Preparation,characterization, and kinetics of nanoscale iron in nitrate nitrogen removal from polluted water

The aim of this study was to examine the production of nanoscale ions via the liquid phase reduction method and the effectiveness of the removal of nitrate nitrogen (NO₃^?–N) as well as measure the products and kinetics of the reactions. The nanoparticles obtained were approximately 50 nm in diameter and the main component was iron (Fe). This custom-made nanoscale Fe was highly positively charged, and reacted rapidly with NO₃^?–N in oxygen-free and neutral conditions at room temperature. A 90% removal rate was achieved when the reaction occurred for 30 min in simulation sample water with vigorous shaking at 250 r/min at NO₃^?–N concentrations of 30, 50, 80 or120 mg N/L. The nanometer Fe dosage was maintained throughout the experiment at 4 g/L. A first-order kinetics equation was applied to the obtained experimental data which followed a pseudo first-order reaction. Data demonstrated that the removal of nitrate nitrogen from polluted groundwater using a nanoscale Fe iron was effective and rapid.     

Kinetics of hexavalent chromium reduction by iron metal

The kinetics of Cr(VI) reduction to Cr(III) by metallic iron (Fe⁰) was studied in batch reactors for a range of reactant concentrations, pH and temperatures. Nearly 86.8% removal efficiency for Cr(VI) was achieved when Fe⁰ concentration was 6 g/L (using commercial iron powder (< 200 mesh) in 120 min). The reduction of hexavalent chromium took place on the surface of the iron particles following pseudo-first order kinetics. The rate of Cr(VI) reduction increased with increasing Fe⁰ addition and temperature but inversely with initial pH. The pseudo-first-order rate coefficients (k _obs) were determined as 0.0024, 0.010, 0.0268 and 0.062 8 min^?1 when iron powder dosages were 2, 6, 10 and 14 g/L at 25°C and pH 5.5, respectively. According to the Arrehenius equation, the apparent activation energy of 26.5 kJ/mol and pre-exponential factor of 3 330 min^?1 were obtained at the temperature range of 288–308 K. Different Fe⁰ types were compared in this study. The reactivity was in the order starch-stabilized Fe⁰ nanoparticles > Fe⁰ nanoparticles > Fe⁰ powder > Fe⁰ filings. Electrochemical analysis of the reaction process showed that Cr(III) and Fe(III) hydroxides should be the dominant final products.     

Optimizing synthesis conditions of nanoscale zero-valent iron (nZVI) through aqueous reactivity assessment

Nanoscale iron particles (nZVI) is one of the most important engineered nanomaterials applied to environmental pollution control and abatement. Although a multitude of synthesis approaches have been proposed, a facile method to screen the reactivity of candidate nZVI materials produced using different methods or under varying synthesis conditions has yet been established. In this study, four reaction parameters were adjusted in the preparation of borohydride-reduced nZVI. The reductive properties of the resultant nanoparticles were assayed independently using two model aqueous contaminants, Cu(II) and nitrate. The results confirm that the reductive reactivity of nZVI is most sensitive to the initial concentration of iron precursor, borohydride feed rate, and the loading ratio of borohydride to ferric ion during particle synthesis. Solution mixing speed, in contrast, carries a relative small weight on the reactivity of nZVI. The two probing reactions (i.e., Cu(II) and nitrate reduction) are able to generate consistent and quantitative inference about the mass-normalized surface activity of nZVI. However, the nitrate assay is valid in dilute aqueous solutions only (50 mg·L⁻¹ or lower) due to accelerated deactivation of iron surface at elevated nitrate concentrations. Additional insights including the structural and chemical makeup of nZVI can be garnered from Cu(II) reduction assessments. The reactivity assays investigated in this study can facilitate screening of candidate materials or optimization of nZVI production parameters, which complement some of the more sophisticated but less chemically specific material characterization methods used in the nZVI research.     

