Al-doped ZnO powdered materials: Al solubility limit and IR absorption properties

Al-doped ZnO powder was synthesized via the Pechini route with a doping rate varying from 1 to 4 mol.%. A solubility limit has been estimated under 0.3 mol.% of Al using X-ray diffraction refinements. The incorporation of aluminium into the ZnO lattice was investigated by ²⁷Al NMR, which suggests an extremely low amount of Al in a distribution of sites in ZnO. In order to assess the impact of such a low dopant amount, diffuse reflection experiments were performed for a wavelength range from 200 to 2500 nm. If the effect of doping was negligible for samples prepared at 850 °C, annealing at 1200 °C clearly reveals enhanced IR absorption properties for the doped samples, which are similar whatever be the nominal Al content.     

Reticular Sn nanoparticle-dispersed PAN-based carbon nanofibers for anode material in rechargeable lithium-ion batteries

Reticular tin nanoparticle-dispersed carbon (Sn/C) nanofibers were fabricated by stabilization of electrospun SnCl₄/PAN composite fibers and subsequent carbonization at different temperatures. These Sn/C composite nanofibers used as anode materials for rechargeable lithium-ion batteries (LIBs) show that the Sn/C nanofibers at 700 and 850 °C present much higher charge (785.8 and 811 mA h g^?1) and discharge (1211.7 and 993 mA h g^?1) capacities than those at 550 and 1000 °C and the as-received CNFs at 850 °C, corresponding to coulombic efficiencies of 64.9% and 81.7%, respectively. The superior electrochemical properties of the intriguing Sn/C nanofibers indicate a promising application in high performance Li-ion batteries.     

Pervaporation separation of methanol/methyl t-butyl ether through chitosan composite membrane modified with surfactants

We investigated the efficiency of pervaporation separation of methanol/methyl-t-butyl ether (MTBE) mixture through chitosan composite membrane modified with sulfuric acid and four surfactants. Effects of feed concentration, temperature, crosslinking degree and type of surfactants were studied. The chitosan composite membrane modified with sulfuric acid showed the pervaporation performance of over 70 wt% methanol in the permeate and flux of 100 g/m² h measured at 25°C. At 50°C, the separation factor decreased while the flux increased exceeding 300 g/m² h. For the membrane complexed with surfactants, the permeate showed 98.3 wt% methanol concentration and 470 g/m² h of permeate flux at 25°C. With increasing operating temperature, the permeate flux remarkably increased to 1170 g/m² h and the permeate showed 97.8 wt% methanol concentrations.     

Macro- and microporous carbon monoliths with high surface areas pyrolyzed from poly(divinylbenzene) networks

Carbon monoliths with well-defined macropores and high surface areas were prepared by carbonization of macroporous poly(divinylbenzene) (PDVB) monoliths. The carbonization reactions of PDVB networks are studied by thermal analysis and FT-IR measurements. According to the measurement results, the PDVB networks are mostly pyrolyzed at 430 °C and their structures dynamically change to graphite-like structure between 600 and 700 °C. The macropore structure retained while the mesopores disappeared after carbonization. In addition, the surface area of the obtained carbons dramatically increased over 900 °C. The typical carbon monolith carbonized at 1000 °C for 2 h had a surface area of 1500 m² g^?1 and uniform macropores with a diameter of 1 μm.     

Study of CuZnMOx oxides (M = Al,Zr, Ce,CeZr) for the catalytic hydrogenation of CO2 into methanol

CuO–ZnO–Al₂O₃ catalysts were synthesized by two methods, sol–gel and co-precipitation syntheses. Al₂O₃ was then substituted with other supports, such as ZrO₂, CeO₂ and CeO₂–ZrO₂ in order to have a better understanding of the support's effect. These catalysts containing 30 wt% of Cu were then tested for CO₂ hydrogenation into methanol. The effect of reaction temperature and GHSV on the catalytic behaviour was also investigated. The best results were obtained with a 30 CuO–ZnO–ZrO₂ catalyst synthesized by co-precipitation and calcined at 400 °C. This catalyst presents a good CO₂ conversion rate (23%) with 33% of methanol selectivity, leading to a methanol productivity of 331 g_MeOH.kg_cata⁻¹·h⁻¹ at 280 °C under 50 bar and a GHSV of 10,000 h⁻¹.     

