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1.
J Synchrotron Radiat ; 28(Pt 6): 1839-1844, 2021 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-34738937

RESUMO

Toxic disinfection byproducts such as trihalomethanes (e.g. CHCl3) are often found after chlorination of drinking water. It has been found that photocatalytic degradation of trace CHCl3 in drinking water generally lacks an expected relationship with the crystalline phase, band-gap energy or the particle sizes of the TiO2-based photocatalysts used such as nano TiO2 on SBA-15 (Santa Barbara amorphous-15), TiO2 clusters (TiO2-SiO2) and atomic dispersed Ti [Ti-MCM-41 (Mobil Composition of Matter)]. To engineer capable TiO2 photocatalysts, a better understanding of their photoactive sites is of great importance and interest. Using in situ X-ray absorption near-edge structure (XANES) spectroscopy, the A1 (4969 eV), A2 (4971 eV) and A3 (4972 eV) sites in TiO2 can be distinguished as four-, five- and six- coordinated Ti species, respectively. Notably, the A2 Ti sites that are the main photocatalytic species of TiO2 are shown to be accountable for about 95% of the photocatalytic degradation of trace CHCl3 in drinking water (7.2 p.p.m. CHCl3 gTiO2-1 h-1). This work reveals that the A2 Ti species of a TiO2-based photocatalyst are mainly responsible for the photocatalytic reactivity, especially in photocatalytic degradation of CHCl3 in drinking water.


Assuntos
Água Potável , Dióxido de Silício , Catálise , Domínio Catalítico , Titânio , Raios X
2.
J Synchrotron Radiat ; 28(Pt 3): 849-853, 2021 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-33949992

RESUMO

Arsenic in groundwater caused the black-foot disease (BFD) in many countries in the 1950-1960s. It is of great importance to develop a feasible method for removal of arsenic from contaminated groundwater in BFD endemic areas. Photocatalytic oxidation of As(III) to less toxic As(V) is, therefore, of significance for preventing any arsenic-related disease that may occur. By in situ synchrotron X-ray absorption spectroscopy, the formation of As(V) is related to the expense of As(III) disappearance during photocatalysis by TiO2 nanotubes (TNTs). Under UV/Vis light irradiation, the apparent first-order rate constant for the photocatalytic oxidation of As(III) to As(V) is 0.0148 min-1. It seems that As(III) can be oxidized with photo-excited holes while the not-recombined electrons may be scavenged with O2 in the channels of the well defined TNTs (an opening of 7 nm in diameter). In the absence of O2, on the contrary, As(III) can be reduced to As(0), to some extent. Cu(II) (CuO), as an electron acceptor, was impregnated on the TNTs surfaces in order to gain a better understanding of electron transfer during photocatalysis. It appears that As(III) can be oxidized to As(V) while Cu(II) is reduced to Cu(I) and Cu(0). The molecular-scale data are very useful in revealing the oxidation states and interconversions of arsenic during the photocatalytic reactions. This work has implications in that the toxicity of arsenic in contaminated groundwater or wastewater can be effectively decreased via solar-driven photocatalysis, which may facilitate further treatments by coagulation.


Assuntos
Nanotubos , Titânio , Oxirredução , Espectroscopia por Absorção de Raios X , Raios X
3.
Environ Sci Technol ; 51(15): 8824-8831, 2017 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-28650619

RESUMO

A novel two-aqueous-phase CO2 capture system, namely the dual alkali solvent (DAS) system, has been developed. Unlike traditional solvent-based CO2 capture systems in which the same solvent is used for both CO2 absorption and stripping, the solvent of the DAS system consists of two aqueous phases. The upper phase, which contains an organic alkali 1-(2-hydroxyethyl) piperazine (HEP), is used for CO2 absorption. The lower phase, which consists of a mixture of K2CO3/KHCO3 aqueous solution and KHCO3 precipitate, is used for CO2 stripping. Only a certain kind of amine (such as HEP) is able to ensure the phase separation, satisfactory absorption efficiency, effective CO2 transfer from the upper phase to the lower phase, and regeneration of the upper phase. In the meantime, due to the presence of K2CO3/KHCO3 in the lower phase, HEP in the upper phase is capable of being regenerated from its sulfite/sulfate heat stable salt, which enables the simultaneous absorption of CO2 and SO2/SO3 from the flue gas. Preliminary experiments and simulations indicate that the implementation of the DAS system can lead to 24.0% stripping energy savings compared to the Econamine process, without significantly lowering the CO2 absorption efficiency (∼90%).


