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A Monte Carlo crystal growth simulation tool, CrystalGrower, 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. CrystalGrower 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., Generic in silico methodology – CrystalGrower – for simulating crystal habit and nanoscopic surface topology to determine crystallisation free energies.

This paper investigates the nano to core-scale geomechanical properties of a maturity series of organic-rich, calcareous shales buried to 100-180°C, with a focus on: (a) the mechanical properties of organic matter; (b) the elastic response and anisotropy of the shale composite at micro and core scale; and (c) the creep response. Atomic force microscopy was used to target kerogen at nanoscale resolution, and it was found that the elastic stiffness increased with thermal maturity from 5.8 GPa in an immature sample to 11.3 GPa in a mature sample. Nanoindentation testing of the shale matrix showed that diagenesis is a key factor in determining the bulk elasticity, with increasingly intense carbonate cementation at higher thermal maturities contributing to a stiffer response. A multiscale model was formulated to upscale the elastic properties from nanoscale solid clay minerals to a microcracked composite at core scale, with good predictions of the micro and core-scale stiffness in comparison to indentation and triaxial results. A negative correlation was found between the creep modulus and clay/kerogen content, with greater creep displacement observed in nanoindentation tests in the immature clay- and kerogen-rich sample compared to samples of higher thermal maturity.

We present this study on FAU-type zeolites were prepared varying the Si/Al ratio (4, 5 and 6) and crystallization time (4, 6 and 8 h) to produce a highly pure and homogeneous material with enhanced surface area values. Bimetallic Pd-Ru and Pt-Ru (0.5 wt.% of each metal) were impregnated onto the zeolites matrix by the incipient wetness impregnation method. The materials were characterized by X-ray diffraction (XRD), nitrogen physisorption, Fourier Transform Infrared spectroscopy (FT-IR), Scattering Electronic Microscopy (SEM), Scattering and Transmission Microscopy (STEM), temperature-programmed desorption (TPD), temperature-programmed desorption (TPR) and Inductively Couples Plasma- Mass Spectrometer (ICP-MS). Results indicated that using lower Si/Al ratios favored the catalytic activity. Also, the longest crystallization time had a positive effect on surface area, homogeneous particle size distribution and crystallinity. The catalytic performance in the esterification of 5-hydroxymethylfurfural (5-HMF) to produce 5-acetoxymethylfurfural (AcMF) was investigated. The maximum 5-HMF conversion of 87.28 % was achieved using pure zeolite with relation Si/Al = 5, and 8 h of crystallization. Pd-Ru supported onto same zeolite showed a conversion of 84.22 %. The highest selectivity towards AcMF of 71.29 % with pure zeolite Si/Al = 5 and 8 h of crystallization was achieved, followed by Pd-Ru/FAU with Si/Al = 5 and 8 h of crystallization, achieving 60.42 %. Finally, results shown that the interaction between the properties of zeolitic support and the metallic species, specifically Pd, had a positive effect in the catalytic process the pristine zeolite showed improved catalytic characteristics related to its acid strength.

Background 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. Methods 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). Results 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. Conclusions 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.

Determination of the mechanical response of shales through experimental procedures is a practical challenge due to their heterogeneity and the practical difficulties of retrieving good-quality core samples. Here, we investigate the possibility of using multiscale homogenisation techniques to predict the macroscopic mechanical response of shales based on quantitative mineralogical descriptions. We use the novel PeakForce Quantitative Nanomechanical Mapping technique to generate high-resolution mechanical images of shales, allowing the response of porous clay, organic matter, and mineral inclusions to be measured at the nanoscale. These observations support some of the assumptions previously made in the use of homogenisation methods to estimate the elastic properties of shale and also earlier estimates of the mechanical properties of organic matter. We evaluate the applicability of homogenisation techniques against measured elastic responses of organic-rich shales, partly from published data and also from new indentation tests carried out in this work. Comparison of experimental values of the elastic constants of shale samples with those predicted by homogenisation methods showed that almost all predictions were within the standard deviation of experimental data. This suggests that the homogenisation approach is a useful way of estimating the elastic and mechanical properties of shales in situations where conventional rock mechanics test data cannot be measured.

Summary The effective exploitation of unconventional shale hydrocarbon resources requires the robust geomechanical characterisation of the reservoir. However, there is still a paucity of mechanical data on well-characterised shale, partly due to the technical and economic difficulties in obtaining high quality core for laboratory testing. Here, we present the results of a study which combines PeakForce Quantitative Nanomechanical Mapping and nanoidentation testing on three shales from the Posidonia of NW Germany, covering a range of thermal maturities. PF-QNM is used to determine the mechanical properties of individual organic, clay mineral and other phases, including their anisotropy. Estimates of bulk elastic and viscoelastic parameters are determined through use of high load instrumented indentation testing. These data form the building blocks for the estimation of the geomechanical properties of shales at larger scales, as a function of mineralogy and organic matter type and content.

