I. Francis Cheng

Reduction of nitrate to ammonia by zero-valent iron

Abstract The reduction of nitrate to ammonia occurs with nearly complete conversion at room temperature and pressure under aerobic conditions in the presence of iron and either HCl or a pH buffer. A 50.0 mL solution of 12.5 millimolar nitrate is rapidly reduced to ammonia when exposed to 4.00 g of 325 mesh iron at pH 5.0, 0.05 M sodium acetate/acetic acid. The pseudo-first order rate constant was 0.053 min −1 , Under conditions of pH 6.0 buffer, (i.e. 0.1 M 4-morpholineethanesulfonic acid adjusted to pH 6.0) and pH 7.0 buffer (0.1 M 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid adjusted to pH 7.0), the rate constants were 0.0408 min −1 and 0.0143 mint, respectively. In unbuffered solutions there was no loss in nitrate and no production of ammonia. A more concentrated nitrate solution (100 mL of 1.0 M sodium nitrate) was also reduced to ammonia in the presence of 2.5 M HCl with the slow addition of 50.0 g of 325 mesh iron.

On the ability of four flavonoids, baicilein, luteolin, naringenin, and quercetin, to suppress the fenton reaction of the iron-ATP complex

Four flavonoids, baicilein, luteolin, naringenin, and quercetin were investigated for their ability to suppress the Fenton reaction characteristic of the iron-ATP complex. Absorption spectroscopy indicates that under the conditions of 18.75% aqueous methanol, 0.0625 mM HEPES pH 7.4 buffer and 1.5:1 quercetin/iron-ATP ratio a mix ligand complex formed. All four flavonoids were found to interfere with the voltammetric catalytic wave associated with the iron-ATP complex in the presence of H2O2. Quercetin and luteolin were able to completely suppress the catalytic wave of the iron-ATP/H2O2 system when a minimum ratio of 1.5:1 of the flavonoid to iron-ATP was reached. At this ratio, the ability of the studied series of flavonoids to suppress the Fenton reaction characteristic of iron-ATP follows as quercetin ≈ luteolin > naringenin ≈ baicilein. Both quercetin and luteolin contain catechol on the B ring, which may enhance the iron chelation of these species over baicilein and naringenin. The common structural feature of all of these flavonoids is the 4-keto, 5-hydroxy region, which may also contribute to the chelation of iron.

Dechlorination of chlorinated phenols by catalyzed and uncatalyzed Fe(0) and Mg(0) particles.

Uncatalyzed, and palladium-catalyzed Fe(0) and Mg(0) systems were examined for their efficiencies of dechlorination of 2.86 mM 4-chlorophenol (4-CP), 2.52 mM 2,6-dichlorophenol (2,6-DCP), 3.03 mM 2,4,6-trichlorophenol (2,4,6-TCP), and 2.48 mM pentachlorophenol (PCP) in 50/50 (v/v) 2-propanol/water under room temperature and pressure conditions. Previous investigators have found that PCP is extremely recalcitrant under these conditions. In this investigation, complete dechlorination of 5.0 ml of 2.48 mM PCP was observed for 1.0 g of 2659 ppm Pd/Mg (20 mesh) after 48 h. The only detectable products were cyclohexanol and cyclohexanone at 25% yield. No other chlorinated or otherwise products were observed by mass spectral analysis. It is hypothesized that volatile low molecular weight species were formed from the Pd/Mg dechlorination of PCP. Under conditions of equal surface area (0.0786 m2), the approximate order of PCP dechlorination power of these systems followed as 2659 ppm Pd/Mg>319 ppm Pd/Mg>Mg approximately 4856 ppm Pd/Fe>Fe. Degradation of the other chlorinated phenols by all metallic systems was more facile than PCP.

The complete dechlorination of DDT by magnesium/palladium bimetallic particles.