Color removal efficiency of dyes using nanozerovalent iron treatment

In this study, zerovalent iron nanoparticles (Fe⁰) were synthesized by chemical reduction method using ferric chloride hexahydrate (FeCl₃?·?6H₂O) as a starting material. Sodium borohydride (NaBH₄) was used as a reducer. The synthesized nanozerovalent iron (NZVI) was separated using magnets. The X-ray diffraction pattern of iron (Fe) nanoparticles showed that the presence of intensive diffraction peak at 2θ value of 45.33° from the lattice plane of face-centered cubic Fe unequivocally indicates that the particles are made of pure Fe. The size of the synthesized NZVI was found to be 16.64?nm. The scanning electron micrograph revealed that the particles have a hexagonal and spherical shape in nature. EDX showed the surface atomic distribution and chemical composition of NZVI. The decolorization efficiency rose with increasing concentration of nanoparticles as well as with time. Maximal color removal efficiency was 90.72% when using 0.5?g/100?mL Fe nanoparticle for acridine orange. Data revealed that the function of NZVI on color removal efficiency was statistically significant. The correlation coefficient between NZVI concentration and time showed a strong negative correlation for dyes used in the experiment.     

Degradation of chlorinated phenols by nanoscale zero-valent iron

Chlorophenols (CPs), as important contaminants in groundwater, are toxic and difficult to biodegrade. Recently nanoscale zero-valent iron received a great deal of attention because of its excellent performance in treating recalcitrant compounds. In this study, nanoscale zero-valent iron particles were prepared using chemical reduction, and the reductive transformations of three kinds of chlorinated phenols (2-CP, 3-CP, and 4-CP) by nanoscale zero-valent iron under different conditions were investigated. The transformation process of the CPs was shown to be dechlorination first, then cleavage of the benzene ring. The removal efficiency of the CPs varied as follows: 2-CP > 3-CP > 4-CP. The reactivity of CPs was associated with their energy of lowest unoccupied molecular orbit (E _LUMO). With the increase in initial concentrations of CPs, removal efficiency decreased a little. But the quantities of CPs reduced increased evidently. Temperature had influence on not only the removal efficiency, but also the transformation pathway. At higher temperatures, dechlorination occurred prior to benzene ring cleavage. At lower temperatures, however, the oxidation product was formed more easily.     

One-step synthesis of bentonite-supported nanoscale Fe/Ni bimetals for rapid degradation of methyl orange in water

Although nanoscale zero-valent iron (nano-Fe⁰) is used to remediate pollutants, this reagent still presents stability and reactivity issues. To solve those issues, we synthesized bentonite-supported nanoscale iron bimetals B-Fe/Ni and B-Fe/Pd. We then used those reagents to degrade the methyl orange dye in water. Results of scanning electron microscopy and X-ray diffraction showed that the presence of bentonite and bimetal decreased nanoscale iron aggregation and increased methyl orange removal efficiency. More than 90 % of methyl orange at 100 mg/L was degraded by B-Fe/Ni (0.15 g/L) in 10 min. By comparison, only 62 % of methyl orange was degraded by B-Fe, and 35 % of methyl orange was degraded by nano-Fe⁰. The degradation rate decreased with the increase of the initial concentration of methyl orange. Lower pH allowed fast removal of methyl orange. Overall our findings show that a nanoscale Fe/Ni on bentonite-supported material is more efficient than nano-Fe⁰. One-step synthesis is more convenient than current two-step-synthesized nanoscale bimetals. Bentonite-supported nanoscale bimetals could therefore be an economic competitive candidate for contaminated water remediation.     

Enhanced degradation of trichloroethylene using bentonite-supported nanoscale Fe/Ni and humic acids

Nanoscale zero-valent iron, named nano-Fe⁰, is a reagent used to degrade trichloroethylene in groundwater. However, the efficiency of nano-Fe⁰ is moderate due to issues of dispersion and reactivity. As an alternative we synthesized bentonite-supported nanoscale Fe/Ni bimetals, named bentonite-Fe/Ni, to test the degradation of trichloroethylene in the presence of Suwannee River humic acids, as a representative of natural organic matter. 0.1 mmol/L trichloroethylene was reacted with 0.5 g/L of nano-Fe⁰, bentonite-Fe, Fe/Ni, and bentonite-Fe/Ni nanoparticles. Results show first that without humic acids the reaction rate constants k _obs were 0.0036/h for nano-Fe⁰, 0.0101/h for bentonite-Fe, 0.0984/h for Fe/Ni, and 0.181/h for bentonite-Fe/Ni. These findings show that bentonite-Fe/Ni is the most efficient reagent. Second, the addition of humic acids increased the rate constant from 0.178/h for 10 mg/L humic acids to 0.652/h for 40 mg/L humic acids, using the bentonite-Fe/Ni catalyst. This finding is explained by accelerated dechlorination by faster electron transfer induced by humic quinone moieties. Indeed, the use of 9, 10-anthraquinone-2, 6-disulfonate as a humic analogue gave similar results.     

