Yimin Sun

Mussel-inspired synthesis of polydopamine-functionalized graphene hydrogel as reusable adsorbents for water purification.

We present a one-step approach to polydopamine-modified graphene hydrogel, with dopamine serving as both reductant and surface functionalization agents. The synthetic method is based on the spontaneous polymerization of dopamine and the self-assembly of graphene nanosheets into porous hydrogel structures. Benefiting from the abundant functional groups of polydopamine and the high specific surface areas of graphene hydrogel with three-dimensional interconnected pores, the prepared material exhibits high adsorption capacities toward a wide spectrum of contaminants, including heavy metals, synthetic dyes, and aromatic pollutants. Importantly, the free-standing graphene hydrogel can be easily removed from water after adsorption process, and can be regenerated by altering the pH values of the solution for adsorbed heavy metals or using low-cost alcohols for synthetic dyes and aromatic molecules.

Real-time electrochemical detection of hydrogen peroxide secretion in live cells by Pt nanoparticles decorated graphene-carbon nanotube hybrid paper electrode.

In this work, we develop a new type of flexible and lightweight electrode based on highly dense Pt nanoparticles decorated free-standing graphene-carbon nanotube (CNT) hybrid paper (Pt/graphene-CNT paper), and explore its practical application as flexible electrochemical biosensor for the real-time tracking hydrogen peroxide (H2O2) secretion by live cells. For the fabrication of flexible nanohybrid electrode, the incorporation of CNT in graphene paper not only improves the electrical conductivity and the mechanical strength of graphene paper, but also increases its surface roughness and provides more nucleation sites for metal nanoparticles. Ultrafine Pt nanoparticles are further decorated on graphene-CNT paper by well controlled sputter deposition method, which offers several advantages such as defined particle size and dispersion, high loading density and strong adhesion between the nanoparticles and the substrate. Consequently, the resultant flexible Pt/graphene-CNT paper electrode demonstrates a variety of desirable electrochemical properties including large electrochemical active surface area, excellent electrocatalytic activity, high stability and exceptional flexibility. When used for nonenzymatic detection of H2O2, Pt/graphene-CNT paper exhibits outstanding sensing performance such as high sensitivity, selectivity, stability and reproducibility. The sensitivity is 1.41 µA µM(-1) cm(-2) with a linear range up to 25 µM and a low detection limit of 10 nM (S/N=3), which enables the resultant biosensor for the real-time tracking H2O2 secretion by live cells macrophages.

One-step synthesis of three-dimensional porous ionic liquid–carbon nanotube–graphene gel and MnO2–graphene gel as freestanding electrodes for asymmetric supercapacitors

We report the design of a new type of high-performance asymmetric supercapacitor using three-dimensional (3D) porous ionic liquid (IL)–carbon nanotube (CNT)–graphene gel and MnO2–graphene gel as freestanding electrodes, both of which are synthesized by a facile and green one-step hydrothermal method. For the synthesis of IL–CNT–graphene gel, the precursor CNT–graphene oxide has firstly been dispersed by IL and then self-assembled into a unique “skeleton/skin” structure with CNTs as the skeleton and graphene nanosheets as the skin. For the synthesis of MnO2–graphene gel, the nucleation and growth of MnO2 nanoparticles as well as the self-assembly of graphene nanosheets occur simultaneously under the hydrothermal treatment, lead to a distinct “plum pudding” structure, where the MnO2 nanoparticles that are decorated on the 3D graphene gel are tightly wrapped by graphene nanosheets. In these two strategies, the introduction of IL, CNT and MnO2 nanoparticles into graphene gel not only acts as the “spacer” to prevent the π–π stacking interactions between graphene nanosheets, but also improves the electrochemical and capacitive properties of the graphene nanohybrid gel. The resultant asymmetric supercapacitor of IL–CNT–graphene gel//MnO2–graphene gel achieves high energy as well as good cycling stability and affordability, and can be reversibly charged/discharged at a maximum cell voltage of 1.8 V in 1.0 M aqueous Na2SO4 electrolyte. The corresponding energy density and power density are 25.6 W h kg−1 and 9.07 kW kg−1 at 1 A g−1, respectively, and the specific capacitance retention remains about 90% after 10 000 cycles.

Printing graphene-carbon nanotube-ionic liquid gel on graphene paper: Towards flexible electrodes with efficient loading of PtAu alloy nanoparticles for electrochemical sensing of blood glucose.

The increasing demands for portable, wearable, and implantable sensing devices have stimulated growing interest in innovative electrode materials. In this work, we have demonstrated that printing a conductive ink formulated by blending three-dimensional (3D) porous graphene-carbon nanotube (CNT) assembly with ionic liquid (IL) on two-dimensional (2D) graphene paper (GP), leads to a freestanding GP supported graphene-CNT-IL nanocomposite (graphene-CNT-IL/GP). The incorporation of highly conductive CNTs into graphene assembly effectively increases its surface area and improves its electrical and mechanical properties. The graphene-CNT-IL/GP, as freestanding and flexible substrates, allows for efficient loading of PtAu alloy nanoparticles by means of ultrasonic-electrochemical deposition. Owing to the synergistic effect of PtAu alloy nanoparticles, 3D porous graphene-CNT scaffold, IL binder and 2D flexible GP substrate, the resultant lightweight nanohybrid paper electrode exhibits excellent sensing performances in nonenzymatic electrochemical detection of glucose in terms of sensitivity, selectivity, reproducibility and mechanical properties.

Incorporating nanoporous polyaniline into layer-by-layer ionic liquid-carbon nanotube-graphene paper: towards freestanding flexible electrodes with improved supercapacitive performance.