The complete dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) by a magnesium/palladium bimetallic system has been accomplished. The reaction takes place under ambient temperature and pressure and mild reaction conditions requiring only 0.25 g of magnesium and 0.3% palladium (wt/wt) to drive the dechlorination of 100 microg DDT (50 ppm in 2 ml). The process is both rapid and complete requiring less than 10 min to attain total dechlorination within the detection limit (approximately 10 pg for DDT) of electron capture detection gas chromatography (GC-ECD). The major product formed, as deduced from mass spectrometry (GC-MS) is the hydrocarbon skeleton, 1,1-diphenylethane. This technology may allow for the development of an economic and environmentally benign method of DDT remediation.

Electrochemical detection of triacetone triperoxide employing the electrocatalytic reaction of iron(II/III)-ethylenediaminetetraacetate and hydrogen peroxide.

An electrochemical method for the detection of triacetone triperoxide (TATP) is proposed and examined. In this method, TATP solutions were treated with 1.08 M HCl for 10min releasing H2O2 and/or hydroperoxides. Subsequently, these peroxides undergo an electrocatalytic reduction through the Fe(II/III)ethylenediaminetetraacetate (EDTA) complex at a glassy carbon electrode. Cyclic voltammetric results indicate that no redox reaction was observed between Fe(II)EDTA and TATP. Acid treated TATP yielded voltammograms indicative of electrocatalysis of ROOH/HOOH reduction via Fe(II/III)EDTA redox cycling. Chronoamperometric results yielded a detection limit of 0.89 microM for TATP and a sensitivity of 0.025 mAmM(-1). The influence of pH and O2 interference on the analytical signal is briefly discussed.

Simultaneous determination of total polychlorinated biphenyl and dichlorodiphenyltrichloroethane (DDT) by dechlorination with Fe/Pd and Mg/Pd bimetallic particles and flame ionization detection gas chromatography

Abstract Simultaneous measurement of total dichlorodiphenyltrichloroethane (DDT, technical mixture) and polychlorinated biphenyl (PCB-Aroclors 1248 and 1260) is facilitated by quantitative dechlorination to diphenylethane and biphenyl. The two-stage dechlorination reaction utilizes a palladium catalyst deposited onto iron and magnesium particles. The treatment has the advantage of converting the complex chromatographic pattern that arises from the multiple congeners and degradation products of PCB and DDT into peaks corresponding to their representative hydrocarbon skeletons. The limit for quantitative measurement (LOQ) using this treatment and GC-FID analysis is 40 parts-per-billion (ppb, μg/l) for Aroclor 1260 and 100 ppb for DDT with a linear response extending to 100 times the LOQ. The calibration was successfully tested with triplicate water samples fortified at 15 (DDT) and 10 (Aroclor 1260) times the LOQ. Accuracy (mean percent) and precision (percent relative standard deviation) were 92% and 6.2% for DDT and 96% and 5.2% for Aroclor 1260. Accuracy and RSD for 35 ppm triplicate spiked soil samples were 76% and 18% for Aroclor 1260 and 68% and 26% for DDT. These results are comparable to the published single laboratory results for EPA method 8082 ‘Polychlorinated Biphenyls by Gas Chromatography’. However, the single laboratory results for EPA method 8081A ‘Organohalide Pesticides by Gas Chromatography,’ failed to resolve DDT and therefore could not be compared with this method.

Detoxification of malathion a chemical warfare agent analog using oxygen activation at room temperature and pressure

The organophosphorus insecticide malathion was selected as an analog for the chemical nerve agent, VX. Degradation of 0.44 mM malathion in a 10 mL aqueous solution containing 0.50 g granular zero valent iron (ZVI) under ambient air and pressure was complete after 4 h to the detection limit of GC-FID. The degradation kinetics demonstrate the system to be pseudo-first-order with respect to malathion disappearance with a rate constant of 0.92 h−1. The only non-polar organic intermediates detected were diethyl succinate and malaoxon, of which malaoxon is degraded to below the limit of detection of the GC-FID after 12 h. Electrospray ionization mass spectral analyses show the final reaction products to be low molecular weight carboxylic acids (propionic, oxalic and iminodiacetic acid).

