The aims of this study were to obtain accurate structural information on the dimethyl sulfoxide (DMSO) and dimethylselenoxide (DMSeO) kaolinite intercalates, paying close attention to the hydrogen-bond geometries, and to provide a detailed interpretation of the individual vibrational modes of intercalates under study and relate their energies to the formation of the hydrogen bonds. Accurate positions of all the atoms in the structures of kaolinite:dimethylsulfoxide (K:DMSO) and kaolinite:dimethylselenoxide (K:DMSeO) intercalates have been obtained by the total energy minimization in solid state at density functional theory (DFT) level of the theory. The bond distances and angles in the kaolinite 1:1 layer are in good agreement with those reported in the most recent single-crystal refinement of kaolinite. Computed geometries of DMSO and DMSeO agree well with the high-quality diffraction data and independent theoretical ab initio calculations. The organic molecules are fixed in the interlayer space mainly by three moderately strong O-H⋯O hydrogen bonds, of different strengths, with the O⋯O contact distances being within 2.739–2.932 Å (K:DMSO) and 2.681–2.849 Å (K:DMSeO). Substantially weaker C-H⋯O and O-H⋯S(Se) contacts play only a supporting role. The optimized atomic coordinates were used to calculate the individual vibrational modes between 0 and 4000 cm−1. The maximum red shifts of the OH-stretching modes caused by the formation of the O-H⋯O hydrogen bonds were 407 cm−1 (K-DMSO) and 537 cm−1 (K-DMeSO), respectively. The Al-O-H bending modes are spread over the large interval of 100–1200 cm−1, but the dominant contributions are concentrated between 800 and 1200 cm−1. Theoretically calculated energies of the OH- and CH-stretching modes show good agreement with the previously published figures obtained from the infrared and Raman spectra of these intercalates.

Twenty two samples were studied to investigate the nature and evolution mechanism of mixed-layer kaolinite-smectite (K-S). We examined the <2 µm or <0.2 µm fraction of K-S formed by hydrothermal and hypergenic alteration of volcanic material. The samples are from three localities: 20 specimens from a Tortonian clay deposit in Almería, Spain; one specimen from weathered Eocene volcanic ash from the Yucatan Peninsula, Mexico; and one sample from a weathered Jurassic bentonite from Northamptonshire, England. The samples were studied using chemical analysis, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The XRD patterns of the oriented, glycolated mounts were modeled using NEWMOD and the proportion of smectite and kaolinite layers was determined, ranging between 0 and 80% kaolinite. The analysis of the OH-stretching region of the FTIR spectra at different temperatures (180–550°C) showed the progressive dehydroxylation of kaolinite domains and, perhaps, of smectite domains, but no detailed information could be obtained about the sequential OH loss in different cation environments. The abundance and short-range ordering of the octahedral cations were studied using the OH-bending bands. The chemical and FTIR-estimated octahedral cation abundances were broadly similar. Aluminum showed a tendency to mix with Fe and Mg rather than to form AlAl pairs. Al-for-Mg substitution accompanying kaolinization was evident from the increase in AlAl pairs and decrease in AlMg pairs. Iron is retained in the structure. No other octahedral cation rearrangement was observed. The intensity of the 750 cm−1 band, assigned to translational vibrations of external OH groups in a kaolinitic environment, was quantified and modeled in relation to kaolinite layer proportion. The chemical data show that there are residual interlayer cations in kaolinite domains, which, in accordance with the model mentioned above, disturb external OH-translation vibrations. These results indicate the persistence of certain chemical and structural smectite features in kaolinite domains and thus support a smectite kaolinization process via a solid-state transformation. This confirms previous XRD, thermal, chemical and NMR analyses of the same sample set.