Assuntos
Álcalis , Dióxido de Carbono/química , Solventes , Aminas , Água
4.
Environ Sci Technol ; 47(13): 7380-7, 2013 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-23790076

RESUMO

Iron based catalysts generally have the advantage of the easily operated magnetically recovery from application sites. In the present work, paramagnetic iron and copper core-shell nanoparticles having the iron fractions (X(Fe) = Fe/(Cu+Fe)) of 0.33-1.0 were prepared and characterized by in situ synchrotron X-ray absorption and scattering spectroscopy. During the temperature-programmed carbonization (TPC) of Cu(2+)- and Fe(3+)-ß-cyclodextrin (CD) complexes, a rapid reduction of Cu(II) occurs at about 453 K together with a growth of the metallic copper (Cu). Iron proceeds in the distinct growth path. At 453-513 K, the Fe(III) → Fe(II) → Fe consecutive reduction is observed. The unreduced Fe(III) (7-13%) is coated on the surfaces of the Fe nanoparticles (as Fe2O3/Fe). Growth of the Fe nanoparticle is inhibited by the surface Fe2O3, while the steady growth in Cu is observed. The Cu has a size range of 14-18 nm in diameter, compared to the small Fe2O3/Fe ones (3-6 nm). Under the UV-visible light irradiation for four hours, methylene blue can be photocatalytically degraded (>90%) by the (Cu-Fe2O3/Fe)@C. The (Cu-Fe2O3/Fe)@C photocatalysts can effectively oxidize dye molecules, providing a promising alternative for dye degradation using solar energy. Recovery of the (Cu-Fe2O3/Fe)@C photocatalysts can be attained by applying external magnetic field to trap the ferromagnetic Cu-Fe2O3/Fe nanoparticles, which suggests an economically attractive process, especially applied in photocatalytic degradation of dye-contaminated wastewater.


Assuntos
Cobre/química , Compostos Férricos/química , Ferro/química , Nanopartículas Metálicas/química , Catálise , Corantes/química , Cobre/efeitos da radiação , Compostos Férricos/efeitos da radiação , Ferro/efeitos da radiação , Fenômenos Magnéticos , Nanopartículas Metálicas/efeitos da radiação , Nanopartículas Metálicas/ultraestrutura , Azul de Metileno/química , Microscopia Eletrônica de Transmissão , Fotólise , Raios Ultravioleta
5.
Water Sci Technol ; 68(9): 2007-11, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-24225101

RESUMO

Toxic arsenics in an AsH(3) scrubber sludge were thermally stabilized in the temperature range of 973-1,373 K. To better understand how the high-temperature treatments can stabilize arsenics in the sludge, their synchrotron X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra of arsenics were determined. It is found that the reduced arsenic leachability may be associated with the formation of As(2)O(5) (51-59%) and embedded As(V) within the Ca(3)(PO(4))(2) matrix (41-49%) in the stabilized sludge. In addition, the As-O bond distances in the stabilized As(2)O(5) are much less than that of normal As(2)O(5) by 0.05-0.07 Å. The shorter As-O bond distances accompanied with the higher bonding energy also have a contribution to the thermal stabilization of arsenics.


