Deactivation and reactivation behavior of microporous and hierarchical ZSM-5 zeolites have been studied in the methanol-to-hydrocarbon (MTH) reaction. The location of the coke deposits in the ...deactivated materials depends on their textural properties. Display omitted
•Coke deposits in microporous and hierarchical ZSM-5 are studied in MTH reaction.•EDX line scans along particle cross-section show different localization of coke.•Coke removal for reuse in MTH reaction results in different acidity properties.•Therefore, reactivated materials have different catalytic performances.
The deactivation and reactivation of microporous and hierarchical ZSM-5 zeolites have been studied in the methanol-to-hydrocarbon (MTH) reaction. The hierarchical ZSM-5 was synthesized via the desilication reassembly technique using cetyltrimethylammonium bromide as a surfactant. The catalysts differed significantly in the catalytic behavior after the reactivation procedure. This is ascribed to a different coke location in the deactivated catalysts arising from the difference in the porosity. The microporous ZSM-5 showed a coke gradient over the particle with a stronger accumulation of carbonaceous species in the outer particle layers, whereas a homogeneous coke distribution was observed for the deactivated hierarchical ZSM-5. Due to the diverging coke distribution, the irreversible damage of the zeolitic structure caused by reactivation differs for both catalysts. This fact is assumed to be the reason for the different deactivation/reactivation behaviors of these two zeolitic systems.
The realization of ferromagnetism in semiconductors is an attractive avenue for the development of spintronic applications. Here, we report a semiconducting layered metal-organic framework (MOF), ...namely K
Fe
(2,3,9,10,16,17,23,24-octahydroxy phthalocyaninato)Fe (K
Fe
PcFe-O
) with spontaneous magnetization. This layered MOF features in-plane full π-d conjugation and exhibits semiconducting behavior with a room temperature carrier mobility of 15 ± 2 cm
V
s
as determined by time-resolved Terahertz spectroscopy. Magnetization experiments and
Fe Mössbauer spectroscopy demonstrate the presence of long-range magnetic correlations in K
Fe
PcFe-O
arising from the magnetic coupling between iron centers via delocalized π electrons. The sample exhibits superparamagnetic features due to a distribution of crystal size and possesses magnetic hysteresis up to 350 K. Our work sets the stage for the development of spintronic materials exploiting magnetic MOF semiconductors.
Ordered mesoporous carbide‐derived carbon (OM‐CDC) materials produced by nanocasting of ordered mesoporous silica templates are characterized by a bimodal pore size distribution with a high ratio of ...micropores. The micropores result in outstanding adsorption capacities and the well‐defined mesopores facilitate enhanced kinetics in adsorption processes. Here, for the first time, a systematic study is presented, in which the effects of synthesis temperature on the electrochemical performance of these materials in supercapacitors based on a 1 M aqueous solution of sulfuric acid and 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ionic liquid are reported. Cyclic voltammetry shows the specific capacitance of the OM‐CDC materials exceeds 200 F g−1 in the aqueous electrolyte and 185 F g−1 in the ionic liquid, when measured in a symmetric configuration in voltage ranges of up to 0.6 and 2 V, respectively. The ordered mesoporous channels in the produced OM‐CDC materials serve as ion‐highways and allow for very fast ionic transport into the bulk of the OM‐CDC particles. At room temperature the enhanced ion transport leads to 75% and 90% of the capacitance retention at current densities in excess of ∼10 A g−1 in ionic liquid and aqueous electrolytes, respectively. The supercapacitors based on 250–300 μm OM‐CDC electrodes demonstrate an operating frequency of up to 7 Hz in aqueous electrolyte. The combination of high specific capacitance and outstanding rate capabilities of the OM‐CDC materials is unmatched by state‐of‐the art activated carbons and strictly microporous CDC materials.
Ordered mesoporous carbide‐derived carbon (OM‐CDC) materials produced by nanocasting of ordered mesoporous silica templates showed fast rate capability and specific capacitance up to 200 F g−1 in aqueous electrolytes and ionic liquids. At room temperature, the enhanced ion transport in OM‐CDC allowed up to 90% of the capacitance retention at current densities in excess of ∼10 A g−1.
The storage of metastable compounds and modifications of elements are of great interest for synthesis and other, e.g., semiconductor, applications. Whereas white phosphorus is a metastable ...modification that can be stored under certain conditions, storage of the extremely (light- and air-)sensitive form of arsenic, yellow arsenic, is a challenge rarely tackled so far. Herein, we report on the facile storage and release of these tetrahedral E
molecules (E = P, As) using activated carbon as a porous storage material. These loaded materials are air- and light-stable and have been comprehensively characterized by solid-state
P{
H} MAS NMR spectroscopy, powder X-ray diffraction analysis, nitrogen adsorption measurements, and thermogravimetric analysis. Additionally, we show that these materials can be used as a suitable E
source for releasing intact white phosphorus or yellow arsenic, enabling subsequent reactions in solution. Because the uptake and release of E
are reversible, these materials are excellent carriers of these highly reactive modifications.
