Preparation of alginate/vermiculite composite functionalized with silanol group for controlled drug delivery: Effect of CaCl2 concentration, release kinetics, cytotoxicity, and antimicrobial activities

In this study, alginate/vermiculite (Alg/VMT) hydrogel with 3-aminopropyl triethoxysilane (Alg/VSN) and tetraethoxysilane (Alg/VS) synthesized with various concentrations of CaCl2 (10 %-15 %-20 % M) to extend the release of 6-Aminopenicillanic acid (AP). Composites characterized by XRD, FTIR and BET. The result of Alg/VS composite shows an excellent loading of 243.90 mg/g through AP intercalated in the VMT layer. The equilibrium and Kinetic studies indicated that AP adsorption on Alg/VS and Alg/VSN was heterogeneous with chemical interaction. The in-vitro release Alg/VS showed a rapid burst release of 14 % in the first half an hour and only 75 % of the drug remained in the composite. Whereas, the in-vitro release Alg/VSN showed substantially less burst release with the cumulative release of 9 % (in the first 0.5 h). In-vitro release kinetics in the presence of CaCl2 concentrations showed that maximum 19 % of AP released within 12 h. The kinetic release was followed by a controlled release pattern (Korsmeyer-Peppas model) with Fick's law mechanism. The composites behaved as barriers against cell growth and had better biocompatibility against standard strains of Pseudomonas aeruginosa and Methicillin-Resistant Staphylococcus. MTT assay results from per cent cell viability composites modified by silanol groups were 96 % the means samples were nontoxic. The types of newly synthesized composites were able to finely decrease cell toxicity and improve AP release in vitro.

Role of Exchange Cations and Layer Charge on the Dynamics of Confined Water

Describing the dynamic behavior of water confined in clay minerals is a fascinating challenge and crucial in many research areas, ranging from materials science and geotechnical engineering to environmental sustainability. Water is the most abundant resource on Earth, and the high reactivity of naturally occurring hydrous clay minerals used since prehistoric times for a variety of applications means that water-clay interaction is a ubiquitous phenomenon in nature. We have attempted to experimentally distinguish the rotational dynamics and translational diffusion of two distinct populations of interlayer water, confined and ultraconfined, in the sodium (Na) forms of two smectite clay minerals, montmorillonite (Mt) and hectorite (Ht). Samples hydrated at a pseudo one-layer hydration (1LH) state under ambient conditions were studied with quasi-elastic neutron scattering (QENS) between 150 and 300 K. Using a simplified revised jump-diffusion and rotation-diffusion model (srJRM), we observed that while interlayer water near the ditrigonal cavity in Ht forms strong H-bonds to both adjacent surface O and structural OH, H-bonding of other more prevalent interlayer water with the surface O is weaker compared to Mt, inducing a higher temperature for dynamical changes of confined water. Given the lower layer charge and faster dynamics observed for Ht compared to Mt, we consider this strong evidence confirming the influence of the interlayer cation and surfaces on confined water dynamics.

Selective Adsorption of Organic Micro-Pollutants by Smectite Clays Revealed from Atomistic Simulations

In this study, atomistic simulations were carried out to study the difference in the adsorption process between two similar molecules, diazepam and oxazepam, on Na+-montmorillonite. Kinetic and XRD measurements showed a contrasting adsorption mechanism of these two molecules, differing only by the presence/absence of methyl and hydroxyl groups, with a larger adsorption amount and intercalation for the oxazepam. The structural characterization of these molecules was investigated through DFT calculations and showed the vicinity of hydroxyl and carbonyl groups for only the chair conformation of oxazepam compared to the boat conformation. Classical molecular dynamics simulations of diazepam and the two forms of oxazepam on the external surface of Na+-montmorillonite highlighted the better coordination of the oxazepam-chair conformation, compared to its boat counterpart and diazepam. This has been confirmed through DFT calculations, from which a coordination energy that is greater by 10 kcal·mol-1 is observed. This strongly suggests that the experimentally observed intercalation of oxazepam occurs only in the chair form because of the strong coordination with the Na+ cation present in the Na-Mt interlayer. Classical MD simulations of the intercalated oxazepam chair molecule in the Na-Mt interlayer allowed the evaluation of the interlayer spacing d001, which was in very good agreement with the experimental XRD measurement.

Spatial distribution of pharmaceuticals within the particulate phases of a peri-urban stream

Pharmaceutical products (PPs) are consumed worldwide and are continuously released into hydrological environments, but are not efficiently removed by sewage treatment plants. Their occurrence within the dissolved phase has been extensively studied, but only a few articles concern solid matrices. The mechanisms and extent of sorption depend on the properties of both the molecules (degradability, charge, hydrophobicity) and the matrices (clay content, organic matter content), making the spatio-temporal distribution of PPs in natural environments complex and poorly elucidated. To improve our understanding of PP distribution at a catchment scale, this study investigated different groups of molecules with varying solubility and charges, in water, suspended particulate matter, bed-load and pond sediments. The Egoutier stream, which collects the sewage effluents from two health institutions sewage effluents, is a good candidate for this investigation. Results indicate that PP occurrences in the different particulate compartments were mainly regulated by their wastewater occurrences and charges. Particulate phases all along the Egoutier stream were characterized by a limited clay content (i.e. less than 1%) and significant organic carbon content (i.e. between 0.3% and 18.0%) favouring non-specific adsorption. Therefore, neutral PPs, exhibiting higher discharge rates, persistence and hydrophobicities in comparison with cationic and anionic molecules, were the most abundant PPs in the particulate phases of this catchment. In bed-load sediments, global PP spatial distributions reflected discharge sites and sedimentary accumulation zones, mostly that of organic matter. Spatial distributions of the more hydrophobic and persistent PP in the particulate phases thus followed the stream sedimentary dynamic.

