Reports of scientific investigations published in Clays and Clay Minerals address a wide range of topics covering virtually every physical and natural science and thousands of industrial products and processes worldwide. Even though these nano-sized materials occur naturally throughout the Earth's crust, a large proportion of the studies carried out in the past regarding their origins, nature, and uses, as reported in Clays and Clay Minerals, have arisen predominantly from North America and Europe. In recent years, however, manuscript submissions from China have increased appreciably (Figure 1). In the current issue, a number of those studies were selected for a compilation in order to highlight the contributions being made by Chinese colleagues, which gives a glimpse into the types of clay research under way in that country. The manuscripts selected do not, of course, represent a comprehensive treatise of clay research in China, but rather an opportune emphasis that is intended to call attention to the work being done there.

Among the many techniques used to remove toxic dyes from the environment, layered double hydroxides (LDH) are considered to be especially environmentally friendly, but, this quality may be altered by variations in the octahedral Mg/Al molar ratios in the LDH structure. The aim of the present study was to synthesize environmentally sound LDH for use as an economically viable sorbent for the adsorption of reactive brilliant orange X-GN. Layered double hydroxides with Mg/Al molar ratios of 2:1 and 4:1 were prepared by co-precipitation. The materials obtained were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, X-ray fluorescence spectroscopy (XRF), and surface-area analysis. Batch experiments were carried out to investigate the effects of contact time, pH, adsorbent dosage, and initial dye concentration on the adsorption behavior of the reactive brilliant orange X-GN by Mg-Al LDH. The results showed that the optimum pH value for dye adsorption was 3.0, at which the adsorption capacities of the reactive brilliant orange X-GN by the 2:1 LDH and the 4:1 LDH at 298 K were 79.370 mg/g and 83.343 mg/g, respectively. Further analysis of the dye-adsorption kinetics show that they fit the pseudo second-order model well. The adsorption equilibrium data showed that the Langmuir model provided better correlation of the equilibrium data than the Freundlich model. This result indicates that LDH provide specific homogeneous sites where monolayer dye adsorption occurs. The results of XRD and FTIR analyses of LDH before and after the dye adsorption demonstrated that the adsorption mechanisms were ion exchange and coulombic attraction.

Most natural and synthetic rubbers have inherently high flammability, a property which limits their uses. The aim of the present work was to study the effect of organo-montmorillonite (OMMT) and modified OMMT on the flame-retardance and mechanical properties of natural rubber (NR) composites. The OMMT was modified with hyper-branched polymer via condensation polymerization between the intercalation agent, N,N-di(2-hydroxyethyl)-N-dodecyl-N-methylammonium chloride, and the monomer, N,N-dihydroxyl-3-aminomethyl propionate. This modified OMMT was then reacted with phosphate, and a novel flame-retardant hyper-branched organic montmorillonite (FR-HOMMT) was thus obtained. The surface morphology, interlayer space, interlamellar structure, and thermal properties of these modified clays were investigated by Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis. The FR-HOMMT showed increased basal spacing and better thermal stabilities due to the different arrangement and thermal stability of the novel organic macromolecular surfactant. Natural rubber NR/OMMT and NR/FR-HOMMT composites were prepared by conventional compounding with OMMT and the phosphorus-based organo-montmorillonite. The cure characteristics, tensile strength, wear resistance, thermal stabilities, and flame-retardant properties were researched and compared. The best dispersion of this modified clay was observed for 20 phr (parts per hundred of rubber) of FR-HOMMT-filled composite, which resulted in the best mechanical performance with an increase of 47% in tensile strength, of 40% in elongation at break, and decrease of 140% in abrasion loss compared with 20 phr of the OMMT-filled matrix. A mechanism for reinforcing and flame retardance is proposed here. The 'anchor' effect caused by the hyper-branched polymer may decrease the number and size of the voids in the NR matrix, and thus increase the crack path during tensile drawing. Meanwhile, the flame retardance of the OMMT and the phosphate may increase the number of carbonaceous layers, thus inhibiting the degree of pyrolysis of the NR matrix during burning.

