Suitable Synthesis Conditions Research Articles

Comparison of structural and electric properties of ZnO-based n-type thin films with different dopants for thermoelectric applications

This paper presents a study on ZnO-based n-type thin films doped with Al, Ga, and Sn deposited on the glass substrates, using the solution derived by sol–gel reactions. The basic material properties associated with using the alternative chemical substances in synthesis process and different dopants to generate n-type conductivity in ZnO-based thin films which are transparent oxides, are investigated and discussed. Namely, the crystal structure and surface morphology of the obtained films were examined by means of XRD analysis and field-effect scanning electron microscope (FESEM). The electric properties of those films were characterized by Hall-effect measurements and temperature dependence of electrical conductivity, as well as Seebeck coefficients. The remarkable advantages corresponding to the certain characterization of each material composition were compared together. The aim is to fully understand the performance limitation of known materials and to set the scene for a suitable synthesis condition to get optimized materials for thermoelectric applications.

Theoretical insight into the effect of Si-doped sites on the photocatalytic properties of SrTiO3

The perovskite-type SrTiO3 is an excellent photocatalyst for water splitting under ultraviolet light and the photocatalytic activity can be improved by the doped elements. In this paper, the effects of the different Si-doped ways on SrTiO3 are explored using the first-principles hybrid density functional theory calculations. The Si atom replacing Sr, Ti, and both atoms are considered. The calculated results demonstrate that the different doping ways produce different effects on the band energy gap, the light absorption, and the charge transfer properties. An obvious enhancement absorption in the visible light range is identified for the doping way of replacing both Sr and Ti atoms with two Si atoms. The formation energy calculations are used to explore the suitable synthesis condition of the Si-doped structures.

Influence of Synthesis Conditions on Microstructure and NO₂ Sensing Properties of WO₃ Porous Films Synthesized by Non-Hydrolytic Sol⁻Gel Method.

Nanostructured tungsten trioxide porous films were prepared by a non-hydrolytic sol–gel method following the inorganic route in which ethanol and PEG were used as the oxygen-donor and structure-directing reagent, respectively. The effects of aging time of the precursor solution, PEG content, and calcination temperature on the structure, morphology, and NO2 sensing properties of WO3 films were systematically investigated by using the techniques of X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and gas sensing measurements. The results demonstrated that a series of WO3 films with different microstructures could be obtained by manipulating the synthesis parameters. Furthermore, a suitable synthesis condition of WO3 films for NO2 sensing application was determined.

Solar Light Induced Photon-Assisted Synthesis of TiO₂ Supported Highly Dispersed Ru Nanoparticle Catalysts.

Ru/TiO2 are promising heterogeneous catalysts in different key-reactions taking place in the catalytic conversion of biomass towards fuel additives, biofuels, or biochemicals. TiO2 supported highly dispersed nanometric-size metallic Ru catalysts were prepared at room temperature via a solar light induced photon-assisted one-step synthesis in liquid phase, far smaller Ru nanoparticles with sharper size distribution being synthesized when compared to the catalysts that were prepared by impregnation with thermal reduction in hydrogen. The underlying strategy is based on the redox photoactivity of the TiO2 semi-conductor support under solar light for allowing the reduction of metal ions pre-adsorbed at the host surface by photogenerated electrons from the conduction band of the semi-conductor in order to get a fine control in terms of size distribution and dispersion, with no need of chemical reductant, final thermal treatment, or external hydrogen. Whether acetylacetonate or chloride was used as precursor, 0.6 nm sub-nanometric metallic Ru particles were synthesized on TiO2 with a sharp size distribution at a low loading of 0.5 wt.%. Using the chloride precursor was necessary for preparing Ru/TiO2 catalysts with a 0.8 nm sub-nanometric mean particle size at 5 wt.% loading, achieved in basic conditions for benefitting from the enhanced adsorption between the positively-charged chloro-complexes and the negatively-charged TiO2 surface. Remarkably, within the 0.5–5 wt.% range, the Ru content had only a slight influence on the sub-nanometric particle size distribution, thanks to the implementation of suitable photo-assisted synthesis conditions. We demonstrated further that a fine control of the metal Ru nanoparticle size on the TiO2 support was possible via a controlled nanocluster growth under irradiation, while the nanoparticles revealed a good resistance to thermal sintering.

