Surface modification of sepiolite with quaternary amines

Soil water solutes reduce the critical micelle concentration of quaternary ammonium compounds

Quaternary alkyl ammonium compounds (QAACs) are produced in large quantities for use as surfactants and disinfectants and also found in soils, sediments, and surface waters, where they are potentially involved in the selection of antibiotic resistance genes. Micelle formation influences fate and effects of QAACs. The critical micelle concentration (CMC) of six homologs of benzylalkylammonium chlorides (BAC) was determined in deionized water, 0.01 M CaCl₂ solution, and aqueous soil extracts, using both spectrofluorometric and tensiometric methods. Additionally, eight organic model compounds were employed at concentrations of 15 mg C L^-1 as background solutes in order to test the effect of dissolved organic carbon (DOC) on CMCs. Results found CMCs decreased with an increasing length of the alkyl chain from 188 mM for BAC-C8 to 0.1 mM for BAC-C18. Both methods yielded similar results for measurements in water and CaCl₂ solution; however, the spectrofluorescence method did not work for soil extracts due to fluorescence quenching phenomena. In soil extracts, CMCs of BAC-C12 were reduced below 3.7 mM, while the CMC reduction in soil extracts was less pronounced for BAC-C16. Besides ionic strength, molecular structures of BACs and dissolved organic compounds also affected the CMC. The number of carboxyl groups and small molecular weights of the DOC model compounds reduced the CMCs of BAC-C12 and BAC-C16 at pH 6. This study highlights that CMCs can be surpassed in soil solution, pore waters of sediments, or other natural waters even at (small) concentrations of QAACs typically found in the environment.

Wound Healing Activity of Nanoclay/Spring Water Hydrogels

BACKGROUND

hydrogels prepared with natural inorganic excipients and spring waters are commonly used in medical hydrology. Design of these clay-based formulations continues to be a field scarcely addressed. Safety and wound healing properties of different fibrous nanoclay/spring water hydrogels were addressed.

METHODS

in vitro biocompatibility, by means of MTT assay, and wound healing properties were studied. Confocal Laser Scanning Microscopy was used to study the morphology of fibroblasts during the wound healing process.

RESULTS

all the ingredients demonstrated to be biocompatible towards fibroblasts. Particularly, the formulation of nanoclays as hydrogels improved biocompatibility with respect to powder samples at the same concentration. Spring waters and hydrogels were even able to promote in vitro fibroblasts motility and, therefore, accelerate wound healing with respect to the control.

CONCLUSION

fibrous nanoclay/spring water hydrogels proved to be skin-biocompatible and to possess a high potential as wound healing formulations. Moreover, these results open new prospects for these ingredients to be used in new therapeutic or cosmetic formulations.

Sonochemical and sonocatalytic destruction of methylparaben using raw, modified and SDS-intercalated particles of a natural clay mineral

The first part of the study is about the degradation of a common PPCP-methylparaben by high-frequency ultrasound to highlight the operation parameters, the reaction sites, the oxidation byproducts and the role of OH radicals. The second part covers the catalytic effect of a highly abundant and cost-effective clay mineral-sepiolite, and investigates the role of surface modification and SDS-composites of the clay in improving the efficiency of the degradation reactions. It was found that the compound (C₀ = 10 mg L^-1) was readily and totally decomposed by 30-min sonication at neutral pH, producing phenolic and aliphatic intermediates, but with insignificant mineralization. The major reaction site was the bubble-liquid interface, where the reactions were governed by OH radical attack. Modification of the sepiolite surface by pre-sonication in an ultrasonic bath improved the rate of reaction and the degree of TOC decay. Further modification by the synthesis of 20-min sonicated (200 kHz bath) SDS-intercalates of the clay was found to yield significant enhancement in the rate of target compound decomposition and the fraction of TOC decay, provided that the reaction was operated at acidic pH.

