High-resolution scanning electron microscopy coupled with argon ion-beam cross-section polishing and atomic force microscopy were used to reveal details about the interconnectivity of meso- and ...macroporous networks in silica hierarchical porous material. The material studied has ordered macro- and mesoporosity as well as a disordered microporosity that are created using organic templating agents. Latex spheres template the macro- porosity, mesophase self-assembly of block co-polymers template the mesoporosity and individual polymer chains template the microporosity. By polishing this composite material with an argon ion beam it is possible to reveal the internal structure with minimal structural damage. Direct imaging of the mesoporous network within such cross sections is possible using high-resolution scanning electron microscopy. These observations demonstrate a lack of interconnectivity between the mesoporous and macroporous networks.
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Synopsis: The internal interconnectivity in a hierarchical porous silica material has been verified by a combination of Ar-ion polishing, high- resolution scanning electron microscopy and atomic force microscopy.
Sr partitioning on calcite crystals growing from Ca2+–Sr2+–CO32− solutions was studied by means of friction force microscopy (FFM). Experiments were performed with various Sr2+(aq)/Ca2+(aq) ...concentration ratios and total Sr2+(aq) concentration in order to examine conditions under which Sr-calcite growth is self-limiting (e.g., the so-called “template effect”) and also to investigate continuous Sr-calcite growth, where spiral growth predominates and Sr incorporation is sector-dependent. In these latter experiments, the goal was to evaluate the utility of friction force microscopy to discriminate sector zoning. Results from the experiments show that friction increases with the incorporation of Sr into the growing calcite layers. The maximum increase in friction was measured at high Sr2+(aq)/Ca2+(aq), although a quantitative link between a specific amount of increase in friction to a specific amount of Sr incorporation was not possible to determine due to experimental uncertainties. Nevertheless, it was possible to establish that no change in friction is detectable when Sr incorporation yields a solid composition of Sr0.05Ca0.95CO3. Friction was found to increase during growth of several layers in an incremental fashion. The increase can be linked either to an incremental increase in Sr content in the newly formed calcite, controlled by the thermodynamics of the strained layers necessitated by the substitution of larger Sr cations into the calcite, or to the incremental increase in layer thickness which in turn leads to increases in the probe-surface contact area. No difference in friction could be observed between acute and obtuse sectors under any of the experimental conditions, which was primarily due to the limits of the friction measurement sensitivity.
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•Sr-bearing monolayers displayed 15% higher friction compared to calcite substrate.•Acute and obtuse sector zoning of Sr was not detectable using FFM.•The detection limit for the FFM method is about 5% Sr in Sr-bearing overgrowths.
A new zeolitic–imidazolate framework (ZIF), Zn(imidazolate)2−x(benzimidazolate)x, that has the zeolite A (LTA) framework topology and contains relatively inexpensive organic linkers has been revealed ...using in situ atomic force microscopy. The new material was grown on the structure‐directing surface of Zn(imidazolate)1.5(5‐chlorobenzimidazolate)0.5 (ZIF‐76) crystals, a metal–organic framework (MOF) that also possesses the LTA framework topology. The crystal growth processes for both Zn(imidazolate)2−x(benzimidazolate)x and ZIF‐76 were observed using in situ atomic force microscopy; it is the first time the growth process of a nanoporous material with the complex zeolite A (LTA) framework topology has been monitored temporally at the nanoscale. The results reveal the crystal growth mechanisms and possible surface terminations on the {100} and {111} facets of the materials under low supersaturation conditions. Surface growth of these structurally complex materials was found to proceed through both “birth‐and‐spread” and spiral crystal‐growth mechanisms, with the former occurring through the nucleation and spreading of metastable and stable sub‐layers reliant on the presence of non‐framework species to bridge the framework during formation. These results support the notion that the latter process may be a general mechanism of surface crystal growth applicable to numerous crystalline nanoporous materials of differing complexity and demonstrate that the methodology of seeded crystal growth can be used to discover previously unobtainable ZIFs and MOFs with desirable framework compositions.
Surface inspired: A new zeolitic–imidazolate framework that has the zeolite A framework topology and contains relatively inexpensive organic linkers has been grown on the structure‐directing surface of ZIF‐76 (Zn(imidazolate)1.5(5‐chlorobenzimidazolate)0.5) crystals (see figure). Structural aspects, crystal growth mechanisms and possible surface terminations of both materials are revealed using in situ atomic force microscopy. The work exemplifies the use of this methodology to discover new MOFs with desirable frameworks.
