Mingjie Li

KOH self-templating synthesis of three-dimensional hierarchical porous carbon materials for high performance supercapacitors

We report a KOH self-templating synthesis of three-dimensional hierarchical porous carbon using resol as the precursor and KOH as both the template and activating agent. The resulting resol-derived porous carbon (RPC) exhibits a high surface area (up to 2700 m2 g−1) and well-interconnected macropores with micropores and mesopores decorated on the carbon walls. Consequently, the RPC shows low internal resistance, high specific capacitance, good rate capability and excellent cycling stability in 6 M KOH as a supercapacitor electrode. Because of its easy fabrication and low cost, it offers a good alternative method for synthesis of carbon electrodes for energy-storage devices such as Li-ion batteries, fuel cells and supercapacitors.

Bioinspired Coupling of Inorganic Layered Nanomaterials with Marine Polysaccharides for Efficient Aqueous Exfoliation and Smart Actuating Hybrids

WS2 and marine alginate are perfectly coupled to ensure scalable production of exfoliated WS2 with unprecedented efficiency, further providing super mechanical properties and the photothermal effect to their composites. Combined with the water-intake and cation-binding capabilities of alginate, biomimetic soft devices are designed with stimuli-responsiveness and actuating properties, capable of serving as a photo-driven motor, a walking robot, and a gripper.

Amyloid-graphene oxide as immobilization platform of Au nanocatalysts and enzymes for improved glucose-sensing activity

Two-dimensional GO nanosheets and one-dimensional lysozyme nanofibrils were hybridized through electrostatic interaction to get a novel amyloid-GO composite, which promised a biocompatible immobilization platform for Au nanocatalysts as well as enzymes. The immobilization platform could load a large and tunable amount of Au NPs while maintaining their high catalytic activity. The immobilized catalysts showed high electrochemical behaviors, being ideal as glucose sensing systems. Furthermore, enzymes could also be immobilized on the residual bare surfaces of amyloid-GO, and served by a colorimetric method for a sensitive and selective analytical glucose-detecting platform. The introduction of amyloid fibrils with super large aspect ratios (>103) on GO nanosheets offers an unprecedented possibility of designing and developing novel biomimetic catalysts for broad applications in biotechnology.

Biomimetic Hybridization of Kevlar into Silk Fibroin: Nanofibrous Strategy for Improved Mechanic Properties of Flexible Composites and Filtration Membranes

Silk, one of the strongest natural biopolymers, was hybridized with Kevlar, one of the strongest synthetic polymers, through a biomimetic nanofibrous strategy. Regenerated silk materials have outstanding properties in transparency, biocompatibility, biodegradability and sustainability, and promising applications as diverse as in pharmaceutics, electronics, photonic devices and membranes. To compete with super mechanic properties of their natural counterpart, regenerated silk materials have been hybridized with inorganic fillers such as graphene and carbon nanotubes, but frequently lose essential mechanic flexibility. Inspired by the nanofibrous strategy of natural biomaterials (e.g., silk fibers, hemp and byssal threads of mussels) for fantastic mechanic properties, Kevlar was integrated in regenerated silk materials by combining nanometric fibrillation with proper hydrothermal treatments. The resultant hybrid films showed an ultimate stress and Youngs modulus two times as high as those of pure regenerated SF films. This is not only because of the reinforcing effect of Kevlar nanofibrils, but also because of the increasing content of silk β-sheets. When introducing Kevlar nanofibrils into the membranes of silk nanofibrils assembled by regenerated silk fibroin, the improved mechanic properties further enabled potential applications as pressure-driven nanofiltration membranes and flexible substrates of electronic devices.

A Highly Sensitive and Selective Hydrogen Peroxide Biosensor Based on Gold Nanoparticles and Three-Dimensional Porous Carbonized Chicken Eggshell Membrane

A sensitive and noble amperometric horseradish peroxidase (HRP) biosensor is fabricated via the deposition of gold nanoparticles (AuNPs) onto a three-dimensional (3D) porous carbonized chicken eggshell membrane (CESM). Due to the synergistic effects of the unique porous carbon architecture and well-distributed AuNPs, the enzyme-modified electrode shows an excellent electrochemical redox behavior. Compared with bare glass carbon electrode (GCE), the cathodic peak current of the enzymatic electrode increases 12.6 times at a formal potential of −100mV (vs. SCE) and charge-transfer resistance decreases 62.8%. Additionally, the AuNPs-CESM electrode exhibits a good biocompatibility, which effectively retains its bioactivity with a surface coverage of HRP 6.39×10−9 mol cm−2 (752 times higher than the theoretical monolayer coverage of HRP). Furthermore, the HRP-AuNPs-CESM-GCE electrode, as a biosensor for H2O2 detection, has a good accuracy and high sensitivity with the linear range of 0.01–2.7 mM H2O2 and the detection limit of 3μM H2O2 (S/N = 3).

Carbon materials derived from chitosan/cellulose cryogel-supported zeolite imidazole frameworks for potential supercapacitor application

In order to promote sustainable development, green and renewable clean energy technologies continue to be developed to meet the growing demand for energy, such as supercapacitor, fuel cells and lithium-ion battery. It is urgent to develop appropriate nanomaterials for these energy technologies to reduce the volume of the device, improve the efficiency of energy conversion and enlarge the energy storage capacity. Here, chitosan/cellulose carbon cryogel (CCS/CCL) were designed and synthesized. Through the introduction of zeolite imidazole frameworks (ZIFs) into the chitosan/cellulose cryogels, the obtained materials showed a microstructure of ZIF-7 (a kind of ZIFs) coated chitosan/cellulose fibers (CS/CL). After carbonizing, the as-prepared carbonized ZIF-7@cellulose cryogel (NC@CCL, NC is carbonized ZIF-7) and carbonized ZIF-7@chitosan cryogel (NC@CCS) exhibited suitable microspore contents of 34.37% and 30%, respectively, and they both showed an internal resistance lower than 2Ω. Thereby, NC@CCL and NC@CCS exhibited a high specific capacitance of 150.4Fg-1 and 173.1Fg-1, respectively, which were much higher than those of the original materials. This approach offers a facile method for improving the strength and electronic conductivity of carbon cryogel derived from nature polymers, and also efficiently inhibits the agglomeration of cryogel during carbonization in high temperature, which opens a novel avenue for the development of carbon cryogel materials for application in energy conversion systems.

