Synthesis and properties of Bi0.5(Na1−x−yKxAgy)0.5TiO3 lead-free piezoelectric ceramics

Bi_0.5(Na_1−x−yK_xAg_y)_0.5TiO₃ piezoelectric ceramics were prepared by conventional ceramic processes. X-ray diffraction patterns show a pure perovskite structure, indicating that the K⁺ and Ag⁺ ions substitute for the Na⁺ ions in Bi_0.5Na_0.5TiO₃. The temperature dependence of the dielectric constant and dissipation factor shows all ceramics to experience two phase transitions: from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric. The transition temperature from ferroelectric to anti-ferroelectric and the temperature at which the dielectric constant reaches its maximum value decrease with the increase of K⁺ amount. At room temperature, the ceramics containing 17.5–20 mol% K⁺ and 2 mol% Ag⁺ exhibit high piezoelectric constant (d₃₃ = 180 pC/N) and high electromechanical coupling factor (k_p = 35%).     

Polymerization of methyl methacrylate in the presence of molecular oxygen — a kinetic study

Methyl methacrylate was polymerized in aqueous medium initiated by a copper(II)-ascorbic acidoxygen system at 40°C and a kinetic study of the reaction is presented. The rate of polymerization, R_p showed an increase, constancy and then a decrease with increase in the [Cu²⁺]. The order with respect to [Cu²⁺] was 0.5 in the rate increase region. The order in monomer concentration changed gradually from 1.0 to 2.0 with increase in [Cu²⁺]. R_p became independent of ascorbic acid (AA) concentration and oxygen concentration at high concentrations. These results indicate that termination by mutual interaction of chain radicals predominates at low [Cu²⁺] while termination was exclusively by metal ions at high [Cu²⁺]. R_p was also observed to increase with temperature and ionic strength and to K_p/K_t^1/2 value was calculated and compared with literature values. Chain lengths were determined by viscometry for the polymers obtained under various experimental conditions.     

Copper-based efficient catalysts for propylene epoxidation by molecular oxygen

Among a series of SBA-15-supported transition metal oxides with and without modification, the CuO_x/SBA-15 after K⁺ modification exhibited the best catalytic performance for the epoxidation of propylene by molecular oxygen. Potassium was the best modifier among various alkali and alkaline earth metal ions examined, and potassium acetate was a superior precursor of K⁺ for propylene oxide formation. The highest propylene oxide selectivity was obtained over a catalyst with copper content of 1 wt.% and K/Cu molar ratio of 0.7. Kinetic studies reveal that the allylic oxidation mainly proceeds over the CuO_x/SBA-15 providing acrolein as the main partial oxidation product, and the K⁺ modification switches the main reaction route from allylic oxidation to epoxidation. The characterizations suggest that copper species with content of ≤5 wt.% are located in the mesoporous channels of SBA-15 existing mainly as CuO_x clusters and Cu²⁺ ions, and there exists an interaction between K⁺ and the copper species. This interaction is proposed to play pivotal roles in epoxidation of propylene. As compared with other reported Cu-based catalysts for propylene epoxidation, the present catalyst possesses several distinct features.     

Conformation of isotactic polystyrene (IPS) in the bulk crystallized state as revealed by small-angle neutron scattering

Neutron scattering experiments have been performed on isotactic polystyrene (IPS) samples in the bulk crystallized state (T_{crystallization} = 185°C). The determination of the conformation of tagged chains ranging from 2.5 × 10⁵ to 7 × 10⁵ has been undertaken on two different hydrogenated IPS matrices. A matrix of usual molecular weight (M_w = 4 × 10⁵) leads to results which do not agree with Flory's model. In this case, measurements on radius of gyration R_g show on the one hand an important increase of this parameter (40%) with increasing crystallinity for the highest molecular weight tagged chains and on the other hand a variation with molecular weight like M^0.78. These results are interpreted with a schematic model involving a long crystalline sequence incorporated in the monocrystal along the 110 plane and two amorphous wings. Such an assumption is confirmed by the scattering behaviours in the intermediate range. On the other hand, by using an IPSH matrix of very high molecular weight (M_w = 1.75 × 10⁶), and the same tagged chains previously considered, a very weak variation of R_g with increasing crystallinity is observed. This leads to consider in this case Flory's conformation which is corroborated by data obtained in the intermediate range.     

