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We conducted measurements of hydrogen adsorption on three coal samples of varying ranks at high pressure (0 to 102 bar) and elevated temperatures (303 K to 333 K) to assess their hydrogen storage potential. The excess adsorption capacity increased with increasing pressure but decreased with increasing temperature irrespective of coal rank. The highest hydrogen adsorption recorded was 0.721 mol/kg for the anthracite coal at 303 K and 102 bar. Furthermore, the hydrogen adsorption capacity correlated positively with coal vitrinite and fixed carbon contents (i.e. the high-rank coal exhibited greater adsorption), while all samples depicted predominantly type-I adsorption behavior for the entire pressure range. Micropore analysis and Fourier-transform infrared spectroscopy measurements were conducted to explore the microstructural and surface chemistry associated with these adsorption trends. The micropore content of the three samples followed the order: anthracite sub-bituminous bituminous, while H

The impact of macrocycles on calcium oxalate formation. Calcium oxalate is a major component of kidney stones, an ailment that affects many people globally.

Kaolinite dissolves faster at edges, and steps have a fast-dissolution direction.

Interfacial ion transfer from organic phase to aqueous phase is employed as the basis for formation of barium sulfate crystals close to the interface.

Various studies have found a trend connecting diabetes mellitus or carbohydrate malabsorption syndromes to kidney stone formation. However, it is unclear what the underlying mechanism causing this impact is. An important aim of this work was to investigate whether some of this correlation is due to the underlying chemistry of sugars as crystal growth modifiers. Thus, the impact of major dietary monosaccharides (glucose, fructose and galactose) and disaccharides (lactose, sucrose) on the formation of calcium oxalate, a major component of kidney stones, was investigated. Evaluating the impact of monosaccharides on the nucleation of calcium oxalate shows that generally, a promotion in the nucleation rate of particles is seen. Evidence was also obtained of monosaccharides being present within the crystal, showing a close association between the sugars and calcium oxalate. In the case where lactose was present there was also an obvious promotion of nucleation in the solution. This may give context to the observed incidence of stones in lactose-intolerant patients. When sucrose was present as an additive an interaction with both the crystal and the solution ions was observed. This sucrose-ion interaction has been observed previously in literature. There is minimal impact of most sugars on the zeta potential of particles formed. Only the presence of galactose and lactose showed some interaction on zeta potential when zinc ions were also present. The results presented in this work suggests that sugars in urine can promote calcium oxalate formation and agglomeration and as such may suggest a chemical basis, in addition to a biological basis, to the higher prevalence of stones in diabetic patients. This work, therefore, may assist in understanding what the role of dietary sugar malabsorption has on the formation of kidney stones.

Crystallisation is performed in a non-aqueous solvent, dimethylsulfoxide (DMSO), in order to determine what the role of water is on the crystallisation pathway. In both water and DMSO environments the particles do not appear to grow by ion addition but rather appear to grow through aggregation. The main difference in water is that the aggregation processes are not random and result in particle morphologies that bear relation to the single-crystal faces, suggesting an oriented attachment mechanism. In DMSO, the aggregation processes appear less oriented and while there is some lattice registry, lattice mismatch is also observed and the aggregate shape is spherical overall. This is confirmed in the 1200 cm−1 infrared band shift to 1174 cm−1 suggesting a strained solid is formed. It is observed that the solubility of barium sulfate in DMSO is higher than in water (presumably caused by a strong Ba2+⋯OS(CH3)2 interaction), which explains the lower nucleation rates in DMSO compared to water at the same concentration. Intriguingly, there is a lower nucleation rate observed (even at a relatively high supersaturation) when Ba2+ is solvated with DMSO supporting the hypothesis that de-solvation of the cation is the rate determining step in nucleation and is of higher activation energy in DMSO than in water.

Aragonite formation and stabilization in seawater is still an area of active investigation since the thermodynamically stable product at room temperature is calcite. In this manuscript, purely inor...

