Structure and properties of hybrid PLA nanocomposites with inorganic nanofillers and cellulose fibers

Polylactide reinforced with 3 wt% of organo-modified montmorillonite, 5 wt% of stearic acid-modified calcium carbonate nanoparticles, 15 wt% of cellulose fibers (PLA/MMT, PLA/NCC, PLA/CF) and hybrid composites containing 15 wt% of fibers in addition to montmorillonite (PLA/MMT/CF) or calcium carbonate (PLA/NCC/CF) were prepared and examined. The nanoparticles were dispersed in polylactide almost homogeneously; montmorillonite was exfoliated during processing. T_g of polylactide remained unaffected but its cold crystallization was enhanced; the cold-crystallization behavior of the hybrid composites was dominated by nanofillers nucleating ability. The fibers and calcium carbonate decreased whereas exfoliated montmorillonite improved the thermal stability of the materials. Polylactide, PLA/NCC and PLA/MMT exhibited ability to plastic deformation, although the latter the weakest. Tensile behavior of the hybrid composites was strongly influenced by the fibers and similar to that of PLA/CF. All the fillers increased the storage modulus below T_g; that of PLA/MMT/CF and PLA/NCC/CF was improved with respect to polylactide by 50% and 45%, respectively.     

Synthesis and characterization of HDA/NaMMT organoclay

In this study, the rheologic and colloidal characterizations of sodium montmorillonite (NaMMT) were examined. Hexadecylamine (CH₃(CH₂)₁₅NH₂, HDA) was added to the bentonite water dispersion (2%, w/w) in different concentrations in the range 5.6 × 10⁻⁴−9.4 × 10⁻³ mmol/l. The rheological and electrokinetic behaviour of aqueous montmorillonite dispersions was investigated as a function of solid content and HDA concentration. The basal spacings of the HDA/NaMMT composites were studied by X-ray diffraction. The FTIR spectra were obtained from the modified bentonite products, which revealed the characteristic absorbances after treatment with HDA.     

New Insights to Characterize Mineralogical and Physicochemical Properties of Nanoporous and Nanostructured Bentonites (Montmorillonites)

Bentonite is rich in montmorillonite, which is a nanostructured and nanoporous member of smectite group. Mineralogical and physicochemical properties of bentonites play a key role in choosing appropriate bentonites for different applications. Scanning electron microscopy (SEM) reveals the morphological form and size of mineral phase of the studied bentonite samples. X-ray diffraction (XRD) analysis showed that the studied bentonites predominantly consist of montmorillonites accompanying other impurities such as quartz, calcite, and plagio feldspar. The amount of organic components CHNO (carbon, hydrogen, nitrogen, and oxygen) in the samples was so low that it had no significant effect on the result of XRF analyses. X-ray fluorescence (XRF) analysis showed that there was a large amount of Al₂O₃ in sample ES3 and this large amount of Al₂O₃ indicates a greater amount of montmorillonite in this sample compared to that in sample GH1. Due to a larger amount of CaO, the type of GH1 montmorillonite is Ca-montmorillonite and due to a lower amount of CaO compared to that of Na₂O the type of ES3 montmorillonite is Na-montmorillonite. This study aims at examining a novel insight to characterize bentonites to find out the mineralogical and physicochemical properties of studied samples.     

Adsorption of mercury cation on chemically modified clay

A montmorillonite clay (M) sample from the Amazon region, Brazil, was intercalated with pyridine (Py), dimethyl sulfoxide (DS) and 3-aminopropyltriethoxysilane (APS). The chemically modified montmorillonite (M_P/APS) sample showed modification of its physical-chemical properties including: specific area 41.39 m² g⁻¹ (M) to 198.45 m² g⁻¹ (M_P/APS). Solid-state ²⁹Si CPMAS/NMR of the silylated montmorillonite samples showed Q² and Q³ signals as well as T² and T³ signals. The appearance of T² and T³ signals can be attributed to the grafting of APS to the interlayer surface silanol groups. The natural and modified clays were used for mercury cation adsorption from aqueous solutions at room temperature and pH 3.0. The energetic effects (Δ_intH°, Δ_intG° and Δ_intS°) caused by mercury cation adsorption were determined through calorimetric titrations.     