Effects of H3PO4 and KOH in carbonization of lignocellulosic material

Samples of lignocellulosic material, stem of date palm (Phoenix dactylifera), were carbonized at different temperatures (400–600 °C) to investigate the effects of their impregnation with aqueous solution of either phosphoric acid (85 wt%) or potassium hydroxide (3 wt%). The products were characterized using BET nitrogen adsorption, helium pycnometry, Scanning Electron Microscopy (SEM) and oil adsorption from oil–water emulsion (oil viscosity, 60 mPa s at 25 °C). True densities of the products generally increased with increase in carbonization temperature. Impregnated samples (acid/base) showed wider differences in densities at 400 (1.978/1.375 g/cm³) than at 600 °C (1.955/2.010 g/cm³). Without impregnation, the sample carbonized at 600 °C showed higher density of 2.190 g/cm³. This sample has impervious surface with BET surface area of 124 m²/g. Acid-impregnated sample carbonized at 500 °C has the highest surface area of 1100 m²/g and most regular pores as evidenced by SEM micrographs. The amounts of oil adsorbed decreased with increase in carbonization temperature. Without impregnation, sample carbonized at 400 °C exhibited equilibrium adsorption of 4 g/g which decreases to about a half for sample carbonized at 600 °C. Impregnation led to different adsorptive capacities. There are respective increase (48 wt%) and decrease (5 wt%) by the acid- or base-impregnated samples carbonized at 600 °C. This suggests higher occurrence of oil adsorption-enhancing surface functional groups such as carbonyl, carboxyl and phenolic in the former sample.     

Optical and Raman studies of Zn1-xMgxO ceramic pellets

The undoped and Mg-doped ZnO ceramics have been successfully synthesized using the conventional solid state sintering method. The doping effect of MgO content on the structural properties of ZnO/MgO composites has been investigated by X-ray diffraction (XRD) and Raman spectroscopy. The XRD patterns reveal that all the samples are polycrystalline and have a prominent hexagonal crystalline structure with (002) and (101) as preferred growth directions. The formation of the hexagonal ZnMgO alloy phase and the segregation of MgO-cubic phase took place for an MgO composition x ≥ 20 wt%. This finding is in good agreement with the Raman spectroscopy measurements which prove the existence of multiple-order Raman peaks originating from ZnO-like and MgO phonons. The band gap energy and the carrier concentration of ZnO pellets were found to be dependent upon the Mg doping whose values vary from 3.287 to 3.827 eV and from 1.6 × 10¹⁷ to 5.2 × 10²⁰ cm⁻³, respectively.     

Cobalt-free cathode material SrFe0.9Nb0.1O3−δ for intermediate-temperature solid oxide fuel cells

A cobalt-free cubic perovskite oxide, SrFe_0.9Nb_0.1O_3?δ (SFN) was investigated as a cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD results showed that SFN cathode was chemically compatible with the electrolyte Sm_0.2Ce_0.8O_1.9 (SDC) for temperatures up to 1050 °C. The electrical conductivity of SFN sample reached 34–70 S cm^?1 in the commonly operated temperatures of IT-SOFCs (600–800 °C). The area specific resistance was 0.138 Ω cm² for SFN cathode on SDC electrolyte at 750 °C. A maximum power density of 407 mW cm^?2 was obtained at 800 °C for single-cell with 300 μm thick SDC electrolyte and SFN cathode.     

Electrochemical synthesis of orientation-ordered ZnO nanorod bundles

The high density and orientation-ordered ZnO nanorod bundles with wurtzite structures were prepared on Cu substrates by electrochemical deposition in solution of ZnCl₂ + tartaric acid at a temperature of 90 °C. This approach is a unique and size controlled synthetic method for the large-scale preparation of ZnO nanorod bundles. Cyclic voltammogram measured in solution of the mixture of ZnCl₂ and tartaric acid shows a restraining role of tartaric acid for the electro-reduction of Zn(II). The formation mechanism of ZnO on the surface of the cathode can be explained that the high temperature (⩾90 °C) promotes the corrosion of electrodeposited Zn via reacting with H₂O and O₂ to form the stable passive phase of ZnO. The compositions of the nanorod bundles can be entirely ZnO or Zn and ZnO composites determined by the temperature and deposition rate. The photoluminescence (PL) properties indicate that these ZnO deposits are highly crystallized and of excellent optical quality.     

