Multifunctional Mesoporous Nanoellipsoids for Biological Bimodal Imaging and Magnetically Targeted Delivery of Anticancer Drugs

A general polyelectrolyte‐mediated self‐assembly technique is adopted to prepare multifunctional mesoporous nanostructures as an effective biological bimodal imaging probe and magnetically targeted anticancer drug (doxorubicin) delivery systems (DDSs). A positively charged polyelectrolyte (PAH) and negatively charged fluorescent quantum dots (QDs) are successfully assembled onto the surface of ellipsoidal Fe₃O₄@SiO₂@mSiO₂ composite nanostructures to combine the merits of tunable fluorescent/magnetic properties, mesoporous nanostructures for drug loading, and the uniform ellipsoidal morphology for enhanced uptake by cancer cells. The resultant nanoellipsoids are homogeneously coated with four layers of PAH/QDs, with an additional PAH layer to make the ellipsoidal surface positively charged. This acts to enhance cellular uptake, which is driven by electrostatic interactions between the positive nanoparticle surface and the negative cell surface. The high biocompatibility of the achieved multifunctional nanoellipsoids is demonstrated by a cell‐cytotoxicity assay, hemolyticity against human red blood cells, and coagulation evaluation of fresh human blood plasma after exposure to the nanoparticles. Moreover, confocal microscopy and bio‐TEM observations show that the cell uptake of nanocarriers is dose‐dependent, and the nanoparticles accumulate mostly in the cytoplasm. The excellent capability of the nanocarriers as contrast agents for MRI is demonstrated by the relatively high r₂ value (143 mM^?1s^?1) and preliminary in vivo characterization. More importantly, the doxorubicin‐loaded DDSs show higher cytotoxicity than the free doxorubicin drug as contributed by the intracellular release pathway of doxorubicin from the DDSs, indicating the potential application of the obtained multifunctional mesoporous nanoellipsoids as highly effective bimodal imaging probes and DDSs for cancer diagnosis and chemotherapy, simultaneously.     

Graphene‐Based Nanoporous Materials Assembled by Mediation of Polyoxometalate Nanoparticles

A kind of graphene‐based nanoporous material is prepared through assembling graphene sheets mediated through polyoxometalate nanoparticles. Owing to the strong interaction between graphene and polyoxometalate, 2D graphene sheets with honeycomb‐latticed carbon atoms could assemble into a porous structure, in which 3D polyoxometalate nanoparticles serve as the crosslinkers. Nitrogen and hydrogen sorption analysis reveal that the as‐prepared graphene‐based hybrid material possesses a specific surface area of 680 m² g^?1 and a hydrogen uptake volume of 0.8?1.3 wt%. Infrared spectrometry is used to probe the electron density changes of polyoxometalate particle in the redox‐cycle and to verify the interaction between graphene and polyoxometalate. The as‐prepared graphene‐based materials are further characterized by Raman spectroscopy, X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy.     

Sponge‐Templated Preparation of High Surface Area Graphene with Ultrahigh Capacitive Deionization Performance

Capacitive deionization (CDI) is a competent water desalination technique offering an appropriate route to obtain clean water. However, a rational designed structure of the electrode materials is essentially required for achieving high CDI performance. Here, a novel sponge‐templated strategy is developed for the first time to prepare graphene sheets with high specific surface area and suitable pore size distribution. Sponge is used as the support of graphene oxide to prevent the restack of graphene sheets, as well as to suppress the agglomerate during the annealing process. Importantly, the as‐fabricated graphene sheets possess high specific surface area of 305 m² g^?1 and wide pore size distribution. Ultrahigh CDI performance, a remarkable electrosorptive capacity of 4.95 mg g^?1, and siginificant desorption rate of 25 min, is achieved with the sponge‐templated prepared graphene electrodes. This work provides an effective solution for the synthesis of rational graphene architectures for general applications in CDI, energy storage and conversion.     

