Sepiolite Surface Research Articles

Experimental and Atomic Modeling of the Adsorption of Acid Azo Dye 57 to Sepiolite

AbstractSepiolite is a hydrated magnesium silicate with a microporous and mesoporous structure. The fibrous morphology and the alternating blocks and tunnels along the fiber direction of sepiolite make it an ideal material to sequester a variety of organic and inorganic contaminants. The adsorption of various surfactants by organo sepiolites have been experimentally investigated. How this hydrophobic material adsorbs dye molecules at the atomic level, however, is a great mystery. For this reason, the present study focused on the adsorption of acid azo 57 dye molecules to modified sepiolite. For this purpose, the amenability of sepiolite to remove the anionic textile dye (acid azo red dye 57) was first studied in detail. Additionally, a typical cationic surfactant, hexadecyltrimethylammonium Br (HTAB), was used to modify sepiolite to increase the adsorption capacity. Zeta potential measurements on the sepiolite and the HTAB modified sepiolite were also carried out. Moreover, Density Functional Theory (DFT) studies were performed to understand the mechanism of the adsorption of dye molecules to natural and modified sepiolite surfaces. On the basis of the experimental studies, three general systems were theoretically examined: (i) HTAB molecules on sepiolite basal surfaces to represent four Si tetrahedra, (ii) neutral or charged acid azo red dye 57 molecules on sepiolite basal surfaces to represent four Si tetrahedra, and (iii) HTAB on the surface of neutral or charged acid azo red dye 57 molecules as a substrate. The results clearly indicated good agreement between the experimental studies and the theoretical computational DFT studies. For example, the double layer structure found in experimental studies was also demonstrated in DFT studies and confirmed increased adsorption in the presence of acid azo dye 57.

Sepiolite/Cu2O/Cu photocatalyst: Preparation and high performance for degradation of organic dye

A novel ternary sepiolite/Cu2O/Cu (SCC) nanocomposite was successfully synthesized by a facile one-pot method. The Cu2O/Cu nanoparticles in the SCC nanocomposite are well dispersed on the sepiolite surface. It exhibited enhanced photocatalytic performance in the degradation of congo red (CR), remarkably superior to that of Cu2O or Cu2O/Cu nanoparticles. Elemental copper in the SCC serves as a good electron acceptor to promote the transfer of photo-generated electrons in Cu2O and suppress the recombination of the photo-generated electrons and holes of the composite. The enhanced photocatalytic efficiency is attributed to the synergistic effect of sepiolite and Cu2O/Cu. This type of SCC nanocomposites is a promising candidate as photocatalytic material for environmental protection.

Influence of the Structure and Experimental Surfaces Modifications of 2:1 Clay Minerals on the Adsorption Properties of Methylene Blue

In this work the adsorption capacities of methylene blue on Mg-smectite and sepiolite and its derived material obtained after acid treatment and/or the addition of Fe at its surfaces are studied. Natural smectite with high Mg-content in its octahedral sheet (Mg-smectite) displays higher adsorption capacity than the sepiolite due to the ability of Mg-smectite to expand the basal spacing to accommodate methylene blue cations between adjacent layers and the inability of sepiolite to adsorb these cations within the structural channels. The acid-activation of Mg-smectite causes a clear decrease in the adsorption capacity attributed to the partial loss of the interlayer positions by the loss of the octahedral sheet and subsequent formation of amorphous silica. Moreover, the adsorption of the Mg-smectite decreases even more when iron oxohydroxides species are incorporated in its interlayer spacing making inaccessible the interlayer active sites for the adsorption of methylene blue cations. On the contrary, the microwave-assisted acid treatment of sepiolite causes a slight increase in the adsorption capacity related with the dispersion of fibers. Nevertheless, contrary to that observed with Mg-smectite, higher increasing of adsorption capacities are obtained after the formation of new adsorption centers due to the incorporation of iron oxohydroxides species at the external surfaces of sepiolite.