Assuntos
Arsênio/química , Arsenicais/química , Esgotos/química , Temperatura Alta , Espectroscopia por Absorção de Raios X
6.
ACS Appl Mater Interfaces ; 15(21): 25473-25483, 2023 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-37192387

RESUMO

Visible-light photocatalytic conversion of CO2-to-fuels for green electricity is sustainably attractive for alleviating carbon emissions. Photocatalytic CO2-to-CO frequently suffered from relatively low yields, mainly due to ineffective charge transfer rates. A new approach for photocatalytic CO2-to-CO enhanced with effective H+ from H2O-to-H2O2 through the water oxidation reaction (WOR) has been studied in the present work. Here, the nano palladium (9 wt %), serving as a cocatalyst, dispersed on the g-C3N4/Cu2O heterojunctions (i.e., g-C3N4/Cu2O-Pd) has been prepared to facilitate charge separation for the two-electron reduction of CO2 to CO. Experimentally, the g-C3N4/Cu2O-Pd heterojunctions have a higher photocatalytic H2O-to-H2O2 yield than the g-C3N4/Cu2O heterojunction by 5.3 times. The photocatalytic WOR provides sufficient electrons (e-) and H+ (2H2O → H2O2 + 2H+) for CO2-to-CO (CO2(aq) + 2H+ + 2e- → CO(g) + H2O(l)). Relatively high photocatalytic yields of H2O2 (34.0 µmol/mg) and CO (14.6 µmol/mg) affected by the heterojunctions can be achieved. Also, the heterojunctions have a high photostability with a photocatalytic generated CO/H2 ratio of 1.75 approximately. This visible-light photocatalytic CO2-to-CO and H2O-to-H2O2 by the new g-C3N4/Cu2O-Pd S-scheme heterojunctions demonstrates the feasibility of the zero carbon emission approach with additional green oxidant (H2O2) generation.

7.
ACS Omega ; 8(14): 13315-13322, 2023 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-37065037

RESUMO

Capacitive deionization (CDI), a m ethod with notable advantages of relatively low energy consumption and environmental friendliness, has been widely used in desalination of saltwater. However, due to the weak electrical double-layer electrosorption of ions from water, CDI has suffered from low throughput capacity that may limit its commercial applications. Thus, it is of importance to develop a high-efficiency and engineering-feasible CDI process. Manganese and cobalt and their oxides, being faradic materials, have a relatively high pseudocapacitance, which can cause an increase of positive and negative charges on opposing electrodes. However, their low conductivity properties limit their electrochemical applications. Pseudocapacitive Mn3O4 nanoparticles encapsulated within a conducting carbon shell (Mn3O4@C) were prepared to enhance charge transfer and capacitance for CDI. Desalination performances of the Mn3O4@C (5-15 wt %) core-shell nanoparticles on activated carbon (AC) (Mn3O4@C/AC) serving as CDI electrodes have thus been investigated. The pseudocapacitive Mn3O4@C/AC electrodes with relatively low diffusion resistances have much greater capacitance (240-1300 F/g) than the pristine AC electrode (120 F/g). In situ synchrotron X-ray absorption near-edge structure spectra of the Mn3O4@C/AC electrodes during CDI (under 1.2 and -1.2 V for electrosorption and regeneration, respectively) demonstrate that reversible faradic redox reactions cause more negative charges on the negative electrode and more positive charges on the positive electrode. Consequently, the pseudocapacitive electrodes for CDI of saltwater ([NaCl] = 1000 ppm) show much better desalination performances with a high optimized salt removal (600 mg/g·day), electrosorption efficiency (48%), and electrosorption capacity (EC) (25 mg/g) than the AC electrodes (288 mg/g·day, 23%, and 12 mg/g, respectively). The Mn3O4@C/AC electrode has a maximum EC of 29 mg/g for CDI under +1.2 V. Also, the Mn3O4@C/AC electrodes have much higher pseudocapacitive electrosorption rate constants (0.0049-0.0087 h-1) than the AC electrode (0.0016 h-1). This work demonstrates the feasibility of high-efficiency CDI of saltwater for water recycling and reuse using the low-cost and easily fabricated pseudocapacitive Mn3O4@C/AC electrodes.

