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Two-dimensional montmorillonite nanolayers (2D Mnt) are excellent adsorbents for methylene blue due to the fully exposed active sites, but the separation of 2D Mnt from water is difficult. The objective of the present study was to assemble 2D Mnt and graphene oxide sheets into a three-dimensional aerogel (3D Mnt-rGO Gel) to achieve easy solid–liquid separation. Structural characterization demonstrated that the Mnt-rGO Gel has a porous 3D structure with Mnt nanolayers distributed uniformly within; the introduction of 2D Mnt could reduce significantly the degree of restacking of graphene sheets. Adsorption tests indicated that 2D Mnt enhances the methylene blue (MB) removal performance of Mnt-rGO Gel with a large adsorption capacity of 207 mg g–1, which may be attributed to the adsorption of MB onto 2D Mnt and the increased adsorption surface of rGO resulting from the reduced restacking of graphene sheets. The MB was removed completely by 300 mg L–1 of Mnt-rGO Gel-3 in 180 min. The adsorption process of MB onto Mnt-rGO Gel followed the pseudo-second order kinetic model and the Langmuir isotherm model. Mnt-rGO Gel also showed good reusability. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results suggested that the adsorption of MB onto Mnt-rGO Gel may be attributed to the π–π interactions between aromatic rings of MB and graphene, hydrogen bonding, and the electrostatic interactions between the nitrogen groups on the MB and oxygen-containing groups on the Mnt-rGO Gel. [ABSTRACT FROM AUTHOR]

Carboxymethyl cellulose-based hydrogel enhanced by two-dimensional montmorillonite nanosheets (CMC-MMTs Gel) has been successfully synthesized throguh polymerization for methylene blue (MB) removal from water. Structure characterization shows that the introduction of two-dimensional montmorillonite nanosheets (2D MMTs) into CMC-based hyddrogel results in a roguh surface and increased porosity. Adsorption tests demonstrate that the adsorption rate and adsorption capacity of CMC-based hydrogel increase significantly with the increase in 2D MMTs content, and a high adsorption capacity of 410 mg g−1 can be reached. After 5 cycles, CMC-MMTs Gel still exhibits good removal performance indicating a good reusability and structural stability. The enhanced MB removal performance and improved structural stability might be due to 2D MMTs and the increased porosity. FTIR and XPS characterizations demonstrate that the adsorption mechanism of MB onto CMC-MMTs Gel might be attributed to electrostatic adsorption and ion-exchange between MB molecules and MMTs, and the interactions between MB molecules and the hydroxyl and carboxyl groups of CMC. [ABSTRACT FROM AUTHOR]

N-rich nano-activated carbon/montmorillonite nanosheet with high ability for PMS activation and TC degradation was prepared via in-situ polymerization of ANI and calcination, creating open access for PMS to react with the fully exposed active sites. The prepared catalyst exhibited comparable catalytic ability to metal-based catalysts, achieving 86% degradation of TC (40 mg/L) in just 10 min using 0.3 g/L catalyzer and 0.3 g/L PMS. The degradation rate of TC reached 0.35 min−1, which was higher than that of most catalyst. The reason was attributed to the abundant active sites of graphitic N, pyridinic N, pyrrolic N, nitric oxide, and defects, improving the charge distribution and electron transfer of catalyst, and promoting the self-decomposition of PMS into the radical (•OH, •SO 4 −) and non-radical (1O 2 , predominant) species for TC degradation. Such catalyzer provided a novel design of metal-free catalysts with significant improvements, achieving the efficient bio-safety disposal of antibiotics from wastewater. [Display omitted] • N-rich metal-free catalysts with fully exposed active sites is synthesized. • Radical and non-radical species are both generated. • Rapid degradation of TC is achieved using small amount catalyzer and PMS. [ABSTRACT FROM AUTHOR]

Extracellular polymeric substance (EPS)-mineral associations occur naturally in soil and sediments, and they might play crucial roles in heavy metals immobilization. In this study, EPS-montmorillonite composites with different weight ratios were characterized and investigated for their Cd(II) sorption behavior. The results showed that the EPS chains can intercalate into montmorillonite layers by hydrogen bonding connection and chemical reaction between C O, C–N and COO− groups with interlayer cations of montmorillonite, therefore promoting delamination of montmorillonite, especially under a lower weight ratio. An enhancement adsorption of heavy metals was obtained with the composites at lower weight ratios of 1:50 and 0.5:50, whereas composites with higher weight ratio of 5:50 presented a reduced adsorption ability, demonstrating that adsorption of Cd(II) onto the EPS-montmorillonite composites was weight ratio dependent. AFM, CLSM, FT-IR and XPS analysis illustrated that the enhancement of sorption under low weight ratio can be attributed to the release of surface active sites of EPS because of reduced aggregation, the increase of negative surface charges when EPS and montmorillonite were interacted and additional bridging of cadmium ions between EPS and montmorillonite. These findings extend the knowledge into the mobility and fate of Cd(II) in organic matter rich soils and sediments. Image 1 • Cd(II) sequestration in the composites depends on EPS to montmorillonite mass ratio. • Enhancement of Cd(II) sorption by EPS-montmorillonite composite with low mass ratio. • Promotion of surface charge, reduction of aggregation and Cd(II) bridging contribute to the larger sorption. This study firstly reports an enhanced Cd(II) sorption by EPS-montmorillonite composite at low weight ratio. The results provided basic information for studying the fractionation effect of EPS on minerals in heavy metal retention in the natural soil environment. [ABSTRACT FROM AUTHOR]

Montmorillonite (MMT) can be exfoliated into nanosheets used in a wide range of applications as two‐dimensional (2D) material. The exfoliated MMT nanosheets with high diameter–thickness ratio appear to show superior properties in preparation of nanocomposites and other functional materials. In this work, the correlation of exfoliation performance with interlayer cations of MMT in the preparation of 2D nanosheets was investigated. The thickness and lateral diameter of MMT nanosheets were quantitatively measured by atomic force microscopy (AFM) technique. AFM results showed the exfoliated K‐MMT had larger lateral diameter and thinner thickness than the exfoliated Ca‐MMT under the same exfoliation conditions. Molecular simulation was applied to investigate the interlayer‐binding energy (IBE), population analysis and density of states. K‐MMT structures tend to have higher in‐plane chemical bond intensity than Ca‐MMT because of the impact of antibonding. The IBE of K‐MMT was higher than that of Ca‐MMT after the sorption of water molecules into the neighboring monolayers, indicating that thinner naonosheets tend to be easier obtained from Ca‐MMT than K‐MMT in liquid exfoliation. These findings might be helpful for the preparation and application of 2D MMTNS through controlling interlayer cation species and the exfoliation properties of MMT. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Swelling of montmorillonite (MMT) is a nonnegligible factor in many industrial processes owing to its great ability to absorb water in interlayer space. It is not easy to determine whether the exchangeable cations or the MMT layers interacts much stronger with water molecules to provide the dominant driving force for the swelling of MMT. In this work, driving force for the swelling of montmorillonite as affected by surface charge and exchangeable cations has been investigated through molecular dynamics simulations (MDs). The adsorption energy between water molecules and MMT layers and between interlayer cations and water molecules was calculated to qualitatively characterize the driving force for the swelling of MMT, and higher negative adsorption energy means greater driving force. It is found that the adsorption energy between interlayer cations and water molecules are far higher than that between MMT layers and water molecules. Thus, it is the exchangeable cations that provide the dominant driving force for MMT to swell. Besides, it is observed that interlayer cations with stronger hydration ability (Mg > Ca > Na > K) have more negative adsorption energy to water molecules, which indicates that the stronger the hydration ability of exchangeable cations the greater contribution they make to the total driving force for the swelling of MMT. [ABSTRACT FROM AUTHOR]

