Vapor-phase Transport Method Research Articles

Modification of ZSM-23 zeolite via vapor-phase transport method: Reducing the length along the unidimensional channels for enhanced catalytic performances in methanol-to-hydrocarbons

ZSM-23, a unidimensional zeolite, finds application in the methanol-to-hydrocarbons (MTH) reaction, but commonly suffers from rapid deactivation due to diffusion hindrances. Given the challenges of reducing the length along the a-axis of ZSM-23 zeolite while preserving its catalytic functions using conventional methods, this study introduces a post-modification approach inspired by the vapor-phase transport (VPT) method, wherein ZSM-23 is subjected to the vapor of an iso-propylamine (IPA) solution. The results demonstrated that the crystal lengths aligned with the micropores can be effectively reduced to less than half of the original material (115 nm vs. 289 nm), while preserving much of the microstructure and acidity. Insights into the post-treatment mechanism unveiled a coexistence of etching and re-crystallization processes during the procedure, with conditions finely adjustable by varying the concentrations of the IPA solution. The optimized modification procedure resulted in ZSM-23 zeolite demonstrating an increased C2–C4 olefin yield (62.2 % vs. 53.2 %) and enhanced stability (22 h vs. 5 h) in MTH reaction compared to the untreated sample, which can be attributed to the enhanced diffusion properties of the modified zeolite. This vapor-assisted modification protocol successfully expands the toolkit for synthesizing efficient one-dimensional zeolite for catalytic purposes.

Preparation and optoelectronic properties of bulk black phosphorus crystals

In this paper, dense cylindrical shaped bulk black phosphorus (BBP)s are obtained by establishing a well-developed double growth zone technique through a chemical vapor phase transport (CVT) method. Extensive characterization tests confirm its high degree of orientation. XRD, SEM, TEM and Raman specturum are used to characterize the physical composition and structure of the prepared samples, confirming that the prepared BBP has good crystallinity and purity. Optical properties are evaluated, revealing distinct responses in UV–vis testing for black phosphorus (BP) of different sizes. Furthermore, the electrical properties of the bulk black phosphorus are measured, and it is found that the bulk black phosphorus is a P-type semiconductor. And the carrier mobility of the thin black phosphorus layer is 1233.81 cm2/V/S. The maximum Seebeck coefficient of 65.474 μV·K−1 along the growth direction of the column when the temperature difference is within 100 K.

Micro-mesoporous ferrierite obtained using the cationic polymer Luviquat and post-synthesis treatment

This study investigated for the first time the synthesis of ferrierite zeolite through the vapor-phase transport method using the cationic polymer Luviquat as a mesopores-generating agent, followed by desilication treatment. The effect of ferrierite's textural and acid properties was then evaluated in the catalytic cracking of ultra-high molecular weight polyethylene (UHMWPE). The synthesized zeolites showed a crystallinity of 91%–100% and similar Si/Al ratios. After the desilication, there was a decrease in these values along with an increase in acidity, attributable to the extraction of structural silicon. The strong interaction between the polymer and the zeolite precursor during the self-assembly process led to the formation of intracrystalline mesoporosity. However, an internal diffusion limit and/or steric hindrance hinders the complete incorporation of the polymer into the ferrierite structure, especially at high polymer concentrations. Thus, the optimal composition was 40% Luviquat, which resulted in twice the volume of mesopores compared to the sample prepared without the polymer. The desilication of the samples synthesized with the Luviquat led to a substantial increase in mesoporosity, ranging from 67% to 183%, relative to microporous ferrierite. The introduction of mesoporosity and the modification of acid properties in ferrierite contributed to a reduction in the temperature for the cracking of UHMWPE, between 66 and 93 °C compared to the pure polymer. However, in all cases, there was an increase in the average apparent activation energy in relation to desilicated microporous ferrierite zeolite, possibly due to changes in product distribution.

Investigating the Impact of Deposition Parameters on the Biosensing Performance of Zinc Oxide Nanostructured Thin Films Fabricated via Vapor Phase Transport

Despite huge advancements in biosensing technologies in the last few years, there remains a gap in comprehending the intricate relationship between growth parameters and the corresponding biosensing response characteristics. The present work investigates the correlation between the physical properties of ZnO thin films and their biosensing response to address this gap and further fabricate a urea sensor based on the optimized conditions. The Vapor Phase Transport (VPT) method was used to grow ZnO thin films, with biosensing performance observed to be highly dependent on growth conditions. Under optimal conditions, ZnO films demonstrated biosensing-friendly properties such as low stress, strong carrier mobility for electron transfer, and a large surface area for effective biomolecule loading. The prepared bioelectrode (Urs-GLDH/ZnO/Pt/Si) showed excellent performance in detecting urea with a high sensitivity of 41 μAmM−1cm−2 over a wide range of urea concentrations (5–200 mg dl−1 or 0.83–33.33 mM). The urea sensor also exhibited a low limit of detection (LOD) of 1.82 mg dl−1, a high shelf life lasting for 12 weeks, and superior selectivity. Thus, the present study not only aims at enhancing our understanding of the fundamental properties of ZnO thin films and their relation to processing conditions, but also emphasises their potential for enhanced biosensing applications.

