Yanfeng Ma

Superparamagnetic graphene oxide–Fe3O4nanoparticles hybrid for controlled targeted drug carriers

A superparamagnetic graphene oxide –Fe3O4nanoparticles hybrid (GO–Fe3O4) was prepared via a simple and effective chemical precipitation method. The amount of loading of Fe3O4 on GO was estimated as 18.6 wt% by atomic absorption spectrometry. The hybrid was then loaded with doxorubicin hydrochloride (DXR) and the loading capacity was as high as 1.08 mg mg−1. Both of the GO–Fe3O4 hybrids before and after loading with DXR can be dispersed well in aqueous solution. They can congregate under acidic conditions and move regularly under the force of an external magnet. Furthermore, the aggregated hybrid can be redispersed to form a stable suspension under basic conditions. These properties make it a potential candidate for controlled targeted drug delivery and release.

Porous 3D graphene-based bulk materials with exceptional high surface area and excellent conductivity for supercapacitors

Until now, few sp2 carbon materials simultaneously exhibit superior performance for specific surface area (SSA) and electrical conductivity at bulk state. Thus, it is extremely important to make such materials at bulk scale with those two outstanding properties combined together. Here, we present a simple and green but very efficient approach using two standard and simple industry steps to make such three-dimensional graphene-based porous materials at the bulk scale, with ultrahigh SSA (3523 m2/g) and excellent bulk conductivity. We conclude that these materials consist of mainly defected/wrinkled single layer graphene sheets in the dimensional size of a few nanometers, with at least some covalent bond between each other. The outstanding properties of these materials are demonstrated by their superior supercapacitor performance in ionic liquid with specific capacitance and energy density of 231 F/g and 98 Wh/kg, respectively, so far the best reported capacitance performance for all bulk carbon materials.

Multi-functionalized graphene oxide based anticancer drug-carrier with dual-targeting function and pH-sensitivity

A dual-targeting drug delivery and pH-sensitive controlled release system based on multi-functionalized graphene oxide (GO) was established in order to enhance the effect of targeted drug delivery and realize intelligently controlled release. A superparamagnetic GO–Fe3O4 nanohybrid was firstly prepared via a simple and effective chemical precipitation method. Then folic acid, a targeting agent toward some tumor cells, was conjugated onto Fe3O4 nanoparticlesvia the chemical linkage with amino groups of the 3-aminopropyl triethoxysilane (APS) modified superparamagnetic GO–Fe3O4 nanohybrid, to give the multi-functionalized GO. Doxorubicin hydrochloride (Dox) as an anti-tumor drug model was loaded onto the surface of this multi-functionalized GO via π–π stacking. The drug loading capacity of this multi-functionalized GO is as high as 0.387 mg mg−1 and the drug release depends strongly on pH values. Cell uptake studies were carried out using fluorescein isothiocyanate labeled or Dox loaded multi-functionalized GO to evaluate their targeted delivery property and toxicity to tumor cells. The results show that this multi-functionalized GO has potential applications for targeted delivery and the controlled release of anticancer drugs.

Room-Temperature Ferromagnetism of Graphene

Aiming at molecular-based magnets, ferromagnetism of pure carbon-based materials is fundamentally and technologically extremely important for many applications. While it is still not fully understood, many recent theoretical works have suggested that one-atom-thick two-dimensional graphene materials may show ferromagnetism due to the existence of various defects or topological structures as the spin units and the possible long-range ordered coupling among them. Here, we report the experimental results on the ferromagnetism of graphene-based materials at room temperature. The observed room-temperature ferromagnetism is believed to come from the defects on graphene.

Flexible and Transparent Electrothermal Film Heaters Based on Graphene Materials

High-performance and novel graphene-based electrothermal films are fabricated through a simple yet versatile solution process. Their electrothermal performances are studied in terms of applied voltage, heating rate, and input power density. The electrothermal films annealed at high temperature show high transmittance and display good heating performance. For example, the graphene-based film annealed at 800 °C, which shows transmittance of over 80% at 550 nm, can reach a saturated temperature of up to 42 °C when 60 V is applied for 2 min. Graphene-based films annealed at 900 and 1000 °C can exhibit high steady-state temperatures of 150 and 206 °C under an applied voltage of 60 V with a maximum heating rate of over 7 °C s(-1) . For flexible heating films patterned on polyimide, a steady-state temperature of 72 °C could be reached in less than 10 s with a maximum heating rate exceeding 16 °C s(-1) at 60 V. These excellent results, combined with the high chemical stability and mechanical flexibility of graphene, indicate that graphene-based electrothermal elements hold great promise for many practical applications, such as defrosting and antifogging devices.

Graphene-Based Materials for Lithium-Ion Hybrid Supercapacitors.