Reprint of ZnO/sepiolite heterostructured materials for solar photocatalytic degradation of pharmaceuticals in wastewater

This work deals with the preparation of novel photocatalysts based on the assembly of ZnO nanoparticles on the surface of sepiolite (Sep) fibrous clay mineral, which can be previously modified by treatment with cetyltrimethylammonium bromide, tetramethoxyortosilicate or magnetite (Fe3O4) nanoparticles. The structural and morphological features of the prepared samples were characterized by diverse experimental techniques. The photoactivity of the resulting materials has been tested under solar light irradiation for the degradation of emerging pollutants, such as ibuprofen, acetaminophen and antipyrine. The resulting ZnO/Sep heterostructure exhibits enhanced photocatalytic performance compared to ZnO/SiO2-Sep and ZnO/Fe3O4-Sep materials. Ibuprofen showed higher degradation rates than the other target compounds. Of particular interest is the use of ZnO/Fe3O4-Sep photocatalyst, which shows the simultaneous features of superparamagnetic character and photocatalytic activity, allowing its easy recovery by application of an external magnetic field which improves its reusability.

Sepiolite as replacement of short glass fibre in polyamide composites for injection moulding applications

Abstract Sepiolite polyamide 6 nanocomposites were prepared via melt compounding and in situ polymerization. The effects of the preparation approach, the amount of the clay and the surface clay modification were evaluated in order to check their influence on morphology, thermal, mechanical and flow behaviour of the final nanocomposites. Regardless of the preparation method, all nanocomposites showed good dispersion of the sepiolite in the matrix and significant improvements in Young's modulus, tensile strength and heat-distortion temperature were achieved. However, the nanocomposites obtained in one-step by in situ polymerization presented slightly better mechanical properties, than the obtained by melt compounding, due to the greater dispersion of the nanoclay within polyamide matrix. Especially interesting were the materials reinforced with modified sepiolite, where the grafting of an aminosilane onto the sepiolite surface produced important increases in the elongation at break and impact values as consequence of the improved stress transfer between the sepiolite and polymer matrix. Furthermore, nanocomposites with 10 wt% of sepiolite have been compared with higher loaded glass fibre polyamide. The nanocomposites presented similar or even better performances than commercial composites offering an important weight reduction for final applications.

Sepiolite-carbon nanocomposites doped with Pd as improving catalysts for hydrodechlorination processes

Abstract The present work introduces a new type of improved catalysts based on sepiolite-carbon nanocomposites anchoring Pd nanoparticles. The nanocomposites are prepared by assembly in aqueous media of graphene nanoplatelets (GNP) and the nanofibrous sepiolite under a sonomechanical treatment. The methodology allows the co-assembly of other nanomaterials such as multiwall carbon nanotubes (MWCNT) and Pd nanoparticles, these last ones in situ generated from PdCl2 and further treatment with NaBH4. The presence of silanol groups at the external surface of sepiolite favors the growth and assembly of Pd NP which exhibit a quite narrow size distribution independently of the composition of the prepared sepiolite-carbon nanocomposite. The electrical conductivity of the prepared sepiolite-carbon/Pd materials depends of the composition, being lower in materials with higher content in sepiolite. However, the presence of the clay mineral improves textural properties of the resulting materials. The prepared sepiolite-carbon/Pd nanocomposites were tested as catalysts in the hydrodechlorination (HDC) of 4-chlorophenol (4-CPh) under H2 flux, showing all of them an exclusive selectivity towards phenol, though their catalytic activity depends on their composition. Sepiolite is able to neutralize the evolved HCl, favoring the catalytic process. In addition, the good balance between textural and electrical properties achieved in some of the prepared materials enhances the contact between the catalyst surface and the reagents and also favors the electronic transfer, making this new type of sepiolite-carbon/Pd systems very promising. In fact, the concept here reported could be extended to other catalytic applications where the supported metal acting as active center requires the presence of heat and water resistant conductive supports.