Swelling of montmorillonite (Mt) is an important factor for many industrial applications. In this study, crystalline swelling of alkali-metal- and alkaline-earth-metal-Mt has been studied through energy optimization and molecular dynamics simulations using the clay force field by Materials Studio 8.0. The delamination and exfoliation of Mt are primarily realized by crystalline swelling caused by the enhanced interlayer cation hydration. The initial position of the interlayer cations and water molecules is the dominated factor for the accuracy of the Mt simulations. Crystalline swelling can be carried out in alkali-metal-Mt and Mg-Mt but with difficulty in Ca-Mt, Sr-Mt and Ba-Mt. The crystalline swelling capacity values are in the order Na-Mt > K-Mt > Cs-Mt > Mg-Mt. This order of crystalline swelling of Mt in the same group can be attributed to the differences between the interlayer cation hydration strengths. In addition, the differences in the crystalline swelling between the alkali-metal-Mt and alkaline-earth-metal-Mt can be primarily attributed to the valence of the interlayer cations. [ABSTRACT FROM AUTHOR]

Delamination of montmorillonite (Na-MMT) is an outstanding property of the dispersed MMT particles. Na-MMT particles delaminated in water and isopropanol under shear forces have been studied in this work. The difference in the intercalation and delamination of Na-MMT by water and isopropanol was studied by molecule dynamic simulation and experiment. Molecule dynamic simulation was carried out on Material Studio (MS) 8.0. The experimental study was performed on a Na-MMT through the measurements of Stokes size, optical size, scanning electron microscope, atomic force microscope, and dynamic molecule simulation. The results demonstrated that under the effect of interlayer hydration, the Na+that resides near the siloxane surface was moved to the middle plane of interlayer space, and the interlayer spacing was opened 1.38A. Compared with the interlayer hydration, the interlayer spacing was increased only a little (0.32A) treated by isopropanol; meanwhile, the interlayer sheets were joined together by isopropanol molecule. Because of that the effect of water and isopropanol in the interlayer of Na-MMT was totally different, the Na-MMT particles were indeed delaminated into plate-like super fine particles in water instead of in isopropanol, and delamination was closely correlated with shear force only if hydration was occurred in the interlayer. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effects of inorganic cations (Na+, Ca2+, and Al3+) with different valences and concentrations on the stability of Na-montmorillonite (Na-MMT) suspension. The stability was studied by turbidity and zeta potential measurements and adsorption thermodynamics. The results showed that the Na-MMT particles coagulated at pH 3-4.8, the stability of which was much inhibited by cations with higher concentration and higher valence. This was caused by the adsorption of cations and the reduction of electrostatic repulsion. Adsorption of Ca2+ on Na-MMT surface fits the Freundlich curve model well. Furthermore, the adsorption reduced the zeta potential of Na-MMT and then the energy barrier between the particles which well obeyed the classic DLVO theory. [ABSTRACT FROM AUTHOR]

The effect of water and isopropanol intercalation on montmorillonite (MMT) delamination was investigated in order to compare the roles of hydration and solvation in the delamination. Transmittance results showed that water has a significant effect on the delamination of MMT compared with isopropanol. This observation was attributed to the difference of the intercalation of water and isopropanol. Thermogravimetric (TG) results illustrate that the intercalation mass of water was greater than that of isopropanol when the pressure remained constant. Weighing test results show that the intercalation mass of water was smaller than that of isopropanol when the volume of MMT remained constant. Molecule dynamic simulation results show that the water and isopropanol molecules were interacting with Na and siloxane surface of MMT, respectively. It was demonstrated that the hydration of the MMT interlayer followed two steps: in step 1, the Na in the interlayer was hydrated, thereby expanding the interlayer spacing; in step 2, additional water molecules were absorbed into the expanded interlayer space. It was found that step 2 could not be actuated until the completion of step 1. For the solvation of the MMT interlayer with isopropanol, however, only one step was required, in which isopropanol was absorbed onto the siloxane sites of the interlayer while maintaining the interlayer spacing. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations (MDS) of montmorillonite (001)/water interface system were used for studying the hydration shell on the montmorillonite surface in this work. The study was performed on the simulation of concentration profile and self-diffusion coefficients. The results have shown that there was a hydration shell on the surface with the thickness of approximately 1.74 nm, which was composed of six ordered water molecule layers, including ordered layers and transition layers. The water molecules in the shell were closely and orderly arranged than those in bulk water, leading to a higher concentration of water molecules. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of inorganic cations (Na+, Ca2+, Ba2+, Fe3+, Al3+) with different valence and concentration on the swelling behaviors of montmorillonite. Na-montmorillonite, obtained from China, was chosen as experimental objective. It was first characterized through the measurements of swelling capacity and zeta potential. Then, swelling properties of Na-montmorillonite influenced by cation concentration, valence, and hydration analyzed were studied. The results showed that the swelling capacity was much inhibited by cations of higher concentrations, higher valences, or weaker hydration. This work also verified the conclusion that the decreased degree of potential is more significant caused by cations of higher valence. [ABSTRACT FROM PUBLISHER]

pillared interlayered clays (-PILCs) were synthesized through a novel method, in which nanoparticles were formed in montmorillonite interlayers. In this method, silver ions were first exchanged into montmorillonite interlayers, and then reduced into nanoparticles by trisodium citrate at 100°C in aqueous solutions. The synthesized @montmorillonite nanocomposite was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM), and its surface area was evaluated by using Brunauer-Emmet-Teller (BET) method. Compared to traditional PILCs synthesized through ion exchange method, the formed -PILCs had better thermal stability and stronger structure because their pillars are nanoparticles. Furthermore, this method introduces a possibility to control the size of the pillars and thus the pore size of the PILCs, due to that the nanoparticle pillars can be modified on their forms and diameters in the synthesizing process. Also, it was found that the intercalating nanoparticle pillars were formed at restricted pH values and silver ion concentrations. The TEM image of the Ag@montmorillonite composite synthesized in montmorillonite dispersions showed that there were many nanoparticles, identified as Ag nanoparticles by EDX, with the size of 2 to 20 nm, are observed on montmorillonite. These Ag nanoparticles had an analogous globular shape, which indicates the growth of the silver nanoparticles was on the montmorillonite surface, or was restricted by the montmorillonite interlayer space alone. [ABSTRACT FROM AUTHOR]