Computational investigation of inverse Heusler compounds for spintronics applications

First-principles calculations of the electronic structure, magnetism and structural stability of inverse-Heusler compounds with the chemical formula \textit{X$_2$YZ} are presented and discussed with a goal of identifying compounds of interest for spintronics. Compounds for which the number of electrons per atom for \textit{Y} exceed that for \textit{X} and for which \textit{X} is one of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, or Cu; \textit{Y} is one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, or Zn; and \textit{Z} is one of Al, Ga, In, Si, Ge, Sn, P, As or Sb were considered. The formation energy per atom of each compound was calculated. By comparing our calculated formation energies to those calculated for phases in the Inorganic Crystal Structure Database (ICSD) of observed phases, we estimate that inverse-Heuslers with formation energies within 0.052 eV/atom of the calculated convex hull are reasonably likely to be synthesizable in equilibrium. The observed trends in the formation energy and relative structural stability as the \textit{X}, \textit{Y} and \textit{Z} elements vary are described. In addition to the Slater-Pauling gap after 12 states per formula unit in one of the spin channels, inverse-Heusler phases often have gaps after 9 states or 14 states. We describe the origin and occurrence of these gaps. We identify 14 inverse-Heusler semiconductors, 51 half-metals and 50 near half-metals with negative formation energy. In addition, our calculations predict 4 half-metals and 6 near half-metals to lie close to the respective convex hull of stable phases, and thus may be experimentally realized under suitable synthesis conditions, resulting in potential candidates for future spintronics applications.

One-step synthesis of 3D reduced graphene oxide supported Pd catalyst with high activity and recovery in the hydrogenation of nitrobenzene

Three-dimensional reduced graphene oxide (3D-RGO) supported Pd catalysts were prepared via one-step self-assembly in a mild water bath with ascorbic acid as reducing agent. The as-synthesized catalyst exhibited 3D architectures of graphene with abundant mesopores and uniform pore size of 3.9 nm. Relatively uniform Pd nanoparticles with 20–25 nm diameters were also obtained by the simple method. Under suitable synthesis conditions, 3D-RGO supported Pd catalyst showed a much high catalytic activity along with an excellent stability in the hydrogenation of nitrobenzene. Importantly, a perfect recovery rate of over 95% from liquid system was obtained.

Theory of order-disorder phase transitions of B-cations in AB'1/2B''1/2O3 perovskites.

Perovskite-like oxides AB'1/2B''1/2O3 with two different cations in the B-sublattice may experience cation order-disorder phase transitions. In many cases the degree of cation ordering can be varied by suitable synthesis conditions or subsequent sample treatment, which has a fundamental impact on the physical properties of such compounds. Therefore, understanding the mechanism of cation order-disorder phase transition and estimation of the phase transition temperature is of paramount importance for tuning of properties of such double perovskites. In this work, based on the earlier proposed cation-anion elastic bonds model, a theory of order-disorder phase transitions of B-cations in AB'1/2B''1/2O3 perovskites is presented, which allows reliable estimation of the phase transition temperatures and of the reduced lattice constants of such double perovskites.

Behavior of SAPO-11 as acid function in the direct synthesis of dimethyl ether from syngas and CO2

The kinetic behavior for methanol dehydration of different SAPOs (-11 and -18) and HZSM-5 zeolites (with different acidity and various acidity modification treatments) has been studied under the suitable conditions for the direct synthesis of dimethyl ether (DME) from H2+CO+CO2. SAPO-11 shows a good performance for methanol dehydration, with DME yield above 80% and negligible paraffin formation, and has been assessed as acid function of a bifunctional catalyst in the single-stage synthesis of DME (with CuO–ZnO–ZrO2 as metallic function, metallic/acid mass ratio=1/2). The bifunctional catalyst (CZZr/S-11) shows a stable kinetic behavior with high selectivity to DME (over 80%).

