This article investigates the removal of ammonium from aqueous solutions using zeolite synthesized from fly ash by a fusion method, which combines alkaline fusion followed by hydrothermal treatment. The cation exchange capacity increases from 0.03 to 2.79 meq/g during the synthesis process. The effects of contact time, pH, initial ammonium concentration, adsorbent dosage, and the presence of other cations and anions are examined by batch experiments. The findings show that these parameters have significant effects on the ammonium removal using the synthesized zeolite. The effect of cations follows the order K . The Lagergren first-order, Ho' pseudo-second-order, and intraparticle diffusion kinetic models are employed to describe the kinetic data, and Ho' pseudo-second-order model provides excellent fitting. The equilibrium isotherm data are fitted to the Langmuir, Freundlich, Koble-Corrigan, Tempkin and Dubinin-Radushkevich models; the Koble-Corrigan model gives the best fit. The thermodynamic study reveals that ammonium uptake by the synthesized zeolite is an exothermic reaction. The maximum ammonium uptake capacity obtained is 24.3 mg/g. The regenerated zeolite has almost the same ammonium uptake capacity as the original zeolite. These results indicate that the synthesized zeolite is a promising material for removing ammonium from wastewater.

Two interfaces with opposite orientations of the built-in electric field, nanoporous TiO(2) film/ FTO electrode and nanoporous TiO(2) film/semitransparent Pt substrate, were constructed. The separation and transport of photo-induced charge carriers in the two systems of nanoporous TiO(2)/conductive substrate were studied by the transient photovoltage technique. Various transient photovoltage responses were obtained when the laser beam was incident from the surface of the nanoporous TiO(2) film (top illumination) or the TiO(2)/substrate interface (bottom illumination). A linear and a logarithmic dependence of the photovoltage amplitude on the excitation level were observed for top illumination and bottom illumination, respectively. The results indicate that diffusion is the major way for the separation of charge carriers in the nanoporous TiO(2) film and that the excess carriers were separated by drift under the built-in electric field at the TiO(2)/substrate interfaces.

Transition metal oxide hetero-structure has great potential for multifunctional devices. However, the degraded physical properties at interface, known as dead-layer behavior, present a main obstacle for device applications. Here we present the systematic study of the dead-layer behavior in La 0.67 Sr 0.33 MnO 3 thin film grown on SrTiO 3 substrate with ozone assisted molecular beam epitaxy. We found that the evolution of electric and magnetic properties as a function of thickness shows a remarkable resemblance to the phase diagram as a function of doping for bulk materials, providing compelling evidences of the hole depletion in near interface layers that causes dead-layer. Detailed electronic and surface structure studies indicate that the hole depletion is due to the intrinsic oxygen vacancy formation. Furthermore, we show that oxygen vacancies are partly caused by interfacial electric dipolar field, and thus by dopingengineering at the single-atomic-layer level, we demonstrate the dead-layer reduction in films with higher interfacial hole concentration. PACS numbers: 75.47.Lx, 75.30.Kz, 79.60.Dp The complexity in transition metal oxides and their heterostructures, due to the entangled correlation of charge, spin, orbital, and lattice degrees of freedom, is a double-edged sword. On one hand, it brings out emergent phenomena in condensed matter physics 1-4 and various possibilities for multifunctional device applications 5,6 . On the other hand, it often conceals the physical mechanism of new phenomena due to theoretical difficulties and hinders the solutions to problems in device applications. One typical example is La 0.67 Sr 0.33 MnO 3 /SrTiO 3 (LSMO/STO) hetero-structure. LSMO is well-known for the colossal magnetoresistance, half metallic behavior, room temperature ferromagnetism, and high conductivity. These exotic properties make LSMO the most promising material for metal-based spintronic device, magneto-tunneling junctions, magnetic memory, etc. Success has been achieved in developing LSMO-based field effect transistors 7 and metal-base transistors 8 . However, in spite of a few reported working devices, a large variety of applications are restricted due to the dead-layer behavior, that is, the degraded ferromagnetism and metallicity with decreasing thickness and eventually insulating below certain critical thickness 9,10 . Therefore, it is crucial to investigate the mechanism of the dead-layer behavior in LSMO/STO, for both device application and fundamental understanding of oxide interface.Intensive studies have been conducted, and several scenarios have been proposed to explain the dead-layer behavior, such as magnetic 11,12 and orbital reconstruction at the interface [13][14][15] , and substrate-induced strain 10,16 . However, the situation is still very perplexing, and many issues remain to be understood. For example, it is not clear why the complicated electric and magnetic properties in ultra-thin films are extremely sensitive to film thickness. Extrinsic imperfections induced during fabricati...

Keywords:Low-calcium fly ash High-calcium fly ash Synthesized zeolite Ammonium removal Select criteria of raw fly ash In this study, zeolites are synthesized from low-calcium (LC-Z) and high-calcium (HC-Z) fly ashes, respectively. The changes of mineralogy, morphology, cation exchange capacity (CEC) and specific surface area (SSA) are investigated during the synthesis process. The equilibrium uptake of ammonium on the two synthesized zeolites is compared. The main crystals of LC-Z and HC-Z are identified as faujasite and gismondine, respectively. The CEC and SSA increase significantly following the conversion process. The kinetic studies showed that the adsorption process of ammonium on both LC-Z and HC-Z follows Ho's pseudosecond-order model. Langmuir model agrees better with the equilibrium data for LC-Z, while Freundlich model gives the better fit for HC-Z. The obtained maximum ammonium uptake capacities are 23.8 mg/g for LC-Z and 3.17 mg/g for HC-Z in the synthetic solution. LC-Z also exhibits much better performance in ammonium uptake in effluent from a sewage treatment plant than HC-Z. These results indicate that LC-Z is a promising material for ammonium removal whereas HC-Z is not. The Ca 2+ leaching and the lower zeolite content in HC-Z account for its lower uptake capacity. Thus, the low-calcium fly ash should be chosen preferentially as the raw material of the zeolite synthesis for ammonium removal.

The high piezoelectricity of ABO3-type lead-free piezoelectric materials can be achieved with the help of either morphotropic phase boundary (MPB) or polymorphic phase transition (PPT). Here, we propose a new defect engineering route to the excellent piezoelectric properties, in which doped smaller acceptor and donor ions substituting bivalent A-sites are utilized to bring local lattice distortion and lower symmetry. A concrete paradigm is presented, (Li-Al) codoped BaTiO3 perovskite, that exhibits a largely thermo-stable piezoelectric constant (>300 pC/N) and huge mechanical quality factor (>2000). A systematic analysis including theoretical analysis and simulation results indicates that the Li(+) and Al(3+) ions are inclined to occupy the neighboring A-sites in the lattice and constitute a defect dipole (ionic pairs). The defect dipoles possess a kind of dipole moment which tends to align directionally after thermo-electric treatment. A mechanism related to the defect symmetry principle, phase transition, and defect migration is proposed to explain the outstanding piezoelectric properties. The present study opens a new development window for excellent piezoelectricity and provides a promising route to the potential utilization of lead-free piezoelectrics in high power applications.

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