Efficient Synthesis of Highly Crystalline One-Dimensional CrCl3 Atomic Chains with a Spin Glass State.

One-dimensional (1D) magnetic material systems have attracted widespread interest from researchers because of their peculiar physical properties and potential applications in spintronics devices. However, the synthesis of 1D magnetic atomic chains has seldom been investigated. Here, we developed an iodine-assisted vacuum chemical vapor-phase transport (I-VCVT) method, utilizing single-walled carbon nanotubes (SWCNTs) with 1D cavities as templates, and high-quality and high-efficiency fabrication of 1D atomic chains of CrCl3 was achieved. Furthermore, the structure of CrCl3 atomic chains in the confined space of SWCNTs was analyzed in detail, and the charge transfer between the 1D atomic chains and SWCNTs was investigated through spectroscopic characterization. A comprehensive study of the dynamic magnetic properties revealed the existence of spin glass states and freezing of the 1D CrCl3 atomic chains at around 3 K, which has never been seen in bulk CrCl3. Our work established an effective strategy for the control synthesis of 1D magnetic atomic chains with promising potential applications in further magnetic-based spintronics devices.

Synthesis of crossed twin disks of ZnO and its growth mechanism

Crossed twin disks of zinc oxide were fabricated by the vapor-phase transport method using a mixture of zinc oxide, indium oxide, and graphite powders as the source materials. The obtained nanostructure consisted of two crossed hexagonal disks, where the size of the disks was about 2.5 μm in diagonal and 300 nm in thickness. XRD result indicated that the as-obtained samples were well-crystallized wurtzite hexagonal ZnO nanostructures. Photoluminescence (PL) properties of the ZnO microdisks was characterized by fluorescent spectroscope with 250 nm picosecond LED. In the proposed growth mechanism, indium played the role of the doping element in the formation of special nucleation habits, which led to the crossed growth of the nanodisks. It is anticipated that this type of ZnO nanodisks would have application potentials in various types of nanodevices, such as light emitters and sensors, information storage devices, transducers, etc.

Broadband BiOCl Nonlinear Saturable Absorber for Watt‐Level Passively Q‐Switched Yb:LuAG Single Crystal Fiber Laser

AbstractThe development of nonlinear optical (NLO) devices is limited to the mid‐infrared range due to the lack of broadband NLO response. As an indirect band gap semiconductor, BiOCl has a band gap of ≈3.3 eV. The special anisotropic lamellar structure makes it exhibit excellent electrical and optical properties; however, its NLO saturable absorption effect is rarely reported. In this study, the NLO response, optical properties, and applications of BiOCl crystals grown by chemical vapor phase transport method are studied in detail. The transmission spectrum indicates the BiOCl crystal has a broadband transparent region (0.4–11 µm). The saturable absorption of BiOCl is characterized by the Z‐scan method with 532 and 1030 nm pulsed lasers. With BiOCl as the saturable absorber (SA), watt‐level passively Q‐switched pulsed laser based on Yb:LuAG single crystal fiber (SCF) is realized. This is the first report of BiOCl as SA for passively Q‐switched all‐solid‐state pulsed laser, and the obtained average power is the highest value of passively Q‐switched SCF pulsed lasers reported so far. The high transmittance, high laser damage threshold, wideband NLO response, and environmental stability of BiOCl indicate that BiOCl crystal is a potential candidate for NLO applications.

Large-sized α-MoO3 layered single crystals for superior NO2 gas sensing

Molybdenum trioxide (MoO3) has attracted considerable research interest due to its unique structural and electronic properties. Herein, we report a monolithic and scalable NO2 gas sensor based on centimeter-sized single-crystalline α-MoO3 synthesized via vapor phase transport method. A combination of advanced characterization probes were utilized to study morphology, composition and crystalline structures of the as-synthesized crystals. At the optimal operating temperature of 100 °C, the centimeter-sized α-MoO3 single crystal based sensor shows an outstanding sensitivity towards NO2 with a limit of detection as low as 5 ppb, as well as superior selectivity and reversibility. The scalability and the intrinsic sensing response are further demonstrated by microscale sensor devices fabricated on individual exfoliated α-MoO3 nanoribbons. Our study presents promising opportunities to develop a high-performance gas sensing platform based on crystalline α-MoO3 to enable monolithic, scalable and integrable sensing technologies.

