Legacy Effects of Sorption Determine the Formation Efficiency of Mineral-Associated Soil Organic Matter.

Sorption of dissolved organic matter (DOM) is one major pathway in the formation of mineral-associated organic matter (MOM), but there is little information on how previous sorption events feedback to later ones by leaving their imprint on mineral surfaces and solutions ("legacy effect"). In order to conceptualize the role of legacy effects in MOM formation, we conducted sequential sorption experiments with kaolinite and gibbsite as minerals and DOM derived from forest floor materials. The MOM formation efficiency leveled off upon repeated addition of identical DOM solutions to minerals due to the retention of highly sorptive organic molecules (primarily aromatic, nitrogen-poor, hydrogen-poor, and oxygen-rich molecules), which decreased the sorption site availability and simultaneously modified the mineral surface charge. Organic-organic interactions as postulated in multilayer models played a negligible role in MOM formation. Continued exchange between DOM and MOM molecules upon repeated sorption altered the DOM composition but not the MOM formation efficiencies. Sorption-induced depletion of high-affinity compounds from solutions further decreased the MOM formation efficiencies to pristine minerals. Overall, the interplay between the differential sorptivities of DOM components and the mineral surface chemistry explains the legacy effects that contribute to the regulation of fluxes and the distribution of organic matter in the soil.

Research Progress on Graphite-Derived Materials for Electrocatalysis in Energy Conversion and Storage.

High-performance electrocatalysts are critical to support emerging electrochemical energy storage and conversion technologies. Graphite-derived materials, including fullerenes, carbon nanotubes, and graphene, have been recognized as promising electrocatalysts and electrocatalyst supports for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and carbon dioxide reduction reaction (CO2RR). Effective modification/functionalization of graphite-derived materials can promote higher electrocatalytic activity, stability, and durability. In this review, the mechanisms and evaluation parameters for the above-outlined electrochemical reactions are introduced first. Then, we emphasize the preparation methods for graphite-derived materials and modification strategies. We further highlight the importance of the structural changes of modified graphite-derived materials on electrocatalytic activity and stability. Finally, future directions and perspectives towards new and better graphite-derived materials are presented.

[Species Determination and Spectral Characteristics of Swelling Clay Minerals in the Pliocene Sandstones in Xinghai, Qinghai].

X-ray diffraction (XRD) and Fourier infrared absorption spectroscopy (FTIR) were conducted to deepen our research on specific species and spectral characteristics of swelling clay minerals in the Pliocene sandstones in Xinghai, Qinghai province. XRD results show that swelling clay minerals are dominant clay minerals in the sandstones, which can be up to 97% in percentage. XRD patterns show 060 reflections of the samples occur both remarkably at 1.534 Å and 1.498 Å, indicating the samples contain physical mixtures of trioctahedral and dioctahedral swelling clay minerals, respectively. Further treatment of Li-300 degrees C heat and glycerol saturation shows the swelling clay minerals collapse to 9.3-9.9 Å with a partial expansion to -18 Å. This indicates the swelling clay minerals dominate montmorillonite and contain minor saponite. The montmorillonite shows no swelling after Li-300 degrees C heat and glycerol saturation because of Li+ inserting into the octahedral layers, which balances the layer charge caused by the substitution of Mg to Al. FTIR results show the samples are composed of a kind of phyllosilicate with absorbed and structural water, which is in agreement with the results of XRD. Absorbed peaks at 913, 842, 880 cm(-1), corresponding to OH associated with Al-Al, Al-Mg, and Al-Fe pairs, further indicates the minerals are dominant dioctahedron in structure. Meanwhile, absorbed peaks at 625 and 519 cm(-1), corresponding to coupled Si-O and Al-O-Si deformation, indicates parts of Si is replaced by Al in tetrahedron. The spectral characteristics of the samples are against the presence of beidellite and nontronite based on the results of XRD and FTIR, while demonstrating an,existence of montmorillonite. This study, to distinguish the specific species of swelling clay species in clay minerals, would be of great importance when using clay mineralogy to interpret provenance and climatic information.

[Study on the fine structure of K-feldspar of Qichun granite].