Summary Low-salinity enhanced oil recovery (LSEOR) has shown great effectiveness in improving the oil recovery ratio and therefore extending the life of mature oil reservoirs. This effectiveness is related to the ability of low salinity injection water to change the wettability state of the reservoir to more water-wet. However, the complexity of the chemical relationship between brine, oil and rock is such that no single mechanism has been identified for being responsible for this change in wettability. This said, the role of clay minerals (which are widely present in the pore space of clastic reservoirs) in their interaction to oil molecules has been regarded as critical. In this work, we aim to study the effect of formation water (varying composition), model oil (decanoic acid/dodecane) aging and low salinity treatment (with varying degrees of concentration and cation identity) on clay mineral wettability, as studied by contact angle measurements. To this end, we have developed a method to prepare smooth, oriented, kaolinite films (with the siloxane face exposed to the solution/oil) of several square cm and a submicron roughness. Contact angles of model oil droplets over the clay films were measured using the sessile drop method. Results show that formation water containing Na+ does not result in large contact angle (wettability) variation, but the presence of Ca2+ does. Increasing pH from 6.5 to 8 leads to an overall increase in the measured contact angle, i.e. to decreased oil sorption (or increasing water-wetness) by the kaolinite film. This effect can be explained by the protonation state of the polar molecules (decanoic acid) as well as the surface complexation (which would lead to the formation of cation bridges in the case of Ca2+). Treatment (washing) of oil-aged films by brines of different concentrations (and either CaCl2 or NaCl composition) showed no clear trends in the modification of contact angle but, in general, increasing CaCl2 concentrations leads to lower contact angles, i.e. less oil desorption (oil wet surface). On the other hand most treatment with NaCl led to higher contact angles, or increased waterwetness of the kaolinite films.

This study introduces a new framework to quantify the wettability of powdered carbonate rock from existing correlations between zeta potential and contact angle. The new framework has the potential to be faster and cheaper than conventional approaches and could increase confidence in surface wetting quantification, since the results are insensitive to the inherent heterogeneity of rock surfaces. The obtained results from experiments were used to develop a set of equations for determining the carbonate rock contact angle from streaming potential data. The equations were validated for the evaluation of changes in the wettability of carbonate rock using different stearic acid oily solutions. The contact angles calculated from the proposed equations were then compared with measured values on the calcite surface. The results show that the proposed framework was able to quantify the wettability of carbonate rock with an acceptable range of error of about 4%–14%.

Robust geomechanical characterisation of shale reservoirs is necessary for safe and economic resource exploitation but there is still a lack of mechanical data on well-characterised shale, partly due to the difficulties of obtaining high quality core samples for laboratory testing. The composition of shale also presents challenges when attempting to constrain the mechanical response. Multi-scale homogenisation techniques have recently been used to predict the macroscopic behaviour of shales based on quantitative mineralogical descriptions. However, there is a considerable amount of uncertainty associated with some key inputs into these homogenisation schemes. In particular, the organic matter of shale encompasses a range of scales, from nanometre to micrometre-size material, and its mechanical properties are not well understood. Here, PeakForce Quantitative Nanomechanical Mapping (PF-QNM), a recently developed form of atomic force microscopy (AFM), is combined with nanoindentation testing to characterise the mechanical response of the organic matter and clay phases of Posidonia shale from north-west Germany. The nanoscale testing revealed a clear peak in the histograms of the reduced elastic modulus, which can be attributed to kerogen in the shale matrix. Upscaling of the mechanical properties through homogenisation showed a reasonable prediction when compared with experimental data, including capturing the inherent anisotropy of the shale response. The influence of factors such as the volume fraction of silt inclusions and the applicability of different homogenisation formulations warrant further investigation.

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.

Enhanced oil recovery is becoming commonplace in order to maximize recovery from oil fields. One of these methods, low-salinity enhanced oil recovery (EOR), has shown promise; however, the fundamental underlying chemistry requires elucidating. Here, three mechanisms proposed to account for low-salinity enhanced oil recovery in sandstone reservoirs are investigated using molecular dynamic simulations. The mechanisms probed are electric double layer expansion, multicomponent ionic exchange, and pH effects arising at clay mineral surfaces. Simulations of smectite basal planes interacting with uncharged nonpolar decane, uncharged polar decanoic acid, and charged Na decanoate model compounds are used to this end. Various salt concentrations of NaCl are modeled: 0‰, 1‰, 5‰, and 35‰ to determine the role of salinity upon the three separate mechanisms. Furthermore, the initial oil/water-wetness of the clay surface is modeled. Results show that electric double layer expansion is not able to fully explain the effects of low-salinity enhanced oil recovery. The pH surrounding a clay’s basal plane, and hence the protonation and charge of acid molecules, is determined to be one of the dominant effects driving low-salinity EOR. Further, results indicate that the presence of calcium cations can drastically alter the oil wettability of a clay mineral surface. Replacing all divalent cations with monovalent cations through multicomponent cation exchange dramatically increases the water wettability of a clay surface and will increase EOR.