A Monte Carlo crystal growth simulation tool,
, is described which is able to simultaneously model both the crystal habit and nanoscopic surface topography of any crystal structure under conditions ...of variable supersaturation or at equilibrium. This tool has been developed in order to permit the rapid simulation of crystal surface maps generated by scanning probe microscopies in combination with overall crystal habit. As the simulation is based upon a coarse graining at the nanoscopic level features such as crystal rounding at low supersaturation or undersaturation conditions are also faithfully reproduced.
permits the incorporation of screw dislocations with arbitrary Burgers vectors and also the investigation of internal point defects in crystals. The effect of growth modifiers can be addressed by selective poisoning of specific growth sites. The tool is designed for those interested in understanding and controlling the outcome of crystal growth through a deeper comprehension of the key controlling experimental parameters.
A new zeolitic-imidazolate framework (ZIF), Zn(imidazolate)2-x(benzimidazolate)x, that has the zeoliteA (LTA) framework topology and contains relatively inexpensive organic linkers has been revealed ...using in situ atomic force microscopy. The new material was grown on the structure-directing surface of Zn(imidazolate)1.5(5-chlorobenzimidazolate)0.5 (ZIF-76) crystals, a metal-organic framework (MOF) that also possesses the LTA framework topology. The crystal growth processes for both Zn(imidazolate)2-x(benzimidazolate)x and ZIF-76 were observed using in situ atomic force microscopy; it is the first time the growth process of a nanoporous material with the complex zeoliteA (LTA) framework topology has been monitored temporally at the nanoscale. The results reveal the crystal growth mechanisms and possible surface terminations on the {100} and {111} facets of the materials under low supersaturation conditions. Surface growth of these structurally complex materials was found to proceed through both "birth-and-spread" and spiral crystal-growth mechanisms, with the former occurring through the nucleation and spreading of metastable and stable sub-layers reliant on the presence of non-framework species to bridge the framework during formation. These results support the notion that the latter process may be a general mechanism of surface crystal growth applicable to numerous crystalline nanoporous materials of differing complexity and demonstrate that the methodology of seeded crystal growth can be used to discover previously unobtainable ZIFs and MOFs with desirable framework compositions. PUBLICATION ABSTRACT
Volcanic plumes are complex environments composed of gases and ash particles, where chemical and physical processes occur at different temperature and compositional regimes. Commonly, soluble ...sulphate- and chloride-bearing salts are formed on ash as gases interact with ash surfaces. Exposure to respirable volcanic ash following an eruption is potentially a significant health concern. The impact of such gas-ash interactions on ash toxicity is wholly un-investigated. Here, we study, for the first time, whether the interaction of volcanic particles with sulphur dioxide (SO2) gas, and the resulting presence of sulphate salt deposits on particle surfaces, influences toxicity to the respiratory system, using an advanced in vitro approach.
To emplace surface sulphate salts on particles, via replication of the physicochemical reactions that occur between pristine ash surfaces and volcanic gas, analogue substrates (powdered synthetic volcanic glass and natural pumice) were exposed to SO2 at 500 °C, in a novel Advanced Gas-Ash Reactor, resulting in salt-laden particles. The solubility of surface salt deposits was then assessed by leaching in water and geochemical modelling. A human multicellular lung model was exposed to aerosolised salt-laden and pristine (salt-free) particles, and incubated for 24 h. Cell cultures were subsequently assessed for biological endpoints, including cytotoxicity (lactate dehydrogenase release), oxidative stress (oxidative stress-related gene expression; heme oxygenase 1 and NAD(P)H dehydrogenase quinone 1) and its (pro-)inflammatory response (tumour necrosis factor α, interleukin 8 and interleukin 1β at gene and protein levels).
In the lung cell model no significant effects were observed between the pristine and SO2-exposed particles, indicating that the surface salt deposits, and the underlying alterations to the substrate, do not cause acute adverse effects in vitro. Based on the leachate data, the majority of the sulphate salts from the ash surfaces are likely to dissolve in the lungs prior to cellular uptake.
The findings of this study indicate that interaction of volcanic ash with SO2 during ash generation and transport does not significantly affect the respiratory toxicity of volcanic ash in vitro. Therefore, sulphate salts are unlikely a dominant factor controlling variability in in vitro toxicity assessments observed during previous eruption response efforts.
