the MoS2 powder.In addition,the low density（56.1 mg/cm^3） of the MoS2/RGO aerogel enables it to be used as an efficient adsorption material for organic pollutants.Our results demonstrate that this very promising multifunctional aerogel has potential applications in environmental remediation and clean energy production.

Enhanced cycle performance of Li/S battery with the reduced graphene oxide/activated carbon functional interlayer

The high-energy lithium/sulfur(Li/S) battery has become a very popular topic of research in recent years due to its high theoretical capacity of 1672 m Ah/g. However, the polysulfide shuttle effect remains of great concern with a great number of publications dedicated to its mitigation. In this contribution, a three-dimensional(3D) reduced graphene oxide/activated carbon(RGO/AC) film, synthesized by a simple hydrothermal method and convenient mechanical pressing, is sandwiched between the separator and the sulfur-based cathode, acting as a functional interlayer to capture and trap polysulfide species. Consequently, the Li/S cell with this interlayer shows an impressive initial discharge capacity of 1078 m Ah/g and a reversible capacity of 655 m Ah/g even after 100 cycles. The RGO/AC interlayer impedes the movement of polysulfide while providing unimpeded channels for lithium ion mass transfer. Therefore, the RGO/AC interlayer with a well-designed structure represents strong potential for high-performance Li/S batteries.

Structural and optical properties of thermally reduced graphene oxide for energy devices

Natural intercalation of the graphite oxide, obtained as a product of Hummer＇s method, via ultra-sonication of water dispersed graphite oxide has been carried out to obtain graphene oxide（GO） and thermally reduced graphene oxide（RGO）.Here we report the effect of metallic nitrate on the oxidation properties of graphite and then formation of metallic oxide（MO） composites with GO and RGO for the first time. We observed a change in the efficiency of the oxidation process as we replaced the conventionally used sodium nitrate with that of nickel nitrate Ni（NO_3）_2, cadmium nitrate Cd（NO_3）_2,and zinc nitrate Zn（NO_3）_2. The structural properties were investigated by x-ray diffraction and observed the successful formation of composite of MO–GO and MO–RGO（M = Zn, Cd, Ni）. We sought to study the effect on the oxidation process through optical characterization via UV-Vis spectroscopy and Fourier Transform Infrared（FTIR） spectroscopy.Moreover, Thermo Gravimetric Analysis（TGA） was carried out to confirm 〉 90% weight loss in each process thus proving the reliability of the oxidation cycles. We have found that the nature of the oxidation process of graphite powder and its optical and electrochemical characteristics can be tuned by replacing the sodium nitrate（NaNO_3） by other metallic nitrates as Cd（NO_3）_2, Ni（NO_3）_2, and Zn（NO_3）_2. On the basis of obtained results, the synthesized GO and RGO may be expected as a promising material in antibacterial activity and in electrodes fabrication for energy devices such as solar cell, fuel cell,and super capacitors.

Synergistic Effects of Carbon Nanotube(CNT)and Reduced Graphene Oxide(RGO)on Mechanical and Thermal Properties of ZK61 Alloy

The hybrid of carbon nanotube(CNT)and reduced graphene oxide(RGO)reinforced ZK61 composite was fabricated by a hot extrusion process.Compared with the raw ZK61 alloy and single-reinforced composites,the hybrid-reinforced by RGO+CNT complex exhibited significant enhancements both in mechanical and thermal performance.By adjusting the proportion of RGO and CNT in ZK61 alloy,the obtained optimum ZK61/(0.06 wt%RGO+0.54 wt%CNT)composite exhibited increase of 25.4%in yield strength,26.5%in ultimate tensile strength,104%in failure strain and 30.4%in thermal conductivity,respectively,in comparison with ZK61 alloy.The superior properties of the nano-hybrid composite are attributed to the synergetic effects of RGO and CNT,leading to a uniform dispersion and integrated structure as well as the enhanced interfacial bonding with matrix.The strengthening ability of RGO and CNT was calculated to quantify their individual contribution to the improvement in mechanical and thermal properties of the ZK61 matrix composite.The RGO+CNT hybrids provide a promising way to develop Mg matrix composites with impressive performances.

Heterostructured Co_(3)Se_(4)/CoSe_(2)@C nanoparticles attached on three-dimensional reduced graphene oxide as a promising anode towards Li-ion batteries

In situ carbon-coated Co_(3)Se_(4)/CoSe_(2)(Co_(x)Se_(y))nanoparticles(NPs)attached on three-dimensional(3D)reduced graphene oxide(rGO)sheets were skillfully developed in this work,which involved the environment-friendly hydrothermal method,freeze drying,and selenide calcination.Within the structure,the glucose-derived carbon layer exhibited significantly homogeneous dispersion under an argon environment.This structure not only has enhanced stability,but also can effectively mitigate the volume swell of Co_(x)Se_(y) particles.The resulted Co_(3)Sea/CoSe_(2)@C/rGO(CSe@C/rGO)exhibited a specific surface area(SSA)of 240.9 m^(2)·g^(-1),offering more electrochemically active sites for the storage of energy related to lithium ions.The rGO matrix held exceptional flexibility and functional structural rigidity,facilitating the swift ion intercalation and ensuring the high conductivity and recyclability of the structure.When applied to anodes designed for lithium-ion batteries(LiBs),this material demonstrated distinguished rate and ultra-high reversible capacity(872.98 mA·h·g^(-1) at 0.5 A·g^(-1)).Meanwhile,its capacity retention reached 119.5%after 500 cycles at 2 A·g^(-1),with a coulombic efficiency of 100%.This work potentially paves the way for generating fast and powerful metal selenide anodes and initiating LiBs with good performance.