International audience; Controlled formation of cocrystals is an important objective in drug development. Here, cocrystallisation of caffeine and 1-hydroxy-2-naphthoic acid was investigated at the interface between two immiscible electrolyte solutions under chemical polarisation. In this way, selective cocrystallisation was achieved, as verified by X-ray diffraction and Raman spectroscopy. Positive interfacial potentials favoured the formation of one polymorphic form of caffeine:1-hydroxy-2-naphthoic acid cocrystal. This approach to electrochemically controlled cocrystallisation opens up new possibilities for drug development. The search for innovative crystallisation methods is a subject of constant interest as most drugs appear as crystalline forms whose polymorphs may have different toxicity, hygroscopicity or physical and chemical stability. 1-3 An additional issue encountered in drug development is the low stability in humid environments

Hybrid nanomaterials offer increased flexibility to achieve heterostructures with controlled functionalities and predictable linkages owing to their synergistic interactions. Here, we have developed a synthetic strategy that produced hexagonal-shaped nanoplatelets (NPLs) of gold–pyrrhotite (Au–Fe7S8) with Au embedded inside them by means of a seeded growth method. Using thiol-capped Au nanoparticles (NPs) as a seed, heterogeneous nucleation of the iron precursor was facilitated, leading to the formation of Au–Fe7S8 NPLs. The injection temperature and surface ligand of the seed (Au) were two critical factors that determined the homogeneity and final morphology of the Au–Fe7S8 NPLs. This strategy was further expanded using Ag NPs as the seed to construct heterodimers, producing Ag2S–Fe7S8 heterostructures.

Methane (CH4) wettability of shale is a key parameter which determines pore and reservoir-scale fluid distributions, CH4 reserves estimation, and ultimate recovery efficiency from shale gas reservo...

Dimension, composition and configuration are the primary aspects of semiconductor based hybrid heterostructures that govern their properties. To achieve desired functionalities within a single nanoparticle system, numerous synthetic approaches are available which may be suitable for achieving the target combination but these can be complex and tedious. In this work, a simple seeded-growth approach was employed to obtain an iron oxide–gold–cadmium sulfide (Fe3O4–Au–CdS) heterotrimer with a unique morphology manifesting magnetic, plasmonic and semiconducting properties. In a straightforward two-step synthesis process, Au–Fe3O4 dimer was injected as a seed into the Cd precursor solution for the growth of one-dimensional (1D) kinked CdS-5 nanorods on it. The synthesized Fe3O4–Au–CdS heterotrimer was tested in photocatalytic water-reduction reaction, revealing its potential as a photocatalyst for the hydrogen evolution reaction (HER), where each domain within the heterotrimer played a distinct role including light absorption, charge separation and magnetic separation. A post-synthetic modification on the semiconductor part was also performed where kinked CdS nanorod was cation exchanged with Ag2S leading to the formation of another heterotrimer of Fe3O4–Au–Ag2S while retaining the same morphology and expanding the palette of heterotrimers.

Macrocyclic compounds such as DOTP (1,4,7,10-tetraazacyclododecanetetrakis(methylenephosphonic acid)) and NOTP (1,4,7,-triazacyclononanetri(methylenephosphonic acid)) are found to inhibit precipitation of barium sulfate just as potently as their non-cyclic counterparts depending on the ionisation state of the molecule. Morphologically, DOTP has a more significant influence on the shape of barium sulfate particles formed than NOTP while turbidity results show that NOTP does not significantly affect the induction time observed, unlike DOTP, which does impact the induction time at higher concentrations. Overall, the inhibition of these macrocyclic compounds can be explained by the number of de-protonated phosphonate groups and is not significantly impacted by the presence of the ring. The presence of calcium ions during barium sulfate crystallization lowers the degree of inhibition for both NOTP and DOTP. Molecular modelling showed that an uncomplexed DOTP molecule could lattice match to the barium sulfate lattice but had fewer Ba⋯Ophos interactions than the equivalent non-macrocyclic molecule. The comparison of uncomplexed with complexed DOTP shows that the final configuration is similar for these two situations, thus in this case it is not the Ba⋯Ophos interactions but the overall replacement energy that is important.

