Jimin Shen

Activating persulfate by Fe0 coupling with weak magnetic field: Performance and mechanism

Weak magnetic field (WMF) and Fe(0) were proposed to activate PS synergistically (WMF-Fe(0)/PS) to degrade dyes and aromatic contaminants. The removal rates of orange G (OG) by WMF-Fe(0)/PS generally decreased with increasing initial pH (3.0-10.0) and increased with increasing Fe(0) (0.5-3.0 mM) or PS dosages (0.5-3.0 mM). Compared to its counterpart without WMF, the WMF-Fe(0)/PS process could induce a 5.4-28.2 fold enhancement in the removal rate of OG under different conditions. Moreover, the application of WMF significantly enhanced the decolorization rate and the mineralization of OG. The degradation rates of caffeine, 4-nitrophenol, benzotriazole and diuron by Fe(0)/PS were improved by 2.1-11.1 fold due to the superimposed WMF. Compared to many other sulfate radical-based advanced oxidation technologies under similar reaction conditions, WMF-Fe(0)/PS technology could degrade selected organic contaminants with much greater rates. Sulfate radical was identified to be the primary radical species responsible for the OG degradation at pH 7.0 in WMF-Fe(0)/PS process. This study unraveled that the presence of WMF accelerated the corrosion rate of Fe(0) and thus promoted the release of Fe(2+), which induced the increased production of sulfate radicals from PS and promoted the degradation of organic contaminants. Employing WMF to enhance oxidation capacity of Fe(0)/PS is a novel, efficient, promising and environmental-friendly method since it does not need extra energy and costly reagents.

Ozone enhanced activity of aqueous titanium dioxide suspensions for photodegradation of 4-chloronitrobenzene

The TiO(2)/UV/O(3) process has been employed to remove 4-chloronitrobenzene (4-CNB) and compared to UV/air, O(3), TiO(2)/O(3), TiO(2)/UV/O(2) and UV/O(3) five parallel oxidation pathways. The reaction activities of these six processes were tested in aqueous using electron paramagnetic resonance (EPR) spin trapping technique with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap. Moreover, the effects of ozone dosage, catalyst dosage and initial solution pH on the degradation of 4-CNB by TiO(2)/UV/O(3) process were also investigated. Results showed that the TiO(2)/UV/O(3) is the most efficient process for complete mineralization of 4-CNB since the combination of photocatalytic oxidation with ozone has a synergistic effect. The relative intensity of DMPO-OH follows the order of UV/air<O(3)<TiO(2)/O(3)<UV/O(3)<TiO(2)/UV/O(2)<TiO(2)/UV/O(3). In TiO(2)/UV/O(3) process, the ozone and catalyst dosage are found to have a significant impact on the process efficiency whereas initial pH has relatively less effect. Chlorine atoms of 4-CNB are absolutely oxidized to chloride anions when the ozone dosage in the range of 5-18 mg/min, or the catalyst dosage ranging from 1.0 to 2.0 g/L. Part of chloride anions would be further oxidized to chlorate(V) ions if the ozone dosage exceeds 24 mg/min, or the catalyst dosage exceeds 2.0 g/L.

Plasticity of a TiCu-based bulk metallic glass: Effect of cooling rate

Compressive deformation was experimentally investigated for Ti 41.5 Cu 42.5 Zr 2.5 Hf 5 Ni 7.5 Si 1 bulk metallic glass (BMG) fabricated at different cooling rates. It was found that the ductility of the BMG alloy increased with increasing of the cooling rate in solidification. The alloy with a monolithic amorphous structure exhibited a large ductility, up to 12%. The effect of cooling rate on the ductility of the BMG alloy is interpreted in terms of the variation in amorphous nature and free volume of the as-cast materials.