Heavy metals removal from mine runoff using compost bioreactors

Permeable bioreactors have gained both research and management attention as viable methods for treating mine runoff waters. We examined the operation of a field‐scale bioreactor (containing mixed compost, straw and gravel) for treatment of runoff from the Mother Load (ML) mine in northern Idaho, U.S. and compared it to an experimental laboratory‐scale reactor, containing a similar matrix and treating similar mine runoff water. In general both reactors were efficient in removing most of the metals assayed, Al, As, Cd, Fe, Ni, Pb and Zn, with the exception of Mn. Both systems showed evidence of bacterial‐mediated sulphate reduction and concomitant metal sulphide complexes. However, the experimental laboratory bioreactor showed greater proportions of immobile metals reductions than did the ML bioreactor, presumably due to the greater action of sulphate‐reducing bacteria. The major metal removal mechanism in the ML bioreactor was surmised to be adsorption. Differences in metal removal mechanisms between the reactors were hypothesized to be due to fluctuating hydraulic residence times at the ML site, in turn, due to unregulated runoff flow.

Sulfur as an important co-factor in the formation of multilayer graphene in the thermolyzed asphalt reaction

The results indicate a first ever hypothesized role of sulfur in the low temperature formation of graphene. Multilayer graphene was prepared with various hydrocarbons and sulfur mixtures by the University of Idaho Thermolyzed Asphalt Reaction (UITAR). Graphene films were synthesized with the UITAR process through the original flame-heated crucible, and in thermogravimetric analysis apparatuses. The latter was carried out under N2 purge. The morphology of these films synthesized by cyclohexanol and sulfur was characterized by scanning electron, transmission electron, and atomic force microscopies, which indicate a flat (over several mm2) and layered structure consistent with graphitic structures. Elemental composition as determined by X-ray photoelectron spectroscopy indicated primarily sp2 C with trace O and N impurities. Raman spectra of the UITAR graphene have D and G bands at 1350 cm−1 and 1594 cm−1. Based on the wavenumber positions of these bands, the Ferrari amorphization trajectory indicates that the UITAR graphene films are primarily sp2 C with nano-crystalline characteristics. The I(D)/I(G) ratio is 0.97 with an average grain size of 5 nm as determined by the Tuinstra–Koenig relationship. A proposed scheme illustrates the role of sulfur in graphene growth based on thermogravimetric analyses. We hypothesize that elemental sulfur is involved with the dehydration/dehydrogenation and eventual crosslinking of cyclohexanol between 100 and 140 °C. In the range of 240–400 °C further dehydrogenation steps occur giving an unidentified intermediate with a sharp Raman peak at 1450 cm−1. At 550 °C a mixture of graphene-like Raman D and G bands appear with the 1450 cm−1 intermediate. At 600 °C the intermediate peak is lost with only bands characteristic of UITAR graphene. Therefore the minimum temperature of graphene formation with the UITAR reaction is 600 °C. The proposed mechanism is reinforced by results with other hydrocarbons. Other organics succeeded or failed in the UITAR reaction based on melting and boiling considerations.

Aqueous sulfur species determination using differential pulse polarography

Sulfur species play pivotal roles in biogeochemistry; however, quantification remains difficult because such species are transitory. Our objective was to determine the utility of using differential pulse polarography (DPP) to characterize soluble sulfur species of potential interest in agriculture and environmental quality. Polarographic responses for sulfide, disulfide, pentasulfide, sulfite, thiosulfate, tetrathionate, pentathionate, cysteine, and glutathione were determined. Sulfur in the compounds was categorized as cysteine-S, thiosulfate-S, nonpurgeable or purgeable sulfide-S, or sulfite based on characteristic polarographic responses for each respective category. Nonpurgeable sulfide-S, cysteine-S, and thiosulfate-S were polarographically separated using a pH 8.0 phosphate buffer. Nitrate/bicarbonate (pH 10.0) and acetate (pH 5.0) buffers were used to determine purgeable sulfide-S and sulfite, respectively. Sulfur in water extracts from cysteine-amended soils was quantified using the developed DPP method. Cysteine-, thiosulfate-, and sulfide-S were measured from these extracts without interferences during a 16-d incubation period. The developed DPP method provides qualitative and quantitative information concerning sulfur species in aqueous solutions and is potentially applicable to soil and sediment extracts.