The cocrystals of two reagents of mismatch solubility, hydrophilic caffeine and lipophilic 1-hydroxy-2-naphthoic acid, were obtained at a water-oil interface. 1 By analysing the product collected at the phase interface by X-ray diffraction and Raman spectroscopy, we confirmed that we obtained the molecular cocrystals of caffeine and 1-hydroxy-2-naphthoic acid, free of starting reagents and solvents. Polarisation of the interface allowed the electrochemical control of the cocrystallisation process: for non-polarised interfaces, a mixture of phase I and II cocrystals were obtained, whereas cocrystals of phase I were formed when a high interfacial potential was applied. The difference between the polymorphs obtained in the absence or in the presence of interfacial polarisation is attributed to the different cocrystallisation mechanisms. In the absence of interfacial polarisation, caffeine and 1-hydroxy-2-naphthoic acid are cocrystallising through an interfacial process. When the interface is positively polarised, cationic form of caffeine is transferred to the organic phase, the complex with naphthoic acid is formed and the proton is released. The pH increased after cocrystallisation, suggesting that the liberated H+ remained in the organic phase. On the contrary, in the absence of polarisation or in the case of low interfacial potential the protons are remaining in the aqueous phase what resulted in a decrease in pH after cocrystallisation process. We demonstrated an indirect evidence of the transfer of caffeine upon chemical polarization of the interface. We observed almost no deposits in the organic phase by analysing it with a scanning electron microscope. We investigated here the mechanism behind the formation of cocrystals by using the polarized interface between two immiscible electrolyte solutions (ITIES).2 For the purpose of this study, the two solutions have been placed in contact3 : one being an aqueous solution of caffeine, as a model drug substance, and the second being organic solution of 1-hydroxy-2-naphthoic acid (cocrystal component) and the salt inducing the suitable imposed potential difference. The formation of the caffeine: 1-hydroxy-2-naphthoic acid complex was studied by changing the salts present in the aqueous phase, the chemical compounds imposing potential in organic phase, varying the organic solvents and the temperature at the liquid-liquid interface. The cocrystals collected at the interface were analysed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and low frequency Raman spectroscopy. We studied the proportions of polymorphic phases as a function of changing conditions. To understand the mechanism behind the caffeine transfer and the formation of different forms of polymorphic crystals at the water-oil interface, Electrochemical Noise Experiments4 have been carried out. A four-electrode system was used to apply zero volts between the working electrode and the counter electrode and then measuring the current and the potential versus the reference electrode. Such a setup allows the measurement of potential and current as the function of time simultaneously. We could thus follow the phenomena that are taking place at the interface. The measurements were carried out by varying the cations (tetraalkylammoniums, Li+, K+) in aqueous and organic phase as well as the anions (derivatives of tetrakis(phenyl-borate) in organic phase). The experimental results were supported by theoretical equations and applied to the system containing caffeine. This novel strategy of cocrystallization, was followed by the investigation of other coformers (3-hydroxy-2-naphthoic acid) and drugs (cocrystals of ketoprofen with amino acids and carboxylic acids) in order to validate the method. Such an electrocrystallization process at the ITIES will open new opportunities for the formation of drugs cocrystals. M. Kaliszczak et al., CrystEngComm (2022) doi: 10.1039/D1CE01281A. Z. Samec, Pure Appl. Chem., 76, 2147–2180 (2004). S. J. Diez et al., Cryst. Growth Des., 18, 3263–3268 (2018). I. B. Obot, I. B. Onyeachu, A. Zeino, and S. A. Umoren, J. Adhes. Sci. Technol., 33, 1453–1496 (2019).

Three-component containing hybrid heterostructures with multiple functionalities are highly desirable but difficult to synthesize. Herein, we have demonstrated the utilization of a simple seeded-growth approach for the synthesis of a hybrid heterotrimer of iron oxide–silver sulfide–zinc sulfide (Fe3O4-Ag2S-ZnS). At first, Fe3O4-Ag was synthesized by using silver nanoparticles (Ag NPs) as a seed followed by its in situ sulfurization to produce a dimer of Fe3O4-Ag2S. This dimer was successively used as a seed under controlled experimental conditions for the synthesis of Fe3O4-Ag2S-ZnS. The availability of such trimers through this approach can shed some light on the integration of entirely different functionalities in one-particle systems.

This study presents the solubility of calcium carbonate in monoethylene glycol (MEG)/water solution at high temperatures and high MEG concentrations. The conditions simulate the water removal proce...

In this manuscript we investigate the impact of oxalate ions on the crystallization of barium sulfate. The organic anion, oxalate, was found to inhibit both nucleation and growth according to atomic force microscopy measurements and dynamic light scattering data. Raman confocal imaging was used to try and determine how the oxalate interacts with the barium sulfate surface. It was found that barium oxalate is only seen at very high oxalate concentrations. At lower concentrations no direct evidence for the presence of oxalate was observed, however, the most probable mode of action for oxalate is via adsorption onto the barium sulfate surface including into key kink or step sites, impacting growth.

