Selective adsorption and release of cationic organic dye molecules on mesoporous borosilicates

Mesoporous materials can play a pivotal role as a host material for delivery application to a specific part of a system. In this work we explore the selective adsorption and release of cationic organic dye molecules such as safranine T (ST) and malachite green (MG) on mesoporous borosilicate materials. The mesoporous silica SBA-15 and borosilicate materials (MBS) were prepared using non-ionic surfactant Pluronic P123 as template via evaporation induced self-assembly (EISA) method. After template removal the materials show high surface areas and in some cases ordered mesopores of dimensions ca. 6–7 nm. High surface area, mesoporosity and the presence of heteroatom (boron) help this mesoporous borosilicate material to adsorb high amount of cationic dye molecules at its surface from the respective aqueous solutions. Furthermore, the mesoporous borosilicate samples containing higher percentage adsorbed dyes show excellent release of ST or MG dye in simulated body fluid (SBF) solution at physiological pH = 7.4 and temperature 310 K. The adsorption and release efficiency of mesoporous borosilicate samples are compared with reference boron-free mesoporous pure silica material to understand the nature of adsorbate–adsorbent interaction at the surfaces.     

Near infrared and mid infrared investigations of adsorbed phenol on HDTMAB organoclays

X-ray diffraction patterns (XRD), infrared Spectroscopy (IR) and near infrared spectroscopy (NIR) have been used to measure the adsorption of phenol on untreated montmorillonite and on hexadecyltrimethylammonium bromide (HDTMAB) modified montmorillonite. The mid infrared spectra indicate that both the surfactant molecule and phenol enter the interlayer of organoclays, replacing the interlayer cations. The higher concentration surfactant leads to a decrease in wavenumber of the bands of organoclays and to increase in intensity. The near infrared spectra (9000–4000 cm^?1) show a prominent band 8260 cm^?1, assigned to the combination result of the CH stretching vibrations of high concentration surfactant and absorbed phenol. The main band observed at 7090 cm^?1 is assigned to the first fundamental overtone of the OH stretching vibrations at 3415 cm^?1 for organoclay. The organoclays are characterised by prominent bands situated between 5900 and 5700 cm^?1. Both the higher concentration of organic molecules and adsorbed phenol causing the near infrared spectra of organic clays to be more complex for spectra in the region from 4700 to 5500 cm^?1. The main band of 4535 cm^?1 for montmorillonite shifts towards the lower wavenumber sites for higher concentration organoclay. The intensity of near infrared spectra generally rises with the value of surfactant concentration increasing, showing certain regularity. It is concluded that phenol is adsorbed to significantly greater amounts on the higher concentration organoclays.     

Fabrication and characterization of a zirconia/multi-walled carbon nanotube mesoporous composite

A zirconia/multi-walled carbon nanotube (ZrO₂/MWCNT) mesoporous composite was fabricated via a simple method using a hydrothermal process with the aid of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy (TEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the as-made samples. The cubic ZrO₂ nanocrystallites were observed to overlay the surface of MWCNTs, which resulted in the formation of a novel mesoporous–nanotube composite. On the basis of a TEM analysis of the products from controlled experiment, the role of the acid-treated MWCNTs and CTAB was proposed to explain the formation of the mesoporous–nanotube structure. The as-made composite possessed novel properties, such as a high surface area (312 m² · g^? 1) and a bimodal mesoporous structure (3.18 nm and 12.4 nm). It was concluded that this composite has important application value due to its one-dimensional hollow structure, excellent electric conductivity and large surface area.     

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.     

Temperature effects on the fracture behavior and tensile properties of silane-treated clay/epoxy nanocomposites

We investigated the effects of clay silane treatment on the fracture behaviors of clay/epoxy nanocomposites by comparing the compliance, critical fracture load, and fracture toughness of silane-treated samples with those of untreated samples. The fracture toughnesses of untreated and silane-treated clay/epoxy nanocomposites were 8.52 J/m² and 15.55 J/m², respectively, corresponding to an 82% increase in fracture toughness after clay silane treatment. Tensile tests were performed at ?30 °C, 25 °C, 40 °C, and 70 °C. Tensile strength and elastic modulus were higher at ?30 °C than at 25 °C for both samples. However, the tensile properties decreased as temperature increased for both samples. In particular, at 70 °C, the tensile properties were less than 10% of the original value at room temperature, independent of surface treatment. The fracture and tensile properties of silane-treated clay/epoxy nanocomposites increased due to good dispersion of the clay in epoxy and improvement in interfacial adhesive strength between epoxy and clay layers.     