Nanoscale zero-valent iron supported on biochar for the highly efficient removal of nitrobenzene

• Biochar supported nanoscale zero-valent iron composite (nZVI/BC) was synthesized. • nZVI/BC quickly and efficiently removed nitrobenzene (NB) in solution. • NB removal by nZVI/BC involves simultaneous adsorption and reduction mechanism. • nZVI/BC exhibited better catalytic activity, stability and durability than nZVI. The application of nanoscale zero-valent iron (nZVI) in the remediation of contaminated groundwater or wastewater is limited due to its lack of stability, easy aggregation and iron leaching. To address this issue, nZVI was distributed on oak sawdust-derived biochar (BC) to obtain the nZVI/BC composite for the highly efficient reduction of nitrobenzene (NB). nZVI, BC and nZVI/BC were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). For nZVI/BC, nZVI particles were uniformly dispersed on BC. nZVI/BC exhibited higher removal efficiency for NB than the simple summation of bare nZVI and BC. The removal mechanism was investigated through the analyses of UV-Visible spectra, mass balance and XPS. NB was quickly adsorbed on the surface of nZVI/BC, and then gradually reduced to aniline (AN), accompanied by the oxidation of nZVI to magnetite. The effects of several reaction parameters, e.g., NB concentration, reaction pH and nZVI/BC aging time, on the removal of NB were also studied. In addition to high reactivity, the loading of nZVI on biochar significantly alleviated Fe leaching and enhanced the durability of nZVI.     

UV light induces Ag nanoparticle formation: roles of natural organic matter,iron, and oxygen

Nanoparticles occurring in the environment originate either from engineered, synthetically produced nanoparticles, or from naturally produced nanoparticles. The latter can be formed in natural media by light-induced reduction of metal ions in presence of natural organic matter, such as humic substances occurring widely in waters, soils and sediments. There is actually few knowledge on the effect of sunlight and of the nature of organic matter on nanoparticle formation. Therefore, we studied here the photoreduction of silver(I) ion to silver nanoparticles with and without ferrous ion under oxic and anoxic conditions, using humic and fulvic acids as proxies of natural organic matter. UV light-induced formation of silver nanoparticles was monitored up to 60 min by measuring surface plasmon resonance in air-saturated mixture and nitrogen-saturated mixture of silver(I) ion–organic matter. Results show that the surface plasmon resonance intensity was about 2.5 times higher in the nitrogen-purged solution mixture than the air-saturated solution. This finding suggests the oxygen-containing species had no major role in forming silver nanoparticles. Therefore, photo-driven formation of silver nanoparticles most likely involved photoactivation of silver(I) ion and natural organic matter complexes. We observed also that both iron(II) and iron(III) ions highly modified the surface plasmon resonance spectra of the particles with broader features. Results also reveal that in the presence of humic acid, the intensity of the surface plasmon resonance peak decreased by at least 50 %, while almost no change in the intensity was seen when fulvic acid was used. Overall, our findings demonstrate that the ligand–metal charge transfer process, affected by the nature of organic matter, i.e., humic acid versus fulvic acid, was influenced by redox iron species.     

