Selective Permeation of Water through Angstrom-Channel Graphene Membranes for Bioethanol Concentration

Graphene-based laminate membranes have been theoretically predicted to selectively transport ethanol from ethanol–water solution while blocking water. Here, robust angstrom-channel graphene membranes (ACGMs) fabricated by intercalating carbon sheets derived from chitosan into thermally reduced graphene oxide (GO) sheets are reported. ACGMs with robust and continuous slit-shaped pores (an average pore size of 3.9 Å) are investigated for the dehydration of ethanol. Surprisingly, only water permeates through ACGMs in the presence of aqueous ethanol solution. For the water-ethanol mixture containing 90 wt% ethanol, water can selectively permeate through ACGMs with a water flux of 63.8 ± 3.2 kg m⁻² h⁻¹ at 20 °C and 389.1 ± 19.4 kg m⁻² h⁻¹ at 60 °C, which are over two orders of magnitude higher than those of conventional pervaporation membranes. This means that ACGMs can effectively operate at room temperature. Moreover, the ethanol can be fast concentrated to high purity (up to 99.9 wt%). Therefore, ACGMs are very promising for production of bioethanol with high efficiency, thus improving its process sustainability.     

Sorption, diffusion, and pervaporation characteristics of dimethylformamide/water mixtures using sodium alginate/polyvinyl pyrrolidone blend membranes

Separation of aqueous dimethylformamide (DMF) solutions in the concentration range of 0-100 wt% were studied using sodium alginate (NaAlg)/polyvinyl pyrrolidone (PVP) blend membranes. The NaAlg was blended in different ratios with PVP. Prepared membranes were crosslinked with CaCl₂ for testing in pervaporation (PV) separation of DMF/water mixtures. Effects of feed composition (0-100 wt%), operating temperature (30-50 °C), and membrane thickness were investigated. Best results were obtained at the conditions of 75/25 NaAlg/PVP blend ratio (w/w), 40 °C temperature, 20 wt% DMF concentration, and 70 μm membrane thickness. Blending of PVP with NaAlg increased permeation flux whereas it decreased the separation factor. NaAlg/PVP membranes gave separation factors of 5.5-27 for permeation flux of 0.96-1.81 kg/m²h depending on the operating temperature and the feed mixture composition. Arrhenius plot of permeation flux data versus reciprocal of temperature exhibited linear trends. Permeation activation energy of DMF and water in the PV was calculated as 6.76 and 1.88 kcal/mol, respectively, using an Arrhenius type relationship. Sorption-diffusion properties of the NaAlg/PVP membranes were also investigated at the operating temperature and the feed composition.     

Electrophoretic technique for hydrothermal synthesis of NaA zeolite membranes on porous α-Al2O3 supports

Uniform and dense NaA zeolite membranes were prepared on the α-Al₂O₃ support by electrophoretic technique. The membrane morphology and membrane thickness were investigated by XRD, SEM and pervaporation properties for dehydration of 95 wt.% isopropanol/water mixture at 343 K, respectively. Under the action of the applied electric field, the negatively charged zeolite particles could migrate to the support surface homogenously and rapidly, forming uniform and dense membranes in a short time. High quality NaA zeolite membrane, with a separation factor (water/isopropanol) of 3281 and a flux of 1.24 kg/m² h, could be prepared by electrophoretic technique with the electrical potential of 1 V. The formation mechanism of zeolite membrane in the electric field is discussed.     

Cermet-type hydrogen separation membrane obtained from fine particles of high temperature proton-conductive oxide and palladium

A mixed ionic and electronic conducting hydrogen separation membrane, which consisted of proton-conductive oxide and metallic palladium, was fabricated. A porous alumina tube was employed as a support, and proton-conductive oxide particles were introduced into a microporous top layer of the support by an impregnation method. Palladium particles were deposited into the same porous layer by chemical vapor deposition. Hydrogen permeated preferentially via the membrane thus obtained with a hydrogen permeance (PH₂) of 1.2 × 10^− 9 mol·m^− 2·s^− 1·Pa^− 1 at 873 K. Selectivity for hydrogen (PH₂/PN₂) increased with the operating temperature due to an increase in proton conductivity of the membrane, and PH₂/PN₂ = 5.7 was attained at 873 K.     

