Aris Giannakas

Preparation, characterization, mechanical and barrier properties investigation of chitosan-clay nanocomposites.

In the current study the effect of dilution of chitosan acetate solution and of the use of a reflux-solution method on the morphology, the mechanical and water barrier properties of chitosan based nanocomposites is being investigated. Two series of nanocomposite films from two chitosan acetate solutions with 2 w/v% and 1 w/v% in chitosan were prepared, with 3, 5 and 10 wt% Na-montmorillonite (NaMMT) and/or 30 wt% glycerol. Intercalation of NaMMT was more effective in films based on 2 w/v% solutions which presented decreased hydrated crystallinity. Upon NaMMT addition an enhancement was found in stiffness and strength (up to 100%) and a remarkable decrease in the elongation at break (up to 75%) and water vapor permeability (WVP) (up to 65%). This enhancement was less pronounced in 1 w/v% systems. Addition of glycerol had a negative effect on the stiffness, strength and WVP, and a positive effect on the elongation at break and the absorbed water. Compared with the conventional solution cast method, the reflux treatment led to a significant improvement of the tested properties of nanocomposite films.

Variation of surface properties and textural features of spinel ZnAl2O4 and perovskite LaMnO3 nanoparticles prepared via CTAB-butanol-octane-nitrate salt microemulsions in the reverse and bicontinuous states.

Two binary oxides, a spinel, ZnAl2O4, and a typical perovskite, LaMnO3, have been prepared via CTAB-1-butanol-n-octane-nitrate salt microemulsion in the reverse and bicontinuous states. The exact point of the reverse and bicontinuous states of the microemulsion used in the synthesis was determined by conductivity experiments. The materials obtained after heating at 800 degrees C were characterized by XRD analysis for their crystal structure, N2 porosimetry for their surface area and porosity, and SEM and TEM photography for their texture. The ZnAl2O4 spinel obtained via the reverse microemulsion appears in SEM in a more fragmented form and with a higher specific surface area (143.7 m(2)g(-1)), compared to the corresponding solid prepared via the bicontinuous microemulsion, which appears more robust with lower surface area (126.7 m(2)g(-1)). Nevertheless both materials reveal in TEM a sponge-like structure. The perovskite materials LaMnO3 prepared via the reverse microemulsion showed in SEM a peculiar doughnut-like texture, each doughnut-like secondary particle having a diameter of 2 microm. The corresponding sample developed via the bicontinuous microemulsion showed in SEM uniform secondary particles of size approximately 0.2 microm. Both perovskite samples LaMnO3 appear well crystallized with relative low surface areas, 23.7 m(2)g(-1) for the reverse sample and 10.9 m(2)g(-1) for the bicontinuous one. The TEM photographs reveal that both of them, of reversed and bicontinuous origin, are made up of primary nanoparticles in the size range 40-100 nm. In SEM those materials showed a different secondary structure.

Preparation, characterization, mechanical, barrier and antimicrobial properties of chitosan/PVOH/clay nanocomposites

In the current study low molecular weight poly(vinylalcohol) (PVOH) was used to prepare chitosan/PVOH blends and chitosan/PVOH/montmorillonite nanocomposites via a reflux - solution - heat pressing method. The effect of PVOH content and montmorillonite type (hydrophylic vs. organically modified) on the morphology, mechanical, thermomechanical, barrier and antimicrobial properties of the obtained polymer blends and nanocomposite films was studied. Higher amounts of PVOH (20 and 30%) resulted in plasticization of the films, with an increase in the elongation at break and decrease of the stiffness and the strength while effective blending between chitosan and PVOH chains was observed based on the XRD and DMA findings. Addition of PVOH was beneficial for water and oxygen barrier properties of the obtained films while it did not influence the antimicrobial activity of films against the growth of Escherichia coli. Intercalated structures were obtained after the addition of hydrophilic and organo-modified clays leading into stiffening of the nano-modified films and enhancement of their barrier and antimicrobial properties.

Preparation and characterization of acetylated corn starch-(PVOH)/clay nanocomposite films

Acetylated corn starch (ACS)-based clay (NaMMT) nanocomposite films, with or without addition of polyvinyl alcohol (PVOH), were prepared by casting with glycerol as a plasticizer. The obtained nanocomposite structure was ascertained by XRD study for all polymer-clay nanocomposites. XRD patterns are indicative of an intercalated nanocomposite structure. Mechanical and thermomechanical properties of polymer nanocomposites were studied. The addition of clay induces significant reinforcing effects in the thermoplastic ACS systems. Replacement of glycerol with PVOH in the ACS-NaMMT system results in superior mechanical strength, due to the creation of hydrogen bonds between the ACS and the PVOH chains. Enhancement in water barrier properties was observed for all nanocomposite films, which reaches up to 67% for acetylated starch-PVOH-clay nanocomposites in comparison to acetylated thermoplastic starch, as indicated by water vapor transmission measurements.

Preparation and Characterization of Polystyrene/Organolaponite Nanocomposites

PS/laponite nanocomposites were prepared by a solution blending method. Laponite used was organically modified by octadecyltrimethylammonium bromide (OCTA), octyltrimethylammonium bromide (OCTYL) and di(hydrogenated tallow) dimethylammonium chloride (2HT) at various surfactant loadings. Exfoliated nanocomposite structure was probably obtained when 2HT was used as laponite modifier, yet conventional composites were received in cases using OCTA and OCTYL, as shown by X-ray diffraction measurements. Thermal stability and mechanical properties were evaluated and correlated to the obtained composites structure. Enhancement in water barrier properties was observed for exfoliated PS-nanocomposites compared to that of pristine polymer.