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.     

Preparation and characterization of carbon/montmorillonite composites and nanocomposites from waste bleaching sodium montmorillonite clay

Waste bleaching sodium montmorillonite clay was used to prepare carbon/clay nanocomposites and composites by calcination in a reducing atmosphere. The main purpose of this study was to determine the influence of the calcination temperature and solvent washing in the material structure and its adsorption properties. X-ray diffraction patterns detected the nanocomposite formation only in the samples calcinated at 350 °C, whose structures were also described by Fourier transform infrared spectra. SEM images showed that all the samples were composed of various agglutinated grains and the non-washed sample calcinated at 350 °C presented the highest carbon recovery as its surface was the smoothest one, as confirmed by thermogravimetry curve. As a result of this higher carbon content, its methylene blue and gasoline adsorption capacities were the highest, albeit a bit lower in comparison to activated carbon due to the hydrocarbon formation onto sample surface. Finally, BET and BJH studies showed that porosity should also be improved in order to achieve higher adsorption values.     

Extremely high surface area of ordered mesoporous MCM-41 by atrane route

Silatrane synthesized from inexpensive oxide precursor, silica and TEA was used as the precursor for MCM-41 synthesis at low temperature because of its stability in aqueous solutions. Using cationic surfactant hexadecyltrimethyl ammonium bromide (CTAB) as a template, the resulting meso-structure mimics the liquid crystal phase. Varying the surfactant concentration, ion concentration and temperature of the system, changes the structure of the liquid crystal phase, resulting in different pore structures and surface area. After heat treatment, very high surface area mesoporous silica was obtained and characterized using XRD, BET and TEM. XRD and TEM results show a clear picture of hexagonal structure. The surface area is extraordinarily high, up to more than 2400 m² g⁻¹ at a pore volume of 1.29 cm³ g⁻¹. However, the pore volume is up to 1.72 cm³ g⁻¹ when the surface area is greater than 2100 m² g⁻¹.     

Performance of phosphoric acid activated montmorillonite as buffer materials for radioactive waste repository

In this study, the performance of phosphoric acid activated montmorillonite (PAmmt) was evaluated by cesium ions adsorption experiments. The PAmmt samples were obtained by activating with 1, 3 and 5 mol L^?1 of phosphoric acid, respectively under reflux for 3, 12, and 24 h. Experimental results demonstrated that the treatment of raw K-10 montmorillonite with phosphoric acid increased the materials’ affinity for Cs uptake and no significant amount of suspension solids were produced. A relatively insignificant variation in the CEC value was observed. Furthermore, PAmmt also showed high adsorption selectivity toward Cs ions. The improved sorptive properties were mainly related to the increased surface area and the relatively higher surface charge density. Increased specific surface area was the resulted from partial decomposition of lamellar structure of mmt; while the higher surface charge density was caused by the protonation of octahedral Al–OH sites during the acid activation. Generally speaking, stronger acid concentration and longer activation times would produce relatively more decomposed PAmmt particles. However, as the activation exceeds 3 h, the precipitation of Si⁴⁺ would passivate PAmmt against further acid attacks. Based upon our results, acid activation by phosphoric acid could produce PAmmt samples with high sorption capacity and selectivity, and good structural integrity, which are beneficial to be used at radioactive waste repository.     