Synthesis and characterization of layered zinc hydroxychlorides

Layered material of zinc hydroxychlorides (Zn₅(OH)₈Cl₂·nH₂O: ZHC), which is one of the basic zinc salts (BZS), was synthesized from ZnO nano-particles aged with aqueous ZnCl₂ solutions at different temperatures ranging from 6 to 140 °C for 48 h. X-ray diffraction (XRD) results indicated that the diffraction peaks of ZnO completely disappeared by aging at 6 °C and the ZHC peaks were developed. By increasing the aging temperature, crystallinity of the layered structure was improved. At 6 °C, the ZHC particles were thin hexagonal plate particles with sizes ranging from 1 to 3 μm. The particle size of ZHC was independent of aging temperature. The atomic Cl/Zn ratios of all the ZHC materials were almost 0.2 less than 0.4 of the theoretical ratio, indicating that the synthetic ZHC is Cl-deficient. It seemed that half of Cl atoms in the layer were replaced with HCO₃⁻ and/or OH⁻. The specific surface areas of ZHC estimated from N₂ adsorption isotherms were ca. 10 m² g⁻¹ and were independent of the aging temperature. However, the H₂O monolayer adsorption capacity per unit surface area (n_w) for all the samples was higher than that of ZnO particles, revealing the high affinity of ZHC to H₂O molecules. The n_w values were increased by reducing the crystallinity of ZHC. This enhancement of H₂O adsorption selectivity was thought to be related with less-crystallized parts of the particles.     

Proton-conducting membranes based on poly(2,5-benzimidazole) (ABPBI) and phosphoric acid prepared by direct acid casting

We report the preparation of phosphoric acid doped poly(2,5-benzimidazole) (ABPBI) membranes for PEMFC by simultaneously doping and casting from a poly(2,5-benzimidazole)/phosphoric acid/methanesulfonic acid (MSA) solution. The evaporation of MSA yields a very homogeneous membrane having a better controlled composition, avoiding the use of solvent-intensive procedures. Membranes have been prepared with contents of up to 3.0H₃PO₄ molecules per ABPBI repeating unit. These membranes achieve a maximum conductivity of 1.5 × 10⁻² S cm⁻¹ at temperatures as high as 180 °C in dry conditions. These ABPBI membranes are more conveniently prepared than those conventionally formed and doped in separate steps while featuring comparable conductivities (ABPBI × 2.7H₃PO₄ prepared by the soaking method showed a conductivity of 2.5 × 10⁻² S cm⁻¹ at 180 °C in dry conditions).     

Low-temperature chemical bath deposition of crystalline ZnO

ZnO crystals can be grown from alkaline aqueous solution not only by the standard hydrothermal technique at temperatures between 350 °C and 400 °C, but also by chemical bath deposition (CBD) at temperatures below 100 °C. In the presence of ZnO and ScAlMgO₄ (SCAM) substrates almost all ZnO deposits on the substrate, with different habits, however. Under optimized conditions even homoepitaxial layers can be obtained, while rod-like structures are obtained on SCAM substrates. The chemistry and the driving forces behind the two processes are considered in detail and the temperature dependence of the solution composition has been calculated. The driving force for the ZnO crystal growth in the standard hydrothermal technique is the difference in the ZnO solubility in alkaline solutions at different temperatures. In contrast, the driving force for the chemical bath deposition of ZnO at low temperatures is the decay of zinc ion complex molecules with increasing temperature.     

Thermal decomposition pathway of undoped and doped zinc layered gallate nanohybrid with Fe3+, Co2+ and Ni2+ to produce mesoporous and high pore volume carbon material

A series of brucite-like materials, undoped and doped zinc layered hydroxide nitrate with 2% (molar) Fe³⁺, Co²⁺ and Ni²⁺ were synthesized. Organic–inorganic nanohybrid material with gallate anion as a guest, and zinc hydroxide nitrate, as an inorganic layered host was prepared by the ion-exchange method. The nanohybrid materials were heat-treated at various temperatures, 400–700 °C. X-ray diffraction, thermal analysis and also Fourier transform infrared results showed that incorporation of the doping agents within the zinc layered hydroxide salt layers has enhanced the heat-resistivity of the nanohybrid materials in the thermal decomposition pathway. Porous carbon materials can be obtained from the heat-treating the nanohybrids at 600 and 700 °C. Calcination of the nanohybrids at 700 °C under nitrogen atmosphere produces mesoporous and high pore volume carbon materials.     

