Vapor-phase Transport Synthesis Research Articles

ZnO Nanorod/Graphene Hybrid-Structures Formed on Cu Sheet by Self-Catalyzed Vapor-Phase Transport Synthesis.

High crystalline ZnO nanorods (NRs) on Zn pre-deposited graphene/Cu sheet without graphene transfer process have been fabricated by self-catalyzed vapor-phase transport synthesis. Here, the pre-deposited Zn metal on graphene not only serves as a seed to grow the ZnO NRs, but also passivates the graphene underneath. The temperature-dependent photoluminescence spectra of the fabricated ZnO NRs reveal a dominant peak of 3.88 eV at 10 K associated with the neutral-donor bound exciton, while the redshifted peak by bandgap shrinkage with temperature and electron-lattice interactions leads a strong emission at 382 nm at room temperature. The optical absorption of the ZnO NRs/graphene hetero-nanostructure at this ultraviolet (UV) emission is then theoretically analyzed to quantify the absorption amount depending on the ZnO NR distribution. By simply covering the ZnO NR/graphene/Cu structure with the graphene/glass as a top electrode, it is observed that the current-voltage characteristic of the ZnO NR/graphene hetero-nanojunction device exhibits a photocurrent of 1.03 mA at 3 V under a light illumination of 100 μW/cm2. In particular, the suggested graphene/ZnO NRs/graphene hybrid-nanostructure-based devices reveal comparable photocurrents at a bidirectional bias, which can be a promising platform to integrate 1D and 2D nanomaterials without complex patterning process for UV device applications.

Synergetic photocatalytic effect of high purity ZnO pod shaped nanostructures with H2O2 on methylene blue dye degradation

Zinc oxide (ZnO) nanostructures were successfully synthesized by thermal oxidation of Zn from different sources in the air atmosphere. We aimed to explore the influence of oxidation temperatures and the type of the Zn sources (powder and sheet) on the morphology and physical-chemical properties of the synthesized ZnO nanostructures. X-ray diffraction pattern and elemental analysis results proved that the applied one-step vapor phase transport synthesis method resulted in the synthesis of high purity ZnO nanostructures. Morphological observations using field emission electron microscopy demonstrated two kinds of morphologies, mostly including tetrapods and a trace amount of multi-pod shaped ZnO nanostructures, synthesized from powder and sheet Zn sources, respectively. Attained ZnO nanostructures were investigated for photocatalytic degradation of the methylene blue dye in aqueous solution under UV-light irradiation. Results showed that the multi-pod shaped (∼93%) sample had slightly better photodegradation efficiency than the tetrapod shaped (∼91%) ZnO nanostructures at 150 min of irradiation time. By adding 20 μl of H2O2 as an electron scavenger agent, the photodegradation process was accelerated and the reaction constant rate showed 218% and 173% improvement for multi-pod and tetrapod shaped nanostructured ZnO particles, respectively. Almost the same photocatalytic efficiency results were attained after 30 min of irradiation with the addition of H2O2 for multi-pod (∼92%) and tetrapod (∼90%) shaped ZnO nanostructures. Photocatalytic reusability of multi-pod shaped ZnO nanostructures was evaluated in the presence of H2O2 and efficiency was only 4% lower than in the first cycle. Finally, the presented results showed the synergetic effect of H2O2 as an electron scavenger agent on the photocatalytic activity of pod shaped ZnO nanostructures due to suppressing the recombination process of electron-hole pairs.

Preparation of Binderless Silicoaluminophosphates by Vapor-Phase Crystallization of Kaolin–Phosphoric Acid Grains

Transformations of granules based on kaolin and phosphoric acid under conditions of vapor-phase crystallization in a mixture of water vapor and a structure-directing agent have been studied. It has been shown that silicoaluminophosphate granules obtained in the presence of dipropylamine, triethylamine, or tetramethylammonium hydroxide as a structure-directing agent consist of a shell formed by dense nonporous cristobalite, tridymite, and berlinite phases and the core made mainly of microporous crystalline silicoaluminophosphates. The formation of the shell, which ensures the strength of the silicoaluminophosphate granules, is due to the interaction of steam with the material of the granules at the initial stages of vapor-phase crystallization. It has been established that the selectivity of the structure-directing action of the amines under vapor-phase crystallization conditions basically corresponds to the template hydrothermal synthesis. It has been assumed that the specific features of the structure-directing action of dimethylamine during vapor-phase transport synthesis are due to its low boiling point, which ensures the primary contact of the granules with template, rather than water molecules. As a result, the products of the transformation of granules in the presence of a mixture of dimethylamine and water do not contain dense nonporous phases and are cocrystallized silicoaluminophosphate and calcium aluminosilicate with the gismondine structure.