All‐Carbon Nanoarchitectures as High‐Performance Separation Membranes with Superior Stability

The application of graphene‐based membranes is hindered by their poor stability under practical hydrodynamic conditions. Here, nanocarbon architectures are designed by intercalating surface‐functionalized, small‐diameter, multi‐walled carbon nanotubes (MWCNTs) into reduced graphene oxide (rGO) sheets to create highly stable membranes with improved water permeability and enhanced membrane selectivity. With the intercalation of 10 nm diameter MWCNTs, the water permeability reaches 52.7 L m^?2 h^?1 bar^?1, which is 4.8 times that of pristine rGO membrane and five to ten times higher than most commercial nanofiltration membranes. The membrane also attains almost 100% rejection for three organic dyes of different charges. More importantly, the membrane can endure a turbulent hydrodynamic flow with cross‐flow rates up to 2000 mL min^?1 and a Reynolds number of 4667. Physicochemical characterization reveals that the inner graphitic walls of the MWCNTs can serve as spacers, while nanoscale rGO foliates on the outer walls interconnect with the assimilated rGO sheets to instill superior membrane stability. In contrast, intercalating with single‐walled nanotubes fails to reproduce such stability. Overall, this nanoarchitectured design is highly versatile in creating both graphene‐rich and CNT‐rich all‐carbon membranes with engineered nanochannels, and is regarded as a general approach in obtaining stable membranes for realizing practical applications of graphene‐based membranes.     

Ultrathin MnO2/Graphene Oxide/Carbon Nanotube Interlayer as Efficient Polysulfide‐Trapping Shield for High‐Performance Li–S Batteries

Ultrathin MnO₂/graphene oxide/carbon nanotube (G/M@CNT) interlayers are developed as efficient polysulfide‐trapping shields for high‐performance Li–S batteries. A simple layer‐by‐layer procedure is used to construct a sandwiched vein–membrane interlayer of thickness 2 µm and areal density 0.104 mg cm^?2 by loading MnO₂ nanoparticles and graphene oxide (GO) sheets on superaligned carbon nanotube films. The G/M@CNT interlayer provides a physical shield against both polysulfide shuttling and chemical adsorption of polysulfides by MnO₂ nanoparticles and GO sheets. The synergetic effect of the G/M@CNT interlayer enables the production of Li–S cells with high sulfur loadings (60–80 wt%), a low capacity decay rate (?0.029% per cycle over 2500 cycles at 1 C), high rate performance (747 mA h g^?1 at a charge rate of 10 C), and a low self‐discharge rate with high capacity retention (93.0% after 20 d rest). Electrochemical impedance spectroscopy, cyclic voltammetry, and scanning electron microscopy observations of the Li anodes after cycling confirm the polysulfide‐trapping ability of the G/M@CNT interlayer and show its potential in developing high‐performance Li–S batteries.     

Preparation,Structure, and Electrochemical Properties of Reduced Graphene Sheet Films

This paper describes the preparation, characterization, and electrochemical properties of reduced graphene sheet films (rGSFs), investigating especially their electrochemical behavior for several redox systems and electrocatalytic properties towards oxygen and some small molecules. The reduced graphene sheets (rGSs) are produced in high yield by a soft chemistry route involving graphite oxidation, ultrasonic exfoliation, and chemical reduction. Transmission electron microscopy (TEM), X‐ray diffraction (XRD), scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS) and Raman spectroscopy clearly demonstrate that graphene was successfully synthesized and modified at the surface of a glassy carbon electrode. Several redox species, such as Ru(NH₃)₆^3+/2+, Fe(CN)₆^3?/4?, Fe^3+/2+ and dopamine, are used to probe the electrochemical properties of these graphene films by using the cyclic voltammetry method. The rGSFs demonstrate fast electron‐transfer (ET) kinetics and possess excellent electrocatalytic activity toward oxygen reduction and certain biomolecules. In our opinion, this microstructural and electrochemical information can serve as an important benchmark for graphene‐based electrode performances.     

