Unique Three-dimensional Network Structure Research Articles

N,P-co-doped carbon nanowires prepared from bacterial cellulose for supercapacitor

We report a low cost, environmentally friendly nitrogen (N) and phosphorus (P) co-doped porous carbon nanowires derived from bacterial cellulose which acts as the efficient electrode materials for the supercapacitor. The as-prepared material exhibits a large specific capacitance of 258 F/g at a current density of 1 A/g and an excellent cycling stability of 30000 cycles. The excellent electrochemical performance is attributed to the synergistic effect of P and N doping in carbon nanowires and the unique three-dimensional network and porous structure. In addition, a symmetric supercapacitor has been fabricated by exploiting the as-prepared material as a positive electrode and negative electrode. The as-fabricated symmetric supercapacitor shows promising energy density of 5.4 Wh/kg at high power density of 200 W/kg, along with an excellent cycle stability of 87 % specific capacitance retention after 6000 cycles. The advanced specific capacitance and excellent cycle stability of the carbon nanowires imply that it could be a potential candidate in commercial applications of supercapacitors.

Bacterial cellulose nanofibrous membrane as thermal stable separator for lithium-ion batteries

Thermal shrinkage is a severe problem for the conventional polyolefin separators. In this work, we report the excellent performance of bacterial cellulose (BC) nanofibrous membranes as separators for lithium (Li) ion batteries. Properties of BC separator including morphology, ionic conductivity, electrochemical stability, thermal stability, mechanical strength and battery charge–discharge performance are characterized and compared to a commercial separator membrane (Celgard® 2325). Because of the unique fibrous and cross-linked three-dimensional network structure, BC separator shows excellent dimensional stability up to 180 °C, good ionic conductivity and competitive battery performance.

Free-standing nitrogen-doped carbon nanotubes at electrospun carbon nanofibers composite as an efficient electrocatalyst for oxygen reduction

Efficient and non-Pt catalysts are highly desirable for many kinds of electrochemical applications. Herein, we have investigated the free-standing nitrogen-doped carbon nanotubes/carbon nanofibers composite (NCNT/CNFs) as an efficient cathode catalyst for the oxygen reduction reaction (ORR). The composite with a hierarchical structure is prepared by the pyrolysis of pyridine over flexible electrospun carbon nanofibers film (CNFs) supported with the nano-Fe catalyst. Scanning electron microscopy and transmission electron microscopy characterizations indicated that the curved NCNTs are sparsely, but tightly distributed on CNF surface. The as-prepared composite displayed good catalytic activity for ORR in an alkaline medium, with a favorable four-electron pathway, better long-term stability (94.6% retention after 10000 s), selectivity and resistance to the methanol crossover compared to the powder-form NCNTs and commercial Pt/C catalyst. The improved electrochemical performance of the NCNT/CNFs can be mainly attributed to the pyridinic-N doping and unique three-dimensional network structure. The results indicate that this novel composite can be used as a promising Pt-free ORR electrocatalyst.

Facile fabrication of a three-dimensional cross-linking TiO2 nanowire network and its long-term cycling life for lithium storage.

We describe a simple preparation of amorphous TiO2 nanomaterial through a simple dealloying method with high throughput at room temperature. The as-made TiO2 sample has a unique three-dimensional network structure built by cross-linking nanowires with the diameter of ∼5 nm. As an anode material for Li-ion batteries, the TiO2 product exhibits high capacities and a long cycling life at high rates of 500 and 1000 mA g(-1). In addition, it has a good rate capability. The as-made TiO2 nanowire network shows great application potential as an anode material with the advantages of unique performance and easy preparation.

Three-dimensional polypyrrole/MnO2 composite networks deposited on graphite felt as free-standing electrode for supercapacitors

Polypyrrole/MnO2 composites with unique three-dimensional network structure were successfully deposited on graphite felt (GF) fibers at the temperature of 50°C to fabricate PYMG-HT composite, which can be used as a free-standing electrode for supercapacitors. For comparison, PYMG-LT electrode was also prepared in ice bath, and the polypyrrole/MnO2 deposits on GF prepared at 0°C exhibit nano-flower shape, which is different from PYMG-HT. The PYMG-HT electrode displays specific capacitance as high as 821.3Fg−1 at the current density of 0.5Ag−1, which is much higher than that of PPy/MnO2 reported previously. Moreover, the PYMG-HT exhibits enhanced capacitive performance compared to PYMG-LT electrode.