Hydrothermal synthesis of TiO2 hollow microspheres for the photocatalytic degradation of 4-chloronitrobenzene

TiO(2) hollow microspheres were synthesized by a simple hydrothermal method followed by calcination at different temperatures ranging from 400 to 800°C. The prepared samples were characterized by XRD, SEM, TEM, SAED, HRTEM, N(2) adsorption, and UV-vis spectroscopy. The photocatalytic activities of the hollow microspheres were evaluated by photocatalytic decomposition of 4-chloronitrobenzene (4-CNB). Results showed that the TiO(2) hollow microspheres, which had an average external diameter of 1.75 μm, were composed of numerous TiO(2) nanoparticles. Photocatalysis experiments indicated that the TiO(2) hollow microspheres calcined at 500°C exhibited the highest photocatalytic activity, which was nearly 2 and 1.5 times higher than that of the uncalcined sample and Degussa P25, respectively. The catalyst crystallinity, catalyst dosage and 4-CNB concentration were found to have a significant impact on the degradation efficiency whereas solution pH has relatively less effect. The removal of total organic carbon (TOC) and formation of chloride, nitrate (V) anions were monitored to follow the mineralization process of 4-CNB. In addition, it was demonstrated that these TiO(2) hollow microspheres could be recycled easily without decreasing their photocatalytic activities.

Removal of phosphate from secondary effluent with Fe2+ enhanced by H2O2 at nature pH/neutral pH.

Removal of phosphate in secondary effluents was investigated in presence of Fe(2+)/H(2)O(2). The effect of H(2)O(2)-dose, Fe-dose and initial phosphate concentration were assessed. The results indicated that Fe(2+)/H(2)O(2) could greatly increase the removal of phosphate compared with those achieved by Fe(2+) alone. For initial phosphate concentration of 0.97-3.75 mg P/L, phosphate removal rates of 50-60% were observed at 1:1 molar addition of Fe(II). However, a 125% excess of Fe-dose was necessary for complete phosphate removal. The experimental data demonstrated that removal of phosphate with Fe(2+)/H(2)O(2) was higher than that observed with ferric coagulation alone. This fact suggested that in situ formed Fe(III) having much affinity for ligand phosphate. Chemical co-precipitation was considered as the dominant mechanism about phosphate removal in presence of Fe(2+)/H(2)O(2). The electron paramagnetic resonance (EPR) spectra tests in secondary effluents showed that Fe(2+)/H(2)O(2) could produce an increasing hydroxyl radical concentration with a decrease in both H(2)O(2) dosage and phosphate concentration. Fe(2+)/H(2)O(2) had the potential to be utilized for removal of phosphate due to the lower cost and the higher phosphate removal capability.

Degradation and detoxification of microcystin-LR in drinking water by sequential use of UV and ozone.

Microcystins (MCs) produced by cyanobacteria are strong hepatotoxins and classified as possible carcinogens. MCs pose a considerable threat to human health through tainted drinking and surface waters. Herein filtrated water from a waterworks in Harbin, China, was spiked with microcystin-LR (MC-LR) extracted from a toxic scum of microcystis aeruginosa, and the spiked sample waters were treated using UV irradiation with consequent ozonation process (UV/O3), compared with ozonation at a dose range commonly applied in water treatment plants, UV irradiation at 254 nm and UV irradiation combined with ozonation (UV+O3), respectively. The remaining of toxins were analyzed using high-performance liquid chromatography and also determined using a protein phosphatase type 2A inhibition assay, which was utilized to evaluate the reduction in toxicity. Results indicated that in comparison to other three processes (O3, UV, and UV+O3), UV/O3 process could effectively decrease both the concentration and toxicity of MC-LR at 100 microg/L level after 5 min UV irradiation with consequent 5 min ozonation at 0.2 mg/L (below 1 microg/L), while 0.5 mg/L ozone dose was required for the level below 0.1 microg/L. The addition of an UV treatment step to the existing treatment train may induce significant transformation of micropollutants and breaks down the natural organic matters into moieties unfavorable for ozone decomposition, stabilizing the ozone residual. These findings suggested that sequential use of UV and ozone may be a suitable method for the removal of these potentially hazardous microcystins from drinking water.