Fine structure of K-feldspar from the Qichun granite was investigated using X-ray diffraction (XRD), Fourier infrared absorption spectroscopy (FTIR), and inductively coupled plasma mass spectrometry methods to understand the evolution of the granitic magmatism and its correlation to molybdenite mineralization. The XRD results showed that K-feldspar of the potassic alteration veins has higher ordering index and triclinicity and is namely microcline with triclinic symmetry. K-feldspar of the early cretaceous granite has relatively lower ordering index and has widening [131] peak and is locally triclinic ordering. K-feldspar of the late cretaceous granite has lowest ordering index and sharp [131] peak and is honiogeneously monoclinic. The FTIR results showed that the IR spectra of the Qichun K-feldspar are similar to that of orthoclase reported by Farmer (1974). The 640 cm-1 absorption band increases while the 540 cm-' absorption band decreases with increase in K-feldspar ordering index, also, the 1,010 cm-1 absorption band separates into 1,010 and 1,046 cm-1 absorption bands, with a change in the band shape from widening to sharp outline. The ICP-MS results suggested that K-feldspar of the early cretaceous granite has relatively higher metal elements and rare earth elements, and the granite exhibits better mineralization background, K-feldspar of the potassic alteration veins has markedly lower Sr and Ba, indicating that the alteration fluid originated from the granitic magmatism, and hence, potassic alteration is a good indicator for molybdenite exploration.

[Occurrence relationship between iron minerals and clay minerals in net-like red soils: evidence from X-ray diffraction].

The high purity of clay minerals is a key factor to reconstruct the palaeoclimate in clay mineralogy, however, the existence of iron minerals (such as goethite and hematite) and organics lead to the intergrowth of clay minerals and other minerals, producing other mineral impurities in enriched clay minerals. Although the removal of organics in soil sediments has been fully investigated, the occurrence state of iron minerals remains controversial, hindering the preparation of high-purity clay minerals. Therefore, the occurrence relationship of iron minerals and clay minerals in Jiujiang net-like red soils of the middle to lower reaches of the Yangtze River was investigated using the sequential separation method, which provided some implications for the removal of iron minerals in soil sediments. The results indicated that goethite and hematite were mostly absorbed on the surface of hydroxy-interlayered smectite and illite in the form of films, and the rest were absorbed by kaolinite.

[Effect of treatments of hydrogen peroxide and sodium dithionite-citrate-bicarbonate on clay minerals of red earth sediments].

As classical procedures for pretreatment of soil sediments, hydrogen peroxide (H2O2) and sodium dithionite-citrate-bicarbonate (DCB) treatment methods are very important in removing the organic matter and iron oxides acting as cementing agents in the soils. However, both of these methods have less been focused on the effect on the clay minerals when separating. Here, we report the comparable methods between H2O2 and DCB to reveal their effect on clay minerals in red earth sediments using X-ray diffraction (XRD). The XRD results suggested that mineral particles can be totally decentralized by either H2O2 or DCB method in the soils and high purity clay minerals can be obtained by separating quartz and other impurities from clay minerals effectively. However, the XRD data were distorted by the DCB treatment owning to the cation exchange between Na+ and interlayer cation. On the contrary, the authentic data can be obtained by H2O2 treatment. Therefore, the H2O2 treatment seems to be a more appropriate method to obtain authentic information of clay mineralogy when separating of clay minerals from red earth sediments.

Chemistry of soil-type dependent soil matrices and its influence on behaviors of pharmaceutical compounds (PCs) in soils.

Behaviors of pharmaceutical compounds (PCs) in soil are usually determined by experimental extrapolation of results from separate constitutes to the soil, or from a special soil to other regional soil conditions. However, such extrapolation is problematic due to variations in soil clay mineral and organic matter (OM) compositions with soil types, which dominate the interaction mechanisms of PCs in soil. It is essential to review current literature to enhance our understanding of the soil-type dependent surface chemistry of soil matrices and the environmental behavior of PCs in different soil types. Major types of soils occur globally in parallel to the latitudinal or altitudinal zonation due to regional climate conditions with distinct clay mineral and OM compositions. The soil-type dependent surface chemistry results in variations in retention, distribution, transport, and transformation PCs in soil. The mixture of PCs of different classes usually exhibited enhanced sorption due to the cooperative multilayer sorption on soil constituents, and that of the same class often caused differential adsorption capacity compared to the sorption from single compound due to competitive sorption. PCs preferentially adsorb to a soil component, or to a special soil type, and exhibit notably soil-type dependent sorption affinity, mobility, and dissipation. The soil-dependent surface chemistry of soil is critical to predict the persistence and bioavailability of PCs in soil. In the future, more detailed studies of influence of individual soil factor on the behaviors of PCs and especially the practical field site investigation are required to better understand the sorption, transport, transformation, and ecotoxicology of PCs in typical soil types.

