D001 Values Research Articles

Spherical silica particles coated with lamellar nanocomposites based on a hydrophobic functionalized phyllosilicate

The surface of spherical silica particles (monodisperse, 2.6 µm) was modified with inorganic–organic lamellar ordered hybrids for applications as hydrophobic dye supports in cosmetics. The inorganic–organic multilayers comprised a 2:1 phyllosilicate (two sheets of linked SiO4 tetrahedra with one sheet of M2–3(OH)6 octahedra, where M is either magnesium or aluminum), consisting of octyl chains directly bonded to the inorganic sheets via Si–C covalent bonds. Octyltriethoxysilane was allowed to react at room temperature with spherical silica and aluminum acetylacetonate in a mixed aqueous solution of NaOH and NaCl at pH 10. The formation of a 2:1 phyllosilicate grafted with an octyl chain was confirmed by X-Ray powder diffraction, where a lamellar structure with the d001 value of 2.4 nm was displayed. The lamellar structure included the isomorphic substitution of Si by Al and the formation of C–Si–O–Aloct bonds, as shown in 29Si–and 27Al–magic angle spinning (MAS)–nuclear magnetic resonance (NMR) spectra. Further, the 23Na–MAS NMR spectrum indicated the incorporation of Na aquo complex cations into the organophyllosilicate. The hydrated Na ions were exchanged with a cationic dye (methylene blue) to be adsorbed. An anionic dye (Phloxine B), which has frequently been used as cosmetic pigments, was adsorbed onto the resulting hybrid particles when Al3+ was present in the dye solution. The hydrophobic dye supports can be used instead of plastic beads to reduce marine pollution.

A mechanistic insight into the shrinkage and swelling of Ca-montmorillonite upon adsorption of chain-like ranitidine in an aqueous system

Adsorption behavior of ranitidine hydrochloride (RT) on a Ca-montmorillonite (SAz-1) was studied in aqueous system through batch experiments. The adsorption kinetics revealed that the equilibrium reached within 0.25 h and the data fitted well to the pseudo-second order kinetic equation (R2 = 0.98). The maximum RT adsorption capacity of SAz-1 was 369.2 mg/g and the adsorption isotherm data followed the Langmuir model (R2 = 0.99). The adsorption of RT and desorption of exchangeable cations from the clay mineral were linearly correlated, suggesting that cation exchange was the dominant mechanism of RT adsorption. The XRD examination of RT-adsorbed SAz-1 samples (unsaturated/saturated) after heating enabled the calculation of RT occupied area in the interlayer of the clay mineral. The results suggested that adsorbed-RT at low loading rate could lay on the internal surfaces in a free style to reduce the basal spacing (d001 value) of SAz-1. When the RT loading rate was increased, a limited surface space enforced more RT molecules to lay in a tilted style and caused interlayer swelling of SAz-1 increasing the d001 value. The trend of rising decomposition temperature of RT with increasing RT loading rates confirmed intercalation of RT molecules in SAz-1. Infrared spectral analysis revealed the participation of amide and furan groups of RT in binding between RT and SAz-1. Thus, this study indicated that SAz-1 is an efficient adsorbent to remove RT from contaminated water, and the chain-like molecular structure of RT could cause an irregular change in the basal spacing of swelling type clay minerals.

Intercalation of [Ni(bpy)3]2+ complex cation into synthetic saponite: Preparation, characterization and magnetic properties

The magnetic properties of the hybrid materials formed by coordination compounds and clay minerals represent one of the main challenges in material science. The investigation of the intercalation of tris(2,2′-bipyridine)nickel(II) cations [Ni(bpy)3]2+ present in the solution with chloride anions into synthetic saponite (Sap) was carried out by direct exchange of the sodium ions by nickel(II) complex. The final intercalated [Ni(bpy)3]2+ saponite complex was characterized by powder X-ray diffraction (XRD), infrared (IR) spectroscopy, carbon and thermal analysis, and for the first time also by magnetic measurements. The carbon analysis proved a full replacement of Na+ with [Ni(bpy)3]2+ cations. Furthermore, significant increase of the d001 value of the intercalated saponite confirmed the presence of the [Ni(bpy)3]2+ in Sap interlayers. Only limited effect of the saponite layers on the ring C-H or skeletal vibrations of the [Ni(bpy)3]2+ complex was observed. The thermal stability of the [Ni(bpy)3]2+ increased after its intercalation into saponite. The magnetic properties of the [Ni(bpy)3]2+ saponite complex revealed similar magnetic response as the starting compound [Ni(bpy)3]Cl2·nH2O suggesting that the local surroundings of the Ni(II) atoms in [Ni(bpy)3]2+ intercalated into saponite remained unchanged.