Berea sandstone has been used by the petroleum industry as a representative model siliciclastic rock for a number of years. However, only incomplete data has been reported in the literature regarding its petrographic, geochemical, and petrophysical properties. In particular knowledge of the mineral distribution along the pore walls is particularly scarce, despite the fact that mineral exposed in the pore space will be crucial in determining the rock-fluid interactions that occur during core-flooding experiments. In this paper, four Berea sandstone samples (with 4 different permeability ranges from

A general simulation approach that can replicate, and in theory predict, the growth of a wide range of crystal types, including porous, molecular and ionic crystals, is demonstrated. Understanding crystal growth is essential for controlling functionality in modern materials. Michael Anderson et al. describe a simulation approach to predicting crystal growth that can replicate, and in theory predict, the fine details of surface structure and habit for a wide range of crystal types, including porous crystalline materials, metal–organic frameworks and ionic crystals. The method is based on Monte Carlo simulations of 'units of growth'—space-filling tiles or Voronoi polyhedra, depending on the nature of the crystal. This is a coarse-grained alternative to the computationally intensive and sometimes intractable problem of simulating individual atomic positions. The approach replicates the surface structure of experimentally grown crystals that incorporate growth modifiers or common defects, and those grown out of equilibrium, and could be applicable across a variety of crystal systems, the authors say. Understanding and predicting crystal growth is fundamental to the control of functionality in modern materials. Despite investigations for more than one hundred years1,2,3,4,5, it is only recently that the molecular intricacies of these processes have been revealed by scanning probe microscopy6,7,8. To organize and understand this large amount of new information, new rules for crystal growth need to be developed and tested. However, because of the complexity and variety of different crystal systems, attempts to understand crystal growth in detail have so far relied on developing models that are usually applicable to only one system9,10,11. Such models cannot be used to achieve the wide scope of understanding that is required to create a unified model across crystal types and crystal structures. Here we describe a general approach to understanding and, in theory, predicting the growth of a wide range of crystal types, including the incorporation of defect structures, by simultaneous molecular-scale simulation of crystal habit and surface topology using a unified kinetic three-dimensional partition model. This entails dividing the structure into ‘natural tiles’ or Voronoi polyhedra that are metastable and, consequently, temporally persistent. As such, these units are then suitable for re-construction of the crystal via a Monte Carlo algorithm. We demonstrate our approach by predicting the crystal growth of a diverse set of crystal types, including zeolites, metal–organic frameworks, calcite, urea and l-cystine.

The nanoscopic details of the crystal growth of zeolite. A in the presence of the organic modifiers. diethanolmaine (DEA) and triethanolamine (TEA) has been determined using a combination of atomic force microscopy (AFM) and high-resolution scanning electron microscopy (HRSEM) coupled with Monte Carlo simulations. Crystallization of zeolite A in the presence of TEA was faster than when the growing solution contained DEA. In addition, the morphology of the final zeolite A crystals depended on the type of organic molecule, with TEA producing crystals bound only by {100} facets and DEA leading to the formation of relatively large {110} faces. These features can be explained in terms of the relative Si/Al in the growing medium and its control due to the different affinity of the organic molecules to Al. In addition, synthesis Si/Al in the growing medium and its contorl due to the different affinity of the organic molecules to Al. In additon synthesis performed at 90 degrees C showed the apperance of {211} facets Careful review of the HRSEM and AFM images, in addition to comparion with the MC simulations, reveals that these are in fact pseudofacets products of the slow dissolution of the metastable zeolite. A crsytals. This proves that the final habit of the LTA crystals can be governed by very small changes in saturation of the growing medium, and control of this parameter can prove advantageous when designing crystals for industrial applications.

Atomic force microscopy is used to conduct the first detailed nanoscopic study on the crystal growth of a complex mixed metal/metal–organic framework based on the MOF-5 framework topology. Shells of isomorphously substituted Co/Zn-MOF-5 and MOF-5 were epitaxially grown on MOF-5 core crystals at room temperature and low supersaturation to produce complex core–shell–shell structures with a hierarchal mixed metal nature involving mixing at the atomic level in the isomorphously substituted Co/Zn-MOF-5 shell and at the nanometer level through segregation of the Co/Zn-MOF-5 and MOF-5 layers. The presence of cobalt in the growth solutions was found to retard the overall rate of surface growth in comparison to a cobalt-free growth solution and stop growth entirely for a growth solution containing a Zn/Co ratio = 0.6. The presence of cobalt in the growth solutions was also found to affect the relative rates of terrace spreading in different crystallographic directions compared to cobalt-free growth with spreading ...