Functionalizing non-smectic clay via methoxy-modification for enhanced removal and recovery of oxytetracycline from aqueous media

Kaolinite and methoxy-modified kaolinite were used as novel adsorbents for oxytetracycline (OTC) removal and recovery from aqueous media. Batch adsorption experiments were performed to study the effect of pH, ionic strengths, initial concentration, and contact time on OTC adsorption. The adsorbents were characterized using powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) before and after adsorption. Adsorption of OTC reached its maximum when solution pH increased up to 6 for 0.001 M ionic strength, above which adsorption decreased further when solution pH increased. Freundlich and Langmuir's models best fit the equilibrium data with a strong dependency on OTC adsorption capacity giving its maximum at 36 mg g^-1. Binding is postulated for OTC adsorption on pristine kaolinite as a special case of Hill model with independent binding interaction of OTC adsorption onto the clay that affects the adjacent sites on the pristine kaolinite, in contrast with the adsorption of OTC on methoxy-modified kaolinite. Nitrogen peaks of the XPS spectra indicated changes in the oxidation states of C-N bonds in the N1s peaks by forming tertiary amide C-N and methoxy O-CH₃ bonds which corroborated with the results from FTIR spectra. Removal efficiencies and spectroscopic results indicate that performance on methoxy-modified kaolinite is a promising modification on the clay for recovering antibiotics from wastewater.

Swelling layered minerals applications: A solid state NMR overview

Swelling layered clay minerals form an important sub-group of the phyllosilicate family. They are characterized by their ability to expand or contract in the presence or absence of water. This property makes them useful for a variety of applications, ranging from environmental technologies to heterogeneous catalysis, and including pharmaceutical and industrial applications. Solid State Nuclear Magnetic Resonance (SS-NMR) has been extensively applied in the characterization of these materials, providing useful information on their dynamics and structure that is inaccessible using other characterization methods such as X-ray diffraction. In this review, we present the key contributions of SS-NMR to the understanding of the mechanisms that govern some of the main applications associated to swelling clay minerals. The article is divided in two parts. The first part presents SS-NMR conventional applications to layered clay minerals, while the second part comprises an in-depth review of the information that SS-NMR can provide about the different properties of swelling layered clay minerals.

Adsorption of Pharmaceuticals onto Smectite Clay Minerals: A Combined Experimental and Theoretical Study

The adsorption of two pharmaceuticals, carbamazepine and paracetamol, onto the expandable clay mineral saponite has been studied through the combination of kinetic experiments, X-ray diffraction, and theoretical modeling. Kinetic experiments indicate low adsorption for carbamazepine and paracetamol on expandable smectite clay. Accordingly, X-ray diffraction experiments show that neither compound enters smectite interlayer space. Molecular dynamics simulations were carried out to understand the interactions between the two pharmaceuticals and the saponite basal surface in the presence of Na+ cations. Calculations reveal that paracetamol almost does not coordinate solution cations, whereas a rather low coordination to cation is observed for carbamazepine. As a result, the adsorption onto the clay surface results mainly from van der Waals interactions for both pharmaceuticals. Carbamazepine does adsorb the surface via two configurations, one involving cation coordination, which corresponds to a rather stable adsorption compared to paracetamol. This is confirmed by structural analyses completed with desorption free energy profile.

Use of a clay mineral and its nonionic and cationic organoclay derivatives for the removal of pharmaceuticals from rural wastewater effluents

A Na⁺ exchanged montmorillonite clay (Na-Mt) and its organoclay derivatives prepared with benzyldimethyltetradecylammonium (BDTA) cationic and polyoxyethylene (20)oleyl-ether (Brij-O20) non-ionic surfactants were used for first time at our knowledge as adsorbents the removal diverse pharmaceuticals (PPs) from samples collected in a rural wastewater facility (town of Josnes in France). The selected facility showed a poor efficiency for the elimination of PPs that were permanently release to the environment. Although involving different interactional mechanisms, the whole adsorbents Na-Mt, nonionic Brij-Mt and cationic BDTA-Mt organoclays, could remove the entire PPs of various chemical nature in a low concentration regime (ng L^-1), where electrostatic interactions mainly controlled the adsorption. Thus, the organic PPs cations were preferentially adsorbed onto Na-Mt and Brij_0.4-Mt (with its dual hydrophilic-hydrophobic nature) while anionic PPs showed a bold affinity to BDTA-Mt. The hydrophobic environment generated by the intercalation of surfactants within the interlayer space of organoclays conferred a versatility for the adsorption of numerous PPs through weak molecular forces (Van der Waals and/or pi-pi interactions). The study confirmed the proper efficiency of the studied layered materials including organoclays and emphasized about their promising interests in water remediation strategy.

