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Emilia García-romero - One of the best experts on this subject based on the ideXlab platform.
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Sepiolite PALYGORSKITE: A CONTINUOUS POLYSOMATIC SERIES
Clays and Clay Minerals, 2013Co-Authors: Mercedes Suarez, Emilia García-romeroAbstract:A compositional gap between Sepiolite and palygorskite has long been accepted even though they have similar structures, but recent studies found that such a gap does not exist and that the compositional series is continuous between them. If this is true, intergrowths between these two minerals should exist. The purpose of the present study was to demonstrate the existence of Sepiolite-palygorskite intergrowths in all possible proportions, in order to establish the compositional links between ideal Sepiolite and ideal palygorskite and to define the compositional limits of these two minerals. Sepiolite and palygorskite have similar structures but different chemical compositions: Sepiolite is the most trioctahedral and magnesic extreme, while palygorskite is dioctahedral with Al and Mg in its octahedral sheet. The existence of all intermediate compositions between these two pure extremes has led to the definition of the intermediate minerals, Al-Sepiolite and Mg-palygorskite, which can have similar chemical composition. The structural relations between the different minerals of the palygorskite—Sepiolite series were studied here by powder X-ray diffraction (XRD), and continuous variation in the chemical composition is explained by the existence of intergrowths of Sepiolite and palygorskite polysomes forming a continuous polysomatic series. The existence of intergrowths by mixtures of polysomes in modulated structures can be considered in the same way that the mixed-layer minerals in layered structures are considered. The continuous polysomatic series of Sepiolite-palygorskite can be expressed by the general formula: [Si12Mg8O30(OH)4(OH2)4]y∙[Si8O20(Mg2Fe2)x(Mg2Al2)(1-x)(OH)2(OH2)4](1-y)·nH2O, where Sepiolite and palygorskite are the end-members. They and xvalues can be calculated using a ternary plot with the oxide contents of the main octahedral cations (Al2O3, Fe2O3, and MgO). The proposed model, which is based on the intergrowth of Sepiolite and palygorskite polysomes, explains both the variability in the chemical composition and the compositional limit for the identification of these minerals by X-ray diffraction.
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Variability of the surface properties of Sepiolite
Applied Clay Science, 2012Co-Authors: M. Suárez, Emilia García-romeroAbstract:A comparative study of a wide collection of Sepiolites (22 samples from different locations, including samples\ud coming from the greatest deposits of Sepiolite in the world) was made with the aim of understanding the real\ud variability of the surface properties in Sepiolite. The samples have been studied by XRD, Electron Microscopy\ud (TEM and SEM) and the adsorption–desorption of N2. The influence of possible impurities, crystallinity and\ud crystalline defects, and the textural variations, is taken into account to explain the high differences found\ud in the specific surface area of Sepiolites. The studied samples display a high variability in crystallinity, fibre\ud length and texture. The BET surface varies between 77 and 399 m2 g−1, demonstrating the significant variation\ud in the surface properties in natural Sepiolites. Both the external and the microporous area vary between\ud very wide extreme values, from 52 m2 g−1 to 246 m2 g−1 for the microporous area and 6 m2 g−1 to\ud 178 m2 g−1 for the external area. The exceptionally low values of these properties found in some samples\ud cannot be related to the presence of impurities, but rather to their structural and textural features. Two\ud types of microporosity that can be described are structural microporosity and interfibre microporosity. The\ud SSA and the porosity of each Sepiolite is the result of the sum of the intracrystalline or structural microporosity\ud and the textural porosity (interfibre microporosity and mesoporosity). As a consequence, there is a hierarchical\ud distribution of pore sizes, which is different for each Sepiolite. The lowest values of microporosity are\ud related to the presence of very open pores and the Sepiolites with higher SSA are those having a smaller\ud length and a more closed porosity