Summary Enhanced oil recovery (EOR) methods target the residual ca. 50 % of crude oil, found coating the pore surfaces of sandstone reservoirs. Low salinity water flooding EOR involves the injection of waters with low salt concentrations into the reservoir. These methods, through a contested mechanism, alter the wettability of the reservoir rock and promote oil displacement. In this work, we have used environmental scanning electron microscopy (ESEM) to measure and assess the change in wettability on oil-treated detrital quartz grains from Berea sandstone and model single-crystal high-quality quartz. Crude oil, as well as a “model-oil” (decanoic acid) where used. Wettability alteration was brought by flushing the pre-treated crystals with low concentration brines (0.01M) of different composition (NaCl, CaCl2, MgCl2, and KCl). Results show that, in the case of quartz surfaces from Berea sandstone, NaCl has the greater effect in changing the wettability state from oil wet to water wet. Results are noticeably aligned with total organic carbon (TOC) data. In contrast, the model-quartz crystals do not show great changes in wettability. The variation in results is probably due to the influence of nano-mineral coatings in the sandstone’s quartz crystals, as observed by high-resolution SEM. These results also highlight the importance of using natural mineral surfaces in the EOR study.

Nanoporous metal organic frameworks (MOFs) form one of the newest families of crystalline nanoporous material that is receiving worldwide attention. Successful use of MOFs for application requires not only development of new materials but also a need to control their crystal properties such as size, morphology, and defect concentration. An understanding of the crystal growth processes is necessary in order to aid development of routes to control such properties of the crystallites. In this Perspective article we aim to provide a short overview of the current work and understanding concerning the nucleation and growth processes of nanoporous MOFs and how this work may be expanded upon to further our comprehension of this subject. We also focus heavily on in situ studies that provide real time information on the developing materials and generally provide the most conclusive findings on the processes under investigation.

Crystalline nanoporous materials are one of the most important families of complex functional material. Many questions pertaining to the molecular assembly mechanism of the framework of these materials remain unanswered. Only recently has it become possible to answer definitively some of these questions by observation of growing nanoscopic surface features on metal organic frameworks (MOFs) through use of in situ atomic force microscopy (AFM). Here we reveal that a growth process of a MOF, zeolitic imidazolate framework ZIF-8, occurs through the nucleation and spreading of successive metastable unenclosed substeps to eventually form stable surface steps of the enclosed framework structure and that this process is reliant on the presence of nonframework species to bridge the developing pores during growth. The experiments also enable identification of some of the fundamental units in the growth process and the stable crystal surface plane. The former findings will be applicable to numerous nanoporous materials and support efforts to synthesize and design new frameworks and to control the crystal properties of these materials.

The crystallization of zeolite A by the verified synthesis method was studied by means of high-resolution scanning electron microscopy (HRSEM) and atomic force microscopy (AFM). These methods show ...

In this paper we report the first in situ atomic force microscopy study on the crystal growth of zincophosphate-faujasite (ZnPO-FAU). Results show that growth at low to moderate supersaturation conditions takes place by a birth-and-spread and/or spiral growth mechanism. At medium-to-high supersaturation conditions, growth starts preferentially at crystal edges and corners forming macrosteps with a height of several nanometers that advance toward the center of the crystal. This behavior may be explained by nucleation inhibition on the crystal surface due to surface reconstruction and impurity adsorption after synthesis. ZnPO-FAU crystals were found to be metastable at the experimental conditions (25 °C, 1 atm) as initial growth slowed down considerably during the duration of the experiment and was then followed by the dissolution of the crystals and the precipitation of a new phase. Linear defect formation, due to low angle dislocations, was also imaged for the first time and was found to be commonplace in the system. Defect formation was linked to the embedding of microcrystals of the same phase as growth takes place. Owing to the low angle nature of the misfit crystals were able to “heal” themselves after multiple layers have grown.

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.

The combined use of white light interferometry (WLI) and atomic force microscopy (AFM) revealed pentagonal growth spirals on the surface of SAPO-34 crystals. Detailed considerations of the crystal geometry and preferred step energies may explain the unusual shape of these growth spirals. Combining WLI and AFM is an efficient method for screening and detailed analysis of growth hillocks on crystals larger than 10 μm.

Clay–oil interactions play a critical role in determining the wettability of sandstone oil reservoirs, which, in turn, governs the effectiveness of enhanced oil recovery methods. In this study, we have measured the adhesion between –COOH functional groups and the siloxane and aluminol faces of kaolinite clay minerals by means of chemical force microscopy as a function of pH, salinity (from 0.001 M to 1 M) and cation identity (Na+ vs. Ca2+). Results from measurements on the siloxane face show that Ca2+ displays a reverse low-salinity effect (adhesion decreasing at higher concentrations) at pH 5.5, and a low salinity effect at pH 8. At a constant Ca2+ concentration of 0.001 M, however, an increase in pH leads to larger adhesion. In contrast, a variation in the Na+ concentration showed less effect in varying the adhesion of –COOH groups to the siloxane face. Measurements on the aluminol face showed a reverse low-salinity effect at pH 5.5 in the presence of Ca2+, whereas an increase in pH with constant ion concentration resulted in a decrease in adhesion for both Ca2+ and Na+. Results are explained by looking at the kaolinite’s surface complexation and the protonation state of the functional group, and highlight a more important role of the multicomponent ion exchange mechanism in controlling adhesion than the double layer expansion mechanism.

