Microscopic and spectroscopic analysis of atmospheric iron-containing single particles in Lhasa, Tibet.

The Tibetan Plateau, known as the "Third Pole", is currently in a state of perturbation caused by intensified human activity. In this study, 56 samples were obtained at the five sampling sites in typical area of Lhasa city and their physical and chemical properties were investigated by TEM/EDS, STXM, and NEXAFS spectroscopy. After careful examination of 3387 single particles, the results showed that Fe should be one of the most frequent metal elements. The Fe-containing single particles in irregular shape and micrometer size was about 7.8% and might be mainly from local sources. Meanwhile, the Fe was located on the subsurface of single particles and might be existed in the form of iron oxide. Interestingly, the core-shell structure of iron-containing particles were about 38.8% and might be present as single-, dual- or triple-core shell structure and multi-core shell structure with the Fe/Si ratios of 17.5, 10.5, 2.9 and 1.2, respectively. Meanwhile, iron and manganese were found to coexist with identical distributions in the single particles, which might induce a synergistic effect between iron and manganese in catalytic oxidation. Finally, the solid spherical structure of Fe-containing particles without an external layer were about 53.4%. The elements of Fe and Mn were co-existed, and might be presented as iron oxide-manganese oxide-silica composite. Moreover, the ferrous and ferric forms of iron might be co-existed. Such information can be valuable in expanding our understanding of Fe-containing particles in the Tibetan Plateau atmosphere.

Regulation of charge delocalization in a heteronuclear Fe2 ru system by a stepwise photochromic process.

Heteronuclear complexes FeCp2 -DTE-C≡C-Ru(dppe)2 Cl (1 o; dppe=1,2-bis(diphenylphosphino)ethane, Cp=cyclopentadienyl, DTE=dithienylethene) and FeCp2-DTE-C≡C-Ru(dppe)2-C≡C-DTE-FeCp2 (2 oo), with redox-active ferrocenyl and ruthenium centers separated by a photochromic DTE moiety, were prepared to achieve photoswitchable charge delocalization and Fe⋅⋅⋅Ru electronic communication. Upon UV-light irradiation of 2 oo, the Fe⋅⋅⋅Ru heterometallic electronic interaction is increasingly facilitated with stepwise photocyclization, 2 oo→2 co→2 cc; this is ascribed to the gradual increase in π-conjugated systems. The near-infrared absorptions in mixed-valence species [2 oo](+) /[2 co](+) /[2 cc](+) are gradually intensified following the conversion of [2 oo](+) →[2 co](+) →[2 cc](+) , which demonstrates that the extent of charge delocalization shows progressive enhancement with stepwise photocyclization. As revealed by electrochemical, spectroscopic, and theoretical studies, complex 2 exhibits nine switchable states through stepwise photochromic and reversible redox processes.

Dual-ligand lanthanide metal-organic framework for ratiometric fluorescence detection of the anthrax biomarker dipicolinic acid.

Dipicolinic acid (DPA) is a unique biomarker of Bacillus anthracis. Development of a simple, fast, sensitive and timely DPA detection method is of great importance and interest for preventing mass disease outbreaks and treatment of anthrax. In this work, a novel lanthanide-doped fluorescence probe was constructed by coordination of Eu3+ with bifunctional UiO-66-(COOH)2-NH2 MOFs materials for efficient monitoring DPA. UiO-66-(COOH)2-NH2 MOFs were prepared using Zr4+ as a metal node, 1,2,4,5-benzenetetracarboxylic acid (H4BTC) and 2-aminoterephthalic acid (NH2-BDC) as bridging ligand through a simple one-pot synthesis method. By virtue their abundant carboxyl groups, UiO-66-(COOH)2-NH2 can readily grasp Eu3+ to form UiO-66-(COOH)2-NH2/Eu with coordinated water molecules at Eu sites. Upon interaction with DPA molecules, the coordinated H2O molecules were replaced by DPA molecules which transfer energy to Eu3+ in UiO-66-(COOH)2-NH2/Eu and sensitize Eu3+ luminescence. Meanwhile, DPA has a characteristic absorption band at 270 nm, which overlapped with the excitation spectrum of NH2-BDC, allowing the fluorescence of UiO-66-(COOH)2-NH2/Eu at 453 nm to be greatly quenched by DPA through inner filter effect (IFE). Therefore, the rationally designed UiO-66-(COOH)2-NH2/Eu complex not only exhibits strong hydrophilicity and high dispersion, but also serves as ratiometric fluorescence sensing platform for monitoring DPA concentration. This sensing platform showed a satisfactory linear relationship from 0.2 µM to 40 µM with a limit of detection of 25.0 nM and a noticeable fluorescence color change from blue to red, holding a great promise in practical applications.

