Correlation between eletrokinetic mobility and ionic dyes adsorption of Moroccan stevensite

This study aims at establishing a correlation between the electrical charge of Moroccan stevensite particles and ionic dyes adsorption. The electrophoretic mobility, (Ue), of the stevensite particles in water, was measured at pH 2.5–12 by microelectrophoresis. At pH between 2.5 and 8, Ue remained constant (Ue = − 1.6 10− 8 m2/(V s)), as resulting from the permanent charge of the clay mineral planar surfaces. At pH > 8, the magnitude of electrophoretic mobility increased (Ue = − 2.7 10− 8 m2/(V s)) due to the deprotonation of silanol groups on the surfaces. The anionic Orange G adsorption at the clay mineral–water interface was negligible whereas the methylene blue cations were strongly adsorbed due to the electrostatic attraction

Synthesis, characterization and photocatalytic activity of TiO2 supported natural palygorskite microfibers

This study deals with the synthesis of TiO2 supported Moroccan palygorskite fibers and their use as photocatalyst for the removal of Orange G pollutant from wastewater. The TiO2-palygorskite nanocomposite synthesis was accomplished according to a colloidal route involving a cationic surfactant as template (hexadecyltrimethylammonium bromide) assuring hence organophilic environment for the formation of TiO2 nanoparticles. The clay minerals samples were characterized before and after functionalization with TiO2. Anatase crystallizes above ca. 450 °C and remarkably remains stable up to 900 °C. In contrast, pure TiO2 xerogel obtained from titanium tetraisopropoxide (TTIP) showed before calcination a nanocrystalline structure of anatase. By increasing the temperature, anatase readily transforms into rutile beyond 600 °C. The remarkable stability at high temperature of anatase particles immobilized onto palygorskite microfibers was due to the hindrance of particles growth by sintering. Homogeneous monodisperse distribution of anatase particles with an average size of 8 nm was found by TEM and XRD onto palygorskite fibers. This anatase particle size remains below the nucleus critical size (ca. 11 nm) required for anatase–rutile transition. The TiO2 supported palygorskite sample annealed in air at 600 °C for 1 h exhibits the highest photocatalytic activity towards the degradation of Orange G compared to nanocomposite samples prepared under different conditions as well as pure TiO2 powders obtained from the xerogel route or commercially available as Degussa P25

Supported Photocatalyst Based on CuO–TiO2/Palygorskite Nanocomposite Material for Wastewater Treatment

This study deals with the immobilization of mixtures of two semiconductor oxides CuO and TiO2 on fibrous palygorskite clay mineral in order to evaluate their photocatalytic activity for removing Orange G dye as model pollutant from aqueous solutions. The elaboration of CuO–TiO2/Palygorskite nanocomposites was carried out by impregnation with Cu2+ of before hand synthesized TiO2 supported palygorskite (Pal) followed by air annealing for 5 h at 550 °C. In the composite materials, different CuO to CuO + TiO2 molar ratios were used in order to obtain a CuO content in the range 13–30 mol.%. XRD, SEM and TEM equipped with elemental EDS analysis are concordant for showing the crystallization of anatase TiO2 along with CuO whose average size of nanoparticles (NPs) are in the range 6 to 20 nm as determined by TEM. By increasing the CuO content the average size of this oxide remains constant at about 10 nm while that of TiO2 NPs is slightly decreasing from 8.4 to 5.1 nm. Both oxide NPs were successfully attached on palygorskite fibers where they form CuO–TiO2 heterojunctions (grain boundaries like). The CuO–TiO2/Pal supported photocatalyst containing 23% of CuO was found to be the most photoactive material but itremained less active than TiO2/Palygorskite supported photocatalyst. The photocatalytic activity of the mixed nanocomposites is not readily correlated with only one of their main features as CuO content or the average crystallite size of functional oxides indicating that if there are synergistic effects there are also antagonistic effects in particular for high CuO contents

Electrokinetic and ionic dyes adsorption studies of Moroccan stevensite Jbel Rhassoul clay