Zeolites play a crucial part in acid–base heterogeneous catalysis. Fundamental insight into their internal architecture is of great importance for understanding their structure–function relationships. Here, we report on a new approach correlating confocal fluorescence microscopy with focused ion beam–electron backscatter diffraction, transmission electron microscopy lamelling and diffraction, atomic force microscopy and X-ray photoelectron spectroscopy to study a wide range of coffin-shaped MFI-type zeolite crystals differing in their morphology and chemical composition. This powerful combination demonstrates a unified view on the morphology-dependent MFI-type intergrowth structures and provides evidence for the presence and nature of internal and outer-surface barriers for molecular diffusion. It has been found that internal-surface barriers originate not only from a 90∘ mismatch in structure and pore alignment but also from small angle differences of 0.5∘–2∘ for particular crystal morphologies. Furthermore, outer-surface barriers seem to be composed of a silicalite outer crust with a thickness varying from 10 to 200 nm. Characterizing the internal architecture of zeolites is crucial for understanding their structure–function relationships, and for acid–base heterogeneous catalysis. Using a unique combination of diffraction and microscopy techniques provides a unified picture of the morphology of intergrowth structures and confirmation of surface barriers for molecular diffusion.

Atomic force microscopy was used to study the surface of STA-7 crystals. STA-7 is a silicoaluminophosphate, nanoporous solid formed by interlinked double six ring units (D6R). Observations showed the formation of three distinct types of spirals at low supersaturation conditions. The {001} face shows spirals with isotropic shapes and a Burgers vector of 0.9 nm, which corresponds to one D6R or one unit cell along the ⟨001⟩ direction. The {100} face contains two distinct types of spirals. The first has a Burgers vector of 0.9 nm, or half a unit cell along ⟨100⟩. This dislocation produces a change in the “stacking” sequence of the D6Rs generating an overgrowth with the AEI structure. The second type is an interlaced spiral and is generated by a dislocation with a Burgers vector of 1.8 nm or one unit cell, leading to the formation of two substeps each with a different growth anisotropy. This anisotropy is directed by the shape of the substep and the energetics of template attachment. The preponderance of a sur...

The effect of dissolved Zn, Co, Pb, Mg, and Ca on the uptake of cadmium by biogenic aragonite was investigated. Experiments were performed in batch-reactors using metal-cadmium-bearing solutions and shell fragments with diameters in different ranges, the solid/liquid ratio being 10 grams per liter. Different initial concentrations of cadmium and metals (1.0-0.005 mM) were used. Uptake takes place via heterogeneous nucleation of metal-bearing crystallites onto the shell surfaces. Cadmium removal occurs by surface precipitation of otavite. Under the conditions used here, Co and Ca as well as Pbor = 0.3 mM and Znor = 0.3 mM do not have a significant effect on the removal of cadmium. At higher concentrations, Pb and Zn outcompete Cd for the dissolving carbonate ions and thus decrease significantly the Cd removal rates. In contrast, Mg has a slight enhancing effect. Pb and Zn are removed faster than Cd, precipitating as PbCO3, Pb3(CO3)2(OH)2, and Zn5(CO3)2(OH)6. Within 24-72 h, the concentrations of lead, cadmium, and zinc decrease until approximately 0.5 microM, and the presence of aragonite buffers the solution to a pH above 8 avoiding redissolution. The study demonstrates the high effectiveness of biogenic aragonite in removing Cd and other metals from polluted waters.

Crystal growth of the metal–organic framework, MOF-5, using basic zinc benzoate, [Zn4O(O2CC6H5)6], was studied in real time using atomic force microscopy. The two-dimensional nuclei involved in layer growth were found to form by a two-step process whereby 1,4-benzenedicarboxylate units first attach to the MOF-5 surface followed by addition of a layer of Zn species and connecting 1,4-benzenedicarboxylate units. No evidence of a growth mechanism involving nucleophilic substitution of a benzoate group from an intact [Zn4O(O2CC6H5)6] molecule by a surface attached 1,4-benzenedicarboxylate unit was found. This indicates that the [Zn4O(O2CC6H5)6] molecules undergo a degree of dissociation before incorporation into the MOF-5 framework. The [Zn4O(O2CC6H5)6]-containing growth solutions were found to influence the relative growth rates along different crystallographic directions and to lead to a faster nucleation rate under certain conditions when compared to growth solutions containing simpler zinc salts. This suggests a degree of remnant association of the zinc species derived from the [Zn4O(O2CC6H5)6] cluster during crystal growth under these conditions.