The performance of bentonite barriers for high level radioactive waste (HLRW) disposal is currently being tested in various real-and up-scale disposal tests. One of the disposal tests, the ABM test (ABM = alternative buffer material), was conducted by SKB (Svensk Kärnbränslehantering) as a mediumscale experiment at the Äspö hard rock laboratory in Sweden. The present study deals with the second parcel (ABM-II), which was retrieved after 6.5 years with 2.5 years of water saturation and 3–4 years of heating up to 141°C. Nine different bentonites and two marine clays were tested to investigate the performance. The aim of the study was to provide a detailed characterization of the mineralogical and chemical changes that took place in ABM-II, compare the findings with ABM-I (the first of the six test parcels), and try to draw some general conclusions concerning the use of bentonites in such geotechnical barriers. The ABM-II test parcel revealed a set of reactions that a HLRW bentonite might undergo. The most prominent reaction was the rather complete exchange of cations, which was discussed in a second part to this publication (II — cation exchange; Dohrmann and Kaufhold, 2017). The corrosion of the Fe in metal canisters was observed, but no discrete corrosion product was identified. At the interface of bentonite and the metal canister, the formation of smectite-type trioctahedral clay minerals was observed. In contrast to the ABM-I test, anhydrite was present in many of the bentonite blocks of the ABM-II test. In most concepts used for HLRW disposal in crystalline rocks, a temperature below 100°C at the canister surface was applied to avoid boiling. In the ABM-II test, boiling of water was possibly observed. Throughout the experiment, a pressure/water loss was recorded in the upper part of the geotechnical barrier and water was added to maintain pressure in the bentonite. As a result of evaporation, NaCl crusts might have formed and the barrier was partly disintegrated. These results demonstrated that a reasonable assumption is that no boiling of water occurs in disposal concepts in which a pressure loss can occur.

Dioctahedral vermiculite commonly occurs in soils and fresh sediments, but has not been reported in sedimentary rocks. Little is known of the evolution of this mineral during diagenesis. According to the available literature, dioctahedral vermiculite is likely to exhibit strong potential for selective sorption and fixation of K+ involving interlayer dehydration and collapse. he objective of the present study was to investigate the influence of K+ saturation and seawater treatments on the structure o dioctahedral vermiculite. Due to the fact that no dioctahedral vermiculite standard reference material was available, a natural sample of soil clay containing dioctahedral vermiculite was used in the study. The clay was saturated with K+ using different protocols simulating natural processes taking place in soils and marine environments. The solid products of the experiments were analyzed for potassium content using flame photometry. The effect of the treatments used on the structure of dioctahedral vermiculite was studied using X-ray diffraction (XRD). The percentages of the collapsed interlayers were estimated by modeling the XRD patterns based on a whole-pattern multi-specimen modeling technique. All the treatments involving K+ saturation caused K+ fixation and irreversible collapse (i.e. contraction to 10 Å) of at least a portion of the hydrated (vermiculitic) interlayers. Air drying of the K+-saturated samples greatly enhanced the degree of the collapse. The results obtained gave no clear answer as to whether time had had a significant effect on the degree to which irreversible collapse occurred. Selective sorption of K+ from artificial seawater was observed. These results clearly indicate that collapse of dioctahedral vermiculite is likely to occur in soils during weathering and in sediments during early diagenesis. Both processes need to be taken into consideration in sedimentary basin studies.

Hydrotalcite-like layered double hydroxides (LDHs) containing different ratios of Ni2+, Cu2+, Mg2+ and Al3+ in the layers have been prepared by a new method, the key features of which are a very rapid mixing and nucleation process in a colloid mill followed by a separate ageing process. The compositions and structural parameters of the materials synthesized using the two routes are very similar, although the degree of crystallinity is slightly higher for the LDHs produced using the new method. The major advantage of the new method is that it produces smaller crystallites, having a very narrow range of distribution of crystallite size. In the conventional coprecipitation process at constant pH, the mixing process takes a considerable time during which nuclei formed at the beginning of the process have a much longer time to undergo crystal growth than those formed at the end of the process. The consequence is that a wide dispersion of crystallite sizes is obtained. In the colloid mill process, however, the mixing and nucleation is complete in a very short time and is followed by a separate ageing process.

The zeolites and coexisting minerals of the silicic vitric tuffs in the Alaçatı (Çeşme) area, west of İzmir (Turkey), were studied. Mordenite is the most abundant zeolite in tuffs of the Alaçatı area and usually coexists with clinoptilolite-heulandite, smectite and calcite. Opal-CT was identified by means of its crystal morphology and EDX spectrum. Scanning electron microscopy (SEM) revealed the relative age relationships between the zeolites and coexisting minerals, namely mordenite, clinoptilolite-heulandite, smectite, calcite, and, in addition, opal-CT. Smectite consistently crystallized earlier than any of the zeolites, and it occasionally coats the outer walls of some of the vitric material. The zeolites are commonly located on the smectite, although some mordenites were observed to be in direct contact with glass shards that lacked a smectite coating. Clinoptilolite-heulandite formed after smectite and before mordenite. Opal-CT is seen to postdate both smectite and needle-shaped mordenite. Calcite was probably the latest mineral to crystallize in the Alaçatı tuffs. The zeolites in the tuffs of the Alaçatı area formed by dissolution of silicic vitric tuffs by Na- and Ca-rich thermal waters which passed through the fracture zone. The appearance of zeolites together with smectite along this zone may be attributed to a semi-open system which subdivided into smaller closed systems. Small changes in the pH and chemical composition of the thermal waters during alteration produced the corrosion effects observed by SEM. Small amounts of clinoptilolite-heulandite were corroded prior to crystallization of coexisting mordenite. The different compositions of the thermal waters were probably inherited from water that resulted from mixing of thermal and groundwaters.