Vermiculite is a common layered silicate clay mineral which has good adsorption and ion-exchange properties, and which is used to remove pollutants from groundwater. The adsorption by vermiculite from Heibei Province, China, of low-concentration ammonium in water was assessed here to evaluate the effects of adsorption time, particle size, adsorbent dose, pH, and temperature. Using Fourier-transform infrared spectroscopy, the concentration of NH4+ at 1430 cm−1 was evaluated after ammonium was adsorbed by vermiculite. Based on Langmuir-model analysis, the adsorption capacity of the Chinese vermiculite (in the particle-size range 0.025–0.075 mm) for ammonium was 18 mg/g after 3 h of equilibration. Optimal adsorption occurred at pH 6–7 and 60°C, which is different from that at high ammonium concentrations. Smaller particle-size fractions showed greater degrees of adsorption. Increase in Mg2+, K+, or Na+ concentrations influenced ammonium adsorption and, therefore, indicated that cation exchange was the mechanism for ammonium uptake from low-concentration solutions.

The photochemically assisted Fenton reaction (photo-Fenton) is important because it may be particularly effective for the degradation of harmful organic compounds in the environment using solar light. The purpose of the present study was to determine the effectiveness of hydroxy Fe/Al-intercalated montmorillonites (Fe/Al-Mt) as photo-Fenton catalysts. In particular, different Fe/Al molar ratios were of interest as a means to vary catalytic activity. Intercalation was achieved via an ion-exchange method and brilliant orange X-GN was the test compound for photodegradation by hydrogen peroxide (H2O2) under visible-light irradiation (γ < 420 nm) in the presence of Fe/Al-Mt. The Fe/Al-Mt materials obtained were characterized by powder X-ray diffraction, N2 adsorption/desorption, X-ray fluorescence spectroscopy, X-ray photoelectron spectroscopic analysis, and ultraviolet-visible spectroscopy. The decoloration performance of Fe/Al-Mt was investigated using different experimental parameters, including the synthesis method, the Fe/Al molar ratio of the intercalating solution, the catalyst dosage, the H2O2 dosage, and the pH. The results of photo-Fenton reaction showed that the photocatalytic activity of Fe/Al-Mt was enhanced significantly by the extent of hydroxy Al/Fe intercalation. For optimal reaction conditions, 99.92% degradation efficiency of X-GN was achieved after 140 min of reaction. To obtain further information on the visible-light-assisted photo-Fenton process, a high-performance liquid chromatography-mass spectrometry method was applied to indentify the intermediate products and a degradation pathway was proposed.

In order to better understand the provenance of the sediments and environmental change associated with the Permian-Triassic (P/T) biotic crisis, a comparative clay mineralogical study of the Permian-Triassic boundary (PTB) sediments between the Meishan section (the Global Stratotype Section and Point of the PTB) and the Xiakou section, southern China, was undertaken using X-ray diffraction and differential scanning calorimetry (DSC). The results showed that clay minerals of the packstone bed 24e, in which the preludial mass extinction occurred at Meishan, consist of 56% mixed-layer illite-smectite (I-S), 39% illite, and 5% kaolinite. A dehydroxylation effect was measured at 652°C, indicating that I-S and illite of this bed contain mainly cis-vacant (cv) layers related to volcanic origin. The dehydroxylation event correlates with bed P257 at Xiakou. The white clay bed 25 also corresponding to the main extinction event at Meishan contains 95% I-S and 5% kaolinite, with a strong endothermic effect at 676°C and a weaker one at 514°C in the DSC curve. These results are attributed to dehydroxylation of cv layers in I-S clays, suggesting that I-S in the white clay bed was derived from marine alteration of volcanic ash, in agreement with the conodont-correlated clay (P258) at Xiakou. (Conodonts are tooth-like microfossils and are usually used as an indicator of age in PTB stratigraphy.) Increases in chlorite and illite contents in the black clays (bed 26) at Meishan and the conodont-correlated black clay layer (P259b) at Xiakou probably indicate stronger erosional processes under cooler and more arid conditions. Volcanic materials found in a bed which marked the prelude to the main episode of mass extinction reinforce the temporal link between volcanism and the mass extinction.