An In Situ Simultaneous Reduction‐Hydrolysis Technique for Fabrication of TiO2‐Graphene 2D Sandwich‐Like Hybrid Nanosheets: Graphene‐Promoted Selectivity of Photocatalytic‐Driven Hydrogenation and Coupling of CO2 into Methane and Ethane

A novel, in situ simultaneous reduction‐hydrolysis technique (SRH) is developed for fabrication of TiO₂‐‐graphene hybrid nanosheets in a binary ethylenediamine (En)/H₂O solvent. The SRH technique is based on the mechanism of the simultaneous reduction of graphene oxide (GO) into graphene by En and the formation of TiO₂ nanoparticles through hydrolysis of titanium (IV) (ammonium lactato) dihydroxybis, subsequently in situ loading onto graphene through chemical bonds (Ti–O–C bond) to form 2D sandwich‐like nanostructure. The dispersion of TiO₂ hinders the collapse and restacking of exfoliated sheets of graphene during reduction process. In contrast with prevenient G‐TiO₂ nanocomposites, abundant Ti³⁺ is detected on the surface of TiO₂ of the present hybrid, caused by reducing agent En. The Ti³⁺ sites on the surface can serve as sites for trapping photogenerated electrons to prevent recombination of electron–hole pairs. The high photocatalytic activity of G‐TiO₂ hybrid is confirmed by photocatalytic conversion of CO₂ to valuable hydrocarbons (CH₄ and C₂H₆) in the presence of water vapor. The synergistic effect of the surface‐Ti³⁺ sites and graphene favors the generation of C₂H₆, and the yield of the C₂H₆ increases with the content of incorporated graphene. The work may open a new doorway for new significant application of graphene for selectively catalytic C–C coupling reaction     

Ultrahigh Conductive Graphene Paper Based on Ball‐Milling Exfoliated Graphene

Due to low density, extremely high electrical and thermal conductivities, graphene has great potential to construct lightweight thermal conductive paper for high‐power electric devices. However, the remarkable properties of graphene are on a molecular level and difficult to achieve when processed into macroscopic paper. Here, an effective route to construct ultrahigh conductive graphene paper is developed. First, large‐volume, high‐concentration, plane‐defect‐free, few‐layer graphene dispersion is fast produced from graphite at high yield through ball milling. The exfoliated graphene dispersion is further processed into graphene paper through fast filtration, thermal treatment, and mechanical compression. The electrical and thermal conductivities of the resultant graphene paper are as high as 2231 S cm^?1 and 1529 W m^?1 K^?1, superior to previously reported graphene papers. Structural analyses confirm that the ultrahigh conductivities are attributed to high quality of graphene sheets, their compact ordered stacking, and large graphitic crystalline domain size, which improve electron and phonon transport within basal plane of graphene sheet and between graphene sheets.     

Nanoscale Graphene Doped with Highly Dispersed Silver Nanoparticles: Quick Synthesis,Facile Fabrication of 3D Membrane‐Modified Electrode,and Super Performance for Electrochemical Sensing

The performance of graphene‐based hybrid materials greatly depends on the dispersibility of nanoscale building blocks on graphene sheets. Here, a quick green synthesis of nanoscale graphene (NG) nanosheets decorated with highly dispersed silver nanoparticles (AgNPs) is demonstrated, and then the electrospinning technique to fabricate a novel nanofibrous membrane electrode material is utilized. With this technique, the structure, mechanical stability, biochemical functionality, and other properties of the fabricated membrane electrode material can be easily controlled. It is found that the orientations of NG and the dispersity of AgNPs on the surface of NG have significant effects on the properties of the fabricated electrode. A highly sensitive H₂O₂ biosensor is thus created based on the as‐prepared polymeric NG/AgNP 3D nanofibrous membrane‐modified electrode (MME). As a result, the fabricated biosensor has a linear detection range from 0.005 to 47 × 10^?3m (R = 0.9991) with a supralow detection limit of 0.56 × 10^?6m (S/N = 3). It is expected that this kind of nanofibrous MME has wider applications for the electrochemical detection and design of 3D functional nanomaterials in the future.     