Toxicological studies of zinc oxide nanomaterials in rats

In this study, we have evaluated the ability of zinc oxide (ZnO) nanoparticles to induce pulmonary and extrapulmonary toxicities was examined in rats following intratracheal (IT) instillation. Lungs of rats were instilled IT with either phosphate-buffered saline (PBS)?+?1% Tween 80, ZnO nanoparticles, carbonyl iron or quartz particles at a dose of 1 or 5?mg?kg^?1 body weight. Following exposure, bronchoalveolar lavage (BAL) fluid, blood samples and organs including lung, liver, kidneys, heart, pancreas, and brain were collected at 24?h, 1 week, or 1 month of post instillation of nanoparticles and different parameters estimated to assess toxicity. BAL fluid was analyzed for lactate dehydrogenase (LDH) and alkaline phosphatase (ALP) to assess pulmonary toxicity. Exposures to ZnO or quartz particles produced transient dose-dependant increase in BAL fluid LDH and ALP activities at all post exposure periods. Blood samples were analyzed for the tissue damage biomarkers to assess extrapulmonary toxicity. Histopathological examination of lung, liver and kidneys revealed dose-dependent degeneration and necrosis which worsened at 1 week post-instillation periods but recovered at 1 month post instillation. Histopathological examination of rat pancreas, heart, and brain exposed to quartz or ZnO particles showed no marked changes. Data suggest the instillation of ZnO nanoparticles produced a greater pulmonary toxicity in rats comparable with quartz; and extrapulmonary toxicities of these ZnO nanoparticles might be due to translocation into liver and kidney.     

Iron-carbon composite microspheres prepared through a facile aerosol-based process for the simultaneous adsorption and reduction of chlorinated hydrocarbons

Iron-carbon (Fe-C) composite microspheres prepared through a facile aerosol-based process are effective remediation agents for the simultaneous adsorption and reduction of chlorinated hydrocarbons. Complete dechlorination was achieved for the class of chlorinated ethenes that include tetrachloroethylene (PCE), trichloroethylene (TCE), cis- and trans-1,2-dicloroethylene (c-DCE, t-DCE), 1,1-dichloroethylene (1,1-DCE) and, vinyl chloride (VC). The Fe-C particles potentially provides multi-functionality with requisite characteristics of adsorption, reaction, and transport for the effective in situ remediation of chlorinated hydrocarbons. The carbon support immobilizes the ferromagnetic iron nanoparticles onto its surface, thereby inhibiting aggregation. The adsorptive nature of the carbon support prevents the release of toxic intermediates such as the dichloroethylenes and vinyl chloride. The adsorption of chlorinated ethenes on the Fe-C composites is higher (>80%) than that of humic acid (<35%) and comparable to adsorption on commercial activated carbons (>90%). The aerosol-based process is an efficient method to prepare adsorptive-reactive composite particles in the optimal size range for transport through the porous media and as effective targeted delivery agents for the in situ remediation of soil and groundwater contaminants.     

膨润土负载纳米铁用于降解水体中阿莫西林

采用液相还原法合成膨润土负载纳米铁(B-nZVI)和纳米铁(nZVI)并用于降解水中的阿莫西林.实验结果表明,无论是单独nZVI还是B-nZVI都能有效降解阿莫西林.在25 mL浓度为20 mg.L-1的阿莫西林溶液中加入0.1 g的B-nZVI(其中nZVI的含量为0.05 g),溶液的初始pH值为6.65,摇床的振荡速率为250 r.min-1,反应温度为25℃,反应时间为120 min的条件下,B-nZVI对阿莫西林的降解效率高达93.1%,在此实验条件下,单独nZVI(0.05 g)对阿莫西林的降解效率只有82.3%,这是由于膨润土对nZVI起到分散作用,从而使B-nZVI的反应活性得到提高.降解动力学研究表明,B-nZVI对阿莫西林的降解过程符合表观一级反应动力学规律,相关系数R2均大于0.945.B-nZVI可多次重复用于降解阿莫西林.     

Enhanced dechlorination of chlorobenzene by microwave-induced zero-valent iron: particle effects and activation energy

Organic compounds such as chlorobenzene cannot be effectively decomposed with currently available biological and chemical treatment methods. Preliminary studies show that nano-scale zero-valent iron particles irradiated by microwave is effective in decomposing chemically refractive organic compounds such as chlorobenzene. In this study, microwave is applied to enhance chlorobenzene removal using micron-scale iron particles and nano-scale zero-valent iron particles suspended in the chlorobenzene solution as the dielectric media. The results show that better chlorobenzene removal can be achieved when the chlorobenzene solution is irradiated with 250 W microwave for 150 s than without microwave irradiation. The microwave radiation increases iron reaction rate and surface activity, thus enhancing the chlorobenzene removal. The microwave-induced iron particles cause the chlorobenzene activation energy to drop 34.0% for micron-scale iron and 16.1% for nano-scale zero-valent iron. They can remove 13.6 times more chlorobenzene for micro iron, and 3.6 times more chlorobenzene for nano iron. We have demonstrated that the microwave-induced nano-scale iron particles are effective in treating toxic organic substances as demonstrated in this laboratory study.     

