Remediation of petroleum hydrocarbon contaminated soil by using activated persulfate with ultrasound and ultrasound/Fe.

This study investigates the degradation of petroleum hydrocarbon in contaminated soil using activated persulfate (PS) with ultrasound (US) and US/Fe. Various controlling factors including different PS dosage, ultrasonic power, pH, soil water ratio and soil particle size were considered. It was found that petroleum hydrocarbon degradation efficiency achieved up to 56.41% and 82.23% in US/PS and US/Fe/PS system, respectively. Based on the experimental results, the reaction rate of US/Fe/PS system was faster than US/PS system and the degradation efficiency enhanced significantly with the increasing ultrasonic power. Changing initial solution pH influenced the petroleum hydrocarbon reaction rate and the best performance would be achieved at pH of 5. The present work identified the main components of petroleum hydrocarbon pollutants in shale gas sites. The mechanism of petroleum hydrocarbon degradation on US/Fe/PS system were analyzed.

The In Vivo Bone Response of Ultraviolet-Irradiated Titanium Implants Modified with Spontaneously Formed Nanostructures: An Experimental Study in Rabbits.

PURPOSE: Acid etching in conjunction with storage in an aqueous solution can induce nanostructures forming spontaneously on titanium surfaces, but an inevitable biologic degradation is suspected to accompany the evolution of nanostructures. The aim of this study was to investigate whether ultraviolet (UV) irradiation is effective to solve this problem and further enhance the bioactivity. MATERIALS AND METHODS: Surface characteristics of five groups of titanium implants (SLAnew, SLAold, modSLA, UV-SLA, and UV-modSLA) and their in vivo bone response were analyzed in this study. The surface characteristics were evaluated with contact angle measurements, scanning electron microscopy, and x-ray photon spectroscopy. A total of 160 implants (32 for each group) were inserted into the tibial metaphyses and femoral condyles of 40 rabbits. After 3 and 6 weeks, the rabbits were euthanized for removal torque tests and histomorphometric analysis. RESULTS: Spontaneously formed nanostructures were observed on water-stored surfaces with a size of approximately 15 nm in diameter, and an inevitable contamination of hydrocarbons accompanied the evolution of nanostructures. UV irradiation effectively eliminated hydrocarbon contamination that accompanied nanostructure evolution. UV-modSLA implants showed the highest removal torque value, and UV-irradiated implants exhibited higher bone-to-implant contact and bone area. CONCLUSION: UV irradiation can effectively eliminate the hydrocarbon contamination accompanying the evolution of nanostructures and further enhance the osseointegration. Nanostructures and UV treatment have combined effects in enhancing the interfacial strength between titanium and bone, while UV photofunctionalization has much more overwhelming effects on histologic and histomorphometric performance.

Application of microwave irradiation for the removal of polychlorinated biphenyls from siloxane transformer and hydrocarbon engine oils.

The removal of polychlorinated biphenyls (PCBs) both from siloxane transformer oil and hydrocarbon engine oil was investigated through the application of microwave (MW) irradiation and a reaction system based on polyethyleneglycol (PEG) and potassium hydroxide. The influence of the main reaction parameters (MW irradiation time, molecular weight of PEG, amount of added reactants and temperature) on the dechlorination behavior was studied. Promising performances were reached, allowing about 50% of dechlorination under the best experimental conditions, together time and energy saving compared to conventional heating systems. Moreover, an interesting dechlorination degree (up to 32%) was achieved for siloxane transformer oil when MW irradiation was employed as the unique driving force. To the best of our knowledge, this is the first time in which MW irradiation is tested as the single driving force for the dechlorination of these two types of PCB-contaminated oils.

Hydrocarbon removal from bilgewater by a combination of air-stripping and photocatalysis.