Anchoring Hydrous RuO2 on Graphene Sheets for High‐Performance Electrochemical Capacitors

Hydrous ruthenium oxide (RuO₂)/graphene sheet composites (ROGSCs) with different loadings of Ru are prepared by combining sol–gel and low‐temperature annealing processes. The graphene sheets (GSs) are well‐separated by fine RuO₂ particles (5–20 nm) and, simultaneously, the RuO₂ particles are anchored by the richly oxygen‐containing functional groups of reduced, chemically exfoliated GSs onto their surface. Benefits from the combined advantages of GSs and RuO₂ in such a unique structure are that the ROGSC‐based supercapacitors exhibit high specific capacitance (～570 F g^?1 for 38.3 wt% Ru loading), enhanced rate capability, excellent electrochemical stability (～97.9% retention after 1000 cycles), and high energy density (20.1 Wh kg^?1) at low operation rate (100 mA g^?1) or high power density (10000 W kg^?1) at a reasonable energy density (4.3 Wh kg^?1). Interestingly, the total specific capacitance of ROGSCs is higher than the sum of specific capacitances of pure GSs and pure RuO₂ in their relative ratios, which is indicative of a positive synergistic effect of GSs and RuO₂ on the improvement of electrochemical performance. These findings demonstrate the importance and great potential of graphene‐based composites in the development of high‐performance energy‐storage systems.     

Single‐Crystal Hybrid Perovskite Platelets on Graphene: A Mixed‐Dimensional Van Der Waals Heterostructure with Strong Interface Coupling

Van der Waals (vdW) heterostructures open up excellent prospects in electronic and optoelectronic applications. In this work, mixed‐dimensional metal‐halide perovskite/graphene heterostructures are prepared through selective growth of CH₃NH₃PbBr₃ platelets on patterned single‐layer graphene using chemical vapor deposition. Preferred growth of single‐crystal CH₃NH₃PbBr₃ platelets on graphene surfaces is achieved, which is accompanied by significant photoluminescence quenching. Raman spectra reveal that perovskite platelets cause p‐type doping in the graphene layer. A significant Fermi level decrease of 272 meV in graphene is estimated, which corresponds to a high doping density of 7.5 × 10¹² cm^?2. Surface potentials measured by Kelvin probe force microscopy indicate a negatively charged perovskite surface under illumination, which is consistent with the upward band bending deduced from conducting atomic force microscopy measurements. Moreover, a field‐effect phototransistor is fabricated using the perovskite/graphene heterostructure channel, and the increased Dirac voltage under illumination confirms an enhanced p‐type character in graphene. These findings enrich the understanding of strong interface coupling in such mixed‐dimensional vdW heterostructures and pave the way toward novel perovskite‐based optoelectronic devices.     

Tunable Assembly of sp3 Cross‐Linked 3D Graphene Monoliths: A First‐Principles Prediction

One of the biggest challenges in graphene applications is how one can fabricate 3D architectures comprising graphene sheets in which the resulting architectures have inherited graphene's excellent intrinsic properties but have overcome its shortcomings. Two series of 3D graphene monoliths (GMs) using zigzag or armchair graphene nanoribbons as building blocks and sp³ carbon chains as junction nodes are constructued, and calculations based on first principles are performed in order to predict their mechanical and electronic properties. The perfect match between sp² nanoribbons and sp³ linkers results in favorable energy and mechanical/dynamic stability. Owing to their tailored motifs, wine‐rack‐like pores, and rigid sp³ linkers, these GMs possess high surface areas, appreciable mechanical strength, and tunable band gaps. Negative linear compressibilities in a wide range are found for the zigzag GMs. By solving the problems of zero gap and dimensionality of graphene sheets simultaneously, these GMs offer a viable strategy towards many applications, e.g., microelectronic devices, energy storage, molecular sieves, sensitive pressure detectors, and telecommunication line systems.     

A Controllable Self‐Assembly Method for Large‐Scale Synthesis of Graphene Sponges and Free‐Standing Graphene Films

A simple method to prepare large‐scale graphene sponges and free‐standing graphene films using a speed vacuum concentrator is presented. During the centrifugal evaporation process, the graphene oxide (GO) sheets in the aqueous suspension are assembled to generate network‐linked GO sponges or a series of multilayer GO films, depending on the temperature of a centrifugal vacuum chamber. While sponge‐like bulk GO materials (GO sponges) are produced at 40 °C, uniform free‐standing GO films of size up to 9 cm² are generated at 80 °C. The thickness of GO films can be controlled from 200 nm to 1 µm based on the concentration of the GO colloidal suspension and evaporation temperature. The synthesized GO films exhibit excellent transparency, typical fluorescent emission signal, and high flexibility with a smooth surface and condensed density. Reduced GO sponges and films with less than 5 wt% oxygen are produced through a thermal annealing process at 800 °C with H₂/Ar flow. The structural flexibility of the reduced GO sponges, which have a highly porous, interconnected, 3D network, as well as excellent electrochemical properties of the reduced GO film with respect to electrode kinetics for the [Fe(CN)₆]^3?/4? redox system, are demonstrated.     