Lithium-ion hybrid supercapacitors (LIHSs), also called Li-ion capacitors, have attracted much attention due to the combination of the rapid charge-discharge and long cycle life of supercapacitors and the high energy-storage capacity of lithium-ion batteries. Thus, LIHSs are expected to become the ultimate power source for hybrid and all-electric vehicles in the near future. As an electrode material, graphene has many advantages, including high surface area and porous structure, high electric conductivity, and high chemical and thermal stability, etc. Compared with other electrode materials, such as activated carbon, graphite, and metal oxides, graphene-based materials with 3D open frameworks show higher effective specific surface area, better control of channels, and higher conductivity, which make them better candidates for LIHS applications. Here, the latest advances in electrode materials for LIHSs are briefly summarized, with an emphasis on graphene-based electrode materials (including 3D graphene networks) for LIHS applications. An outlook is also presented to highlight some future directions.

Multichannel and Repeatable Self‐Healing of Mechanical Enhanced Graphene‐Thermoplastic Polyurethane Composites

A novel self-healing material, which was fabricated using few-layered graphene (FG) and thermoplastic polyurethane (TPU) via a facile method, not only exhibits a mechanical enhanced property, but also can be repeatedly healed by various methods including infrared (IR) light, electricity and electromagnetic wave with healing efficiencies higher than 98%.

Controlling the Effective Surface Area and Pore Size Distribution of sp2 Carbon Materials and Their Impact on the Capacitance Performance of These Materials

A series of sp(2) carbon materials with different specific surface area (SSA) and controlled pore size distribution (PSD) were synthesized at large scale through a facile and low-cost method. The SSA and PSD of these carbon materials were controlled by using different carbon sources and preparation methods. With different total and effective SSA (E-SSA) and PSD, the impacts on their capacitance performance were investigated thoroughly, which demonstrated that both E-SSA and PSD played the most important roles in their capacitance performance. Furthermore, theoretical modeling was performed, and the results are in agreement with the experimental results for the influence of E-SSA and PSD on their capacitance performance. Based on these, a general model using the slit/cylindrical NL-DFT approach is proposed for the estimation of the specific capacitance of sp(2) carbon materials, which offers a simple but reliable method to predict the capacitance performance of these materials, thus speeding up the design and screening of the materials for high-performance supercapacitor and other surface area related devices.

Electromechanical Actuator with Controllable Motion, Fast Response Rate, and High-Frequency Resonance Based on Graphene and Polydiacetylene

Although widely investigated, novel electromechanical actuators with high overall actuation performance are still in urgent need for various practical and scientific applications, such as robots, prosthetic devices, sensor switches, and sonar projectors. In this work, combining the properties of unique environmental perturbations-actuated deformational isomerization of polydiacetylene (PDA) and the outstanding intrinsic features of graphene together for the first time, we design and fabricate an electromechanical bimorph actuator composed of a layer of PDA crystal and a layer of flexible graphene paper through a simple yet versatile solution approach. Under low applied direct current (dc), the graphene-PDA bimorph actuator with strong mechanical strength can generate large actuation motion (curvature is about 0.37 cm(-1) under a current density of 0.74 A/mm(2)) and produce high actuation stress (more than 160 MPa/g under an applied dc of only 0.29 A/mm(2)). When applying alternating current (ac), this actuator can display reversible swing behavior with long cycle life under high frequencies even up to 200 Hz; significantly, while the frequency and the value of applied ac and the state of the actuators reach an appropriate value, the graphene-PDA actuator can produce a strong resonance and the swing amplitude will jump to a peak value. Moreover, this stable graphene-PDA actuator also demonstrates rapidly and partially reversible electrochromatic phenomenon when applying an ac. Two mechanisms-the dominant one, electric-induced deformation, and a secondary one, thermal-induced expansion of PDA-are proposed to contribute to these interesting actuation performances of the graphene-PDA actuators. On the basis of these results, a mini-robot with controllable direction of motion based on the graphene-PDA actuator is designed to illustrate the great potential of our discoveries for practical use. Combining the unique actuation mechanism and many outstanding properties of graphene and PDA, this novel kind of graphene-PDA actuator exhibits compelling advantages to traditional electromechanical actuation technology and may provide a new avenue for actuation applications.

Photoconductivity of Bulk-Film-Based Graphene Sheets

Time-resolved photoconductivity measurements are carried out on graphene films prepared by using soluble graphene oxide. High photocurrent generation efficiency is observed for these graphene-based films, and the relationships between their photoconductivity and different preparation methods, incident light intensity, external electric field, and photon energies are investigated. Higher photoconductivity is observed with higher photon energy at same incident light intensity. By fitting the experimental data to the Onsager model, the primary quantum yields for charge separation to generate bound electron-hole pairs and the initial ion-pair thermalization separation distance are calculated.