In this work, a Ti-pillared montmorillonite with high thermal stability has been prepared by using a Na-montmorillonite as the host clay and polyhydroxy-titania ions as the pillaring precursor. The formation of Ti-pillared montmorillonite has been confirmed from the characterizations through X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric–differential scanning calorimeter, and specific surface area analyses. In the preparation of Ti-pillared montmorillonite several parameters, such as the type of solvent in which the synthesis is realized, the ratio of polyhydroxy-titania ions and montmorillonite, the intercalation time, the calcining temperature, and calcining time, were tested to understand their effects on the basal spacing. It was shown that this method could produce a Ti-pillared montmorillonite with the basal spacing of 3.74 nm, specific surface area of 409 m2/g, and mean pore size of 2.94 nm, as well as a high thermal stability up to 900°C. [ABSTRACT FROM AUTHOR]

The beneficiation of montmorillonite fines from ores has been studied with the dispersion-sedimentation process by using sodium phosphates as the dispersant in this work. This study was performed on a Ca-montmorillonite ore from China through the measurements of MB (methylene blue) adsorption and X-ray diffraction. Several parameters in the dispersing step, such as type and dosage of dispersant, solid concentration, and slurry stirring time, were tested to understand their effects on beneficiation. It was shown that the beneficiation process was very effective in upgrading montmorillonite, producing a high-grade montmorillonite concentrate. Simultaneously, the Ca-montmorillonite was transformed to Na-montmorillonite. It has been found that sodium pyrophosphate was the best phosphate dispersant for achieving a good beneficiation of montmorillonite from the ore, which might be due to the fact that pyrophosphate ions adsorbed on montmorillonite surfaces lead to a smaller swelling capacity of the mineral particles than other phosphate ions. [ABSTRACT FROM AUTHOR]

Polymer–clay membranes constructed via the layer-by-layer (LbL) assembly, with a nanobrick wall structure, are known to exhibit high flame retardancy. In this work, chitosan–montmorillonite nanosheet (CH–MMTNS) membranes with different thickness of MMTNS were constructed to suppress the flammability of flexible polyurethane (FPU) foam. It was found that a thinner MMTNS membrane was more efficient in terms of reducing the flammability of the FPU foam. This was because such MMTNS membrane could deposit cheek by jowl and form a dense CH–MMTNS membrane on the foam surface, thus greatly limiting the translation of heat, oxygen, and volatile gases. In contrast, a thicker MMTNS constructed a fragmentary CH–MMTNS membrane on the coated foam surface, due to its greater gravity and weaker electrostatic attraction of chitosan; thus, the flame retardancy of a thick MMTNS membrane was lower. Moreover, the finding of different deposition behaviors of MMTNS membranes with different thickness may suggest improvements for the application of clay with the LbL assembly technology. [ABSTRACT FROM AUTHOR]

The colloidal stability of montmorillonite (MMT) dispersions in aqueous NaCl solution and in alcohol-water mixture has been studied in this work. The study was performed through the measurements of particle size, zeta potential, surface tension and swelling capacity. The experimental results have shown that the stability of colloidal MMT dispersion is distinct in the two cases, although the zeta potential has the same change trend. This observation might be attributed to the different behavior of surface tension in aqueous NaCl solution with alcohol-water mixture. The former would increase the surface tension of the media that deteriorate the wettability and swelling capacity of MMT, while the latter would decrease the surface tension. It is demonstrated that the surface tension of the media would affect strongly the colloidal stability of aqueous MMT dispersions, which is of great importance in many industrial processes as well as in soil chemistry and environmental science. [ABSTRACT FROM AUTHOR]

In this work, the effect of the exfoliation degree of montmorillonite (MMT) platelets on their electrophoretic mobility distributions in aqueous suspensions was investigated in order to approach into the correlation of MMT exfoliation with electrokinetic property. The experimental results have shown that the negative mobility increased with the increase of exfoliation degree or with the decrease of MMT thickness. This observation might be attributed to the “exposing” of permanent layer negative charge during the exfoliation processing and the “spillover” of electrostatic potential from basal surfaces onto edges. The former would increase the permanent negative charge of the MMT platelets because of the large amounts of layer charge; the latter would decrease the positive edge charge. It is demonstrated that MMT exfoliation would change the electrokinetic property, which might be helpful of the applications of MMT in the related industries. [ABSTRACT FROM AUTHOR]

In this work, the heterocoagulation of fine montmorillonite (MMT) and fluorite particles in aqueous suspensions was investigated through the measurement of electrophoretic mobility distributions. The experimental results have shown that the heterocoagulation closely correlated to the electrophoretic mobility distribution of the mixed mineral dispersion. If a strong heterocoagulation happened, a single-modal electrophoretic mobility distribution with only one peak could be determined, and the peak located between the peaks of the two individual minerals. Without heterocoagulation, a bimodal electrophoretic mobility distribution with two peaks could be observed, which was consistent with the peaks of the two individual minerals. It is demonstrated that the heterocoagulation of two mineral fines in aqueous suspensions could be predicted by the electrophoretic mobility distribution of the mixed mineral dispersion. [ABSTRACT FROM AUTHOR]

As a new type of separation material, two-dimensional membrane has attracted wide attention due to its special transport mechanism. However, due to the hydration swelling of montmorillonite nanosheets, there are still challenges in preparing two-dimensional membrane with stable channel structure and fixed interlayer spacing. In order to overcome the problems caused by swelling, this study used polyvinyl alcohol and polyacrylic acid to stabilize the channel structure of two-dimensional membranes. Moreover, the crosslinking between Fe3+ and montmorillonite nanosheets was proposed to fix the interlayer spacing of two-dimensional membrane. It is found that various polymers had different effects on the mechanical property of two-dimensional membrane. The addition of polyvinyl alcohol and polyacrylic acid can significantly improve the tensile strength of the membrane. And the introduction of them reduces the hydrophilicity of the membrane surface, thus improving the stability of the membrane in water. In addition, the interlayer cations affect the stability of interlayer spacing of the membrane in water. After crosslinking the membrane with Fe3+, the interlayer spacing is fixed and can be maintained at about 0.94 nm in water for a long time. When a certain dosage of polyvinyl alcohol and PAA are added into the membrane and the crosslinking conditions are suitable, two-dimensional membrane has good selectivity to Li+ and Mg2+ in high Mg/Li ratio brine. Inspired by the natural ion exchange properties of montmorillonite, this study found a new method for inhibiting the hydration swelling of two-dimensional membrane and realizing precise control of interlayer spacing. [Display omitted] • A new method to inhibit hydration swelling of 2D MMT membrane was developed. • Fe3+-crosslinking inhibited the hydration swelling of 2D MMT membrane. • Stability of channel structure realized by cooperation of polymer and metal cation. [ABSTRACT FROM AUTHOR]

