Papers by Panagiota Stathi
Two organic-modified montmorillonite clays were prepared by embedding organosilanes bearing diffe... more Two organic-modified montmorillonite clays were prepared by embedding organosilanes bearing different chelating amino-functional groups [Apteos] (3-amino-propyltriethoxysilane), and [Edaptmos] (3-(2-aminoethylamino)propyltrimethoxysilane), in the interlayer space of a Zenith montmorillonite. XRD and FTIR spectroscopic data show that the amino organosilanes are intercalated into the interlamelar space forming cube-like structures bearing one polymanino tail at each cube apex. The intercalated cubes cause an increase of the interlayer spacing of the clay sheets by 6.6 A in [Zenith-Apteos] and by 7.1 A in [Zenith-Edaptmos]. The H-binding properties of the intercalated polyamino organosilanes were studied by potentiometric titration. The Cu-, Cd-, and Pb-binding capacity of [Zenith-Apteos] and [Zenith-Edaptmos] were evaluated in aqueous solution as a function of the pH. Both [Zenith-Apteos] and [Zenith-Edaptmos] showed improvement vs Zenith for metal binding in the order Cu > Pb > Cd. [Zenith-Edaptmos] showed the most important results vs Zenith. Theoretical analysis of the pH edge, achieved by a surface complexation model, shows that (a) the amino-functionalized cube-like structures constitute high affinity metal-binding sites; and (b) the metal ions are bound in a monodendate mode with the amino group of the cube, thus resulting in a maximization of metal-binding efficiency.
Journal of hazardous materials, Jan 15, 2009
Hydroxylamine (HA) and hydroxylamine nitrate (HAN) have been involved independently in several tr... more Hydroxylamine (HA) and hydroxylamine nitrate (HAN) have been involved independently in several tragic accidents, which incurred numerous fatalities and injuries. Following these incidents, adiabatic calorimetry and computational chemistry research was conducted on those compounds, suggesting potential reaction pathways of their decomposition, but the mechanism of their unstable behavior, still have not been completely understood. In the present work, isothermal decomposition tests were performed accompanied with HPLC, ion chromatography and UV analyses in the temperature range 80-160 degrees C. Condition-dependent autocatalytic decompositions were demonstrated for HA and HAN, and an intermediate formation has been observed that is most likely responsible for their autocatalytic behavior. These findings corroborate previously reported computational chemistry results.
Journal of Hazardous Materials, 2009
Hydroxylamine (HA) and hydroxylamine nitrate (HAN) have been involved independently in several tr... more Hydroxylamine (HA) and hydroxylamine nitrate (HAN) have been involved independently in several tragic accidents, which incurred numerous fatalities and injuries. Following these incidents, adiabatic calorimetry and computational chemistry research was conducted on those compounds, suggesting potential reaction pathways of their decomposition, but the mechanism of their unstable behavior, still have not been completely understood.In the present work, isothermal decomposition tests
Journal of Materials Science, 2011
Journal of Colloid and Interface Science, 2010
Three SiO(2)-based materials were prepared via covalent immobilization of carboxyl groups (COOH),... more Three SiO(2)-based materials were prepared via covalent immobilization of carboxyl groups (COOH), phenolic groups (GA), or humic acid on an SiO(2) surface. Their sorbing properties were evaluated for removal of heavy metals (Pb(2+), Cd(2+), Cu(2+), Zn(2+), and Mg(2+)) from aqueous solution. The data show a significant improvement for metal uptake, compared to unmodified silica that can be attributed to the adsorption of metals to the deprotonated form of functional groups (COOH, GA, HA). The metal-uptake capacity of the SiO(2)-HA material was 10 times higher that those of the other two materials. The present data provide direct experimental proof that HA can be viewed and modeled as a combination of -COO and R-OH functional groups.
Environmental Science & Technology, 2006
The adsorption of thiram and disulfiram onto R-Al 2 O 3 and montmorillonite clay has been studied... more The adsorption of thiram and disulfiram onto R-Al 2 O 3 and montmorillonite clay has been studied in the presence of small carboxylate anions, bicarbonate, formate, and oxalate. At natural concentrations, HCO 3enhances dramatically the adsorption of both pesticides on R-Al 2 O 3 and clay. An analogous significant enhancement of pesticide adsorption is also observed in the presence of formate and oxalate. Density functional theory calculations demonstrate that in solution a stable molecular complex between one molecule of thiram and one molecule of HCO 3is formed with interaction energy-35.6 kcal/mol. In addition, two H 2 O molecules further stabilize it by an interaction energy of-3.6 kcal/mol. This clustering [thiram-HCO 3-2H 2 O] leads to a change of the electronic structure and the ultraviolet-visible spectrum of thiram that is observed experimentally. Surface complexation modeling shows that the molecular cluster [thiram-HCO 3-2H 2 O], which bears a total net charge of-1, is responsible for the observed enhanced adsorption on the charged surface of alumina and clay at pH below their points of zero surface charge. The results reveal a novel pervasive role of carboxylate anions and particularly HCO 3on the adsorption of dithiocarbamate pesticides in natural waters.