Heterostructures formed by nanoparticles hybridized with porous hosts are of great potential in many practical applications such as catalysis, adsorption, and environmental remediation, based on their intrinsic properties. The objectives of this study were to synthesize zerovalent iron nanoparticles/montmorillonite heterostructures and to investigate their textural evolution under different Fe loadings. Iron nanoparticles were hybridized with montmorillonite by impregnation of montmorillonite by ferric ions followed by chemical reduction with sodium borohydride in solution. These hybridized Fe nanoparticles were well dispersed on the montmorillonite surface, size adjustable, and resistant to oxidation under the protection of native Fe-oxide shells. The textural evolution of these heterostructures under various Fe loadings was investigated using nitrogen physisorption, X-ray diffraction, electron microscopy, and elemental analyses. As the Fe loadings increased, the total pore and mesopore volumes were almost unchanged; the total, micropore, and external surface areas as well as the micropore volume decreased; and the average pore diameter increased. These textural changes could be attributed to the filling of the interparticle pores of montmorillonite by a variable amount of Fe nanoparticles. In addition, with increasing Fe loadings, the mesoporous character was enhanced for these heterostructures. These fundamental results are important in understanding the structure of these heterostructures as well as in developing some novel applications in related fields.

Kaolinite is often a cause of deformation in soft-rock tunnel engineering, leading to safety problems. In order to gain a better predictive understanding of the governing principles associated with this phenomenon, the physical and chemical properties of kaolinite were investigated using an efficient, firstprinciples scheme for studying isomorphic substitution of Al ions in kaolinite by two kinds of other elements (namely, the dual defect). Elements that are relatively common in natural kaolinite were chosen from groups II (Be, Mg, Ca, and Sr) and III (Fe and Sc) of the Periodic Table as dual-defect ions to substitute for Al ions in kaolinite. By systematically calculating the impurity-formation energies (which characterize the difference in the total crystal energy before and after the defect arises) and transitionenergy levels, which characterize the energy cost for the transformation between two different charge states, the (Be + Sc)Al (i.e. the replacement of two specific Al ions in kaolinite by external Be and Sc ions), (Ca + Sc)Al, (Mg + Sc)Al, and (Sr + Sc)Al ion pairs were determined to have low formation energies, suggesting that these combinations of ions can easily substitute for Al ions in kaolinite. The (Be + Fe)Al, (Ca + Fe)Al, (Mg + Fe)Al, and (Sr + Fe)Al ion pairs have relatively high formation energies which make isomorphic substitution (or doping) in kaolinite difficult. Moreover, these combinations of elements from groups II and III were found to have relatively low transition-energy levels compared with other element pairs. Among them, (Sr + Sc)Al have the lowest transition-energy level at 0.06 eV above the valence band maximum. When compared with single external substitutional defects in kaolinite, remarkably, the dual defects have relatively low formation energies and transition-energy levels. The results are helpful in understanding the chemical and physical properties of natural kaolinite.

Few studies have explored the change in thermal stability of poly(oxypropylene) (POP) ammonium ions after intercalation, even though several studies have focused on the modification of montmorillonite (Mt) with POP amine hydrochloride. The purpose of the present study was to understand the effect of chain length of POP amine hydrochlorides on the basal spacing of modified Mt, and the amount and thermal stability of the ammonium ions intercalated. The relations between basal spacing, organic fraction, and thermal stability of the ammonium ions intercalated were also explored. Series of modified Mt were prepared via ion-exchange between Na+-montmorillonite (Na+-Mt) and POP diammonium ions or POP triammonium ions with different chain lengths, and were then characterized by Fourier-transform infrared spectroscopy, X-ray diffraction, and simultaneous differential scanning calorimetry-thermogravimetric analysis. The results revealed that the basal spacing of modified Mt increased with the hydrophobic chain length of the POP ammonium ions. The amount of triammonium ions intercalated was close to the theoretical amount, while the organic fraction of modified Mt was directly proportionalto the basalspacing of modified Mt. The intercalated ammonium ions were, therefore, contained within the interlayer space ofMt. After intercalation, the thermal stability of the POP ammonium ions with various chain lengths was reduced; i.e.Tonset was reduced by 7–60°C for short-chain POP ammonium ions (D400 and T403) and by 177–192°C for long-chain ions (D2000, D4000, T3000, and T5000).