Fluoride is an essential component in the mineralization of bones and in the formation of dental enamel. Excessive intake may result, however, in teeth mottling and dental and skeletal fluorosis. With an average fluoride concentration of ~2.4 mg L−1 in Tunisian drinking water, the present study focused on promoting low-cost materials for removal of excess fluoride. Two Tunisian raw clays were used as adsorbents in a batch process to eliminate excess fluoride ions from drinking water and, thus, avoid fluorosis phenomena. Physicochemical characterization and chemical analysis of the raw clays were carried out using X-ray fluorescence, X-ray diffraction, and the BET method. For fluoride removal, the effects of contact time, adsorbent dose, and pH were evaluated. The optimum defluoridation capacity was at 30 min of contact time, 20 g/L of clay dose, and at pH = 3. The kaolinite tested removed more fluoride than smectite. The selected clay was used successfully to remove fluoride from contaminated water with high concentrations of foreign ions that exceeded the potability limits. Adsorption isotherms revealed that the data fitted well to both the Langmuir and Freundlich adsorption isotherms, thus confirming both monolayer and multilayer adsorption.

Clay minerals are abundant in soils and sediments and often contain Fe. Some varieties, such as nontronites, contain as much as 40 wt.% Fe2O3 within their molecular structure. Several studies have shown that various Fe-reducing micro-organisms can use ferric iron in Fe-bearing clay minerals as their terminal electron acceptor, thereby reducing it to ferrous iron. Laboratory experiments have also demonstrated that chemically or bacterially reduced clays can promote the reductive degradation of various organics, including chlorinated pesticides and nitroaromatics. Therefore, Fe-bearing clays may play a crucial role in the natural attenuation of various redox-sensitive contaminants in soils and sediments. Although the organochlorinated pesticide p,p′-DDT is one of the most abundant and recalcitrant sources of contamination in many parts of the world, the impact of reduced Fe-bearing clays on its degradation has never been documented. The purpose of the present study was to evaluate the extent of degradation of p,p′-DDT during the bacterial reduction of Fe(III) in an Fe-rich clay. Microcosm experiments were conducted under anaerobic conditions using nontronite (sample NAu-2) spiked with p,p′-DDT and the metal-reducing bacteria Shewanella oneidensis MR-1. Similar experiments were conducted using a sand sample to better ascertain the true impact of the clay vs. the bacteria on the degradation of DDT. Samples were analyzed for DDT and degradation products after 0, 3, and 6 weeks of incubation at 30°C. Results revealed a progressive decrease in p,p′-DDT and increase in p,p′-DDD concentrations in the clay experiments compared to sand and abiotic controls, indicating that Fe-bearing clays may substantially contribute toward the reductive degradation of DDT in soils and sediments. These new findings further demonstrate the impact that clay materials can have on the natural attenuation of pollutants in natural and artificial systems and open new avenues for the passive treatment of contaminated land.

In this article, I propose a new reading for both law and narrative in the Aramaic Levi Document (ALD). In the first section, I show that the passage of “the law of the priesthood” pertains to the daily morning service in the Temple. In the second section, I suggest that the narrative that contains these instructions, in which Isaac speaks to Levi at Abraham’s home, exegetically connects the laws to the story of Isaac, whose father offered him up on an altar, and reflects a priestly theology that views the priest himself as an offering.