Effect of aqueous Si/Mg ratio and pH on the nucleation and growth of sepiolite at 25 °C

Sepiolite [Mg4Si6O15(OH)2·6H2O] is a trioctahedral 2:1 Mg-silicate that has been often used to reconstruct the evolution of sedimentary environments and facies in the geological record. To date, however, the reaction paths underlying sepiolite formation are poorly constrained and most of the existing models are based on empirical observations. In order to shed light on the mechanisms controlling the formation of this mineral phase, in the present study, sepiolite was precipitated at 25 ± 1 °C from modified seawater and MgCl2 solutions undersaturated with respect to brucite and amorphous silica. Although a suite of hydrous Mg-silicates, such as kerolite, saponite, stevensite and talc, were oversaturated in the solutions at a higher level relative to sepiolite at any time of reaction, poorly crystallized, aluminous sepiolite was the only precipitate after 91 days. The precipitated sepiolite [Mg3.4-3.8Al0.1-0.4)∑3.8-3.9(Si5.9-6.0Al0-0.1)O15(OH)2·nH2O] shares a number of structural and chemical similarities with natural sepiolite, such as a fibrous crystal shape and an atomic Si/(Si + Mg+Al) ratio of ∼0.61.The proposed reaction path for the formation of sepiolite is based on the temporal evolution of the chemical compositions of the experimental solution and solids: (i) Nucleation and growth of Al-sepiolite occurred during the first 8 days of the experimental runs via condensation and polymerization of SiOH tetrahedra onto Mg–Al–O–OH template sheets at a precipitation rate of ∼2.19 ± 0.01 × 10−10 mol s−1. (ii) At decreasing pH and in the absence of [Al]aq this intermediate phase transformed into aluminous sepiolite at a slower crystal growth rate of ∼1.08 ± 0.02 × 10−12 mol s−1. This finding explains the high abundances of sepiolite in highly alkaline, evaporitic, lacustrine and soil environments, where the growth rates of sepiolite are considered faster (10−11 to 10−10 mol s−1, Brady, 1992). We propose that (i) low rates of Mg2+ ion dehydration and silica condensation and polymerization at the surface of the initial precipitate, (ii) the formation of MgS040 aquo-complexes and (iii) the reduced sorption rates of [Si]aq and [Mg]aq at the active growth sites on sepiolite surfaces at pH ≤ 8.3 retard the precipitation of sepiolite in marine-diagenetic environments.

Improvement of stability of insecticidal proteins from Bacillus thuringiensis against UV-irradiation by adsorption on sepiolite

The adsorption characteristics of protoxin and toxin from Bacillus thuringiensis by sepiolite were studied. The kinetic results showed that the protoxin and toxin could be adsorbed by sepiolite rapidly, and the equilibrium was reached within 1 h. The adsorption isotherms of both proteins followed Langmuir equation (R2>0.98) and the curves belonged to L type. The adsorption capacity, adsorption rate and the insecticidal activity of toxin were higher than those of protoxin. The results of ultraviolet irradiation showed that sepiolite could protect the toxin from ultraviolet irradiation damage, but it accelerated the damage of protoxin. Therefore, the toxin is suitable for preparing long-term formulations of B. thuringiensis using the carrier of sepiolite. The results of Fourier transform infrared, X-ray diffraction, and scanning electron microscopy indicated that toxin did not influence the structure of sepiolite and the adsorption of toxin only on the surface of sepiolite. The adsorption of toxin by sepiolite was enhanced by metal ions in the range of concentration from 0 to 4.0 mmol L−1, and the enhancement extent of metal ions on the adsorption of toxin was in the order: Ca2+>Mg2+>K+>Na+. The higher the loading of toxin per mass sepiolite, the lower the 50% of the larvae of sepiolite–toxin complex. The zeta potential of sepiolite suspension increased with the addition of metal ions, indicating that the driving forces of the adsorption of toxin to negatively charged sepiolite was electrostatic interaction.