In order to prevent hydrocarbon discharge at sea from the bilge of ships, the International Maritime Organization (IMO) enacted the MARPOL 73/78 convention in which effluents are now limited to those with maximum oil content of 15 ppmv. Thus, photocatalysis and air-stripping were combined for the hydrocarbon removal from a real oily bilgewater sample and an original monitoring of both aqueous and gaseous phases was performed by GC/MS to better understand the process. Our results show that the hydrocarbon oil index [HC] can be reduced to its maximum permissible value of 15 ppmv (MARPOL) in only 8.5h when photocatalysis and air-stripping are used together in a synergistic way, as against 17 h when photocatalysis is used alone. However, this air-assisted photocatalytic process emits a large quantity of volatile organic compounds (VOC) and, within the first four hours, ca. 10% of the hydrocarbon removal in the aqueous phase is actually just transferred into the gaseous one. Finally, we highlight that the n-alkanes with a number of carbon atoms higher than 15 (N(C)>15) are those which most decrease the rate of [HC] removal.

Oil refinery wastewater treatment using physicochemical, Fenton and Photo-Fenton oxidation processes.

The objective of this study was to investigate the application of advanced oxidation processes (AOPs) to the treatment of wastewaters contaminated with hydrocarbon oil. Three different oil-contaminated wastewaters were examined and compared: (i) a 'real' hydrocarbon wastewater collected from an oil refinery (Conoco-Phillips Whitegate refinery, County Cork, Ireland); (ii) a 'real' hydrocarbon wastewater collected from a car-wash facility located at a petroleum filling station; and (iii) a 'synthetic' hydrocarbon wastewater generated by emulsifying diesel oil and water. The AOPs investigated were Fe(2+)/H(2)O(2) (Fenton's reagent), Fe(2+)/H(2)O(2)/UV (Photo-Fenton's reagent) which may be used as an alternative to, or in conjunction with, conventional treatment techniques. Laboratory-scale batch and continuous-flow experiments were undertaken. The photo-Fenton parametric concentrations to maximize COD removal were optimized: pH = 3, H(2)O(2) = 400 mg/L, and Fe(2+) = 40 mg/L. In the case of the oil-refinery wastewater, photo-Fenton treatment achieved approximately 50% COD removal and, when preceded by physicochemical treatment, the percentage removal increased to approximately 75%.

Pyrolysis of heavy hydrocarbons under microwave heating of catalysts and adsorbents.

The main features of high temperature chemical reactions under microwave (MW) heating have been considered. The efficiency of the MW power to heat conversion in a MW cavity is estimated, theoretically and experimentally, for different substances and conditions. The new approaches for MW processing of high-molecular hydrocarbons are proposed: (i) thermal decomposition in contact with microwave absorbing catalyst particles placed into liquid substrate; (ii) cracking of hydrocarbons pre-absorbed inside porous granules under rapid MW heating of adsorbent. It has been experimentally found that these approaches provide non-traditional conditions of reaction and can lead to the formation of valuable chemical products.

Hydrocarbon oxidation catalyzed by vanadium polyoxometalate supported on mesoporous MCM-41 under ultrasonic irradiation.

Vanadium polyoxometalate (PVMo) supported on mesoporous MCM-41, MCM-41-NH(2), as efficient and heterogeneous catalysts, with large surface area, for hydrocarbon oxidation with hydrogen peroxide is reported. Oxidation of the alkenes and alkanes gave product selectivities, which are similar to those observed for corresponding homogeneous catalyst. PVMo-MCM was prepared by introduction of PVMo into the mesoporous molecule sieves of MCM-41 by impregnation and adsorption techniques. The samples were characterized by X-ray diffraction (XRD), thermal gravimetric-differential thermal analysis (TG-DTA), FT-IR, scanning electron microscopy (SEM), UV-Vis and cyclic voltametry (CV). Ultrasonic irradiation has a particular effect on MCM-41 structural uniformity and reduced the reaction times and improved the product yields. In addition, the solid catalysts could be recovered and reused several times without loss of its activity.

What have we learnt about heavy carbenes through laser flash photolysis studies?

Time resolved gas-phase kinetic studies have contributed a great deal of fundamental information about the reactions and reactivity of heavy carbenes (silylenes, germylenes and stannylenes) during the past two decades. In this article we trace the development of our understanding through the mechanistic themes of intermediate complexes, third body assisted associations, catalysed reactions, non-observed reactions and substituent effects. Ab initio (quantum chemical) calculations have substantially assisted mechanistic interpretation and are discussed where appropriate. Trends in reactivity are identified and some signposts to future studies are indicated. This review, although detailed, is not comprehensive.