Using response surface methodology for modeling and optimizing tensile and impact strength properties of fiber orientated quaternary hybrid nano composite

In current study, weight percentage of nano silica and nano clay and also fiber orientation have been chosen as independent variables and the affect of these variables on tensile and izod impact strength of epoxy/glass fiber/SiO₂/clay hybrid laminate composite has been investigated. Central composite design (CCD) which is subset of response surface methodology has been employed to present mathematical models as function of physical factors to predict tensile and impact behavior of new mentioned hybrid nano composite and also optimizing mentioned mechanical properties. Totally 20 experiments were designed with 6 replicates at center point. The maximum and minimum value of tensile strength were 450.90 MPa and 158.16 MPa which occurred in design levels 1 and 14 respectively, also the maximum and minimum of izod impact strength were 10.47 kJ/m² and 2.56 kJ/m² which occurred in design levels 13 and 14 respectively. The optimization results using optimization part of Minitab software showed that the best tensile strength was obtained 488.53 MPa and occurred in 3.5 wt% of nano silica, 1.1 wt% of nano clay and 9° of fiber orientation and after preparing and testing five samples average value of tensile strength was obtained about 480 MPa. Also the results showed that the best impact strength obtained from software was 11.35 kJ/m² and occurred in 4.03 wt% of nano clay, 5 wt% of nano silica and 0° of fiber orientation. The optimization results also showed that tensile and impact strength at optimum values improved up to 6.4% and 203.5% compared to level 1 and 14 and 6.02% and 303.6% compared to level 13 and 14 respectively. In addition, the fracture surface morphologies of the quaternary nano composites were investigated by scanning electron microscopy (SEM).     

Evidence of ammonium ion-exchange properties of natural bentonite and application to ammonium detection

Ammonium exchange with hybrid PVC–bentonite (mineral montmorillonite clay) thin film was revealed using FTIR spectroscopy, EDX, cyclic voltammetry and electrochemical impedance spectroscopy. The effect of ammonium exchange on the charge transfer resistance of PVC–bentonite hybrid thin film was attributed to a modification of the intersheet distance and hydration of bentonite crystals.The obtained impedimetric ammonium sensor shows a linear range of detection from 10^? 4 M to 1 M and a detection limit around 10^? 6 M.     

Formation of cobalt hollow nanospheres via surfactant-assisted hydrothermal progress

In the paper we present the synthesis of Co hollow nanospheres by surfactant-assisted hydrothermal method at mild condition. The XRD pattern indicates the sample is hexagonal close-packed (hcp) Co with cell constants a = 2.512 Å and c = 4.102 Å. The Co hollow nanospheres have the outer diameter of about 50–200 nm with the thin wall of 10–20 nm. Room temperature magnetic measurement of the Co hollow nanospheres demonstrates its enhanced ferromagnetic property. The surfactant CTAB might play a vital role in the formation of the hollow Co nanospheres, and simply adapting different reaction temperatures can control the size of these hollow nanospheres. The possible formation mechanism was also discussed.     

Effect of groups difference in surfactant on solubilization of aqueous phenol using MEUF

Micellar-enhanced ultrafiltration (MEUF) was used to remove phenol from simulant aqueous solutions. The effect of groups difference of cationic surfactant on the solubilization of phenol was investigated through orthogonal experiment, namely, surfactants with the same length of hydrocarbon chain but different hydrophilic head group and vice versa. The effects on the solubilization of phenol of various operating parameters in the practical application of MEUF with OTAB were studied, including surfactant concentration, electrolyte concentration, feed phenol concentration, operating pressure, temperature, respectively. The results showed that the rejection of phenol increased in the order as follows: cetyltrimethylammonium bromide (CTAB) < octadecyl trimethyl ammonium bromide (OTAB) < cetylpyridinium chloride (CPC). With the introduction of feed surfactant concentration, the retention recovery of phenol increased. Electrolyte concentration, feed phenol concentration, operating pressure and temperature all had a slight influence on the retention of phenol.     