Degradation of C.I. Acid Orange 7 by the advanced Fenton process in combination with ultrasonic irradiation.

The combination of ultrasound and the advanced Fenton process (AFP, zero-valent iron and hydrogen peroxide) for the degradation of C.I. Acid Orange 7 was studied. The effect of hydrogen peroxide concentration, initial pH, ultrasonic power density, dissolved gas, and iron powder addition on the decolorization of C.I. Acid Orange 7 was investigated. A modified pseudo-first order kinetic model was used to simulate the experimental results. The results showed that the decolorization rate increased with the increase of hydrogen peroxide concentration and power density, but decreased with the increase of initial pH value. There existed an optimal iron powder addition when decolorization rate was concerned. The decolorization efficiency also increased with the increase of hydrogen peroxide concentration, but decreased with the increase of initial pH value. It varied little at different power densities or iron powder additions at the fixed hydrogen peroxide concentration. The presence of dissolved gas would enhance color removal, and the enhancement was more significant when dissolved oxygen was present. More hydrogen peroxide dosage and reaction duration are required to achieve a relatively high COD removal than those employed to simply break the chromophore group.

Treatment of landfill leachate with combined biological and chemical processes: changes in the dissolved organic matter and functional groups.

Leachates contain complicated and hazardous substances that need multiple treatment processes to meet the discharge standards. Few studies have considered the changes in different fractions, based on their molecular weight (MW), of dissolved organic matter, during the different treatment processes. In this study, we investigated the application of a biological method, using sequencing batch reactors, and a chemical method, using the electro-Fenton oxidation process, in combination. The combined treatment, and the electro-Fenton process alone, was applied to a landfill leachate. Samples taken at various points during the treatment processes were fractionated according to their MW using ultra-membranes; this divided the samples into their less biodegradable constituents (0.45 µm: >10 kDa MW), their bio-refractory constituents (10-1 kDa MW) and their biodegradable constituents (<1 kDa MW). The dominant contributors to the chemical oxygen demand (COD) in the raw leachate comprised the biodegradable constituents (79% of total COD). The COD was reduced to 33.6% and 18.5% of its original levels, by the electro-Fenton process alone and the combined treatment, respectively. Based on the absorption intensities in the Fourier transform infrared (FTIR) spectra, the functional groups in the raw leachate were reduced by the biological treatment, but changed by the electro-Fenton process.

Absorption kinetics of ozone in water with ultrasonic radiation.

A mathematical model was proposed to depict classical unsteady state method that was used to determine volumetric mass transfer coefficient of ozone from gaseous phase to aqueous phase during sonolysis. The rate constant of ozone self-decomposition with ultrasonic radiation, which was one of the parameters in the model, was determined with separate experiments. The results showed that self-decomposition rate constants of ozone were enhanced by ultrasound. The self-decomposition rate constant of ozone is linearly dependent on ultrasonic power, but the increase of the decomposition rate could not enhance ozone mass transfer coefficient. The volumetric mass transfer coefficients of ozone were also enhanced by ultrasonic radiation, while ultrasonic power had little effect on volumetric mass transfer coefficient of ozone. The degassing effect of ozone due to ultrasonic radiation was insignificant in the sparged system when ozone was bubbled during sonolysis.