Photodegradation of polyfluorene and fluorene oligomers with alkyl and aromatic disubstitutions.

The stability of fluorene-based compounds and polymers, especially at the bridged C-9 position under photoirradiation and thermal treatment, has claimed wide attention. We report the electronic, vibrational, and MALDI-TOF mass spectral combined studies for the fluorene oligomers with alkyl and aromatic substitutions under UV-light irradiation. The low-energy emission and the formation of ketonic defects after degradation highly depend on the proportion of alkyl substitution. The oligomer with fully aromatic substitution shows good stability, but when the proportion of alkyl substitution increases, their photostability rapidly decreases. The mass spectra show not only the mass of the fluorenone-fluorene trimer but also another new degradation product with a large mass (pristine oligomer plus 14) from alkyl oxidation, which testify to the assistance of alkyl side chain during degradation. We propose that the degradation of fluorene is a radical chain process propagated by alkyl side chains, and then the different stability between alkyl and aromatic substitution can be well explained.

Time-resolved kinetic studies on quenching of HCF(A1A'') by alkane and alcohol molecules.

HCF(X1A') radicals were produced by laser photolysis of CHFBr2 at 213 nm and were electronically excited from the ground state to A1A''(030) at 492.7 nm with a dye laser pumped by a Nd:YAG laser. With the analysis of the lifetime of the time-resolved total fluorescence signals collected in the reaction cell where the total pressure was fixed to be 14.0 Torr, the quenching data of HCF(A1A'') by alkane and alcohol molecules at room temperature were derived from variation of pseudo-first-order rate constant with different quencher pressures. It is found that the quenching rate constants are close to the collision rate constants (10(-10) cm3 molecule(-1) s(-1)), indicating the long-range attractive forces between the collision partners play an important role in the entrance channel of quenching process. Several kinetic models were applied to analyze the mechanism of the quenching process. The complex formation cross sections are calculated with the collision complex model. Correlations of the quenching rate constant for the removal of the HCF(A1A'') state with ionization potential of the quenching partners show that the insertion reactive mechanism is probably the dominant reaction channel, which is analogous to the behaviors of other three-atom carbenes in corresponding electronic states.

Photooxidation and its effects on the carboxyl content of dissolved organic matter in two coastal rivers in the southeastern United States.

Photodecarboxylation (often stoichiometrically expressed as RCOOH + (1/2)O2 --> ROH + CO2) has long been postulated to be principally responsible for generating CO2 from photooxidation of dissolved organic matter (DOM). In this study, the quantitative relationships were investigated among O2 consumption, CO2 production, and variation of carboxyl content resulting from photooxidation of DOM in natural water samples obtained from the freshwater reaches of the Satilla River and Altamaha River in the southeastern United States. In terms of loss of dissolved organic carbon (DOC), loss of optical absorbance, and production of CO2, the rate of photooxidation of DOM was increased in the presence of Fe redox chemistry and with increasing O2 content. The ratio of photochemical O2 consumption to CO2 photoproduction ranged from approximately 0.8 to 2.5, depending on the O2 content, the extent of involvement of Fe, and probably the initial oxidation state of DOM as well. The absolute concentration of carboxyl groups ([-COOH]) on DOM only slightly decreased or increased over the course of irradiation, possibly depending on the stages of photooxidation, while the DOC-normalized carboxyl content substantially increased in the presence of Fe redox chemistry and sufficient O2. Both the initial [-COOH] and the apparent loss of this quantity over the course of irradiation was too small to account for the much larger production of CO2, suggesting that carboxyl groups were photochemically regenerated or that the major production pathway for CO2 did not involve photodecarboxylation. The results from this study can be chemically rationalized by a reaction scheme of (a) photodecarboxylation/ regeneration of carboxyl: CxHyOz(COOH)m + aO2 + (metals, hv) --> bCO2 + cH2O2 + Cx-bHy'Oz'(COOH)m-b(COOH)b or of (b) nondecarboxylation photooxidation: CxHyOz(COOH)m + aO2 + (metals, hv) --> bCO2 + cH2O2 + Cx-bHy'Oz'(COOH)m.

