Mohamad Al-Sheikhly

The Mechanisms of Removal of Heavy Metals from Water by Ionizing Radiation

Abstract The removal of heavy metal ions from water using electron beam and gamma irradiation has been investigated for the cases of Pb 2+ and Hg 2+ ions. These metal ions are reduced by hydrated electrons and hydrogen atoms to lower or zero valence state and eventually precipitate out of solution. Ethanol is applied as a relatively non-toxic additive to scavenge · OH radicals, to enhance reduction and inhibit oxidation. Mercury can be completely (>99.9%) removed from aqueous solution of 1×10 −3 mol L −1 mercury (II) chloride by using a 3 kGy dose. However, a 40 kGy dose is required to remove 96% of lead ions from a 1×10 −3 mol L −1 of PbCl 2 solution. The effect of dissolved oxygen and carbonate were also investigated. E-beam irradiation of 1×10 −3 mol L −1 lead ions complexed with ethylenediamine tetraacetic acid (EDTA) in deoxygenated as well as air-saturated solutions in the absence of ethanol resulted in removal of about 97% of the lead.

Anionic Triphenylmethane Dye Solutions for Low-Dose Food Irradiation Dosimetry

Abstract The radiolytic bleaching of aryl sulfonic-substituted para-diethyl-amino triphenylmethane dye solutions can be used for dosimetry in the absorbed dose range 10 to 400 Gy. The sulfonic anions provide solubility of these acid dyes in water. Two of these dyes are supplied as stable greenish-blue biological stains when dissolved in weakly-acidic aqueous solution, Light Green SF Yellowish and Fast Green FCF. They have, respectively, linear molar absorption coefficients of 7.14 × 103(at pH5.4) and 10.0 × 103 (at pH4.2) m2mol−1, when measured at the peaks of the primary absorption bands, 630 nm and 622 nm, respectively. The bleaching due to irradiation with gamma rays shows a linear function with a positive slope between the negative logarithm of the absorbance and the absorbed dose. The effect of pH on the response is studied, as well as the effects of light and temperature on pre- and post-irradiation stability. A mechanism, based mainly on radiolytic oxidation of the protonated phenolic or sulfonated phenyl group by .OH, with the abstraction of H-atom to water, is postulated for neutral to slightly acidic aerated aqueous solutions. The influence of alcohol on diminishing the negative yield is demonstrated. Alkaline aqueous solutions of these dyes (pH 10.2) have a shorter-wavelength absorption maximum than acidic aqueous solutions. The effect of irradiation is to cause acidification (to pH 7) due to displacement of OH groups and degradation of the dye molecule to lower molecular weight organic acids.

Attachment of DNA probes on gallium arsenide surface

Chemical attachment of the thiol-derivatized DNA monolayers on arsenic terminated GaAs (001) has been achieved. The sulfur-As-based covalent bonds of the thiolated oligonucleotids on the arsenic terminated GaAs (001) were observed using x-ray photoelectron spectroscopy. The purpose of our work is to investigate the self-assembly of thiol-derivatized single-stranded DNA oligonucleotides (probes) on GaAs substrate. In this letter, we demonstrate that both the S–H group in the thiolated single-strand DNA, and the N–H group in the DNA bases are functional groups that can be utilized to anchor the DNA molecule, or other biological molecules on the As-terminated GaAs surface.

Large-scale dosimetry using dilute methylene blue dye in aqueous solution

Abstract The radiolytic bleaching of neat aerated methylene blue solutions is relatively stable, when irradiated to doses in the range of 50 to 500 Gy and measured at the main peak of absorption band of the dye (664 nm). The useful range can be extended up to about 5 kGy if the aqueous dye solution contains about 0.1% ethanol by volume and to 10 kGy with 5 % ethanol. By increasing the concentration of the dye in the presence of 5% ethanol doses up to about 30 kGy can be measured. The spectrophotometric readings have to be made during a period of post irradiation stability of 24 hours, after which there is about a 10% increase in absorbance over the next three days due to regeneration of the dye by spontaneous oxidation. Since the industrial grade monovalent dye salt is very inexpensive and is relatively non-toxic, it may be used for dosimetry studies in quality control tests of electron beam processing of large volumes of waste water, when typical doses in the range of 5–30 kGy are required. The influences of dose, dose rate and solute concentration on the bleaching process have been investigated in terms of the decrease of the absorbance of the dye.