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Variability in Sepiolite: Diffraction studies
American Mineralogist, 2011Co-Authors: Manuel Sanchez Del Rio, Emilia García-romero, Mercedes Suarez, Ivan Da Silva, Luis Fuentes-montero, Gema Martínez-criadoAbstract:Twenty Sepiolites of known composition from different origins were analyzed to quantify the variability in structural parameters and its possible relationships with composition and morphology. Morphology SEM analyses led to classify the Sepiolites into several groups, beyond the two simple macroscopic or clay groups. X-ray powder diffraction with synchrotron light was used to discuss the variability of the a and b cell parameters with the nature of the cations and occupancy of the octahedral shell. Rietveld refinement using the ideal Sepiolite model is performed on Sepiolites at two temperatures: 225 °C (for zeolitically dehydrated Sepiolite) and 25 °C (for hydrated ambient Sepiolite). The latter permitted to locate ca. six molecules of the zeolitic H2O within the tunnels. A few samples were selected to evaluate the feasibility and potential of single-crystal diffraction methods: X-ray microdiffraction and electron diffraction. The macroscopic Sepiolites gave well-structured and rich X-ray fiber diffraction patterns, in excellent agreement with ab initio simulations. High-quality single-crystal electron diffraction patterns for three axis zones are indexed and compared with simulations. The experimental and modeling results for X-ray microdiffraction and electron diffraction open a new path for quantitative crystallography on Sepiolite and other fibrous clays from the Sepiolite-palygorskite group.
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Advances in the Crystal Chemistry of Sepiolite and Palygorskite
Developments in Clay Science, 2011Co-Authors: Mercedes Suarez, Emilia García-romeroAbstract:Abstract The structure and chemical composition of Sepiolite and palygorskite are known from the first half of the twentieth century. Ideal palygorskite Si 8 O 20 (Al 2 Mg 2 )(OH) 2 (OH 2 ) 4 ⋅H 2 O) 4 has dioctahedral character, and Sepiolite Si 12 O 30 Mg 8 (OH) 4 (OH 2 ) 4 (H 2 O) 8 is a pure trioctahedral mineral. In the two minerals, isomorphic substitutions in both tetrahedral and octahedral sheets are frequent. In addition, Mg-rich palygorskites, Fe-rich palygorskites and Al-rich Sepiolites have been reported and it seems that the compositional limits accepted until now could be too narrow. Therefore, Sepiolite and palygorskite can be classified into different types depending on the composition. In this chapter, the variations in the chemical composition of natural Sepiolites and palygorskites as well as the limit of chemical composition of both minerals, if it exists, using the data from the literature available are established. Sepiolite can be classified into two types: Sepiolite and Al-Sepiolite. A limit for these two types can be established from the octahedral occupancy, and Al-Sepiolites are those that have more than 10% of octahedral positions vacant and more than 0.5% VI Al atoms. On the other hand, palygorskite is classified into Ideal palygorskite with an octahedral composition near to the ideal palygorskite. Common palygorskite : where VI Al content is less than in the ideal formula and as a consequence that the Mg content is higher, but the number of octahedral cations is close to 4. Magnesic palygorskite is the most trioctahedral extreme, and Aluminic-palygorskite , which is defined by a total number of octahedral cations (p.h.u.c.) 3 ) > Mg. Magnesic palygorskite and aluminic Sepiolite can have very similar chemical composition. There is no a compositional gap between the two minerals. Palygorskite can be so rich in Mg and Sepiolite so rich in Al that is possible to affirm that a continuous composition series exist and all the intermediate compositions between the two extremes corresponding to the two pure minerals can be found. The intermediate compositions can be explained by intergrowths of Sepiolite and palygorskite ribbons or polysomes.