Mineral weathering is linked to microbial priming in the critical zone.

Decomposition of soil organic matter (SOM) can be stimulated by fresh organic matter input, a phenomenon known as the 'priming effect'. Despite its global importance, the relationship of the priming effect to mineral weathering and nutrient release remains unclear. Here we show close linkages between mineral weathering in the critical zone and primed decomposition of SOM. Intensified mineral weathering and rock-derived nutrient release are generally coupled with primed SOM decomposition resulting from "triggered" microbial activity. Fluxes of organic matter products decomposed via priming are linearly correlated with weathering congruency. Weathering congruency influences the formation of organo-mineral associations, thereby modulating the accessibility of organic matter to microbial decomposers and, thus, the priming effect. Our study links weathering with primed SOM decomposition, which plays a key role in controlling soil C dynamics in space and time. These connections represent fundamental links between long-term lithogenic element cycling (= weathering) and rapid turnover of carbon and nutrients (= priming) in soil.

[Mineralogy and genesis of mixed-layer clay minerals in the Jiujiang net-like red soil].

Mineralogy and genesis were investigated using X-ray diffraction (XRD), Fourier infrared absorption spectroscopy (FTIR) and high resolution transmission electron microscopy (HRTEM) to understand the mineralogy and its genesis significance of mixed-layer clay minerals in Jiujiang red soil section. XRD and FTIR results show that the net-like red soil sediments are composed of illite, kaolinite, minor smectite and mixed-layer illite-smectite and minor mixed-layer kaolinite-smectite. HRTEM observation indicates that some smectite layers have transformed into kaolinite layers in net-like red soil. Mixed-layer illite-smectite is a transition phase of illite transforming into smectite, and mixed-layer kaolinite-smectite is a transitional product relative to kaolinite and smectite. The occurrence of two mixed-layer clay species suggests that the weathering sequence of clay minerals in net-like red soil traversed from illite to mixed-layer illite-smectite to smectite to mixed-layer kaolinite-smectite to kaolinite, which indicates that net-like red soil formed under a warm and humid climate with strengthening of weathering.

Influence of chain lengths and loading levels on interlayer configurations of intercalated alkylammonium and their transitions in rectorite.

There have been extensive studies on intercalation of alkylammonium into swelling clay minerals for the purpose of surface charge determination of the clay minerals, as well as their interlayer configurations in the clay minerals. The most accepted findings are that the intercalated alkylammonium molecules adopted horizontal monolayer, bilayer, pseudotrilayer, and vertical paraffin-like configurations in the interlayer space of the swelling clay minerals depending on the chain length and loading level of the alkylammonium used. This study examined the interlayer configurations of intercalated alkyltrimethylammonium and their transition structure as a function of alkylammonium inputs and chain lengths. As the amount of alkylammonium intercalation increased, the bilayer configuration of the intercalated alkylammonium was absent during a transition from a horizontal monolayer to a pseudotrilayer intercalation. Instead, the transition structure involved a mixed layer made of rectorite intercalated with one layer and rectorite intercalated with pseudotrilayer of alkylammonium molecules. When intercalated in horizontal monolayer, the alkylammonium molecules took a random, more gauche-like arrangement. On the other hand, as alkylammonium molecules adopted a pseudotrilayer, particularly the vertical paraffin-like arrangement, a more ordered all-trans configuration was achieved. As layer charge is one of the most important properties of swelling clay minerals, commonly determined by intercalation of n-alkylammonium ions, the identification of mixed-layer transition structure in this study may suggest a need for further investigations on principles of layer charge determination of swelling clays by the alkylammonium method.

Photocatalytic degradation of diphenhydramine in aqueous solution by natural dolomite.

