Juliusz Warzywoda

Crystallization of high-silica ZSM-5 in the presence of seeds

A series of Al-free ZSM-5 crystallizations was carried out with Al-free ZSM-5 seeds in order to investigate the effect of the presence of crystal surface during synthesis. With sufficient seed surface present in the crystallization medium, only growth of the seed crystals should be observed. However, in spite of relatively large seed crystal additions, very little growth was observed. Instead, new populations were observed to form both around the seeds and on the seed surface. This polycrystalline formation was observed on seeds both in conventional batch autoclave systems and in thermal gradient systems

Crystallization phenomena in seeded zeolite syntheses

Abstract Evidence of several different crystallization phenomena is shown under different circumstances. Polycrystalline breeding, surface nucleation, and particle agglomeration are shown to occur in different zeolite systems. These pheomena have been observed in simpler classical crystallization systems, but have not been discussed in detail for zeolite syntheses.

Direct synthesis of zeolite Y with large particle size

Abstract Large zeolite Y particles have been synthesized directly from gels (4.76Na2O: 1.0Al2O3: xSiO2: 454H2O: 5TEA, x=5.25–8.75) aged at ∼293 K before static heating at 368 K. Product purity, size, and Si/Al ratio of zeolite Y depended on the gel composition and aging time. Two-day aging of gels (x=5.25 and 7.0) resulted in nearly pure zeolite Y (

Synthesis of zeolite A in the Na/K system and the effect of seeding

Crystallizations were carried out with a standard zeolite A batch composition, but using pure Na, pure K, or mixtures of Na and K with a constant total cation concentration. Larger zeolite A crystals were formed in the presence of K ions; however, other zeolite phases coprecipitated with zeolite A in increasing amounts as the K ion content increased. No zeolite A was formed in the pure K ion system; however, zeolites K-F and K-G did coprecipitate. Using zeolite A seeds in these preparations is shown to promote the formations of new populations of zeolite A, even in the presence of pure K ion systems. Adding smaller amounts of seeds is shown to reduce the crystallization time of the co-precipitated phases in the pure K ion system, even though new zeolite A crystals do not nucleate.

The role of the dissolution of silicic acid powders in aluminosilicate synthesis mixtures in the crystallization of large mordenite crystals

The role of the dissolution of silicic acid powders in alkaline aluminosilicate synthesis mixtures in the crystallization of mordenite was investigated. Three different as-received lots of silicic acid (Aldrich lots 01807PW (lot A), 04720KX (lot B), and 18913LY (lot C)) were used to synthesize mordenite from the same initial batch composition (4.32 Na 2 O: Al 2 O 3 : 19 SiO 2 : 293.6 H 2 O). Different overall crystallization times (lot A ≈ 10 h, lots B and C ≈ 28 h), conversion rates at the 50% point (lot A ≈ 44% h 1 lots B and C ≈ 12% h 1 ) and maximum crystal sizes (lot A= 10–15 μn, lot B = 35–40 μm, lot C = 30–35 μm) were observed. The prismatic crystal morphologies were the same in all cases. Heat treatment of as-received lots A and B in air at 550°C before syntheses resulted in about 6- and 2-fold decreases of mordenite conversion rates, respectively; and in about 6- and 2-fold increases of mordenite crystal sizes, respectively. Heat treatment of asreceived lot C in air at 850°C resulted in about a 6-fold decrease of mordenite conversion rate and in about a 6-fold increase of mordenite crystal size. Induction periods and overall crystallization times also increased in these cases. Large crystals of mordenite with sizes of up to 250 μm were obtained using lot C heat treated at 850°C. These results reflect different silica dissolution rates that were correlated with the variation of specific surface area and average pore diameter of silicic acid powders. The dissolution of silicic acid in the investigated crystallization of mordenite intervened in the rate-determining step for nucleation and growth of mordenite crystals.

