Mohamed Osman Awaleh

Gold(I)-dithioether supramolecular polymers: synthesis, characterization, and luminescence.

A series of discrete compounds and supramolecular polymers were synthesized by self-assembly of dithioether building blocks and HAuCl4.3H2O. In complexes 1 {[AuL(1-Me)Cl], where L(1-Me) is bis(methylthio)methane} and 2 {[Au2L(2-Ph)Cl2], where L(2-Ph) is 1,2-bis(phenylthio)ethane}, adjacent units are connected via aurophilic interactions. Complex 1, a one-dimensional (1D) supramolecular polymer, and complex 2, a two-dimensional supramolecular network, both feature nearly linear [Au-Au-](infinity) chains. Complexes 4a, 4b, and 4c, all of which contain 1,3-bis(phenylthio)propane (L(3-Ph)), are polymorphs having the composition [Au2L(3-Ph)Cl2]. Complex 3 {[Au2L(1-Ph)Cl2], where L(1-Ph) is bis(phenylthio)methane}and complexes 4a and 4b consist of nearly identical 1D supramolecular polymers formed through Au-Au interactions. The third polymorph, 4c, is a molecular complex, as it does not have metal-metal interactions. Complex 5 {[Au2L(4-Ph)Cl2], where L(4-Ph) is 1,4-bis(phenylthio)butane} is also molecular. UV-vis spectra showed that the absorption bands of these complexes are allowed ligand-centered transitions between 230 and 260 nm. Complexes 1, 2, and 6 {[AuL(3-Me)Cl], where L(3-Me) is 1,3-bis(methylthio)propane} exhibited solid-state luminescence at 5 K with vibronic progressions and band maxima at approximately 570 nm. It is suggested that complex 6 contains [Au-Au-](infinity) chains.

Waste Water Treatment in Chemical Industries: The Concept and Current Technologies

The world’s chemical industries face formidable environmental regulatory challenges in treating their wastewater effluents. The present work aims at highlighting the various industrial wastewater treatment technologies currently available including physico-chemical and biological processes as well as constructed wetland and conventional or advanced oxidation processes. Activated carbon prepared from low cost material, Agricultural by-product materials or modified natural polymers, which is considerably efficient for removal of direct dyes from wastewater, is also discussed. Combinations of anaerobic and aerobic treatment processes are found to be efficient in the removal of soluble biodegradable organic pollutants. The use of membrane in final stage of industrial wastewater treatments is increasing. The chemical oxidation techniques to treat wastewater, classical chemical treatment and advanced oxidation processes, is discussed.

Microwave-assisted synthesis, crystal structures and thermal behaviour of Na5Y(CO3)4 and Na5Yb(CO3)4·2H2O

Abstract Two new carbonates, Na 5 Y(CO 3 ) 4 and Na 5 Yb(CO 3 ) 4 ·2H 2 O, are synthesized by microwave-assisted hydrothermal method and their crystal structures are established by single crystal X-ray diffraction. Na 5 Y(CO 3 ) 4 is monoclinic: P2 1 /c ; a =12.209(3) A, b =10.085(4) A, c =8.783(4) A and β =90.39(3)°; V =1081.4(5) A 3 ; Z =4. Na 5 Yb(CO 3 ) 4 ·2H 2 O, isostructural with Na 5 Sc(CO 3 ) 4 ·2H 2 O, is tetragonal: P-42 1 c ; a =7.593(2) A, c =11.528(8) A; V =664.6(3) A 3 ; Z =2. Dehydration of Na 5 Yb(CO 3 ) 4 ·2H 2 O under argon leads to Na 5 Yb(CO 3 ) 4 , which is isostructural with Na 5 Y(CO 3 ) 4 . In the structure of Na 5 Y(CO 3 ) 4 , YO 9 and Na(1)O 8 polyhedra share vertices and form, with carbonate C(2)O 3 2− and C(3)O 3 2− groups, infinite (100) layers [NaY(CO 3 ) 2 O 6 ] ∞ at x≈ 1 4 ; and x≈ 3 4 . In Na 5 Yb(CO 3 ) 4 ·2H 2 O, YbO 8 and Na(1)O 4 polyhedra share carbonate groups and build [NaYb(CO 3 ) 4 ] ∞ layers.

Levels and sources of heavy metals and PAHs in sediment of Djibouti-city (Republic of Djibouti)

Selected heavy metals and polycyclic aromatic hydrocarbons (PAHs) were determined in marine sediment from 28 sites Djibouti city. The concentrations of trace elements varied from 0 to 288.1mg/kg with relative abundance of trace metals in sediments was in the order of Zn>Cu>Ni>Cr>Co>Pb>Cd. Zn, Cu and Ni exceeded consensus based sediment quality guideline values 7, 14, 15 sites respectively. Enrichment factor and pollution load index showed relatively low to moderate contamination. The concentrations of total 16 PAHs varied widely depending on the sample location and ranged from 2.65 to 3760.11ng·g-1, with the mean concentration value of 387.87ng·g-1. Compositions and relative abundance of individual PAH using molecular diagnostic ratio using congeners m/z 178 and 202 indicated pyrolytic origin and reflecting a petroleum combustion, grass/wood and coal combustion and a petrogenic source. This study represents the first pollution baseline and a reference for future studies in Djibouti.

Sorption behaviors of a persistent toxaphene congener on marine sediments under different physicochemical conditions

Sorptive processes are important parameters affecting the mobility, availability and fate of persistent organic pollutants (POPs), such as toxaphene, in aquatic systems. The sorption and desorption behaviors of the B7-1450, a stable toxaphene congener in environment, on marine sediment was studied under different temperature and salinity conditions to better understand the B-1450 distribution in estuarine systems. The data were fitted to different sorption models to characterize sorption behaviors by evaluating sorption coefficients and sequestrated fraction of B7-1450 on sediments. High carbon-normalized sorption coefficients (Koc) of the B7-1450 were observed with values ranging from 3.2×104 to 6.0×104 mL g(-1) under experimental conditions. The data showed an increase of B7-1450 sorption coefficients with the salinity and a decrease with temperature. These investigations indicate that B7-1450 is three times more sequestred on sediments in cold (2°C, 30 psu) than in warm marine conditions (20°C, 30 psu). These results suggest that the mobility and bioavailable of B7-1450 or other POPs from the sediments could be less important in cold marine comparatively in warm marine and warm freshwater media. As a result of climate changes, the warming of mid and high latitudes coastal waters could enhance the mobility of POPs.

Wastewater reclamation using discarded reverse osmosis membranes for reuse in irrigation in Djibouti, an arid country.

The purpose of this paper is to establish the feasibility of recovering discarded reverse osmosis (RO) membranes in order to reduce the salinity of domestic treated wastewater. This study shows that the reuse of RO membranes is of particular interest for arid countries having naturally high mineralized water such as Djibouti. The pilot desalination unit reduces the electrical conductivity, the turbidity and the total dissolved salt respectively at 75-85, 96.7 and 95.4%. The water produced with this desalination unit contains an average of 254 cfu/100 mL total coliforms and 87 cfu/100 mL fecal coliforms. This effluent meets the World Health Organization standards for treated wastewater reuse for agricultural purposes. The annual cost of the desalination unit was evaluated as US

Influence of the anion on the structure of bis(methylthio)methane supramolecular coordination complexes

/m(3) 0.82, indicating the relatively high cost of this process. Nevertheless, such processes are required to produce an effluent, with a high reuse potential.