Reactivity Of Zero-valent Iron Research Articles

Effect of carboxylic acids on the properties of zerovalent iron toward adsorption and degradation of trichloroethylene

Zerovalent iron (ZVI) based technology has been applied to remediate contaminated groundwater and has been paid great attention as an economic alternative. But it is still remains highly challenging to remove chlorinated pollutants such as trichloroethylene (TCE) with ZVI. Low molecular weight carboxylic ligands (formic acid (FA), oxalic acid (OA), and citric acid (CA)) were chosen to study the influence on the performance of ZVI in groundwater, including the morphology of Fe surface and the Fe dissolution. The removal rate of TCE with ZVI in the presence of 30 mM carboxylic groups followed an order of FA > OA > pure water ≅ CA. FA provides protons to promote the surface corrosion and generated more magnetite on the ZVI surface, which was further responsible for a high adsorption of TCE. With the strong complexing ability of OA and CA, passive layers could form dissoluble complexes via a ligand-promoted dissolution process. However, high concentration of OA resulted in Fe oxalate reprecipitated back onto the ZVI surface then inhibited the reactivity of ZVI. The Fe-ligand complexes also have ability to transform TCE depending on their redox properties. It is expected that effectiveness of carboxylic ligands on the ZVI: those low molecular weight carboxylic ligands in groundwater and soil may enhance the reaction efficiency of ZVI by altering the surface characteristics of ZVI. Therefore, the carboxylic ligands could increase the reactivity and the longevity of ZVI.

Aging of zerovalent iron in various coexisting solutes: Characteristics, reactivity toward selenite and rejuvenation by weak magnetic field

Abstract Aging can influence the performance and subsequent application of zerovalent iron (ZVI) in water treatment. In this study, eight aged ZVI (AZVI) samples were fabricated in different coexisting solutes and their reactivity toward selenite removal were investigated. It showed that the characteristics and reactivity of ZVI varied widely with the aging matrices. The rate constants for selenite removal by ZVI aged in different backgrounds for 24 h were ranked in the order (from most to least reactive): HCO3− (10.00 mM) > NO3− (5.00 mM) > SO42− (2.00 mM) > Cl− > none (i.e., pristine ZVI without pretreatment, Pri-ZVI) > PO43− (0.50 mM) > H2O > SiO32− (2.50 mM) > synthetic groundwater (SGW, 1.50 mM SO42−, 4.50 mM Cl−, 2.00 mM HCO3−, 1.00 mM NO3−, 0.89 mM SiO32−, 0.05 mM PO43−, 5.00 mg/L DOC, 2.00 mM Ca2+, and 12.43 mM Na+). Additionally, the selenite sequestration rates by AZVI were enhanced by 4.3–39.6 folds due to the application of a weak magnetic field (WMF). Moreover, the enhancing effect of WMF on AZVI samples was more outstanding than that on Pri-ZVI based on a wide-spectrum analysis, which may be ascribed to the promoted mass transfer and enrichment of reactants by coupled effects of WMF and aging. In sum, WMF was proved to be a promising method to rejuvenate AZVI samples for wastewater treatment.

Enhanced reductive removal of bromate using Acid-Washed Zero-Valent iron in the presence of oxalic acid

While zero-valent iron (ZVI) has been demonstrated to reduce bromate to bromide, ZVI rapidly loses its reductive power because it is oxidized and a passivation layer forms on its surface. In this study, oxalic acid (OA) is introduced to prevent the formation of passivation layer and maintain reductive reactivity of acid-washed ZVI (AZVI). Despite the fact that AZVI is able to remove bromate, bromate reduction by AZVI is remarkably enhanced in the presence of a very small amount of OA (250μM). OA can coordinate with oxidized iron species (Fe3+) and thus prohibit the formation of passivation layer of iron oxides and hydroxides, allowing AZVI to remain highly reactive for reducing bromate to bromide completely. AZVI+OA also exhibits much lower activation energy than AZVI, indicating that AZVI+OA is much preferred for bromate reduction over AZVI. While bromate reduction by AZVI is considerably hindered under alkaline conditions, the presence of OA lessens the adverse effect and especially retains the reductive reactivity of ZVAI under weakly alkaline conditions. OA is also proven to make AZVI highly reactive even in the presence of co-existing anions without efficiency loss. More importantly, the presence of OA enables AZVI to be reused for bromate reduction quite efficiently even without acid-washing regeneration. These findings reveal that OA-mediated AZVI can enhance bromate reduction, enable AZVI to be highly reactive even under unfavorable conditions, and improve recyclability of AZVI for bromate reduction. These features validate that introduction of OA into bromate reduction by AZVI is advantageous and promising.