CO2 and CH4 wettabilities of organic-rich shale are important physicochemical parameters that significantly influence CO2 sequestration and CH4 production. However, there is a serious lack of understanding of these aspects because the data available are scarce. Thus, we evaluated organic-rich shale CO2 and CH4 wettabilities (i.e., brine/shale/gas systems) through advancing and receding brine contact angle measurements as a function of pressure, temperature, salinity, and ion type (as these can vary significantly in underground formations). The results indicated that the brine contact angles for both CO2/CH4–brine–shale systems increased with pressure and salinity, but decreased with temperature. However, these effects were much less significant for CH4. Furthermore, the brine contact angles for the CO2–brine–shale system reached 180° (i.e., the shale was completely wetted by CO2) when the pressure reached 30 MPa at 343 K and ∼9 MPa at 298 K. The brine contact angles for the analogue CH4 systems was much l...

To overcome the limited potency of energy devices such as alkaline water electrolyzers, the construction of active materials with dramatically enhanced oxygen evolution reaction (OER) performance is of great importance. Herein we developed an ion diffusion-induced doping strategy that is capable of producing Ni2+/Co2+ doped two-dimensional (2D) Au-Fe7S8 nanoplatelets (NPLs) with exceptionally high OER activity outperforming the benchmark RuO2 catalyst. The co-existence of Co and Ni in Au-Fe7S8 NPLs led to the lowest OER overpotential of 243 mV at 10 mA cm-2 and fast kinetics with a Tafel slope of 43 mV dec-1. Density functional theory (DFT) calculations demonstrated that Ni2+/Co2+ doping improves the binding of OOH species on the {001} surfaces of Au-Fe7S8 NPLs and lowers the Gibbs free energy of the OER process, which are beneficial to outstanding OER activity of the nanoplatelets.

A great deal of effort has been dedicated to improve the fundamental understanding of the mechanism of desilication product crystallization under Bayer process refinery conditions. Differences in the mineralogy of the reactive silica found in bauxite could change the kinetics and possibly the formation pathways of the desilication product. In this work, halloysite was investigated and compared to kaolinite, which is commonly found in bauxite. Different ratios of kaolinite and halloysite were used to form desilication product and the solids formed were characterized thoroughly to determine the impact the presence of the clay had. In addition, differences in dissolution rate due to the presence of halloysite was determined. The results show that the presence of halloysite led to a faster dissolution rate of the clay overall, which can be attributed to the total specific surface area of the reactive silica source. Thus, the crystallinity of the clay was found to have limited impact. The presence of halloysite also increased the measured maximum solution [SiO2] in solution, which in turn increases the driving force for the formation of desilication product. The increase in halloysite content thus results in desilication product being observed at an earlier stage and, overall, leads to an enhanced rate of desilication product formation.

Confocal Raman Microscopy (CRM) in combination with a photophysical investigation has been employed to give insight into the interaction between calcium oxalate monohydrate (COM) and a series of tetrazole containing crystal growth modifier's (CGM's), in conjunction with characterisation of morphological changes using scanning electron and optical microscopy. The tetrazole CGM's were found to interact by surface adsorption with minimal morphological changes to the COM crystals however, significant interactions via chemisorption were observed; it was discovered that the chemisorption is sufficiently strong for aggregation of the tetrazole species to occur within the crystal during crystallisation.