Natural dolomite, an inexpensive and vastly available natural material, was demonstrated as a potential heterogeneous photocatalyst for the efficient removal of diphenhydramine (DP) from aqueous solution under simulated solar light in this study. About 65% DP removal and 14% mineralization were achieved with dolomite as a catalyst after 75 min irradiation. The electron spin resonance analysis and scavenger experiments verified that 1O2, ˙OH, and O2 -˙ produced in the dolomite system were the main reactive species responsible for DP degradation. Furthermore, first-principle calculations combined with deoxygenation experiments were employed to elucidate the photocatalytic mechanism. The results revealed that the dolomite changed from an insulator to a semiconductor after partial substitution of Mg2+ by Fe2+, suggesting that natural dolomite could act as a semiconductor photocatalyst in photoreactions. Under irradiation, photo-excited electrons and holes separate and migrate to the surface of dolomite, and subsequently react to form reactive species resulting in the DP degradation. Product studies demonstrated that the main degradation pathways of DP included hydroxylation of the aromatic ring as well as hydroxyl radical mediated oxidation of the alkylamine side chain. This work indicated that natural dolomite could be applied in water and wastewater treatment as a promising photocatalyst.

Retardation of chromate through packed columns of surfactant-modified zeolite.

In this study, zeolite aggregates with particle size < 0.4, 1.4-2.4, and 3.6-4.8 mm were modified by the cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide to a surfactant loading level of 80, 130, and 250 mmol kg(-1), respectively. The modified and unmodified zeolites were subjected to column tests to study the chromate transport and retardation as affected by particle size. At an input concentration of 11-15 mg L(-1), unmodified zeolite did not retard chromate transport for all three particle size ranges. In contrast, the observed retardation factor for chromate, defined as the number of pore volumes passed when the output concentration equals to half of the input concentration, was 55, 50, and 500 for the columns packed with 3.6-4.8, 1.4-2.4, and < 0.4 mm modified zeolite, respectively. Prolonged tailing of chromate desorption from the modified zeolite was the most striking feature after the feeding solution was switched from chromate to water at full breakthrough. Monitoring of HDTMA and counterion bromide concentration in the effluent revealed that slow but persistent desorption of HDTMA and bromide occurred throughout the transport experiment, which resulted in stripping off of the upper layer of the surfactant bilayer formation on zeolite. The change of HDTMA surfactant surface configuration from bilayer to monolayer resulted in a loss of functionality to absorb and immobilize chromate on the modified zeolite surfaces.

An FTIR investigation of hexadecyltrimethylammonium intercalation into rectorite.

Rectorite is an interstratified clay mineral made at 1:1 ratio of an orderly arrangement of a nonswelling component illite and a swelling component smectite. Due to the presence of two distinct types of components, it is of great interest to study the adsorption of long chain alkylammonium in rectorite. In this study, we conducted batch experiments and used X-ray diffraction (XRD) and Fourier Transform infrared (FTIR) spectroscopy to characterize the interlayer configuration of intercalated long chain hexadecyltrimethylammonium (HDTMA) in rectorite. The FTIR results showed that a monomer-like intercalation with extensive gauche conformers was formed at surfactant loading less than the cation exchange capacity (CEC) of the mineral. At a higher surfactant loading the CH2--symmetric and anti-symmetric vibrations shifted to lower frequencies, suggesting a more ordered all-trans surfactant interlayer configuration. The thermogravimetric and derivative of thermogravimetric analayses showed a high pyrolysis temperature for the monomer-like gauche conformers and lower pyrolysis temperature for the all-trans configuration of the intercalated HDTMA. The XRD analysis confirmed the monomer-like conformation with a d-spacing of 25.2 angstroms at the low surfactant intercalation and a vertical all-trans configuration with a d-spacing of 49.5 angstroms at an HDTMA intercalation of 3.20 CEC. In addition to conformation analyses of intercalated surfactant in the interlayer using FTIR, the absorbance measured by peak height at 1470, 2850, and 2917 cm(-1) increased linearly with surfactant loading, providing a faster, yet efficient method to quantify the amount of surfactant adsorbed.

Photodegradation of ciprofloxacin adsorbed in the intracrystalline space of montmorillonite.