8.
ACS Omega ; 8(15): 13813-13818, 2023 Apr 18.
Artigo em Inglês | MEDLINE | ID: mdl-37091403

RESUMO

Combustible gas (e.g., gasification syngas) cleaning at high temperatures can obtain further gains in energy efficiency for power generation and importantly leads to a simplified process and lower cost as a commercially viable source of clean energy. Thus, a feasibility study for high-temperature desulfurization (HTDS) and additional high-temperature particulate filtration (HTPF) of a raw syngas using ZnO sorbent-dispersed Raney CuO (ZnO/R-CuO) and ceramic filter (ZnO/CF) has been carried out. By synchrotron X-ray absorption near-edge structure (XANES) spectroscopy, mainly Zn(II) and Cu(II) are found in the ZnO/R-CuO sorbents. Both ZnO and R-CuO in the sorbents are involved in HTDS (1% H2S) at 873 K to form ZnS, Cu2S, and a small amount of CuS and reach relatively high HTDS efficiencies (82-90%). In addition, regeneration of the sulfurized sorbent by oxidation with O2 at 873 K (HTRG) for 1 h can restore ZnO and CuO for continuous and repetitive HTDS-HTRG cycles. To facilitate the HTDS engineering applications by the ZnO/R-CuO sorbents, their reaction rate constant (8.35 × 104 cm3/g/min) and activation energy (114.8 kJ/mol) at 873 K have also been determined. Furthermore, the ZnO/CF sorbent/filter can perform HTDS and additional HTPF at 873 K with very high particulate removal efficiencies (>98%). This demonstrates the feasibility for hot-syngas cleaning with a much better energy efficiency and lesser cost for cleaner power generation.

9.
J Hazard Mater ; 445: 130522, 2023 Mar 05.
Artigo em Inglês | MEDLINE | ID: mdl-37055954

RESUMO

The XANES/EXAFS data and quantum chemical simulations presented in this study demonstrate several features of the chemistry of arsenic compounds found in the condensates and solids generated in landfill gas (LFG) processing carried out for renewable natural gas (RNG) production. The XANES data show the decrease in the position of the absorption edge of As atoms, similar to that characteristic for sulfur-containing As solutes and solids. The EXAFS data show that the As-O and As-S distances in these matrixes are similar to those in thioarsenates. Quantum-chemical calculations demonstrated the close agreement between the experimental and modeled As-S and As-O distances determined for a range of methylated and thiolated arsenic solutes. These calculations also showed that the increase of the number of the As-S bonds in the coordination shell of arsenic is accompanied by a consistent decrease of the charges of As atoms. This decrease is correlated with the number of the As-S bonds, in agreement with the trend observed in the XANES data. These results provide insight into the intrinsic chemistry and reactivity of As species present in LFG matrixes; they may be helpful for the development of treatment methods to control arsenic in these systems.

10.
ACS Omega ; 7(27): 23727-23735, 2022 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-35847308

RESUMO

A photocatalytic H2O-to-H2O2 reaction for sustainable organic wastewater treatment is environmentally attractive. Phenolic resins, inexpensive metal-free photocatalysts, are capable of harvesting visible light. Herein, novel nitrogen-enriched resin photocatalysts with a desired band-gap energy (1.83-1.98 eV) for harvesting visible light were prepared by copolymerization of resorcinol and melem for simultaneous photocatalytic H2O-to-H2O2 and oxidation of methylene blue. Under visible light irradiation for 5 h, very high yields of H2O2 (870-975 µM of H2O2/g/h) by RFM resin photocatalysts could be achieved. The photocatalytic H2O2 for reactive oxygen species (•OH) and photogenerated h+ could account for high conversion (40% conversion under visible light irradiation within 3 h) in oxidation of methylene blue. Such unique low-cost metal-free resins demonstrate the visible light photocatalytic H2O-to-H2O2 reaction which can synergize with the oxidation of organic pollutants in wastewater.

11.
Environ Technol ; : 1-11, 2022 Dec 19.
Artigo em Inglês | MEDLINE | ID: mdl-36469603

RESUMO

Deionization of salt, contaminated underground and inorganic waste waters for water recycling and reuse is of increasing importance mainly due to the shortage of freshwater worldwide. Membrane capacitive deionization (MCDI) possessing a high electrosorption capacity and energy efficiency has been considered a promising method for desalination. However, the MCDI reaction system has limited applications because of the high interfacial resistance during operation. In the present work, the novel sulfonated graphene oxide (SGO) serving as a hydrophilic cation exchange membrane that was coated directly on the activated carbon (AC) electrode was prepared to enhance capacitive deionization of saltwater. Experimentally, the electrosorption capacity and charge efficiency of the AC/SGO (negative)||AC (positive) electrode pair using the coated SGO thin film increased from 12.8 to 19.8 mg/g and 56.7 to 89.3%, respectively. The enhancements were associated with the reduction of the co-ion effect during electrosorption. The strong negative PhSO3- group grafted on the SGO thin film could selectively accelerate the transport rate of cations during CDI. The increase of the charge efficiency also led to lower implemented current. This work demonstrates a simple, low-cost and effective desalination method that will likely have many new applications especially in water recycling and reuse.

