Reduction of benzo[a]pyrene with acid-activated magnesium metal in ethanol: a possible application for environmental remediation.

Persistent organic pollutants (POPs) are a well-known threat to the environment. Substances such as polycyclic aromatic hydrocarbons (PAHs) in contaminated soils and sediments can have severe and long-term effects on human and environmental health. There is an urgent need for the development of safe technologies for their effective degradation. Here we present a new technique using ball-milled magnesium powder and ethanol solvent as a convenient electron transfer/proton source for the partial reduction of PAHs under ambient conditions. The rates of degradation were determined while evaluating the influences of acetic acid and type of ball-milled magnesium added to the reaction mixture. The results of these triplicate studies indicate that with the use of acetic acid as an activator and ball-milled magnesium carbon (Mg/C), this reducing system (Mg-EtOH) is able to achieve a 94% conversion of 250 µg/mL of toxic benzo[a]pyrene into a mixture of less toxic and partially hydrogenated polycyclic compounds within 24h. This methodology can be used as a combined process involving ethanol washing followed by reduction reaction and it can also be considered as an easy handling and efficient alternative process to the catalytic hydrogenation of PAHs.

The use of mechanical alloying for the preparation of palladized magnesium bimetallic particles for the remediation of PCBs.

The kinetic rate of dechlorination of a polychlorinated biphenyl (PCB-151) by mechanically alloyed Mg/Pd was studied for optimization of the bimetallic system. Bimetal production was first carried out in a small-scale environment using a SPEX 8000M high-energy ball mill with 4-µm-magnesium and palladium impregnated on graphite, with optimized parameters including milling time and Pd-loading. A 5.57-g sample of bimetal containing 0.1257% Pd and ball milled for 3 min resulted in a degradation rate of 0.00176 min(-1)g(-1) catalyst as the most reactive bimetal. The process was then scaled-up, using a Red Devil 5400 Twin-Arm Paint Shaker, fitted with custom plates to hold milling canisters. Optimization parameters tested included milling time, number of ball bearings used, Pd-loading, and total bimetal mass milled. An 85-g sample of bimetal containing 0.1059% Pd and ball-milled for 23 min with 16 ball bearings yielded the most reactive bimetal with a degradation rate of 0.00122 min(-1)g(-1) catalyst. Further testing showed adsorption did not hinder extraction efficiency and that dechlorination products were only seen when using the bimetallic system, as opposed to any of its single components. The bimetallic system was also tested for its ability to degrade a second PCB congener, PCB-45, and a PCB mixture (Arochlor 1254); both contaminants were seen to degrade successfully.

Dechlorination of polychlorinated biphenyls using magnesium and acidified alcohols.

Polychlorinated biphenyls (PCBs) were widely used in industry until their regulation in the 1970s. However, due to their inherent stability, they are still a widespread environmental contaminant. A novel method of degradation of PCBs (via hydrodehalogenation) has been observed using magnesium powder, a carboxylic acid, and alcohol solvents and is described in this paper. The rates of degradation were determined while varying the type of acid (formic, acetic, propionic, butyric, valeric, benzoic, ascorbic, and phosphoric), the amount of magnesium from 0.05 to 0.25 g, the amount of acetic acid from 0.5 to 50 µL and the concentration of PCB-151 from 0.1 to 50 µg/mL, as well as the alcohol solvent (methanol, ethanol, propanol, butanol, octanol, and decanol). The results of these studies indicate that the most rapid PCB dechlorination is achieved using a matrix consisting of at least 0.02 g Mg/mL ethanol, and 10 µL acetic acid/mL ethanol in which case 50 ng/µL of PCB-151 is dechlorinated in approximately 40 min.

Mechanism of the degradation of individual PCB congeners using mechanically alloyed Mg/Pd in methanol.