Properties of screen-printed Ho-Ba-Cu-O films on YSZ substrates

High-T_c screen-printed Ho-Ba-Cu-O films were prepared on YSZ substrates by a melt processing method. The films were fired at T_s = 1000-1050 °C for 5 min and cooled to 450 °C by two steps in flowing O₂. The maximum critical current density J_c (77 K, 0 T) of 2.0 × 10³ A cm^− 2 was only attained under much limited firing conditions; T_s = 1020 °C and cooled to 800 °C at a cooling rate of 400 °C h^− 1.     

Improved thermoelectric properties by adding Al for Zn in (ZnO)mIn2O3

The grain size and density of the sintered (Zn_1 − xAl_xO)_mIn₂O₃ bodies decreased with the small Al₂O₃ content (≤ 0.012), and then increased gradually by further increasing the Al₂O₃ content. The addition of Al for Zn in the (ZnO)_mIn₂O₃ led to an increase in both the electrical conductivity and the absolute value of the Seebeck coefficient. This indicates that the power factor was significantly enhanced by adding Al for Zn. The thermoelectric power factor was maximized to 1.67 × 10^− 3 W m^− 1 K^− 2 at 1073 K for the (Zn_0.992Al_0.008O)_mIn₂O₃ sample.     

Nonlinear optical properties of laser deposited CuO thin films

In this work we investigate the third-order optical nonlinearities in CuO films by Z-scan method using a femtosecond laser (800 nm, 50 fs, 200 Hz). Single-phase CuO thin films have been obtained using pulsed laser deposition technique. The structure properties, surface image, optical transmittance and reflectance of the films were characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and UV-vis spectroscopy. The Z-scan results show that laser-deposited CuO films exhibit large nonlinear refractive coefficient, n₂ = − 3.96 × 10^− 17 m²/W, and nonlinear absorption coefficient, β = − 1.69 × 10^− 10 m/W, respectively.     

Crystal structure and magnetic properties of the compound FeDy6Sb2

The crystal structure of a compound FeDy₆Sb₂ was determined by X-ray powder diffraction using the Rietveld method. The compound crystallizes in the hexagonal, space group P6¯2m (No. 189) with the Fe₂P structure type and lattice parameters a = 0.81449(5) nm, c = 0.41641(3) nm, z = 1 and D_calc = 8.842 g/cm³. The maximum magnetic entropy change ΔS_M for the compound is 3.41 J kg^− 1 K^− 1 near its Curie temperature (143.4 K) on the magnetic field changes of 0-2.0 T.     

Polypyrrole thin films for gas sensors prepared by Matrix-Assisted Pulsed Laser Evaporation technology: Effect of deposition parameters on material properties

Thin films of polypyrrole (PPY) were prepared by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technology from two matrices: water and dimethylsulfoxide (DMSO). The deposition was carried out using a KrF excimer laser (laser fluence F ranged from 0.1 to 0.6 J cm^− 2). This work deals with optimization of two deposition parameters - laser fluence and number of pulses - for both matrices. From the deposition curves, the fluence thresholds, F_th, and maximum growth rates were subsequently determined (water matrix: F_th ~ 0.40-0.45 J cm^− 2, maximum growth rate 0.16 nm pulse^− 1; DMSO matrix: F_th ~ 0.25-0.30 J cm^− 2; maximum growth rate 0.20 nm pulse^− 1). The changes in chemical composition of deposited layers were studied by Attenuated Total Reflection Fourier Transform Infrared spectroscopy. Surface morphology was characterized by Atomic Force Microscopy. A discussion is also presented concerning relationships between laser fluence and chemical composition of deposited layers with respect to their potential application in gas sensors. Finally, the response of a sensor with a MAPLE deposited PPY active layer to air humidity is presented.     