Wettability of CO 2 /water/coal systems is a fundamental petro-physical parameter, which governs the fluid flow and distribution in coal seams and thus directly affects CO 2 -storage and methane recovery from unmineable coal seams. The recognition of wettability of coal/CO 2 /brine systems help to de-risk CO 2 -storage and enhanced methane recovery projects in coal seams. To understand the factors influencing the wetting characteristics of coals, a detailed examination and characterization of coal surface chemistry is essential and literature data in this context is missing. We thus measured zeta potentials as a function of temperature (298–343 K), brine salinity (0 wt% NaCl–5 wt% NaCl) and salt type (NaCl, CaCl 2 and MgCl 2 ) for coals of low, medium and high ranks. Further, we measured water advancing and receding contact angles as a function of temperature and salinity for the same experimental matrix in order to associate wettability changes to the surface charge at the coal/brine interface. Moreover, coal surfaces were investigated by Fourier transformed infrared (FTIR) spectroscopy and the surface functional groups responsible for a particular wetting behaviour were identified. We found that zeta potential increased with temperature, salinity and cation valency. Both advancing and receding contact angles decreased with temperature, and increased with salinity and cation valency irrespective of the coal rank. Finally the XRD measurements and infrared spectra revealed that the presence of polar surface functional groups (e.g. Si OH and carboxylic acid groups) which is responsible for the hydrophilic behaviour of low rank coals and the absence of these groups in high rank coal is responsible for their hydrophobic behaviour even at lower pressure. The high rank coal seams at high pressure are better for CO 2 storage and methane recovery.

The nature of crystallisation processes is of major interest, as they are among the most frequently occurring reactions associated with a variety of relevant processes in chemistry, biochemistry, and geochemistry. In this study, an innovative approach towards fundamentally understanding crystallisation pathways in a seemingly simple system – gypsum – has been developed via infrared spectroscopic techniques. Specifically, infrared attenuated total reflection spectroscopy (IR-ATR) was instrumental in revealing detailed information on inter- and intramolecular interactions during gypsum crystallization via subtle changes in the vibrational spectra of the involved reactants. When applying D2O as an isotope marker, it was shown that isotopically labelled water may serve as a viable spectroscopic probe during mid-infrared (3–15 μm) studies providing unique insight into the crystallization process at molecular-level detail. In addition, it was revealed that H2O and D2O give rise to distinctly different reaction kinetics during the crystallization process.

An aspartic acid functionalised azobenzene derivative is found to be a light-switchable crystal growth modifier of calcite. UV irradiation of the molecule reversibly switches it to the cis isomer, which is a significantly less effective crystal growth inhibitor than the trans isomer. Visible light, or heat switches the inhibitor back “on”. Extended irradiation degrades the inhibitor such that it is irreversibly switched “off”. It was shown that the trans isomer is preferentially absorbed on to the crystal surface, which is consistent with its greater efficacy as an inhibitor.

Aragonite formation and stabilisation in seawater is still an area of active investigation since the thermodynamically stable product at room temperature is calcite. In this manuscript, purely inorganic systems that were found to stabilise aragonite were analysed by various techniques. Dynamic Light Scattering was used to characterise the nucleation behaviour of the system and it was found that the presence of magnesium ions during crystal formation inhibits nucleation overall, not just calcite nucleation. In addition, it was found that sulfate is not necessary to stabilise aragonite. Microanalysis by energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) revealed that the aragonite that was formed had a disordered core with, sodium, magnesium and sulfate ions incorporated into the structure. To the best of the authors’ knowledge this is the first time an ACC core in aragonite has been visualised in a completely abiotic, synthetic system (in the absence of organic molecules). Inclusion of these impurities into the structure may explain the stability of aragonite in natural seawaters.

Aragonite formation and stabilisation in seawater is still an area of active investigation since the thermodynamically stable product at room temperature is calcite. In this manuscript, purely inorganic systems that were found to stabilise aragonite were analysed by various techniques. Dynamic Light Scattering was used to characterise the nucleation behaviour of the system and it was found that the presence of magnesium ions during crystal formation inhibits nucleation overall, not just calcite nucleation. In addition, it was found that sulfate is not necessary to stabilise aragonite. Microanalysis by energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) revealed that the aragonite that was formed had a disordered core with, sodium, magnesium and sulfate ions incorporated into the structure. To the best of the authors’ knowledge this is the first time an ACC core in aragonite has been visualised in a completely abiotic, synthetic system (in the absence of organic molecules). Inclusion of these impurities into the structure may explain the stability of aragonite in natural seawaters.