•First study to assess the impact of in-plume processing on ash toxicity in vitro.•Ash surface salts are likely to dissolve in the lungs prior to cellular uptake.•No adverse biological impact to lung model was observed in acute exposure scenario.•Volcanic ash-SO2 reactions do not significantly affect ash respiratory toxicity.
Hierarchical silica porous materials have been successfully synthesized using polystyrene nanospheres as macropore template, triblock copolymer Pluronic F127 as mesopore template, tetramethyl ...orthosilicate as silica source and ethanol as cosurfactant. The obtained materials were characterized by XRD, TG-DTA, N2 adsorption, SEM, TEM and AFM. These materials consist of a system of macropores with diameters of ca. 300 nm whose walls are filled with mesoporous material with average pore diameter 10 nm. The materials are also integrated with non-crystalline micropores. The XRD pattern indicates one sample with structure Fmm, which consists of the mesopores organized in a face-centred cubic arrangement. The hierarchical porous material created after template extraction by solvent washing exhibited a BET surface area of 277 m2 g-1. Following calcination the material has a BET surface area of 469 m2 g-1. Such properties give these materials potential for a wide range of applications in which high surface area combined with a well-defined system of pores at different length scales are required, such as adsorption, catalysis and enzyme immobilization.
The uptake of Cd
2+ by aragonite and calcite is investigated by combining macroscopic measurements with some qualitative sorption experiments performed in a hydrogel medium. Both biogenic and ...abiogenic aragonites were studied in order to evaluate the process on materials with different textures. Assuming that sorption occurs by surface precipitation of metal-bearing solids, the gel produces a drastic decrease in the nucleation density, which allows for the precipitation of crystallites that are large enough to be analysed by scanning electron microscopy and characterized by glancing-incidence X-ray techniques. The macroscopic study reveals that aragonite is a powerful sorbent for cadmium in aqueous environments. Microscopic observations indicate that cadmium is sorbed onto aragonite by surface precipitation of (Cd, Ca)CO
3 solid solutions with a calcite-type structure. The precipitating individuals grow randomly oriented on the surface to reach sizes in the micrometre range. As a consequence, the concentration of cadmium in the aqueous solution decreases dramatically to values controlled by the low solubility of the cadmium-rich end member. This mechanism involves simultaneous dissolution-crystallization and is the same for both abiogenic and biogenic aragonites, the only difference being a result of the higher specific surface area of the biogenic starting material. Long-term uptake of cadmium by calcite occurs through a similar dissolution-crystallization mechanism, the final outcome being virtually the same, that is, surface precipitation of (Cd,Ca)CO
3 solid solutions. In this case, however, substrate and precipitate are isostructural and the process occurs by oriented overgrowth of thin lamellar crystallites, which spread to quickly cover the surface by a layer a few nanometers thick. This epitaxial layer armors the substrate from further dissolution, so that the process stops when only a small amount of cadmium has been removed from the fluid. As a result, the “sorption capacity” of calcite is considerably lower than that of aragonite. The study illustrates reaction pathways and “partial” equilibrium endpoints in surface-precipitation processes involving solid solutions.
A combination of atomic force microscopy (AFM), high‐resolution scanning electron microscopy (HR‐SEM), focused‐ion‐beam scanning electron microscopy (FIB‐SEM), X‐ray photoelectron spectroscopy (XPS), ...confocal fluorescence microscopy (CFM), and UV/Vis and synchrotron‐based IR microspectroscopy was used to investigate the dealumination processes of zeolite ZSM‐5 at the individual crystal level. It was shown that steaming has a significant impact on the porosity, acidity, and reactivity of the zeolite materials. The catalytic performance, tested by the styrene oligomerization and methanol‐to‐olefin reactions, led to the conclusion that mild steaming conditions resulted in greatly enhanced acidity and reactivity of dealuminated zeolite ZSM‐5. Interestingly, only residual surface mesoporosity was generated in the mildly steamed ZSM‐5 zeolite, leading to rapid crystal coloration and coking upon catalytic testing and indicating an enhanced deactivation of the zeolites. In contrast, harsh steaming conditions generated 5–50 nm mesopores, extensively improving the accessibility of the zeolites. However, severe dealumination decreased the strength of the Brønsted acid sites, causing a depletion of the overall acidity, which resulted in a major drop in catalytic activity.
Which zeolite micropores dislike steaming conditions? A combination of microspectroscopic techniques was used to unravel the dealumination process at the level of a single zeolite crystal. By steaming under mild and severe conditions, the significant influence of the steaming temperature on the accessibility, acidity, and catalytic activity of the studied materials was revealed.
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