Alcohol solutions of triphenyl-tetrazolium chloride as high-dose radiochromic dosimeters

Abstract The radiolytic reduction of colorless tetrazolium salts in aqueous solution to the highly colored formazan dye is a well-known acid-forming radiation chemical reaction. Radiochromic thin films and three-dimensional hydrocolloid gels have been used for imaging and mapping absorbed dose distributions. The high solubility of 2,3,5-triphenyl-tetrazolium chloride (TTC) in alcohols provides a useful liquid dosimeter (45 mM TTC in aerated ethanol) and shows a linear response of absorbance increase (λ max = 480 nm) with dose over the range 1–16 kGy. The linear molar absorption coefficient (ɛ m ) for the formazan at the absorption peak is 1.5 × 10 3 m 2 mol −1 , and the radiation chemical yield for the above solution is G (formazan) = 0.014 μ mol J −1 . The irradiation temperature coefficient is about 0.8 percent per degree Celsius rise in temperature over the temperature range 0–30 °C but is much larger between 30° and 60 °C. The unirradiated and irradiated solutions are stable over at least five days storage at normal laboratory temperature in the dark, but when stored in daylight at elevated temperature, the unirradiated solution in sealed amber glass ampoules undergoes slow photolytic dye formation, and the irradiated solution experiences initial fading and subsequent reversal (photochromism) when exposed to direct sunlight.

Applications of ionizing radiation to the remediation of materials contaminated with heavy metals and polychlorinated biphenyls

Abstract We have investigated the removal from water of heavy metals and chelated heavy metal compounds using electron beam and gamma radiation. Parameter analyses include the effect of dissolved oxygen and the influence of adding various buffers and radical scavengers. Complete removal (>99%) of mercury, lead and cadmium ions, both free and chelated within EDTA, was achieved using radiation doses ranging from 3–100 kGy. We have also studied the radiation induced degradation of polychlorinated biphenyls (PCBs) in aqueous-organic and aqueous micellar systems. Rates and extent of dechlorination have been quantified in different solution matrices; reaction by-products and intermediate species have been identified; and the influences of dissolved oxygen and pH have been evaluated. The presence of a carbonate buffer was observed to significantly enhance PCB dechlorination yields by reducing concentrations of H 3 O + . Ionizing radiation was effective in degrading PCBs in micellar solutions but scavenging of e aq − by the surfactant lowered reaction efficiencies.

The reactivity of adenyl and guanyl radicals towards oxygen

Abstract A strong oxidant [Tl(II)] oxidizes adenine (A) and guanine (G) to adenyl and guanyl radical cations, A + and G + , respectively. In neutral solutions these cation radicals lose protons and become adenyl, ·A(-H), and guanyl, ·G(-H), radicals. From the pulse radiolysis experiments and the measurements of oxygen uptake, it was concluded that, in contrast with carbon centered radicals, the adenyl and guanyl radicals do not react rapidly with oxygen. Their reaction rate constants are estimated to be of the order of 10 2 M -1 s -1 or less. The low reactivity of ·A(-H) and ·G(-H) with oxygen is suggested to be a consequence of the unpaired electron being mostly on the oxygen and nitrogen rather than on carbon. In contrast, OH-adducts generated in the reaction of ·OH radical with guanine (·G-OH) and adenine (·A-OH) react with oxygen rapidly.

Electron Beam Irradiation for Mercury Oxidation and Mercury Emissions Control

A variety of air pollution control strategies have been investigated to reduce mercury emissions from coal-fired sources. The most developed and deployed technologies are based on adsorption of mercury onto powdered activated carbon followed by carbon collection. Mercury oxidation over selective catalytic reduction catalysts followed by wet scrubbing is another potential technique, and tests suggest that emissions reductions of 20–80% are possible, but test results are variable and ultrahigh removal ( 95%+ ) is unusual. The objective of this study was to investigate the effectiveness of electron beam irradiation to oxidize mercury vapor, to improve mercury removal with wet scrubbers or wet electrostatic precipitators (ESPs). Metallic mercury vapor samples in air and other atmospheres were prepared at concentrations of approximately 16 μ g/m3 . Samples were electron irradiated at energy levels of 2.5–10 kGy, equivalent to 3.1–12.4 kJ/ m3 stack gas. Results show that mercury oxidation rate was dependent on ...

Radiolytic dechlorination of polychlorinated biphenyls in transformer oil and in marine sediment

Abstract Radiolytic dechlorination of polychlorinated biphenyls (PCBs) in transformer oil and in marine sediments has been studied. At low PCB concentrations, complete degradation of the PCBs in transformer oil was achieved without degradation of the oil. Addition of an organic base, triethylamine, enhances the radiolytic dechlorination yield. The mechanism of dechlorination has been shown to involve electron transfer to PCBs from various aromatic radical anions formed in the irradiated oil. At high PCB concentrations, large amounts of triethylamine were necessary to achieve complete radiolytic dechlorination. Preliminary results on PCB-contaminated marine sediments demonstrate that addition of 2-propanol to the sediment/water slurry increases the effectiveness of the electron beam treatment.

On the mechanisms of radiation-induced curing of epoxy-fiber composites

Depending on the monomer molecular structure, the mechanisms of radiation-induced polymerization proceed via either C-centered radical mechanisms or cationic polymerization. While polymerization via C-centered radicals can be impeded by the presence of oxygen and high dose-rate, polymerization through cationic polymerization is inhibited even by the presence of trace amounts of water. Synergy by the combination of radiation and thermal curing can help to achieve various desired properties of polymer-fiber composite materials.