12.
Int J Mol Sci ; 12(12): 8750-72, 2011.
Artigo em Inglês | MEDLINE | ID: mdl-22272102

RESUMO

This work includes specific basic characterization of synthesized glycine-based Ionic Liquid (IL) [QuatGly-OEt][EtOSO(3)] by NMR, elementary analysis and water content. Thermophysical properties such as density, ρ, viscosity, η, refractive index, n, and conductivity, κ, for the binary mixture of [QuatGly-OEt][EtOSO(3)] with poly(ethylene glycol) (PEG) [M(w) = 200] are measured over the whole composition range. The temperature dependence of density and dynamic viscosity for neat [QuatGly-OEt][EtOSO(3)] and its binary mixture can be described by an empirical polynomial equation and by the Vogel-Tammann-Fucher (VTF) equation, respectively. The thermal expansion coefficient of the ILs is ascertained using the experimental density results, and the excess volume expansivity is evaluated. The negative values of excess molar volume for the mixture indicate the ion-dipole interactions and packing between IL and PEG oligomer. The results of binary excess property (V(m) (E) ) and deviations (Δη, Δ(x)n, Δ(Ψ)n, Δ(x)R, and Δ(Ψ)R) are discussed in terms of molecular interactions and molecular structures in the binary mixture.


Assuntos
Glicina/análogos & derivados , Líquidos Iônicos/química , Polietilenoglicóis/química , Compostos de Amônio Quaternário/química , Glicina/síntese química , Glicina/química , Compostos de Amônio Quaternário/síntese química , Temperatura , Viscosidade
13.
J Synchrotron Radiat ; 17(2): 202-6, 2010 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-20157272

RESUMO

Speciation of copper in a copper-rich chemical-mechanical polishing sludge during electrokinetic treatment has been studied by in situ extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectroscopy. The least-squares-fitted XANES spectra indicate that the main copper species in the sludge are Cu(OH)(2) (74%), nanosize CuO (20-60 nm) (13%) and CuO (>100 nm) (13%). The average bond distance and coordination number (CN) of Cu-O are 1.96 A and 3.5, respectively. Under electrokinetic treatment (5 V cm(-1)) for 120 min, about 85% of the copper is dissolved in the electrolyte, 13% of which is migrated and enriched on the cathode. Notably the copper nanoparticles in the sludge can also migrate to the cathode under the electric field. By in situ EXAFS, it is found that during the electrokinetic treatment the bond distance and CN of Cu-O are increased by 0.1 A and 0.9, respectively.

14.
J Synchrotron Radiat ; 17(2): 173-8, 2010 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-20157268

RESUMO

Cr(VI) chemical reduction in natural organic matter (NOM)-bearing latosol soil was investigated under various heating conditions at < or = 378 K. An enhanced Cr(VI) reduction rate has been observed for the reaction at 353-378 K. The effect of Fe(II) naturally occurring in the latosol soil on Cr(VI) chemical reduction is negligible compared with the effect of NOM. Cr(OH)(3) was quantitatively specified by X-ray absorption spectroscopy to be the key chromium species ( approximately 80%) after approximately 90% of Cr(VI) was chemically reduced by NOM at 353-378 K. This study indicates a potential strategy for using the heat extracted from industrial flue gas with a heat exchanger to chemically reduce Cr(VI) in NOM-bearing or organics-amended soils that contain Cr(VI).