Local structure determination of Zn-smectite

Abstract An aluminum-free zinc-bearing smectite (Zn-smectite) was synthesized under hydrothermal conditions, together with its magnesium substituted products. Its layer charge calculated by cation exchange capacity (CEC) is 117.4 mmol/100 g. Powder X-ray diffraction (XRD) revealed turbostratic stacking and showed that the d06l value of the Zn-smectite was >1.525 Å, indicating that it is trioctahedral. Its d001 value increased from ca.12.8 Å to ca. 16.0 Å after ethylene glycol (EG) saturation. The Zn-smectite did not irreversibly collapse after heating the Li+-saturated sample to 300 °C, suggesting that its layer charge was generated from octahedral-site vacancies (defects). The Zn-smectite resembles zincsilite-like minerals with interlayer Na+ and Zn2+. The intralayer structure of zincsilite was confirmed by pair distribution function (PDF) analysis, and the whole crystal structure was built and optimized by DFT calculation in the CASTEP module of the Materials Studio software. Synthetic zincsilite is triclinic, space group P1, and its optimized unit-cell parameters are: a = 5.294 Å, b = 9.162 Å, c = 12.800 Å, α = 90.788°, β = 98.345°, and γ = 90.399°.

Tunable polycationic organohalloysite electrocatalyst: Synthesis and characterisation

Methylamine and 1,4-butanediol diglycidyl ether were used as monomers, in a sequential manner, to build from the surface of an aminosilane-grafted halloysite a quaternary ammonium polyelectrocatalyst. The as obtained material was characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms (BET method), elemental analysis (EA), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). XRD analysis showed that the pristine halloysite was in a partial dehydrated state with a d001 value of 0.74 nm. Not only was the success of the grafting process ascertained but also the tubular nature of the used halloysite sample as seen on the SEM micrographs. The significant increase in the d value of the modified clay (H-polyQ22) suggested interlayer grafting. FTIR results showed that grafting was through OH groups, certainly interlayer, lumen and edge aluminol groups as well as defect site silanol groups. The electron transfer enhancing properties of the prepared polyelectrolyte were investigated by electrochemical impedance spectroscopy (EIS). The charge transfer resistance dropped significantly when H-polyQ22 was used as electrode modifier. The electrocatalytic behaviour of the H-polyQ22 modified electrode was further investigated using [Fe (CN)6]3− as anionic target. The halloysite polymer nanocomposite proved to be a good candidate for electrocatalysis.

Modifying a Smectite using Organic Nutrients to Enhance its Efficacy at Removing Aflatoxin B1 from Corn Fermentation Solution