Microstructure and heavy metal adsorption mechanisms of hydrothermally synthesized Al-substituted tobermorite

Due to the properties of tobermorite as a cation exchanger and its potential applications in catalysis, and in hazardous waste disposal, attention has been drawn to the properties of tobermorite. In this study, fresh calcium oxide (CaO), fumed silica powder (SiO2) and aluminum nitrate nonahydrate (Al(NO3)3·9H2O) were used for synthesizing tobermorite with/without aluminum. The suitable synthesis condition was confirmed as 5 h in an autoclave at 180 °C and saturation vapor pressure around 1 MPa, marked as samples T and TA, respectively. The BET surface areas of T and TA were 198.83 and 80.48 m2/g, respectively. The pore sizes were mainly distributed between 100 and 300 nm, and pore volume of TA significantly lower than T. Laser scattering particle analysis indicated that the particle size of T and TA were both distributed between 1 and 100 μm, and the median diameter was 27.41 and 19.44 μm, respectively. These results indicated that the aluminum refined pore structure and particle size. The adsorption effectiveness was affected by adsorbent contents and adsorption time. For both of T and TA, the adsorption effectiveness of Cr6+, Pb2+, and Cu2+ could be higher than 97.62. 96.4, and 94.13%, respectively. The residues after adsorption were further studied by XRD, ATR-IR, and SEM. The results of XRD and ATR-IR showed that there was no other significant phase and functional group, except hydrocerussite (Pb3(CO3)2(OH)2) in T–Pb residue. The results indicate that the uptake of heavy metals (Cr6+, Pb2+, and Cu2+) by T or TA mainly through two ways which are surface complexation and uptake in the interlayer. SEM showed TA has better structural stability with the uptake of heavy metals than T. It indicated that chemical effects were the dominant factor, and physical effect took second place.

Characterization of highly sulfonated PEEK based membrane for the fuel cell application

In this study, poly(bisphenol-A-ether ketone) (PBAEK) is synthesized via nucleophilic aromatic substitution poly condensation between bisphenol A and 4,4-difluorobenzophenone, and the synthesized polymers are sulfonated using chlorosulfuric acid and suitable synthesis conditions for the temperature and sulfonating reagent content. The sulfonation degree of polymer is calculated using element analyses. The prepared sulfonated polymers are characterized for potential fuel cell applications through determining their water uptake, proton conductivity, and thermal stability. The significant advantage of the synthesized sulfonated PBAEK (sPBAEK) is its better solubility relative to commercial PEEK in various solvents, because sPBAEK backbones contain bisphenol A. The water uptake of the membrane increases with increases in the sulfonation degree. The sPBAEK membrane exhibits increased proton conductivity compared with the PBAEK membrane at 100% relative humidity conditions. As the sulfonation degree increases, the proton conductivity increases due to the increasing content in the hydrophilic domain. This property allows the prepared membranes to be potential candidates for proton exchange membrane fuel cells.

Synthesis and characterization of hydrotalcite from South African Coal fly ash

The synthesis of adsorbents such as hydrotalcites (HT) from mineral waste (e.g. blast furnace slag) is receiving increasing attention. This study reports a novel procedure to prepare HT from a South African coal-combustion fly ash, an ubiquitous waste generated by coal-fired power stations. The second point of novelty is the optimization process, which highlights the boundary conditions for crystallization of this mineral phase. The parameters investigated for the optimization of HT synthesis from fly ash included HCl concentration, aging time and temperature, pH during the aging step, and crystallization time and temperature. The most suitable synthesis conditions were: HCl concentration of 3M, aging time of 30min, aging temperature of 65°C, pH of 11.5 during aging, crystallization time of 12h, and crystallization temperature of 70°C. HT had a large external surface area and very low microporosity. Morphologically, synthesized HT was mostly made up of sub-micron plate-like particles. The structural characteristics of HT synthesized from fly ash were similar to those of HT produced from analytical grade chemicals, except for the presence of calcite. A novel use of the waste South African Class F fly ash was a suitable feedstock for the synthesis of high quality HT under the optimized process conditions that minimized the formation of secondary undesired mineral phases such as calcite or hydrogarnet.

Preparation of a hydroxyethyl–titanium dioxide–carboxymethyl cellulose hydrogel cage and its effect on the removal of methylene blue

ABSTRACTA novel TiO2 hydrogel cage model was built for the removal of methylene blue (MB), an organic pollutant. This TiO2 hydrogel cage was prepared with the biomass materials of hydroxyethyl cellulose (HEC) and carboxymethyl cellulose (CMC), and this hydrogel cage structure was characterized by scanning electron microscopy, transmission electron microscopy, and X‐ray diffraction. The contents of the encased TiO2 and its swelling properties with different CMC proportions of this hydrogel cage were studied to obtain a suitable crosslinking network structure and optimal synthesis conditions. Compared to an equivalent amount of pure TiO2, the much higher removal efficiency of MB with our prepared TiO2 hydrogel cage was attributed to the synergistic effect of the photocatalytic degradation for TiO2 and the adsorption enrichment for cellulose hydrogels. Furthermore, the adsorption kinetics of the intraparticle diffusion model were used to study the adsorption enrichment process of the TiO2 hydrogel cage. In addition, on the basis of the results of photocatalytic degradation and recycling experiments, excellent performances with respect to self‐cleaning, regenerative ability, and easy recovery, were shown for this HEC–TiO2–CMC cage material, which demonstrated ideal application potential for MB removal. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44925.