ZnO/sepiolite heterostructured materials for solar photocatalytic degradation of pharmaceuticals in wastewater

Abstract This work deals with the preparation of novel photocatalysts based on the assembly of ZnO nanoparticles on the surface of sepiolite (Sep) fibrous clay mineral, which can be previously modified by treatment with cetyltrimethylammonium bromide, tetramethoxyortosilicate or magnetite (Fe3O4) nanoparticles. The structural and morphological features of the prepared samples were characterized by diverse experimental techniques. The photoactivity of the resulting materials has been tested under solar light irradiation for the degradation of emerging pollutants, such as ibuprofen, acetaminophen and antipyrine. The resulting ZnO/Sep heterostructure exhibits enhanced photocatalytic performance compared to ZnO/SiO2-Sep and ZnO/Fe3O4-Sep materials. Ibuprofen showed higher degradation rates than the other target compounds. Of particular interest is the use of ZnO/Fe3O4-Sep photocatalyst, which shows the simultaneous features of superparamagnetic character and photocatalytic activity, allowing its easy recovery by application of an external magnetic field which improves its reusability.

In situ polymerization of isotactic polypropylene sepiolite nanocomposites and its copolymers by metallocene catalysis

Isotactic Polypropylene (iPP)-sepiolite nanocomposites were prepared by in situ polymerization using nanoclays as support of the catalytic system. This study proposes a method of immobilization that considers the use of the density of the polar groups present on sepiolite surface, to fix the co-catalyst. In addition, the resulting polymerization process defines the reaction time as a variable which will provide a mechanism for controlling the productivity of the reaction, making possible the obtaining of a masterbatch which may be useful in increasing the PP-clay compatibility in melt blending processes. The results of the proposed method have allowed not only the additivation of polypropylene during the synthesis, but also the structure control in terms of stereo-specificity and molecular weight, improving its final properties. Furthermore, in an effort to improve the impact properties of the iPP matrix, iPP copolymers were synthesized with 1-olefins of different chain lengths as co-monomers. The influence of the amount of co-monomer, amount of filler and type of branching obtained on the final properties of iPP nanocomposites were studied.

Comparison of organo-sepiolite modified by different surfactants and their rheological behavior in oil-based drilling fluids

Abstract Sepiolite modified by surfactants has been used in adsorption, catalysts, etc. While few studies focus on organo-sepiolite (OSep) which is used in oil-based drilling fluid. In this paper, a kind of cationic-anionic organo-sepiolite (CA-OSep) was prepared to be applied in oil-based drilling fluids. The structure and properties of OSep were characterized by X-ray diffraction, FTIR spectrum, thermal analysis and surface contact angle (SCA) analysis. The effect of dosage and chain length of surfactants, and the ratio of cationic to anionic surfactants on OSep were discussed as well as the rheological properties of OSep/diesel system. Cationic surfactant of long chains had better adhesion to the surface of sepiolite than surfactants of short chains. Compared with cationic organo-sepiolite (C-OSep), CA-OSep has an advantage in thermal stability. The apparent viscosity, plastic viscosity and yield value of oil-based drilling fluids with OSep as additives were further studied at different temperatures. Results indicated that organic surfactants had been adsorbed on the surface of sepiolite, and the CA-OSep had higher surface polarity and better thermal stability in 5# diesel oil than C-OSep. CA-OSep presented a new kind of potential rheological control additive for oil-based drilling fluids, and would exhibit excellent thermal stability.