The author to the Hebrews makes the seemingly strange choice to introduce two quotations from the LXX with indefinite markers (Heb 2.6; 4.4). While some commentators do not consider these introductions, others have argued that they function either rhetorically to engage the audience or theologically to highlight the divine speaker. This article argues that a hermeneutical function better explains the author's choices: the author uses the indefiniteness to guide his audience in how to interpret each quoted passage. The author uses the indefinite marker of place (που) to remove both Gen 2.2 and Ps 8.5–7 LXX from their salvation-historical context; this results in the rest of God (Heb 3–4) and the role of humanity within creation (Heb 2) applying equally to the present and the coming ages. He pairs this with the indefinite marker of person (τις) in his introduction to Ps 8 to indicate that the audience should not interpret it prosopologically as the speech of the Son to the Father; rather the Psalm testifies to the role of humanity within the present and the coming worlds, a role which the Son incarnate fulfils. This hermeneutical explanation aligns with other instances of indefinite citation markers in Second Temple Judaism, most notably in Philo. This argument, therefore, both adds depth to the characterisation of the author as a careful reader of Scripture and brings out the intended meaning and function of Ps 8 and Gen 2 in the discourse of Hebrews more clearly.

Repentance is central to the message of Christianity. Yet, repentance has received little analysis in recent scholarship despite being emphasized by the church fathers. In particular, there has been minimal effort to understand the necessity of repentance in light of Christ’s atoning work. With this as the background, I explore fundamental questions such as repentance’s definition, scope, and role in salvation history. Furthermore, I attempt to more precisely outline repentance’s role in Christ’s salvific work. Underpinning the project is my view that repentance should be understood as metanoia or transformation. This transformation of repentance is ordered toward divine metanoia – participation in Christ. In developing repentance, I put forward a synthesis of Thomas Aquinas’s framework of penance and John McLeod Campbell’s account of Christ’s vicarious repentance. Through this synthesis, I attempt to make sense of the relationship between repentance and atonement. I finish by suggesting that it would be appropriate to conclude that Thomas would endorse a vicarious repentance account of the atonement and hint at how it might fit into broader soteriologies.

The provenance of clays in shaley intervals across the Permian-Triassic boundary (PTB) in the Xiakou section was investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), and the results suggest that the layers have three different provenances. The layer P267-b has a loose texture with an oriented arrangement of detrital clay particles, consisting mainly of illite and minor chlorite with irregular outlines or ragged edges. The dehydroxylation reaction of the clays in this layer is characterized by an intense overlapping endothermic effect at ∼600°C, produced by mixed-layer illite-smectite (I-S) consisting of a mixture of cis-vacant (cv)and trans-vacant (tv) octahedral sheets derived from weathering of detrital illite. Layer P259-b shows a more condensed texture with a dark color, and is composed mainly of I-S and minor illite and chlorite. Evidence for alteration of detrital materials to clay mineral aggregates was observed under SEM. Similar to layer P267-b, an intense dehydroxylation reaction occurs at ∼600°C, indicating clays consisting of a mixture of tv and cv sheets and, therefore, that the sediments were derived from a mixture of terrigenous and volcanic sources, combining the texture and the clay-mineral composition of those sediments. However, the undisturbed lamination and relatively small grain size in this bed indicate a low-energy depositional environment. The clay-mineral compositions of the other layers are mainly of I-S with minor amounts of illite and chlorite. Their endothermic dehydroxylation reaction, however, occurs mainly at ∼660°C, indicating that cv sheets are dominant in the clays, and thus, are derived from smectites of volcanic origin. Observations by SEM show that clay minerals grow at the expense of detrital materials, confirming the diagenetic alteration of volcanic ashes in marine sediments. Illite and chlorite are the detrital clay minerals in the clay layers across the PTB in the Xiakou section. The presence of detrital illite and chlorite in the sediments means that an arid climate prevailed in the region during the end-Permian and early Triassic period.

Particle–particle interactions in natural clays can be evaluated by their rheological behavior, but the results are often affected by the physicochemical properties of the clays. The behaviors of two fundamentally different types of clays (low-activity and high-activity) differ with respect to salinity and a time factor (duration of shearing at a given shear rate): illite-rich Jonquiere clay (low-activity clay, Canada) and montmorillonite-rich Wyoming bentonite (high-activity clay, USA). The purpose of the present study was to investigate these different behaviors. Most natural clays exhibit shear-thinning and thixotropic behavior with respect to salinity and the volumetric concentration of the solids. Natural clays also exhibit time-dependent non-Newtonian behavior. In terms of index value and shear strength, lowactivity and high-activity clays are known to exhibit contrasting responses to salinity. The geotechnical and rheological characteristics as a function of salinity and the shearing time for the given materials are compared here. The clay minerals were compared to estimate the inherent shear strengths, such as remolded shear strength (which is similar to the yield strength). Low-activity clay exhibits thixotropic behavior in a time-dependent manner. High-activity clay is also thixotropic for a short period of shearing, although rare cases of rheopectic behavior have been measured for long periods of shearing at high shear rates. The change from thixotropic to rheopectic behavior by bentonite clay has little effect at low shearing speeds, but appears to have a significant effect at higher speeds.