Computational investigation of half-Heusler compounds for spintronics applications

We present first-principles density functional calculations of the electronic structure, magnetism, and structural stability of 378 $\textit{XYZ}$ half-Heusler compounds (with $X=$ Cr, Mn, Fe, Co, Ni, Ru, Rh, $Y=$ Ti, V, Cr, Mn, Fe, Ni, $Z=$ Al, Ga, In, Si, Ge, Sn, P, As, Sb). We find that a "Slater-Pauling density of states" with a gap or pseudogap at three states per atom below the gap in at least one spin channel is a common feature in half-Heusler compounds. We find that the presence of such a gap at the Fermi energy in one or both spin channels contributes greatly to the stability of a half-Heusler compound. We calculate the formation energy of each compound and systematically investigate its stability against all other phases in the Open Quantum Materials Database (OQMD). We represent the thermodynamic phase stability of each compound as its distance from the convex hull of stable phases in the respective chemical space and show that the hull distance of a compound is a good measure of the likelihood of its experimental synthesis. We identify 26 18-electron semiconductors, 45 half-metals, and 34 near half-metals with negative formation energy, that follow the Slater-Pauling rule of three electrons per atom. Our calculations predict new thermodynamically stable semiconducting phases NiScAs, RhTiP, and RuVAs, which merit further experimental exploration. Further, two interesting zero-moment half-metals, CrMnAs and MnCrAs, are calculated to have negative formation energy. In addition, our calculations predict a number of new, hitherto unreported, semiconducting (e.g., CoVGe, FeVAs), half-metallic (e.g., RhVSb), near half-metallic (e.g., CoFeSb, CoVP) half-Heusler compounds to lie close to the respective convex hull of stable phases, and thus may be experimentally realized under suitable synthesis conditions, resulting in potential candidates for various spintronics applications.

Zn–Ca–Al mixed oxide as efficient catalyst for synthesis of propylene carbonate from urea and 1,2-propylene glycol

A series of Zn–Ca–Al oxides with different CaO and ZnO contents have been prepared and evaluated in the synthesis of propylene carbonate (PC) from 1,2-propylene glycol (PG) and urea in a batch reactor. The effect of catalyst composition, basicity and reaction process parameters such as temperature, catalyst dose, molar ratio of PG to urea, purge gas flow and reaction time has been studied to find suitable reaction conditions for the PC synthesis. The PC selectivity and yield under the desired conditions could reach 98.4% and 90.8%, respectively. The best performing catalyst also exhibited a good reusability without appreciable loss in the PC selectivity and yield after five consecutive reaction runs. In addition, a stepwise reaction pathway involving a 2-hydroxypropyl carbamate intermediate was proposed for the urea alcoholysis to PC in the presence of Zn–Ca–Al catalysts, according to the time dependences of reaction intermediates and products.

Performance of CuO–ZnO–ZrO2 and CuO–ZnO–MnO as metallic functions and SAPO-18 as acid function of the catalyst for the synthesis of DME co-feeding CO2

The kinetic behavior of the CuO–ZnO–ZrO2 (CZZr) and CuO–ZnO–MnO (CZMn) metallic functions in the methanol synthesis step has been studied under suitable operating conditions for DME synthesis, and the values of methanol yield and selectivity have been compared with those corresponding to the conventional CuO–ZnO–Al2O3 (CZA) metallic function. On the other hand, the performance (DME yield and selectivity) of SAPO-18 in the methanol dehydration step has also been compared with the conventional γ-Al2O3 acid function. Based on the kinetic behavior of the bifunctional catalysts with different mass ratios between the metallic and acid functions, a 2/1 ratio has been determined to be suitable in the single-step synthesis of DME. Moreover, the performance of the catalysts in the synthesis of DME has been compared using different reaction conditions (temperature, pressure, CO2/CO and H2/COx molar ratios in H2+CO+CO2 feed). The results show the good behavior of the CZZr/S and CZMn/S catalysts for the valorization of CO2, since they provide higher DME yield and selectivity than a CZA/γ-Al2O3 catalyst. Although the CZZr/S catalyst has a higher CO2 sequestration capacity, the lower preparation cost of the CZMn/S catalyst means an incentive for its use.