The effects of copper doping on morphology and room-temperature photoluminescence of ZnO nanocolumns.

In this study, a versatile vapor phase transport method for the synthesis and copper-doping of ZnO nanocolumns is demonstrated. Doping percentage (up to 5%) showed no effect on the wurtzite structural phase of ZnO nanocolumns. However, a decrease in nanocolumn diameter (cross-sectional length of longest side or diagonal) due to doping was observed by scanning electron microscopy. Reduced rate of electron-hole recombination was inferred from a decrease in the intensity of the near-band edge emission peak shown in room-temperature photoluminescence spectra. Expression of structural defects in both doped and undoped nanocolumns suggest p-type conductivity. Observed copper-doping effects show promise for utilizing such structures as electrode components in dye-sensitized solar cells.

Cladding cubic boron nitride powders with Ticompounds

The paper provides the reasoning behind the choice of an iodine-transport method for vapor phase deposition of a Ti-compounds’ layer with uniform thickness on the surface of cubic boron nitride powder grains, to be used as a precursor for subsequent formation of a nitrideboride binder phase for the final composite material, which is promising candidate for thermally stable, high-hardness cutting tools, resistant to impacts and corrosion. The process of plating cubic boron nitride (CBN) powder with titanium compounds via vapor phase transport method was studied experimentally. The paper presents the results of microstructure imaging and XRD analysis of phase composition of the processed powders.

Complex features of the photoluminescence from ZnO nanorods grown by vapor-phase transport method

We present photoluminescence (PL) studies of ZnO nanorods synthesized by high-temperature vapor-phase transport method under pulse laser excitation. The PL spectrum contains a strong near band edge (NBE) emission located at around 387 nm and no emission bands in the visible range were observed. Our studies show that an increase in power density of pulse UV laser results in appearance of a so-called P-band centered at 389 nm and it overlaps the NBE emission. The variations in excitation intensity and detection angles revealed that the band at 389 nm can be deconvoluted into Lorentzian components at ~382 and ~395 nm. Excitation intensity dependence of the band at 389 nm exhibits a clear threshold behavior while the intensity of the band at ~395 nm grows almost linearly with the increase in the excitation intensity. It is possible that the emission band at 395 nm is associated with emission centers caused by zinc vacancy defects or their complexes in ZnO nanorods.

Novel preparation of binder-free Y/ZSM-5 zeolite composites for VOCs adsorption

• Shaped binder-free Y/ZSM-5 were prepared through gas–solid phase crystallization. • Steaming and acid treatment increased the SiO 2 /Al 2 O 3 ratios of Y/ZSM-5 composites. • Y/ZSM-5 composites exhibit mesopores and high adsorption capacities for VOCs. • Dealuminated Y/ZSM-5 exhibit pronounced hydrophobicity under humid conditions. Hydrophobic zeolites have been considered as effective adsorbents for capturing volatile organic compounds (VOCs). In this contribution, a series of binder-free Y/ZSM-5 zeolite composites were prepared through crystallization of shaped precursors by a vapor-phase transport (VPT) method. The obtained Y/ZSM-5 composites were dealuminated by steaming and hydrochloric acid (HCl). The presence of both ZSM-5 and Y zeolites was verified with XRD. FE-TEM was used to confirm the co-existence of lattice fringes of ZSM-5 and Y in the particles. The samples were also characterized by SEM, N 2 adsorption–desorption and ICP-OES. By selecting toluene (TOL), cyclohexane (CYH), butyl acetate (BAC), methyl ethyl ketone (MEK) and isopropanol (IPA) as representative VOCs of aromatics, alkanes, esters, ketones and alcohols, respectively, the dynamic adsorption performance and temperature-programmed desorption performance of the samples were systematically studied. The results showed that the zeolite composites had larger adsorption capacities for TOL, CYH and BAC than ZSM-5 due to larger surface area, wider pore diameter and higher micropore volume. On the other hand, the adsorption capacities of the composites for MEK and IPA were lower than ZSM-5, indicating that they are more suitable to adsorb larger molecules. The composites also exhibited excellent adsorption performance under humid conditions due to high SiO 2 /Al 2 O 3 ratios and hydrophobicity. By comparing the temperature corresponding to the maximum of the desorption peaks, it was found that the adsorbates were easier to desorb on the zeolite composites than on ZSM-5. Furthermore, the adsorbents have good regeneration ability due to high thermal stability and hydrothermal stability.