Effect of adding a smart potassium ion-responsive copolymer into polysulfone support membrane on the performance of thin-film composite nanofiltration membrane

Thin-film composite (TFC) nanofiltration (NF) membranes were fabricated via the interfacial polymerization of piperazine (PIP) and 1,3,5-benzenetricart)oiiyl trichloride on polysulfone (PSf) support membranes blended with K^+-responsive poly(N-isopropylacryamideco- acryloylamidobenzo-15-crown-5)(P(NIPAM-co- AAB15C5)). Membranes were characterized by attenuated total reflection Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscope, scanning electron microscope, contact angle, and filtration tests. The results showed that:(1) Under K^+-free conditions, the blended P(NIPAM-co-AAB15C5)/PSf supports had porous and hydrophilic surfaces, thereby producing NF membranes with smooth surfaces and low MgSO4 rejections;(2) With K^+ in the PIP solution, the surface roughness and water permeability of the resultant NF membrane were increased due to the K^+-induced transition of low-content P(NIPAM-co-AAB15C5) from hydrophilic to hydrophobic;(3) After a curing treatment at 95℃, the improved NF membrane achieved an even higher pure water permeability of 10.97 L·m^-2·h^-1 - bar1 under 200 psi. Overall, this study provides a novel method to improve the performance of NF membranes and helps understand the influence of supports on TFC membranes.     

Nickel(II) ion-intercalated MXene membranes for enhanced H2/CO2 separation

Hydrogen fuel has been embraced as a potential long-term solution to the growing demand for clean energy. A membrane-assisted separation is promising in producing high-purity H₂. Molecular sieving membranes (MSMs) are endowed with high gas selectivity and permeability because their well-defined micropores can facilitate molecular exclusion, diffusion, and adsorption. In this work, MXene nanosheets intercalated with Ni²⁺ were assembled to form an MSM supported on Al₂O₃ hollow fiber via a vacuum-assisted filtration and drying process. The prepared membranes showed excellent H₂/CO₂ mixture separation performance at room temperature. Separation factor reached 615 with a hydrogen permeance of 8.35 × 10⁻⁸ mol·m⁻²·s⁻¹·Pa⁻¹. Compared with the original Ti₃C₂T_x/Al₂O₃ hollow fiber membranes, the permeation of hydrogen through the Ni²⁺-Ti₃C₂T_x/Al₂O₃ membrane was considerably increased, stemming from the strong interaction between the negatively charged MXene nanosheets and Ni²⁺. The interlayer spacing of MSMs was tuned by Ni²⁺. During 200-hour testing, the resultant membrane maintained an excellent gas separation without any substantial performance decline. Our results indicate that the Ni²⁺ tailored Ti₃C₂T_x/Al₂O₃ hollow fiber membranes can inspire promising industrial applications.     

杂质离子对MgCl2和CO2反应-萃取-醇析耦合过程的影响

通过反应-萃取-醇析耦合过程，将MgCl₂和CO₂制备成碳酸镁和氯化氢气体是盐湖老卤资源化利用的有效途径。系统地研究了老卤中Na⁺、K⁺、Ca²⁺对MgCl₂和CO₂反应-萃取-醇析耦合过程得到的固体产物晶型晶貌的影响。结果表明，Na⁺和K⁺对耦合过程的影响相似，固体产物均为高纯棒状三水碳酸镁（MgCO₃·3H₂O），且Na⁺和K⁺均能选择性吸附在MgCO₃·3H₂O晶体的轴面（101），阻碍该晶面的生长，使得棒状MgCO₃·3H₂O直径变小；Ca²⁺对反应-萃取-醇析耦合过程有不利的影响，由于CaCl2能参与反应，生成球状无定形纳米钙镁碳酸盐，使得三水碳酸镁纯度降低。     