Polychlorinated biphenyls (PCBs) are a continuing concern in the environment, although legislation restricting the production and use of PCBs was introduced more than 30 years ago. The combination of zero-valent metals and hydrogenation catalysts has been proven effective in the remediation of PCBs, although the exact mechanism of degradation is not known as of yet. The use of mechanically alloyed zero-valent magnesium and palladium (on graphite) has shown great success in the dechlorination of PCBs. Knowing the mechanism for this dechlorination would be helpful in optimizing the bimetallic Mg/Pd for use in the field. A variety of experiments have been performed on a single PCB congener (PCB-151, 2,2',3,5,5',6-polychlorobiphenyl) in an attempt to determine the mechanism by which the degradation occurs. The studies are carried out in methanol to mimic the solvent system which will be used in field applications. Results of these studies have suggested three possible mechanisms, all of which include the removal of the chlorine atom by a hydrogen as the rate-limiting step, varying only in the exact nature of the hydrogen species (radical, hydride, or "hydride-like" radical). BRIEF: A series of studies has suggested three possible mechanistic pathways for the degradation of PCBs in methanol by Mg/Pd.

Dechlorination comparison of mono-substituted PCBs with Mg/Pd in different solvent systems.

It is widely recognized that polychlorinated biphenyls (PCBs) are a dangerous environmental pollutant. Even though the use and production of PCBs have been restricted, heavy industrial use has made them a wide-spread environmental issue today. Dehalogenation using zero-valent metals has been a promising avenue of research for the remediation of chlorinated compounds and other contaminants that are present in the environment. However, zero-valent metals by themselves have shown little capability of dechlorinating polychlorinated biphenyls (PCBs). Mechanically alloying the metal with a catalyst, such as palladium, creates a bimetallic system capable of dechlorinating PCBs very rapidly to biphenyl. This study primarily aims to evaluate the effects of solvent specificity on the kinetics of mono-substituted PCBs, in an attempt to determine the mechanism of degradation. Rate constants and final byproducts were determined for the contaminant systems in both water and methanol, and significant differences in the relative rates of reaction were observed between the two solvents.

Analysis of triacetone triperoxide by gas chromatography/mass spectrometry and gas chromatography/tandem mass spectrometry by electron and chemical ionization.

The explosive triacetone triperoxide (TATP) has been analyzed by gas chromatography/mass spectrometry (GC/MS) and sub-nanogram detection limits are reported by ammonia positive ion chemical ionization (PICI), electron ionization (EI) and methane negative ion chemical ionization (NICI). Analysis by methane PICI and ammonia NICI gave detection limits in the low nanogram range. Analyses were carried out on (linear) quadrupole and ion trap instruments. Analysis of TATP by PICI using ammonia reagent gas is the preferred analytical method, producing low limits of detection as well as an abundant (greater than 60% of base peak) diagnostic adduct ion at m/z 240 corresponding to [TATP + NH4]+. Isolation of the [TATP + NH4]+ ion with subsequent collision-induced dissociation (CID) produces extremely low abundance product ions at m/z values greater than 60, and the m/z 223 ion corresponding to [TATP + H]+ was not observed. Density functional theory (DFT) calculations at the B88LYP/DVZP level indicate that dissociation of the complex to form NH4+ and TATP occurs at energies lower than peroxide bond dissociation, while protonation of TATP leads to cleavage of the ring structure. These results provide a method for pico-gram detection levels of TATP using commercial instrumentation commonly available in forensic laboratories. As a point of comparison, a detection limit of 15 ng was obtained by flame ionization detection.

Essential fatty acids and phenolic acids from extracts and leachates of southern cattail (Typha domingensis P.).

We have been able to isolate several phytotoxic compounds from aqueous extracts and leachates of cattails (Typha domingensis) using activated charcoal as an absorbant, followed by successive extraction with organic solvents, analysis by GC/MS, and structural elucidation by NMR spectroscopy when possible. The phytotoxins were identified as essential fatty acids (linoleic acid and alpha-linolenic acid) and phenolic compounds of known phytotoxic activity (caffeic acid from the aqueous extracts; caffeic, p-coumaric, and gallic acid from the leachates). Both extracts and the phytotoxins in the extracts have the potential of inhibiting the growth and chlorophyll production of several ecologically relevant species.