Thermal and mechanical properties of novel substrate crystal Mg0.4Al2.4O4

Mg_0.4Al_2.4O₄ single crystal was grown by the Czochralski method. The measured specific heat values are 0.804-1.06 J g^− 1 K^− 1 in the temperature range from 298.15 to 573.15 K. The calculated thermal conductivity components are 11.37, 11.47 and 10.77 W m^− 1 K^− 1 along the [111], [004] and [22?0] direction at 298.15 K. The Vickers microhardness values are 1328-1414 kg mm^− 2. These experimental results show that Mg_0.4Al_2.4O₄ crystal is a promising substrate for GaN-based LEDs.     

Microhardness studies on calcium hydrogen phosphate (brushite) crystals

Vicker's and Knoop microhardness studies were carried out on grown calcium hydrogen phosphate dihydrate (CaHPO₄·2H₂O) crystals over a load range of 10-50 g. The Vickers (H_V) and Knoop (H_K) microhardness numbers for the above loads were found to be in the range of 94-170 kg/mm² and 28-35 kg/mm² respectively. It was also found that these numbers increased with increase in load. The Mayer's index (n) was found to be greater than 1.6 showing soft-material characteristics. The fracture toughness values (K_c), determined from measurements of crack length, were estimated to be 6 ± 0.5 × 10³ kg m^−3/2 and 4.5 ± 0.5 × 10³ kg m^−3/2 at 25 g and 50 g respectively. The brittleness indices (B_i) were found as 2.3 ± 0.1 × 10⁴ m^−1/2 for 25 g and 3.7 ± 0.1 × 10⁴ m^−1/2 for 50 g. Using Wooster's empirical relation, the elastic stiffness coefficient (c₁₁) has been calculated from Vicker's hardness values as 4.8 ± 0.5 × 10¹⁵ Pa for 10 g, 9.7 ± 0.5 × 10¹⁵ Pa for 25 g and 13.3 ± 0.5 × 10¹⁵ Pa for 50 g. The Young's modulus was calculated as 1.5 ± 0.1 × 10¹⁰ N m⁻² from Knoop microhardness values.     

Composition dependent thermoelectric properties of sintered Mg2Si1−xGex (x = 0 to 1) initiated from a melt-grown polycrystalline source

Fabrication of Mg₂Si_1−xGe_x (x = 0-1.0) was carried out using a spark plasma sintering technique initiated from melt-grown polycrystalline Mg₂Si_1−xGe_x powder. The thermoelectric properties were evaluated from RT to 873 K. The power factor of Mg₂Si_1−xGe_x with higher Ge content (x = 0.6-1.0) tends to decrease at higher temperatures, and the maximum value of about 2.2 × 10^− 5 Wcm^− 1K^− 2 was observed at 420 K for Mg₂Si and Mg₂Si_0.6Ge_0.4. The coexistence of Si and Ge gave rise to a decrease in the thermal conductivity in the Mg₂Si_1−xGe_x. The values close to 0.02 Wcm^− 1K^− 1 were obtained for Mg₂Si_1−xGe_x (x = 0.4-0.6) over the temperature range from 573 to 773 K, with the minimum value being about 0.018 Wcm^− 1K^− 1 at 773 K for Mg₂Si_0.4Ge_0.6. The maximum dimensionless figure of merit was estimated to be 0.67 at 750 K for samples of Mg₂Si_0.6Ge_0.4.     