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On the Chemical Composition of Sepiolite and Palygorskite
Clays and Clay Minerals, 2010Co-Authors: Emilia García-romero, Mercedes SuarezAbstract:Many studies of the chemical composition of Sepiolite and palygorskite have been carried out using analytical electron microscopy (AEM). According to the literature, a compositional gap exists between Sepiolites and palygorskites, but the results presented here show that they may all be intermediate compositions between two extremes. The results of >1000 AEM analyses and structural formulae have been obtained for the samples studied (22 samples of Sepiolite and 21 samples of palygorskite) and indicate that no compositional gap exists between Sepiolite and palygorskite. Sepiolite occupies the most magnesic and trioctahedral extreme and palygorskite the most aluminic-magnesic and dioctahedral extreme. Sepiolite and palygorskite with intermediate compositions exist between the two pure extremes: (1) Sepiolite with a small proportion of octahedral substitution; (2) palygorskite with a very wide range of substitution (the pure dioctahedral extreme is unusual); and (3) intermediate forms, Al-Sepiolite and Mg-palygorskite with similar or the same chemical composition. The chemical compositions of the intermediate forms can be so similar that a certain degree of polymorphism exists between Al-Sepiolite and Mg-palygorskite.
Eduardo Ruiz-hitzky - One of the best experts on this subject based on the ideXlab platform.
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Responses of human cells to Sepiolite interaction
Applied Clay Science, 2020Co-Authors: Sandrine Ragu, Eduardo Ruiz-hitzky, Pilar Aranda, Elodie Dardillac, David Adame Brooks, Fidel Antonio Castro-smirnov, Bernard S. LopezAbstract:Abstract We showed that Sepiolite can transfer DNA into mammalian cells, opening alluring avenues for biothechnological and biomedical applications. Importantly, mammalian cells spontaneously internalize Sepiolite, facilitating the spontaneous transport and delivery of bound molecules, but increasing the risks of potential toxicity. In addition, the fibrous nature of Sepiolite raised health concerns about possible asbestos-like effects, especially because Sepiolite can transfer DNA into bacteria through Yoshida effect. In spite that extrapolations from bacteria to mammalian cells could correspond to over-interpretations and the classification by IARC as non-hazardous and non-carcinogenic, we addressed here the response of human cells to interactions with Sepiolite. We tested three classical cell responses to stress. We show that mammalian cells respond to Sepiolite exposure, inducing the production of reactive oxygen species and the expression of inflammatory cytokines. This shows that cells detect Sepiolite contamination and respond. Remarkably, Sepiolite exposure did not alter the cell cycle distribution and triggers neither the DNA damage response program nor apoptosis, suggesting that it does not significantly assault the genetic material in mammalian cells. The potential toxicity of chronic versus transient exposure to Sepiolite is discussed.
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Biotechnological applications of the Sepiolite interactions with bacteria: Bacterial transformation and DNA extraction
Applied Clay Science, 2020Co-Authors: Fidel Antonio Castro-smirnov, Eduardo Ruiz-hitzky, Pilar Aranda, Olivier Pietrement, Eric Le Cam, Bernard LopezAbstract:Among the various clay minerals, Sepiolite, which is a natural nanofibrous silicate that exhibit a poor cell toxicity, is a potential promising nanocarrier for the non-viral and stable transfer of plasmid DNA into bacteria, mammalian and human cells. We first show here that Sepiolite binds to bacteria, which can be useful in decontamination protocols. In a previous research we have shown that is possible to modulate the efficiency of the absorption of different types of DNA molecules onto Sepiolite, and that the DNA previously adsorbed could be recovered preserving the DNA structure and biological activity. Taking advantage of both, the Sepiolite/bacteria and Sepiolite/DNA interactions, we show that pre-assembly of DNA with Sepiolite and incubation of bacteria with this obtained biohybrid strongly improve the transformation efficiency, in a rapid, convenient and inexpensive method that doesn't require competent cell preparation. In addition, we also show that the controlled Sepiolite and DNA binding capacities can be used to purify plasmids from bacteria, representing an advantageous alternative to onerous commercial kits. All of these results open the way to the use of Sepiolite-based bionanohybrids for the development of novel biological models of interest for academic and applied sciences.