The rapid formation or restoration of biocrusts by human intervention, such as constructing artificial biocrusts, is considered a promising technology for desertification control. To date, most of the studies mainly focused on the role of cyanobacteria and their excreted exopolysaccharides (EPSs) in the process of biocrusts formation and development, while few studies have been concerned about clay minerals, which play an important role in soil development as the abiotic factor. In this study, two clay minerals (montmorillonite and kaolinite) were added to crushed natural biocrusts at different ratios(0.5 %, 1 %, 2 %, 5 %, 10 %; w/w), aiming to explore the effects and mechanism of clay minerals on the formation of biocrusts. The results showed that low-level montmorillonite (0.5–2 %; w/w) addition significantly increased the photosynthetic biomass by about 50 % (indicated by Chlorophyll-a and gene copies) and promoted the accumulation of total nitrogen, nitrate nitrogen, ammonia nitrogen, and total organic carbon. The results of the structural equation model showed that the enhancement effect of clay minerals on the formation of biocrusts is mainly ascribed to its direct positive effect on biocrust physical stability and indirect positive effects through increasing both the cyanobacterial biomass and EPS excretion. Notably, the addition of montmorillonite increased the physical stability of the biocrusts by 18 %-53 %, while kaolinite did not play a positive role in the formation of biocrusts. Moreover, excessive montmorillonite (more than 2 %) and kaolinite caused the significant shift of dominance from Cyanobacteria to Proteobacteria, and a sharp decrease in EPS excretion, posing a high risk of biocrust disintegration. Overall, our findings demonstrate the stimulation mechanism of clay addition on restoring natural biocrusts, providing new insight for constructing artificial biocrusts and restoring degraded biocrusts in dryland. • The type and content of clay both affect the formation of biocrusts. • Cyanobacterial biomass, EPS content, and clay determine biocrusts' stability. • Montmorillonite promotes cyanobacteria growth and EPSs excretion. • There is a negative feedback mechanism between biocrust growth and kaolinite. • Montmorillonite enhances the biocrusts' physical stability and nutrient retention. [ABSTRACT FROM AUTHOR]

The origin of the difference in activity between calcined kaolinite and calcined montmorillonite is not well understood. Herein, reactive force field molecular dynamic (ReaxFF MD) simulations were adopted to study the thermal activation behavior of montmorillonite and kaolinite. It was found that during the calcination process, the removal of hydroxyl groups from kaolinite and montmorillonite not only leads to the break of Al (Mg)-O bonds, but also results in the formation of Si[5] and the break of Si-O bonds. The octahedral alumina sheet in kaolinite is more easily destroyed than that of montmorillonite. Most of the hydroxyl groups in kaolinite can be removed after calcination at 800 °C. While only 32.5% of the hydroxyl groups in montmorillonite are removed after calcination at 900 °C. The combination of free hydroxyl groups with Si[4] mainly causes the break of Si-O bonds in Si-O-Al(Mg) structure and the destruction of connection between the tetrahedral silica sheet and octahedral alumina sheet. While the Si-O-Si networks in both kaolinite and montmorillonite are difficult to disrupt. Disrupting the network structures of Si-O-Si sheet is the key to improving the activity of montmorillonite. This work provides an insight into the thermal activation of montmorillonite and kaolinite at atomic level, and is beneficial for exploring suitable pathways for simultaneous activation of kaolin and montmorillonite. • The removal of hydroxyl groups leads to the break of Al-O bonds, the formation of Si[5] and the break of -O bonds. • The octahedral alumina (AlO 6) sheet in kaolinite is more easily destroyed than that of montmorillonite. • The Si-O-Si network in both kaolinite and montmorillonite are difficult to disrupt. • The violently moving ions Na+ ions do not destroy the Si-O-Si network of tetrahedral silica (SiO 4) sheet. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3D reticular-structured MMT nanosheets-based hydrogel beads were prepared. • High exfoliation degree of MMT nanosheets improve adsorption performance of hydrogel beads. • Hydrogel beads have high mechanical strength and adsorption capacity for methylene blue of 543.1 mg/g. • Hydrogel beads also shows excellent dynamic adsorption performance and recycling performance. In this work, hydrogel beads with 3D network structure were successfully prepared using montmorillonite nanosheets (MMTNS) combined with macromolecule polymers. Batch adsorption tests revealed that the increase in exfoliation degree of MMTNS was beneficial to improve the methylene blue (MB) adsorption on hydrogel beads (HB). In addition, the HB with 25 % MMTNS-3 dosage achieved high mechanical strength and reached the maximum adsorption capacity of 543.1 mg/g. Effects of MB concentration (40–120 mg/L), adsorbent dosage (1–1.5 g) and flow rate (5–15 mL/min) on fixed-bed column adsorption indicated that the HB column exhibited an excellent dynamic adsorption performance and recycling performance, much better than the D113 resin. The good fits of Pseudo-first-order model and Pseudo-second-order model and a better Langmuir model fitting result implied a monolayer chemical adsorption and physical adsorption nature of MB on HB. Moreover, scanning electron microscope combined with the energy dispersive spectrometer, fourier transform infrared spectroscope and X-ray photoelectron spectroscopy measurements indicated that the adsorption mechanism was mainly attributed to Ca ion-exchange and chemical bonding of –COOH and –OH groups with MB. Such hydrogel beads showed a good potential in the application of practical wastewater treatment. [ABSTRACT FROM AUTHOR]

Nanofluids showing enhanced thermal diffusivity and thermal conductivity have potential applications in the fields of thermal science, engineering, and sustainable energy. It is still a challenge, however, to facilely prepare nanofluids with good dispersion stability using an environmentally friendly method. In the present study, natural layered montmorillonite was exfoliated into two-dimensional montmorillonite nanosheets (MtNS) using a physical ultrasonic method in aqueous solutions. The obtained MtNS suspensions can be directly used as nanofluids without any further operation or any addition of dispersants. Owing to electrostatic repulsion and hydration repulsion among the MtNS nanoparticles in aqueous solution, MtNS/water nanofluids show excellent dispersion stability even over a long time. In addition, owing to the good light absorption ability of MtNS and the thermal diffusion properties of nanofluids, MtNS/water nanofluids exhibit outstanding photothermal conversion efficiency and dramatic solar thermal energy collection performance. Experimental results also proved that suspensions with a high MtNS concentration and small MtNS particle size increase the efficiency of solar energy harvesting. In addition, the stable dispersion of MtNS in fluids leads to extremely good suspension sustainability and recycling performance of the nanofluids. The facile and green preparation method, low cost, excellent dispersion stability, and good solar energy collection performance of MtNS/water nanofluids enable them to be promising solar energy collection mediums. The large-scale application of MtNS/water nanofluids can take full advantage of green solar energy, which can be used in green buildings and contribute to building a sustainable society. • MtNS/water with superior stability has been developed. • MtNS/water nanofluid can be prepared with facile and green method. • The electrostatic repulsion and hydration repulsion lead to stable suspension. • Outstanding photo-thermal conversion of MtNS/water has been proved. • MtNS/water nanofluid shows huge potential in solar energy utilization. [ABSTRACT FROM AUTHOR]