Although photolysis of antibiotics in aqueous solution was widely studied for a better understanding of their photolytic behavior in aqueous phase, the knowledge about photodegradation of antibiotics adsorbed on solid surfaces is still very limited. In this study, photodegradation of ciprofloxacin (CIP), a fluoroquinolone antibiotic, adsorbed in the intracrystalline space of montmorillonite (MMT) was examined using a xenon light source (300 W, λ > 320 nm). The gradual decrease of basal spacing of MMT from 1.66 to 1.46 nm with irradiation confirmed CIP decomposition in the intracrystalline space under simulated solar irradiation. Nearly 70 percent of adsorbed CIP was degraded after 5 h irradiation, and the reaction followed the first-order kinetics with a rate constant roughly 3 times than that in aqueous solution, indicating more efficient photodegradation of CIP after being adsorbed in the intracrystalline space of MMT. Spectroscopic analysis revealed that direct photolysis was the main photolytic mechanism. The hydroxyl radical induced by irradiated MMT might play an important role. The major photoproducts were identified with liquid chromatography-tandem mass spectrometry, and the main degradation pathways were proposed. The results demonstrated that the photoproduct distribution and degradation pathways of CIP adsorbed in the intracrystalline space differed from those in aqueous solution.

Influences of Sedimentary Environments and Volcanic Sources on Diagenetic Alteration of Volcanic Tuffs in South China.

Permian-Triassic (P-Tr) altered volcanic ashes (tuffs) are widely distributed within the P-Tr boundary successions in South China. Volcanic altered ashes from terrestrial section-Chahe (CH) and marine section-Shangsi (SS) are selected to further understand the influence of sedimentary environments and volcanic sources on diagenetic alterarion on volcanic tuffs. The zircon 206Pb/238U ages of the corresponding beds between two sections are almost synchronous. Sedimentary environment of the altered tuffs was characterized by a low pH and did not experience a hydrothermal process. The dominant clay minerals of all the tuff beds are illite-smectite (I-S) minerals, with minor chlorite and kaolinite. I-S minerals of CH (R3) are more ordered than SS (R1), suggesting that CH also shows a higher diagenetic grade and more intensive chemical weathering. Besides, the nature of the volcanism of the tuff beds studied is derived from different magma sources. The clay mineral compositions of tuffs have little relation with the types of source volcanism and the depositional environments. Instead, the degree of the mixed-layer clay minerals and the REE distribution are mainly dependent upon the sedimentary environments. Thus, the mixed-layer clay minerals ratio and their geochemical index can be used as the paleoenvironmental indicator.

Fe-oxide mineralogy of the Jiujiang red earth sediments and implications for Quaternary climate change, southern China.

Diffuse reflectance spectrophotometry (DRS) is a new, fast, and reliable method to characterize Fe-oxides in soils. The Fe-oxide mineralogy of the Jiujiang red earth sediments was investigated using DRS to investigate the climate evolution of southern China since the mid-Pleistocene. The DRS results show that hematite/(hematite + goethite) ratios [Hm/(Hm + Gt)] exhibit an upward decreasing trend within the Jiujiang section, suggesting a gradual climate change from warm and humid in the middle Pleistocene to cooler and drier in the late Pleistocene. Upsection trends toward higher (orthoclase + plagioclase)/quartz ratios [(Or + Pl)/Q] and magnetic susceptibility values (χlf) support this inference, which accords with global climate trends at that time. However, higher-frequency climatic subcycles observed in loess sections of northern China are not evident in the Jiujiang records, indicating a relatively lower climate sensitivity of the red earth sediments in southern China.

Desorption of ciprofloxacin from clay mineral surfaces.