Fe3O4/sepiolite magnetic composite particles and their magneto- responsive characteristics

To prepare a new magnetorheological (MR) material of magnetite/clay composite-based MR material and test its rheological characteristics, Fe3O4/sepiolite clay nanocomposite particles were fabricated by loading Fe3O4 particles on the surface of sepiolite using an in situ chemical co-precipitation method, and their MR characteristics under applied magnetic fields were examined. Scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction confirmed successful composite formation. Vibrating sample magnetometry also revealed their typical superparamagnetic behavior. The synthesized composites were dispersed in mineral oil to form a MR fluid with a particle concentration of 10 vol%. Various magneto-rheological tests of the MR fluids were attempted at different magnetic field strengths, including flow curve and dynamic oscillation test. While shear viscosity, yield stress, and dynamic modulus increased with magnetic field strengths, the yield stress as a function of magnetic field strength demonstrated a slope of 1.0 on a log–log scale.

Carbon-coated sepiolite clay fibers with acid pre-treatment as low-cost organic adsorbents

Carbon-nanoparticle-coated sepiolite hydrous-magnesium-silicate clay fibers are prepared by 220°C-autoclave hydrothermal carbonization of cellulose using 1.2-mol/L-hydrochloric-acid-pretreated sepiolite fibers. The deposited amorphous carbon nanoparticles (30–150 nm) nonuniformly and partially covering the sepiolite surface have surface functional groups (CH2, CH3, CC and CO), which enhance the organophilicity. Compared to a mixture of pristine sepiolite and hydrothermal carbon prepared without sepiolite, the carbon-coated sepiolite exhibits lower specific surface area but greater organic adsorption, due to the smaller pore size and particle size of the hydrothermal carbon coating compared to the hydrothermal carbon prepared without sepiolite. The acid pre-treatment decreases the sepiolite crystallinity and increases the deposited carbon content from 24.67 to 31.63 vol%, while increasing the specific surface area from 26.53 to 33.98 m2/g, increasing the fraction of phenol removed from 47.1% to 57.1%, and increasing the monolayer phenol adsorption capacity from 4.1 to 5.26 mg/g. Compared to the acid treated but uncoated sepiolite, the carbon coating decreases the density from 2.227 to 1.696 g/cm3 and decreases the specific surface area from 118 to 34 m2/g, but increases the fraction of phenol removed from 6.1% to 57.1%. The acid pre-treatment gives greater adsorption than the addition of acid to the hydrothermal process liquid.

The influence of silver and copper ions on the antibacterial activity and local electrical properties of single sepiolite fiber: A conductive atomic force microscopy (C-AFM) study

This is a study to analyze antibacterial and electrically-conductive sepiolite, and to evaluate its potential usage as biomaterials, medical products, sensors and electronics. Silver and copper ions were used to modify the properties of sepiolite through a multi-step procedure. During the modification of the sepiolite fibers, the most significant adsorption rates were obtained at metal uptake concentrations of 50mg/g for Ag+ and 80mg/g for Cu2+. This was found to fit the Langmuir isotherm model, thereby indicating the formation of a monolayer on the sepiolite surfaces by silver and copper ions. The effects of adsorbed silver and copper ions at the optimum metal uptake concentrations were then compared in terms of their antibacterial activity and electrical conductivity.Serial broth dilution and Kirby-Bauer disk diffusion susceptibility tests on Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 25923) were both utilized in this study. Metal ions that neutralized bacteria, and their minimum inhibitory concentrations (MIC), were measured at 50mg/L for Ag+ and 100mg/L for Cu2+. Additionally, the current distributions of metal ions over a single sepiolite fiber could also be characterized through the use of C-AFM. Interestingly, for the first time, local electric current variations and the potential gradients of Ag+ and Cu2+ sorped sepiolite fiber surfaces were detected. Their C-AFM generated current image and line scans showed that silver electrons transfer much more rapidly than those of copper; however, raw sepiolite demonstrates no antibacterial or current properties. Therefore, the fibrous clay mineral used in this study might be a good candidate for highly effective and innovative clay-based applications.