MMTNS were introduced into carboxymethyl cellulose-chitosan system to synthesize porous hydrogel adsorbent with stable structure and high dye handling capacity. Al-OH on edge of MMTNS formed hydrogen-bond (-OH···+NH 3 -) with -NH 2 on CS, CS then cooperated with CMC via amidation and chains interleaving, forming three-dimensional hydrogel. Morphology characterization revealed that hydrogel possessed microporous open-framework structure, facilitating free entrance of macromolecular MB dye to react with internal reaction sites in hydrogel. Factor tests indicated that high removal (97%) of MB was achieved via 0.2 g/L hydrogel within 360 min even after 5 adsorption-regeneration cycles. Adsorption process followed Pseudo-first-order, Pseudo-second-order kinetic model and Sips isotherm model, owing to both monolayer physical and chemical adsorption behavior of MB molecules onto homogeneous surface of hydrogel. Adsorption mechanism was attributed to ion-exchange, groups combination of carboxyl and hydroxyl, and Si active sites reaction. Such hydrogel realized promotion of polysaccharide polymers in materials design and wastewater treatment. Unlabelled Image • Hydrogel with open-framework structure facilitated free entrance of macromolecular MB dye to reacted with internal sites. • High removal of MB was achieved via 0.2 g/L hydrogel within 360 min even after 5 adsorption-regeneration cycles. • Such hydrogel realized the performance promotion of polysaccharide polymers in materials design and wastewater treatment. [ABSTRACT FROM AUTHOR]

In this work, the montmorillonite (MMT) with different interlayer ions (Na+ and Ca2+) were exfoliated to prepare high aspect ratio 2D montmorillonite nanosheets (MMTNS). The effect of interlayer cations was experimentally and theoretically studied through the atomic force microscope (AFM) and molecular simulation. Na-MMT could be more easily exfoliated to monolayer with the thickness of 0–1 nm compared to Ca-MMT, and the exfoliated Na-MMTNS have higher lateral diameter than Ca-MMTNS under the same condition, leading to that the Na-MMTNS with high aspect ratio can be more readily obtained. This observation was sufficiently interpreted by molecular dynamic simulation and first principles calculations including band structure, density of states, electron density difference and electron localization function. It is indicated that the interlayer binding energy of Na-MMT was weaker while its in-plane structure was stronger compared with Ca-MMT. The strong interacting force between interlayer Ca atoms and the in-plane atoms will cause structural failure after exfoliating Ca-MMT off to 2D nanosheets. It is suggested that the interaction between the extranuclear electrons of atoms in MMT layer and interlayer cations will affect the overall intensity and apparent exfoliation properties. Image 1 [ABSTRACT FROM AUTHOR]

Highlights • Comminution of malachite with different minerals results in different surface roughness. • The rougher is the surface, the more wettable is the mineral. • Higher flotation recovery was obtained with minerals of rougher surface. Abstract In this research, malachite particles with different roughness values were produced by grinding malachite sample together with quartz (mohs hardness: 7) and montmorillonite (mohs hardness: 1–2), respectively. Micro-flotation results showed that higher recovery was achieved by using malachite particles of higher surface roughness as feed. The contact angle measurements demonstrated that the contact angle of natural malachite surface decreased with the increase of its surface roughness, while the contact angle of malachite conditioned with 5 × 10−5 mol/L sodium oleate increased with the increase of its surface roughness. It might be concluded that grinding media can influence minerals surface roughness, thus affecting the wettability of their surface and, consequently, the flotation performance. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The cations have much stronger affinity to water molecules than that of MMT surface. • Cations-H 2 O were adsorbed on MMT surfaces in the form of hydration shell structure. • The hydration ability of the cations dominant the hydrophilic nature on MMT surface. • The more cations and stronger hydration cations, the more hydrophilicity of MMT. Abstract Surface wettability of swelling clay minerals plays an important role in the flocculation-dispersion, sorption, flotation and interfacial interactions behaviors. But it is difficult to determine, not only for the small particle size, but also for the abilities of hydration and swelling. In this work, surface wettability of montmorillonite (0 0 1) surfaces as affected by surface charge and exchangeable cations has been investigated through molecular dynamic (MD) simulations. The adsorption energy between montmorillonite (0 0 1) surface and water molecules was calculated to qualitatively characterize the wettability behaviors, and more negative adsorption energy means stronger affinity between montmorillonite surface and water molecules. It has been found that the negative charged montmorillonite surface has very weak adsorption energy for water molecules but very strong electrostatic attraction for exchangeable cations. Besides, these exchangeable cations have very strong hydration ability thus to acquire several layers of hydration shells around the cations, the effect of which is to impart an overall hydrophilic nature to the clay mineral. As a result, exchangeable cations are being adsorbed on montmorillonite (0 0 1) surface in the form of ionic hydration shell. And it is the exchangeable cations that have much stronger affinity to water molecules than montmorillonite surface, thus the adsorbed exchangeable cations on montmorillonite surface play the dominant role in determining the surface wettability behaviors. [ABSTRACT FROM AUTHOR]

Poly(vinyl alcohol)-sodium alginate-chitosan-montmorillonite nanosheets (MMTNS) hydrogel beads with porous and steady structure were fabricated via hydrogen-bond and electrostatic interactions, and were characterized by FTIR, TG, SEM and effecting tests. The results suggested MMTNS could support and maintain the porous structure, making an open excess for MB molecules. The increasing proportion of MMTNS in hydrogel beads enhanced the MB removal. Hydrogel beads possessed higher affinity to MB at high pHs due to the stronger electronegativity triggered by deprotonation of hydroxyls. Moreover, hydrogel beads had a good stability and reusability. The adsorption process was correlated with Elovich kinetics model, and fitted well with Freundlich, Redlich-Peterson and Sips isotherm models. The adsorption of MB on hydrogel beads was a disorderliness, endothermic and spontaneous process detected by the thrmodynamic. MB molecules reacted with the oxygen atoms in hydroxyl and substitute the Na + in MMTNS were proved by EDS, XPS and Na + concentration variation. [ABSTRACT FROM AUTHOR]

Sodium carboxymethyl cellulose (CMC) molecule binding montmorillonite (MMT) layers in aqueous suspension has been studied in this work. This study was performed through the measurements of adsorption capacity, swelling capacity and Fourier transform infrared spectroscopy, as well as molecular dynamics simulations. The results have shown that CMC molecules adsorbed on MMT edges through the formation of hydrogen bond with the Si OH. However, the swelling capacity of MMT in water was almost the same in the presence and absence of CMC, meaning that CMC could not bind swelling montmorillonite layers in water. The molecular dynamics simulation with the CLAYFF force field indicated that the adsorption energy of CMC onto MMT edges was much less than that of MMT hydration swelling, which might be attributed to that CMC molecules could not bind swelling montmorillonite layers in water. [ABSTRACT FROM AUTHOR]