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Silica-Sepiolite nanoarchitectures
Journal of nanoscience and nanotechnology, 2013Co-Authors: Almudena Gómez-avilés, Pilar Aranda, Francisco M. Fernandes, Carolina Belver, Eduardo Ruiz-hitzkyAbstract:Silica-Sepiolite heterostructured materials have been prepared as novel nanoarchitectures by generation of SiO2 nanoparticles (NPs) on the surface of the Sepiolite fibrous clay mineral. The synthetic approach implies the use of organo-Sepiolites dispersed in isopropanol to which is incorporated a selected silicon alcoxysilane, such as tetramethoxysilane (TMOS), that then is slowly hydrolyzed to procure the formation of a viscous gel under ultrasound irradiation. Once the sol gel reaction is achieved the intermediate silica-Sepiolite organo-heterostructures can be submitted to a thermal treatment for the removal of the organic matter, which finally gives rise to the silica-Sepiolite nanoarchitectures. Influence of different experimental variables, such as nature of both alkoxysilane precursor and organo-Sepiolite as well as their relative ratio in the reaction media, in the characteristics of both intermediate silica-Sepiolite organo-heterostructures and final nanoarchitectures has been explored. Both type of heterostructured materials have been characterized by means of diverse experimental techniques such as CHN chemical analysis, TG-DTA, XRD, FTIR, Si-29 NMR, FE-SEM and TEM. Special attention has been devoted to the analysis of changes in the morphological and textural features of the SiO2-Sepiolite samples before and after the thermal treatment carried out for removing the organic matter and consolidation of the silica network. This study describes the resulting nanoarchitectures as Sepiolite microfibers covalently assembled to silica nanoparticles exhibiting specific surface areas ca. to 350 m(2)/g, practically without microporous contribution. Preliminary tests regarding the use of the SiO2-Sepiolite nanoarchitectures as nanofillers in polymer nanocomposites have been also investigated in order to show one of their potential fields of application. Mechanical properties of epoxy resin nanocomposites have been determined and discussed considering the different nature of the external surface of the intermediate organo-heterostructures and the final inorganic nanoarchitectures.
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Gelatin renaturation and the interfacial role of fillers in bionanocomposites
Phys. Chem. Chem. Phys., 2011Co-Authors: Francisco M. Fernandes, Inderchand Manjubala, Eduardo Ruiz-hitzkyAbstract:This work describes a systematic study of gelatin-Sepiolite structural bionanocomposites to show how the renaturation level of the biopolymer is highly dependent on the type of mineral particle used. The aim of the work is to prove that chemical interactions between both components (hydrogen and covalent bonding) determine the organization level of the biopolymer which in turn results in drastic differences in the elastic properties of the prepared bionanocomposites. To assess this, several systematic modifications were introduced into the silicate structure and surface, generating four derivatives. Two derivatives prepared by thermal treatments, monohydrated Sepiolite and protoenstatite, and two chemically modified Sepiolites, amino and epoxy terminated, were prepared and used as the inorganic (or hybrid) phase in the bionanocomposites. The thermal and chemical modifications performed on the Sepiolite surface induced a dramatic decrease in the renaturation level as determined by DSC and FTIR techniques. On the other hand, untreated Sepiolite induced a higher renaturation level in the polypeptide, probably due to the alignment of the collagen-like triple helix along Sepiolite external surface channels. The measured mechanical properties of the studied compositions confirm that the renaturation level of gelatin is a key factor in understanding the elastic properties of bionanocomposites. These results suggest that mineral particles introduced in the polypeptide matrix provide an effective control over the matrix crystallinity giving rise to tunable mechanical properties of the final bionanocomposite.
Mahir Alkan - One of the best experts on this subject based on the ideXlab platform.