Sepiolite nanoplatform for the simultaneous assembly of magnetite and zinc oxide nanoparticles as photocatalyst for improving removal of organic pollutants

Novel ternary ZnO/Fe3O4-sepiolite nanostructured materials were developed in a two-step procedure based on the incorporation of ZnO nanoparticles on a substrate composed by magnetite nanoparticles previously assembled to the sepiolite fibrous silicate (Fe3O4-sepiolite). The structural and morphological characterization shows that both, ZnO and Fe3O4 nanoparticles, were homogeneously dispersed on the surface of sepiolite. Therefore, the resulting material is characterized as a multifunctional nanoplatform simultaneously providing magnetic and photoactive properties. ZnO/Fe3O4-sepiolite materials exhibit superparamagnetic properties at room temperature, which is one of the sought properties in view to facilitate their recovery from the reaction medium after application as heterogeneous catalysts. ZnO/Fe3O4-sepiolite materials were tested as photocatalysts using methylene blue dye in water as model of a pollutant molecule, showing full decolorization after 2h of UV irradiation. Moreover, the photocatalytic activity of this nanoplataform may be maintained after reuse in several consecutive cycles of treatment. Remarkably, the ZnO/magnetite-sepiolite nanostructured material displays a similar activity as ZnO/sepiolite materials, but shows the additional advantage of easier recovery by means of a magnet which facilitates its reuse.

Sepiolite-TiO2 nanocomposites for photocatalysis: Synthesis by microwave hydrothermal treatment versus calcination

Sepiolite-TiO2 nanocomposites were synthesized by conventional calcination process and microwave hydrothermal (M-H) treatment and were tested and compared for their photocatalytic activity. XRD analysis indicated that nanocomposites after calcination at 500°C or M-H treatment for 40min at about 200°C appear to be the optimal conditions, which assured the amorphous TiO2 to crystalline anatase phase transition. The deposition of the TiO2 on the surface of sepiolite by M-H treatment yielded small dispersed nanoparticles at all treatment times used in this study. However, TiO2 particle size increased with increasing calcination temperature, which was confirmed by SEM and TEM. N2-adsorption-desorption isotherms indicated that calcination process reduced the specific surface areas of the nanocomposites while the M-H treatment led to a higher surface area with better photocatalytic performance for the degradation of Orange G. The intact structure of sepiolite and the homogeneous dispersion of the TiO2 nanocrystals on sepiolite surfaces led to enhanced photocatalytic activity in M-H treated samples.

Preparation of Ag@AgCl-doped TiO2/sepiolite and its photocatalytic mechanism under visible light

A cube-like Ag@AgCl-doped TiO2/sepiolite (denoted Ag@AgCl–TiO2/sepiolite) was successfully synthesized via a novel method. X-ray diffraction, scanning electron microscopy, energy dispersion X-ray fluorescence, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and diffuse reflectance ultraviolet–visible spectroscopy were performed to determine the structure and physicochemical properties of Ag@AgCl–TiO2/sepiolite. SEM micrographs revealed that Ag@AgCl nanoparticles and TiO2 film are well deposited on the surface of tube-like sepiolite. As a result, Ag@AgCl–TiO2/sepiolite exhibits a red shift relative to TiO2/sepiolite. Photocatalytic experiments demonstrated that the dosage of catalysts plays an important role during photocatalysis. The photoelectrochemical activities of Ag@AgCl–TiO2/sepiolite and TiO2/sepiolite were also investigated. Photocurrent responses confirmed that the ability of Ag@AgCl–TiO2/sepiolite to separate photo-generated electron–hole pairs is stronger than that of TiO2/sepiolite. Methylene Blue degradation is also improved under alkaline conditions and visible light irradiation because more OH is produced by visible light excitation. This excellent catalytic ability is mainly attributed to the formed Ag nanoparticles and the Schottky barrier at the Ag/TiO2 interface. Active species analysis indicated that O2− and h+ are implicated as active species in photocatalysis. Therefore, catalysts are excited to produce abundant electron–hole pairs after they absorb photons in photocatalysis.