In this work, self-assembled hydrogels were prepared with exfoliated montmorillonite nanosheets (MMTNS) and chitosan (CS) as the adsorbent for removing methylene blue (MB) from water. Adsorption properties were determined by studying the kinetics and thermodynamic of MB adsorption onto the hydrogels from aqueous solutions, and AFM, FTIR, SEM, and XPS were used for the characterization of the MMTNS and hydrogels. The experimental results have shown that the montmorillonite nanosheets/chitosan hydrogels were superb adsorbents for removing MB from water, reaching the maximum adsorption capacity of 530 mg/g. The adsorption well followed the pseudo-second-order kinetics and Langmuir isotherm, and was spontaneous endothermic. The adsorption of MB on the hydrogels could be easily realized through cation exchange and hydrogen binding. It was also found that the hydrogels prepared with lower solid concentration of MMTNS had a looser stratified structure and thus a greater adsorption capacity for MB in aqueous solutions. [ABSTRACT FROM AUTHOR]

In this work, the exfoliation of montmorillonite related with electric charges on the layers in aqueous solutions were investigated through the measurements of zeta potential, turbidity and atomic force microscopy, as well as molecular dynamics simulation. The charge amount on montmorillonite layers was adjusted by blocking or neutralizing the layer charges with tetraethylenepentaminecopper (II) ([Cu(tetren)] 2+ ) through cation exchange reaction. The experimental results have shown that the exfoliation closely correlated to the amount of the layer charges. The larger are the charge amount on montmorillonite layers, the more easily the montmorillonite is exfoliated. This observation might be attributed to the repulsive energy (electrostatic and hydration repulsion) was stronger between the high charged montmorillonite layers than low charged ones. [ABSTRACT FROM AUTHOR]

The hydration of two-dimensional (2D) particles in aqueous solutions plays an important role in many scientific and technological fields. In this work, a novel method for the determination of the thickness of hydration shell on nanosheets in water has been presented, which was realized through the measurements of the viscosity of aqueous nanosheet dispersion as the function of solid volume concentration and the thickness and size of the nanosheets with atomic force microscope. The principle of the method was based on the viscosity theory of the dispersions of solid nanosheets. This method was applied to montmorillonite nanosheets, showing that the thickness of the hydration shell on the nanosheets was of 1.63 nm. This value of the thickness was verified by molecular dynamics simulation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel method for removing cristobalite from Mt by exfoliating Mt nanosheets. • Method proposed base on difference of structure and hydration expansion property. • Mechanisms of separation investigated from particle size and hydration shell. • Hydration shell is the main factor affecting the separation of Mt and cristobalite. • Density of Mt decreases significantly after exfoliation when considering hydration. The preparation of high purity montmorillonite (Mt) is of great significance for its high-value application. However, the difficulty in removing fine cristobalite from Mt hinders the preparation of high purity Mt. In this work, a novel method for removing cristobalite from Mt is studied through exfoliating Mt to two-dimensional nanosheets, which is proposed based on the difference of the structure and hydration expansion property between the two minerals. The XRD pattern of the purified sample shows that the cristobalite in Mt has been removed completely. Meanwhile, the mechanisms of the separation of Mt and cristobalite were investigated from the differences of particle size and hydration shell. The results show that the decrease of Mt particle size provides the possibility for the separation of cristobalite and Mt, but it is not the main factor. The densities of hydrated Mt and cristobalite before and after exfoliation were calculated by molecular dynamics simulation. After considering the hydration shell, the density of the initial Mt is 2.22 g/cm3, while the density of the exfoliated MtNS is 1.52 g/cm3 because of its two-dimensional structure. In addition, the difficulty level of the separation changes from greatly difficult to easy after considering the hydration shell, which indicates that the hydration shell is the main factor affecting the separation of Mt and cristobalite. This work explains the reasons why this new method can satisfactorily remove cristobalite from Mt and will guide the preparation and application of high purity Mt. [ABSTRACT FROM AUTHOR]

• A novel janus binary membrane was designed for efficient solar desalination. • Hydrophilic MMT membrane was prepared for quick water supply. • High photothermal conversion efficiency was achieved with 84.86%. • Mechanism of increasing water transportation for MMT was calculated by DFT. This paper declared a janus membrane using MXene and montmorillonite (MMT) through simple vacuum filtration. This janus membrane not only can float under surface of water, but also has hydrophilic surface. The hydrophilic surface of membrane promotes the water transportation from bottom to the top of membrane, thus to increase photothermal conversion efficiency. The floatable janus membrane ensure energy limited under interface between water and air, which is important for improving the photothermal conversion efficiency. In addition, the janus membrane can generate steam with 1.22 kg m-2 h−1 under one sun illumination. Furthermore, under different illumination, the janus membrane still has a high conversion efficiency. The janus membrane also can produce fresh water from organic wastewater and heavy metal wastewater. It can be concluded that the janus membrane has a huge potential for practical application due to the simple preparation method, floatability, high photothermal conversion efficiency and excellent stability. The Density functional theory (DFT) calculation explained the mechanism of chitosan (CS) improving water transportation of MMT. [ABSTRACT FROM AUTHOR]

[Display omitted] • The montmorillonite nanosheets based composite hydrogels loaded with Fe(III) and La(III) were synthesized. • The addition of Fe(III) into the hydrogel can improve the As(V) adsorption capacity. • As(V) adsorbed on the hydrogel through electrostatic interaction and the formation of As-O-M complexes. Montmorillonite nanosheets composite hydrogel loaded with Fe(III) and La(III) (Fe-La-Mts-CS-PVA Gel) were synthesized for arsenic removal from water. The structure and As(V) adsorption performance of Fe-La-Mts-CS-PVA Gels were investigated, respectively. Structure characterization shows that Fe-La-Mts-CS-PVA Gel has porous structure with abundant large pores for easy diffusion of waster water. However, excessive Fe(III) leads to uniform distribution of iron in the hydrogel. Adsorption experiments show that the addition of Fe(III) can improve the adsorption capacity of As(V) to 69.64 mg g−1. But excess iron in the hydrogel cannot further increase the adsorption capacity. The adsorption mechanism of As(V) on Fe-La-Mts-CS-PVA Gel can be attributed to the electrostatic adsorption between Fe-La-Mts-CS-PVA Gel and As(V), and the formation of As-O-M complexes of As(V) with Fe(III) and La(III). [ABSTRACT FROM AUTHOR]