Laponites® for the Recovery of 133Cs, 59Co, and 88Sr from Aqueous Solutions and Subsequent Storage: Impact of Grafted Silane Loads

In this study, silylated Laponites^® (LAP) were synthetized with various loads of 3-aminopropyltriethoxysilane (APTES) to evaluate their adsorption properties of ¹³³Cs, ⁵⁹Co, and ⁸⁸Sr during single-solute and competitive experiments. The increase in the initial load of APTES increased the adsorbed amount of APTES in the resulted grafted clay. The characterization of LAP-APTES exhibited a covalent binding between APTES and LAP and emphasized the adsorption sites of APTES for each tested load. In comparison with raw LAP, LAP-APTES displayed significantly higher adsorption properties of Co²⁺, Cs⁺, and Sr²⁺. The competitive adsorption of these three contaminants provides a deeper understanding of the affinity between adsorbate and adsorbent. Therefore, Co²⁺ displayed a strong and specific adsorption onto LAP-APTES. Except for Cs⁺, the adsorption capacity was improved with increasing the load of APTES. Finally, the desorption behavior of the three contaminants was tested in saline solutions. Cs⁺ and Sr²⁺ were significantly released especially by inorganic cations displaying the same valence. Conversely, desorption of Co²⁺ was very low whatever the saline solution. LAP-APTES, therefore, presented suitable adsorption properties for the removal of radionuclides especially for Co²⁺, making this material suitable to improve the decontamination of radioactive wastewaters.

Cation-group interaction as the predominant force for adsorption of substituted dinitrobenzenes by smectite clays

Elucidation of the interaction between NACs and smectites is important to the understanding of the potential for transport of nitroaromatic compounds (NACs) in soils and to implementation of NAC-contaminated soil remediation. The adsorption of dinitrotoluene isomers (DNTs) and substituted dinitrobenzenes (SDNBs) by smectite was determined by batch equilibration and characterized by FTIR and XPS, along with molecular dynamics simulations. The adsorption of DNTs differed substantially among the isomers, attributed to the overall degree of nitro deflection relative to the aromatic ring plane. The substituents in SDNBs strengthened the electrostatic interaction between smectite K⁺ and nitro groups, facilitating SDNB adsorption to smectite. The competition between 2,4-DNT and 1,3-DNB, as well as the inclusion complexation of K⁺ by crown ether 18c6e, both reduced 2,4-DNT adsorption to smectite by weakening the K⁺-nitro interaction. All the results demonstrated that the electrostatic interaction between smectite K⁺ and nitro of NACs was the predominant force in mediating their adsorption. This was supported by FTIR spectra that the N-O bands shifted due to the weakening of N-O bonds and strengthening of C-N bonds via the electron transfer to cations. The XPS of smectite further manifested the cation-nitro interactions that the binding energies of K 2p 1/2, K 2p 3/2, and Si 2p shifted higher with 1,3-DNB adsorbed. Molecular dynamics simulations indicated the aromatic planes of 2,4-DNP and 2,4-DNAs were parallel to the basal plane of smectite and the oxygens of nitro groups in the molecules were directly coordinated with smectite K⁺.

Competitive Association of Antibiotics with a Clay Mineral and Organoclay Derivatives as a Control of Their Lifetimes in the Environment

A Na-smectite clay mineral (Na-Mt) was exchanged with two concentrations of benzyldimethyltetradecyl ammonium chloride cationic surfactant up to one time the cation exchange capacity. Nonionic organoclay was prepared with polyoxyethylene (20) oleyl ether (Brij-O20) nonionic surfactant at one concentration. The resulting organoclays displayed lateral layer organization of the surfactants within their interlayer space.. The adsorption properties of these organoclays and the starting raw clay mineral were evaluated for three extensively used antibiotic pharmaceutical products: the amoxicillin (AMX), the sulfamethoxazole (SMX), and the trimethoprim (TRI), recognized as recalcitrant compounds to conventional water treatments and to display a complex behavior for different pH and temperature experimental conditions. Besides showing short half-life time with possible degradation by UV radiation, these antibiotics associated with mineral phases cause serious environmental issues of which the toxic effect can be exacerbated in the presence of other chemical compounds. From the set of data obtained by complementary techniques: UV and Fourier transform infrared spectroscopy, high-performance liquid chromatography coupled with mass spectrometry, and X-ray diffraction, it appears that the nonionic organoclay shows its versatility for the adsorption of individual molecules as well as a pool of antibiotics. The mixing of the three antibiotics showing different electric charged species (cations, anions, and zwitterions) mimics the natural context drives to a deep modification of the adsorption behavior onto the different materials that can act as possible carrier mineral phases in aquatic environment. These competition effects can be measured through the significant decrease of the K _F Freundlich constants for AMX in the presence of other molecules (or electrolytes), whereas TRI and SMX, by their possible association, create a synergistic effect that favors their adsorption on the whole layered materials.