Biosynthesis of iron nanoparticles and their application in removing phosphorus from aqueous solutions

This paper reports the biosynthesis of nanoscale zero-valent iron (nZVI) using the extracts of Shirazi thyme leaf (Th-nZVI) and pistachio green hulls (P-nZVI). Scanning electron microscopy verified the successful synthesis of the poorly crystalline nZVI with a spherical shape and diameter in the range of 40–70 nm. According to X-ray diffraction and Fourier transform infrared spectroscope analyses, the synthesised nZVI were composed of iron oxides nanoparticles and ployphenol obtained from Shirazi thyme leaf and pistachio green hulls extracts acting as both reducing and capping agents. The phosphorus removal efficiency of Th-nZVI and P-nZVI increased with time and reached equilibrium at about 4 and 2h, respectively. Sorption of phosphorus on both sorbents was observed to be pH-dependent with maximum phosphorus removal occurring in the pH range of 2–5. Langmuir, Freundlich, Redlich–Peterson, and Temkin models were used to describe phosphorus sorption at pH 5 and maximum sorption capacity for Th-nZVI and P-nZVI was about 40.52 and 29.33?mg?g^?1, respectively. Correlation coefficient (R²) and standard errors of estimate showed that the Elovich model was better than other models at describing the kinetic data. These results suggested that the synthesised nZVI with Shirazi thyme leaf and pistachio green hulls extracts could be employed as an efficient sorbent for the remediation of phosphorus from contaminated water sources.     

Large-scale green synthesis of Cu nanoparticles

This article reports a novel, eco-friendly herbal method to synthesize Cu nanoparticles in large scales. Cu nanoparticles are an alternative to Ag and Au nanoparticles and have potential applications in many industrial areas. Many synthetic routes have been documented for the preparation of copper nanoparticles, but very few routes are eco-friendly and large-scale. We report here the preparation of Cu nanoparticles from aqueous CuSO₄ using non-toxic and inexpensive materials like curd, milk, and herbal extracts such as tamarind and lemon juice as capping agents. X-ray diffraction and transmission electron microscopy show that produced particles are nanocrystalline copper 20–50 nm in size with a face-centered cubic structure. Fourier-transformed infrared spectroscopy evidences the role of organic acids in the capping process. The novelty of this work is the synthesis of Cu nanoparticles from CuSO₄ without electricity and using non-toxic, cheap capping agents.     

Photodegradation of an azo dye by silver-doped nano-particulate titanium dioxide

The synthesis of silver doped nano-particulate titanium dioxide (Ag/TiO₂) using a microemulsion method and an investigation of its photocatalytic activity for the degradation of Acid Red 27 in distilled water under UV-irradiation is reported. The prepared Ag/TiO₂ is characterized using transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. The size of the Ag nanoparticles is around 5–15?nm, with almost uniform distribution on the TiO₂ particles. The efficiency of the photocatalytic process is evaluated to establish the optimum conditions, found to be at 2?wt% of Ag loading on TiO₂, catalyst dosage of 400?mg?L^?1, and calcination temperature of 300°C. Complete decolorization of the dye solution on Ag/TiO₂ was observed in 20?min of UV irradiation in the optimum conditions.     

