Andrei Sarbu

Tailor-made polymer beads for gallic acid recognition and separation

Highly selective gallic acid imprinted polymers were synthesized by a suspension polymerization technique. Poly (hydroxyethyl methacrylate-co-ethyleneglycol dimethacrylate) and poly (dimethoxystyrene-co-divinylbenzene) beads were studied for gallic acid separation from green tea leaves. Isothermal binding was explained using Langmuir and Freundlich models. Recovery of gallic acid molecules was significantly improved up to 83xa0% when water was used as extraction solvent. Competitive adsorption, from a green tea leaves alcoholic extract, revealed higher affinities of imprinted polymers for gallic acid. An 18.8 selectivity coefficient was obtained for poly (hydroxyethyl methacrylate-co-ethyleneglycol dimethacrylate) imprinted beads. The performances of the imprinted polymers were in agreement with morphology and nitrogen adsorption analyses.

Selecting the nature of imprinted molecular organosilica sieves with gallic acid via thermal analyses

The stability of the organosilica–gallic acid (GA) complex, and thus the strength of initial interactions which influences directly the sorption parameters of imprinted materials, is mostly given by the nature of co-monomers. Therefore, combining tetraethoxysilane, tetrametoxysilane, vinyl triethoxysilane and vinyl benzyl triethoxysilane as functional monomers, six formulations were obtained in order to optimise the nature of imprinted sieves. Vinyl benzyl trimethylammonium chloride and tertamethyl ammonium hydroxide directed the mesophase formation. Morphology and thermal properties of imprinted organosilica sieves were evaluated and compared to those of blank polymers synthesised in the same conditions as the imprinted ones but without GA. Thermal analysis results corroborated with the morphology of imprinted sieves were confirmed by specific GA sorption tests.

The structure effect upon gallic acid re-binding in molecularly imprinted organosilica

AbstractnThis paper debates the effect of the stabilizer (vinyl benzyl trimethyl ammonium chloride—VBTAC or cetyl trimethyl ammonium chloride—CTAC) and the structure (typical SiO2 matrix or inorganic–organic interpenetrated matrix) influence in molecular imprinting of gallic acid-polyphenol class of templates. For this purpose, gallic acid-imprinted particles were obtained via typical polycondensation sol–gel reactions and via sol–gel/radical polymerization concurrent reactions of tetraethoxy silane (TEOS) and aminopropyl ethoxy silane (APTES) or vinyl triethoxy silane (VTES), respectively. The influence of the mesophase formation and stabilizer nature upon the re-binding of gallic acid was investigated using thermal, infrared and morphology measurements. Adsorption assays of organosilica particles were well correlated with their physical properties. Unlike the polycondensation of TEOS with APTES in the presence of CTAC, concurrent radical polymerization of VBTAC consumed the vinyl functionalities of VTES, decreasing the capacity of VBTAC to mediate the mesophase formation and the capacity of VTES to coordinate template molecules; hence, both the binding capacity and the “memory” effect of the interpenetrated organosilica structure were significantly affected.Graphical Abstract

Removal of Copper Ions from Simulated Wastewaters Using Different Bicomponent Polymer Membranes

The main goal of this study was to explore the suitability and performance of bicomponent polymer membranes based on acrylonitrile copolymers-polyvinyl alcohol (PVA) mixtures and small quantities of anion (Purolite A100) or cation exchange resin (Purolite C150), prepared by phase inversion. Membranes were used for copper removal from synthetic wastewater solutions. A three detachable cylindrical compartment electrodialysis cell without recirculation of the electrolytes and synthetic solutions of various concentrations, similar to a copper electrowinning electrolyte, were used. The electrodialysis unit operates under galvanostatic control. The effect of pH on electrodialysis separation of Cu2+ and on the solution conductivity has been also investigated. The laboratory electrodialysis cell performance was evaluated in terms of percent of extraction (pe) and current efficiency (ce). Experimental results showed that the ionic transfer in electrodialysis cell was especially affected by concentration. The highest values for the pe (>81xa0%) and the ce (>25xa0%) of copper ions were obtained at maximum concentration in copper ions (3xa0g/L), indicating a better performance of the ion extraction. The transport of copper ions was also correlated with flux data. The ion exchange membranes were characterized using FT-IR spectroscopy, ESEM, and electrochemical impedance spectroscopy.

Characterization of New Inorganic-Organic Composites Based on Mesoporous Silica and Vinyl Acetate

New polymer composites were synthesized by a new approach: radical polymerization in an ultrasonic field of the vinyl acetate inside the silica pores. The systems were extensively characterized by different techniques: X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The formation of hybrid materials was proved by XPS. The molecular weight of the entrapped polymer in the cavities of the inorganic structure was assessed by GPC. The thermal properties of the composites were determined by TGA/DTG and DMA.

Numerical and Experimental Investigation of Surface Plasmon Resonance Excitation Using Whispering Gallery Modes in Bent Metal-Clad Single-Mode Optical Fiber

We present a numerical and experimental study of surface plasmon resonance (SPR) excitation in a bent single-mode optical fiber with metalized cladding. It is shown that with a suitable combination of bend radius and metal film thickness surface plasmon waves can be excited in the film as a result of coupling between fundamental and surface plasmon modes via whispering gallery modes supported by the bent fiber cladding. The coupling brings about a dip in the transmission spectrum at the resonant wavelength which is strongly dependent on the ambient refractive index. This enables one to build a fiber optic SPR-refractometer with a standard single-mode fiber without breaking integrity of the fiber or using any additional elements. Refractometric sensitivity of ∼5 μm per refractive index unit and resolution of ∼4·10−6 are experimentally demonstrated for the measured refractive index around 1.43. The reported results may find wide application in bio- and chemosensing.

Detection of Bisphenol A in aqueous medium by screen printed carbon electrodes incorporating electrochemical molecularly imprinted polymers

Electrochemical molecularly imprinted polymers (e-MIPs) were for the first time introduced in screen-printed carbon electrodes (SPCE) as the sensing element for the detection of an organic pollutant. To play this sensing role, a redox tracer was incorporated inside the binding cavities of a cross-linked MIP, as a functional monomer during the synthesis step. Ferrocenylmethyl methacrylate was used for this purpose. It was associated with 4-vinylpyridine as a co-functional monomer and ethylene glycol dimethacrylate as cross-linker for the recognition of the endocrine disruptor, Bisphenol A (BPA), as a target. Microbeads of e-MIP and e-NIP (corresponding non-imprinted polymer) were obtained via precipitation polymerization in acetonitrile. The presence of ferrocene inside the polymers was assessed via FTIR and elemental analysis and the polymers microstructure was characterized by SEM and nitrogen adsorption/desorption experiments. Binding isotherms and batch selectivity experiments evidenced the presence of binding cavities inside the e-MIP and its high affinity for BPA compared to carbamazepine and ketoprofen. e-MIP (and e-NIP) microbeads were then incorporated in a graphite-hydroxyethylcellulose composite paste to prepare SPCE. Electrochemical properties of e-MIP-SPCE revealed a high sensitivity in the presence of BPA in aqueous medium compared to e-NIP-SPCE with a limit of detection (LOD) of 0.06u202fnM. Selectivity towards carbamazepine and ketoprofen was also observed with the e-MIP-SPCE.