This study aims at establishing correlation between the nature of electrical charge of morocan stevensite Jbel Rhassoul clay particles and ionic dyes adsorption phenomenon. The electrical charges of the clay mineral particles were assessed by measuring zeta potential (z) using micro electrophoresis technique. Measurements were carried out onto aqueous clay dispersions by varying the pH in the range 2.5 – 12 with additions of HCl or NaOH. On the whole, the electrical charges of stevensite particles remain negative in the whole pH range. Nevertheless, depending on the pH values, two behaviours were observed. For pH ranging from 2 to around 8, the negative electrical charge remains constant (z = - 20 mV) and corresponds to permanent charges of basal surfaces formed of –O-Si-O- groups insensitive to pH variation. Beyond pH = 8, the electrical charge increases (z = - 35 mV) as a result of deprotonation of silanol edge groups. Ionic dyes adsorption experiments show that anionic orange G adsorption is negligible whereas that of cationic methylene blue is greater due to columbic interactions. In accordance with eletrokinetic measurements, the methylene blue adsorption capacity onto stevensite particles significantly increases beyond pH » 8 due to the increase of the whole electrical charge of stevensite particles evolved by silanol edge sites deprotonation

On the key role of the surface of palygorskite nanofibers in the stabilization of hexagonal metastable β-Ag2CO3 phase in palygorskite-based nanocomposites

This study reports an original remarkable effect of fibrous palygorskite clay mineral in the stabilization at the ambient temperature of the metastable hexagonal β-phase of Ag2CO3 along with the stable monoclinic one (m-Ag2CO3) and the refinement of their particles size (≈5–10 nm). These structural and microstructural features likely arise owing to heterogeneous nucleation induced by the surface of palygorskite fibers between CO32– anions in solution and Ag+ exchanged palygorskite (Ag+-Pal) as reactants kept maturing for short periods, which should not exceed 1 h. Besides, the phase composition of Ag2CO3 supported on palygorskite, namely β- and m-structures can be monitored by carrying on appropriate low temperature treatments under CO2 atmosphere coupled with aging during several months in such a way that either pure β or m single-phases as well as biphased mixtures with controlled composition can be obtained. Taking into account experimental results and literature data, a growth mechanism is discussed

Influence of the crystal structure of Ag2CO3 on the photocatalytic activity under visible light of Ag2CO3-Palygorskite nanocomposite material

In a companion paper, it has been demonstrated the remarkably beneficial effect of palygorskite clay (Pal) fibers as support material coupled to appropriate thermal treatments and aging under CO2 atmosphere in monitoring the phase composition of Ag2CO3-Pal composite. In this new nanocomposite material, the structure of the functional component Ag2CO3 can be controlled from 100% stable monoclinic (m) to 100% metastable hexagonal β through an adjusted mixture of m- and β-Ag2CO3. The present study deals with the assessment of the visible photocatalytic properties of these various nanocomposite materials towards the removal of Orange G dye from aqueous solutions. It was found that the Ag2CO3-Pal nanocomposite in which Ag2CO3 was single-phased and crystallized with the stable monoclinic structure was more active than the one crystallizing entirely with the metastable β-Ag2CO3 structure. Nevertheless, the composite material containing a mixture of both Ag2CO3 phases with a relative content of 32% of β- and 68% of m-phase was found to be the most photoactive compound of the series. This behavior reveals likely a synergetic effect between both phases in the photocatalytic degradation of the dye under visible light

Enhanced RCP and large inverse magnetocaloric effect of CoFe2_2O4_4 nanoparticles synthesized by auto-combustion method

This work focuses on the microstructure, magnetic properties and magnetocaloric effect of CoFe$_2$O$_4$ (CFO) nanoparticles elaborated by sol-gel auto combustion method. The XRD investigation indicates that CFO is crystallized in a cubic spinel structure and the SEM micrograph shows a fine quasi-spherical with an average grain sizes of 160 nm. The temperature dependence of the Raman spectra reveals the ferromagnetic to paramagnetic (FM-PM) transition started from 723 K and the magnetization versus temperature measurements shows the Curie temperature located at T$_{\rm C}$ = 785 K. Large value of magnetocaloric temperature change of $\Delta$T =11.2 K with a high RCP of 687.56 J Kg$^{-1}$ are achieved indirectly via the Maxwell approach making our CFO nanopowder suitable candidate for both environmentally friendly magnetic refrigeration and medical applications at ambient temperature