Vapor-phase transport synthesis of microfibrous-structured SS-fiber@ZSM-5 catalyst with improved selectivity and stability for methanol-to-propylene

Microfibrous-structured SS-fiber@HZSM-5 catalyst prepared by cost-effective and high-efficiency VPT method delivers remarkable improvement in selectivity and stability for the MTP reaction due to the improved diffusion in zeolite shell.

Hollow SAPO-34 Cubes with Hierarchically Organized Internal Structure

We herein report novel hollow SAPO-34 cubes with a hierarchical internal structure. They are prepared from dry gels containing gelatin by a vapor-phase transport method. Microscopic characterization reveals that the cubes are constructed by symmetrically packed four two-top-point truncated octahedrons encapsulated by dense crystalline shells, exhibiting a structure-in-structure formation. The cubes show either +-shaped or the butterfly like X-shaped black spots on their faces under light. Investigation of the formation process of the hollow SAPO-34 cubes demonstrates a surface to core crystal growth route, which has not been found in vapor-phase transport synthesis of zeolites. A possible formation mechanism is proposed.

Progress in Synthesis of Micro- and Mesoporous Composite Molecular Sieve

Micro- and mesoporous composite molecular sieves enable to achieve grades distribution of pore sizes and appropriate collocation of acidity,which have potential applications in catalysis and adsorption of large molecules.This review focus on some of the most recent results during the last decades.The techniques applied to synthesize different micro-mesoporous composite molecular sieves includes single template, dual template, crystallization of mesoporous walls, alkaline desilication, vapor-phase transport synthesis,and microwave radiation hydrothermal synthesis.

Morphology of tin oxide nanocrystals grown by vapor-phase transport method

Technological regimes of vapor-phase transport (VPT) synthesis of filamentous nanocrystals (nanowhiskers) of tin oxide (SnO2) are considered. It is experimentally established that the morphology of VPT-grown SnO2 nanocrystals depends on the initial charge composition, carrier gas, and degree of vapor phase supersaturation in the growth zone. The VPT synthesis has been successfully used to obtain fractal volume single crystals, nanofilaments, and nanowhiskers with diameters ranging from 50 to 1000 nm.

Microwave-assisted fast vapor-phase transport synthesis of MnAPO-5 molecular sieves

MnAPO-5 was prepared by a microwave-assisted vapor-phase transport method at 180 °C in short times. The products were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectra, UV–vis spectroscopic measurement, NH 3-temperature-programmed desorption and esterification reaction. It was found that dry gels prepared with aluminum isopropoxide, phosphoric acid and manganese acetate could be transferred to MnAPO-5 in the vapors of triethylamine and water by the microwave-assisted vapor-phase transport method at 180 °C for less than 30 min. The crystallization time was greatly reduced by the microwave heating compared with the conventional heating. The resulting MnAPO-5 exhibited much smaller particle sizes, higher surface areas and slightly higher catalytic activity in the esterification of acetic acid and butyl alcohol than those prepared by the conventional vapor-phase transport method and hydrothermal synthesis.

Vapor phase transport synthesis of SAPO-34 films on cordierite honeycombs

SAPO-34 films coated on cordierite honeycombs were synthesized by a vapor phase transport (VPT) technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG) and differential scanning calorimeter (DSC) were used to characterize the films. It was found that SAPO-34 films could be prepared on the cordierite honeycombs only when triethylamine (TEA) was presented in both the liquid phase and the SAPO-34 synthesis sol. The loading of SAPO-34 could be adjusted by changing the reaction conditions, such as the impregnation time and the molar ratio of SiO 2/Al 2O 3 in the synthesis sol. Continuous SAPO-34 films, with a thickness of ca. 20–60 μm, were composed of microsized crystals and the adhesion between SAPO-34 films and cordierites was strong.