In this manuscript the impact of three organic molecules (in the presence and absence of zinc ions) in a more realistic solution medium is presented. The impact of the synthetic urinary medium on the morphology of the calcium oxalate monohydrate formed is similar to that seen in the presence of citric acid, the dominant component. The particles formed are relatively flat, rounded particles. In the presence of zinc ions, the particles are little changed with the main change being more rounded particles. The presence of the different organic acids show different impacts for different organics. Ethylenediamintetraacetic acid complexes calcium ions and lowers the supersaturation as a chelator would be expected to. It also impacts the growing crystal changing the morphology. In the case of tartaric acid, adsorption onto critical nuclei and/or growth features leads to incorporation. Finally, the most complex impact was found for maleic acid. Maleic acid interacts with citric acid, inhibiting the citric acid effect. This can be seen in the morphology of particles being similar to those in pure water. The presence of zinc ions generally led to zeta potential values that were closer to zero and therefore would increase the propensity for these particles to coagulate.

Four possible models for anhydrous calcium oxalate (COA) polymorphs have been investigated through ab initio quantum mechanical methods. Their structural properties, infrared and Raman spectra, and thermodynamic stability in the range of 0–800 K have been analyzed and compared. Along with the known β-COA structure, two models turn out to be possible candidates for the α- and γ-polymorphs that were observed during dehydration of weddellite (calcium oxalate dihydrate, COD) by Walter-Levy and Laniepce (C. R. Acad. Sci. Paris 1964, 259, 4685). While the calculated vibrational frequencies show that the four COA models correspond to minimum energy structures, β-COA is the thermodynamically favored phase over the range of temperatures examined in the present study. Despite the fact that computed vibrational spectra and X-ray diffraction (XRD) patterns of these polymorphs exhibit some different features, a definitive assignment of the structures based on computational results is not possible due to the lack of ac...

Barium sulfate was crystallized in a synthetic seawater mixture that was chosen to better reflect ocean conditions. The synthetic seawater contained monovalent ions, magnesium, strontium, and calcium as well as bicarbonate and boric acid. The natural pH of the synthetic seawater is 8.1, and this seawater was used to determine the impact on morphology, nucleation rates, and incorporation of foreign ions. It was found that dendritic and diamond-shaped particles are both formed. The main parameters influencing the formation of dendritic particles were the saturation index and the ion ratio, but there was also a significant synergistic effect with the other ions present. The diamond-shaped particles formed later at a lower saturation index. The nucleation rate in synthetic seawater was found to be higher than expected based on an ion ratio basis. This is most probably because the divalent ions induce a higher nucleation rate by lowering the surface free energy. Strontium was found to be the dominant ion subst...

Cystallization of calcium oxalate monohydrate was investigated in the presence of various organic molecules in combination with zinc ions. This work looked at the impacts at physiological pHs (6–8) and temperature (37 °C). It was found that the number of carboxylate and hydroxyl groups was critical in determining the degree of inhibition. This inhibition was found to be mainly due to the ability of the organics to chelate with calcium ions when zinc ions are not present. Zinc ions were found to chelate with oxalate ions leading to lower nucleation rates, but this is not strictly inhibition but a lowering of the supersaturation due to lowering of the activity of the oxalate. Organics have variable impact depending on whether the zinc ions or calcium ions preferentially chelate with the organic.

Empirical molecular modelling was used to investigate the impact of organic additives on crystal morphology and inhibition. The replacement energy was found to correlate reasonably well with the degree of inhibition as determined from conductivity data. The replacement energy was also able to predict the barium sulfate face on which additive adsorption was most likely. While the ability of the organic functional groups to sit in the vacant sulfate lattice positions (the so-called ‘lattice matching’ criteria) appears intuitively sensible, it was found that this is not a sufficient criterion to predict real behaviour. A better criterion is the overall replacement energy as it takes into consideration the number of Ba–Oorganic interactions and whether the adsorption process overall is energetically favourable (by including the hydration energy of the ions). Thus, the replacement energy can successfully predict the effect of organic molecules on the crystal growth modification of barium sulfate.