The swelling of Na- and Ca-montmorillonites (MMTs) has been studied through energy optimization and molecular dynamics simulations with the Universal Force Field (UFF) in this work. It was performed to reveal the interlayer spacing and water density in the interlayer as the function of water molecules increasing from 0 to 96, and the structural and diffusive properties of interlayer species when formed one-, two-, three-layer hydrates in interlayer. The results presented the swelling pattern of the MMTs, and the process of that water molecules formed layers in MMT interlayers. It has been found that Ca-MMT had a stronger hydration swelling than Na-MMT in the crystalline swelling regime, which might be due to that Ca 2+ had a larger hydrated radius than Na + . Water molecules in the interlayers of Na-MMT had a larger self-diffusion coefficient than those of Ca-MMT at the same water content. Moreover, Na + had a higher self-diffusion coefficient than Ca 2+ . It was demonstrated that the difference at the swelling of the two MMTs was attributed to that Ca 2+ had a stronger hydration than Na + in the MMT interlayers. [ABSTRACT FROM AUTHOR]

Solar steam generation is an environment-friendly, low-cost, efficient and sustainable approach to produce fresh water, which has been widely researched recently as a promising technology. However, practical application of solar steam generation is always restricted by the photothermal conversion efficiency and long-term stability. Herein, the self-assembly hierarchical binary gel (HBG) containing a MXene (Ti 3 C 2) gel as the upper structure and montmorillonite (MMT) gel as based materials was designed to achieve the efficient solar desalination toward water purification applications. The result indicated that Ti 3 C 2 gel exhibited high light absorption efficiency (over 94%) in a wide solar spectrum range, meanwhile, MMT gel showed remarkable thermal isolation with a low conductivity of 0.04366 (W/m·K) as well as quick water supply ability. In addition, the HBG achieved the evaporation rate of 1.37 kg m−2 h−1 with the high photothermal conversion efficiency of 93.7%. This hierarchical design also performed an excellent stability in cycle tests and salt-rejecting experiments as well as achieved remarkable water purification performance by rejecting organics and metal ions. In a word, the HBG is proved to be an efficient and advanced design with excellent stability for solar steam generation. • A novel hierarchical binary gel was designed for efficient solar desalination. • Porous MXene gel as upper structure with high light absorption efficiency. • MMT gel as based materials with low conductivity and quick water supply. • High photothermal conversion efficiency was achieved with 93.7%. [ABSTRACT FROM AUTHOR]

• 2D Mts can significantly increase the hydrophilicity of MoS 2 @ 2D Mts composites. • 2D Mts provide active sites to interact with polymers to form hydrogel for easy separation of MoS 2 from water. • MoS 2 @2D Mts-PVA composite hydrogel shows an enhanced Pb2+ removal performance. To improve the hydrophilicity and achieve easy separation of MoS 2 adsorbent fines from water, composite hydrogel of MoS 2 supported by two-dimensional montmorillonite nanosheets in poly vinyl alcohol (MoS 2 @2D Mts-PVA Gel) has been designed and synthesized. 2D Mts act as carriers to load MoS 2 and interact with polymers. The MoS 2 @2D Mts shows high hydrophilicity, and the MoS 2 @2D Mts-PVA Gel has porous three-dimensional structure for the adsorption and separation of metal ions in water. Therefore, 2D Mts are ideal carriers to load MoS 2 for well dispersion in water and interact with polymers. Adsorption tests demonstrate that the Pb2+ adsorption capacity of MoS 2 @2D Mts-PVA Gel increases significantly with the increase of MoS 2 @2D Mts content and solution pH, and a high Pb2+ adsorption capacity of 257 mg g−1 can be reached. The adsorption of Pb2+ onto MoS 2 can be attributed to the complexation of Pb2+ with S and O atoms on the surface, and electrostatic adsorption. [ABSTRACT FROM AUTHOR]

In this study, Chlorella sorokiniana FK, isolated from lead-zinc tailings, was employed for Pb(II) biomineralization with or without montmorillonite (MMT) addition in soil. Batch experiment results showed that montmorillonite facilitated Pb 3 (CO 3) 2 (OH) 2 formation on the surface of Chlorella -MMT composite, thus increasing algal cells' tolerance to Pb(II) poisoning. Surprisingly, Pb(II) adsorbed and biomineralized by Chlorella -MMT composite was 2.69 times and 3.76 times as much as that by Chlorella alone, respectively. The montmorillonite facilitated Chlorella- induced Pb biomineralization by promoting both photosynthesis and urea hydrolysis, mainly due to more hydroxyl functional groups generated during its binding with Chlorella and its high pH buffering capacity. Moreover, the SEM-EDS analysis indicated that the biomineral particles shifted from algal cell surface to montmorillonite surface in the composite during long-term Pb-detoxification. In-situ soil Pb(II) remediation experiments with Chlorella -MMT composites further showed that Pb was immobilized as carbonate form in the short term and as residue fraction in the long term. This study made the first attempt to explore the facilitating effects of montmorillonite on metal-carbonate precipitation mediated by microalgae and to develop a green, sustainable, and effective strategy for immobilization of heavy metal in soil by combining clay minerals and microalgae. [Display omitted] • Enhanced Pb(II) biomineralization by Chlorella -MMT composite was found. • MMT helped Chlorella Pb detoxification and solidification. • Both photosynthesis and urea hydrolysis pathways were involved and promoted by MMT. • Pb biomineral particles shifted from the surface of Chlorella to montmorillonite. • Pb in real soil was immobilized as residue fractions. [ABSTRACT FROM AUTHOR]

The shortage of fresh water is becoming a great challenge all over the world, solar desalination is an emerging green and sustainable strategy to produce clean water from seawater or waste water by utilization of renewable solar energy. However, the accumulation of salt will depress the long-term sustainable use of solar evaporators. In this work, a hydrogel evaporator with montmorillonite (Mt) and MoS 2 integrated layered structure has been fabricated for stable and efficient solar steam generation. The perfect hydrophilicity of Mt. can facilitate water transmission and salt redissolution speed. The vertical radial porous structure and low thermal conductivity of Mt. hydrogel ensures the shortest water transport path and superior heat localization performance. The upper MoS 2 layer has a light absorption rate of up to 92% in the entire solar spectrum (200–2500 nm), which enables an excellent solar to thermal conversion efficiency. Under a low solar irradiation intensity of only 1 kW·m−2, the Mt./MoS 2 double-layer aerogel can achieve a high evaporation rate of 1.31 kg·m−2·h−1. More importantly, the Mt./MoS 2 double-layer aerogel can produce freshwater with salt ions (Na+, K+, Mg2+, Ca2+) rejection rate over than 99.9%. The as-prepared solar evaporator aerogel is turned out to show good mechanical strength, superior water supply, excellent durability and outstanding desalination performances. As a result, the developed Mt./MoS 2 double-layer aerogel with low cost and high-quality of condensed water may provide a good prospect in solar desalination application and wastewater treatment. [Display omitted] • Mt. aerogels showed excellent water transmission and thermal insulation properties. • MoS 2 aerogels has good light absorption and solar-thermal conversion efficiency. • Mt./MoS 2 aerogels can achieve high evaporation rate under irradiation of 1 kW·m−2. • Mt./MoS 2 aerogels can produce freshwater with 99.9% salt ions rejections. [ABSTRACT FROM AUTHOR]