AbstractAflatoxins in contaminated corn do not degrade in corn fermentation solution (CFS) during biofuel production; rather, they are enriched in the co-product, dried distillers grain. Aflatoxin B1 (AfB1) is the most toxic form of all aflatoxins. Removing AfB1 from CFS is desirable to minimize its toxicity to animals. Smectites can adsorb AfB1 from aqueous solutions and, therefore, inactivate the toxin, but proteins in CFS inhibit the adsorption of AfB1 by smectites. The current study aimed to minimize the interference by CFS in adsorption of AfB1 on smectite by modifying a calcium-smectite (Ca-3MS) with a small nutritive organic compound, e.g. carnitine, choline, arginine, histidine, or tryptophan. The organo-smectites were characterized by X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy, and adsorption of AfB1 in CFS by these composites was examined. Various degrees of intercalation of the organic nutrients into the smectites were observed with XRD and FTIR. After immersing the smectite and organo-smectites in the CFS, the d001 values of Ca-3MS expanded to ~1.82 nm due to protein interaction, but the organo-smectites were confined to ~1.39 nm, which indicated that the protein had limited access to the organo-smectite interlayers. The IR bands at ~1652, 1544, 1538, and 1454 cm–1 from the organo-smectites revealed, however, that complete protein inhibition was not achieved. The organo-smectites were capable of adsorbing AfB1 in simple aqueous solution with maximal adsorption capacity up to 0.55 mol kg–1. Significantly greater (p ≤ 0.05) AfB1 adsorption was achieved by choline- and carnitine-modified smectites compared with the original Ca-3MS in the presence of competing protein (pepsin) in simple aqueous solution. In real CFS, both AfB1 adsorption capacities (Qmax) and affinities (K) by all organo-smectites were greater (Qmax = up to 0.45 mol kg–1 and K = up to 0.165 μM–1) than those by Ca-3MS (Qmax = 0.22 mol kg–1 and K = 0.031 μM–1). The study suggested that using smectites modified with an organic nutritive compound could be an effective, economical, and safe strategy for removing mycotoxins, including aflatoxins, during biofuel production.

Adsorption of amino acids by montmorillonite and gibbsite: Adsorption isotherms and spectroscopic analysis

The adsorption of glycine, cysteine and glutamic acid by gibbsite and montmorillonite was studied as a function of amino acid concentration and solution pH. Zeta potential measurements, X-ray diffraction (XRD), and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopic analysis were performed to deduce the mechanism(s) of adsorption and to observe changes in the basic structure of the minerals after interaction with amino acids. The ATR-FTIR analysis revealed that both NH3+ and COO− groups of amino acids were very vital for interactions with the surface of gibbsite and montmorillonite. XRD analysis revealed that the formation of mineral-amino acid composites decreased the d001 value of montmorillonite from 17.95 to 14.2 (glycine), 15.49 (cysteine), and 15.22 Å (glutamic acid). This observation suggests that amino acid adsorption induced structural stress on montmorillonite and expanded its interlayer space. Also, the adsorption of glycine and cysteine to gibbsite and montmorillonite increased their zeta potentials at pH 5.0 while glutamic acid decreased the zeta potentials. Thus, amino acid-induced increase/decrease in the surface positive/negative charge of the minerals indicates that chemical bonds were formed between glycine, cysteine, glutamic acid and the minerals. The findings of this study can serve as a reference for studies related to understanding the bonding interactions and distribution of different amino acids in soils.

Dispersion and Swellability of Ternary Surfactant Co-Modified Montmorillonites

AbstractOrgano-montmorillonite (OMnt) has wide applications in paints, clay-polymer nanocomposites, biomaterials, etc. In most cases, the dispersibility and swellability of OMnt dictate the performance of OMnt in the target products. Previous studies have revealed that the properties can be improved when multiple organic species are co-introduced into the interlayer space of montmorillonite (Mnt). In the present study, single surfactant erucylamide (EA), dual-surfactants cetyltrimethyl ammonium bromide (CTAB) and octadecyltrimethyl ammonium chloride (OTAC), and ternary-surfactants EA, CTAB, and OTAC were co-introduced into Mnt by solution intercalation. The resulting OMnts were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry-differential thermogravimetry (TG-DTG), water contact-angle tests, scanning electronic microscopy (SEM), laser particle-size analysis, and swelling indices. Mnt co-modified by ternary CTAB, OTAC, and EA led to a large d001 value (4.20 nm), surface hydrophobicity with a contact angle of 95.6°, swellability (50 mL/g) with small average particle sizes (2.1−2.8 μm) in xylene, and >99% of the OMnt particles were kept as <5 μm in deionized water. The formation of EA-modified-Mnt was proposed according to hydrophobic affinity, hydrogen bonding, and van der Waals forces. The nanoplatelets of the CTA+, OTA+, and EA co-modified OMnts in xylene were assembled into a house-of-cards structure by face-to-edge and edge-to-edge associations. The electrostatic attractions, electrostatic and steric repulsions, and hydrophobic interactions were responsible for the good dispersibility of OMnt in xylene. The ternary surfactant co-modified OMnt with high dispersion and swellability will make OMnt better suited for real-world applications.

