Zhonglin Zhang

Separation of low concentration of cesium ion from wastewater by electrochemically switched ion exchange method: Experimental adsorption kinetics analysis

A series of experiments were performed to evaluate the continuous separation of cesium based on an electrochemically switched ion exchange (ESIX) process using a diaphragm-isolated reactor with two identical nickel hexacyanoferrate/porous three-dimensional carbon felt (NiHCF/PTCF) electrodes as working electrodes. The effects of applied potential, initial concentrations and pH values of the simulation solutions on the adsorption of cesium ion were investigated. The adsorption rate of cesium ion in the ESIX process was fitted by a pseudo-first-order reaction model. The experiments revealed that the introduction of applied potential on the electrodes greatly enhanced the adsorption/desorption rate of Cs(+) and increased the separation efficiency. H(3)O(+) was found to play a dual role of electrolyte and competitor, and the adsorption rate constant showed a curve diversification with an increase in pH value. Also, it was found that the electrochemically switched adsorption process of Cs(+) by NiHCF/PTCF electrodes proceeded in two main steps, i.e., an ESIX step with a fast adsorption rate and an ion diffusion step with a slow diffusion rate. Meanwhile, the NiHCF/PTCF film electrode showed adsorption selectivity for Cs(+) in preference to Na(+).

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.

Mild catalytic depolymerization of low rank coals: a novel way to increase tar yield

Mild catalytic depolymerization of two kinds of low-rank coals named as Neimeng and Xinjiang coals sprayed with Mo- and Fe-based catalysts were performed in a batch reactor. The obtained tar was analyzed by gas chromatography/mass spectrometry (GC/MS), and the coal and char were characterized by Raman and Fourier transform infrared spectroscopy (FTIR). The results indicated that the tar yields for Neimeng coal were increased from 3.6% to 5.0% and 7.8% while those for Xinjiang coal were increased from 8.1% to 11.4% and 10.9% after the addition of Mo- and Fe-based catalysts, respectively. Based on the GC/MS analysis, it is found that the hydroxybenzene content was significantly decreased while naphthalene content was increased in the tar derived from Neimeng coal when the Mo-based catalyst was used. In contrast, the production of light aromatics was enhanced by the addition of Fe-based catalyst. For comparison, the production of aromatics from Xinjiang coal was remarkably inhibited but the content of aliphatic hydrocarbon was significantly increased after the addition of the catalyst. The Raman and FTIR analyses results indicated that the catalyst could improve the reaction of hydrogen free radicals with char, which was beneficial to the depolymerization of coal.

Continuous Separation of Cesium Based on NiHCF/PTCF Electrode by Electrochemically Switched Ion Exchange

Abstract Nickel hexacyanoferrate (NiHCF) film was synthesized on porous three-dimensional carbon felt (PTCF) substrate by repetitious batch chemical depositions, and the NiHCF/PTCF electrode was used as electrochemically switched ion exchange (ESIX) electrode in a packed bed for continuous separation for cesium ions. The morphologies of the prepared electrodes were characterized by scanning electron microscopy and the effects of solution concentration on the ion-exchange capacity of the electrodes were investigated by cyclic voltammetry technique. Cycling stability and long-term storage stability of NiHCF/PTCF electrodes were also studied. The NiHCF/PTCF electrodes with excellent ion-exchange ability were used to assemble a diaphragm-isolated ESIX reactor for cesium separation. Continuous separation of cesium and regeneration of NiHCF/PTCF electrode based on the diaphragm-isolated reactor were performed in a laboratory-scale two-electrode system.

Performance of Pt/C Doped with Ni for Oxygen Electro-Reduction in Alkaline Media

Abstract Carbon-supported Pt-Ni catalyst samples were prepared by the colloidal method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopic (XPS) and transmission electron microscopy (TEM). Potentiodynamic was used to measure the performance of the electro-catalysts for the oxygen electro-reduction. The results indicate that the Pt-Ni alloy particles are distributed homogeneously on the carbon surface, and their particle sizes are 3−5 nm. In the same alkali concentration solution, the activity and methanol-tolerance of Pt nano-particle catalysts are greatly enhanced by doping Ni. For the catalyst, the optimum atom ratio of Pt to Ni is Pt 50 Ni 50 /C, and its methanol-tolerance is enhanced markedly as compared with Pt/C. The maximal current of the oxygen electro-reduction over Pt 50 Ni 50 /C reaches 106 mA/mg, and the onset over potential is 50 mV less than that over Pt/C in 0.1 mol/L KOH solution.