International audience; Coupled CaCO3 dissolution-otavite (CdCO3) precipitation experiments have been performed to 1) quantify the effect of mineral coatings on dissolution rates, and 2) to explore the possible application of this coupled process to the remediation of polluted waters. All experiments were performed at 25°C in mixed-flow reactors. Various CaCO3 solids were used in the experiments including calcite, aragonite, and ground clam, mussel, and cockle shells. Precipitation was induced by the presence of Cd(NO3)2 in the inlet solution, which combined with aqueous carbonate liberated by CaCO3 dissolution to supersaturate otavite. The precipitation of an otavite layer of less than 0.01 ?m in thickness on calcite surfaces decreases its dissolution rate by close to two orders of magnitude. This decrease in calcite dissolution rates lowers aqueous carbonate concentrations in the reactor such that the mixed-flow reactor experiments attain a steady-state where the reactive fluid is approximately in equilibrium with otavite, arresting its precipitation. In contrast, otavite coatings are far less efficient in lowering aragonite, and ground clam, mussel, and cockle shell dissolution rates, which are comprised primarily of aragonite. A steady-state is only attained after the precipitation of an otavite layer of 3 10 ?m thick; the steady state CaCO3 dissolution rate is 1 2 orders of magnitude lower than that in the absence of otavite coatings. The difference in behavior is interpreted to stem from the relative crystallographic structures of the dissolving and precipitating minerals. As otavite is isostructural with respect to calcite, it precipitates by epitaxial growth directly on the calcite, efficiently slowing dissolution. In contrast, otavite?s structure is appreciably different from that of aragonite. Thus, it will precipitate by random three dimensional heterogeneous nucleation, leaving some pore space at the otavite-aragonite interface. This pore space allows aragonite dissolution to continue relatively unaffected by thin layers of precipitated otavite. Due to the inefficiency of otavite coatings to slow aragonite and ground aragonite shell dissolution, aragonite appears to be a far better Cd scavenging material for cleaning polluted waste waters.

The dissolution rates of calcite, aragonite, and ground clam, cockle, and mussel shells were measured at 25 °C as a function of reactive fluid saturation state. All experiments were performed in mixed-flow reactors using a pH-4 HCl inlet solution. Reactive solution pH ranged from 5.1 to 9.8, and the chemical affinity of the dissolving carbonates ranged from 0 to 47 kJ/mol in the experiments. BET surface area-normalized dissolution rates for calcite are of the same order of magnitude as those of aragonite. In contrast, geometric surface area-normalized calcite dissolution rates are ∼30% lower than corresponding aragonite rates. The dissolution behaviour of the biogenic samples depends on their composition and the surface area used to normalize rates. In all cases, measured BET-normalized dissolution rates of shells are approximately one order of magnitude lower than corresponding mineral dissolution rates. In contrast, measured geometric surface area-normalized bivalve dissolution rates are equal to within uncertainty of those of aragonite or calcite. Geometric surface area-normalized dissolution rates (rgsa) of both aragonite and crushed clam and cockle shells, which are composed of aragonite, can be described within uncertainty using: r gsa mol / cm 2 / s = ( 2.69 ± 0.5 ) × 10 − 10 ( 1 − Ω ) 0.86 ± 0.11 where Ω stands for the saturation state of the dissolving carbonate. Similarly, rgsa of calcite can be described using: r gsa mol / cm 2 / s = ( 1.82 ± 0.2 ) × 10 − 10 ( 1 − Ω ) 1.25 ± 0.16 where rgsa for mussel shells, which are composed of ∼90% calcite and ∼10% aragonite, are similar to those of calcite, but display a complex variation with chemical affinity due to the presence of two minerals. Consistent with previous studies, rgsa is found to be accurately described as a function of saturation index independent of pH at neutral to basic conditions.

The uptake of Cd2+ 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)CO3 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)CO3 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.

High-resoln. SEM (HRSEM) has recently been added to the arsenal of characterization tools for material scientists to observe nanoscale surface features on both conducting and insulating materials. It is now therefore crucial to understand whether the intense electron beam will damage the features of interest. The authors were able, for the 1st time, to measure and quantify this damage using a combination of HRSEM and at. force microscopy (AFM), and as a consequence, the bulk of the damage, expressed as a depression on the crystal surface, is confined primarily to a subsurface vol. Simulations demonstrate that the depth of the depression is proportional to the interaction vol. of impact electrons below the crystal surface. More importantly, the nanometer surface features are conserved, and there is negligible assocd. loss of the crit. information in nanoscopic surface topog. These results confirm the usefulness of HRSEM as a tool for surface anal. not only for scientists studying crystal growth but also for materials scientists analyzing any surface at the nanoscale.

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.

Microporous zincophosphate sodalite crystal growth has been studied in situ by atomic force microscopy. This simple model system permits an in depth investigation of some of the axioms governing crystal growth of nanoporous framework solids in general. In particular, this work reveals the importance of considering the growth of a framework material as the growth of a dense phase material where the framework structure, nonframework cations, and hydrogen-bonded water must all be considered. The roles of the different components of the structure, including the role of strict framework ordering, are disentangled, and all of the growth features, both crystal habit and nanoscopic surface structure, are explained according to a simple set of rules. The work describes, for the first time, both ideal growth and growth leading to defect structures on all of the principal facets of the sodalite structure. Also, the discovery of the presence of anisotropic friction on a framework material is described.