Ion-Exchange Modeling of Divalent Cation Adsorption on SWy-3 Montmorillonite

AbstractIon-exchange modeling is used widely to describe and predict ion-adsorption data on clay minerals. Although the model parameters are usually optimized by curve fitting experimental data, this approach does not confirm the identity of the adsorption sites. The purpose of the present study was to extend to divalent cations a previous study on the retention of monovalent cations on Na-saturated montmorillonite (NaMnt) which optimized some of the model parameters using density functional theory (DFT) simulations. The adsorption strength of divalent cations increased in the order Mg2+ < Cd2+ < Ca2+ < Sr2+ < Ba2+. After adding adsorption of metal hydroxide species (MOH+), the three-site ion-exchange model was able to describe adsorption data over a wide pH range (pH 1–10) on NaMnt. X-ray diffraction (XRD) analyses were conducted to investigate the interlayer dimension of clay samples under various conditions. The cation retention strengths of divalent cations did not correlate with interlayer dimensions. The XRD analyses of the Mnt showed a d001 value of 19.6 Å when saturated with alkaline earth cations, 22.1 Å with Cd2+, 15.6 Å with Na+, and 15.2 Å with H+. In the case of Na+, the 15.6 Å peak decreased gradually and disappeared, and new peaks at 22.1 and 19.6 Å appeared when the percentages of Mg2+ and Ba2+ adsorbed increased on NaMnt. The peak shifted from 22.1 to 20.3 and 19.6 Å when the pH increased for all cations except Cd2+, which stayed constant at 22.1 Å. The coexistence of multiple d001 peaks in the XRD patterns suggested that the interlayer cations were segregated, and that the interlayer ion–ion interactions among different types of ions were minimized.

Synthesis of C21H38ClN Assisted Si Pillared Clays and the Effects of CeO2 Addition on Its Supported Palladium Catalyst for Benzene Oxidation

Mesoporous silica-pillared clays (SPC) were prepared with C21H38ClN cationic surfactant as template and supported PdOx catalysts were prepared by impregnation method. The influence of addition of CeO2 on benzene combustion was evaluated. The samples were characterized by N2 adsorption–desorption, XRD, XPS, HRTEM and TPSR. Compared with the raw montmorillonite, the d001 value of SPC increased from 0.96 to 3.45 nm. Furthermore, the surface area was increased from 30 to 835 m2/g and the pore volume was increased from 0.11 to 1.30 cm3/g, respectively. The addition of CeO2 increased oxygen vacancies and improved the dispersion of PdOx on SPC, and the optimal addition of CeO2 was 10%. Therefore, of all the catalysts, 0.3%Pd/10%Ce/SPC could completely oxidize benzene at 280 °C, showing the highest catalytic activity. This catalyst showed high activity for benzene oxidation in wet conditions with or without Cl− displaying good durability, which should be related to the presence of Ce3+ on the surface of catalyst after reaction. The excellent pore structure of SPC, improved dispersion of PdOx and high concentration of Ce3+ on the catalyst surface were the key factors for the high catalytic activity of 0.3%Pd/10%Ce/SPC. Mesoporous silica-pillared clays (SPC) were synthesized and SPC supported CeO2 and PdO catalysts were prepared by impregnation method. The 0.3% Pd/10% Ce/SPC catalyst displayed the highest activity for benzene combustion.