Surface Charge Research of Graphene Oxide, Chemically Reduced Graphene Oxide and Thermally Exfoliated Graphene Oxide

In this contribution, the surface electrical properties of graphene oxide (GO), chemically reduced graphene oxide (RGO) and thermally exfoliated graphene oxide (EGO) were characterized by zeta potential. Their surface morphologies were observed by scanning electron microscope. Then they were immobilized on glass carbon electrodes and their electrochemical behaviors for different charged redox systems were also investigated by using the cyclic voltammetry (CV) method. Results indicated that the density of surface negative charge on GO is much more than those on RGO and EGO. Furthermore, the electrochemical performances of electrodes modified with GO, RGO and EGO for detecting the model analyte Cu2+ by CV were compared. The results demonstrate that negative charge on the surface of graphene materials affects their performances as electrochemical sensors significantly.

Guiding growth orientation of two-dimensional Au nanocrystals with marine chitin nanofibrils for ultrasensitive and ultrafast sensing hybrids

We demonstrate that marine chitin nanofibrils are able to modulate the growth direction of two-dimensional Au nanocrystals from nanoribbons, nanokites to nanosheets. The mechanism investigation reveals that deacetylation and exfoliation of chitin nanofibrils are essential to template directional growth of Au nanocrystals. The tight adhesion of chitin nanofibrils on the Au surface enables the design of functional hybrids as ultrafast and ultrasensitive responsive devices for humidity and pressure. Interestingly, the humidity responsive device shows an abrupt increase in resistance of up to 3 orders of magnitude with a tiny variation of relative humidity from 62% RH to 63% RH, and was capable of precisely sensing speech. As a conductive filler, only 0.09 vol% gold nanoribbons are able to append to tissue paper with a sheet resistance of up to 220 Ω sq-1, which can be used as a frequently-used pressure-sensing device. These sensing hybrids are highly promising in smart clothing and electronic skins.

Emerging investigator series: Dispersed Transition Metal on Nitrogen Doped Carbon Nanoframework for Environmental Hydrogen Peroxide Detection

Hydrogen peroxide (H2O2) is a key species in many environmental processes such as the electro-Fenton system to remove organic pollutants in wastewater treatment. Traditional methods for measuring H2O2 are often complex and time-consuming. Due to their low cost and high catalytic activity, transition metals (TM) can be used as high-performance electrochemical sensing materials for detecting H2O2. However, the aggregation of metal atoms will severely limit their catalytic efficiency and exposure area. In this study, we explored a method to disperse TM homogeneously on a zeolitic imidazolate framework-8 (ZIF-8) derived nitrogen-doped carbon (N/C) nanoframework and used it as the electrocatalyst for detecting H2O2 in an electro-Fenton system. Cu and Mn were used as the examples. Benefitting from the homogeneously dispersed TM, the synthesized nanoframework with a low content of TM exhibits superior electrocatalytic activity and an anti-interference ability in detecting H2O2. It has a wide linear range (0.0005–50 mM for 1% Cu–N/C and 0.0001–50 mM for 1% Mn–N/C) and a low detection limit (0.047 μM for 1% Cu–N/C and 0.036 μM for 1% Mn–N/C). Using the synthesized nanoframework, a system for continuously detecting the H2O2 concentration in an electro-Fenton system in situ was presented. The reported method to fabricate such nanomaterials with a higher catalytic efficiency of TM has implications in other applications such as environmental treatment, catalysis, and energy conversion.

Activation of Actuating Hydrogels with WS2 Nanosheets for Biomimetic Cellular Structures and Steerable Prompt Deformation

Macroscopic soft actuation is intrinsic to living organisms in nature, including slow deformation (e.g., contraction, bending, twisting, and curling) of plants motivated by microscopic swelling and shrinking of cells, and rapid motion of animals (e.g., deformation of jellyfish) motivated by cooperative nanoscale movement of motor proteins. These actuation behaviors, with an exceptional combination of tunable speed and programmable deformation direction, inspire us to design artificial soft actuators for broad applications in artificial muscles, nanofabrication, chemical valves, microlenses, soft robotics, etc. However, so far artificial soft actuators have been typically produced on the basis of poly(N-isopropylacrylamide) (PNiPAM), whose deformation is motived by volumetric shrinkage and swelling in analogue to plant cells, and exhibits sluggish actuation kinetics. In this study, alginate-exfoliated WS2 nanosheets were incorporated into ice-template-polymerized PNiPAM hydrogels with the cellular microstructures which mimic plant cells, yet the prompt steerable actuation of animals. Because of the nanosheet-reinforced pore walls formed in situ in freezing polymerization and reasonable hierarchical water channels, this cellular hybrid hydrogel achieves super deformation speed (on the order of magnitude of 10° s), controllable deformation direction, and high near-infrared light responsiveness, offering an unprecedented platform of artificial muscles for various soft robotics and devices (e.g., rotator, microvalve, aquatic swimmer, and water-lifting filter).