Crystal growth of the metal-organic framework MOF-5 was studied by atomic force microscopy (AFM) for the first time. Growth under low supersaturation conditions was found to occur by a two-dimensional or spiral crystal growth mechanism. Observation of developing nuclei during the former reveals growth occurs through a process of nucleation and spreading of metastable and stable sub-layers revealing that MOFs may be considered as dense phase structures in terms of crystal growth, even though they contain sub-layers consisting of ordered framework and disordered non-framework components. These results also support the notion this may be a general mechanism of surface crystal growth at low supersaturation applicable to crystalline nanoporous materials. The crystal growth mechanism at the atomistic level was also seen to vary as a function of the growth solution Zn/H(2)bdc ratio producing square terraces with steps parallel to the direction or rhombus-shaped terraces with steps parallel to the direction when the Zn/H(2)bdc ratio was >1 or about 1, respectively. The change in relative growth rates can be explained in terms of changes in the solution species concentrations and their influence on growth at different terrace growth sites. These results were successfully applied to the growth of as-synthesized cube-shaped crystals to increase expression of the {111} faces and to grow octahedral crystals of suitable quality to image using AFM. This modulator-free route to control the crystal morphology of MOF-5 crystals should be applicable to a wide variety of MOFs to achieve the desired morphological control for performance enhancement in applications.

Nanoporous metal organic frameworks (MOFs) form one of the newest families of crystalline nanoporous material that is receiving worldwide attention. Successful use of MOFs for application requires not only development of new materials but also a need to control their crystal properties such as size, morphology, and defect concentration. An understanding of the crystal growth processes is necessary in order to aid development of routes to control such properties of the crystallites. In this Perspective article we aim to provide a short overview of the current work and understanding concerning the nucleation and growth processes of nanoporous MOFs and how this work may be expanded upon to further our comprehension of this subject. We also focus heavily on in situ studies that provide real time information on the developing materials and generally provide the most conclusive findings on the processes under investigation.

A molecular-scale understanding of crystal growth is critical to the development of important materials such as pharmaceuticals, semiconductors and catalysts. Only recently has this been possible with the advent of atomic force microscopy that permits observation of nanoscopic features on solid surfaces under a liquid or solution environment. This allows in situ measurement of important chemical transformations such as crystal growth and dissolution. Further, the microscope can access not only an accurate height measurement of surface topography, important to deduce structural elements, but also the forces involved during nanoscopic processes. We have discovered that it is possible to use these features to "illuminate" critical nanoscopic chemical events at crystal surfaces and at the same time extract the associated energies and unstitch the details of the stepwise mechanism of growth and dissolution. This approach has been developed using nanoporous crystals of the heterogeneous catalyst zeolite L; however, in principle the approach could be adapted to many crystal growth problems.

The influence of the chemical composition and of the storage and activation protocol on the diffusion of methanol into strongly chemically zoned crystals of the silicoaluminophosphate zeotype STA-7 has been investigated by interference microscopy. Analysis of the evolution of transient intracrystalline concentration profiles reveals that just-calcined SAPO STA-7 crystals with lower Si content (Si/(Si + P) = 0.18) exhibit higher surface permeability and bulk diffusivity than those with higher Si content (S/(Si + P) = 0.37). Remarkably, crystals with the higher Si content which were stored in the calcined form crack during activation along planes of weakness already present in the as-prepared crystals, creating fresh surfaces through regions of lower Si that are much more easily penetrated by the adsorbing methanol than are the original surfaces.

A self-limited monolayer grown on dolomite (CaMg(CO(3))(2)), showing distinct friction contrast with the substrate as reported earlier using lateral force microscopy, was investigated with in situ atomic force microscopy (AFM) adhesion mapping and force-modulation techniques. Force-modulation microscopy revealed lower stiffness on a Ca-rich film in comparison to that on the dolomite surface. The friction contrast therefore results from a larger tip-surface contact area when the AFM probe is in contact with the Ca-rich film as opposed to the contact area with dolomite. The Ca-rich film also exhibited a slightly higher adhesion than did the dolomite substrate; however, the critical shear stresses for the two tip-surface contacts were indistinguishable. A comparative study with a Mg-rich film did not yield noticeable force modulation contrast, indicating similar surface stiffness of the film and the dolomite surface. The similarity in these stiffness quantities was further corroborated by friction-load data that demonstrated similar friction forces on the two surfaces. The previously reported film strain in the Ca-rich system is likely linked to the lower stiffness observed, with both of these properties related to the Ca/Mg composition of the film.