Comparative study of alkylammonium- and alkylphosphonium-based analogues of organo-montmorillonites

The organo-montmorillonites are highly attractive materials because of their wide application potential. In this work the basic structural, vibrational and thermal characteristics of the samples from two series of structurally analogous alkylammonium- and alkylphosphonium-montmorillonites are reported for the first time. The first series consisted of the organo-montmorillonites prepared from commercially available tetramethyl-(Me4-N/P), tetrabutyl-(Bu4-N/P) and tetraoctyl-(Oc4-N/P) analogues, while the second series was prepared from tributylalkyl cations with the fourth chain of the increasing length (Bu3-N/P-CX, X = 4, 8, 12, 16). The XRD analysis revealed that for both series, when comparing the equivalent pairs of the surfactants, slightly higher expansion of the interlayer space was observed for phosphonium-based than for ammonium-based montmorillonites. Difference in the d001 values was in accordance with a higher covalent radius of P than N. The impact of the different central atom (N/P) of the cation head-group was also studied by IR spectroscopy in the middle and near region. As a result of differences in the charge density of the nitrogen and phosphorus cationic centers the positions of the C-H bands (stretching and overtones) of phosphonium-Mt were shifted to lower wavenumbers compared to their ammonium counterparts. The effect of the central atom of the head-group was significant for smaller cations, but gradually decreased with increasing size of the ammonium and phosphonium surfactant. DTG profiles showed a significant step above 200°C attributed to the release of the organic phase. The temperature of maximal decomposition rate was higher for phosphonium cations compared to ammonium analogues. The mass profiles and temperature-dependent IR spectra showed the evolution of CO2 and H2O species as the main products. In addition, the C-H stretching and bending bands of the unspecified organic phase were detected in the spectra.

Butylamine-resadiye bentonite composite characterization

The acid activation process increased the specific surface area of raw Resadiye bentonite (33.5 m2/g) by ∼ 4-fold whereas the interaction with n-butylamine caused a surface area reduction of acid-activated bentonite by 40% along with the broadening of the Si-O stretching peak at 1041 cm−1 and the decrease of the d001 value from 14.5 to 13.5 Å. The thermal analysis data confirmed the stability of the mesoporous n-butylamine/acid-activated bentonite composite up to 499 °C which was followed by the cleavage of the interlayer n-butylamine species between 500 and 700 °C.

Ion-Exchange Modeling of Monovalent Alkali Cation Adsorption on Montmorillonite

AbstractIon-exchange modeling is one of the most widely used methods to predict ion adsorption data on clay minerals. The model parameters (e.g. number of adsorption sites and the cation adsorption capacity of each site) are optimized normally by curve fitting experimental data, which does not definitively identify the local environment of the adsorption sites. A new approach for constructing an ion-exchange model was pursued, whereby some of the parameters needed were obtained independently, resulting in fewer parameters being based on data-curve fitting. Specifically, a reversed modeling approach was taken in which the number of types of sites used by the model was based on a previous first-principles Density Functional Theory study, and the relative distribution of these sites was based on the clay’s chemical composition. To simplify the ion-exchange reactions involved, montmorillonite was Na-saturated to produce a well-controlled Na-montmorillonite (NaMnt) adsorbent. Ion adsorption data on NaMnt were collected from batch experiments over a wide range of pH, Cs+ concentrations, and in the presence of coexisting cations. Ion-exchange models were developed and optimized to predict these cation adsorption data on NaMnt. The maximum amount of adsorption of monovalent cations on NaMnt was obtained from the plateau of the adsorption envelope data at high pH. The remaining equilibrium constants (pK) were optimized by curve fitting the edges of the adsorption envelope data. The resultant three-site ion-exchange model was able to predict the retention of Li+, Na+, K+, and Cs+ very well as a function of pH. The model was then tested on adsorption envelopes of various combinations of these cations, and on Cs+ adsorption isotherms at three different pH values. The pK values were constant for all assays. The interlayer spacing of NaMnt was also analyzed to investigate its relation with cation adsorption strength. An X-ray diffraction study of the samples showed that the measured d001 values for these cations were consistent with their adsorption pK values. The Cs+ cation showed a strong ability to collapse the interlayer region of montmorillonite. In the presence of multiple competing cations, the broadening and presence of multiple d001 XRD peaks suggested that the cations in the interlayers may be segregated.

