Vapor-phase Synthesis Research Articles

Vapor phase synthesis of 2,3,6-trimethylphenol from m-cresol and methanol with Fe2O3-SiO2-CuO catalyst

A novel method for synthesis of 2,3,6-trimethylphenol from m-cresol and methanol with Fe2O3-SiO2-CuO catalyst is developed. The catalysts were characterized by X-ray powder diffraction, N2 physisorption, scanning electron microscope and NH3-TPD. The performances of the Fe2O3-SiO2-CuO catalysts were compared with other catalysts such as Fe2O3, Fe2O3-SiO2, Fe2O3-Cr2O3, Fe2O3-V2O5, Fe2O3-SiO2-V2O5. For Fe2O3-SiO2-CuO catalyst with Fe/Si/Cu molar ratio = 200: 5: 1, the yield of 2,3,6-trimethylphenol reached 97.9% under reaction conditions of 340 °C, 1: 5: 1.5 methanol/m-cresol/water molar ratio and 0.7 h−1 LHSV, which exhibited much higher value than other catalysts.

High-Temperature Plateau–Rayleigh Growth of Beaded SiC/SiO2 Nanochain Heterostructures

The Plateau–Rayleigh (P-R) crystal growth was recently proposed and dramatically extended the one-dimensional nanomaterials synthesis due to its tunable morphological features. Previously reported P-R growth is mainly focused on the relative low-temperature reactions (<1273 K, which is less than the melting point of reaction products or intermediate products), while high-temperature P-R growth with a molten state is rarely studied. To extend P-R growth to high temperature and reveal the underlying mechanism, herein we take the synthesis of SiC/SiO2 heterostructures as the prototype. With optimized growth temperature, we reported a novel high-temperature P-R growth of the beaded SiC/SiO2 nanochain heterostructures through a vapor-phase synthesis. The as-obtained SiC/SiO2 nanochain heterostructures involved the single-crystalline 3C-SiC core with diameters of ∼20 nm, the amorphous SiO2 shell with thicknesses of 200–300 nm, and many uniform periodic amorphous SiO2 beads with diameters of 800–1000 nm. Further...

Vapor phase synthesis of glycerol carbonate over honeycomb monolith coated with zirconia based base catalysts

In this article the synthesis, characterization and catalytic activity studies of zirconia based base catalysts such as Mg(II)/ZrO2, Ca(II)/ZrO2 and Ba(II)/ZrO2 coated on honeycomb monoliths is reported. Honeycomb monoliths were coated with Mg(II)/ZrO2, Ca(II)/ZrO2, Ba(II)/ZrO2 and characterized for their physico-chemical properties such as surface basicity, crystallinity and morphology by using relevant techniques. The catalytic activity of these catalytic materials was evaluated in vapor phase synthesis of glycerol carbonate. The reaction conditions were optimized by varying reaction parameters such as nature of catalytic material, molar ratio of the reactants, catalyst bed temperature, feed-rate of the reactants and time-on-stream to obtain highest possible yield of glycerol carbonate with greater selectivity. The catalytic materials were found to be highly efficient in the synthesis of glycerol carbonate with a possible highest yield up to ~98%. These catalytic materials can be easily reactivated and reused in this reaction.Bangladesh J. Sci. Ind. Res.53(1), 21-28, 2018

Vapor-phase synthesis of piperidine over SiO2 catalysts

Vapor phase dehydration of 5-amino-1-pentanol to produce piperidine was investigated over various oxide catalysts such as ZrO2, TiO2, Al2O3 and SiO2. Among the tested catalysts, SiO2 selectively produced piperidine at 300 °C. A high 5-amino-1-pentanol conversion of 99.9% with a piperidine selectivity of 94.8% was achieved over weak acidic SiO2. In an experiment using isotope such as deuterated water, surface hydroxy groups of SiO2 are concluded to be the active centers.

Sinter-Resistant Platinum Catalyst Supported by Metal-Organic Framework.

Single atoms and few-atom clusters of platinum are uniformly installed on the zirconia nodes of a metal-organic framework (MOF) NU-1000 via targeted vapor-phase synthesis. The catalytic Pt clusters, site-isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 °C. In situ IR spectroscopy reveals the presence of both single atoms and few-atom clusters that depend upon synthesis conditions. Operando X-ray absorption spectroscopy and X-ray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novel catalyst. These results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size-selected clusters, including noble metals, on a high surface area support.

Nanotransplantation Printing of Crystallographic-Orientation-Controlled Single-Crystalline Nanowire Arrays on Diverse Surfaces.