Degradation of 4-nitrophenol in aqueous medium by electro-Fenton method.

The degradation of 4-nitrophenol by electro-Fenton (E-Fenton) method was carried out in batch recirculation mode. The effect of operating conditions such as electrical current, Fenton's reagent dosage, Fe(II) to H(2)O(2) molar ratio, and H(2)O(2) feeding time on the efficiency of E-Fenton process was investigated. It was found that E-Fenton method showed the synergetic effect on COD removal. The increase of Fenton's reagent dosage, Fe(II) to H(2)O(2) molar ratio, and the electrical current would lead to the increase of COD removal efficiency. Continuous addition of hydrogen peroxide was more effective than the addition of hydrogen peroxide in a single step and there existed an optimal H(2)O(2) feeding time for COD removal. The reaction system was modeled as a plug flow reactor (PFR) in series with a continuous stirred tank reactor (CSTR), and the pseudo-first order rate constant of COD removal was determined from the model based on the experimental data.

Decolorization of methyl orange by ozonation in combination with ultrasonic irradiation.

The combination of ultrasound and ozone for the decolorization of azo dye, methyl orange, was studied. The effect of ultrasonic power, ozone gas flow rate, gaseous ozone concentration, initial dye concentration, pH and hydroxyl radical scavenger on the decolorization of methyl orange was investigated. The results showed that the synergistic effect was achieved by combining ozone with ultrasonic irradiation for the decolorization of methyl orange. The synergistic effect was more significant when the system temperature was raised due to the heat effect of ultrasonic irradiation. The decolorization of methyl orange fits the pseudo first order kinetic model. The decolorization rate increased with the increase of ultrasonic power, ozone gas flow rate, gaseous ozone concentration. However, the decolorization rate decreased with the increasing initial dye concentration. Either pH or sodium carbonate has little effect on the decolorization rate, indicating that the low frequency ultrasound enhanced ozonation process for the decolorization of methyl orange is mainly a direct reaction rather than radical reaction.

Removal of COD from landfill leachate by electro-Fenton method.

The treatment of landfill leachate by electro-Fenton (E-Fenton) method was carried out in a batch electrolytic reactor. The effect of operating conditions such as reaction time, the distance between the electrodes, electrical current, H(2)O(2) to Fe(II) molar ratio, Fenton's reagent dosage and H(2)O(2) feeding mode on the efficacy of E-Fenton process was investigated. It is demonstrated that E-Fenton method can effectively degrade leachate organics. The process was very fast in the first 30 min and then slowed down till it was complete in 75 min. There exists an optimal distance range between the electrodes so that an over 7% higher chemical oxygen demand (COD) removal was achieved than the electrodes positioned beyond this range. COD removal efficiency increased with the increasing current, but further increase of current would reduce the removal efficiency. Organic removal increased as Fenton's reagent dosage increased at the fixed H(2)O(2) to Fe(II) molar ratio. COD removal was only 65% when hydrogen peroxide alone was applied to the electrolytic reactor, and the presence of ferrous ion greatly improved COD removal. COD removal efficiency increased with the increase of ferrous ion dosage at the fixed hydrogen peroxide dose and reached highest at the 0.038 mol/L of ferrous ion concentration. COD removal would decrease when ferrous ion concentration was higher than 0.038 mol/L. The stepwise or continuous addition of hydrogen peroxide was more effective than the addition of hydrogen peroxide in a single step. E-Fenton method showed the synergetic effect for COD removal as it achieved higher COD removal than the total COD removal by electrochemical method and Fenton's reagent.

Removal of ammonium from municipal landfill leachate using natural zeolites.