Assuntos
Cromo/química , Solo/análise , Compostos Ferrosos/química , Temperatura Alta , Oxirredução , Poluentes do Solo/análise , Espectroscopia por Absorção de Raios X
15.
J Nanosci Nanotechnol ; 10(8): 5456-60, 2010 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-21125918

RESUMO

Visible light active photocatalysts were successfully prepared by incorporating chromium into anatase TiO2 at two Cr/Ti atomic ratios (0.03% and 0.11%) by the use of a modified sol-gel process. Results show that the size of the chromium modified TiO2 particles is approximately 14-25 nm. As indicated by diffuse reflectance ultra violet/visible absorption spectra, heavier chromium dosage tends to result in greater absorption in both ultra violet and visible light. The simulation results from Cr K-edge X-ray absorption spectra suggest that Cr(0) and Cr(III), accounting for approximately 25% and 75% of total Cr, respectively, coexist in the TiO2 catalyst doped with 0.11% Cr. Cr dopant is suggested to be responsible for the phenomenon of enhanced light absorption in both ultra violet and visible regions. Further, Cr(0) can act as an electron remover because of the formation of the Schottky barrier between Cr(0) and TiO2, thus reducing the possibility of electron hole recombination. Photo-catalytic degradation of methylene blue under irradiation of blue light (with peak flux at 460 nm wavelength and a small flux near 367 nm) was considerably enhanced under appropriate reaction time (12 and 24 h) as small amount of Cr was doped into anatase titanium dioxide catalyst. After prolonged reaction time, Cr(0) was suggested to be poisoned and/or oxidized by SO4(2-), one of the final products of mineralizing methylene blue, thus loosing the capability of the electron hole separation.

16.
J Nanosci Nanotechnol ; 10(7): 4782-5, 2010 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-21128499

RESUMO

Deposition of the nanosize copper encapsulated carbon (Cu@C) thin film onto the cathode has been studied to enhance efficiency of the dye-sensitized solar cell (DSSC). The X-ray diffraction (XRD) patterns of the Cu@C are suggestive of existence of metallic copper (Cu) nanoparticles in the thin film. The UV-visible spectrum of the Cu@C coated on indium-doped tin oxide (ITO) shows a red shift (probably due to the longitudinal resonance) as the size of Cu in the Cu@C increases. Moreover, the images observed by field-emission scanning electron microscopy (FE-SEM) indicate that the Cu@C nanoparticles are well dispersed on ITO. By extended X-ray absorption fine structure (EXAFS) spectroscopy, a decrease of the coordination number (CN) of Cu-Cu with decreasing sizes of Cu in the Cu@C is observed. Interestingly, an enhanced efficiency of the DSSC with the Cu@C nanoparticles coated ITO cathode by 50% is found if compared with the relatively expensive Pt electrode. As the size of Cu in the Cu@C on ITO decreases (e.g., 20 --> 7 nm), the efficiency of the DSSC can be increased by 80% approximately.

17.
Water Environ Res ; 82(7): 642-7, 2010 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-20669726

RESUMO

Microwaves were applied to reduce the activation energy of chlorobenzene in aqueous solution and enhance its removal using nanoscale zero-valent iron (Fe0) or zero-valent copper (Cu0) particles as dielectric media. When Fe0 and Cu0 particles absorb microwave energy, the electrical potential difference causes the metal electrons to rotate faster, thus producing more heat. The microwave-irradiated metal particles reduced the chlorobenzene activation energy by 6.1 kJ/mol (13.3 kJ/mol versus 19.4 kJ/mol) for Fe0 and 5.4 kJ/mol (15.8 kJ/mol versus 21.4 kJ/mol) for Cu0 and enhanced the chlorobenzene removal 4.1 times (82.8% versus 20.4%) for Fe0 and 3.7 times (72.1% versus 19.5%) for Cu0. The Fe0 has a higher standard reduction potential than Cu0; it is capable of removing more chlorobenzene than Cu0 (82.8% versus 72.1%). Using the microwave-induced nano-scale iron or copper particle is effective in treating toxic organic substances, as demonstrated in this study.