Lateral Force Microscopy (LFM) studies were carried out on cleaved calcite sections in contact with solutions supersaturated with respect to otavite (CdCO3) or calcite-otavite solid solutions (SS) as a means to examine the potential for future application of LFM as a nanometer-scale mineral surface composition mapping technique. Layer-by-layer growth of surface films took place either by step advancement or by a surface nucleation and step advancement mechanisms. Friction vs. applied load data acquired on the films and the calcite substrate were successfully fitted to the Johnson Kendall Roberts (JKR) model for single asperity contacts. Following this model, friction differences between film and substrate at low loads were dictated by differences in adhesion, whereas at higher load they reflect differences in contact shear strength. In most experiments at fixed load, the film showed higher friction than the calcite surface, but the friction-load dependence for the different surfaces revealed that at low loads (0–40 nN), a calcian otavite film has lower friction than calcite; a result that is contrary to earlier LFM reports of the same system. Multilayer films of calcian-otavite displayed increasing friction with film thickness, consistent with the expectation that the film surface composition will become increasingly Cd-rich with increasing thickness. Both load- and thickness-dependence trends support the hypothesis that the contact shear strength correlates with the hydration enthalpy of the surface ions, thereby imparting friction sensitivity in the LFM to mineral-water interface composition.

It is now possible to observe nanometer features on the surfaces of zeolitic materials using high-resolution scanning electron microscopy. By taking ibidem measurements in combination with atomic force microscopy we are able to illustrate the strengths and weaknesses of both techniques and judge respective resolving power.

Zeolite A is one of most widely used and studied zeolites owing to its cation-exchange properties. Here, we present a computer program that simulates morphology as well as surface topology for zeolite A crystals. Results from simulations were compared with scanning electron microscopy and atomic force microscopy images on the {100}, {110} and {111} faces of synthetic crystals. This allowed to further refine the program by varying the relative attachment/detachment probabilities of individual growth sites.

Understanding the fundamental aspects of the crystal growth of metal organic frameworks (MOFs) is critical to develop better materials for new and enhanced applications. Some of the most pressing questions in this regard are the formation of the structure around the voids in the framework or the factors that control the morphology of the crystals. Only direct observations at the nanoscale under growing conditions can reveal the answers to these fundamental questions. Atomic forcemicroscopy (AFM) can provide these kind of detailed observations. In this paper we report results from in-situ AFM growth experiments for three different MOFs: MOF-5, ZIF-8 and ZIF-76. AFM images of the three types of crystals growing under low supersaturation conditions reveal similar results. In all cases growth was observed to take place by a birth and spread and/or spiral growth mechanism. Detailed height analysis of 2-D nuclei as a function of lateral spreading revealed a complexmechanism of terrace growth for all three systems. For ZIF-76 five different heights were measured: 0.6, 1.0, 1.4, 1.8 and 2.3 nm. The last height is equal to that of a full monolayer height or d100 spacing, which corresponds to a double four ring (D4R) plus a sodalite (SOD) cage of the LTA-type structure of ZIF-76. The other heights correspond to the height of single D4R (0.6 nm) or the sum of a D4R plus an incomplete SOD cage. For ZIF-8, a similar stepwise building process was observed with heights corresponding to the addition of Zn ions or methylimidazole linkers to complete the constituent sodalite cages that provide the step stable termination. In the case of MOF-5 only two heights were measured during 2-D nucleation and growth, corresponding to addition of the Zn clusters and benzendicarboxylic (bdc) linker. These measurements indicate that MOF crystal growth takes place by the nucleation and spreading of successive metastable unenclosed sub-layers to eventually form the stable, enclosed framework structure. This process is dependent on the presence of non-framework species that bridge the developing pores during growth. During the experiments on MOF-5, it was also observed that varying the stoichiometry of theMOF-5 growing solutions resulted in a dramatic change in terrace morphology. Solutions with a Zn/H2bdc ratio > 1 produced square terraces with steps parallel to the d directions. However, if the Zn/H2bdc ratio is approximately one, the steps become parallel to the o direction, resulting in a rhomboid terrace morphology. Additionally, a change in MOF-5 crystal shape was observed from the pure cubic morphology to blunted cubes and octahedra expressing the {111} facets indicating a change in the relative growth rates of the different faces that define the crystal morphology. These results provide a modulator-free route to control the crystal morphology of MOF-5 and potentially other MOFs. MS44-O2 In situ observations of impurity effects during protein crystallization. Mike Sleutel, Dominique Maes, Structural Biology Brussels, Flanders Interuniversity Institute for Biotechnology (VIB), Vrije Universiteit Brussel, Pleinlaan 2, 1050, Elsene, Belgium E-mail: mike.sleutel@vub.ac.be

We present the first in situ observations of the growth of a zeotype using atomic force microscopy. The {100} face of sodalite zincophosphate grows by a spiral growth mechanism forming an interlaced spiral pattern. This is caused by the anisotropic growth of sub-steps formed at the dislocation, which is related to the different condensation rates of zinc and phosphorus.

The resolving power of high-resolution scanning electron microscopy was judged using topographical height data from atomic force microscopy in order to assess the technique as a tool for understanding nanoporous crystal growth.