Efficient Synthesis of Heteroatom (N or S)‐Doped Graphene Based on Ultrathin Graphene Oxide‐Porous Silica Sheets for Oxygen Reduction Reactions

Heteroatom (N or S)‐doped graphene with high surface area is successfully synthesized via thermal reaction between graphene oxide and guest gases (NH₃ or H₂S) on the basis of ultrathin graphene oxide‐porous silica sheets at high temperatures. It is found that both N and S‐doping can occur at annealing temperatures from 500 to 1000 °C to form the different binding configurations at the edges or on the planes of the graphene, such as pyridinic‐N, pyrrolic‐N, and graphitic‐N for N‐doped graphene, thiophene‐like S, and oxidized S for S‐doped graphene. Moreover, the resulting N and S‐doped graphene sheets exhibit good electrocatalytic activity, long durability, and high selectivity when they are employed as metal‐free catalysts for oxygen reduction reactions. This approach may provide an efficient platform for the synthesis of a series of heteroatom‐doped graphenes for different applications.     

High Surface Area MoS2/Graphene Hybrid Aerogel for Ultrasensitive NO2 Detection

A MoS₂/graphene hybrid aerogel synthesized with two‐dimensional MoS₂ sheets coating a high surface area graphene aerogel scaffold is characterized and used for ultrasensitive NO₂ detection. The combination of graphene and MoS₂ leads to improved sensing properties with the graphene scaffold providing high specific surface area and high electrical and thermal conductivity and the single to few‐layer MoS₂ sheets providing high sensitivity and selectivity to NO₂. The hybrid aerogel is integrated onto a low‐power microheater platform to probe the gas sensing performance. At room temperature, the sensor exhibits an ultralow detection limit of 50 ppb NO₂. By heating the material to 200 °C, the response and recovery times to reach 90% of the final signal decrease to <1 min, while retaining the low detection limit. The MoS₂/graphene hybrid also shows good selectivity for NO₂ against H₂ and CO, especially when compared to bare graphene aerogel. The unique structure of the hybrid aerogel is responsible for the ultrasensitive, selective, and fast NO₂ sensing. The improved sensing performance of this hybrid aerogel also suggests the possibility of other 2D material combinations for further sensing applications.     

Electromechanical Actuators Based on Graphene and Graphene/Fe3O4 Hybrid Paper

Exceptionally high specific surface area, mechanical strength, electrical conductivity, and a special two‐dimensional structure make graphene a highly promising material for electromechanical actuators. Electromechanical actuators are fabricated using flexible graphene‐based paper prepared via a filtration process, and the stroke of these graphene‐based actuators is directly measured during electrochemical double‐layer charge injection. Actuation strain up to 0.064% was obtained for pristine graphene paper in response to an applied potential of –1 V in 1 M NaCl solution. Double‐layer charge injection in graphene sheets is believed to induce actuation strain through a combination of coulombic and quantum‐chemical‐based expansion. To increase electrochemical‐double‐layer capacitance and actuator performance, Fe₃O₄ nanoparticles were used to partially prevent graphene sheets from restacking and allow the electrolyte ions to infiltrate the resulting magnetic graphene paper more easily. The magnetic graphene paper exhibits actuation strain as large as 0.1% at –1 V applied potential, which is about 56% higher than that of the pristine graphene paper.     