镧离子插层MoS2膜的制备及印染高盐水处理

二维材料具有独特的层状结构、稳定的物理化学性质等特点。近年来,由二维材料层层堆叠构成的二维膜在膜分离领域展示了非同凡响的应用潜力。本文采用成膜中共混方法将La³⁺插入到MoS₂膜层间,利用原子力显微镜(AFM)和X射线光电子能谱仪(XPS)技术表征了MoS₂片层结构和成分;利用扫描电镜(SEM)和X射线衍射仪(XRD)技术表征了膜结构与层间距;通过加压过滤装置和渗透装置考察了La³⁺-MoS₂膜的渗透截留性能。实验结果表明,La³⁺插层改性后的MoS₂膜由于层间距增加而显著地提高了纯水通量,La³⁺-MoS₂膜的纯水通量相较于MoS₂膜提高了约18.5倍。La³⁺-MoS₂膜对分子量300～800g/mol染料表现出了基于空间位阻理论的截留作用,对金属离子(Na⁺、K⁺、Mg     

Polymer interface changes in electrophoretic deposition

A Monte Carlo computer simulation model for the electrophoretic deposition of polymer chains on a discrete lattice is used to study the polymer density profile, interface growth, and its dependence on field, temperature, and molecular weight. The interface width (W) decreases WE^−1/2 on increasing the field (E). Width (W) depends non-monotonically on the temperature (T): a power-law decay is followed by a power-law increase on raising the temperature. Monotonic decay of the interface width with the molecular weight is possibly a stretched exponential. Conformation and dynamics of a tracer chain is used to probe its characteristics in interface to bulk region. The root mean square (rms) displacement of the center of mass of the tracer chain shows an ultra-slow motion, Rt^ν (ν0.1–0.01 at E=0.1–1.0) as the driven chain moves deeper from interface to bulk. Longitudinal compression of the radius of gyration (R_g) of the chain increases with the field; transverse components (R_gx, R_gy) are larger than the longitudinal component (R_gz). The transverse component (R_gx(y)) becomes oscillatory due to periodic squeezing at high fields as the field competes with the polymer barriers.     

Dehydrogenation of i-butane on CrOx/Al2O3 catalysts prepared by ALE and impregnation techniques

Atomic layer epitaxy (ALE), a technique relying on saturating gas–solid reactions, was applied in the preparation of CrO_x/Al₂O₃ catalysts using Cr(acac)₃ vapor and air as source materials for CrO_x. Vaporized Cr(acac)₃ was reacted with preheated Al₂O₃, and the surface complex formed was treated with air to remove the ligand residues. The Cr loading increased from 1.3 to 12.5 wt.% as the number of saturating Cr(acac)₃ and air reactions was increased from one to 10. CrO_x/Al₂O₃ catalysts were also prepared from solution by incipient wetness impregnation (0.3–21 wt.%). XPS and UV–VIS measurements of the catalysts revealed the presence of both Cr⁶⁺ and Cr³⁺. Although the oxidation state distribution was similar, H₂-temperature programmed reduction (TPR) and solubility measurements indicated that Cr⁶⁺ surface sites were in stronger interaction with Al₂O₃ and more uniformly distributed in the catalysts prepared by ALE than by impregnation. On the basis of the activity of the catalysts in the dehydrogenation of i-butane, we propose that the dehydrogenation reaction uses both reduced Cr⁶⁺, i.e. redox Cr³⁺, and exposed non-redox Cr³⁺ sites. Furthermore, the dehydrogenation reaction must be insensitive to the size of the CrO_x ensembles since activities were similar for the catalysts prepared by ALE and impregnation. The decay of the dehydrogenation activity in successive prereduction–reaction–regeneration cycles was attributed to a decrease in the number of redox Cr³⁺ sites.     