Effect of weak Mn doping on optical properties of ZnGeP2 single crystal grown by vertical gradient freezing method

ZnGeP2 single crystals weakly doped by manganese (Mn) were grown by vertical gradient freezing method from polycrystalline batch which was synthesized by the modified two temperature vapor phase transport method. Energy Disperse Spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared Spectrometry (FTIR) were employed to characterize the doping single crystals. The un-doped and Mn doped single crystals show the same color. XRD results manifest that the obtained Mn doped ZnGeP2 has tetragonal structure with slight lattice distortion and has no segregation. The EDS results indicate a good stoichiometry of ZnGeP2 weakly doped with Mn. From the XPS results, the doped single crystal with no impurity phases were successfully obtained by the vertical gradient freezing method. FTIR spectra show a slight decrease in infrared transmittance of Mn doped single crystals.

Surface Energy of Black Phosphorus Alloys with Arsenic

AbstractBlack phosphorus belongs to the most intensively studied two‐dimensional materials with many unusual properties. It is capable of forming solid solutions with arsenic, which allows continual tuning of its properties. The vapour phase transport method was used for effective synthesis of black phosphorus and its alloys with arsenic of defined composition using SnI4/Sn mineralising agent. The incorporation of arsenic up to over 50 at.% was confirmed by X‐ray photoelectron spectroscopy. Structural changes were observed by X‐ray diffraction and Raman spectroscopy. Density functional theory calculations were used to calculate the change of lattice parameters due to alloying, to model Raman activity of the bP−As alloy and to estimate the surface energy of the alloy. The surface properties of black phosphorus and its alloys with arsenic were measured by inverse gas chromatography. Although the differences of surface energy between black phosphorus and its alloys were relatively low, the surface energy profiles were unusually flat, indicating a sparsity of high‐energy sites on the surface of the alloys.

Strain-modulated high-quality ZnO cavity modes on different crystal orientations

Dynamically regulated coherent light emission offers a significant impact on improving white light generation, optical communication, on-chip photonic integration, and sensing. Here, we have demonstrated two mechanisms of strain-induced dynamic regulation of ZnO lasing modes through an individual ZnO microbelt and microrod prepared by vapor-phase transport method. We systematically explained the dependence on externally applied strain and crystal orientation. Compared with the reduced size of resonant cavity played a major role in the microbelt, the resonant wavelength variation of the microrod under tensile stress is affected by the change in both the cavity size and the refractive index, which tends to antagonize in the direction of movement. It shows that the refractive index can be effectively regulated only when the stress is in the same direction along the c-axis. The results on the linear relationship between the resonance wavelength variation and applied strain imply the capacity of the devices to detect tiny stresses due to the ultra-narrow line width of the cavity mode with a high-quality factor of ∼104. It not only has a positive influence in the field of the modulated coherent light source, but also provides a feasible strategy for implementing color-resolved non-contact strain sensors.

Direct synthesis of hierarchical binder-free ZSM-5 and catalytic properties for MTP

Abstract Hierarchical binder-free ZSM-5 zeolites were prepared via directly crystallizing the shaped precursors by a vapor-phase transport method. Shaped precursors were crystallized at 160 °C for different time (0–6 d) or at different temperatures (120, 140, 160, 180 or 200 °C) for identical time 5 d. The experimental results showed that the typical MFI structure formed in 2 d at 160 °C and the hierarchical binder-free ZSM-5 zeolites were obtained in 5 d attributed to alkaline etching; after crystallization at 160 °C or 180 °C full-crystalline ZSM-5 zeolites were obtained and the ZSM-5 zeolites had hierarchical pores, but, after crystallization at 200 °C, no mesopores were observed. The hierarchical binder-free ZSM-5 crystallized at 160 °C for 5 d showed the best catalytic performance in methanol to propylene reaction, attributed to its lowest ratio of B/L, largest mesoporous volume and external surface area.