Metal–organic frameworks MIL-88A with suitable synthesis conditions and optimal dosage for effective catalytic degradation of Orange G through persulfate activation

Possible mechanism for the activation of PS by MIL-88A involves heterogeneous and homogeneous reaction.

Low-toxic gelcasting of giant dielectric-constant CaCu3Ti4O12 ceramics from the molten salt powder

CaCu3Ti4O12 (CCTO) nano powder was synthesized using a molten salt synthesis method in NaCl flux. Synthesis temperature and holding time were investigated. The suitable synthesis condition is 800°C for 2h. Aqueous CCTO slurry with high solid loading and low viscosity was prepared by using acrylic acid-2-acrylamido-2-methypropane sulfonic acid copolymer (AA/AMPS) as the dispersant. AA/AMPS dosage and pH condition have been optimized as AA/AMPS dosage of 3wt% and pH about 9.08. A low-toxicity and water-soluble monomer, N,N-dimethylacrylamide (DMAA) was used as the gelling agent. CCTO green body fabricated by the gelcasting method has the homogeneous microstructure and relatively high mechanical strength of 9.27MPa. CCTO ceramics obtained by the gelcasting method have higher dielectric constant than those prepared by the cold isostatic pressing method and show relatively low dielectric loss of below 0.2 in the wide frequency range of 102–105Hz.

Enhancement of superconductivity inLa1−xSmxO0.5F0.5BiS2

The superconducting and normal-state properties of La$_{1-x}$Sm$_{x}$O$_{0.5}$F$_{0.5}$BiS$_{2}$ (0.1 $\leqslant$ $x$ $\leqslant$ 0.9) have been studied via electrical resistivity, magnetic susceptibility, and specific heat measurements. By using suitable synthesis conditions, Sm exhibits considerable solubility into the CeOBiS$_{2}$-type LaO$_{0.5}$F$_{0.5}$BiS$_{2}$ lattice. In addition to a considerable enhancement of the superconducting volume fraction, it is found that the superconducting transition temperature $T_{c}$ is dramatically enhanced with increasing Sm concentration to 5.4 K at $x$ = 0.8. These results suggest that $T_{c}$ for SmO$_{0.5}$F$_{0.5}$BiS$_{2}$ could be as high as $\sim$6.2 K and comparably high $T_{c}$ values might also be obtained in $Ln$O$_{0.5}$F$_{0.5}$BiS$_{2}$ ($Ln$ = Eu - Tm) if these compounds can be synthesized.

Pore Size Estimation of Mesoporous Materials through Surfactant Self-Assembly Prediction

Abstract A theoretical model for pore size estimation of mesoporous materials was presented in this paper. It is based on the statistical thermodynamic model of micelle formation proposed by R. Nagarajan. The proposed model was applied to predict the pore size of MSU-X molecular sieve prepared in different synthetic systems. The estimation results were compared with reliable experimental measurements. The level of deviation is acceptable with the substantial simplifications included in the model. Hansen solubility parameter and Dimroth-Reichardt parameter were introduced to explain the discrepancies. The proposed model may help to screen suitable synthesis conditions and guide the controllable synthesis of molecular sieve to some extent.

Ab initiosynthesis of single-layer III-V materials

The discovery of a novel material requires the identification of the material's composition as well as of suitable synthesis conditions. We present a data-mining approach to identify suitable substrates for the growth of two-dimensional materials and apply the method to the recently predicted two-dimensional III-V compounds. We identify several lattice-matched substrates for their epitaxial growth, stabilization, and functionalization. Density-functional calculations show that these substrates sufficiently reduce the formation energies of the metastable two-dimensional materials to make them thermodynamically stable. We show that chemical interactions of the two-dimensional materials with the substrates shift the Fermi level of these materials, resulting in doping. The large adsorption energies and strong doping indicate that these metals should provide good electrical contact to enable transport measurements and electronic applications.