The results of a combined chemico-osmotic/diffusion experiment conducted on a geosynthetic clay liner (GCL) containing Na-bentonite illustrate the destructive role of diffusion on the ability of the GCL to act as a semipermeable membrane. The experiment is conducted by maintaining a concentration difference of 5 mM CaCl2 across the GCL specimen while preventing the flow of solution through the specimen. A time-dependent membrane efficiency is derived from measured pressure differences induced across the specimen in response to the applied concentration difference. The diffusive mass fluxes of the solutes (Cl− and Ca2+) through the specimen are also measured simultaneously. An initial increase in induced pressure difference across the specimen to a peak value of 19.3 kPa is observed, followed by a gradual decrease to zero. The decrease in induced pressure difference is consistent with compression of diffuse double layers between clay particles and particle clusters due to diffusion of Ca2+, resulting in a concomitant increase in pore sizes and decrease in the observed membrane behavior. The time required for effective destruction of the initially observed semipermeable membrane behavior correlates well with the time required to achieve steady-state Ca2+ diffusion. The results have important implications for the ability of clays to sustain membrane behavior.

In the Nuussuaq Basin, West Greenland, a thick succession of Tertiary dolerites has penetrated Upper Cretaceous mudstone. The mixed-layer minerals of mudstone core samples have been analyzed by X-ray diffraction, solid-state 29Si and 27A1 magic-angle spinning nuclear magnetic resonance, Mössbauer and infrared spectroscopies, thermal analysis, chemical analysis, stable isotopes (18O/16O), and K/Ar dating. The mixed-layer minerals include for each sample two mixed-layer phases consisting of pyrophyllite, margarite, paragonite, tobelite, illite, smectite and vermiculite layers. The main, 80 m thick intrusion resulted in the formation of pyrophyllite, margarite, paragonite and tobelite layers. However, the tobelite layers are absent in samples <21 m from this intrusion. Furthermore, chlorite was formed and kaolinite destroyed in samples adjacent to minor intrusions and at distances <60 m from the large intrusion. For the first time, the detailed, complex mixed-layer structures formed during contact metamorphism of kaolinitic, oil-forming mudstones have been investigated accurately. The formation of tobelite layers reveals that oil formation has taken place during contact metamorphism. Furthermore, K/Ar dating of mixed-layer minerals from shale indicates that the intrusives are of early Eocene age. The 80 m thick intrusive is responsible for the main mixed-layer transformations, whereas two thin (3 m and 0.5 m thick) intrusions contribute little. Thus, the detailed mixed-layer investigation has contributed significantly to the understanding of the regional geology and the contact metamorphic processes.

Mineralogical and geochemical variations among the Carboniferous and Cretaceous sedimentary kaolin deposits from Sinai provided an opportunity to examine the effect of the source area on compositions of the deposits. The Carboniferous kaolin deposits are mineralogically and geochemically heterogeneous. The Khaboba and Hasbar deposits consist of kaolinite, quartz, anatase, illite, chlorite, zircon, and leucoxene. The shale-normalized rare earth element (REE) patterns of the Khaboba deposit showed a slight LREE over HREE enrichment ((La/Yb)SN = 1.19–1.51) with a MREE depletion (Gd/Gd*SN = 0.51–0.75), while the Hasbar kaolin had a MREE enrichment. The Abu Natash kaolin deposit consisted of kaolinite, anatase, and a little quartz with larger TiO2, Cr, and V and smaller Zr and Nb contents compared to other Carboniferous deposits. The shale-normalized REE patterns of the Abu Natash deposit exhibited a positive Eu anomaly (Eu/Eu*SN = 1.28–1.40) and a MREE enrichment (Gd/Gd*SN = 1.41–2.05). The Cretaceous deposits were relatively homogeneous in terms of mineralogical composition and geochemistry and are composed of kaolinite, quartz, anatase, rutile, zircon, and leucoxene. The Cretaceous kaolin deposits showed mostly flat shale-normalized REE patterns with a variable LREE depletion.