Investigation on the inhibition mechanism of alkyl diammonium as montmorillonite swelling inhibitor: Experimental and molecular dynamics simulations

Effective inhibition of mud shale hydration and swelling is the major challenge for water-based drilling fluids (WBDFs). In this paper, a series of novel low molecular weight alkyl diammoniums with different alkyl chain lengths was synthesized and evaluated as montmorillonite swelling inhibitor. The inhibition behavior of alkyl diammonium was studied by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), cation exchange capacity (CEC), and molecular dynamics simulation. The XRD results illustrated that the inhibitors (Gs-9, Gs-10, Gs-11, Gs-12, Gs-13 and Gs-14) rapidly lowered the basal spacing (d001 value) of hydrated sodium montmorillonite (Na-Mt) from 1.92 nm to 1.41 nm, which indicates that a flat monolayer of inhibitors was inserted into the interlamination of Na-Mt. The XPS and CEC results showed that the alkyl diammonium displaced exchangeable cations in the interlamination of Na-Mt. The SEM results showed that the alkyl diammonium effectively improved the surface structure and curled edges of hydrated Na-Mt. The simulated results showed that the quaternary ammonium functional groups were fixed firmly on the six- oxygen rings of Na-Mt. The adsorption energy of alkyl diammonium increased with the increase in alkyl chain length. Therefore, alkyl diammonium with long alkyl chain can decrease the amount of inhibitor adsorbed on Na-Mt, thus reducing the dosage of inhibitor used in the WBDFs. This is conducive to reducing drilling costs. Therefore, this research on the inhibition behavior of alkyl diammonium with different hydrophobic chain lengths has important reference value for the development of WBDFs and suitable inhibitors for them.

Preparation and application of CPC/Keggin-Al30 modified montmorillonite composite for Cr (VI) removal

To enhance the adsorption performance of natural calcium-based montmorillonite (Ca-MMT), the polymeric hydroxyaluminum cation - Keggin-Al30 ([Al30O8(OH)56(H2O)24]18+) and cetylpyridinium chloride (CPC) were used to modify Ca-MMT for preparation of CPC-Al30 pillared montmorillonite composite (CPC-Al30PMT). The CPC-Al30PMT was characterized via analysis of its chemical and physical structure, morphology, surface properties, and zeta potential. The results showed that the Al30 polymer cation and CPC successfully intercalated into the interlayer of Ca-MMT, which increased the d001 value from 1.47 nm to 1.93 nm, and increased the pore volume correspondingly. The zeta potential was reversed from negative to positive after modification, presenting a possibility to adsorb anionic contaminants from water. The investigation of hexavalent chromium (Cr (VI)) adsorption on CPC-Al30PMT showed that the removal of Cr (VI) was positively correlated with the dosage of adsorbent, and negatively correlated with the initial concentration of Cr (VI), the ionic strength and the initial pH of the solution. CPC-Al30PMT showed good Cr (VI) removal performance, with the maximum adsorption (qe) of 42.44 mg/g. The adsorption process conformed to Freundlich model and pseudo-second-order kinetic model. Thermodynamics studies showed that adsorption was a spontaneous exothermic process. Electrostatic interaction, ion exchange and reduction were the main mechanisms of the removal.

Preparation of two-dimensional nano montmorillonite/stearic acid energy storage composites with excellent stability and heat storage property

Phase change energy storage materials have the ability to store thermal energy during the phase change process, and release the stored energy when desired. As a result, this technology has been extensively studied due to its potential in improving energy utilization and alleviating the problem of energy shortage. In this paper, two-dimensional montmorillonite nanosheets (2DMts) were prepared by ultrasonic method. With 2DMts as the host and energy storage molecule stearic acid (SA) as the guest, a phase change energy storage composite material (2DMt/SA) was prepared using a self-assembly approach. The d001 value of the 2DMt/SA composite was 4.08 nm, indicating that the layer of Mt. was completely peeled off. Additionally, the 2DMt/SA composite had a high latent heat storage capacity (192.4 J/g), which was nearly identical to that of SA samples. Compared with SA, the thermal stability of 2DMt/SA was significantly improved. After 50 cycles of heating and cooling, only 0.557% of the latent heat was lost. There was no liquid leakage indicating that the composite had an excellent structure stability. In addition, after nano silicon carbide (SiC) was added to the 2DMt/SA system, the thermal conductivity of the system increased by 113.7%. This self-assembly method solved the problem of liquid leakage and poor thermal stability in phase change materials. As a result, the 2DMt/SA composite can be applied to road asphalt materials for surface protection applications.

