Mohamed E. Mahmoud

Speciation, selective extraction and preconcentration of chromium ions via alumina-functionalized-isatin-thiosemicarbazone

A method is presented and described for speciation, extraction and preconcentration of Cr(III) and Cr(VI) based on dynamic and static solid phase extraction techniques. Three newly designed alumina phases-physically adsorbed-isatin-thiosemicarbazone (I-III) were synthesized, characterized, tested for stability and applied as inorganic ion exchangers and chelating solid sorbents for various metal ions. The selectivity characteristics incorporated into these alumina phases were studied and evaluated via determination of the distribution coefficients and separation factors of chromium species versus other interacting metal ions. Quantitative recovery of Cr(VI) was accomplished by alumina phases (I-III) in pH 1.0 giving percentage extraction values of approximately 99.9-100.0%, while Cr(III) was found to be quantitatively recovered by these sorbents in pH 7.0 leading to percentage extraction values approximately 100.0% with minimal or no interference between these two species under the studied buffering conditions. Selective solid phase speciation and preconcentration of Cr(III) and Cr(VI) in various real water samples were successfully performed and accomplished by newly designed alumina phases (I-III) via a preconcentration micro-column.

Dowex anion exchanger-loaded-baker's yeast as bi-functionalized biosorbents for selective extraction of anionic and cationic mercury(II) species.

Dowex anion exchanger-immobilized-bakers yeast [Dae-yeast] were synthesized and potentially applied as environmental friendly biosorbents to evaluate the up-take process of anionic and cationic mercury(II) species as well as other metal ions. Optimization of mass ratio of Dowex anion exchanger versus yeast (1:1-1:10) in presence of various interacting buffer solutions (pH 4.0-9.0) was performed and evaluated. Surface modification of [Dae-yeast] was characterized by scanning electron microscopy (SEM) and infrared spectroscopy. The maximum metal biosorption capacity values of [Dae-yeast] towards mercury(II) were found in the range of 0.800-0.960, 0.840-0.950 and 0.730-0.900 mmol g(-1) in presence of buffer solutions pH 2.0, 4.0 and 7.0, respectively. Three possible and different mechanisms are proposed to account for the biosorption of mercury and mercuric species under these three buffering conditions based on ion exchange, ion pair and chelation interaction processes. Factors affecting biosorption of mercury from aqueous medium including the pH effect of aqueous solutions (1.0-7.0), shaking time (1-30 min) and interfering ions were se arched. The potential applications of modified biosorbents for selective biosorption and extraction of mercury from different real matrices including dental filling waste materials, industrial waste water samples and mercury lamp waste materials were also explored. The results denote to excellent percentage extraction values, from nitric acid as the dissolution solvent with a pH 2.0, as determined in the range of 90.77-97.91+/-3.00-5.00%, 90.00-93.40+/-4.00-5.00% and 92.31-100.00+/-3.00-4.00% for the three tested samples, respectively.

Study of the selectivity characteristics incorporated into physically adsorbed alumina phases. II. Mercaptonicotinic acid and potential applications as selective stationary phases for separation, extraction, and preconcentration of lead(II) and copper(II)

ABSTRACT A method is described for the immobilization of 2-mercaptonicotinic acid on the surface of three different alumina phases. The selected alumina phases are characterized by different acidity properties, acidic phase (I), neutral phase (II), and basic phase (III). Evidences for the physical adsorption of the organic modifier on the surface of the newly synthesized alumina phases (IV–VI) were evaluated on the basis of infrared spectrophotometric analysis, as well as the surface coverage values and pH values of all alumina phases (I–VI). The determined mmol g−1 values for the modified alumina were found to be 0.886, 1.012, and 0.958 for the modified acidic phase (IV), neutral phase (V), and basic phase (VI), respectively. These alumina phases (I–VI) were extensively investigated to identify the possible selectivity characters incorporated into the modified alumina phases and compared with the unmodified ones. This study was accomplished by the determination of the distribution coefficient value (Kd), as well as the separation factor (α) for a series of mono-, di-, and trivalent metal ions. The results of this study were found to confirm the strong affinity and selectivity of the modified alumina phases (IV–VI) for Pb(II) and Cu(II), due to the noticeably high increase in their separation factors versus other interfering metal ions. The advantage of the selectivity character in the modified phases (IV–VI) was also confirmed by the application of a micro-column for selective separation of Cu(II) and Pb(II) from other interfering metal ions, such as Ca(II), Cr(III), Co(II), and Cd(II). Finally, a micro-column was also used and applied for the selective separation, extraction, and preconcentration of Cu(II) and Pb(II) from sea water samples, and the results indicated good recovery values for the spiked 1.0 ng mL−1 of these two metal ions. The percentage recovery values of Cu(II) and Pb(II) were found to be in the range of 95.2– 98.7±2.0 – 4.0% by the three physically adsorbed alumina phases with 2-mercaptonicotinic acid (IV–VI), with a preconcentration factor of 500.

Development of a Method for Chromium Speciation by Selective Solid Phase Extraction and Preconcentration on Alumina-Functionalized Thiosemicarbazide

Abstract A speciation method is developed for Cr(III) and Cr(VI) at selected medium pH range via solid phase extraction on three designed and synthesized chelating inorganic solid sorbents based on adsorption of thiosemicarbazide, as the nitrogen and sulfur containing chelating compound, on alumina surface [Al-TSC (I–III)]. The influence of various parameters including medium pH, time of contact, and interference of matrix and coexistent elements on the speciation and selective extraction processes of chromium species are studied and evaluated on the basis of determination of the metal adsorption capacity, distribution coefficient, and separation factor. Quantitative recovery of Cr(VI) was accomplished by [Al-TSC (I–III)] at pH = 1.0, while Cr(III) was found to be recovered on these sorbents at pH = 7.0 with minimal or no interference between these two species under the studied buffering conditions. The proposed method has been successfully applied for speciation, selective extraction, and preconcentration of Cr(III) and Cr(VI) in water samples with a preconcentration factor of 200.