Highly aligned reduced graphene oxide in alumina composites for strengthening,toughening,and electromagnetic interference shielding

Engineering ceramics with high strength,toughness and electromagnetic interference(EMI)shielding effectiveness(SE)are highly desirable as electromagnetic protecting material in harsh environment.Herein,we show that both excellent mechanical and EMI shielding performance can be realized in alumina composites embedded with highly aligned reduced graphene oxide(RGO),which are readily prepared via sintering of core-shell structured RGO@Al_(2)O_(3)nanoplates with pressure.Compared to monolithic Al_(2)O_(3),the highly aligned RGO/Al_(2)O_(3)composites show simultaneously improved strength and toughness up to~26.1%and~60.2%,respectively.The steeply rising R-curve behavior proves the better crack tolerance in the highly aligned structure with respect to randomly oriented one.Moreover,the RGO/Al_(2)O_(3)composites also exhibit a high specific EMI SE reaching~34 dB/mm in K band,due to the reflection and highly enhanced absorption after percolation in the out-of-plane direction.These findings provide a novel strategy of designing mechanically reliable engineering ceramic for EMI shielding.

Increased utilization and mass activity of PtRu on reduced graphene oxide by heat treatment of its aerogel followed by composite with nanomaterials

The method to increase PtRu utilization and its catalytic activity of PtRu nanoparticles supported on reduced graphene oxide(RGO)by avoiding its restacking was proposed with the aim of developing an active catalyst for a direct methanol fuel cell.The heat treatment at 200◦C of the GO aerogel(GOA)prepared by freeze drying of GO ice was introduced to weaken the attractive force of the hydrogen bonding between the GO sheets followed by the composite with the nanoparticles,i.e.,ketjenblack(KB),TiO_(2)and Ti_(4)O_(7),at different weight ratios.The catalyst supported on the heat-treated GOA(RGOA),PtRu/RGOA,improved the PtRu utilization to some extent and also increased the ECSA and mass activity compared to that of PtRu/RGO.RGOA had fewer oxygen functional groups,especially the epoxy groups.Due to the treatment and composite,the PtRu utilization was increased from 66.5%for PtRu/RGO to 128.6%for PtRu/RGOA+Ti_(4)O_(7)(4:1)and the mass activity was improved from 50.7 A/g-PtRu for PtRu/RGO to 130.5 A/g-PtRu for PtRu/RGOA+Ti_(4)O_(7)(1:1).The Ti_(4)O_(7)nanoparticles showed the best catalytic performance for the composite suggesting that the strong interaction between Ti_(4)O_(7)and the Pt nanoparticles was effective due to its high electronic conductivity.

A review article based on composite graphene@tungsten oxide thin films for various applications

Graphene and its derivatives are the hot topics of research during this decade due to their excellent thermal conductivities,mechanical strength,current densities,electron motilities,and large surface area.This review article explores the outstanding applicability and features of graphene derivatives.The transition metal oxides(TMOs)have also gained considerable research attention due to their unique physicochemical properties in photocatalytic,self-cleaning,and gas sensing applications.Among TMOs,tungsten metal oxides have received a tremendous response as they are naturally abundant,low in cost,less toxic,environmental friendly,and can be manufactured using various physical and chemical methods.It exhibits a cubic perovskite-like structure based on the corner-sharing of regular octahedra with the oxygen atoms at the corner and the tungsten atoms at the centre of each octahedron.It also shows structural polymorphism and sub stoichiometric phase transitions,which attracted the attention of researchers over the past few years to explore their potential in various applications.Pairing graphene and its derivatives with tungsten oxide(WO_(3))to create heterojunction could be an auspicious tool to improve photocatalysis,energy storage,medical,electrochromism,and energy efficiency conversion.In addition,composite exhibits significantly higher efficiency than either individual material due to their well-matched band edge positions,efficient charge separation,and light-harvesting abilities.The morphology and heterojunction were found to be quite beneficial in improving the overall performance of the composite.In this review article,the noteworthy endeavors and turning points are accomplished utilizing heterojunction between WO_(3)and graphene derivatives for different applications.This review article will also provide the research gap and excite new ideas for further improvement of graphene-based tungsten oxide nanocomposites.Conclusively,the scope of future research work to design the ternary composite with high efficiency utilizing WO_(3)and graphene is also explored.