Chromium (VI) removal from water using cetylpyridinium chloride (CPC)-modified montmorillonite

Montmorillonite (Mt) has been used widely for metal removal from water and wastewater due to its various advantages including low cost, large surface area, high structure stability, and high ion exchange capacity. However, the removal of anionic hexavalent chromium (Cr) using Mt is inhibited by the negative charges on the adsorbent. To enhance Cr (VI) adsorption on Mt, a cationic surfactant – cetylpyridinium chloride (CPC) – was utilized to modify the interlayer surface of Mt. Fourier-transform infrared spectroscopy and X-ray diffraction were performed to characterize the CPC modified Mt (CPC-Mt) and the structure change of Mt. Studies have shown that CPC intercalated into Mt interlayers via electrostatic interaction between Mt and CPC, as well as the hydrophobic interaction among CPC molecules. After modification, the CPC-Mt showed a positive zeta potential at pH 2–11; while the specific surface area decreased, CPC effectively increased the interlayer distance of Ca-Mt, with a maximum d001 value of 4.37 nm, and provided more exchange sites for Cr (VI) adsorption. Cr (VI) was efficiently removed using CPC-Mt at low pH values, but the removal was influenced adversely by the increase of pH and ionic strength. The adsorption process was described by a Langmuir isotherm model with the constant of 0.342 L/mg and the maximum adsorption capacity of 43.84 mg/g at 298 K, and by a pseudo-second order kinetic model with a kinetic coefficient of 6.62 g/(mg·min). The adsorption mechanism analysis has shown that electrostatic attraction is the main mechanism for Cr (VI) removal; at the same time, the reduction of Cr (VI) to Cr (III) by Fe (II) in Mt cannot be neglected at low pH values, which increased Cr removal and was confirmed by the X-ray photoelectron spectroscopic analysis.

Structure changes of nanocrystalline mackinawite under hydrothermal conditions

We investigated the structure changes and phase transformation from nanocrystalline mackinawite to pyrite using hydrothermal experiments, synchrotron X–ray diffraction (XRD) technique, atomic Pair Distribution Function (PDF) method, Extended X–ray Absorption Fine Structure (EXAFS) analysis, and transmission electron microscopic (TEM) observation. The first hydrothermal ageing experiment was performed by heating the nanocrystalline mackinawite at 120 °C for 12 h. The nanocrystalline mackinawite remained essentially unchanged for 12 h. The d001 and FWHM values of XRD peaks decreased for the first 2 h and subsequently maintained almost constant. There was no linear relationship between lattice parameters and hydrothermal heating time. The crystallite size quickly increased by the heating of 2 h, leading to the increase of crystallinity and appearance of the medium–range order in the nanocrystalline mackinawite. The nanocrystalline mackinawite preferentially grew in the horizontal direction along the sheet structure. The Fe atoms were distributed in the tetrahedral sites with a site occupancy of approximately 80%. The pre–edge peak energy of Fe K–edge suggested that about 10% Fe3+ was included in the nanocrystalline mackinawite to compensate the charge deficiency of Fe2+. The second hydrothermal ageing experiment was performed by heating the nanocrystalline mackinawite at 120 °C under the presence of elemental sulfur for 24 h. The nanocrystalline mackinawite persisted up to 8 h of heating time. Thereafter, pyrite and greigite instead of the nanocrystalline mackinawite appeared. Finally pyrite became dominant. The d001 and lattice parameters of nanocrystalline mackinawite varied significantly compared with those heated under the absence of elemental sulfur. The pre–edge peak energy indicated that the Fe2+ was oxidized to Fe3+ by elemental sulfur acting as the oxidant during the phase transformation from nanocrystalline mackinawite to greigite. In the phase transformation to pyrite, on the other hand, the Fe3+ was reduced to Fe2+ by sulfur in mackinawite and greigite acting as the reductant. The EXAFS analysis revealed that the second peak from the Fe–Fe interaction appeared at the heating time of 2 h, implying the formation of sheet structure consisting of edge–sharing FeS4 tetrahedra. Intensity of the second shell peak from the Fe–Fe interaction reduced after the heating time of 8 h. Instead, new peaks corresponding to the Fe–S and Fe–Fe interaction appeared after the heating time of 12 h. This result was strongly associated with formation of the disulfide bonds (S–S bonds) in pyrite. Consequently, the elemental sulfur can be recognized as one of the most important factors to promote the phase transformation from mackinawite to pyrite in the reducing lake and marine sediments.