Vertically aligned VO2(B) nanobelt forest and its three-dimensional structure on oriented graphene for energy storage

Assembling two-dimensional (2D) nanomaterials into an ordered forest structure that provides an easily accessible large surface area and/or chemically active 2D edges will present numerous opportunities, including as electrodes for energy storage. We report a densely packed vertically aligned VO2(B) nanobelt (NB) based forest structure synthesized by a solvothermal method using a vertically oriented graphene (VOG) network as the underlying support. We further expanded this forest structure into a folded three-dimensional (3D) forest structure using VOG-covered metallic foam as the scaffold. To demonstrate its potential, this free-standing 3D ordered structure built from 2D nanomaterials was directly used as the electrode for lithium-ion batteries. Excellent performance was confirmed by a stable discharge capacity of 178 mA h g−1 at a current density of 10 A g−1 (or a rate of 59 C) and 100 mA h g−1 at 27 A g−1 (300 C), contributed by both lithium ion intercalation into the crystal lattice and surface-related pseudocapacitance. A high cycling stability over 2000 cycles under a high current density was also demonstrated. We expect that our method can be expanded to synthesize 2D sheet based forest structures of other layered oxides and hydroxides by using VOG as a versatile platform for numerous applications such as energy storage and catalytic energy conversion.

Electrocatalytic properties of a vertically oriented graphene film and its application as a catalytic counter electrode for dye-sensitized solar cells

Vertically oriented graphene (VOG), with graphene sheets perpendicular to the substrate, exhibits meritorious electrocatalytic properties due to the fully exposed graphene (or graphitic) edges and other plasma introduced defects, even without any heteroatom functionalization. We report the growth and electrocatalytic properties of VOG by plasma-enhanced chemical vapor deposition using methane and nitrogen as source gases. Nitrogen was adopted as plasma ancillary gas to obtain a higher plasma temperature that promotes VOG growth with better electrocatalytic performance, as comparative studies demonstrated. Electron transfer dynamics measurement using a Fe(CN)63−/4− redox couple found reduction and oxidation peak-to-peak separation as low as 70 mV, indicating rapid electron-transfer kinetics. The electrocatalytic activity of the VOG electrode on an I−/I3− redox couple was found approaching that of platinum. Using VOG as the counter electrode for dye-sensitized solar cells (DSSCs), a promising power conversion efficiency of 7.63% was demonstrated. Electrochemical impedance spectroscopic study further discloses the impact of VOG properties on DSSC performance.

Analysis of zeolite crystallization with autocatalytic nucleation

Abstract Recently, the use of an empirical expression of the form f = Kt a to describe zeolite crystallization kinetics has been suggested. The incorporation of heterogeneous nucleation and autocatalytic nucleation mechanisms has been discussed previously. It is shown here that a complete and proper development of such a model can lead to ambiguous results. Furthermore, it is shown that these nucleation mechanisms can be incorporated in the population balance formalism, which allows gel and solution material balances to be included. Finally, it is shown that the nucleation history corresponding to such proposed mechanisms is unlike that observed experimentally.

Soybean-derived hierarchical porous carbon with large sulfur loading and sulfur content for high-performance lithium–sulfur batteries

An hierarchical porous carbon nanostructure with intrinsic O- and N-dopants and an ultrahigh specific surface area of 1500 m2 g−1 is reported towards the goal of designing and achieving a better sulfur electrode for lithium–sulfur batteries (LSBs) that can provide both large sulfur loading and large sulfur content and are based on a facile fabrication process. This nanostructure was derived from crude soybeans in a facile pyrolysis process. Using it as a sulfur host, the S/C active composite with 80% sulfur content was made. Cells with different sulfur loadings were investigated and were found to demonstrate large capacity, high coulombic and energy efficiencies, and high cycling stability. In particular, for a sulfur loading of 5.5 mg cm−2 and a sulfur content of 80%, cells displayed a specific capacity of ca. 950 mA h g−1, which corresponds to an areal capacity of 5.2 mA h cm−2. Such a performance moves LSB technology closer to practical applications.

Spin-spray deposited NiZn-Ferrite films exhibiting μr′ > 50 at GHz range

Ni0.27ZnxFe2.73-xO4 (with x = 0.03−0.1) thin films with high real permeability μr′ in the GHz range were fabricated by the spin spray process onto glass substrates in the presence of an external magnetic field of 360 Oe. These films exhibit high permeabilities that exceeded the Snoek limit for bulk NiZn-ferrite films and those previously reported for spin spray deposited ferrites. The NiZn-ferrite film with x = 0.06 is low in magnetic losses, having tanδm (μr″/μr′) ∼ 0.027 from 1 to 1.5 GHz, and a high ferromagnetic resonance (FMR) frequency of 2.7 GHz, while the x = 0.1 film exhibited a high μr′ of ∼50 and μr″ > 50 at 1 GHz. These properties are ideal for microwave applications such as antennas, inductors and electromagnetic interference (EMI) suppression in the GHz range.