Reduction of N-Nitrosodimethylamine with zero-valent zinc

N-Nitrosodimethylamine (NDMA) is known as the disinfection by-product and the pollutant in the source water. Reduction with zero-valent zinc (Zn(0)) was investigated as a potential technology to treat NDMA. The results showed that Zn(0) was effective for NDMA reduction at initial pH 7.0. There were lag period and rapid period during the process, the corresponding zero-order rate constant (k(zero)) was 2.968 ± 0.245 μg L(-1) h(-1) ([Zn(0)](0) = 10g L(-1)),the mass normalized pseudo-first-order rate (k(M)) was 0.1215 ± 0.0171 L g(-1) h(-1). The reactivity of zinc on NDMA removal was consistent with the zinc corrosion rate. NDMA had little effect on the corrosion of zinc. Lower solution pH benefited the reduction of NDMA with Zn(0). The consumption of the oxygen and the localized acidification should be the cause of the shift from lag to rapid reaction period in the aerobic experiments. 1,1-dimethylhydrazine (unsymmetrical dimethylhydrazine, UDMH), dimethylamine (DMA) were detected as the products of NDMA degradation. The nitrogen mass balance at 24 h was 56%, the loss can be due to the formation of ammonium, the degradation of UDMH and other unmeasured products. DMA formed during the degradation of UDMH with Zn(0), the nitrogen loss could be caused by the formation of unmeasured products. Catalytic hydrogenation is proposed to be the mechanism based on the results and the redox properties of zinc and NDMA. One reduction process is: the active hydrogen atoms initially cleave and reduce the N=O bond in NDMA, generating UDMH. Then the N-N bond in UDMH is cleaved to form DMA and ammonium.

Shear deformation capability of different metallic glasses

The mechanical properties of Zr 52.5 Ni 14.6 Al 10 Cu 17.9 Ti 5 and Ti 40 Zr 25 Ni 3 Cu 12 Be 20 metallic glasses were investigated under uniaxial compressive loading and small punch loading, respectively. The Zr-based metallic glass displays higher density of shear bands, larger critical shear offsets and higher energy absorbing capability than the Ti-based metallic glass under the small punch tests. A concept of critical shear offset is proposed to explain the difference in shear deformation abilities or plasticity of different metallic glasses. The current experiments demonstrate that, in contrast with the small difference between the responses of the Zr- and Ti-based metallic glasses under uniaxial compressive loading, the biaxial tension produced by the small punch test is an effective way to evaluate the difference in shear deformation abilities and can be used to distinguish the brittleness or plasticity of various metallic glasses.

Influence of humic acid on the removal of arsenate and arsenic by ferric chloride: effects of pH, As/Fe ratio, initial As concentration, and co-existing solutes

The influence of humic acid (HA) on the removal of arsenic by FeCl3 was systematically studied in this paper. Jar tests were performed to investigate the influence on arsenic during FeCl3 coagulation of the pH adjusting method, the initial As/Fe ratio, the equilibrium As concentration, and co-occurring anions and cations. Compared with results in HA-free systems, the removal trends of arsenic in HA solutions were quite different. It was found that As(V) removal was higher at low equilibrium concentration, yet the opposite was true for As(III) removal. The presence of HA influenced the effective number of active sites for arsenic removal by FeCl3 flocculation. In addition, in the presence of HA, the impacts of co-existing solutions on arsenic removal were also different from that of an HA-free system. This study examined the influence of co-occurring anions, such as phosphate, sulfate, and silicate on arsenic removal, depending on their ability to compete for sorption sites and to hinder or facilitate the aggregation of ferric hydroxide flocs. The presence of Ca2+ or Cd2+ significantly increased arsenic removal at higher pH. Low concentrations of dissolved HA and high concentrations of colloid affected the adsorption of arsenic onto iron oxide. The influence of HA on the adsorption of arsenic onto iron oxide primarily depended on the relative content of the dissolved and mineral combination states of HA and the interface combination forms.

Sensitized chemiluminescence of 2-phenyl-4,5-di(2-furyl)-1H-imidazole/K3Fe(CN)6/propyl gallate system combining with solid-phase extraction for the determination of propyl gallate in edible oil

In this paper, a novel chemiluminescence (CL) method has been developed for the determination of propyl gallate (PG). The proposed method was based on the enhancing effect of PG on the CL signal of 2-phenyl-4,5-di(2-furyl)-1H-imidazole (PDFI) and K3Fe(CN)6 reaction in an alkaline solution. Under the optimum conditions, the enhanced CL intensity was linearly related to the concentration of PG. The linear range of the calibration curve was 0.05-8 μg/mL, and the corresponding detection limit (3σ) was 0.036 μg/mL. The relative standard deviation for determining 1.0 μg/mL PG was 2.8% (n=11). The proposed method has been successfully applied to the determination of PG in edible oil. The edible oil samples were prepared by the solid-phase extraction (SPE) with a C18 column served as the stationary phase. Furthermore, the possible CL mechanism was also discussed briefly based on the photoluminescence (PL) and CL spectra.