Combined Effect of Weak Magnetic Fields and Anions on Arsenite Sequestration by Zerovalent Iron: Kinetics and Mechanisms.

In this study, the effects of major anions (e.g., ClO4-, NO3-, Cl-, and SO42-) in water on the reactivity of zerovalent iron (ZVI) toward As(III) sequestration were evaluated with and without a weak magnetic field (WMF). Without WMF, ClO4- and NO3- had negligible influence on As(III) removal by ZVI, but Cl- and SO42- could improve As(III) sequestration by ZVI. Moreover, the WMF-enhancing effect on As(III) removal by ZVI was minor in ultrapure water. A synergetic effect of WMF and individual anion on improving As(III) removal by ZVI was observed for each of the investigated anion, which became more pronounced as the concentration of anion increased. Based on the extent of enhancing effects, these anions were ranked in the order of SO42- > Cl- > NO3- ≈ ClO4- (from most- to least-enhanced). Furthermore, the inhibitory effect of HSiO3-, HCO3-, and H2PO4- on ZVI corrosion could be alleviated taking advantage of the combined effect of WMF and SO42-. The coupled influence of anions and WMF was associated with the simultaneous movement of anions with paramagnetic Fe2+ to keep local electroneutrality in solution. Our findings suggest that the presence of anions is quite essential to maintaining or stimulating the WMF effect.

Biochar supported Ni/Fe bimetallic nanoparticles to remove 1,1,1-trichloroethane under various reaction conditions

In this study, Ni/Fe nanoparticles supported by biochar to stimulate the reduction of 1,1,1-trichloroethane (1,1,1-TCA) in groundwater remediation was investigated. In order to enhance the reactivity of ZVI (zero valent iron) nanoparticles, surface modification of ZVI was performed using nickel and biochar. The removal efficiency of 1,1,1-TCA increased from 42.3% to 99.3% as the biochar-to-Ni/Fe mass ratio increased from 0 to 1.0. However a higher biochar-to-Ni/Fe ratio showed little difference in the 1,1,1-TCA degradation efficiency. In the presence of Ni, atomic hydrogen generated by ZVI corrosion could be absorbed in the metal additive's lattice and then produce a hydride-like species (H) that represented the primary redox-active entity. The effects of various factors were evaluated, including pH, humic acid (HA) and inorganic matters (Cl−, CO32–, HCO3−, NO3− and SO42–). The degradation of 1,1,1-TCA was greatly affected by pH. The presence of Cl−, CO32–, HCO3− and SO42− had negligible effects, but NO3− and HA showed a significant inhibitory effects on 1,1,1-TCA degradation. In conclusion, biochar supported Ni/Fe nanoparticles could be highly effective for 1,1,1-TCA degradation.

Zero-valent iron for the abatement of arsenate and selenate from flowback water of hydraulic fracturing