Electrochemical Characterization of Ion Selectivity in Electrodeposited Nickel Hexacyanoferrate Thin Films

The ion selectivity of electrodeposited nickel hexacyanoferrate (NiHCF) thin films was investigated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). NiHCF thin films were prepared by cathodic deposition on Pt and Al substrates. EJS and CV curves were determined in 1 mol/L (KNO3+CsNO3) and 1 mol/L (NaNO3+CsNO3) mixture solutions, which were sensitive to the concentration of Cs(superscript +) in the electrolytes. Experimental results show that all Nyquist impedance plots show depressed semicircies in the high-frequency range changing over into straight lines at lower frequencies. With increasing amounts of Cs(superscript +), the redox potentials in CV curves shift toward more positive values and the redox peaks broaden; the semicircle radius in corresponding EIS curves and the charge transfer resistance also increase. EIS combining CV is able to provide valuable insights into the ion selectivity of NiHCF thin films.

Potential-induced reversible uptake/release of perchlorate from wastewater by polypyrrole@CoNi-layered double hydroxide modified electrode with proton-ligand effect

In this study, CoNi-layered double hydroxide (CoNi-LDH) nanosheets coated conducting polypyrrole (PPy) nanowire was controllably fabricated on Pt plate or carbon cloth by using unipolar pulse electrodeposition (UPED) method and served as a novel electrochemically switched ion exchange (ESIX) hybrid film with proton-ligand effect for the removal of perchlorate anions (ClO4-). It is expected that the space among CoNi-LDH nanosheets of the shell could act as the reservoir for the anions while the PPy core serve as the potential-induced element for proton-ligand. The effects of pulse potential during film deposition and initial pH of the wastewater on the ClO4- removal performance of this core-shell hybrid film were investigated. It is found that ClO4- adsorption onto PPy@CoNi-LDH followed pseudo-second-order model, and the film fabricated with -1.5 V pulse potential showed an excellent performance for the rapid removal of ClO4- with a high selectivity, and the ClO4- adsorption quantity reached as high as 302 mg g-1. In a wide pH range (3-10), the hybrid film removed ClO4- efficiently. The proton-ligand effect in PPy@CoNi-LDH was proved by using XPS analysis and density functional theory. Such a PPy@CoNi-LDH hybrid core-shell film should be a potential electroactive material for the separation of ClO4- and other anions from wastewater.

Catalytic depolymerization of a typical lignite for improving tar yield by Co and Zn catalyst

A novel process for improving tar yield through catalytic depolymerization of a typical lignite was put forward. The catalytic depolymerization of the lignite over CoCl2 and ZnCl2 catalyst in different concentrations were investigated by a Gray-King apparatus. The optimal catalyst concentrations of CoCl2 and ZnCl2 catalyst that could obtain the highest tar yield was achieved, by which the tar yield increased about 20.3% and 6.6% compared with that of the raw coal, respectively. Different with the traditional catalytic pyrolysis process for which the tar yield decreased, more tar was produced by the catalytic depolymerization method. The GC × GC-MS analysis showed that the components of alkanes and two-ring aromatics in tar increased dramatically with the addition of the optimal CoCl2 and ZnCl2 catalyst. The Raman measurement revealed that more large aromatic ring systems ( > 6 rings) were formed in the char from depolymerization with catalyst and the elemental analysis showed that the hydrogen content decreased slightly. The gas products analysis reflected the contents of methane showed an obvious decrease. All of this reflects that more fragments and small free radicals cracked were enhanced by catalysis in the catalytic depolymerization process, thereby leading to an enhancement of the tar formation possibilities.