A simple method of electrochemical lithium intercalation within graphite from a propylene carbonate-based solution

Electrochemical lithium intercalation within graphite from 1 mol dm^− 3 solution of LiClO₄ in propylene carbonate (PC) was investigated at 25 and − 15 °C. Lithium ions were intercalated into and de-intercalated from graphite reversibly at − 15 °C despite the use of pure PC as the solvent. However, ceaseless solvent decomposition and intense exfoliation of graphene layers occurred at 25 °C. The results of the Raman spectroscopic analysis indicated that the interaction between PC molecules and lithium ions became weaker at − 15 °C by chemical exchange effects, which suggested that the thermodynamic stability of the solvated lithium ions was an important factor that determined the formation of a solid electrolyte interface (SEI) in PC-based solutions. Charge–discharge analysis revealed that the nature of the SEI formed at − 15 °C in 1 mol dm^− 3 of LiClO₄ in PC was significantly different from that formed at 25 °C in 1 mol dm^− 3 of LiClO₄ in PC containing vinylene carbonate, 3.27 mol kg^− 1 of LiClO₄ in PC, and 1 mol dm^− 3 of LiClO₄ in ethylene carbonate.     

Investigation of the dynamics of radiolytic formation of ZnO nanostructured materials by pulse radiolysis

ZnO nanostructures have been synthesized by radiolytic methods. A Cobalt-60 γ-source and a 7 MeV linear electron accelerator (LINAC) was used for the radiolysis experiments. Reducing agent like hydrated electron (e_aq⁻), which is produced in radiolysis of water, was used to synthesize ZnO nanostructure materials from zinc salt. 1 M tert-butanol was used to quench the primary oxidizing radical like hydroxyl radical (OH) radiolytic water solution. Doses of about 80–130 kGy were used to perform radiolysis experiments in the present investigation. Time-resolved pulse radiolysis has been used to monitor the transient species involved in the formation of ZnO nanostructures by monitoring at different wavelengths. A scheme for the formation of the ZnO nanostructured materials by the radiolytic method has been described. The formation of ZnO nanostructures was confirmed by X-ray diffraction (XRD) measurements. Dynamic light scattering (DLS) measurements indicated that the size of the nanostructures is in the range of 6–8 nm, which is in agreement with that obtained from XRD. It is interesting to note that ZnO nanostructured materials, as prepared by the radiolytic method, exhibit strong room-temperature fluorescence.     

Life test of DMFC using poly(ethylene glycol)bis(carboxymethyl)ether plasticized PVA/PAMPS proton-conducting semi-IPNs

A novel, low-cost proton-conducting semi-IPN has been successfully prepared from PVA/PAMPS blends by incorporating poly(ethylene glycol)bis(carboxymethyl)ether (PEGBCME) as a novel plasticizer. Although, the polymer is based on a relatively low content of PAMPS as a component of ion conducting sites, the resulting semi-IPN exhibited high proton conductivity (0.1 S cm⁻¹) at 25 °C, which afforded a higher power density of 51 mW cm⁻² at 80 °C. A striking feature is that a long-term initial performance is achieved with a 130 h of stable fuel cell operation in DMFC mode due to effectively suppressed methanol crossover. This is a new record for a fully hydrocarbon membrane in DMFC, seeing that the PVA–PAMPS proton-conducting semi-IPNs are made simply of aliphatic skeletons.     

Separation of hydrogen from steam using a SiC-based membrane formed by chemical vapor deposition of triisopropylsilane

A silicon carbide-based membrane was formed in the macropores of an α-alumina support tube by chemical vapor deposition of triisopropylsilane at 700–800°C with a forced cross-flow through the porous wall. The membrane permeated gases except H₂O mainly by the Knudsen diffusion mechanism at permeation temperatures of 50–400°C. The H₂/H₂O selectivity was near or below unity because of the hydrophilic nature of the membrane. After a heat-treatment in Ar at 1000°C for 1 h, however, the membrane formed at a final evacuation pressure of 1 kPa exhibited a H₂/H₂O selectivity of 3–5, for a mixed feed of H₂–H₂O–HBr system, associated in a thermochemical water-splitting process. The H₂ permeance was (5–6)×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 50–400°C. The membrane maintained the H₂/H₂O selectivity for more than 100 h in the H₂–H₂O–HBr mixture at 400°C.     