Effect of sepiolite bed material on gas composition and tar mitigation during C. cardunculus L. gasification

Sepiolite, a clay mineral that is commonly used as adsorbent, is proposed as bed material for biomass gasification in a lab-scale bubbling fluidized bed. In order to compare the obtained gas composition and tar generation, silica sand has been used as reference bed material. C. cardunculus L. has been employed as biomass feedstock. The operating temperature is varied from 830 to 875°C, at constant equivalence ratio (ER) of 0.30. The gas produced with sepiolite as bed material has a slightly lower quality than the gas generated with silica sand, the lower heating value (LHV) is 0.4–1.4MJ/Nm3 lower for sepiolite than for silica sand. However, the tar generation is rather reduced in the sepiolite bed and the tar composition is also different among the bed materials: the polycyclic aromatic hydrocarbons fraction (PAH) is drastically reduced while oxygenated compounds arise in the sepiolite tests. Sepiolite properties such as surface area and morphology have been analysed by means of specific surface area (BET) and scanning electron microscopy (SEM-EDS) before and after the experiments. The fuel behaviour and the properties of sepiolite induce the adsorption of tars and molten ashes on the sepiolite surface, leading to a much better performance in terms of tar mitigation and agglomeration.

Preparation and Characterization of Nanoscale Zero-Valent Iron-Loaded Porous Sepiolite for Decolorizing Methylene Blue in Aqueous Solutions

The preparation and characterization of nanoscale zero-valent iron-loaded porous sepiolite, as well as its application in the decolorization of methylene blue in aqueous solution, have been studied in this work through the measurements of field emission scanning electron microscope with energy dispersive spectrometry, x-ray photoelectron spectrometry, Fourier transform infrared spectroscopy and specific surface area. The results showed that nanoscale zero-valent iron particles were successfully loaded on the surface and interior pores of sepiolite through physical adsorption. It was revealed that the decoloration capacity of methylene blue on nanoscale zero-valent iron-loaded porous sepiolite in water was comparable to that of nanoscale zero-valent iron, and nine times higher than that of natural sepiolite. This indicates that porous sepiolite was a good supporter for the loading of nanoscale zero-valent iron and nanoscale zero-valent iron-loaded sepiolite was a good decolorant because of its high decoloration efficiency and easy separation.

Adsorption of Pyrene from Aqueous Solutions onto Sepiolite

AbstractPolycyclic aromatic hydrocarbons (PAHs) are a large class of organic compounds which are commonly mentioned and have been shown to be highly carcinogenic and to persist in the environment for many years. An inexpensive remediation method has yet to be found, so the current study was undertaken to test the use of sepiolite, a fibrous clay mineral, as a potentially inexpensive and effective solid-phase adsorbent for sequestering PAHs. Pyrene was chosen as a model PAH due to the specific volatility, miscibility, and relatively soluble properties of the compound. A sepiolite of Turkish origin was then investigated to explore its potential to adsorb hydrophobic organic compounds from aqueous solution. The microstructure and morphology of the sepiolite were characterized using elemental analysis, X-ray diffractometry (XRD), Fourier-transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), and specific surface area from N2 adsorption isotherms. The pyrene adsorption isotherms were closely fitted to the Langmuir model and the coefficients of determination (RP2) were higher than 0.999. The results indicated that the high affinity of pyrene for sepiolite surfaces was dominated by the structural channels and the large number of Si-OH groups located on the basal surfaces. The intracrystalline interactions of pyrene with the sepiolite were, however, more favorable than pyrene interactions with sepiolite surface Si-OH groups, which can react directly with pyrene to form true covalent bonds (chemical interactions). Finally, the FE-SEM images initially revealed that, after sepiolite was loaded with adsorbed pyrene, a fairly straight and rigid arrangement of fibers occurred due to the aggregation of laths to form rods and the increased amounts of adsorbed pyrene.