The fabrication of a highly ordered array of single-crystalline nanostructures prepared from solution-phase or vapor-phase synthesis methods is extremely challenging due to multiple difficulties of spatial arrangement and control of crystallographic orientation. Herein, we introduce a nanotransplantation printing (NTPP) technique for the reliable fabrication, transfer, and arrangement of single-crystalline Si nanowires (NWs) on diverse substrates. NTPP entails (1) formation of nanoscale etch mask patterns on conventional low-cost Si via nanotransfer printing, (2) two-step combinatorial plasma etching for defining Si NWs, and (3) detachment and transfer of the NWs onto various receiver substrates using an infiltration-type polymeric transfer medium and a solvent-assisted adhesion switching mechanism. Using this approach, high-quality, highly ordered Si NWs can be formed on almost any type of surface including flexible plastic substrates, biological surfaces, and deep-trench structures. Moreover, NTPP provides controllability of the crystallographic orientation of NWs, which is confirmed by the successful generation of (100)- and (110)-oriented Si NWs with different properties. The outstanding electrical properties of the NWs were confirmed by fabricating and characterizing Schottky junction field-effect transistors. Furthermore, exploiting the highly flexible nature of the NWs, a high-performance piezoresistive strain sensor, with a high gauge factor over 200 was realized.

Formation phenomena of iron oxide-silica composite in microwave plasma and DC thermal plasma

Iron oxide-silica composite was synthesized using atmospheric microwave plasma and DC thermal plasma. There has recently been increasing interest in predicting the final product during vapor phase synthesis using plasma because of difficulty obtaining desirable product. In this study, vapor phase synthesis of iron oxide-silica composite from iron pentacarbonyl (Fe(CO)5) and tetraethyl orthosilicate (SiC8H20O4, TEOS) was conducted using various Fe/Si ratios and different types of plasma to identify the formation mechanism in the Fe-Si-O multi-component system. The morphologies and phase compositions of the synthesized particles were analyzed and compared. The results showed that the Fe/Si ratio and the type of plasma influenced the morphologies and the phase composition. A thermodynamic consideration was introduced to investigate the particle formation phenomena, which could explain the differences induced by varying the Fe/Si ratio and type of plasma. The particle formation mechanism was divided into a condensation step and a diffusion step. At the condensation step, the Fe/Si ratio determined the condensation temperature, which is related to the morphology. At the diffusion step, the quenching rate of the plasma determined the degree of diffusion, which was related to the phase composition and formation of the external layer.

Catalytic activity of vanadium-substituted molybdophosphoric acid supported on titania for the vapor-phase synthesis of isophthalonitrile

ABSTRACTDifferent wt% of vanadium-substituted molybdophosphoric acid H4PMo11VO40 loaded on titania (TiO2) are prepared by wet impregnation method. The catalytic activity of PMoV-supported titania catalyst for the vapor-phase ammoxidation of m-xylene at different temperatures is reported here. The synthesized catalysts were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, N2 adsorption–desorption, thermogravimetric/differential thermal analysis, temperature programmed desorption (TPD), temperature programmed reduction (TPR) scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). FTIR studies confirmed that the Keggin structure of PMoV does not change even up to 460°C when loaded on TiO2 surface. Among all the PMoV-supported TiO2 catalysts, 1.7% PMoV/TiO2 showed excellent activity for vapor-phase ammoxidation of m-xylene with 85.4% yield of isophthalonitrile.

Surfactant-Free Vapor-Phase Synthesis of Single-Crystalline Gold Nanoplates for Optimally Bioactive Surfaces

We report the surfactant-free vapor-phase synthesis of atomically flat and ultraclean gold nanoplates. These gold nanoplates can offer optimally functional surfaces through the immobilization of molecules without unspecific adsorption and defect, which could be quite valuable for diverse applications including biomedical sensing, plasmonics, molecular electronics, electrochemistry, etc. The ultraflat, ultraclean, and single-crystalline nanostructures, including gold nanoparticles (NPs), gold nanowires (NWs), gold nanobelts, and gold nanoplates, are stereoepitaxially grown on a substrate with a specific orientation. Moreover, the nanostructures can be selectively synthesized by experimental conditions and locations of the substrate. The geometry and orientation of the nanostructures show strong correlations, suggesting a growth process of seed NPs → NWs → nanobelts → nanoplates. This synthetic process can be explained by the mechanism in which the height-to-width ratio of gold nanostructures is determined ...