Chromium speciation, selective extraction and preconcentration by alumina-functionalised 2-pyridenecarboxyladehyde thiosemicarbazone

A method is proposed and explored for speciation of Cr(III) and Cr(VI), selective extraction and preconcentration in various water samples based on dynamic and static techniques. Three newly designed alumina phases-physically adsorbed-2-pyridenecarboxyladehyde-thiosemicarbazone [Al-2PC-TSC (I–III)] were synthesised and characterised. Stability tests and application of [Al-2PC-TSC (I–III)] as inorganic ion exchangers and chelating solid sorbents for various metal ions were studied and evaluated. The distribution coefficient and separation factors of chromium species versus other interfering metal ions were determined to examine the incorporated selectivity into these alumina phases. Quantitative recovery of Cr(VI) was accomplished by [Al-2PC-TSC (I–III)] at pH = 1.0 while Cr(III) was found to be quantitatively recovered on these sorbents at pH = 7.0 with minimal or no interference between these two species under the studied buffering conditions. Selective solid phase speciation and preconcentration of Cr(III) and Cr(VI) in various real water samples were successfully performed and accomplished via a micro-column, with 200 as a preconcentration factor. Selective speciation of Cr(VI) and Cr(III) via preconcentration from seawater and industrial water samples by alumina phases in pH = 1 was found to give percentage recovery values of Cr(VI) in the range 93.5–97.3 ± 3.0–5.0% and 94.0–97.5 ± 3.0–4.0%, for seawater and industrial water samples, respectively.

Characterization of Surface Modification, Thermal Stability, and Metal Selectivity Properties of Silica Gel Phases‐Immobilized Dithiocarbamate Derivatives

Abstract Carbon disulphide was used to modify the surface of silica gel phases containing amine moieties for the formation of four phases-immobilized dithiocarbamate derivatives (I–IV). Characterization of the surface modification by the organic modifier was accomplished by several means of instrumental analysis. These include infrared, secondary ion mass spectrometry (SIMS), as well as, thermal desorption analysis for determination of the surface coverage values (1.051–1.501 mmol g−1). The thermal stability and structure characterization of the modified silica gel phases (I–IV), along with their mercury(II) adducts, were studied and evaluated on the basis of electron impact mass spectrometric analysis (EI‐MS). The results of this study proved higher thermal stability characters incorporated into the metal adduct compared to the free silica gel phase. The selectivity properties incorporated into the modified silica gel phases for binding and interaction with a series of bi‐ and trivalent metal ions were studied and evaluated by determination of the distribution coefficient and separation factor. The results of these evaluation processes were found to point out the higher selectivity and preference of these four phases for binding with mercury(II), copper(II), and cadmium(II) compared to other metal ions.

Comparative study of the reactivity and selectivity characteristics of three silica gel phases: Immobilized-8-hydroxyquinoline for separation and pre-concentration of chromium (III) from water samples

Abstract 8‐Hydroxyquinoline (8HQ) was used to modify the silica gel surface via the physical adsorption method (phase I), as well as a chemical immobilization approach (phases II and III). The loading process of 8‐hydroxyquinoline on the surface of silica gel is simple, direct, and based on only a one step reaction procedure. The three synthesized silica gel phases (I–III) were analytically compared according to their metal‐uptake, extraction, and selective properties toward a series of di‐ and trivalent metal ions. The study of the selectivity characters incorporated into these modified silica gel phases revealed that silica gel phase (I) is the highest selective one for Cr (III), with a minimum interference of the other metal ions, and silica gel phase (III) is the highest selective one for Cu (II) but with a high pronounced interference from other metal ions as Cr (III), Ni (II), and Co (II) ions. Silica gel phase (II) was found to be the lowest in metal capacity values, as well as selectivity study and kinetics of the chemical binding processes. The applications of silica phase (I) as a potential selective solid phase extractor for separation and pre‐concentration of Cr (III) from natural tap water spiked with 1.0 and 4.0 ppb Cr (III) were successfully accomplished via a pre‐concentration micro‐column with percentage extraction and pre‐concentration of 100% ± 1.5∼2.0%. The possible use of phase (I) for the direct determination of real Cr (III) concentration in sea water samples was also performed via a pre‐concentration micro‐column, and the results showed an actual concentration range of 0.320–1.67 ng mL−1 of Cr (III) in the studied samples.

Enhanced removal of lead by chemically and biologically treated carbonaceous materials.

Hybrid sorbents and biosorbents were synthesized via chemical and biological treatment of active carbon by simple and direct redox reaction followed by surface loading of bakers yeast. Surface functionality and morphology of chemically and biologically modified sorbents and biosorbents were studied by Fourier Transform Infrared analysis and scanning electron microscope imaging. Hybrid carbonaceous sorbents and biosorbents were characterized by excellent efficiency and superiority toward lead(II) sorption compared to blank active carbon providing a maximum sorption capacity of lead(II) ion as 500 μmol g−1. Sorption processes of lead(II) by these hybrid materials were investigated under the influence of several controlling parameters such as pH, contact time, mass of sorbent and biosorbent, lead(II) concentration, and foreign ions. Lead(II) sorption mechanisms were found to obey the Langmuir and BET isotherm models. The potential applications of chemically and biologically modified-active carbonaceous materials for removal and extraction of lead from real water matrices were also studied via a double-stage microcolumn technique. The results of this study were found to denote to superior recovery values of lead (95.0–99.0 ± 3.0–5.0%) by various carbonaceous-modified-bakers yeast biosorbents.