FeAl12-polyoxocations intercalated nano-bentonite fabrication in concentrated suspension using one-step ultrasonic-microwave irradiation for arsenic removal from alkaline wastewater

Arsenic in alkaline wastewater often takes place from gold mining process and creates a major problem to ecosystems and human health. In alkaline condition for arsenic removal, the application of adsorbent with a high positive surface charge is necessary. The current study is focused on the synthesis and characterization of an eco-friendly FeAl12-polyoxocations intercalated nano-bentonite with a high positive surface charge for As(V) removal. Therefore, this pillared nano-bentonite was synthesized in different concentrations of clay suspension through a novel combination of the ultrasonic and microwave devices in one-step with decreasing water and time consumption. The characterization results showed that the incorporation of Al3+ and Fe3+ in pillared nano-bentonites increased the pH of zero point charge (pHZPC), d001 value, specific surface area, and micropore volume for arsenic removal. Various conditions such as the effect of coexisting anions and cations, arsenic concentration, adsorbent dosage, and contact time were investigated in the adsorption experiments. FeAl12-pillared samples represented the maximum adsorption capacity of 121.3 mg L−1 to remove 10–500 mg L−1 of As(V). The adsorbability of products was also evaluated by using the two, three, and four parameters adsorption isotherms. The presence of a heterogeneous surface with more active sites under endothermic reaction played an important role for immobilization of As(V) with ligand exchange reaction. In the regeneration study, the high removal efficiency of arsenic (more than 87%) was found even after four cycles.

Synthesis and Characterization of Novel Organomodified Nanoclays for Application in Dental Materials

Background: Nanoclays incorporated in dental resins have been previously investigated. However, limited reports are associated with nanoclays that exhibit high functionality. Objective: The aim of this study was the targeted synthesis and characterization of organomodified nanoclays with methacrylic groups suitable for incorporation in dental nanocomposite resins. Methods: Quaternary ammonium methacrylates were synthesized and characterized by means of proton nuclear magnetic resonance and Fourier-transform infrared spectroscopy. Consequently, they were inserted into the interlayer space of nanoclay through a cation exchange reaction, while silane was also used for simultaneous surface modification. The produced organomodified nanoclays were characterized by means of X-ray diffraction, Fourier-transform infrared spectroscopy and thermogravimetric analysis. Results: Fourier-transform infrared spectra confirmed the successful synthesis of the quaternary ammonium methacrylates. X-ray diffraction analysis showed that organoclays exhibited higher d001- values (up to 1.78 nm) compared to raw nanoclay (1.37 nm), indicating an accomplished intercalation in each case. X-ray diffraction spectra mainly disclosed the presence of methacrylic functional groups in all nanoclays. Thermogravimetric analysis curves verified the different thermal stability of organoclays due to the diversity of their organic modifiers. Conclusion: The experimental results showed that nanoclay was successfully modified with ammonium methacrylates and silane. Τhe combination of X-ray diffraction and thermogravimetric analysis data revealed a high degree of intercalation and methacrylated organic loading as well. These phenomena may favor a good dispersion and high polymerization degree of nanoclays with dental resin monomers, rendering them potentially useful materials for the development of advanced dental nanocomposites resins.