Zno nanostructures fabricated through a double-tube vapor-phase transport synthesis

A double-tube vapor-phase transport system has been used to synthesize ZnO nanostructures. Nanofeatures of ZnO nanocombs, nanoblades and nanowires were achieved in different temperature zones. The scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed to study the nanostructure dependence with temperature. The vapor–liquid–solid (VLS) and vapor–solid (VS) growth mechanism are applied to explain the growth processes. ZnO two-sided nanocomb formed between 950 and 980 °C is dominated by VS growth. With growth temperature decreasing (820–950 °C), Au catalyst directed ZnO one-sided nanocombs and nanoblades growths are controlled by VLS and VS mechanisms. At low growth temperature zone between 710 and 820 °C, VLS growth dominates ZnO nanowire growth. A consistent orientation relationship between Au catalysts and ZnO nanocombs, nanoblades and nanowires is observed, i.e., 〈 2 1 ¯ 1 ¯ 0 〉 ZnO / / 〈 0 1 1 〉 Au and { 0 1 1 ¯ 0 } ZnO / / { 1 1 ¯ 1 } Au . The growth mechanism has a strong relationship with growth temperature of the ZnO nanostructures. Understanding the relationship of growth mechanisms and nanostructures is very important for future controlled growth.

Vapor phase transport synthesis of un-supported ZSM-22 catalytic membranes

ZSM-22 has been synthesized from a dry amorphous gel via vapor phase transport crystallization, as bulk crystalline powder as well as an un-supported membrane. Crystalline products were characterized by powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, chemical analysis, and thermal analysis. Catalytic testing was performed to demonstrate the membrane's ability to perform as an on-line catalyst. The ZSM-22 catalytic membrane showed 1-butene to isobutene conversions in excess of 60% with selectivites close to 40%, which compares well with conventionally synthesized bulk crystals.

Vapor phase transport synthesis of zeolites from sol–gel precursors

A study of zeolite crystallization from sol–gel precursors using the vapor phase transport synthesis method has been performed. Zeolites (ZSM-5, ZSM-48, zeolite P, and sodalite) were crystallized by contacting vapor phase organic or organic–water mixtures with dried sodium silicate and dried sodium alumino-silicate gels. For each precursor gel, a ternary phase system of vapor phase organic reactant molecules was explored. The vapor phase reactant mixtures ranged from pure ethylene diamine, triethylamine, or water, to an equimolar mixture of each. In addition, a series of gels with varied physical and chemical properties were crystallized using the same vapor phase solvent mixture for each gel. The precursor gels and the crystalline products were analyzed via scanning electron microscopy, electron dispersive spectroscopy, X-ray mapping, powder X-ray diffraction, nitrogen surface area, Fourier transform infrared spectroscopy, and thermal analyses. The product phase and purity as a function of the solvent mixture, precursor gel structure, and precursor gel chemistry is discussed.

Vapor-phase transport synthesis of ZnAPO-34 molecular sieve

ZnAPO-34 molecular sieve can be synthesized by the vapor-phase transport technique using triethylamine as a structure-directing agent.

Single-Crystal Electrical Resistivities of Some Ta-Rich Chalcogenides

Vapor phase transport synthesis of several Ta-rich chalcogenides affords us good single crystals for four-probe measurements of their electrical resistivities. A comparison of the temperature dependent resistivities of Ta2S and Ta3S2 show that the latter compound is a considerably poorer conductor for all temperatures from 15 to 270 K, as predicted in our earlier band structure study of these materials and consistent with the recent work of Nozaki and coworkers. In both cases, resistivities were measured along the direction parallel to the 1x [Ta5Ta] chains that serve as these materials' basic structural building blocks. The compounds Ta9M2S6 (M = Fe, Co, Ni) show normal metallic behavior over the same range of temperatures. A distortion that leads to a doubling of the c-axis length for the Fe and Co containing compounds seems to have no significant effect on the electronic density of states at the Fermi level in either material. In contrast, the compounds Ta11M2Se8 (M = Fe, Co, Ni) exhibit markedly different resistivities as a function of temperature. While Ta11Fe2Se8 and Ta11Ni2Se8 behave much like the structurally similar Ta9M2S6 compounds, the resistivity of Ta11Co2Se8 shows a curiously weak temperature dependence and a high residual value at the lowest temperatures of measurement (15 K). Powder diffraction data for this compound suggests that crystals prepared at low temperature have lower symmetry than the Pnnm space group originally reported.