The mineral goethite (α-FeOOH) has previously been investigated as a thermodynamically stable repository for many potentially toxic metals (e.g., Cd, Pb, Cu). The substitution of uranium (U as uranyl, UO22+) for Fe, however, has been studied sparingly, and conclusive uranium incorporation into the goethite structure has been obscured by formation of ploymineralic Fe systems that all appeared involved in U’s sequestration. In this study, we investigated the formation of goethite from FeCl2 in the presence of seven nominal uranyl concentrations (0.2–4 mole percent, U/(U + Fe) × 100) and characterised the solids using quantitative X-ray diffraction (QXRD), X-ray absorption fine structure (XAFS) spectroscopy at the U LIII edge (17,166 eV), diffuse reflectance infrared Fourier Transform (DRIFT) spectrometry and congruency of acid dissolution. Our findings show that U does indeed, however sparingly, incorporate into the goethite structure. The unit cell volume, ascertained from Rietveld models of XRD patterns, increased linearly as a function of U content, which could be ascribed to a linear increase of the unit cell length a and c. The highest U-for-Fe substitution was 0.48 mole percent, however, most U-containing goethite samples showed substitution levels around 0.2 mole percent, which was in good agreement with previous findings. DRIFT spectra showed a shift of the symmetric Fe–O and asymmetric Fe–OH stretch modes (τ–O and τ–OH bands, respectively) to lower frequency, which by Hooks analogy, can only occur if a heavier atom substitutes for Fe, i.e., U. The congruency of acid dissolution results showed that fractional U release was greater than the corresponding fractional Fe release into solution, suggesting that U was overall more soluble. In two of the synthates, however, (initial U mole percent of 2 and 4), the dissolution was congruent. XAFS data collected on a selected subset of samples showed the disappearance of the uranyl moiety with higher levels of U incorporation and acid extraction. In sample S6, non-linear least-square fits of the extended XAFS data demonstrated that the coordination environment around U atoms was sixfold occupied by O/OH atoms and was further coordinated by next nearest Fe neighbours that are 1.063 ± 0.008 times inflated in distance to the normal Fe–Fe distances in goethite without U substitution. Despite low levels of incorporation, U bound by goethite was recalcitrant to desorption/dissolution in increasingly acidic solutions thus warranting further research into the possibility of using iron oxides as a sink for U.

Jarosite was formed in the presence of five amino acids at two pHs, namely 1.75 and 2.9, to determine what impact amino acids have on its formation. It was found that at the lower pH glycine was the most potent in terms of morphological and yield impacts. XRD analysis showed that incorporation of the amino acid occurs at this low pH for glycine and proline. Dynamic light scattering studies showed that glycine impacts significantly on the jarosite nucleation rate while proline and alanine do not. At the higher pH all of the amino acids had much less impact on morphology or yield. At pH 3 the solids were found to be a 3-phase system consisting of goethite, schwertmannite and jarosite. In this case, alanine appeared to stabilise the presence of schwertmannite more than the other amino acids.

Molecules containing tetrazole substituents have become of interest due to their being bioisosteres of carboxylic acids and like their carboxylate counterparts, tetrazolate anions have been able to affect the crystal growth of barium sulphate and calcium carbonate. In this proof of principle study, we show that this behaviour also extends to calcium oxalate and therefore opens the possibility of using tetrazole-based additives for investigating mineralization processes of human pathological relevance.

The assembly and disassembly of supramolecular gel fibres are observed in situ using variable temperature scanning probe microscopy. The results show that fibre formation can be monitored at high resolution at a surface, and the final fibre morphologies are broadly consistent with those found by ex situ analysis of the bulk gel. The impact of a gelation inhibitor upon the fibre morphology is successfully investigated, providing direct evidence for the mechanism of inhibition as a function of additive concentration.

This study focused on the formation of the jarosite-alunite solid solution at relatively low temperature, 90 °C. It was found that the transition from jarosite to alunite results in significant changes in the powder X-ray diffraction pattern, the infrared spectrum and thermal behavior when the degree of substitution reached ≥50%. The initial Al/(Al + Fe) in solution, however, required to achieve these substitution levels in the solid is ≥90%. The morphology shows that the faceted jarosite form goes through an intergrown transition to a spherical morphology of pure alunite. This morphology has not been previously observed for alunite and most likely reflects the formation temperature. Rietveld analysis shows that the a lattice parameter obeys Vegard’s Rule while the c lattice parameter behavior is more complex. Empirical modelling of the incorporation of Fe into alunite supports the general trends found in the X-ray diffraction data for the behaviour of the a-axis with Al/Fe content. The dehydration of the Al3+ ion could be a significant contribution to the activation energy barrier to alunite formation as found for other minerals. Finally, dynamic light scattering showed that the nucleation behavior for jarosite and Fe-containing alunite are significantly different. Alunite appears to nucleate continuously rather than in a single nucleation event.