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preparation and characterization of Sepiolite poly ethyl methacrylate and poly 2 hydroxyethyl methacrylate nanocomposites
Polymer Composites, 2009Co-Authors: Ruhan Benlikaya, Mahir Alkan, Ismet KayaAbstract:Poly(ethyl methacrylate) (PEMA) and poly(2-hydroxyethyl methacrylate) (PHEMA) nanocomposites with Sepiolite in pristine and silylated form were prepared using the solution intercalation method and characterized by the measurements of XRD, TEM, FTIR-ATR, TG/DTG, and DSC. The TEM analysis indicated that the volume fraction of fibers in Sepiolite decreased and the fiber bundles dispersed in PEMA and PHEMA at a nanometer scale. These results regarding TEM micrographs were in agreement with the data obtained by XRD. The increase in thermal stability of nanocomposites of PEMA is higher than that of PHEMA according to the data obtained from TG curves. The DTG analysis revealed that Sepiolite/modified Sepiolite caused some changes, as confirmed by FTIR in the thermal degradation mechanism of the polymers. Tg temperatures of PEMA and PHEMA usually increased upon the addition of Sepiolite/modified Sepiolite. In addition, modification of Sepiolite with 3-APTS had a slight influence on thermal properties of the nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers
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Characterization and Adsorption Properties of Chemically Modified Sepiolite
Industrial & Engineering Chemistry Research, 2008Co-Authors: Yasemin Turhan, Pınar Turan, Mehmet Doǧan, Mahir Alkan, And Hilmi Namli, Özkan DemirbaşAbstract:Modification of Sepiolite clay has been performed using triethoxy-3-(2-imidazolin-1-yl)propylsilane in the presence of toluene solution. The modified material was characterized by FTIR spectroscopy, XRD, and simultaneous DTA/TG analysis. It was found that the chemical bonding takes place between the hydroxyl groups and/or oxygen atoms within the structure of Sepiolite and the silane group of the triethoxy-3-(2-imidazolin-1-yl)propylsilane by releasing the ethoxy groups to the solvent. Thermal decomposition of natural and modified Sepiolites was carried out with a thermogravimetric analyzer. In TG and DTA analysis, during gradual heating in an oxidizing atmosphere, the modified Sepiolite was oxidized, giving rise to significant exothermic peaks. The exothermic peak in the temperature range of 200−650 °C depended on the modifier loading and provided evidence of bond formation on the Sepiolite surface. For natural Sepiolite, a mass loss of 20.43% was observed up to 900 °C, whereas this value increased to 31....
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Adsorption of cationic polyacrylamide onto Sepiolite.
Journal of hazardous materials, 2005Co-Authors: Nalan Tekin, Özkan Demirbaş, Aziz Dinçer, Mahir AlkanAbstract:The adsorption of PAM onto Sepiolite from aqueous solutions has been investigated systematically as a function of some parameters such as calcination temperature of Sepiolite, pH, ionic strength and temperature. The adsorption of cationic polyacrylamide (PAM) increases with pH from 5.50 to 11.00, temperature from 25 to 55 degrees C and ionic strength from 0 to 0.1molL(-1). The Sepiolite sample calcined at 200 degrees C has a higher adsorption capacity than the other calcined samples. Adsorption isotherms of PAM onto Sepiolite have been determined and correlated with common isotherm equations such as Langmuir and Freundlich isotherm models. The Langmuir isotherm model appeared to fit the isotherm data better than the Freundlich isotherm model. The physical properties of this adsorbent are consistent with the parameters obtained from the isotherm equations. The zeta potentials of Sepiolite suspensions have been measured in aqueous solutions of NaCl and different PAM concentrations and pH. From the experimental results: (i) pH strongly alters the zeta potential of Sepiolite, (ii) Sepiolite has an isoelectric point at about pH 6.6 in water and about pH 8 in 250mgL(-1) PAM concentration, (iii) PAM changes the interface charge from negative to positive for Sepiolite. Effect of temperature on adsorption has been quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy and entropy. The dimensionless separation factor (R(L)) has shown that Sepiolite can be used for adsorption of PAM from aqueous solutions.