The growing demand for lightweight and flexible supercapacitor devices necessitates innovation in electrode materials and electrode configuration. We have developed a new type of three-dimensional (3D) flexible nanohybrid electrode by incorporating nanoporous polyaniline (PANI) into layer-by-layer ionic liquid (IL) functionalized carbon nanotube (CNT)-graphene paper (GP), and explored its practical application as a freestanding flexible electrode in a supercapacitor. Our results have demonstrated that the surface modification of graphene nanosheets and CNTs by hydrophilic IL molecules makes graphene and CNTs well-dispersed in aqueous solution, and also improves the hydrophility of the assembled graphene-based paper. Furthermore, the integration of highly conductive one-dimensional (1D) CNTs with two-dimensional (2D) graphene nanosheets leads to 3D sandwich-structured nanohybrid paper with abundant interconnected pores, which is preferred for fast mass and electron transport kinetics. For in situ electropolymerization of PANI on paper electrodes, the IL functionalized CNT-GP (IL-CNT-GP) offers large surface area and interlayer spacing and the unique π surface of graphene and CNTs for efficient and stable loading of PANI. A key finding is that the structural integration of multiple components in this 3D freestanding flexible sheet electrode gives rise to a synergic effect, leading to a high capacitance of 725.6 F g(-1) at a current density of 1 A g(-1) and good cycling stability by retaining 90% of the initial specific capacitance after 5000 cycles.

In Situ Electrochemical Sensing and Real-Time Monitoring Live Cells Based on Freestanding Nanohybrid Paper Electrode Assembled from 3D Functionalized Graphene Framework

In this work, we develop a new type of freestanding nanohybrid paper electrode assembled from 3D ionic liquid (IL) functionalized graphene framework (GF) decorated by gold nanoflowers (AuNFs), and explore its practical application in in situ electrochemical sensing of live breast cell samples by real-time tracking biomarker H2O2 released from cells. The AuNFs modified IL functionalized GF (AuNFs/IL-GF) was synthesized via a facile and efficient dopamine-assisted one-pot self-assembly strategy. The as-obtained nanohybrid assembly exhibits a typical 3D hierarchical porous structure, where the highly active electrocatalyst AuNFs are well dispersed on IL-GF scaffold. And the graft of hydrophilic IL molecules (i.e., 1-butyl-3-methylimidazolium tetrafluoroborate, BMIMBF4) on graphene nanosheets not only avoids their agglomeration and disorder stacking during the self-assembly but also endows the integrated IL-GF monolithic material with unique hydrophilic properties, which enables it to be readily dispersed in aqueous solution and processed into freestanding paperlike material. Because of the unique structural properties and the combinational advantages of different components in the AuNFs/IL-GF composite, the resultant nanohybrid paper electrode exhibits good nonenzymatic electrochemical sensing performance toward H2O2. When used in real-time tracking H2O2 secreted from different breast cells attached to the paper electrode without or with radiotherapy treatment, the proposed electrochemical sensor based on freestanding AuNFs/IL-GF paper electrode can distinguish the normal breast cell HBL-100 from the cancer breast cells MDA-MB-231 and MCF-7 cells, and assess the radiotherapy effects to different breast cancer cells, which opens a new horizon in real-time monitoring cancer cells by electrochemical sensing platform.

Lightweight and Flexible Carbon Foam Composite for High-efficientElectromagnetic Interference Shielding

Extended Abstract In recent years, considerable attentions have been paid on the development of microwave shielding materials due to the increasing applications of electromagnetic radiation in military and telecommunications, as well as the potential hazardous effect on human health. Despite the tremendous push in the research for advancing microwave shielding materials, the achievements of critical physical properties including high shielding efficiency, light-weight, and flexibility in recently developed materials have remained to be technically challenging. To overcome those hurdles, porous materials engineered with the microcellular structure by the incorporation of nano-scale building blocks are specially designed for high performance microwave shielding. In contrast to impermeable shielding materials, porous materials provide the following competitive advantages: (i) reduction of total weight and cost, ii) high porosity and low density, (iii) strong microwave-absorbing ability, enhancing attenuation of incident microwaves by the multi-reflections on the numerous cell/wall interfaces within the three-dimensional (3D) architecture. In this work, we develop a novel type of carbonized melamine foam (cMF) by integrative modification with Au nanoparticles, graphene (G), Fe3O4 (IO) and poly(dimethyl siloxane) (PDMS). Our main goal is to construct a lightweight and flexible cMF composite with precisely engineered 3D hierarchical architecture for high-efficiency electromagnetic interference (EMI) shielding (Fig. 1). Through the engineering of the typical closed-cell structure and synergistic effect of the multifunctional components, the resultant cMF-Au-G-IO/PDMS composite demonstrate superior physical properties including low density (116 mg/cm3), high conductivity (81.3 S/m), large specific surface area (m2/g), superparamagnetism (Ms=22.6 emu/g), and moderate compressive strength (110 KPa), collectively leading to the significant attenuation effect towards EMI. The total EMI shielding effectiveness (SE) of cMF-Au-G-IO/PDMS film with the thickness of 2 mm was 30.5 dB in X band (8.2-12.4 GHz), which clearly matched the technical requirement of EMI shielding materials in most commercial and military applications. Interestingly, SE was further raised up to 52.5 dB when the film thickness increases to 10 mm. The electromagnetic wave absorption mechanism can be attributed to the simultaneously incorporation of dielectric loss and magnetic loss. Hence, we envision that this multifunctional cMF-based composite is a promising candidate for the most demanding requirement in EMI shielding.