Reducing off-Flavour in Commercially Available Polyhydroxyalkanoate Materials by Autooxidation through Compounding with Organoclays

Polyhydroxyalkanoates (PHAs) are nowadays considered competent candidates to replace traditional plastics in several market sectors. However, commercial PHA materials exhibit unsatisfactory smells that can negatively affect the quality of the final product. The cause of this typical rancid odour is attributed to oxidized cell membrane glycolipids, coming from Gram-negative production strains, which remain frequently attached to PHAs granules after the extraction stage. The aim of this research is the development of customised PHA bio-nano-composites for industrial applications containing organomodified nanoclays with high adsorbance properties able to capture volatile compounds responsible for the displeasing fragrance. To this end, a methodology for the detection and identification of the key volatiles released due to oxidative degradation of PHAs has been established using a headspace solid-phase microextraction technique. We report the development of nine bio-nano-composite materials based on three types of commercial PHA matrices loaded with three species of nanoclays which represent a different polar behaviour. It has been demonstrated that although the reached outcoming effect depends on the volatile nature, natural sepiolite might result in the most versatile candidate for any the PHA matrices selected.

Synthesis and Characterization of Clay Polymer Nanocomposites of P(4VP-co-AAm) and Their Application for the Removal of Atrazine

Atrazine (ATZ) is an herbicide which is applied to the soil, and its mechanism of action involves the inhibition of photosynthesis. One of its main functions is to control the appearance of weeds in crops, primarily in corn, sorghum, sugar cane, and wheat; however, it is very toxic for numerous species, including humans. Therefore, this work deals with the adsorption of ATZ from aqueous solutions using nanocomposite materials, synthesized with two different types of organo-modified clays. Those were obtained by the free radical polymerization of 4-vinylpyridine (4VP) and acrylamide (AAm) in different stoichiometric ratios, using tetrabutylphosphonium persulfate (TBPPS) as a radical initiator and N,N′-methylenebisacrylamide (BIS) as cross-linking agent. The structural, morphological, and textural characteristics of clays, copolymers, and nanocomposites were determined through different analytical and instrumental techniques, i.e., X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Adsorption kinetics experiments of ATZ were determined with the modified and synthesized materials, and the effect of the ratio between 4VP and AAm moieties on the removal capacities of the obtained nanocomposites was evaluated. Finally, from these sets of experiments, it was demonstrated that the synthesized nanocomposites with higher molar fractions of 4VP obtained the highest removal percentages of ATZ.

Phosphate removal from wastewaters by a naturally occurring, calcium-rich sepiolite

Developing an easily handled and cost-effective phosphate absorbent is crucial for the control of water eutrophication. In this study, a naturally occurring, calcium-rich sepiolite (NOCS) was evaluated for its feasibility as a phosphate absorbent candidate. Batch studies showed that phosphate sorption on NOCS followed a stepwise isotherm for concentrations between 5 and 1000 mg P/l, and the phosphate sorption was fitted well by the Freundlich equation. The estimated maximum phosphorus sorption capacity was 32.0 mg P/g, which was quite high compared with other natural materials and was comparable to some efficient manmade P absorbents. The NOCS sorption kinetics followed a pseudo-first-order model with an R(2) value of 0.999. The adsorption of phosphate was highly pH dependent. Phosphate adsorption decreased moderately with increasing pH values from 3.0 to 6.0, and it decreased sharply in alkaline conditions. Ionic strength, sulfate, nitrate and chloride anions had no effects on the phosphate removal capacity of NOCS, but fluoride and bicarbonate anions exerted large effects. Phosphorus fractionation indicated that phosphate removed from the solution was primarily formed as a calcium-bound phosphorus precipitation, which was further confirmed by SEM-EDS analysis. Moreover, phosphate was barely (<1.5%) desorbed from the phosphorus-adsorbed sepiolite regardless of pH value.

Surface modification of sepiolite in aqueous gels by using methoxysilanes and its impact on the nanofiber dispersion ability

Surface modification reactions on needle-like sepiolite using alkyl and functional silanes have been carried out in the form of aqueous gels. In contrast with modifications in organic solvents, reactions in water make it possible to modify the surface of almost-individual sepiolite fibers and produce either a continuous coating or a nanotexturization of the sepiolite fiber surface, depending on the reaction conditions. This clean procedure substitutes advantageously organic solvent surface modifications and allows the tuning of surface properties such as specific surface area, wetting behavior, and chemical functionalization. A consequence of such tuning is, for example, the excellent dispersion of modified sepiolite nanofibers in a great variety of polymers by routine compounding and processing techniques.