GeOx/Reduced Graphene Oxide Composite as an Anode for Li‐Ion Batteries: Enhanced Capacity via Reversible Utilization of Li2O along with Improved Rate Performance

A self‐assembled GeO_x/reduced graphene oxide (GeO_x/RGO) composite, where GeO_x nanoparticles are grown directly on reduced graphene oxide sheets, is synthesized via a facile one‐step reduction approach and studied by X‐ray diffraction, transmission electron microscopy, energy dispersive X‐ray spectroscopy, electron energy loss spectroscopy elemental mapping, and other techniques. Electrochemical evaluation indicates that incorporation of reduced graphene oxide enhances both the rate capability and reversible capacity of GeO_x, with the latter being due to the RGO enabling reversible utilization of Li₂O. The composite delivers a high reversible capacity of 1600 mAh g^?1 at a current density of 100 mA g^?1, and still maintains a capacity of 410 mAh g^?1 at a high current density of 20 A g^?1. Owing to the flexible reduced graphene oxide sheets enwrapping the GeO_x particles, the cycling stability of the composite is also improved significantly. To further demonstrate its feasibility in practical applications, the synthesized GeO_x/RGO composite anode is successfully paired with a high voltage LiNi_0.5Mn_1.5O₄ cathode to form a full cell, which shows good cycling and rate performance.     

Highly Conductive Porous Graphene/Ceramic Composites for Heat Transfer and Thermal Energy Storage

A novel architecture of 3D graphene growth on porous Al₂O₃ ceramics is proposed for thermal management using ambient pressure chemical vapor deposition. The formation mechanism of graphene is attributed to the carbothermic reduction occurring at the Al₂O₃ surface to initialize the nucleation and growth of graphene. The graphene films are coated on insulating anodic aluminum oxide (AAO) templates and porous Al₂O₃ ceramic substrates. The graphene coated AAO possesses one‐dimensional isolated graphene tubes, which can act as the media for directional thermal transport. The graphene/Al₂O₃ composite (G‐Al₂O₃) contains an interconnected macroporous graphene framework with an extremely low sheet electrical resistance down to 0.11 Ω sq^?1 and thermal conductivity with 8.28 W m^?1 K^?1. The G‐Al₂O₃ provides enormous conductive pathways for electronic and heat transfer, suitable for application as heat sinks. Such a porous composite is also attractive as a highly thermally conductive reservoir to hold phase change materials (stearic acid) for thermal energy storage. This work displays the great potential of CVD direct growth of graphene on dielectric porous substrates for thermal conduction and electronic applications.     

Advanced Asymmetric Supercapacitors Based on Ni(OH)2/Graphene and Porous Graphene Electrodes with High Energy Density

Hierarchical flowerlike nickel hydroxide decorated on graphene sheets has been prepared by a facile and cost‐effective microwave‐assisted method. In order to achieve high energy and power densities, a high‐voltage asymmetric supercapacitor is successfully fabricated using Ni(OH)₂/graphene and porous graphene as the positive and negative electrodes, respectively. Because of their unique structure, both of these materials exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high‐voltage region of 0–1.6 V and displays intriguing performances with a maximum specific capacitance of 218.4 F g^?1 and high energy density of 77.8 Wh kg^?1. Furthermore, the Ni(OH)₂/graphene//porous graphene supercapacitor device exhibits an excellent long cycle life along with 94.3% specific capacitance retained after 3000 cycles. These fascinating performances can be attributed to the high capacitance and the positive synergistic effects of the two electrodes. The impressive results presented here may pave the way for promising applications in high energy density storage systems.     

Battery Performance and Photocatalytic Activity of Mesoporous Anatase TiO2 Nanospheres/Graphene Composites by Template‐Free Self‐Assembly

Nanosized mesoporous anatase TiO₂ particles have important applications in high‐performance lithium ion batteries and efficient photocatalysis. In contrast to the conventional synthesis routes where various soft or hard templates are usually employed, the direct growth of uniform mesoporous anatase TiO₂ nanospheres on graphene sheets by a template‐free self‐assembly process is presented. Compared to the conventional mesoporous anatase particles consisting of polycrystalline TiO₂, the microstructure of obtained mesoporous anatase nanospheres on graphene sheets is single‐crystal‐like. The growth mechanism, lithium ion battery performance, and photocatalytic activity of the resultant mesoporous anatase TiO₂ nanospheres/graphene composites are thoroughly investigated. In comparison to the reference TiO₂, the composite shows substantial improvement in lithium specific capacity from 1 C to 50 C, and photocatalytic removing organic pollutant and hydrogen evolution. More strikingly, the specific capacity of the composite at the rate of 50 C is as high as 97 mA h g^?1, 6 times higher than that of the reference TiO₂.