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ftir and zeta potential measurements of Sepiolite treated with some organosilanes
Microporous and Mesoporous Materials, 2005Co-Authors: Mahir Alkan, Gamze Tekin, Hilmi NamliAbstract:Sepiolite has been treated with some organosilanes including dimethyloctadecylchlorosilane (DMODCS), dimethyldichlorosilane (DMDCS), and 3-aminopropyltriethoxysilane (3-APT). FTIR measurements have been used to discuss the interactions between Sepiolite surface and organosilane molecules. The disappearance of OH stretching peaks of Sepiolite has shown the strong interactions between the surface and organosilane molecules. H-bonds have also been indicated by the frequency shifts of OH stretching vibrations. The changes in the electrokinetic properties of the treated Sepiolite samples have been investigated by following the zeta potential of the particles as a function of pH. The treatment of Sepiolite with 3-APT causes a shift of isoelectronic point (IEP) from 7.8 to 9.7, to a more basic value compared to Sepiolite itself. DMODCS and DMDCS-treated Sepiolite samples have, however, been found to have isoelectronic points in more acidic region than that of Sepiolite, which are 5.2 and 5.6, respectively.
Miguel Angel Rodriguezperez - One of the best experts on this subject based on the ideXlab platform.
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mechanical properties of pmma Sepiolite nanocellular materials with a bimodal cellular structure
Macromolecular Materials and Engineering, 2019Co-Authors: Victoria Bernardo, Frederik Van Loock, Judith Martinde Leon, N A Fleck, Miguel Angel RodriguezperezAbstract:© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Bimodal cellular poly(methyl methacrylate) with micro- and nano-sized (300–500 nm) cells with up to 5 wt% of Sepiolite nanoparticles and porosity from 50% to 75% are produced by solid-state foaming. Uniaxial compression tests are performed to measure the effect of Sepiolite concentration on the elastic modulus and the yield strength of the solid and cellular nanocomposites. Single edge notch bend tests are conducted to relate the fracture toughness of the solid and cellular nanocomposites to Sepiolite concentration. The relative modulus is independent of Sepiolite content to within material scatter when considering the complete porosity range. In contrast, a mild enhancement of the relative modulus is observed by the addition of Sepiolite particles for the foamed nanocomposites with a porosity close to 50%. The relative compressive strength of the cellular nanocomposites mildly decreases as a function of Sepiolite concentration. A strong enhancement of the relative fracture toughness by the addition of Sepiolites is observed. The enhancement of the relative fracture toughness and the relative modulus (at 50% porosity) can be attributed to an improved dispersion of the particles due to foaming and the migration of micro-sized aggregates from the solid phase to the microcellular pores during foaming.
Sridhar Komarneni - One of the best experts on this subject based on the ideXlab platform.
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Sepiolite/TiO2 and metal ion modified Sepiolite/TiO2 nanocomposites: synthesis, characterization and photocatalytic activity in abatement of NOx gases
Applied Clay Science, 2019Co-Authors: D. Papoulis, K. Somalakidi, N. Todorova, C. Trapalis, Dionisios Panagiotaras, Dimitra Sygkridou, Elias Stathatos, E. Gianni, A. Mavrikos, Sridhar KomarneniAbstract:Abstract Un-exchanged and Zn or Cu ion exchanged samples of a newly discovered Sepiolite clay from Greece were combined with nanophase anatase titania for the synthesis of Sepiolite based nanocomposites and tested for oxidation of NOx gases. The Zn or Cu ion exchanged clay was modified by replacing the exchangeable cations with Zn or Cu ions. Three separate single phase Sepiolite samples were prepared, i.e., the Sepiolite (S), the one modified with Zn (Zn-S) and the one modified with Cu (Cu-S). Additionally, three nanocomposites were synthesized combining the above three Sepiolite samples with TiO2 in weight ratios of 30:70 and named S-TiO2, Zn-S-TiO2 and Cu-S-TiO2, respectively by depositing TiO2 (anatase) on the Sepiolite surfaces using titanium isopropoxide as a precursor under hydrothermal treatment at 180 °C. The phase composition, particle morphology and physical properties of the Sepiolite samples and the nanocomposites were characterized by XRD, ATR-FTIR, TEM, DRS-UV–Vis and N2-sorption/desorption analyses. The photocatalytic activity of all the clay mineral-titania nanocomposites was examined in the decomposition NOx gases. Sepiolite and especially Zn modified Sepiolite based nanocomposites showed better photocatalytic activity for the oxidation of NOx gases compared to that of reference photocatalyst titania P25 under UV-light irradiation.