Mineralogical and Physico-Chemical Characterizations of Ferruginous Beidellite-Rich Clay from Agadir Basin (Morocco)

The mechanism of formation of detrital, beidellite-rich clay occurring in the Agadir basin (Morocco) is well documented, but its detailed characterization is incomplete which limits its application. The aim of the present study was to provide further details of the mineralogical and physico-chemical characteristics of this clay. Bulk raw clay and its Na+-saturated, <2 mm fraction were characterized using chemical, structural, and thermal techniques. Measurements of induced streaming potential (e.g. particle charge) and of specific surface area and porous volume are reported. The raw clay contained carbonate and quartz as associated minerals along with phyllosilicates (<2 mm particle size). X-ray diffraction and scanning electron microscopy analyses showed that the <2 mm fraction was dominated by a dioctahedral smectite. Because dehydroxylation of this mineral occurred at 510ºC, and because it re-expanded in ethylene glycol after Li+-saturation followed by heating at 240ºC for 24 h, the mineral was shown to be a beidellite rather than montmorillonite. This assertion was further supported by 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectra showing predominantly negative charges in the tetrahedral sheets due to notable Al-for-Si substitutions. The chemical composition of the <2 mm fraction showed an Fe2O3 content which was ~7.52 wt.% greater than those of other beidellite occurrences but not so much that it would be identified as a nontronite. The absence of stretching and bending absorption bands corresponding to characteristic (Fe2OH) units in mid-infrared spectra and their corresponding fundamental overtones or combination bands in near-infrared spectra supported this notion. The structural formula of the beidellite in the present study was determined to be (Si7.51Al0.49)(Al2.99Fe0.68Mg0.33) (Ca0.03Na0.54Mg0.11)O20(OH)4, having dioctahedral ferruginous characteristics with almost 60% of the negative charge found in tetrahedral sheets. The cation exchange capacity determined from the structural formula was ~108 meq/100 g. The specific surface area and total pore volume were ~82.2 m2/g and 0.136 cm3/g, respectively. Interestingly, a detrital rather than a hydrothermal-alteration origin, as reported for other beidellite occurrences, explains its natural abundance and emphasizes the great interest in it

Synthèse, caractérisations et tests photocatalytiques d’un matériau argileux d’origine naturelle à base de beidellite fonctionnalisée par TiO2

Cette étude porte sur la fonctionnalisation par TiO2 d’une argile marocaine de type beidellite et sur l’évaluation de son activité photocatalytique pour l’élimination d’un colorant anionique : l’orange G (OG), utilisé dans l’industrie textile. Les échantillons argileux ont été caractérisés, avant et après fonctionnalisation, par DRX, MEB et MET couplé à l’analyse EDX, TG-ATD, FTIR, ICP et RMN du solide. La beidellite est aluminifère, dioctaédrique, de formule chimique (Si7,57Al0,43)8 (Al2,75Fe0,73Mg0,38Ti0,14)4 (Na0,37K0,23Mg0,01) avec une CEC, une surface spécifique et un volume poreux total de l’ordre de 48 méq/100 g, 72 m2/g et 0,128 cm3/g respectivement. Les matériaux argileux nanocomposites obtenus sont constitués de nanoparticules de TiO2 (taille moyenne 10 nm) supportées par les feuillets de la beidellite. Leurs surfaces spécifiques sont quasiment du même ordre de grandeur que celle de la beidellite tandis que leurs volumes poreux augmentent pour atteindre 0,226 cm3/g. L’échantillon calciné à 600 ◦C, dans lequel TiO2 est sous forme d’anatase, manifeste une activité photocatalytique remarquable vis-à-vis de l’élimination de l’OG en milieu aqueux