Carbon microfibers with hierarchical porous structure from electrospun fiber-like natural biopolymer.

Electrospinning offers a powerful route for building one-dimensional (1D) micro/nanostructures, but a common requirement for toxic or corrosive organic solvents during the preparation of precursor solution has limited their large scale synthesis and broad applications. Here we report a facile and low-cost way to prepare 1D porous carbon microfibers by using an electrospun fiber-like natural product, i.e., silk cocoon, as precursor. We surprisingly found that by utilizing a simple carbonization treatment, the cocoon microfiber can be directly transformed into 1D carbon microfiber of ca. 6 μm diameter with a unique three-dimensional porous network structure composed of interconnected carbon nanoparticles of 10~40 nm diameter. We further showed that the as-prepared carbon product presents superior electrochemical performance as binder-free electrodes of supercapacitors and good adsorption property toward organic vapor.

One template approach to synthesize C-doped titania hollow spheres with high visible-light photocatalytic activity

Carbon-doped titania hollow spheres (THS) with unique hollow three-dimensional network structure were synthesized by a facile method using carbon spheres as template. The resultant samples, such as carbon spheres, carbon spheres coated with titania precursor, and final THS were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), Brunauer–Emmett–Teller (BET) and UV–vis absorption spectrum. Based on the results of these characterizations, a reasonable formation mechanism of the hollow three-dimensional network structure was proposed. The photocatalytic activity of as-prepared THS was evaluated by decoloration of methylene blue solution under visible light irradiation. Results indicated that THS possessed higher visible light-induced photocatalytic activity than commercial P25, which could be attributed to its visible light absorption characteristic created by C-doping and the unique hollow three-dimensional network structure.

Nanomaterial/Ionophore-Based Electrode for Anodic Stripping Voltammetric Determination of Lead: An Electrochemical Sensing Platform toward Heavy Metals

A novel nanomaterial/ionophore-modified glassy carbon electrode for anodic stripping analysis of lead (Pb(2+)) is described. Nanosized hydroxyapatite (NHAP) with width of 20-25 nm and length of 50-100 nm has been prepared and used to improve the sensitivity for detection of Pb(2+) because it provides unique three-dimensional network structure and has strong adsorption ability toward Pb(2+). An ionophore, usually used in ion-selective electrodes, is utilized here for its excellent selectivity toward Pb(2+). Nafion, a cation-exchange polymer, is employed as the conductive matrix in which NHAP and the ionophore can be tightly attached to the electrode surface. Such a designed NHAP/ionophore/Nafion-modified electrode shows remarkably improved sensitivity and selectivity to Pb(2+). The electrode has a linear range of 5.0 nM to 0.8 microM with a 10 min accumulation time at open-circuit potential. The sensitivity and detection limit of the proposed sensor are 13 microA/microM and 1.0 nM, respectively. Interference from other heavy metal ions such as Cd(2+), Cu(2+), and Hg(2+) associated with lead analysis can be effectively diminished. The practical application of the proposed sensor has been carried out for determination of trace levels of Pb(2+) in real water samples.

Nafion-impregnated electrospun polyvinylidene fluoride composite membranes for direct methanol fuel cells

Composite membranes consisting of polyvinylidene fluoride (PVdF) and Nafion have been prepared by impregnating various amounts of Nafion (0.3–0.5 g) into the pores of electrospun PVdF (5 cm × 5 cm) and characterized by scanning electron microscopy, differential scanning calorimetry, X-ray diffraction, and proton conductivity measurements. The characterization data suggest that the unique three-dimensional network structure of the electrospun PVdF membrane with fully interconnected fibers is maintained in the composite membranes, offering adequate mechanical properties. Although the composite membranes exhibit lower proton conductivity than Nafion 115, the composite membrane with 0.4 g Nafion exhibits better performance than Nafion 115 in direct methanol fuel cell (DMFC) due to smaller thickness and suppressed methanol crossover from the anode to the cathode through the membrane. With the composite membranes, the cell performance increases on going from 0.3 to 0.4 g Nafion and then decreases on going to 0.5 g Nafion due to the changes in proton conductivity.