The thermal annealing behaviour of an electrolyte-triggered calixarene hydrogelator is found to depend strongly on the specific metal chloride used. While the lithium chloride gel showed typical gel–sol transitions as a function of temperature, the magnesium chloride gel was found to repeatedly strengthen with heat–cool cycles. Structural investigations using small-angle neutron scattering, and scanning probe microscopy, suggest that the annealing behaviour is associated with a change in morphology of the fibrous structures supporting the gel. On prolonged standing at room temperature, the magnesium chloride gel underwent a gel–crystal transition, with the collapsing gel accompanied by the deposition of crystals of a magnesium complex of the proline-functionalised calix[4]arene gelator.

The dissolution of boehmite in synthetic Bayer liquors is inhibited in the presence of anatase. It has been suggested both by us and others (e.g. Loan et al., 2005) that dissolved titanate adsorbs onto the surface of the boehmite limiting its dissolution. This manuscript reports on digestion, X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigations of boehmite solids partially dissolved in synthetic Bayer liquor in the presence of anatase. Energy filtered transmission electron microscopy (EFTEM) is used to obtain elemental distribution maps, which support the adsorption hypothesis and show enrichment of titanium on the boehmite crystals. Interestingly, the aluminium also becomes associated with some of the Ti-rich particles.

Calix[4]arenes functionalised at the upper rim with acidic amino acid residues are found to have a significant impact on the crystal growth of model mineral systems, calcium carbonate and barium sulphate. The aspartic acid derivative is found to be most efficacious, matching or exceeding the impact of commercial phosphonate-based scale inhibitors. In some cases, the modified morphologies are found to be similar to those induced by proteins isolated from biomineralised systems.

Dipositive cation substitution in sulfate minerals has been a topic of investigation both experimentally and computationally. Here the possibility of tripositive cation substitution with accompanying vacancy formation is considered, specifically lanthanum ion substitution in barium sulfate. Experimentally, the lanthanum ions impact “bulk” crystallization in a way that is best explained by considering the solution phase ion-pair interactions. However, morphological results suggest that lanthanum ions do more than impact the free sulfate levels. Atomic force microscopy results showed that both lanthanum and calcium ions are strong inhibitors of barite growth. X-ray diffraction on bulk samples showed that lanthanum ions do indeed incorporate, as determined by lattice parameter changes. Finally, computational modeling suggests that while calcium incorporation is more energetically favorable, lanthanum ions prefer to substitute on the surface more so than calcium ions.

Calixarenes can be used as well-defined scaffolds for investigating structure–activity relationships of additives and their impact on crystallization. In this work, we present the crystal growth modification of barium sulfate by p-phosphonic acid calix[n]arenes that vary in size (n = 4, 5, 6, and 8) and thus vary in the size of the internal cavity for the same functionality in the upper rim. The tetrameric, hexameric, and octameric macrocycles induce nanoparticle formation with clear superstructure. In the case of the hexameric calix[6]arene, the initial mesocrystalline superstructure fuses over time to form almost hollow spheres, while the mesocrystals formed in the presence of the tetramer and octamer are stable over an extended period. The pentameric calix[5]arene forms more disordered aggregates of single crystals. Thermogravimetric data shows that a significant proportion of the mass of the barium sulfate-containing solid is the macrocycle, regardless of the choice of macrocycle.

Focused beam reflectance measurement (FBRM), where a scanning laser focused through a sapphire window measures real-time reflected chord distributions without solids dilution, is attractive for characterizing flocculation performance. An enhanced measurement principle in new FBRM instruments has implications for flocculation studies, demonstrated using hematite in synthetic Bayer liquor. Comparisons of previous (M500) and new (G400) instruments were complicated by the impact of their different physical dimensions upon flocculation hydrodynamics, but the G400 clearly measured larger chords. The original measurement principle based on a reflected intensity threshold counts large low-density aggregates as multiple chords; in contrast, the change to “edge detection” (very low threshold) is more likely to see a single chord, an advantage for studying mineral systems (aggregates often >500 µm). The G400 also captures bimodal character in unweighted chord distributions, producing distinct peaks for aggregates and fines after suboptimal flocculation; such peaks are rarely well resolved in older FBRM. © 2013 American Institute of Chemical Engineers AIChE J, 60: 251–265, 2014