Synthesis of LiNi0.9Co0.1O2 cathode material for lithium secondary battery by a novel route

The cathode material, LiNi_0.9Co_0.1O₂ was prepared using a rheological phase reaction method with LiOH·H₂O, home-made Ni(OH)₂, and Co₂O₃ as starting materials. At first, the mixture of reactants and a proper amount of water reacted to form a rheological precursor. Then the dried precursor was heated at 730 °C in one step to yield the product. The effects of calcination time (between 0.5 and 10 h) on the structural, morphological and electrochemical properties were investigated. All obtained powders show a single phase with α-NaFeO₂ structure (R-3m space group). The sample prepared in 2.5 h delivers the largest initial discharge capacity of 218 mA h g^− 1 (3.0-4.35 V, 25 mA g^− 1) and still remains 192 mA h g^− 1 after 15 cycles. The method is simple, economical and effective and is promising for practical application.     

Crystal structure, thermal expansion and electrical properties of a new compound Al0.33DyGe2

A new ternary compound Al_0.33DyGe₂ has been synthesized and studied from 298 K to773 K by means of X-ray powder diffraction technique. The crystal structural refinement of Al_0.33DyGe₂ has been performed by using the Rietveld method. The ternary compound Al_0.33DyGe₂ crystallizes in the orthorhombic of the defect CeNiSi₂-type structure (space group Cmcm, a = 0.41018(2)nm, b = 1.62323(6)nm, c = 0.39463(1)nm, Z = 4 and D_calc = 8.004 g/cm³). The average thermal expansion coefficients α_a, α_b and α_c of Al_0.33DyGe₂ are 1.96 × 10^− 5 K^− 1, 0.93 × 10^− 5 K^− 1 and 1.42 × 10^− 5 K^− 1, respectively. The bulk thermal expansion coefficient α_V is 4.31 × 10^− 5 K^− 1. The resistivity is observed to fall from 387 to 308 µΩ cm between room temperature and 25 K.     

Oxygen permeation and electrical transport of Gd1−xPrxBaCo2O5 + δ dense membranes

Double-perovskite Gd_1−xPr_xBaCo₂O_5 + δ membranes showed appreciable oxygen permeability at moderate temperatures. The overall oxygen permeation process of GdBaCo₂O_5 + δ was found to be controlled mainly by the bulk diffusion step with the membrane thickness larger than 0.8 mm, and the limitation by oxygen surface exchange came into play at reduced thickness of 0.8 mm. The electrical conductivity measurement showed Gd_1 - xPr_xBaCo₂O_5 + δ samples possessed a semiconducting behavior at a wide temperature range below 300 °C and a metallic behavior at 300-850 °C with a high conductivity of nearly 10³ S cm^− 1.     

Ag-ZSM-5 zeolite as high-temperature water-vapor sensor material

The effect of the presence of water vapor in the gas stream on the absorption spectra of AgH-ZSM-5 zeolites at high temperatures was investigated using UV-Vis DR spectroscopy. Ag_mⁿ⁺ silver species exhibiting an absorption band at 37 700 cm^− 1 are formed in highly loaded AgH-ZSM-5 treated in an oxygen stream. The presence of water in the gas stream results in the fast erosion of the band at 37 700 cm^− 1 and the intensity of the band is fully recovered under water-free conditions. Ag_mⁿ⁺ silver species in the AgH-ZSM-5 zeolite and their optical properties are stable under high-temperature treatment of zeolite under various conditions. Thus, the preparation of chemically/thermally stable sensing material based on silicon-rich zeolites containing metal ion species suitable for sensor applications under sever conditions was demonstrated.     

Effect of TiOx seed layer on the texture and electric properties in La and Ca modified PbTiO3 thin films

Lanthanum-and calcium-modified PbTiO₃ (PLCT) ferroelectric thin films were successfully prepared on Pt(111)/Ti/SiO₂/Si substrates by pulsed laser deposition. Influence of TiO_x seed layer on texture and electric properties of PLCT films was investigated. It is found the PLCT films without seed layer exhibited highly (100)-textured, while using about 9 nm TiO_x as seed layer lead to highly (301)-textured. The PLCT film with TiO_x seed layer possess higher remnant polarization (Pr = 26 µC/cm²), better pyroelectric coefficient and figure of merit at room temperature (p = 370 µC/m²k, F_d = 190 × 10^− 5 Pa^− 1/2) than that of film without seed layer. The mechanism of the enhanced electric properties was also discussed.     