Simultaneous Photocatalytic Reduction of Cr(VI) and Oxidation of Benzoic Acid in Aqueous N-F-Codoped TiO2 Suspensions: Optimization and Modeling Using the Response Surface Methodology

The simultaneous photocatalytic reduction of Cr(VI) and oxidation of benzoic acid (BA) in aqueous suspensions using N-F-codoped TiO2 and simulated solar irradiation were investigated in the present study. Chemometric optimization tools such as response surface methodology (RSM) and experimental design were used to model and optimize selected operational parameters of the simultaneous photocatalytic reduction of Cr(VI) and oxidation of BA. RSM was developed by considering a central composite design with three input variables, that are, N-F-codoped TiO2 mass, ratio of Cr/BA, and pH. The removal of Cr(VI) and BA in binary systems, containing both Cr(VI) and BA, showed a synergistic photocatalytic decontamination as BA significantly facilitated Cr(VI) reduction, whereas Cr(VI) accelerated also BA degradation. Due to the anionic-type adsorption onto TiO2 and its acid-catalyzed photocatalytic reduction, the removal of Cr(VI) decreased with increasing pH, while the degradation of BA followed also the same trend. Under the optimum conditions (N-F-TiO2) = 600 mg L−1, ratio of Cr(VI)/BA = 5, pH = 4, the removal for both Cr and BA followed a pseudo first-order kinetic model. It was found that the selected variables have significant effect both on Cr(VI) removal and BA degradation efficiency. The results revealed the feasibility and the effectiveness of using N-F-codoped TiO2 as photocatalyst for simultaneous decontamination of Cr(VI) and organic pollutants such as BA due to the appropriate oxidation and reduction ability of the photogenerated h

A novel solution blending method for using olive oil and corn oil as plasticizers in chitosan based organoclay nanocomposites

In the current study a novel reflux-solution blending method is being followed with the introduction of small ethanol volumes into chitosan acetic acid aquatic solution in order to incorporate olive oil and corn oil in chitosan and its organoclay nanocomposites. Ethanol enables the direct interaction of chitosan with oils and results in effective plasticization of chitosan/oil films with remarkable increase of the strain at break from 8% of chitosan and chitosan/oil aquatic samples to app. 22% for chitosan/oil ethanol samples. Compared with olive oil, corn oil is less effective as plasticizer (max strain at break app. 14%). Addition of oils is beneficial for water sorption, water vapor permeability and oxygen permeability response of the obtained films. Barrier properties are further improved after the use of OrgMMT, however OrgMMT results in significant reduction of strain at break of all oil containing samples (app. 8%) acting as stress concentrator upon deformation.

Adsorption of Cr(VI) from aqueous solutions by HNO3-purified and chemically activated pyrolytic tire char

ABSTRACT Pyrolytic tire char adsorbents either demineralized by nitric acid (purified char, PC) or activated with KOH-calcination (activated char, AC) were used for Cr(VI) removal from aquatic solutions and studied by adsorption kinetics, isotherms, and thermodynamics. Adsorbent’s physicochemical characteristics were studied by several techniques such as X-ray diffraction, porosimetry, scanning electron microscopy, elemental analysis, and Boehm titration. For PC, acid treatment leads partially to a mesoporous structure while for AC, KOH activation creates also a microporosity enhancing the specific surface area at 443 m2g−1. Cr(VI) adsorption onto both adsorbents followed better second-order kinetics and Langmuir isotherm models and it was exothermic (ΔH < 0) and spontaneous (ΔG < 0). The maximum Cr(VI) adsorption capacity for AC and PC was 114 and 79.47 mg g−1, respectively, at pH = 4. The present work reveals that AC and PC can be efficient sorbents for the removal of heavy metal ions, contributing both positively to wastewater treatment and waste tire pyrolysis plants. GRAPHICAL ABSTRACT

Structure and Thermal Stability of Polystyrene/Layered Silicate Nanocomposites

Polystyrene/layered silicates nanocomposites were prepared by intercalation in solution method, using CHCl3 and CCl4 as solvents. The clay used was organically modified by hexadecyltrimethyl–ammonium bromide (CTAB) at various surfactant loadings. It was found that intercalated nanocomposite structure was obtained using CHCl3 as solvent while exfoliated or partially exfoliated was the predominant form in the case of CCl4. X-ray diffraction and thermogravimetric analysis were used to characterize the nanocomposite morphology and thermal stability, respectively. Enhancement in thermal stability was observed for PS-nanocomposites compared to that of pristine polymer as indicated by TGA measurements. This increment was more prevalent for exfoliated nanocomposites prepared with carbon tetrachloride as solvent.

Mechanism of Synergistic Photocatalytic Cr(VI)-reduction and Benzoic Acid Oxidatiοn by Visible Light Active TiO2 Photocatalysts

Abstract The photocatalytic activity of nanostructured N-doped TiO2 catalyst towards the simultaneous photocatalytic reduction of Cr(VI) and benzoic acid degradation, was investigated under various UV and visible light irradiation conditions. Commercial TiO2 Degussa P25 was also used for comparison purposes. The effect of irradiation wavelength on the photogeneration of hole/electron pairs was evaluated in detail by electron paramagnetic resonance (EPR) spectroscopy. EPR measurements revealed that P 25 becomes total inactive in terms of Ti3+ centers at λ>455 nm in contrast with N-TiO2 which retains 80% of its maximum capacity. Both catalysts were also tested under simulated solar irradiation and visible light. The photocatalytic results demonstrated that N-TiO2 possessed much higher photocatalytic activity than P 25 for reduction of aqueous Cr(VI) under both simulated-solar and visible irradiation.