The exfoliation of montmorillonite (Mt) into nanosheets with mono or few-layer is significant for controllable preparation of Mt. functional nanocomposites, whereas Mt. nanosheets (MtNS) prepared in aqueous solutions usually encountered restack problems suffering from dehydration. In this work, anhydrous MtNS with few layers were successfully prepared through a novel gasification exfoliation method. The quality of morphology, structural and stability characteristics of MtNS were investigated by an atomic force microscope, scanning electron microscope, BET and turbidity. The anhydrous MtNS with a thickness of 0–5 nm were prepared by the liquid nitrogen (LN 2) gasification exfoliation. In addition, MtNS prepared through gasification exfoliation presented a looser interlayer structure, higher BET specific surface area and better dispersion stability than those prepared by ultrasonic exfoliation and freeze drying. Thus, the gasification exfoliation perfectly addressed the obstacle of nanosheet restacking. Moreover, molecular dynamics simulation found the LN 2 could enter the interlayer domain of Mt. When heating under 70 °C, the drastic gasification of LN 2 destroyed the weak interlayer binding force of Mt., leading to the successful preparation of anhydrous few-layered MtNS. These findings are expected to provide theoretical guidance for the scalable application of MtNS as functional materials. [Display omitted] • A novel gasification exfoliation method proposed to avoid restack of Mt nanosheets. • The prepared MtNS through gasification has similar thickness to that by sonication. • The G-MtNS possesses higher BET specific surface area than MtNS-FD. • The G-MtNS suspensions shows better stability than MtNS-FD suspensions. [ABSTRACT FROM AUTHOR]

Two-dimensional montmorillonite nanosheets (2DMMT), acrylic acid and acrylamide were used as raw materials to synthesize the three-dimensional reticular-structured hydrogel via hydrogen-bond, polymerization, amidation and electrostatic interactions. Morphology characteristics shown the porous structure of montmorillonite hydrogel, offering an open-access for Pb(II) to react with internal adsorption sites. Adsorption tests indicated that 2DMMT hydrogel could achieve the effective removal (99%) for high concentrated Pb(II) solution (125 mg/L) via small hydrogel dosage (1 g/L) within short contact time (60 min). High removal of Pb(II) (70%, adsorption capacity: 90 mg/g) could be still achieved even after five adsorption-regeneration cycles, achieving the long-term servicing for wastewater treatment with cost-optimal operation. Adsorption kinetics and isotherm tests indicating the homogeneous monolayer physical and chemical adsorption between Pb(II) and hydrogel, and the adsorption capacity of Pb(II) was controlled by the amount of adsorption sites on hydrogel. Characteristics of XPS and EDS revealed the adsorption mechanism of ion exchange, chelation reaction and chemical precipitation. Two-dimension montmorillonite with high surface area and fully-exposed active sites formed the reticular-structured hydrogel, showing high removal ability for Pb(II). [Display omitted] • Hydrogen-bond, polymerization, amidation and electrostatic interaction generated the 3D reticular-structured hydrogel. • 3D reticular structure offered an open-access for Pb(II) to react with internal adsorption sites in hydrogel. • Efficient removal for Pb(II) at high concentration is achieved via small dose of hydrogel within a short time. [ABSTRACT FROM AUTHOR]

Three-dimensional reduced graphene oxide/montmorillonite nanosheet aerogels (RGMTAs) have been successfully fabricated through hydrothermal method. X-ray diffraction and field-emission scanning electron microscope were used to characterize the structures of RGMTAs, and the electrochemical performance was investigated by electrochemical measurements. The restacking of reduced graphene oxide aerogel can be effectively inhibited without obvious structure change by using a small amount of montmorillonite nanosheets (Mts). The reduced graphene oxide/Mts aerogel shows enhanced electrochemical performance with a high specific capacitance of 275 F g−1 at a current density of 1 A g−1, and excellent rate capability. Moreover, though it is not conductive, excessive Mts only slightly increase the equivalent series resistance and charge transfer resistance. This work demonstrates that 2D Mts can reduce the restacking degree of graphene sheets, and the 3D reduced graphene oxide/Mt. nanosheet aerogel is a potential electrode material for supercapacitor applications. • 2D montmorillonite nanosheets can inhibit the restacking of reduced graphene oxide sheets. • Excessive montmorillonite nanosheets only slightly increase the equivalent series resistance and charge transfer resistance. • The reduced graphene oxide/montmorillonite nanosheet aerogel shows enhanced electrochemical performance. [ABSTRACT FROM AUTHOR]

[Display omitted] Montmorillonite (MMT), having special property of hydration expansion, can be easily exfoliated into two-dimensional (2D) nanosheets, which are the promising blocks for making multifunctional nanocomposites. In this work, the exfoliation performances of MMTs from different region including Inner Mongolia (IM), Zhejiang (ZJ) and Liaoning (LN) were investigated from the perspective of layer charge density. All the MMTs were prepared as Na-MMTs first to avoid the effect of the interlaminar ion. Atomic force microscope (AFM) measurements indicated that the exfoliation performance increased as: IM-MMT < ZJ-MMT < LN-MMT. Alkyl ammonium ion exchanged method was applied to study the layer charge density of the MMTs. It was found that the exfoliation performance decreased with the layer charge density of MMT increased. The characterizations of zeta potential, swelling index and BET specific surface area were used to reveal the effects of layer charge density on the exfoliation performance of MMT. The results showed that with increasing the layer charge density, MMT was with more negative zeta potential, thus leading to the stronger binding forces between the layers. The swelling index of LN-MMT was the highest who had the lowest layer charge density, demonstrated by the largest specific surface area and pore diameter after hydration swelling, which explained the best exfoliation behavior of LN-MMT. This study correlates the exfoliation performances with the layer charge density of MMT, and it will provide a guidance to prepare much thinner and larger MMT nanosheets. [ABSTRACT FROM AUTHOR]

• Various clays cause different behaviors of coal flotation by cationic regulation. • Montmorillonite aggregation formed and flotation enhanced by cationic regulation. • Kaolinite coating on coal and deteriorating flotation when cationic regulation. • Select suitable regulating method according to co-existing clay species. The effects of different clay minerals on coal flotation under cationic regulation were systematically investigated. Batch flotation experiments indicated that the cationic regulating effects successfully embodied in presence of montmorillonite (MMT), while deteriorated with kaolinite. SEM-EDS measurements demonstrated that MMT initially coating on coal came off due to the formation of aggregates after adding cations, while kaolinite was more dispersed just as the higher turbidity thereby easily adhering to coal. It was due to the surface charging situations and specific Al-OH distributions of MMT and kaolinite that led to various interacting relationship with coal and affected the cationic regulation effects. [ABSTRACT FROM AUTHOR]