Environmental Science & Technology, 2007
The sorption of a hydrophobic pesticide, thiram, on humic acid (HA) occurs via a specific pH-depe... more The sorption of a hydrophobic pesticide, thiram, on humic acid (HA) occurs via a specific pH-dependent binding of thiram at the deprotonated carboxylates of humic acid, forming a species thiram-[HACOO-] with K = 0.69. Similarly, thiram was sorbed by two model polycarboxylate-{SiO2COOH} materials via the formation of a surface species thiram-{SiO2COO-} with K = 0.45 between thiram and the eprotonated carboxylates grafted on SiO2 particles. In all cases, allowance of presence of bicarbonate at natural concentration caused severe inhibition of thiram's sorption. Oxalate and formate mimic the inhibitive effect of bicarbonate. Theoretical fit of the data showed that the inhibitive effect of HCO3- is due to the formation of the anionic species [thiram-HCO3](-1) (with K = 0.90) which is water soluble and competes with the bound species thiram-{HACOO-}. The same phenomena were observed for the sorption of disulfiram. The specific interaction phenomena reported here bear relevance to the sorption properties of thiram and disulfiram on real soils and, therefore, may determine their environmental fate.
… A European Journal, 2009
Journal of colloid and …, 2007
Four organic-modified clays based on a SWy-2 montmorillonite were prepared by embedding ammonium ... more Four organic-modified clays based on a SWy-2 montmorillonite were prepared by embedding ammonium organic derivatives with different chelating functionalities (-NH 2 , -COOH, -SH or -CS 2 ) in the interlayer space of montmorillonite. Organic molecules such as (a) hexamethylenediamine, (b) 2-(dimethylamino)ethenethiol, (c) 5-aminovaleric acid and (d) hexamethylenediamine-dithiocarbamate were used for the clay modification in order to study the effect of the chelating functionality on heavy metal ions binding from aqueous solutions. The organoclays were characterized by powder X-ray diffraction (XRD), infrared (FTIR) and NMR spectroscopies. The experimental data showed that the organic molecules are intercalated into the interlamelar space with the long dimension parallel to the clay sheets. Their sorbing properties were evaluated for the removal of heavy metals, Pb, Cd and Zn, from aqueous solutions as a function of the pH. When compared with the unmodified SWy-2 montmorillonite, the modified clays show significant improvement in terms of sorbing selectivity as well as of metal loading capacity. The fit to adsorption data by a Surface Complexation Model shows that the intercalated molecules act as specific binding sites in the clay. These contribute additional sorption capacity which is additive to the variable charge edge-sites of the clay in competition with the permanent charge sites. (Y. Deligiannakis). heavy metals. Moreover, due to their abundance in soil systems, their high specific surface area and exchange capacity, clay minerals such as montmorillonite play a significant role in determining the availability and transport of metals species in soil and sediments .
Journal of Colloid and Interface Science, 2010
A novel hybrid MCM-41-based material was synthesized by incorporation of AEDTC [N-(2-aminoethyl)d... more A novel hybrid MCM-41-based material was synthesized by incorporation of AEDTC [N-(2-aminoethyl)dithiocarbamate] in the MCM-41 pores. The derived MCM-41 AEDTC material possesses high AEDTC loading 35% [w:w], and a well-defined array of regular mesopores with a specific surface area of 632 m 2 /g. Heavy metal, Cd, Pb, Cu, and Zn, uptake was studied in detail at physiological pH values 6-8, by a combination of analytical and electron paramagnetic resonance (EPR) spectroscopic techniques. The analytical data show a significant improvement, i.e., 200-500%, for Pb, Cu, and Zn uptake by the MCM-41 AEDTC hybrid vs the unmodified MCM-41. In contrast, Cd shows an exceptional behavior: (a) Cd uptake by MCM-41 AEDTC is very low. (b) Competitive metal uptake experiments reveal that Cd ions cause a characteristic inhibition of Cu or Pb uptake by the MCM-41 AEDTC while Cd binding itself always remained low. The present findings are analyzed by a combination of surface complexation modeling and EPR spectroscopy. Accordingly, in the MCM-41 AEDTC the sulfur atoms of AEDTC provide strong binding sites for metal binding, with a stoichiometry [S AEDTC ]:[Metal] = 1:1. Cd inhibits accessibility of Cu or Pb ions in the AEDTC sites.
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Papers by Panagiota Stathi