Xiao Du

Facile preparation of ion-imprinted composite film for selective electrochemical removal of nickel(II) ions.

A facile unipolar pulse electropolymerization (UPEP) technique is successfully applied for the preparation of ion-imprinted composite film composed of ferricyanide-embedded conductive polypyrrole (FCN/PPy) for the selective electrochemical removal of heavy metal ions from wastewater. The imprinted heavy metal ions are found to be easily removed in situ from the growing film only by tactfully applying potential oscillation due to the unstable coordination of FCN to the imprinted ions. The obtained Ni(2+) ion-imprinted FCN/PPy composite film shows fast uptake/release ability for the removal of Ni(2+) ions from aqueous solution, and the adsorption equilibrium time is less than 50 s. The ion exchange capacity reaches 1.298 mmol g(-1) and retains 93.5% of its initial value even after 1000 uptake/release cycles. Separation factors of 6.3, 5.6, and 6.2 for Ni(2+)/Ca(2+), Ni(2+)/K(+), and Ni(2+)/Na(+), respectively, are obtained. These characteristics are attributed to the high identification capability of the ion-imprinted composite film for the target ions and the dual driving forces resulting from both PPy and FCN during the redox process. It is expected that the present method can be used for simple preparation of other ion-imprinted composite films for the separation and recovery of target heavy metal ions as well.

Selective catalytic conversion of bio-oil over high-silica zeolites.

Four high silica zeolites, i.e., HSZ-385, 890, 960, and 990 were utilized for the selective catalytic conversion of bio-oil from Fallopia japonica to certain chemicals in a fixed-bed reactor. The Beta-type HSZ-960 zeolite showed the highest selectivity to hydrocarbons, especially to aromatics as well as PAH compounds with the lowest unwanted chemicals while HSZ-890 showed high selectivity to aromatics. NH3-Temperature Programmed Desorption (TPD) analysis indicated that different amounts of acid sites in different zeolites determined the catalytic activity for the oxygen removal from bio-oil, in which the acid sites at low temperature (LT) region gave more contribution within the utilized temperature region. The reusability test of HSZ-960 showed the stability of hydrocarbons yield at higher temperature due to the significant contribution of coke gasification which assisted further deoxygenation of bio-oil. These results provide a guidance to select suitable zeolite catalysts for the upgrading of bio-oil in a practical process.

Facile preparation of electroactive amorphous α-ZrP/PANI hybrid film for potential-triggered adsorption of Pb2+ ions

An electroactive hybrid film composed of amorphous α-zirconium phosphate and polyaniline (α-ZrP/PANI) is controllably synthesized on carbon nanotubes (CNTs) modified Au electrodes in aqueous solution by cyclic voltammetry method. Electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM) and X-ray power diffraction (XRD) analysis are applied for the evaluation of the synthesis process. It is found that the exfoliated amorphous α-ZrP nanosheets are well dispersed in PANI and the hydrolysis of α-ZrP is successfully suppressed by controlling the exfoliation temperature and adding appropriate supporting electrolyte. The insertion/release of heavy metals into/from the film is reversibly controlled by a potential-triggered mechanism. Herein, α-ZrP, a weak solid acid, can provide an acidic micro-environment for PANI to promote the electroactivity in neutral aqueous solutions. Especially, the hybrid film shows excellent potential-triggered adsorption of Pb(2+) ion due to the selective complexation of Pb(2+) ion with oxygen derived from P-O-H of α-ZrP. Also, it shows long-term cycle stability and rapid potential-responsive adsorption/desorption rate. This kind of novel hybrid film is expected to be a promising potential-triggered ESIX material for separation and recovery of heavy metal ions from wastewater.