Thin-felt hollow-B-ZSM-5/SS-fiber catalyst for methanol-to-propylene: Toward remarkable stability improvement from mesoporosity-dependent diffusion enhancement

A hollow-B-ZSM-5/SS-fiber catalyst is developed through alkali leaching of the full-silica core of the silicalite-1@B-ZSM-5 in situ structured onto a thin-felt stainless-steel fiber (20 μm SS-fiber), which is synthesized by a seed-assisted dry-gel vapor-phase transport method. As-obtained catalyst shows marked improvement in the mesoporosity-dependent diffusion (by o-xylene diffusion measurement). Boron incorporation is essential for preventing the framework dealumination during alkali leaching treatment due to the increased framework negative charges. The hollow-B-ZSM-5/SS-fiber catalyst shows remarkable stability improvement in the methanol-to-propylene (MTP) reaction because of the enhanced diffusion of the nano-hollow-structure and the boron-incorporation stabilized framework aluminum. A boron-free hollow-ZSM-5/SS-fiber is also obtainable with the textural properties comparable to the hollow-B-ZSM-5/SS-fiber but shows undesired degeneration of the tetra-coordinated aluminum. The preferential generation of coke in the micropores of the hollow-ZSM-5/SS-fiber causes a rapid deactivation even compared to the parent silicalite-1@ZSM-5/SS-fiber, due to the existence of extra-framework aluminum.

High responsivity, self-powered carbon–zinc oxide hybrid thin film based photodetector

A self-powered n-Si/C–ZnO/SiO2/p-Si heterojunction photodetector (PD) which comprises of carbon (C) and zinc oxide (ZnO) nanostructures on a n-type silicon (n-Si) substrate was prepared via vapor phase transport method. Excellent photodetection under 468 nm light illumination for powers ranging from 2.78 to 2910 µW delivered a quick response of about 9.5 µs. A high photoresponsivity of 2.082/AW and external quantum efficiency about 551% were obtained. The mechanism involved for the generation of a photocurrent at a zero bias voltage was discussed for future energy efficient optoelectronics devices. The morphology and composition of C, Zn and O were confirmed by field emission scanning electron microscope, energy dispersive X-ray and Raman scattering analysis. The formation of ZnO nanowires range from 10 to 100 nm, aided by the photoconduction mechanism. The Raman E2high mode of 437/cm of ZnO and the presence of D and G bands show the formation of a hybrid C–ZnO thin film. The calculated rectifying ratio is found to shift as the direct current bias voltage and light power increased. The deposition of C particles on the ZnO surface creates point defects and sub-energy levels in the ZnO bandgap which favour fast responsivity in the PD.

High-performance thin-felt SS-fiber@HZSM-5 catalysts synthesized via seed-assisted vapor phase transport for methanol-to-propylene reaction: Effects of crystal size, mesoporosity and aluminum uniformity

A series of thin-felt SS-fiber@HZSM-5 catalysts are fabricated via the seed-assisted vapor-phase transport (VPT) method. The crystal size and mesoporosity of zeolite shell are controllably tuned toward enhanced diffusion by increasing the silicalite-1 seeding gel (SG) amount used. The microstructured catalyst obtained with a high SG amount of 50% contains a smaller crystal size of ∼70 nm and higher mesopore volume of 0.21 cm3 gzeolite−1, which markedly prolonged single-run lifetime with a remarkable decrease in the coking rate in the MTP process. The adverse effect of non-uniform aluminum in the zeolite shell on the MTP stability is revealed. The use of aluminum-containing SG to replace the pure-silica one makes the acid sites of as-obtained ZSM-5 mounted on SS-fiber distributed homogeneously thereby leading to a marked suppression of hydrogen transfer, and as a result, the catalyst single-run lifetime is further increased by ∼40%. This promising SS-fiber@HZSM-5 catalyst is stable for at least 1600 h (>94% conv.) with a high propylene selectivity of ∼36% at 450 °C using a WHSV of 1 h−1 for a feed of MeOH/H2O molar ratio of 1:1, by taking advantage of improved diffusion from mesoporosity development and uniform aluminum distribution as well as our distinctive microfibrous-engineered design.

Enhanced Photoresponsivity From Hybrid-ZnO Nanowires With White LED 400–700-nm Illumination

This paper highlights the photoresponsivity property of a hybrid-ZnO nanowire (ZnO NW) photodetector to a white LED source with a wavelength range of 400–700 nm. The use of methanol via the vapor phase transport method was utilized to achieve the incorporation of carbon and oxygen particles with Zn to form hybrid-ZnO NWs. Field emission scanning electron microscope, X-ray diffraction, and Raman scattering techniques were used in the identification of morphology, polycrystalline structure, and ${D}$ -, ${G}$ -, and 2-D bands, respectively. Positive photoresponsivity and negative photoresponsivity of the hybrid-ZnO NWs were studied with the LED distances 1–4 cm from the hybrid-ZnO NWs for varied bias voltage from 1 to 4 V. A reproducible photoresponsivity with response times ranging from 182 to $345~\mu \text{s}$ was measured using an oscilloscope. The proposed technique demonstrates the great potential possessed by hybrid-ZnO NWs in optoelectronic applications in the near future.