Flammability,thermal and physical-mechanical properties of cationic polymer/montmorillonite composite on cotton fabric

The flammability, thermal and mechanical properties on cotton fabric were improved by being finished with the composite containing montmorillonite. To this aim, polymer dimethyl diallyl ammonium chloride-allyl glycidyl ether (P_DMDAAC-AGE) was prepared and its structure characterized by Fourier transform infrared (FT-IR) and Nuclear magnetic resonance (¹H NMR). The quaternary ammonium salt copolymer/montmorillonite composite (P_DMDAAC-AGE/MMT) was obtained by polymer intercalation method. The X-ray diffraction (XRD) indicated that the MMT interlayer spacing increased after the polymer intercalation. Composite materials were loaded onto the cotton fabrics by a dip-pad-dry method. The thermo gravimetric analysis (TGA), vertical flame test and limiting oxygen index (LOI) results showed that the thermal and flammability properties of the cotton fabric were improved after it was finished with the composite. Tensile testing revealed an increase on mechanical properties of the finished fabric, but the physical properties hardly changed from the bending length and whiteness results. Scanning electron microscope (SEM) and energy disperse X-ray spectroscope (EDX) results verified the improvement of those properties due to the presence of montmorillonite in the composite.     

Pillared montmorillonite clay as a raw material for the synthesis of β′-sialon

To control the SiO₂/Al₂O₃ ratio in a starting clay material for the synthesis of β′-sialon by the carbothermal nitridation process, montmorillonite was pillared with Al₂O₃. Conversions to sialon of pillared clay (31% Al₂O₃) and reference unpillared montmorillonite (18% Al₂O₃) have been compared. Pillared montmorillonite yielded a mixture of β′-sialon and various oxynitrides and oxycarbides of alumina as intermediate products. Pillared clay transformed faster during annealing than structural components of smectite alone. For the proper thermal treatment and clay/carbon ratio, both pillared and unpillared clays resulted in β′-sialon solid solutions.     

Synthesis and characterization of polyaniline nanorods/Ce(OH)3-Pr2O3/montmorillonite composites through reverse micelle template

Polyaniline (PANI) nanorods/Ce(OH)₃-Pr₂O₃/montmorillonite (MMT) nanocomposites were synthesized via in situ polymerization of aniline monomer through reverse micelle template (RMT) in the presence of montmorillonite and Ce(OH)₃, Pr₂O₃. In the experiment, sulphosalicylic acid was used as dopant, aniline was designated as oil phase and the aqueous solution comprising Ce³⁺ and Pr³⁺ as water phase. The nanocomposites were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetry-differential thermal analysis (TG-DTA). The results showed that PANI nanorods were synthesized in the interlayer spaces of MMT with uniform spherical rare earth nanoparticles. The thermal stability of the nanocomposites prepared was enhanced drastically compared with pure polyaniline.     

Changes in the surfaces on DDOAB organoclays adsorbed with paranitrophenol—An XRD, TEM and TG study

The adsorption of paranitrophenol on organoclays synthesised by the ion exchange of the surfactant molecule dimethyldioctadecylammonium bromide (DDOAB) of formula (CH₃(CH₂)₁₇)₂NBr(CH₃)₂ has been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis. The expansion of the montmorillonite depends on the loading of the montmorillonite with dimethyldioctadecylammonium bromide and is related to the arrangement of the surfactant molecules within the clay interlayer. This expansion is altered by the adsorbed paranitrophenol and is observed in the transmission electron microscopic images of the organoclay with adsorbed paranitrophenol. Changes in the surfactant molecular arrangements were analysed by thermogravimetry. The paranitrophenol is sublimed simultaneously with the loss of surfactant. The dehydroxylation temperature of the montmorillonite is decreased upon adsorption of the paranitrophenol indicating a bonding between the paranitrophenol and the hydroxyl units of the montmorillonite.     

Isotherm,kinetic, and thermodynamic studies on the adsorption behavior of malachite green dye onto montmorillonite clay

ABSTRACT

Systematic batch mode studies of adsorption of malachite green (MG) on montmorillonite clay were carried out as a function of process parameters which include pH, adsorbent dosage, agitation speed, ionic strength, initial MG concentration, and temperature. Montmorillonite was found to have excellent adsorption capacity. Equilibrium adsorption isotherms were measured for the single-component system, and the experimental data were analyzed by using Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm equations. It was found that the Langmuir equation appears to fit the equilibrium data. The monolayer (maximum) adsorption capacity (q_m) was found to be 262.494 mg g^?1 for montmorillonite. The experimental kinetic data were analyzed using the first-order, second-order, Elovich, and intraparticle kinetic models and the second-order kinetic model described the adsorption kinetics accurately for MG. Thermodynamic activation parameters such as ΔG*, ΔS*, and ΔH* of the adsorption of MG on montmorillonite were also calculated.     