Novel coprecipitation–oxidation method for recovering iron from steel waste pickling liquor

Waste pickling liquors (WPLs) containing high concentrations of iron and acid are hazardous waste products from the steel pickling processes. A novel combined coprecipitation–oxidation method for iron recovery by Fe₃O₄ nanoparticle production from the WPLs was developed in this study. An oxidation–reduction potential monitoring method was developed for real-time control of the Fe²⁺/Fe³⁺ molar ratio. The key coprecipitation–oxidation parameters were determined using the orthogonal experimental design method. The use of promoters greatly improved the Fe₃O₄ nanoparticle crystallinity, size, magnetization, and dispersion. X-ray diffraction patterns showed that the produced Fe₃O₄ nanoparticles were single phase. The Fe₃O₄ nanoparticles were approximately spherical and slightly agglomerated. Vibrating sample magnetometry showed that the Fe₃O₄ nanoparticles produced from the WPLs had good magnetic properties, with a saturation magnetization of 80.206 emu·g^–1 and a remanence of 10.500 emu·g^–1. The results show that this novel coprecipitation–oxidation method has great potential for recycling iron in WPLs.

Open image in new window

     

Iron-mediated effects on nitrate reductase in marine phytoplankton

The potential activity of nitrate reductase was determined in uni-algal cultures in the laboratory and in natural marine phytoplankton assemblages. In the laboratory bioassays, distinct differences in nitrate reductase activity were observed in iron replete versus depleted cultures for Emiliania huxleyi, Isochrysis galbana and Tetraselmis sp. Cells from iron-depleted cultures had 15 to 50 percent lower enzyme activity than those from iron-replete cultures. Upon addition of iron, nitrate reductase activity was enhanced in depleted cells up to levels comparable to those of the replete cells. Bioassays in the northern North Sea conducted in 1993, under low iron conditions, demonstrated similar results. Upon addition of 2.5 nM iron, a distinct enhancement, to a maximum of three times, of nitrate reductase activity was observed within 32 h after addition. Therefore, iron can stimulate nitrate reductase activity. In spite of the clean techniques used, some nitrate reductase activity was always observed. Iron deficiency was shown to impair nitrate reductase activity, but it is unlikely that nitrate reduction would cease completely.     

In vitro cytotoxicity of multi-wall carbon nanotubes on human cell lines

The aim of this study was to evaluate the in vitro toxicity of two multi-wall carbon nanotubes on four different cell lines: human alveolar epithelial (A549) cells, hepatocytes (Hep 3B cells), human embryonic kidney cells, and intestinal (P407 cells) cells. The adverse effects of carbon nanoparticles were analyzed after 24 h incubation with different cell lines using the trypan blue dye exclusion method. Incubation of carbon nanotubes with different cells produced a concentration-dependent inhibition of growth of the cells. The TC₅₀ or IC₅₀ values (toxic concentration 50, i.e., concentration of particles inducing 50% cell mortality) of two nanoparticles were (1) found to be in the range 23.5–30.5 µg mL^?1, and (2) less than that of quartz (known toxic agent, 28.8–66.9 µg mL^?1), indicating the greater cytotoxic effect of carbon nanoparticles than quartz particles.     

粒状铁与甲醇支持的生物-化学联用法去除富氧地下水中硝酸盐

针对富氧地下水中硝酸盐,采用粒状铁和甲醇支持的生物-化学联用法开展了批实验研究,优化了脱氮反应参数,初步探讨了脱氧脱氮的能力及途径。结果表明,该法的优化参数是粒状铁种类为GI-北京,m（粒状铁）∶m（水）为3∶800,粒状铁粒径为0.425~1.0 mm,反应时间为5 d,甲醇用量为210.59 mg.L-1。生物-化学法、粒状铁和好氧异养菌完全脱氧所需的时间分别是174、206和2 746 min。生物-化学法脱氧依赖于粒状铁化学还原和好氧异养菌有氧呼吸,并且前者起着关键作用。随着反应时间的增加,异养脱氮、自养脱氮和化学还原各自引起的NO3-去除率亦增加。当反应时间≤5 d时,自养脱氮和化学还原的去除率均〈10%,而当反应时间为5 d时,生物-化学法的NO3-去除率达到近100%。生物-化学法内存在异养脱氮、自养脱氮和化学还原3种脱氮途径,其中异养脱氮是最主要的途径,且三者存在共生、协同和促进作用。生物-化学法脱氮期间硝酸盐还原速率≥亚硝酸盐还原速率。生物-化学法去除地下水中硝酸盐是有效可行的。