Assuntos
Clorobenzenos/química , Cobre/química , Ferro/química , Água/química , Cromatografia Gasosa-Espectrometria de Massas , Microscopia Eletrônica de Varredura , Soluções
18.
Chemosphere ; 72(11): 1734-8, 2008 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-18589474

RESUMO

Chemical structure of zinc in the electrokinetic treatments of an electroplating sludge has been studied by in situ extended X-ray absorption fine structural (EXAFS) and X-ray absorption near edge structural (XANES) spectroscopies in the present work. The least-square fitted XANES spectra indicate that the main zinc compounds in the sludge were ZnCO(3) (75%), ZnOSiO(2) (17%) and Zn(OH)(2) (7%). Zinc in the sludge possessed a Zn-O bond distance of 2.07 A with a coordination number (CN) of 5. In the second shells, the bond distance of Zn-(O)-Si was 3.05 A (CN=2). An increase of Zn-(O)-Si (0.05 A) with a decrease of its CN (from 5 to <1) was found in the early stage of the electrokinetic treatment. Prolong the electrokinetic treatment time to 180 min, about 34% of Zn(II) was dissolved into the aqueous phase and about 68% of Zn(II) in the sludge (or 23% of total zinc) was migrated to the cathode under the electric field (5 V cm(-1)). The dissolution and electromigration rates of Zn(II) in the sludge were 1.0 and 0.6 mmol h(-1)g(-1) sludge, respectively during the electrokinetic treatment. This work also exemplifies the utilization of in situ EXAFS and XANES for revealing speciation and possible reaction pathways during the course of zinc recycling from the sludge by electrokinetic treatments.


Assuntos
Galvanoplastia/métodos , Esgotos/química , Zinco/química , Conservação dos Recursos Naturais , Galvanoplastia/instrumentação , Cinética
19.
J Hazard Mater ; 151(2-3): 461-4, 2008 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-17659831

RESUMO

Photocatalytic decomposition of CCl4 (80 mg L(-1) in H2O) effected by Zr-MCM-41 (Zr incorporated in the amorphous wall of MCM-41) has been studied in the present work. Experimentally, photocatalytic decomposition of CCl4 on Zr-MCM-41 was enhanced by about 1.96 times over that on ZrO2. Photocatalytic decomposition of CCl4 may proceed via a two-electron transfer process that yields mainly CHCl3, Cl- and H2. Since little C2Cl2, C2Cl6 or CH2Cl2 was found, it is unlikely that CHCl3 involved in the secondary photocatalytic degradation process. In addition, photocatalytic splitting of H2O on Zr-MCM-41 was also enhanced. The yield of H2 was 6.5 mmol(gZrO2)(-1). About 68% of this hydrogen (6.5 mmol(gZrO2)(-1)) was consumed in the photocatalytic decomposition of CCl4.


Assuntos
Tetracloreto de Carbono/análise , Técnicas de Química Analítica/métodos , Fotoquímica/métodos , Dióxido de Silício/química , Zircônio/análise , Tetracloreto de Carbono/química , Catálise , Desenho de Equipamento , Hidrogênio/química , Fotólise , Espectrofotometria Ultravioleta/métodos , Fatores de Tempo , Água/química , Difração de Raios X , Zircônio/química
20.
Mar Pollut Bull ; 57(6-12): 895-8, 2008.
Artigo em Inglês | MEDLINE | ID: mdl-18395757

RESUMO

Experimentally, a feasibility study for adsorption and catalytic pyrolysis of spill oils on Cu/ZSM-5 for recycling of light oils has been conducted in the present work. The adsorption and pyrolysis of model compounds such as heptane, toluene, and diesel (to stimulate the spill oils) on Cu/ZSM-5 have been investigated on a continuous fixed-bed reactor. By component fitted X-ray absorption near edge structural (XANES) spectroscopy, catalytic active species such as metallic copper (Cu) (77-84%) and Cu(2)O (6-7%) are found in the channels of ZSM-5 during pyrolysis of heptane or toluene. Pyrolysis of diesel effected by Cu/ZSM-5 yields gas (C(1)-C(5)) (32%) and light oil (68%) that can be used as auxiliary fuels.


Assuntos
Conservação dos Recursos Naturais , Temperatura Alta , Petróleo , Eliminação de Resíduos , Zeolitas/química , Adsorção , Desastres
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