Ammonium ion-exchange performance of the natural zeolite was investigated in both batch and column studies. The effects of zeolite dosage, contact time, stirring speed and pH on ammonium removal were investigated in batch experiments. The result showed that ammonium removal efficiency increased with an increase in zeolite dosage from 25 to 150 g/L, and an increase in stirring speed from 200 to 250 r/min. But further increase in zeolite dosage and stirring speed would result in an unpronounced increase of ammonium removal. The optimal pH for the removal of ammonium was found as 7.1. In the column studies, the effect of flow rate was investigated, and the total ammonium removal percentage during 180 min operation time decreased with the flow rate though the ion-exchange capacity varied to a very small extent with the flow rate ranging from 4 to 9 mL/min. The spent zeolite was regenerated by sodium chloride solution and the ammonia removal capacity of zeolite changed little or even increased after three regeneration cycles.

Factorial design analysis for COD removal from landfill leachate by photoassisted Fered-Fenton process.

The Fered-Fenton process has been shown to be an effective method for leachate treatment, but it still faces problems of inadequate regeneration of ferrous ion. However, the use of the photoassisted Fered-Fenton process could overcome this difficulty and improve the efficiency of chemical oxygen demand (COD) removal since photoassisted Fered-Fenton process induces the production of hydroxyl radicals from the regeneration of ferrous ions and the reaction of hydrogen peroxide with UV light. As there are so many operating parameters in photoassisted Fered-Fenton process, it is necessary to develop a mathematical model in order to produce the most economical process. In the present study, a factorial design was carried out to evaluate leachate treatment by photoassisted Fered-Fenton process. The influence of the following variables: H2O2 concentration, Fe(2+) concentration, current density, and initial pH in the photoassisted Fered-Fenton process was investigated by measuring COD removal efficiencies after 60-min reaction. The relationship between COD removal and the most significant independent variables was established by means of an experimental design. The H2O2 concentration, Fe(2+) concentration, initial pH, and the interaction effect between current density and initial pH were all significant factors. The factorial design models were derived based on the COD removal efficiency results and the models fit the data well.

Evaluation of electro-oxidation of biologically treated landfill leachate using response surface methodology.

Box-Behnken statistical experiment design and response surface methodology were used to investigate electrochemical oxidation of mature landfill leachate pretreated by sequencing batch reactor (SBR). Titanium coated with ruthenium dioxide (RuO(2)) and iridium dioxide (IrO(2)) was used as the anode in this study. The variables included current density, inter-electrode gap and reaction time. Response factors were ammonia nitrogen removal efficiency and COD removal efficiency. The response surface methodology models were derived based on the results. The predicted values calculated with the model equations were very close to the experimental values and the models were highly significant. The organic components before and after electrochemical oxidation were determined by GC-MS.

Application of response surface methodology to the treatment landfill leachate in a three-dimensional electrochemical reactor.

The influence of different variables on the removal of ammonia nitrogen and COD from landfill leachate was investigated in a three-dimensional electrochemical reactor. Box-Behnken statistical experiment design and the response surface methodology were used to investigate operating condition effects, such as current density, activated carbon to water ratio and the reaction time, on ammonia nitrogen removal efficiency and COD removal efficiency. The positive and negative effects of variables and the interaction between variables on ammonia nitrogen removal and COD removal were determined. The response surface methodology models were derived based on the results and the response surface plots were developed accordingly.

Degradation of C.I. Acid Orange 7 by ultrasound enhanced heterogeneous Fenton-like process.

The effect of ultrasonic power density, goethite addition, hydrogen peroxide concentration, initial pH, hydroxyl radical scavenger, and initial dye concentration on the decolorization of C.I. Acid Orange 7 by ultrasound/goethite/H(2)O(2) process was investigated. The results showed that the decolorization rate increased with power density, goethite addition, and hydrogen peroxide concentration, but decreased with the increase of initial dye concentration. The ultrasonic power density, goethite addition, and initial dye concentration have little effect on decolorization efficiency after 30 min reaction, while the increase of hydrogen peroxide concentration results in the increase of decolorization efficiency. There existed an optimal initial pH to achieve the highest decololrization rate and decolorization efficiency. The presence of hydroxyl radical scavenger would inhibit the decolorization reaction. Only less than half of total organic carbon (TOC) was removed after 90 min reaction, indicating more aggressive conditions are required to achieve the complete mineralization than those employed to simply break the chromophore group.