Low temperature synthesis of nanocrystalline magnesium aluminate with high surface area by surfactant assisted precipitation method: Effect of preparation conditions

A surfactant assisted co-precipitation method was employed for the low temperature synthesis of magnesium aluminate spinel with nanocrystalline size and high specific surface area. Pluronic P123 triblock copolymer and ammonia solution were used as surfactant and precipitation agent, respectively. The prepared samples were characterized by thermal gravimetric and differential thermal gravimetric analyses (TG/DTG), X-ray diffraction (XRD), N₂ adsorption (BET) and transmission electron microscopy (TEM) techniques. The effects of several process parameters such as refluxing temperature, refluxing time, pH, P123 to metals mole ratio (P123/metals) and calcination temperature on the structural properties of the samples were investigated. The obtained results showed that, among the process parameters pH and refluxing temperature have a significant effect on the structural properties of samples. The results revealed that increase in pH from 9.5 to 11 and refluxing temperature from 40 °C to 80 °C increased the specific surface area of prepared samples in the range of 157–188 m² g^?1 and 162–184 m² g^?1, respectively. The XRD analysis showed the single-phase MgAl₂O₄ was formed at 700 °C.     

Voltammetric behaviour of nitroxazepine in solubilized system and biological fluids

This study reports the development and validation of sensitive and selective assay method for the determination of the antidepressant drug in solubilized system and biological fluids. Solubilized system of different surfactants including cationic, anionic and non-ionic influences the electrochemical response of drug. Addition of cationic surfactant cetrimide to the solution containing drug enhances the peak current signal while anionic and non-ionic showed an opposite effect. The current signal due to reduction process was function of concentration of nitroxazepine, pH, type of surfactant and preconcentration time at the electrode surface. The reduction process is irreversible and adsorption controlled at HMDE. Various chemical and instrumental parameters affecting the monitored electroanalytical response were investigated and optimized for niroxazepine hydrochloride determination. The proposed SWCAdSV and DPCAdSV methods are linear over the concentration range 2.0 × 10^-7– 5.0 × 10^-9 mol/L and 6.1 × 10^-7– 1.0 × 10^-8 mol/L with detection limit of 1.62 × 10^-10 mo/L and 1.4 × 10^-9 mo/L respectively. The method shows good sensitivity, selectivity, accuracy and precision that makes it very suitable for determination of nitroxazepine in pharmaceutical formulation and biological fluids.     

Influence of thermal conditions on the tensile properties of basalt fiber reinforced polypropylene–clay nanocomposites

In this paper, a comparative study on the tensile properties of clay reinforced polypropylene (PP) nanocomposites (PPCN) and chopped basalt fiber reinforced PP–clay nanocomposites (PPCN-B) is presented. PP matrix are filled with 1, 3 and 5 wt.% of nanoclays. The ultimate tensile strength, yield strength, Young’s modulus and toughness are measured at various temperature conditions. The thermal conditions are included the room temperature (RT), low temperature (LT) and high temperature (HT). The basal spacing of clay in the composites is measured by X-ray diffraction (XRD). Nanoscale morphology of the samples is observed by transmission electron microscopy (TEM). Addition of nanoclay improves the yield strength and Young’s modulus of PPCN and PPCN-B; however, it reduces the ultimate tensile strength. Furthermore, the addition of chopped basalt fibers to PPCN improves the Young’s modulus of the composites. The Young’s modulus and the yield strength of both PPCN and PPCN-B are significantly high at LT (−196 °C), descend at RT (25 °C) and then low at HT (120 °C).     

Preparation and characterization of LiFe1/2Ni1/2VO4

A layered ceramic oxide, LiFe_1/2Ni_1/2VO₄ has been prepared using solid-state reaction technique. The preparation conditions have been optimized using thermogravimmetric analysis (TGA) studies. The formation of the material sample under the reported condition has been confirmed by X-ray diffraction (XRD) analysis. XRD analysis indicates the crystal structure to be orthorhombic with lattice parameter: a = 3.5637 Å, b = 17.7486 Å, c = 12.2884 Å. The phase morphology and surface properties studied using scanning electron microscopy (SEM), suggest a polycrystalline texture with reasonable number of the voids. Complex impedance analysis of the sample has indicated: (i) conduction due to bulk contribution at T ≤ 200 °C, (ii) the presence of grain boundary effects at T ≥ 200 °C, (iii) negative temperature coefficient of resistance (NTCR) behaviour and (iv) evidence of temperature dependent electrical relaxation phenomena in the sample. The DC conductivity (σ_DC) shows typical Arrhenius behaviour when observed as a function of the temperature. The activation energy value has been estimated to be 0.42 eV. σ_DC, as evaluated from complex impedance spectrum, shows a jump of nearly ∼4 orders of magnitude in the value at higher temperature when compared to that of the room temperature value. AC conductivity spectrum obeys Jonscher's universal power law. The results of σ_AC as a function of frequency are also discussed.     