Switchable metal–organic frameworks (MOFs) change their structure in time and selectively open their pores adsorbing guest molecules, leading to highly selective separation, pressure amplification, ...sensing, and actuation applications. The 3D engineering of MOFs has reached a high level of maturity, but spatiotemporal evolution opens a new perspective toward engineering materials in the 4th dimension (time) by t‐axis design, in essence exploiting the deliberate tuning of activation barriers. This work demonstrates the first example in which an explicit temporal engineering of a switchable MOF (DUT‐8, M1M2(2,6‐ndc)2dabcon, 2,6‐ndc = 2,6‐naphthalene dicarboxylate, dabco = 1,4diazabicyclo2.2.2octane, M1 = Ni, M2 = Co) is presented. The temporal response is deliberately tuned by variations in cobalt content. A spectrum of advanced analytical methods is presented for analyzing the switching kinetics stimulated by vapor adsorption using in situ time‐resolved techniques ranging from ensemble adsorption and advanced synchrotron X‐ray diffraction experiments to individual crystal analysis. A novel analysis technique based on microscopic observation of individual crystals in a microfluidic channel reveals the lowest limit for adsorption switching reported so far. Differences in the spatiotemporal response of crystal ensembles originate from an induction time that varies statistically and widens characteristically with increasing cobalt content reflecting increasing activation barriers.
A pillared layer metal–organic frameworks can be tuned along a time axis by adjusting the ratio of nickel and cobalt in the paddle wheel node. Advanced in situ methodologies reveal switching rates ranging from 1 to 200 s. Individual crystal observations in a microfluidic device reveal prolonged induction time in particular for highly cobalt substituted frameworks.
Negative gas adsorption (NGA) in ordered mesoporous solids is associated with giant contractive structural transitions traversing through metastable states. Here, by systematically downsizing the ...crystal dimensions of a mesoporous MOF (DUT-49) from several micrometers to less than 200 nm, counterintuitive NGA phenomena are demonstrated to critically depend on the primary crystallite size. Adsorbing probe molecules, such as n-butane or nitrogen, gives insights into size-dependent activation barriers and thermodynamics associated with guest-induced network contraction. Below a critical crystal size, the nitrogen adsorption-induced breathing is completely suppressed as detected using parallelized synchrotron X-ray diffraction-adsorption instrumentation. In contrast, even the smallest particles show NGA in the presence of n-butane, however, associated with a significantly reduced pressure amplification. Consequently, the magnitude of NGA in terms of amount of gas expulsed and pressure amplification can be tuned, potentially paving the way towards innovative concepts for pressure amplification in micro- and macro-system engineering.
Best of both worlds: PtxPdy, Pt, and Pd aerogels with high surface area and porosity can be synthesized in a controlled fashion by a straightforward and environmentally benign strategy. These ...materials, which are highly active and stable catalysts for the oxygen reduction reaction in PEFC cathodes, combine the high stability of extended surfaces with the high surface area of nanoparticles.
There is significant interest in high‐performance materials that can directly and efficiently capture water vapor, particularly from air. Herein, we report a class of novel porous carbon cuboids with ...unusual ultra‐hydrophilic properties, over which the synergistic effects between surface heterogeneity and micropore architecture is maximized, leading to the best atmospheric water‐capture performance among porous carbons to date, with a water capacity of up to 9.82 mmol g−1 at P/P0=0.2 and 25 °C (20 % relative humidity or 6000 ppm). Benefiting from properties, such as defined morphology, narrow pore size distribution, and high heterogeneity, this series of functional carbons may serve as model materials for fundamental research on carbon chemistry and the advance of new types of materials for water‐vapor capture as well as other applications requiring combined highly hydrophilic surface chemistry, developed hierarchical porosity, and excellent stability.
Thirsty materials: A new class of ultra‐hydrophilic porous carbon cuboids shows the best performance for atmospheric‐water capture among porous carbons to date. It may serve as a model material for research on carbon chemistry, a new material for water capture, and find use in applications requiring highly hydrophilic surfaces, porosity, and stability.
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► PEGylated hollow mesoporous silica nanoparticles exhibit much better dispersity and stability in aqueous solution. ► PEGylation facilitates cell uptake of nanoparticles by Hela and ...NIH3T3 cells. ► PEGylated nanoparticles have sustained release property. ► DOX-loaded PEGylated nanoparticles induce higher cytotoxicity against Hela and NIH3T3 cells.
Herein we reported the PEGylated hollow mesoporous silica (HMS-PEG) nanoparticles as drug vehicles for drug delivery. Hollow mesoporous silica (HMS) nanoparticles with the diameter of ca. 100
nm were synthesized using the colloidal carbon spheres as templates, and HMS-PEG nanoparticles were successfully prepared by covalently grafting poly(oxyethylene)bis(amine) on amino-group modified HMS nanoparticles with
p-phenylene diisothiocyanate (DITC) as a cross linker. HMS-PEG nanoparticles exhibited much better dispersity and stability in aqueous solution than HMS nanoparticles. In vitro cytotoxicity and cell uptake of HMS-PEG nanoparticles to Hela and NIH3T3 cells were evaluated. HMS-PEG nanoparticles have little in vitro cytotoxicity up to a concentration of 150
μg/ml, and the uptake amount of HMS-PEG nanoparticles is approximately two times than that of HMS nanoparticles in Hela and NIH3T3 cells. Doxorubicin hydrochloride (DOX), an anticancer drug, was loaded into HMS-PEG nanoparticles, and the DOX-loaded HMS-PEG nanoparticles had a sustained release property. Furthermore, the DOX-loaded HMS-PEG nanoparticles exhibited higher cytotoxicity than the DOX-loaded HMS nanoparticles against Hela and NIH3T3 cells. Therefore, the PEGylation of HMS nanoparticles is a promising strategy toward their potential application as drug delivery vehicles.
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