The presence of illite and chlorite, the absence of rutile, large Zr and Nb contents, and the REE patterns suggested a component of weathered low-grade metasediments as a source for the Carboniferous deposits in the Khaboba and Hasbar areas, while the large Ti, Cr, and V, and small quartz contents indicated mafic source rocks for the Abu Natash deposit. The abundance of high-Cr rutile and the absence of illite and chlorite, and large Zr, Ti, Cr, and V contents suggested a mixture of medium- to high-grade metamafic and granitic rocks as source rocks for the Cretaceous kaolin deposits. The occurrence of alkaline rocks in the source of the deposits studied was identified by high-Nb contents and the presence of bastnaesite. The mineralogical and geochemical heterogeneity and lesser maturity of the Carboniferous deposits suggested local sources for each deposit and their deposition in basins close to the sources. The mineralogical and geochemical homogeneity and maturity of the Cretaceous deposits, on the other hand, indicated common sources for all deposits and their deposition in relatively remote basins.

Natural and synthetic micas have been used widely as substrates to study biological systems; but, as in the case of negatively charged DNA, anionic charge repulsion may render micas a less than ideal templating surface for many biological systems. The purpose of this study was to investigate the potential for the chlorite clinoclore, which contains a positively charged interlayer octahedral sheet, to serve as a substrate for DNA adsorption. The relationships between clinochlore cleavage characteristics, in terms of nano-morphology, and surface potential are investigated, as are its average crystal chemistry and topology. That the structural features of clinochlore can be used successfully to condense, order, and self assemble complex biomolecules, such as DNA is also proven.

A natural IIb-4 clinochlore [$C\overline{1}$\$\end{document} symmetry, unit-cell parameters a = 0.53301(4); b = 0.92511(6); c = 1.4348(1) (nm); α = 90.420(3); β = 97.509(3); γ = 89.996(4) (°)] with chemical composition $\left({\text{Mg}}_{1.701}{\text{Fe}}_{0.245}^{2+}{\text{Ti}}_{0.004}{\text{Al}}_{0.998}{\text{Cr}}_{0.052}^{3+}\right){\text{Mg}}_3\left({\text{Si}}_{2.939}{\text{Al}}_{1.015}{\text{Fe}}_{0.046}^{3+}\right){\text{O}}_{10}\left({\text{OH}}_{7.913}{\text{F}}_{0.087}\right)$\$\end{document} was selected. The octahedral sites of the silicate layer (<M(1)−O> = 0.2080 nm and <M(2)−O> = 0.2081 nm) are equal and occupied by Mg, whereas the octahedral sites in the interlayer M(3) and M(4) (<M(3)−O> = 0.2088 nm and <M(4) − O> = 0.1939 nm) show different sizes and are mostly completely occupied by divalent (Mg2+ and Fe2+) and trivalent (Al3+) cations, respectively.

The clinochlore cleaved surface is present in two forms: (1) the stripe type (0.40 nm in height, up to several micrometers long and ranging from some nanometers to a few microns in lateral size); and (2) the triangular type (0.40 nm in height). Both features may result either from interlayer sheets whose cleavage weak directions are related to the different M(3) and M(4) site occupancy, or from weak interlayer bonding along specific directions to the 2:1 layer underneath. The cleaved surface, particularly at the cleaved edges, presents high DNA affinity, which is directly related to an average positive surface and ledge potential.

Phenol and its derivatives are regarded as ‘priority pollutants’ and p-nitrophenol (p-NP), in particular, is of great interest due to its toxicity and frequent presence in waste waters and fresh waters. Straightforward, inexpensive methods to identify p-NP in water, however, is lacking. In the present study, an electrochemical technique using clay-modified electrodes to measure p-NP was investigated as a potentially promising method to fill that gap. A glassy carbon electrode (GCE) was modified with a thin layer of Na-enriched bentonite and a series of benzyltrimethylammonium (BTMA+)-bentonites (BTMA+-B) in order to confirm these materials as p-NP electrosensitive. A series of organobentonites was synthesized using different BTMA+/bentonite ratios. The materials obtained were characterized using X-ray diffraction, Fourier-transform infrared spectroscopy, and a low-temperature nitrogen adsorptiondesorption method. A monolayer arrangement of BTMA+ within the interlamellar region of beidellite-rich smectite was confirmed. Deterioration of the textural properties was observed with increase of BTMA+ loading. The electro-oxidation of p-NP in an acidic medium on BTMA+-B-modified GCE was investigated. The cyclic voltammetry method with a three-electrode cell was used. The reference electrode was Ag/AgCl in 3 M KCl and a Pt foil was the counter electrode. For each electrochemical measurement, a different BTMA+ loading in BTMA+-B was used as the material for GCE coating and applied as the working electrode. The electrochemical activity of BTMA+-B-based electrodes increased with BTMA+ loading. The results confirmed that the organophylic character of the BTMA+-B-modified surface was the main influence on the electrochemical activity of the BTMA+-B-based GCE; the influence of textural properties was almost negligible. The increased electrode activity toward p-NP was achieved by the adsorption of p-NP on the electrode surface, the process that commonly precedes the electro-oxidation. The present study showed that synthesized materials could potentially be used in an electrochemical test for the presence of p-NP in water solutions.