基于rGO-SnO_(2)复合材料的丙酮气体传感器制备与特征分析

制备并研究了一种基于还原氧化石墨烯(rGO)掺杂二氧化锡(SnO_(2))的可工作在室温的丙酮气体传感器。采用简单的水热合成法和物理混合法制备rGO-SnO_(2)复合材料,并在平面微型叉指电极上沉积敏感膜,以此构建气体传感器。敏感材料的形貌和结构用场发射扫描电子显微镜(FESEM)和X射线衍射仪(XRD)进行表征,并研究了rGO-SnO_(2)在室温下对丙酮气体的敏感性能。实验结果表明:室温下,rGO掺杂量的质量分数为7%的rGO-SnO_(2)复合材料构建的传感器对体积分数为200×10^(-6)的丙酮气体响应为48.4%,是纯SnO_(2)的1.73倍,具有更加优异的气体敏感性。

PEO/rGO复合电热膜的制备及电热性能研究

采用导电性能优异的还原氧化石墨烯(rGO)为导电填料,以高分子聚合物聚氧化乙烯(PEO)为粘结剂,以N-甲基-2-吡咯烷酮(NMP)为溶剂配制成导电浆料,通过刮涂法高温固化得到聚氧化乙烯/还原氧化石墨烯(PEO/rGO)复合电热膜。通过X射线衍射仪、扫描电子显微镜、傅里叶变换红外光谱仪对复合电热膜进行分析表征,并测试了其电学特性和电加热性能。结果表明:PEO/rGO复合电热膜的方阻随着rGO含量的增加而逐渐下降,且方阻的下降速度由快到慢;PEO/rGO复合电热膜的升温速度随着导电填料rGO含量的增加逐渐变缓;当rGO含量较多、PEO含量较少时,会造成升温速率下降,也会造成电热平台不稳定;当rGO质量分数为20%时,在施加18V直流电压下复合电热膜可快速升温至43℃,并且表现出平稳的电热平台和较高的电加热效率,能够满足低温高效率复合电热膜的使用要求。

Synthesis of hydrophobic carbon nanotubes/reduced graphene oxide composite films by flash light irradiation

Carbon nanotubes/graphene composites have superior mechanical, electrical and electrochemistry prop- erties with carbon nanotubes as a hydrophobicity boosting agent. Their extraordinary hydrophobic performance is highly suitable for electrode applications in lithium ion batteries and supercapacitors which often employ organic electrolytes. Also the hydrophobic features enable the oil enrichment for the crude oil separation from seawater. The ever reported synthesis routes towards such a composite either involve complicated multi-step reactions, e.g., chemical vapor depositions, or lead to insufficient extru- sion of carbon nanotubes in the chemical reductions of graphene oxide, e.g., fully embedding between the compact graphene oxide sheets. As a consequence, the formation of standalone carbon nanotubes over graphene sheets remains of high interests. Herein we use the facile flash light irradiation method to induce the reduction of graphene oxides in the presence of carbon nanotubes. Photographs, micrographs, X-ray diffraction, infrared spectroscopy and thermogravimetric analysis all indicate that graphene oxides has been reduced. And the contact angle tests confirm the excellent hydrophobic perfor- mances of the synthesized carbon nanotube/reduced graphene oxide composite films. This one-step treatment represents a straightforward and high efficiency way for the reduction of carbon nanotubes/graphene oxides composites.

Improved Electrochemical Performance Based on Nanostructured SnS_2@CoS_2–rGO Composite Anode for Sodium-Ion Batteries

A promising anode material composed of SnS_2@CoS_2 flower-like spheres assembled from SnS_2 nanosheets and CoS_2 nanoparticles accompanied by reduced graphene oxide(rGO) was fabricated by a facile hydrothermal pathway. The presence of rGO and the combined merits of SnS_2 and CoS_2 endow the SnS_2@-CoS_2–rGO composite with high conductivity pathways and channels for electrons and with excellent properties as an anode material for sodium-ion batteries(SIBs). A high capacity of 514.0 mAh g^(-1) at a current density of200 m A g^(-1) after 100 cycles and a good rate capability can be delivered. The defined structure and good sodium-storage performance of the SnS_2@CoS_2–rGO composite demonstrate its promising application in high-performance SIBs.

Ambient flash sintering of reduced graphene oxide/zirconia composites:Role of reduced graphene oxide

Fabrication of graphene/ceramic composites commonly requires a high-temperature sintering step with long times as well as a vacuum or inert atmosphere,which not only results in property degradation but also significant equipment complexity and manufacturing costs.In this work,the ambient flash sintering behavior of reduced graphene oxide/3 mol% yttria-stabilized ZrO_(2)(rGO/3 YSZ) composites utilizing rGO as both a composite component and a conductive additive is reported.When the sintering condition is carefully optimized,a dense and conductive composite can be achieved at room temperature and in the air within 20 s.The role of the rGO in the FS of the rGO/3 YSZ composites is elucidated,especially with the assistance of a separate investigation on the thermal runaway behavior of the rGO.The work suggests a promising fabrication route for rGO/ceramic composites where the vacuum and furnace are not needed,which is of interest in terms of simplifying the fabrication equipment for energy and cost savings.