Kinetic Monte Carlo simulation for homogeneous nucleation of metal nanoparticles during vapor phase synthesis

We present a free‐energy driven kinetic Monte Carlo model to simulate homogeneous nucleation of metal nanoparticles (NPs) from vapor phase. The model accounts for monomer‐cluster condensations, cluster–cluster collisions, and cluster evaporations simultaneously. Specifically, we investigate the homogeneous nucleation of Al NPs starting with different initial background temperatures. Our results indicate good agreement with earlier phenomenological studies using the Gibbs# free energy formulation from Classical Nucleation Theory (CNT). Furthermore, nucleation rates for various clusters are calculated through direct cluster observations. The steady‐state nucleation rate estimated using two different approaches namely, the Yasuoka‐Matsumoto (YM) and mean first passage time (MFPT) methods indicate excellent agreement with each other. Finally, our simulation results depict the expected increase in the entropy of mixing as clusters approach the nucleation barrier, followed by its subsequent drastic loss after the critical cluster formation resulting from first‐order phase transitions. © 2017 American Institute of Chemical Engineers AIChE J, 63: 18–28, 2018

Facile vapor-phase synthesis of copper nanostructures on cuprous iodide films

One-dimensional growth of copper (Cu) is observed when Cu is deposited on cuprous iodide (CuI) films at elevated temperatures by thermal evaporation in high vacuum. The morphology, crystallinity, and chemical composition were examined for the samples using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Straight single-crystalline Cu nanowires can be formed on polycrystalline CuI films at 200 °C. Anisotropic growth of Cu in one-dimension was promoted by enhancing grain growth and continuity of CuI films. At a lower temperature of 100 °C, fuzzy branching nanowires were grown on the surface of CuI films, enabling to simply fabricate a self-supporting, highly porous film of Cu. It is revealed that a CuI film serves as a functional substrate to synthesize nanostructured Cu at low temperatures. Possible growth processes are proposed to explain the observed morphology evolution of Cu with respect to synthesis conditions. The characterization of water wettability showed that the hydrophobicity was remarkably enhanced due to the formation of nanostructured Cu on the CuI films.

Morphology Control of Energy-Gap-Engineered Nb2O5 Nanowires and the Regioselective Growth of CdS for Efficient Carrier Transfer Across an Oxide-Sulphide Nanointerface

Semiconductor nanowires with both nano- and micrometre dimensions have been used as effective materials for artificial photosynthesis; however, a single synthesis approach to provide rational control over the macroscopic morphology, which can allow for the high-throughput screening of photocatalytic performance, and carrier transfer between oxide and sulphide nanostructures has been poorly known. Our recent findings indicate that a single parameter, Nb foil thickness, in a vapor-phase synthesis method can alter the macroscopic morphology of resulting Nb2O5 nanowires. Thick Nb foil results in a free-standing Nb2O5 film, whereas a thinner foil leads to fragmentation to give a powder. During the synthesis process, a Rh dopant was provided through metal-organic chemical vapor deposition to reduce the Nb2O5 energy gap. Upon irradiation with visible light (λ > 440 nm), the free-standing nanowire film [Nb2O5:Rh-NW(F)] showed photoanodic current with a Faradaic efficiency of 99% for O2 evolution. Under identical irradiation conditions, the powdered counterpart [Nb2O5:Rh-NW(P)] showed activity for O2 evolution in the presence of an electron acceptor. The poor water-reduction ability was greatly enhanced by the Au-catalysed vapor-liquid-solid (VLS) growth of H2-evolving CdS onto the reduction sites of Nb2O5:Rh-NW(P) [Au/CdS/Nb2O5:Rh-NW(P)].

Solid Conical Cap-closing Hollow Tube Growth by Axial Screw Dislocations

Exploration of the mechanisms for growth of the nanostructures is the key point to achieve nanomaterial syntheses with precisely controlled morphology and structure. Herein, we reported a new mechanism that realized the growth of solid conical cap-closing hollow tube by axial screw dislocations in the formation α-Al2O3 nanowires. A hollow tube was firstly grown by axial screw dislocations in the formation α-Al2O3 nanowires through vapor-phase synthesis. Afterwards, the hollow tube was closed up by generating a solid conical cap with axial screw dislocations based on the competition between the surface energy and the strain energy of screw dislocation controlled by the growth environment. The solid conical cap-closing hollow tube growth model based on the axial screw dislocations is expected to be a general growth mechanism for nanowires within low supersaturation. This study enriches the fundamental understanding with respective to the kinetics of nanostructured crystal growth and provides guidance to the precise structure control in nanosynthesis and manufacturing.

Vapor-phase synthesis of poly(p-xylylene) membranes for gas separations

We report a vapor-phase deposition of poly(p-xylylene) (parylene) membranes for gas separations. Three parylene membranes, poly[(2-chloro-p-xylylene)] (parylene C), poly[(4-amino-p-xylylene)-co-(p-xylylene)] (parylene A), and poly[(2-carboxylic acid N-hydroxysuccinimide ester)-co-(p-xylylene)] (parylene NHS ester), were evaluated. These membranes were deposited on a support of porous poly(vinylidene fluoride) with a dense layer of poly(vinyl alcohol) cast on its top surface. The as-synthesized parylene membranes were characterized by scanning electron microscopy, FT-IR spectroscopy, and the measurements of water contact angle. Single-gas permeation with hydrogen, nitrogen, methane, and carbon dioxide was performed on the parylene membranes for assessing their molecular transport properties. These parylene membranes showed gas permeability of up to hundreds of barrer. To further enhance the gas separation performance of the parylene membranes, polyethylenimine (PEI) was used for modifying the surface of the membranes composed of parylene NHS ester.