333.15 K K+,NH4+//Cl-,SO42——H2O和K+,NH4+//Cl-,SO42——(CH2OH)2-H2O体系固液相平衡

采用等温溶解法研究333.15 K体系（K⁺,NH₄⁺//Cl^-,SO₄^2--H₂O）和（K⁺,NH₄⁺//Cl^-,SO₄^2--（CH₂OH）₂-H₂O）[w（（CH₂OH）₂）=30%]的固液相平衡关系。测定了平衡溶液的溶解度数据及物化性质,包括密度、黏度、折射率、pH。根据实验数据,绘制了相应的干盐相图、水图及物化性质-组成图。实验中的物化性质（黏度、密度、折射率、pH）随J（2NH₄⁺）的变化呈现相似性规律。实验结果表明：在333.15 K下,体系（K⁺,NH₄⁺//Cl^-,SO₄^2--H₂O）和（K⁺,NH₄⁺//Cl^-,SO₄^2--（CH₂OH）₂-H₂O）[w（（CH₂OH）₂）=30%]的相图相似,均含有一个四元共饱和点,四条单变曲线及四个固相结晶区域。这两个体系均为复杂体系,存在（K,NH₄）Cl、（NH₄,K）Cl、（K,NH₄）₂SO₄、（NH₄,K）₂SO₄四种固溶体。实验所获数据和结论,可优化以硫酸盐型固体废弃物为硫酸根来源,转化法生产硫酸钾工艺。     

An experimental study of electroreduction of CO2 to HCOOH on SnO2/C in presence of alkali metal cations (Li+, Na+, K+, Rb+ and Cs+) and anions (HCO3-, Cl-, Br- and I-)

It is well-known that the electrolytes can influence the electrochemical reduction of carbon dioxide (ERCO₂) in aqueous media. In this work, we explore the effects of alkali metal cations and anions (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, HCO₃^-, Cl^-, Br^-, I^-) on the current density and product selectivity for the ERCO₂ into formic acid (HCOOH) on the SnO₂/carbon paper (SnO₂/C) electrode. Results of the ERCO₂ experiments show that for the cations, the promotion effects on current density and faradaic efficiencies (FEs) are in the order of Li⁺ < Na⁺ < K⁺ < Cs⁺ < Rb⁺. For the anions, the current density values are in the order of NaHCO₃ < NaCl < NaBr < NaI and KHCO₃ < KCl ≈ KI < KBr, respectively, and that on the FEs for the formation of the HCOOH (FE_HCOOH) is HCO₃^- < Cl^- < Br^- < I^-. Based on this result, the effects of alkali metal cations and anions on ERCO₂ are discussed.     

Study of the impedance of a platinum electrode in the system Br2/Br (HClO4, aq.)—II. Mechanism of the electrode reaction

The Randles circuit well represents impedance measurements carried out with activated Pt electrodes. This enables us to study the variation of j_o for redox reactions with concentration of the reactants, at constant potential, and also the variation of j_o with potential, keeping constant the concentration of one of the reactants. The results thus obtained indicate that the step Br₂ + e Br₂⁻ is rate-determining; it is followed or preceded by the rapid equilibria Br₂⁻ Br⁻ + Br 2Br Br₂. The mechanisms proposed hitherto for the electrochemical behaviour of the halogen/halide systems at inert electrodes are discussed, and it is reasoned that the ‘reversibility’ of these systems increases in the order Cl₂/Cl⁻ < Br₂/Br⁻ < I₂/I.     

Preparation of carbon-based adsorbents from sewage sludge pyrolysis to remove metals from water

The objective of this study was to evaluate the use of cheap carbon-based adsorbents from sewage sludge pyrolysis to remove Na⁺, K⁺, Ca²⁺ and Mg²⁺ from saline water. Four model solutions of NaCl, KCl, CaCl₂ and MgCl₂ that simulated seawater composition were used. The model solutions were 456.54 mmol_c L⁻¹ NaCl, 9.72 mmol_c L⁻¹ KCl, 19.96 mmol_c L⁻¹ CaCl₂ and 111.09 mmol_c L⁻¹ MgCl₂. Two carbon adsorbents, one with chemical activation, were prepared by a new method and evaluated for ion adsorption. The results indicated that carbon adsorbent without chemical activation was the most effective in removing ions from different solutions and the removal of metals followed the sequence: Na⁺ (76.78−69.66) >K⁺ (66.0−57.80) >Mg²⁺ (44.84−42.85) >Ca²⁺ (35.12−12.38). Results showed that it is to possible prepare carbon-based adsorbents from sewage sludge following inexpensive and environmentally acceptable methods.     