Electroactive ion exchange materials: current status in synthesis, applications and future prospects

Electroactive ion exchange materials (EIXMs) with unique electrochemically switched ion exchange function have been extensively applied in various fields including high value-added ion recovery, toxic ion removal, energy storage devices and electrochemical ion sensors. In particular, the charge and discharge of EIXMs can be electrochemically controlled by an external electric field or by a redox agent while the charge balance is compensated via the ion exchange with electrolyte solution. To date, the discovered EIXMs mainly involve inorganic compounds with mixed-valence transition metals, organic conducting polymers and organic–inorganic hybrid materials. Compared with their bulk forms, nanostructured EIXMs have aroused considerable research interest recently owing to their unique properties such as larger surface area, better ion diffusion path and excellent electron transfer property. In this article, the design principles and synthetic routes for the development of various nanostructured EIXMs and their applications in the fields of selective ion separation, supercapacitors and electrochemical ion sensors are reviewed. In addition, the main challenges and future prospects for the further development of high-performance EIXMs are discussed.

Homogeneous nanosheet Co3O4 film prepared by novel unipolar pulse electro-deposition method for electrochemical water splitting

A unipolar pulse electro-deposition (UPED) method is used to prepare nanosheet Co3O4 film on a carbon rod substrate in aqueous solution and compared with other conventional methods, i.e., the cyclic voltammetry (CV) method, potentiostatic method (PM) and pulse potentiostatic method (PPM). Co3O4 films prepared by the UPED method show a more uniform structure on carbon rod and higher catalytic activity than those by other methods, and oxygen evolution reaction over it with an overpotential of 275 ± 2.3 mV results in a current density of 10 mA cm−2 in 1.0 mol L−1 KOH. Such an excellent performance should be attributed to its highly porous nanosheet structure with honeycomb-like morphology.

Cobalt hydroxide [Co(OH)2] loaded carbon fiber flexible electrode for high performance supercapacitor

Cobalt hydroxide nanoflakes are uniformly loaded on flexible carbon fiber (CF) paper, and provide good electrical connectivity to the current collector for use as supercapacitors. The unique porous nanostructure offers low ion diffusion and charge transfer resistance in the electrode. The effect of loading mass on electrochemical properties is investigated. The electrode with a mass loading of 2.5 mg cm−2 shows the maximum specific capacitance of 386.5 F g−1 at a current density of 1 mA cm−2. Also the same electrode provides a good rate capability with energy and power densities of 133.5 W h kg−1 and 1769 W kg−1, respectively even at a higher current density of 10 mA cm−2. The electrode reveals a cyclic stability of 92% over 2000 cycles. This kind of flexible, lightweight electrode could be effectively utilized for flexible supercapacitor fabrication, especially for wearable electronics.

A novel electroactive λ-MnO2/PPy/PSS core–shell nanorod coated electrode for selective recovery of lithium ions at low concentration

A novel electroactive Li+ ion-imprinted hybrid film consisting of λ-MnO2/PPy/PSS core–shell nanorods is successfully fabricated on an electrode by using the unipolar pulse electrodeposition (UPED) technique. When the electrode is applied for selective electrochemical extraction of low concentrations of Li+ ions from aqueous solutions via an electrochemically switched ion exchange (ESIX) process, the Li+ ion adsorption capacity reaches 35.2 mg g−1 with an adsorption equilibrium time of less than 2 h. The excellent ion separation performance of this hybrid film should be attributed to its low ion transfer resistance due to its porous structure and the high electric driving force during the ESIX process. In particular, owing to the unique Li+ ion imprinted vacant sites in the crystal structure of spinel λ-MnO2 nanorods, the selectivity factor for Li+/Na+ reaches 46.0 with a molar ratio of 1 : 1. It is expected that this λ-MnO2/PPy/PSS hybrid film can be applied as a promising electroactive material for effective separation of Li+ ions from seawater.