Desorption from soil clay components may affect the transport and fate of antibiotics in the environment. In this study, ciprofloxacin (CIP) desorption from a kaolinite and a montmorillonite was investigated under different pHs, different concentrations of metal cations of various valencies (Na(+), Ca(2+) and Al(3+)) and a cationic surfactant hexadecyltrimethylammonium (HDTMA), and different desorption cycles. Desorption of CIP from kaolinite and montmorillonite was strongly pH-dependent and desorption isotherms were well fitted with the Langmuir equation. The percentage of CIP desorbed increased with increasing initial CIP loadings, desorbing cation concentrations, and desorption cycles. Comparatively, CIP was more readily desorbed from kaolinite than from montmorillonite. Moreover, the hysteresis index values were all negative, suggesting that the presence of metal cations and HDTMA in solution promoted CIP desorption from clay minerals, owing to cation exchange. The XRD analyses indicated that desorption of CIP occurred from both external and interlayer surfaces of montmorillonite. Formation of Al-CIP complex on solid surface and then detachment of Al-CIP from the solid surface may contribute to the higher CIP desorption by Al(3+) in comparison to Na(+) and Ca(2+).

A mechanistic study of ciprofloxacin removal by kaolinite.

As one of the most important soil components, kaolinite plays a vital role in transport and retention of ionizable contaminants in soils of warm and wet climate. Ciprofloxacin (Cip) is a second generation fluoroquinolone (FQ) antibiotic of high use. It has high aqueous solubility under high and low pH conditions and higher stability in soil system. In this study, the interactions between Cip and kaolinite in aqueous solution were investigated by batch experiments, XRD and FTIR analyses. Quantitative correlation between the exchangeable cations desorbed and Cip adsorbed confirmed experimentally that cation exchange was the dominant mechanism of Cip adsorption on kaolinite. Fitting of experimental data to the cation exchange model resulted in a selectivity coefficient of 27, suggesting a strong affinity of Cip on negatively charged kaolinite surfaces. At the adsorption maximum 190-200 Å(2) was available per Cip molecule, much larger than the Cip molecule area, confirming charge-limited instead of surface-limited Cip adsorption. The invariable d-spacing after uptake of different amounts of Cip suggested that the adsorption of Cip was on the external surfaces of kaolinite. As solution pH increased beyond 8, the amount of Cip adsorption decreased significantly and reached close to zero at pH 11. The high adsorption rate constant due to surface adsorption instead of intercalation and the wide distribution of kaolinite in different soils suggest that the fate and transport of Cip may be governed by the transport of colloidal sized clays.

Removal of diphenhydramine from water by swelling clay minerals.

Frequent detection of pharmaceuticals in surface water and wastewater attracted renewed attention on studying interactions between pharmaceuticals and sludge or biosolids generated from wastewater treatment. Less attention was focused on studying interactions between pharmaceuticals and clay minerals, important soil and sediment components. This research targeted on investigating interactions between diphenhydramine (DPH), an important antihistamine drug, and a montmorillonite, a swelling clay, in aqueous solution. Stoichiometric desorption of exchangeable cations accompanying DPH adsorption confirmed that cation exchange was the most important mechanism of DPH uptake by the swelling clay. When the solution pH was below the pK(a) of DPH, its adsorption on the swelling clay was less affected by pH. Increasing solution pH above the pK(a) value resulted in a decrease in DPH adsorption by the clay. An increase in d(001) spacing at a high DPH loading level suggested interlayer adsorption, thus, intercalation of DPH. The results from this study showed that swelling clays are a good environmental sink for weak acidic drugs like DPH. In addition, the large cation exchange capacity and surface area make the clay a good candidate to remove cationic pharmaceuticals from the effluent of wastewater treatment facilities.

Removal of azobenzene from water by kaolinite.

The use of natural kaolinite clay to remove azobenzene from aqueous solutions under different pHs, ionic strengths, initial solid mass used, and initial solution concentrations was investigated. Batch kinetic experiments showed that the adsorption of azobenzene onto kaolinite followed a pseudo-second-order kinetics with an initial rate of 7.2 mg/g-h and a rate constant of 0.19 g/mg-h. The equilibrium azobenzene adsorption on kaolinite was well described by the Langmuir and Freundlich isotherms with an adsorption capacity of 11 mg/g, or 60 mmol/kg, corresponding to a monolayer adsorption on the surface of kaolinite. Adsorption increased with decreases in solution pH and increases in solution ionic strength. The enthalpy change of adsorption was -38 kJ/mol, suggesting that both physical and chemical adsorption was responsible for the retention of azobenzene on kaolinite. The high affinity of azobenzene for siloxane and gibbsite surfaces was attributed to the attractive Coulombic and van der Waals' forces between the surface and the planar structure of the organic molecule.