Low permeability asphalt concrete gamma ray shielding properties.

Energy-dependent gamma ray shielding properties were measured as a function of gamma ray energy for a low permeability asphalt concrete that is used as a cap to prevent water infiltration into radioactive waste sites. Experimental data were compared to ISO-PC point kernel shielding calculations. Calculated dose equivalent rates compared well with experimental values, especially considering the poor detector resolution involved. The shielding properties of the asphalt concrete closely resembled those of aluminum. The results presented can be used to determine the asphalt concrete thickness required to reduce dose equivalent rates from several gamma ray emitting radionuclides.

Ion irradiation: its relevance to the evolution of complex organics in the outer solar system.

Ion irradiation of carbon containing ices produces several effects among which the formation of complex molecules and even refractory organic materials whose spectral color and molecular complexity both depend on the amount of deposited energy. Here results from laboratory experiments are summarized. Their relevance for the formation and evolution of simple molecules and complex organic materials on planetary bodies in the external Solar System is outlined.

The linear energy transfer dependence of excited singlet-state lifetimes of hydrocarbon liquids exposed to X rays.

The absorption of X rays in liquids provides low-energy electrons in the energy range 2 to 20 keV when synchrotron radiation is used as the X ray source. Such low-energy electrons have short ranges and produce a dense track of ionization where dE/dx = 10(7) to 10(8) eV/cm. Fluorescent molecules provide a sensitive probe of the early-time structure of such tracks. From the extent of quenching of excited states and the consequent decrease in fluorescence lifetimes, the concentration of free radicals in the track can be inferred. Experiments done with the hydrocarbons cis-decalin and dodecane demonstrate this effect. In both hydrocarbons, the lifetimes (tau) are significantly smaller with excitation by X rays than with UV radiation, and tau-1 increases linearly with dE/dx.

Ionization yields in hydrocarbons under electron irradiation.

Ionization yields and W-values in several hydrocarbon gases under electron irradiation have been calculated using Inokuti's solution of the Fowler equation, i.e., incorporating a linear dependence of ionization yield on source electron energy. Collision stopping powers of hydrocarbons were evaluated using the Bethe formula with mean excitation energies determined using the additivity rule with modification based on molecular bond strengths. Contributions to the collision stopping powers from discrete level excitations were estimated by multiplying collision stopping powers by the excitation fractions constructed from atomic calculations. Average energy transfers for ionizing collisions producing subionization electrons were calculated using differential ionization cross sections proposed by Khare and co-workers. The calculated W-values are in good agreement with those recommended by ICRU.

Organic solids produced from simple C/H/O/N ices by charged particles: applications to the outer solar system.

CH4, CO, and CO2 are all potential one-carbon molecular repositories in primitive icy objects. These molecules are all found in the Comet Halley coma, and are probable but, (except for CH4 detected on Triton and Pluto) undetected subsurface constituents in icy outer solar system objects. We have investigated the effects of charged particle irradiation by cold plasma discharge upon surfaces of H2O:CH4 clathrate having a 200:1 ratio, as well as upon ices composed of H2O plus C2H6 or C2H2 (sometimes plus NH3) which are also plausible constituents. These materials color and darken noticeably after a dose 10(9) - 10(10) erg cm-2, which is deposited rapidly (< or = 10(4) yr.) in solar system environments. The chromophore is a yellowish to tan organic material (a tholin) which we have studied by UV-VIS reflection and transmission, and IR transmission spectroscopy. Its yield, -1 C keV-1, implies substantial production of organic solids by the action of cosmic rays and radionuclides in cometary crusts and interiors, as well as rapid production in satellite surfaces. This material shows alkane bands which Chyba and Sagan have shown to well match the Halley infrared emission spectrum near 3.4 microns, and also bands due to aldehyde, alcohol and perhaps alkene/aromatic functional groups. We compare the IR spectral properties of these tholins with the spectra of others produced by irradiation of gases and ices containing simple hydrocarbons.