A green method to increase yield and quality of bio-oil: ultrasonic pretreatment of biomass and catalytic upgrading of bio-oil over metal (Cu, Fe and/or Zn)/γ-Al2O3

A green method is developed to increase the yield and quality of bio-oil by ultrasonic pretreatment of biomass followed by in situ catalytic upgrading of bio-oil over metal (Cu, Fe and/or Zn)/γ-Al2O3. It is found that the yield of bio-oil is increased up to 10 wt% after cedar is pretreated by ultrasound before pyrolysis. Various metals (Cu, Fe and Zn) are loaded on γ-Al2O3 and applied for upgrading the bio-oil derived from the pyrolysis of pretreated cedar. It is found that the catalysts promote the conversion of oxygenated compounds into aromatic and aliphatic hydrocarbons. In particular, production of monocyclic aromatic hydrocarbons such as benzene and toluene is favored. The best catalytic activity is achieved by using 2.5 wt% Zn/γ-Al2O3 with a maximum hydrocarbon yield of 80.3%. The catalyst is reused for up to four cycles. The results show that the catalysts after regeneration by calcination at 550 °C for 30 min exhibit long-term stability for upgrading of bio-oil.

Silver-doped molybdenum carbide catalyst with high activity for electrochemical water splitting

A hybrid catalyst composed of silver (Ag) doped wire-like molybdenum carbide (MoxCy) with pure β-phase and carbon nanotubes (CNTs) was coated well on a carbon rod electrode for the hydrogen evolution reaction (HER). The effects of Ag loading amount and carbonization temperature on the crystal form of MoxCy were investigated in detail. It is found that the MoxCy crystal form can be tuned by adjusting the preparation conditions, and nanostructured wire-like Mo2C with pure β-phase was obtained at a temperature over 750 °C. Ag/MoxCy composite nanomaterials were investigated by X-ray diffraction, UV/vis spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy and Brunauer-Emmett-Teller surface area analysis. The hybrid catalyst was further deposited on the carbon nanotube (CNT) modified carbon rod substrate. Due to the high surface area and 3D porous network-like microstructure, the Ag/Mo2C/CNTs hybrid electrode showed enhanced catalytic performance when comparing with the corresponding pure one. Particularly, for the Ag-doped Mo2C/CNTs hybrid electrode with an optimum 1 Ag : 5 Mo molar ratio of the precursors, a current density of 10 mA cm-2 was obtained by applying an overpotential of 142 mV in 0.5 mol L-1 H2SO4 solution. It is expected that such a hybrid electrode can be widely applied for effective electrolysis of water to produce hydrogen.

Unique allosteric effect-driven rapid adsorption of carbon dioxide in a newly designed ionogel [P4444][2-Op]@MCM-41 with excellent cyclic stability and loading-dependent capacity

To achieve low cost, high rate and attractive capacity of CO2 adsorption by using ionic liquids (IL), a new mesostructured ionogel, pyridine-containing anion functionalized IL tetrabutylphosphonium 2-hydroxypyridine ([P4444][2-Op]) encapsulated silica MCM-41 (noted as PM-w), is fabricated by loading the IL [P4444][2-Op] with multiple active sites into porous silica MCM-41 through a simple moisture-controlled impregnation–evaporation method. Allosteric effect driven gas sorption on the electronegative oxygen and nitrogen atoms of the nanoconfined IL [P4444][2-Op] makes it take no more than 2 min for the ionogel PM-5 to achieve the 90% of saturated adsorption capacity. The corresponding adsorption rate is 30 times faster than that of the bulk IL. The ionogel PM-5 with the low IL loading of 5.0% shows the highest CO2 adsorption capacity up to 1.21 mmol (g-ionogel)−1 (14.89 mmol (g-IL)−1) at 50 °C in a gas mixture with N2, which is 9.25 times higher than that of the pure IL. Its excellent cyclic stability of more than 96% of the initial CO2 uptake repeatedly displayed after performing 10 cycles of adsorption–desorption tests. The enhanced thermal stability up to 450 °C in N2 is observed for the low loading ionogels since the strong interfacial layering of the IL prefers to dot the silica nanopores as monomolecular islands. Reversely, the high loading IL may aggregate into nanosized clusters that recover the poor thermal stability of the bulk IL. Reasonable decreases in their surface area, pore volume and pore size are observed with the IL loading up to 45%. They still exhibit highly ordered hexagonal mesostructures. The features of low loading and cost, rapid adsorption, high capacity and excellent cyclic stability make the ionogel PM-5 a competitive candidate in CO2 capture from flue gas.