Surface structure modification on the gas separation performance of carbon molecular sieve membranes

Carbon molecular sieve (CMS) membranes for separating gases were deposited on porous Al₂O₃ disks using CH₃COCH₃+CH₄, by a remote inductively coupled-plasma (ICP) chemical vapor deposition (CVD). The new method for preparing membranes with a high H₂/N₂ selectivity without any reduction of the permeance was introduced by combining the surface treatment with high-energy ion bombardment and subsequent high-temperature pyrolysis study. The H₂/N₂ selectivity reached 50 with an extremely high permeance of approximately 1.6×10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹ at 423 K. The O₂/N₂ selectivity reached 2.5 and the O₂ permeance was approximately 2×10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹ at 398 K.Short and optimized surface treatment periods were required to ensure high efficiency. Without pyrolysis, surface treatments alone markedly reduced the H₂ and N₂ permeances but did not affect selectivity. Besides, without any surface treatment, pyrolysis alone markedly increased the H₂ and N₂ permeances, but did not improve selectivity, because the desorption of carbon left large pores. Surface treatment must be combined with pyrolysis to enhance simultaneously the permeance and selectivity of CMS membranes, in a manner very different from that associated with conventional pore-plugging mechanism in typical CVD.     

Performance of a biofilter for the removal of high concentrations of styrene under steady and non-steady state conditions

The performance of a laboratory scale perlite biofilter inoculated with a mixed culture was evaluated for gas phase styrene removal under various operating conditions. Experiments were carried out by subjecting the biofilter to different flow rates (0.15–0.9 m³ h⁻¹) and concentrations (0.03–17.3 g m⁻³), corresponding to inlet loading rates varying from as low as 3 g m⁻³ h⁻¹ to as high as 1390 g m⁻³ h⁻¹. A maximum elimination capacity (EC) of 382 g m⁻³ h⁻¹ was achieved at an inlet loading rate of 464 g m⁻³ h⁻¹ with a removal efficiency of 82%. The high elimination capacity reached with this system could have been due to the dominant presence of filamentous fungi among others. The impact of relative humidity (RH) (30%, 60% and >92%) on the biofilter performance was evaluated at two constant loading rates, viz., 80 and 260 g m⁻³ h⁻¹, showing that inhibitory effects were only significant when combining the highest loads with the lowest relative humidities. Biomass distribution, moisture content and concentration profiles along the bed height were significantly dependent on the relative humidity of the inlet air and on the loading rate. The dynamic behaviour of the biofilter through vigorous short and long-term shock loads was tested at different process conditions. The biofilter was found to respond apace to rapid changes in loading conditions. The stability of the biomass within the reactor was apparent from the fast response of the biofilter to recuperate and handle intermittent shutdown and restart operations, either with or without nutrient addition.     

Structural and magnetic properties of Co-N thin films synthesized by direct current magnetron sputtering

Influence of nitrogen fractions [N_f = N₂/(N₂ + Ar)] and sputtering powers (P_s) on the structural and magnetic properties of Co-N thin films synthesized by direct current magnetron sputtering have been studied. With increasing N_f from 0 to 20%, a series of phases from β-Co, β-Co (N), Co₄N to Co₃N were obtained. However, when N_f was fixed at 10%, only Co₄N phase with different Co contents in the films was prepared, whose values of saturation magnetism (M_s) increased from 12.9 ± 8.2 Am²/kg to 103.9 ± 6.1 Am²/kg with the increase of P_s. Interstitial nitrogen caused the decrease of coercivity from 24.12 kAm^− 1 (for β-Co film) to 2.71 kAm^− 1. However, the addition of interstitial nitrogen was not observed to increase the M_s of β-Co.