Synthesis of coaxial nanotubes of polyaniline and poly(hydroxyethyl methacrylate) by oxidative/initiated chemical vapor deposition

Vapor-phase synthesis techniques of polymeric nanostructures offer unique advantages over conventional, solution-based techniques because of their solventless nature. In this work, we report the fabrication of coaxial polymer nanotubes using two different chemical vapor deposition methods. The fabrication process involves the deposition of an outer layer of the conductive polyaniline (PANI) by oxidative chemical vapor deposition, followed by the deposition of the inner layer of poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel by initiated chemical vapor deposition. The vapor-phase techniques allowed for fine-tuning of the thickness of the individual layers, keeping the functionalities of the polymers intact. The response of the single components and the coaxial nanotubes to changes in humidity was investigated for potential humidity sensor applications. For single-component conductive PANI nanotubes, the resistance changed parabolically with relative humidity because of competing effects of doping and swelling of the PANI polymer under humid conditions. Introducing a hydrogel inner layer increased the overall resistance, and enhanced swelling, which caused the resistance to continuously increase with relative humidity.

Sub-oxide passivation of silicon nanoparticles through rapid mechanical attrition

Inks produced from the inclusion of silicon nanoparticles in a suitable polymer present the best opportunity for true printability of silicon with purely additive patterning under ambient conditions with no thermal post-processing. For large scale production of silicon nanoparticles, the most appropriate methods are vapor phase synthesis by pyrolysis of silane or the milling of bulk material. In this work, we compare low energy ball milling using zirconium ball with a rapid attrition of bulk silicon using a high-energy vibratory disk mill and show that the later process passivates the further growth of surface oxide on the nanoparticles. XPS results indicated a significant surface oxidation for silicon nanoparticles produced using low energy ball milling relative to the rapid attrition using the high-energy vibratory disk. HRTEM shows a pronounced surface oxide thickness on the nanoparticles produced via low energy ball mill. This surface oxide resulted in charge trapping and drastically effected the carrier transport of the compacted powder. The powder produced from the high-energy mill, in contrast, does not show a distinct surface oxide layer under HRTEM and the carrier transport was generally ohmic.

Vapour Phase Synthesis and Characterization of TiN Nanoparticles

Vapour Phase Synthesis and Characterization of TiN Nanoparticles

Vapor phase synthesis of TaS2 nanocrystals with iodine as transport agent

TaS2 is a transition metal dichalcogenide material with a layered two-dimensional crystal structure and physically interesting behavior. 1T-TaS2 in particular exhibits a complex interaction between electron–electron and electron–lattice, as well as unique two-dimensional charge density wave characteristics with varying phase transitions depending on the temperature range. However, few reports exist on the synthesis of TaS2 crystals, and a relatively long time is required for the synthesis of TaS2 nanostructures. Here, we present an efficient method for 1T-TaS2 synthesis by chemical vapor deposition using iodine as a transport agent. We successfully synthesized 1T-TaS2 nanocrystals or thin films in a short processing time of a few hours, and their structural and chemical properties were characterized.

A novel approach to vapor-phase synthesis of 2- and 4-methylquinoline from lactic acid and aniline

A novel and green route for vapor-phase synthesis of 2- and 4-methylquinoline was provided in this work, in which lactic acid as one of the reactants was for the first time employed. Various influencing factors, including types of catalysts, reaction temperature and stability of catalyst were investigated systematically. The results showed that a 67.6% total yield of quinolines was obtained over the HBeta catalyst. The characterization by using BET, NH3-TPD and pyridine-IR techniques revealed that strong Brønsted acid sites are favorable for generation of 2- and 4-methylquinoline whereas Lewis acid sites could increase the proportion of 4-methylquinoline in target products. Besides, a feasible reaction pathway to synthesize 2- and 4-methylquinoline was proposed on the basis of the reaction products.

Vertical growth of cadmium sulfide crystals on a silicon substrate

The results of the technological and microscopy studies of the mechanisms of the vertical growth of cadmium sulfide crystals during vacuum synthesis from the vapor phase were reported. Whisker crystals with a diameter from 10 nm to a few micrometers and with a length of dozens of millimeters can be grown by the vacuum vapor phase synthesis in a quasi-closed volume. The results of studies are satisfactorily explained in terms of the classical vapor–liquid–crystal model. The SEM micrographs are presented.