The role of Bronstead acidity in poisoning the SCR-urea reaction over FeZSM-5 catalysts

Two series of FeZSM-5 catalysts prepared from Na⁺ and NH₄⁺ ZSM-5 precursors are studied in the selective reduction of NO_x using NH₃ and urea as reducing agents. All Fe-containing catalysts are active for NO_x reduction in the SCR-NH₃ reaction with ex-NH₄⁺ catalysts being more active than ex-Na⁺ materials and the activity depending (to a minor extent within each series of catalysts) upon [Fe]. Catalysts with Bronstead acid sites also show a small transient deNO_x activity at low temperatures. All catalysts are less active for the SCR-urea reaction but the ex-Na⁺ catalysts retain far more deNO_x activity than the ex-NH₄⁺ materials. NH₃ TPD shows that strongly binding Bronstead acid sites are present on the ex-NH₄⁺ materials and H⁺-treated parent zeolites while Urea TPD shows that the mode of decomposition of urea differs as a function of initial zeolite counter-ion. Urea TPSR shows that the reaction between adsorbed urea and gaseous NO/O₂ is related to [Fe]. It is proposed that the decreased activity of the ex-NH₄⁺ catalysts in the SCR-urea reaction is due to a less favourable mode of decomposition over these catalysts. Furthermore it is suggested that the Bronstead acidity plays some part in this less favoured decomposition.     

Fabrication and thermoelectric properties of heavily rare-earth metal-doped SrO(SrTiO3)n (n = 1, 2) ceramics

To clarify the effect of substitutional electron doping on the thermoelectric figure of merit (ZT = S²σTκ⁻¹) of Ruddlesden–Popper phase SrO(SrTiO₃)_n (or Sr_n+1Ti_nO_3n+1), measurements were conducted for several thermoelectric parameters, e.g. electrical conductivity (σ), Seebeck coefficient (S) and thermal conductivity (κ), of (Sr_1−xRE_x)_n+1Ti_nO_3n+1 (n = 1 or 2, RE (rare earth): La or Nd, x = 0.05 and 0.1) dense ceramics prepared by a conventional solid-state reaction and hot-pressing technique. Crystal structures of the resultant ceramics were represented as (Sr_1−xRE_x)_n+1 Ti_nO_3n+1 evaluated by powder X-ray diffraction followed by the Rietveld analysis. All the ceramics exhibited electrical conductivity and the σ values simply depended on the dopant concentration, indicating that both La³⁺ and Nd³⁺ ions act as electron donors. The |S| values increased with temperature due to decrease in the chemical potential. Significant reduction of the κ values was observed as compared to cubic-perovskite SrTiO₃. The ZT value increased with temperature and reached 0.15 at 1000 K for (Sr_0.95La_0.05)₃Ti₂O₇.     

Internal burning of pulverized semi-anthracite: the relation between particle structure and reactivity

Measurements have been made of structural properties of particles of pulverized semi-anthracite at various stages of combustion at temperatures in the range 1400–2200 K. Four size-graded fractions of the particles (mass-median sizes 78, 49, 22 and 6 μm) were burned at oxygen partial pressures of about 0.1 and 0.2 atm. The structural properties determined included specific surface areas, helium densities, X-ray diffraction patterns, and pore-volume distributions. The relation of these properties to the temperatures prevailing during reaction and to the degree of burn-off which took place showed that macropores (pores above 0.02 μm width) developed during reaction and that the micropore volume was reduced. The opening up of the macropores results from the combustion process, but the reduction in micropore volume is due mainly to the effect of the higher temperatures on the structure of the solid. The structural data are combined with kinetic data relating to the reaction of oxygen with the particles to determine values of the intrinsic reactivity coefficient R_s (the rate of carbon consumption per unit of total internal area per unit pressure of oxygen) under various conditions. R_s is independent of particle size and is given by the equation R_s(g/cm² s atm O₂) = 55 [−40 000/(RT_p)] where T_p is the temperature of the particles and R is in cal/mol K^*. Calculations of the intrinsic reactivity via two routes, treating the pores as having either a unimodal or bimodal distribution of sizes respectively, gave similar values of the reactivity. Values of R_s are used to predict, within a factor of two, the results of other workers' measurements of semi-anthracite combustion rates.     

