In this work, we report the successful synthesis of hierarchical porous carbon microrods via a one-step pyrolysis and activation treatment at different temperatures. The optimized porous carbon ...microrods have many advantages, including high specific area (2757.63 m2 g−1) with a total pore volume (1.47 cm3 g−1), high self-doping N contents, and unique porous microrod structure. As a result, the optimized porous carbon microrods show a fairly high specific capacitance of 406 F g−1 at 0.5 A g−1 (335 F g−1 at 10 A g−1) in 6 M KOH electrolyte and a good rate capability of 86.1%. Furthermore, the symmetric supercapacitor of porous carbon.
microrods with 1 M Na2SO4 electrolyte exhibits a high energy density of 26.3 W h kg−1 at a power density of 429 W kg−1. The symmetric supercapacitor also shows excellent cycle ability with a capacitance retention of 94% over 10,000 cycles. This study provides a valuable approach for preparation of electrode materials for energy storage systems by using abundant biomass.
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Graphene oxide (GO) aerogels were prepared by a unidirectional freeze-drying method (UFDM), their structure was observed and their adsorption performance for Cu2+ in aqueous solution was evaluated. ...The results show that GO aerogels have unidirectional porous structure and good adsorption ability for Cu2+. The adsorption system is depended on the Cu2+ concentration and follows a pseudo second-order kinetic model. The adsorption equilibrium is reached soon. The adsorption isotherms are simulated well by the Langmuir model. The adsorption of Cu2+ on GO aerogels is strongly dependent on pH, indicating an ion exchange mechanism. The obtained results demonstrated that the GO aerogels can be used as an effective adsorbent for Cu2+ removal from water.
An environment-friendly approach to synthesizing reduced graphene oxide (RGO) was developed by using chitosan (CS) as both a reducing and a stabilizing agent. Factors that affect the reduction of ...graphene oxide (GO), such as the ratio of CS/GO, pH and temperature, were explored to obtain optimum reaction conditions. The RGO was characterized with UV visible absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction spectroscopy, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy and transmission electron microscopy. Analysis shows that CS macromolecules can efficiently reduce GO at a comparatively low temperature and their adsorption onto the RGO nanosheets allows a stable RGO aqueous dispersion to be formed. Since CS is a natural, nontoxic and biodegradable macromolecule, this approach provides a new green method for GO reduction that would facilitate the large scale production of RGO, which has great value for graphene applications. Moreover, CS can reduce GO and AgNO3 (or HAuCl4) in one pot to obtain Ag nanoparticle-RGO hybrids or Au nanoparticle-RGO hybrids that exhibit good electrochemical activity.
Reduced graphene oxide coated polyurethane (rGPU) sponges were fabricated by a facile method. The structure and properties of these rGPU sponges were characterized by Fourier transform infrared ...spectroscopy, thermal gravimetric analysis, X-ray diffraction, and scanning electron microscopy. The rGPU sponges are hydrophobic and oleophilic and show extremely high absorption for organic liquids. For all the organic liquids tested, the absorption capacities were higher than 80 g g–1 and 160 g g–1 (the highest value) was achieved for chloroform. In addition, the absorption capacity of the rGPU sponge did not deteriorate after it was reused 50 times, so the rGPU sponge has excellent recyclability.
In this paper, we consider the signal-dependent diffusion and sensitivity in a chemotaxis–competition population system with two different signals in a two-dimensional bounded domain. We consider ...more general signal production functions and assume that the signal-dependent diffusion is a decreasing function which may be degenerate with respect to the density of the corresponding signal. We first obtain the global existence and uniform-in-time bound of classical solutions and show that the blow-up effect can be precluded for signal-dependent diffusion and sensitivity with certain properties. Then, by constructing Lyapunov functionals, we study the global attractivity of nonzero (boundary/positive) homogeneous steady states under three different strengths of competition. In particular, we obtain that the nonzero boundary constant steady states are globally asymptotically stable when they are globally attractive, which means no pattern formation occurs, while for interior constant steady state, its global attractivity can imply the global stability for some special signal production functions. Finally, numerical simulations show that for large signal sensitivity, different signal production functions can lead to various complex spatial–temporal patterns around the positive homogeneous steady state. In particular, for a given signal production mechanism, various patterns are observed for different population growth rates.
The SEM photo (a), wet-state stability (b) and effective adsorption ability for metal ions (c) of porous CGGO monoliths.
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► Ordered porous chitosan–gelatin/graphene oxide (CGGO) ...monoliths have a very high porosity (over 97%) and good stability which should make them a potentially effective adsorbent for metal ions or other chemicals, such as proteins or DNA macromolecules. And the experimental result has proved which they have an extremely high adsorbing ability for metal ions. ► Chitosan–gelatin/graphene oxide monoliths have a very high porosity (over 97%). ► They show high mechanical strength and good stability in aqueous solutions. ► They exhibit an extremely high adsorbing ability for metal ions. ► They can be recycled several times with only a slight loss in adsorption ability.