Landfill leachate is one of the most difficult effluents with which to deal from an environmental perspective because of its concentration and complex composition, including refractory and toxic components such as heavy metals or xenobiotic organic compounds. The objective of the present study was to use organically modified bentonite (OMB) to dispose of landfill leachate >10 y old. The OMB was synthesized using a new method, which removed four steps (filtering, washing, drying, and grinding) from the traditional process. After treatment using OMB, the chemical oxygen demand concentration (COD concentration, an index of the organic pollutants in the landfill leachate, was determined using the potassium dichromate method) of the landfill leachate sample decreased from 2400 to 245 mg/L in 5 h, i.e. the organic pollutants reduction efficiency was as high as 90%. Gas chromatography-mass spectrometry results indicated that most of the organic compounds were removed during the process. The modified and unmodified bentonite contained in the OMB deal with the hydrophobic and hydrophilic organic pollutants, respectively, resulting in significant degradation of the leachate. The study results have provided a new cost-effective method for treatment of landfill leachate.

The role of Mn oxide in the abiotic formation of humic substances has been well demonstrated. However, information on the effect of crystal structure and surface-chemical characteristics of Mn oxide on this process is limited. In the present study, hexagonal and triclinic birnessites, synthesized in acidic and alkali media, were used to study the influence of the crystal-structure properties of birnessites on the oxidative polymerization of hydroquinone and to elucidate the catalytic mechanism of birnessites in the abiotic formation of humic-like polymers in hydroquinone-birnessite systems. The intermediate and final products formed in solution and solid-residue phases were identified by UV/Visible spectroscopy, atomic absorption spectrometry, Fourier-transform infrared spectroscopy, X-ray diffraction, solid-phase microextraction-gaschromatography-mas ss pectrometry, ion chromatography, and ultrafiltration. The degree of oxidative polymerization of hydroquinone wasenhanced with increase in the interlayer hydrated H+, the average oxidation state (AOS), and the specific surface area of birnessites. The nature of the functional groups of the humic-like polymers formed was, however, almost identical when hydroquinone was catalyzed by hexagonal and triclinic birnessites with similar AOS of Mn. The results indicated that crystal structure and surface-chemistry characteristics have significant influence on the oxidative activity of birnessites and the degree of polymerization of hydroquinone, but have little effect on the abiotic formation mechanism of humic-like polymers. The proposed oxidative polymerization pathway for hydroquinone isthat, asit approachesthe birnessite, it formsp recursor surface complexes. Asa strong oxidant, birnessite accepts an electron from hydroquinone, which is oxidized to 1,4-benzoquinone. The coupling, cleavage, polymerization, and decarboxylation reactionsaccompany the generation of 1,4-benzoquinone, lead to the release of CO2 and carboxylic acid fragments, the generation of rhodochrosite, and the ultimate formation of humic-like polymers. These findings are of fundamental significance in understanding the catalytic role of birnessite and the mechanism for the abiotic formation of humic substances in nature.

Mineral-microbe interactions are widespread in a number of environmental processes such as mineral weathering, decomposition, and transformation. Both clay minerals and silicate-weathering bacteria are widely distributed in nature, and the latter contribute to weathering, diagenesis, and mineralization of major rock-forming minerals. The purpose of this study was to observe changes in the chemical composition and structure, especially the phase transformation, of smectite after processing by a silicate-weathering bacterium. The interaction between Bacillus mucilaginosus and bentonite was studied using custom culture media. Results from Inductively Coupled Plasma-Atomic Emission Spectrometry revealed that the bacterium promoted release of Si and Al from solid bentonite to solution. Concomitantly, the Ka nd Fe contents of the mineral increased as shown by X-ray photoelectron spectroscopy results. After interaction with the bacterium, the montmorillonite underwent a possible structure transformation to smectite, as indicated by the emergence of a new weak peak (d = 9.08 Å) shown by X-ray diffraction patterns. The mineralogical changes were also demonstrated by the decrease in the specific surface area of the mineral from 33.0 to 24.0 m2/g (these lower values for SSA of bentonite are related to the particle size of the smectite examined (120-160 mesh) and the weakened absorption bands in Al-O-H and Si-O-Si vibrations by Micro Fourier-transform infrared spectroscopy. The morphology changes in the bacteria observed by environmental scanning electron microscopy and atomic force microscopy revealed an obvious growth of the flagella in the presence of bentonite.