Catalytic behavior of La–Sr–Ce–Fe–O mixed oxidic/perovskitic systems for the NO+CO and NO+CH4+O2 (lean-NOx) reactions

Mixed oxides of the general formula La_0.5Sr_xCe_yFeO_z were prepared by using the nitrate method and characterized by XRD and Mössbauer techniques. The crystal phases detected were perovskites LaFeO₃ and SrFeO_3−x and oxides -Fe₂O₃ and CeO₂ depending on x and y values. The low surface area ceramic materials have been tested for the NO+CO and NO+CH₄+O₂ (“lean-NO_x”) reactions in the temperature range 250–550°C. A noticeable enhancement in NO conversion was achieved by the substitution of La³⁺ cation at A-site with divalent Sr⁺² and tetravalent Ce⁺⁴ cations. Comparison of the activity of the present and other perovskite-type materials has pointed out that the ability of the La_0.5Sr_xCe_yFeO_z materials to reduce NO by CO or by CH₄ under “lean-NO_x” conditions is very satisfying. In particular, for the NO+CO reaction estimation of turnover frequencies (TOFs, s⁻¹) at 300°C (based on NO chemisorption) revealed values comparable to Rh/-Al₂O₃ catalyst. This is an important result considering the current tendency for replacing the very active but expensive Rh and Pt metals. It was found that there is a direct correlation between the percentage of crystal phases containing iron in La_0.5Sr_xCe_yFeO_z solids and their catalytic activity. O₂ TPD (temperature-programmed desorption) and NO TPD studies confirmed that the catalytic activity for both tested reactions is related to the defect positions in the lattice of the catalysts (e.g., oxygen vacancies, cationic defects). Additionally, a remarkable oscillatory behavior during O₂ TPD studies was observed for the La_0.5Sr_0.2Ce_0.3FeO_z and La_0.5Sr_0.5FeO_z solids.     

Potential rare-earth modified CeO2 catalysts for soot oxidation part II: Characterisation and catalytic activity with NO + O2

Ceria (CeO₂) and rare-earth modified ceria (CeReO_x with Re = La³⁺, Pr^3+/4+, Sm³⁺, Y³⁺) supports and Pt impregnated supports are studied for the soot oxidation under a loose contact with the catalyst with the feed gas, containing NO + O₂. The catalysts are characterised by XRD, H₂-TPR, DRIFT and Raman spectroscopy. Among the single component oxides, CeO₂ is significantly more active compared with the other lanthanide oxides used in this study. Doping CeO₂ with Pr^3+/4+ and La³⁺ improved, however, the soot oxidation activity of the resulting solid solutions. This improvement is correlated with the surface area in the case of CeLaO_x and to the surface area and redox properties of CePrO_x catalyst. The NO conversion to NO₂ over these catalysts is responsible for the soot oxidation activity. If the activity per unit surface area is compared CePrO_x is the most active one. This indicates that though La³⁺ can stabilise the surface area of the catalyst in fact it decreases the soot oxidation activity of Ce⁴⁺. The lattice oxygen participates in NO conversion to NO₂ and the rate of this lattice oxygen transfer is much faster on CePrO_x. In general, the improvement of the soot oxidation is observed over the Pt impregnated CeO₂ and CeReO_x catalysts, and can be correlated to the presence of Pt°. The surface reduction of the supports in the presence of Pt occurred below 100 °C. The surface redox properties of the support in the Pt catalysts do not have a significant role in the NO to NO₂ conversion. In spite of the lower surface area, the Pt/CeYO_x and Pt/CeO₂ catalysts are found to be more active due to larger Pt crystal sizes. The presence of Pt also improved the CO conversion to CO₂ over these catalysts. The activation energy for the soot oxidation with NO + O₂ is found to be around 50 kJ/mol.     

四元体系Na+,K+//Br-,SO42——H2O373K相平衡

采用等温溶解平衡法研究了四元体系Na⁺,K⁺//Br^-,SO₄^2--H₂O在373 K条件下的相平衡关系,测定了平衡溶液的溶解度和密度,并根据实验数据绘制相应的相图、水图和密度图。研究发现:交互四元体系Na⁺,K⁺//Br^-,SO₄^2--H₂O在373 K温度下,有复盐钾芒硝Na₂SO₄·3K₂SO₄生成,相图由3个共饱和点、7条单变量曲线和5个结晶区组成。其中,5个结晶区分别对应单盐:K₂SO₄,KBr,NaBr,Na₂SO₄和复盐Na₂SO₄·3K₂SO₄(Gla)。