Preparation and photocatalytic degradability of TiO 2/polyacrylamide composite

Based on the unique absorbent characters and three-dimensional network structure of polyacrylamide (PAM) superabsorbent polymer, a photocatalytic degradable TiO 2/PAM composite was synthesized by an aqueous solution polymerization method with N, N′-methylene bisacrylamide as crosslinker, potassium peroxydisulfate as initiator, acrylamide as monomer, and TiO 2 (P-25) as functional filler. The photocatalytic degradability of the composite was evaluated using methyl orange as photodegradation target, and the recovery and reproducibility of the composite was investigated. It was found that TiO 2/PAM composite had a good photocatalytic degradability, the composite also possessed a good reproducibility of photocatalytic degradability, which is possible to be used in practical process.

Effect of solvent mixture on the properties of temperature- and pH-sensitive polysaccharide-based hydrogels

Novel partially biodegradable, temperature- and pH-sensitive polysaccharide-based hydrogels (NDF) were synthesized from modified dextran (dextran-maleic acid, Dex-MA) and N-isopropylacrylamide precursors over a wide range of mixed solvent ratios of dimethyl formamide (DMF) to water. N-Isopropylacrylamide monomers were chosen to impart thermo-responsive capability to Dex-MA, while Dex-MA was chosen to impart pH-responsive capability to N-isopropylacrylamide. The pH-sensitive precursor (Dex-MA) was synthesized by reacting dextran with maleic anhydride in the presence of triethylamine catalyst. To fabricate multi-stimuli hybrid hydrogel networks, both Dex-MA and N-isopropylarylamide precursors were photo-cross-linked via UV at a fixed Dex-MA to N-isopropylarylamide feed ratio over a wide range of DMF to water mixed solvent ratios. The newly synthesized PNIPAAm/Dex-MA hybrid hydrogels (NDF) were characterized by Fourier transform infrared spectroscopy for chemical structure determination, differential scanning calorimetry for thermal analysis and scanning electron microscopy for morphological study. The properties of the hybrid hydrogels, such as thermo-induced deswelling, pH-sensitivity, ionic strength sensitivity and thermoreversibility, were also examined. The swelling data obtained clearly showed that newly synthesized multi-stimuli NDF hydrogels exhibited multi-responsive capability to external stimuli like temperature and pH. The morphological data obtained showed that this new class of PNIPAAm/Dex-MA hybrid hydrogels had a wide range of unique three-dimensional porous network structures that depended on the composition ratio of the mixed DMF/water solvent during cross-linking reaction. This unique but versatile 3D porous network structures of NDF hydrogels were correlated to the data from thermo-induced swelling behavior, thermo-reversibility, pH-dependent swelling and ionic strength sensitivity.

Three-dimensional LnIII–WIVcomplexes with cyanido and carboxylato bridges

The reaction of Ln(NO3)3·6H2O with 5-methyl-2-pyrazinecarboxylic acid (Hmpca) and K4[W(CN)8]·2H2O has led to the formation of a unique three-dimensional network structure which contains open channels.

Charge-transfer complexes of benzylviologen (1,1′-dibenzyl-4,4′-bipyridinium(2+) cation) with cyanocuprate(I) and the structure of (BzV) 3Cu 9(CN) 15·H 2O

Reactions between 1,1′-dibenzyl-4,4′-bipyridinium(2+) (benzylviologen, BzV) chloride and cyanocuprates(I) gave two charge-transfer complexes having different colors: dark brown (BzV) 3Cu 9(CN) 15·H 2O and light brown (BzV)Cu(CN) 3·2H 2O. An X-ray crystal analysis of the former compound showed that nine crystallographically nonequivalent Cu atoms form three kinds of triad Cu(CN)Cu screws, which are linked by CN groups resulting in a unique three-dimensional network structure. Three of the nine Cu atoms have distorted tetrahedral (td) coordination geometries while the others have triangular plane (tp) geometries. Each screw consists of a (-tp-td-tp-) n array. There are three crystallographically nonequivalent viologen molecules. Certain CuCN moieties are located above a viologen ring or by the side of a viologen ring, with close interatomic contacts. These close contacts are characteristic of the charge-transfer complex and are responsible for the deep color of the complex.