Experimental Studies on Swelling and Non-Swelling Bentonites

Swelling and non-swelling properties of bentonite particles play an important role in their performance as well as their applications. Swelling bentonites, containing montmorillonite as the main constituent, are mainly used in drilling fluids, bonding sands in foundry molds, iron ore palletizing, and environmental sealing, while non-swelling ones are primarily used as adsorbents in bleaching earth and heavy metal removal. Experimental studies on 10 natural bentonite samples, namely S1 to S10, were conducted to identify the swelling behavior of the samples. XRD studies showed the presence of nanoporous and nanostructured montmorillonite species along with some other clay and non-clay mineral impurities. XRF studies through the measurement of CaO and Na ₂ O weight percents provided a good measure to determine swelling or non-swelling properties of bentonites. XRD and XRF analyses demonstrated that Na ₂ O in samples S5 to S8 belongs to montmorillonite, which is a clay mineral. The first main peak of montmorillonite in its XRD pattern was another guide in assigning the type of the bentonites. BET surface area measurement was employed to verify the former observations. A higher surface area was measured for swelling bentonites, while the highest surface area of 78 m ²/g was obtained for the swelling S8 bentonite. The studies showed that samples S9 and S10 are non-swelling, samples S4, S7, and S8 are swelling, samples S2, S5, and S6 are swelling/non-swelling, and sample S3 is a non-swelling/swelling bentonite.     

The formation of β′-sialon from a montmorillonite-polyacrylonitrile composite by carbothermal reduction: an NMR,TGA, XRD and EM study

The products of carbothermal reduction in N₂ of a nanocomposite between dodecylammonium-exchanged montmorillonite and polyacrylonitrile (PAN) have been studied by solid-state ²⁷Al and ²⁹SiNMR spectroscopy, X-ray diffraction, transmission electron microscopy and thermogravimetry. Comparison with analogous reactions involving sodium-exchanged montmorillonite and dodecylammonium-exchanged montmorillonite (without PAN) shows that in the presence of PAN, the formation of silica, cordierite or mullite is almost completely suppressed. The only crystalline phase detected between 1000 and 1300 °C was a -sialon, having a much higher SiAl ratio (7.051) than that of the precursor clay (2.441). Reduction of the octahedral AlO₆ begins near 1200 °C, forming increasing amounts of Al(N,O)₄ tetrahedra with temperature, so that by 1600 °C, complete reduction to AlN₄ (i.e. bulk AlN) has occurred. In contrast, reduction of the tetrahedral SiO₄ is appreciable at 1100 °C, and is almost complete (SiN₄ tetrahedra only) by 1200 °C. No intermediate Si(N,0)₄ environments are found. By 1600 °C, only the SiC₄ environment (i.e. bulk SiC) remains. A mechanism is suggested, involving the formation of alternating slabs of an amorphous aluminosilicate and carbon at 1000 °C, followed by diffusion of silicon from the outer regions of the aluminosilicate band towards the centre, and sequential reduction of Si(OSi)₄ and Si(OSi)₃ (OAl) groups.     

Effect of the SiO2/TiO2 ratio on the solid acidity of SiO2-TiO2/montmorillonite composites

SiO₂-TiO₂/montmorillonite composites with varying SiO₂/TiO₂ molar ratios were synthesized and the effect of the SiO₂/TiO₂ ratio on the solid acidity of the resulting composites was investigated. Four composites with SiO₂/TiO₂ molar ratios of 0, 0.1, 1 and 10 were synthesized by the reaction of colloidal SiO₂-TiO₂ particles prepared from alkoxides with sodium-montmorillonite at room temperature. The composites showed slight expansion and broadening of the XRD basal reflection, corresponding to the intercalation of fine colloidal SiO₂-TiO₂ particles into the montmorillonite sheets and incomplete intercalation to form disordered stacking of exfoliated montmorillonite and colloidal SiO₂-TiO₂ particles. The colloidal particles crystallized to anatase in the low SiO₂/TiO₂ composites but remained amorphous in the high SiO₂/TiO₂ composites. The specific surface areas (S_BET) of the composites measured by N₂ adsorption ranged from 250 to 370 m²/g, considerably greater than in montmorillonite (6 m²/g). The pore size increased with decreasing SiO₂/TiO₂ molar ratio of the composites. The NH₃-TPD spectra of the composites consisted of overlapping peaks, corresponded to temperatures of about 190 and 290 °C. The amounts of solid acid obtained from NH₃-TPD were 186-338 μmol/g in the composites; these values are higher than in the commercial catalyst K10 (85 μmol/g), which is synthesized by acid-treatment of montmorillonite. The present sample with SiO₂/TiO₂ = 0.1 showed the highest amount of acid, about four times higher than K10.     