Nitroaromatic compounds (NACs) are components of munitions commonly found as soil contaminants at military training sites and elsewhere. These compounds pose possible threats to human health and ecological systems. Recent studies indicate that these compounds are strongly retained by smectite clays. The adsorption mechanisms are not fully reconciled, but it is known that the type of exchangeable cation strongly affects NAC affinity for smectites. This study examined the sorption of 1,3-dinitrobenzene, 2,4-dinitrotoluene and naphthalene from water by a smectite clay (SWy-2) saturated with ammonium, tetramethylammonium (TMA), trimethylphenylammonium (TMPA) and hexadecyltrimethylammonium (HDTMA). In all cases, we observed greater sorption of 2,4-dinitrotoluene compared with 1,3-dinitrobenzene. The sorption isotherms for 2,4-dinitrotoluene and 1,3-dinitrobenzene displayed a concave-downward curve for NH4-SWy-2 and TMA-SWy-2, whereas the isotherms for sorption of HDTMA-SWy-2 and TMPA-SWy-2 were essentially linear. The magnitude of sorption followed the order: NH4-SWy-2 > TMA-SWy-2 > TMPA-SWy-2 > HDTMA-SWy-2 for both compounds. The greater affinity of NACs for NH4- and TMA-SWy-2 is due in part to complex formation between the exchangeable cation and −NO2 groups. These clays also provide near optimal interlayer distances that approximate the molecular thickness of NACs hence promoting the simultaneous interaction of the planar aromatic rings with opposing siloxane surfaces and solute dehydration. Both processes are energetically favorable. In HDTMA-SWy-2, sorption of all solutes is via a partition-dominated process. Solute competition (diminished uptake of one solute in the presence of a second) was observed for TMA-SWy-2 but not HDTMA-SWy-2. This is consistent with an adsorptive mechanism for TMA-SWy-2 and a partitioning mechanism for HDTMA-SWy-2. This study demonstrates that the dominant molecular mechanism of NAC sorption by smectite changes fundamentally from complexation between −NO2 groups and the exchangeable cation (viz. NH4 and TMA) to partitioning for a systematic series of ammonium and quaternary ammonium cations in which the locus of positive charge (the central N atom) is progressively shielded by organic moieties of increasing size.

Mineralization of microbial biomass is a common phenomenon in geothermal habitats, but knowledge of the structure of the minerals formed in these environments is limited. A combination of spectroscopic, microscopic, and stable isotopic methods, as well as the chemical analysis of spring water, were employed in the present study to characterize calcium carbonate minerals deposited in filamentous cyanobacterial mats in different locations of La Duke hot spring, a circumneutral thermal feature near the north entrance of Yellowstone National Park, Montana, USA. Calcite was the primary crystalline mineral phase associated with biofilm-containing deposits closest to the source of the spring and the suspended microbial biomass in a pool further from the source. The carbonate minerals at all sites occurred as aggregated granules, ~2 μm in diameter, in close association with the microbial biomass. Only in the deposits closest to the source were the granules organized as laminated structures interspersed with microbial biomass. The calcium carbonate grains contained two distinct regions: a dense monolithic calcite core and a porous dendritic periphery containing organic matter (OM). Electron energy loss spectroscopy (EELS) indicated that the voids were infilled with OM and carbonates. The EELS technique was employed to distinguish the source of carbon in the organic matter and carbonate mixture. The studies of carbon isotope compositions of the calcium carbonates and the saturation indices for calcite in the spring waters suggest that processes (abiotic vs. biotic) controlling the carbonate formation may vary among the sampling sites.