Ordered porous chitosan–gelatin/graphene oxide (CGGO) monoliths with over 97% porosity were prepared by a unidirectional freeze-drying method and used as adsorbents for metal ions. They were characterized by X-ray diffraction, scanning electron microscopy and thermogravimetric analysis. In addition, their water absorption, wet-state stability and compressive strength were measured. The adsorption behavior of the CGGO monoliths and influencing factors such as pH, graphene oxide (GO) concentration, metal ion concentration as well as the effect of ethylenediaminetetraacetic acid (EDTA) were investigated. The incorporation of GO significantly increased the compressive strength of the CGGO monoliths in both their wet and dry states, and changed their porous structure. They exhibited an extremely high adsorbing ability for metal ions, which decreased at low pH, but increased from 20% to 88% upon the addition of EDTA at low pH. The CGGO monoliths have good stability and can be recycled several times with only a slight loss in adsorption ability. In addition, they are biodegradable, non-toxic, efficient and regenerable.
•The characteristics of the fixation transition in a foggy environment are studied.•A natural driving behavior test method and noncontact eye tracker are utilized.•A wider range of visual search is ...obtained in environments with a higher visibility.•A lower visibility results in a more focused visual search range.•For a visibility <50 m, the driver’s visual search focus increases by 23.6%.
To study the fixation behavior of drivers and the characteristics of the fixation transition in the path-finding process in a foggy environment, a natural driving behavior test method and noncontact eye tracker were used to conduct a real vehicle test and obtain the fixation distribution data of drivers. Dynamic and density clustering methods were used to analyze the distribution characteristics of a driver’s fixation area and to draw the zone of interest in a foggy environment. By using a Markov chain to analyze the driver’s fixation point transition, the driver’s fixation transfer probability matrix was constructed, and the driver’s fixation transition state was obtained. When the driver was driving in an environment with low visibility, the focus of his attention was concentrated in the nearby area, and a lower visibility resulted in a more focused visual search range. When the visibility was below 50 m, the driver’s visual search focus increased by 23.6%.
We investigate the existence, structure and stability of the nonconstant steady states for a predator–prey system with density-dependent motility under the Neumann boundary condition. By applying the ...Leray–Schauder degree theory, we show that under certain conditions, a small prey diffusion rate can ensure the existence of the nonconstant steady states, which is verified by numerical simulations. Over 1D domain, we treat prey diffusion rate as a bifurcation parameter and obtain the local and global structure of steady states near the homogeneous steady states with the aid of bifurcation theory and index theory. Moreover, a stability criterion of the bifurcating steady states is also presented. Finally, we give the existence and stability of time-periodic nontrivial solutions.
Radix Codonopsis, derived from the roots of
(Franch.) Nannf.,
(Franch.) Nannf. Var.
(Nannf.) L.T. Shen and
Oliv., has been used as traditional Chinese medicine for improving poor gastrointestinal ...function, treating gastric ulcers and chronic gastritis in China. Inulin-type fructans are carbohydrates consisting mainly of β (2→1) fructosyl-fructose links in chemical structure and exhibit a range of properties such as prebiotic activity, fat substitutes in low-calorie foods and disease-modifying effects. The prebiotic effects of inulin-type fructans are hypothesized to improve gastrointestinal function through alterations to gut microbiota composition and metabolism. In the present study, three inulin-type fructans with high degree of polymerization (DP = 16, 22, and 31) were isolated from the roots of
(Franch.) Nannf. and their structures were confirmed by MALDI-TOF-MS, 1D- and 2D-NMR. The prebiotic activity of these fructans was evaluated by detecting growth stimulation on
. The results demonstrated that three fructans at a concentration of 2.0 g/L exhibited significant growth stimulation on
in a time-dependent manner (
< 0.01). The data indicated that inulin-type fructans in Radix Codonopsis could be used as potential prebiotics.
•Porous GO/CMC monoliths were prepared by a unidirectional freeze-drying method.•The incorporation of GO increased the compressive strength of the GO/CMC monoliths.•The porous GO/CMC monoliths ...exhibited a strong ability to absorb metal ions.•Ni@GO/CMC monoliths could catalyze the reduction of 4-nitrophenol to 4-aminophenol.
Orderly porous graphene oxide/carboxymethyl cellulose (GO/CMC) monoliths were prepared by a unidirectional freeze-drying method. The porous monoliths were characterized by Fourier transform infrared spectra, X-ray diffraction and scanning electron microscopy. Their properties including compressive strength and moisture adsorption were measured. The incorporation of GO changed the porous structure of the GO/CMC monoliths and significantly increased their compressive strength. The porous GO/CMC monoliths exhibited a strong ability to adsorb metal ions, and the Ni2+ ions adsorbed on GO/CMC monolith were reduced by NaBH4 to obtain Ni GO/CMC monolith which could be used as catalyst in the reduction of 4-nitrophenol to 4-aminophenol. Since CMC is biodegradable and non-toxic, the porous GO/CMC monoliths are potential environmental adsorbents.
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