Anionic Dye Removal with a Thin Cationic Polyaniline Coating on Cellulosic Biomaterial.

This paper reports the development of novel adsorbent materials using polyaniline (PANI) grafted onto Posidonia (POS) fibers, aimed at efficiently removing phenol red (PSP), an anionic dye, from aqueous solutions. The synthesis involved the copolymerization of aniline grafted on the surface of the POS and aniline monomer in solution, resulting in a chemically bound thin PANI layer on the POS bioadsorbent. Structural characteristics and binding affinities of these adsorbents with PANI under its emeraldine salt (POS@PANI-ES) or emeraldine base (POS@PANI-EB) forms are reported. The rapid adsorption kinetics observed are attributed to enhanced accessibility to PANI adsorption sites on the POS surface. The binding percentages of PSP to POS@PANI-ES and POS@PANI-EB materials were found to be 97 and 50%, respectively, after 15 min of contact time. The Langmuir model for localized adsorption sites and the Volmer model for nonlocalized adsorption as a mobile layer were fitted to the experimental adsorption isotherms of PSP to POS@PANI-EB and POS@PANI-ES, yielding the thermodynamic parameters of adsorption. The adsorption capacities of PSP on POS@PANI-EB and POS@PANI-ES were 37.8 and 71.5 µmol g-1, respectively. The adsorption of PSP remained above 80% at moderate salt concentrations of around 0.1 mol L-1; however, higher concentrations of NaCl and CaCl2 in PSP solutions significantly reduced the adsorption on POS@PANI-ES.

Low-cost Posidonia oceanica bio-adsorbent for efficient removal of antibiotic oxytetracycline from water.

The presence of antibiotics as micro-contaminants in the water and aqueous environments is a health concern to humans and the ecosystem. Therefore, their elimination by adsorption to available and cheap materials in water treatment plants is a research topic of high relevance. The present paper reports on the adsorption behavior of oxytetracycline on a bio-adsorbent prepared from Posidonia oceanica; an abundant Mediterranean biomass. Characterization of the pretreated Posidonia biomaterial was achieved using several analyses such as Boehm acid-base titration method, pHPZC determination, and analysis techniques (FTIR, 13C CP-MAS NMR, optical microscopy, and TGA). The pHPZC occurred around pH 2.11. Posidonia biomaterial showed a fast and high uptake rate throughout the adsorption process, which is a definite advantage for analytical applications such as water decontamination. The experimental kinetic data fitted very rightly the pseudo-second-order kinetic model and the equilibrium uptake can adopt the bi-Langmuir isotherm model for all studied pH values which assumes adsorptions at the two localized sites. Maximum adsorption capacities of 11.8 mg∙g-1 and 4.4 mg∙g-1 for the two adsorption sites are reached at pH 6. The oxytetracycline adsorption process onto Posidonia bio-adsorbent is spontaneous (ΔadsG0 < 0), exothermic (ΔadsH0 < 0), and entropically favorable (ΔadsS0 > 0). The effect of pH on adsorption behavior and the thermodynamic parameters of adsorption are consistent with a possible origin of adsorption of oxytetracycline by means of hydrogen bonding interactions between surface hydroxyl and phenolic groups of the biomaterial and oxytetracycline. The proposed green and environmentally friendly biomaterial offers potential benefits as a bio-adsorbent in the remediation of aquatic environments contaminated by various organic materials.

Molecular Imprints Frozen by Strong Intermolecular Interactions in Place of Cross-Linking.

A new way to freeze molecular imprints in a polymer material is reported. So far, molecular imprinted polymers (MIP) involve copolymerization of a functional monomer and large amounts of cross-linking agent, which keeps the template shape memory in rigid molecular imprints. MIP materials are prepared herein without cross-linking agent. Stiff chains of polyaniline grafted on a solid support as a brush-like material achieve the necessary rigidity. Differential adsorption to imprinted and non-imprinted materials provides evidence of molecular imprints. A correct adsorption isotherm for mobile adsorbed layers (Volmer isotherm) is introduced instead of the popular but inadequate Langmuir isotherm. Non-selective adsorption is entropic, whereas adsorption to molecular imprints has an enthalpic contribution coming from specific interactions. Fast adsorption kinetics are a definite benefit with regards to applications such as chromatographic separations and chemical sensors.

Loading antifungal drugs onto silica particles grafted with cyclodextrins by means of inclusion complex formation at the solid surface.

Immobilization of antifungal drugs to solid particles has been addressed in order to limit the skin penetration to the skin surface during topical administration. Antifungal drug griseofulvin has been immobilized at the surface of silica particles by formation of its inclusion complex with ß-cyclodextrins grafted to silica. A simple and fast process for loading griseofulvin into the hydrophobic cavity of cyclodextrins at the surface of the solid particles in aqueous suspension has been designed. It allowed the formation of the griseofulvin:cyclodextrin inclusion complex of 1:1 stoichiometry to completion. Grafting ß-cyclodextrins to silica surface has been performed in a two-step procedure. The coupling agent 3-amino-propylmethyldiethoxysilane was reacted onto fumed silica particles as a first step. The second step was the reaction of grafted primary amino groups with tosylated ß-cyclodextrin that led to ß-cyclodextrin grafted silica. Loading griseofulvin onto grafted silica particles have been investigated by IR spectroscopy and by tracking possible crystals of griseofulvin in aqueous suspension by optical and scanning electron microscopy and X-ray diffraction. Successful formation of the inclusion complex at the surface of grafted silica suggested a strong adsorption of griseofulvin by means of heterogeneous nucleation of crystals, followed by inclusion complexation taking place between the partners being in close proximity at the surface of silica particles. The high adsorption capacity of CD-grafted silica for griseofulvin compared to bare silica and amino-grafted silica supports this interpretation.