Low temperature synthesis of nanocrystalline calcium aluminate compounds with surfactant-assisted precipitation method

Nanocrystalline calcium aluminates with different CaO:Al₂O₃ and surfactant/metal ion molar ratios were prepared by wet chemical synthesis method using Poly (ethylene glycol)-block-poly(propylene glycol)-block poly(ethylene glycol) (PEG–PPG–PEG, MW:5800) as surfactant. X-ray diffraction (XRD) and N₂ adsorption–desorption results showed that the increase in CaO:Al₂O₃ ratio decreased the specific surface area and increased the particle sizes of prepared samples while the surfactant/metal ion molar ratios were kept constant. These analyses also declared that for the sample with CaO:Al₂O₃ = 1:2 (CA2) addition of polymeric surfactant increased the specific surface area and decreased the crystallite size. Scanning electron microscopy (SEM) results confirmed that size of particles for CaO:Al₂O₃ = 1:6 (CA6) sample are smaller than CA2. Transmission electron microscopy (TEM) revealed no particular particle shape for the CA2 sample but it showed the high degree of crystallinity and single phase for the prepared sample at 1100 °C.     

Effects of soluble surfactants on the Langmuir monolayers compressibility: A comparative study using interfacial isotherms and fluorescence microscopy

Langmuir monolayer isotherms and fluorescence microscopy (FM) techniques have been used to study the effect of two soluble surfactants on the methyl octadecanoate monolayer's compressibility at the air/water interface. The combination of these two techniques allows one to bridge the mechanical and morphological properties of the monolayer at different surfactant subphase concentrations. Our results show that the presence of sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium bromide (DTAB) affects the monolayer elasticity differently. In addition, the outcome of this study emphasizes the role of the cationic and anionic surfactants on the monolayer compressibility. In fact, their effect was found to be primly depending on the monolayer thermodynamic situation. The isotherms of the monolayers at different surfactant concentrations underneath the monolayer preserve the characteristics behavior of the monolayer as imaged by FM. The calculated monolayer compressibility shows two different trends depending on the monolayer pressure and the surfactant type. A decreasing compressibility as a function of SDS concentration was found at pressure π = 5 mN/m, while no noticeable effect was found due to DTAB. At π = 10 mN/m both surfactants convert the monolayer from rigid to soft monolayer. Such characteristic behavior of the monolayer has been confirmed by FM.     

Characterization of sodium dodecyl sulfate modified iron pillared montmorillonite and its application for the removal of aqueous Cu(II) and Co(II)

Anionic surfactant modified Fe-pillared montmorillonites were prepared by Fe-hydrate solution and sodium dodecyl sulfate (SDS) solution. These organo–inorgano complex montmorillonites were divided into three types (CM1, CM2 and CM3) depending on different intercalation processes. X-ray diffraction spectra, the Fourier transform infrared (FTIR) spectra were used to analyze the structure of the raw and modified montmorillonites. X-ray photoelectron spectra of the simples have been studied to determine spectral characteristics to allow the identification of Fe(III) hydroxide. The specific surface area of the host montmorillonite (M0) is 73.2 m²/g, while for the modified montmorillonites it is 114.0 m²/g, 117.2 m²/g, and 115.8 m²/g, respectively. The mesopore volumes of the montmorillonites decrease after modification. Ions of copper and cobalt were selected as adsorbates to evaluate the adsorption performance of each montmorillonite. The adsorption data was analyzed by both Freundlich and Langmuir isotherm models and the data was well fit by the Langmuir isotherm model. The adsorption was efficient and significantly influenced by metal speciation, metal concentration, contact time, and pH. Higher adsorption capacity of the modified montmorillonites were obtained at pH 5–6. The results of desorption indicated that the metal ions were covalently bound to the modified montmorillonites.