TEM observation of iron oxide pillars in montmorillonite

The microstructures of iron oxide-pillared montmorillonite have been investigated by highresolution transmission electron microscopy. The iron oxide is incorporated in the interlayer space of montmorillonite as Fe₂O₃ crystallites. The crystallites are present in two different morphologies: isolated particles 10 nm long and 4 nm thick, and bands (possibly plates) with a thickness 1 nm running parallel to the basal plane.     

An efficient and robust heterogeneous mesoporous montmorillonite clay catalyst for the Biginelli type reactions

Three component coupling reactions of aldehyde, β-ketoester (or β-diketone) and urea (or substituted urea) were carried out by using acid activated montmorillonite clay (AT-Mont.) catalyst having surface area about 400 m²/g for the facile synthesis of 3,4-dihydropyrimidin-2(1H)-ones via the Biginelli reactions under mild reaction conditions. The activation of montmorillonite clay was carried out with HCl under controlled conditions for generating nanopores (size 2–7 nm) into the matrix. This porous catalyst has promising feature for Biginelli reaction such as easy removal of the catalyst, short reaction time, high yield with 100% selectivity and easy workup procedure. Powder XRD, SEM-EDX, N₂ adsorption, pyridine adsorbed FT-IR and TPD analysis were carried out to characterize the solid porous AT-Mont. The catalysts can be recycled and reused several times without significant loss of their catalytic activity.     

Synthesis and characterization of a PbO2-clay nanocomposite: Removal of lead from water using montmorillonite

The aim of this paper is to present the results obtained with Pb(II) sorption on an Algerian Clay. The experiments were carried out using a batch process. Powder X-rays diffraction patterns (PXRD) prove that in the montmorillonite Pb replaces Na ions. A significant restructuring at the particle scale is observed leading to the disappearance of the d_0 0 1 reflection of the clay at high concentrations of lead. The replacement of hydrated Na with Pb ions influenced significantly the thermal behaviour of the montmorillonite samples with regard to their dehydration and dehydroxilation capacities with a lowering of the water content. A PbO₂-clay composite material with good electrical conductivity is synthesized.     

Montmorillonite/polypyrrole nanocomposites. The effect of organic modification of clay on the chemical and electrical properties

Montmorillonite/polypyrrole (MMT/PPy) nanocomposites, with 15% mass loading of PPy, were prepared by the in situ polymerization of pyrrole in the presence of montmorillonite (MMT) or organo-modified montmorillonite (oMMT) in aqueous solutions containing an oxidant and an anionic surfactant. The morphology of MMT/PPy nanocomposites distinctly differs from that of the untreated MMT as shown by SEM. X-ray photoelectron spectroscopy showed that the MMT/PPy nanocomposite has an MMT-rich surface, whereas the oMMT/PPy nanocomposite surface has a rather organic nature. Due to the organic modification of MMT by the alkylammonium chloride, polymerization of pyrrole at the surface of oMMT is much more efficient in producing a conductive adlayer resulting in an enhancement of conductivity of the oMMT/PPy nanocomposites (1.1 S cm^− 1) compared to MMT/PPy (3.1 × 10^− 2 S cm^− 1). The difference in the behaviour of oMMT/PPy and MMT/PPy is interpreted in terms of surface energy minimization by the alkylammonium ions present at the surface of organo-modified MMT. Indeed, the dispersive contribution to the surface energy (γ_s^d), as determined by inverse gas chromatography at 150 °C, was estimated to be 34.0 mJ/m² for oMMT, much lower than the value of 216 mJ/m² determined for MMT.     