Electrochemical deposition of (Mn, Co)-codoped ZnO nanorod arrays without any template

(Mn, Co)-codoped ZnO nanorod arrays were successfully prepared on Cu substrates by electrochemical self-assembly in solution of 0.5 mol/l ZnCl₂–0.01 mol/l MnCl₂–0.01 mol/l CoCl₂–0.1 mol/l KCl–0.05 mol/l tartaric acid at a temperature of 90 °C, and these nanorods were found to be oriented in the c-axis direction with wurtzite structure. Energy dispersive X-ray spectroscopy and x-ray diffraction show that the dopants Mn and Co are incorporated into the wurtzite-structure of ZnO. The concentrations of the dopants, and the orientations and densities of nanorods can easily be well controlled by the current densities of deposition or salt concentrations. Magnetization measurement indicates that the prepared (Mn, Co)-codoped ZnO nanorods with a coercivity of about 91 Oe and a saturation magnetization (M_s) of about 0.23 emu/g. The anisotropic magnetism for the (Mn, Co)-codoped ZnO nanorod arrays prepared in solution of 0.5 mol/l ZnCl₂–0.01 mol/l MnCl₂–0.01 mol/l CoCl₂–0.1 mol/l KCl–0.05 mol/l tartaric acid with current density of 0.5 mA/cm² was also investigated, and the crossover where the magnetic easy axis switches from parallel to perpendicular occurs at a calculated time of about 112 min. The anisotropic magnetism, depending on the rod geometry and density, can be explained in terms of a competition between self-demagnetization and magnetostatic coupling among the nanorods.     

Surface structures and electrochemical characteristics of surface-modified carbon anodes for lithium ion battery

Petroleum coke and those heat-treated at 1860 °C, 2100 °C, 2300 °C 2600 °C and 2800 °C (abbreviated as PC, PC1860, PC2100, PC2300, PC2600 and PC2800) were fluorinated by elemental fluorine of 3 × 10⁴ Pa at 200 °C and 300 °C for 2 min. Natural graphite powder samples with average particle sizes of 5 μm, 10 μm and 15 μm (abbreviated as NG5μm, NG10μm and NG15μm) were also fluorinated by ClF₃ of 3 × 10⁴ Pa at 200 °C and 300 °C for 2 min. Transmission electron microscopic (TEM) observation revealed that closed edge of PC2800 was destroyed and opened by surface fluorination, which increased the first coulombic efficiencies of PC2300, PC2600 and PC2800 by 12.1–18.2% at 60 mA/g and by 13.3–25.8% at 150 mA/g in 1 mol/dm³ LiClO₄–ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1 in volume). Light fluorination of NG10μm and NG15μm increased the first coulombic efficiencies by 22.1–28.4% at 150 mA/g in 1 mol/dm³ LiClO₄–EC/DEC/PC (PC: propylene carbonate, 1:1:1 in volume).     

Facile synthesis of flat crystal ZnO thin films by solution growth method: A micro-structural investigation

Flat crystal ZnO thin films were prepared by chemical bath deposition technique onto glass substrates. XRD patterns of the films deposited at about 80 °C and annealed at 200 °C for 1 h in oxygen environment revealed the existence of polycrystalline hexagonal wurtzite phase with c-axis orientation of crystallites in the films. The crystallite size and lattice strain from X-ray line broadening profile were evaluated using the Scherrer method and Williamson–Hall method. Structural parameters such as dislocation density, stacking faults probability, lattice constants, lattice stress, unit cell volume, internal parameter, texture and number of crystallites per unit area have also been calculated. Surface morphology of the films was analyzed by scanning electron microscopy and atomic force microscopy. Photoluminescence spectrum at room temperature exhibited two luminescence centers, one is for UV emission (near band edge emission) located at 3.18 eV and another is for deep level emission located at 2.56 eV.