Bi2WO6 quantum dot-intercalated ultrathin montmorillonite nanostructure and its enhanced photocatalytic performance

The kinetic competition between electron-hole recombination and water oxidation is a key limitation for the development of efficient solar water splitting materials. In this study, we present a solution for solving this challenge by constructing a quantum dot-intercalated nanostructure. For the first time, we show the interlayer charge of the intercalated nanostructure can significantly inhibit the electron-hole recombination in photocatalysis. For Bi₂WO₆ quantum dots (QDs) intercalated in a montmorillonite (MMT) nanostructure as an example, the average lifetime of the photogenerated charge carriers was increased from 3.06 μs to 18.8 μs by constructing the intercalated nanostructure. The increased lifetime markedly improved the photocatalytic performance of Bi₂WO₆ both in solar water oxidation and environmental purification. This work not only provides a method to produce QD-intercalated ultrathin nanostructures but also a general route to design efficient semiconductor-based photoconversion materials for solar fuel generation and environmental purification.      

Synthesis and photochemical properties of semiconductor pillared layered compounds

CdS and ZnS mixtures, Fe₂O₃ and TiO₂ pillars were constructed in the interlayer of montmorillonite, layered double hydroxide, H₄Nb₆O₁₇ and H₂Ti₄O₉ by the intercalation reactions. The thicknesses of the semiconductors incorporated were less than 1 nm and the band gap energies of them were slightly larger than those of normal crystalline ones. The photocatalytic activities of the semiconductors incorporated were superior to those of unsupported ones. The incorporation of semiconductors in the interlayers of semiconducting layered compounds such as H₂Ti₄O₉ and H₄Nb₆O₁₇ was much more efficient in enhancing the hydrogen production activity than when an insulator such as montmorillonite and layered double hydroxide was used, since the recombination of photo-induced electrons and holes was depressed by the electron transfer from the incorporated semiconductors to the semiconducting host layer.     

Flower-like hierarchical Sn3O4/montmorillonite nanostructure for the enhanced microwave-induced degradation of rhodamine B

A flower-like hierarchical nanostructure of Sn₃O₄/montmorillonite is first reported in this work. The nanomaterial was prepared by a one-pot hydrothermal synthesis method using tin chloride as the precursor, and the physicochemical characteristics of the material were examined by instrumental analyses. The prepared nanostructure was evaluated as a catalyst in the microwave-induced removal of rhodamine B (RhB). The influences of Sn content, oxidant, time of irradiation, and initial concentration of RhB were investigated. The results showed homogeneously dispersed Sn₃O₄ in a montmorillonite support with a cubic phase, and crystallite size smaller than to Sn₃O₄ was obtained. XPS investigation revealed the Sn₃O₄ phase, which is consistent with the band gap energy of 2.75 eV from UV-DRS measurements. The homogeneous distribution of the Sn₃O₄ nanoparticles influenced the increasing specific surface area of the nanocomposite compared to montmorillonite. The enhanced physicochemical properties significantly enhanced the catalytic activity in microwave induced RhB oxidation, with the degradation efficiency reaching 99.9% after 20 min of treatment. The kinetics of catalytic oxidation were best fitted to the pseudo-second-order equation and obeyed the Langmuir-Hinshelwood kinetics model. Furthermore, the catalytic oxidation condition optimization using a Box-Behnken Design revealed the contribution of oxidant, pH and catalyst dose as influencing factors for the efficiency.     

Performance of montmorillonite/graphene oxide/CoFe2O4 as a magnetic and recyclable nanocomposite for cleaning methyl violet dye-laden wastewater

The purpose of this research was to improve the adsorption properties of montmorillonite (MMT) using graphene oxide (GO) and CoFe₂O₄ magnetic nanoparticles for methyl violet (MV) removal. The surface analyses were done on the fresh and used composite. The Langmuir isotherm had more ability to describe data than other studied models (Freundlich, Redlich–Peterson, and Toth). The maximum adsorption capacity of MV by MMT, MMT/CoFe₂O₄, and MMT/GO/CoFe₂O₄ was computed to be 59.61 mg/g, 91.27 mg/g, and 97.26 mg/g, respectively. Obtained data for all adsobers were more consistent with the pseudo-second-order kinetic model (R² > 0.92). The thermodynamic study showed that the MV adsorption by MMT, MMT/CoFe₂O₄, and MMT/GO/CoFe₂O₄ is spontaneous and exothermic. The ad(de)sorption of MV pollutant was studied up to 10 stages. A textile wastewater sample was treated by using the adsober. The MMT/GO/CoFe₂O₄ magnetic composite demonstrates the high adsorption capacity and suitable reusability toward the MV removal from aqueous media.