Zero-valent iron (ZVI) was tested for the removal of 150 μg L−1 As(V) and 350 μg L−1 Se(VI) in high-salinity (ionic strength 0.35–4.10 M) flowback water of hydraulic fracturing. Over 90% As(V) and Se(VI) was removed by 2.5 g L−1 ZVI in Day-14 flowback water up to 96-h reaction, with the remaining concentration below the maximum contaminant level for As(V) and criterion continuous concentration for Se(VI) recommended by US EPA. The kinetics of As(V) and Se(VI) removal followed a pseudo-second-order rate expression with the observed rates of 4.51 × 10−2–4.91 × 10−1 and 3.48 × 10−2–6.58 × 10−1 h−1 (with 0.5–10 g L−1 ZVI), respectively. The results showed that Se(VI) removal significantly decreased with increasing ionic strength, while As(V) removal showed little variation. Common competing anions (nitrate, bicarbonate, silicate, and phosphate), present in shallow groundwater and stormwater, caused marginal Se(VI) desorption (2.42 ± 0.13%) and undetectable As(V) desorption from ZVI. The competition between As(V) and Se(VI) for ZVI removal depended on the initial molar ratio and surface sites, which occurred when the Se(VI) concentration was higher than the As(V) concentration in this study. The characterization of As(V)- and Se(VI)-loaded ZVI by X-ray diffraction and Raman analysis revealed that ZVI gradually converted to magnetite/maghemite corrosion products with lepidocrocite in flowback water over 30 days. Similar corrosion compositions were confirmed in aerobic and anaerobic conditions regardless of the molar ratio of As(V) to Se(VI). The high reactivity and stability of ZVI showed its suitability for in-situ prevention of As(V) and Se(VI) migration due to accidental leakage, spillage, or overflow of flowback water.

Performance enhancement of zero valent iron based systems using depassivators: Optimization and kinetic mechanisms

The long-term ability of Zero-Valent Iron (ZVI) in contaminant removal relies on the effectiveness of iron to serve as electron donor, which makes it a versatile remediation material. However, the formation of oxide and hydroxide layers results in passive layer on ZVI surface during contaminant removal hinders its reactivity. The focus of this research was to evaluate the performance of corrosive agents such as acetic acid (HAc), aluminium sulphate (Alum) and potassium chloride (KCl) as depassivators to overcome passivation for sustainability and longevity. Batch experiments using seven combinations of the above chemicals were conducted to optimize the dosage of depassivators based on passive layer removal. The influence of depassivators in catalytic activity of ZVI in removing Cr6+ was evaluated. The passive layer on ZVI particles was characterized using Scanning Electron Microscopy (SEM) and confirmed by Energy-Dispersive X-ray spectroscopy (EDAX) analysis. The major mechanisms in passive layer removal was found to be H+ ion embrittlement followed by uniform depassivation when [HAc] was used and pitting corrosion when [Alum] and [KCl]were used. All the seven sets of chemicals enabled depassivation, but considering the criteria of maximum depassivation, catalytic activity and long term reactivity the depassivation treatments were effective in order as [HAc-Alum] > [HAc-Alum-KCl] >[HAc] > [Alum] > [HAc-KCl] > [KCl] > [Alum-KCl]. The kinetic rate of ZVI using [HAc-Alum] and [Alum] was relatively unchanged over the pH range of 4–10, made it suitable for ex-situ remediation. This insignificant influence of initial pH in catalytic activity of ZVI along with the improvement in longevity and sustainability makes it suitable for effective water treatment applications. The present work has successfully demonstrated that chemical depassivation can restore considerable reactivity of ZVI in the existing permeable reactive barriers.

Removal of Manganese and Copper from Contaminated Groundwater Generated from Mines Landfills Waste Using ZV-I, AC and NZ in PRB Technology

In this study, Zero Valent Iron (ZV-I), Activated Carbon (AC) and Natural Zeolite (NZ) were utilized as reactive material for testing its effectiveness for removal manganese and copper in the waste of Mine Landfills. Hereby, four parameters were taken in this study which is initial concentration of metal, initial groundwater alkalinity PH and dosage of reactive ZV-I, AC, or NZ. Batch results show that ZV-I is the most effective materials for removal manganese and copper up to 48 ppm at low concentration of ZV-I 1990-4990 ppm while initial pH range varies between three through seven. The study discovered that ZV-I reactive compound can be used effectively for manganese removal through settling and adsorption on ZV-I, while copper is basically removed by ZV-I through direct reductive settling. Also, ACcompared to ZV-I reactive material has not significant effect on manganese removal whereas AC basically removed manganese by adsorption while Copper is removed basically by settling. The removal of Copper and manganese can be increased by increasing detention time and dosage of carbon. The study showed that manganese and copper are removed slowly and ineffective by NZ compound.

Characterization of Behavior of Colloidal Zero-Valent Iron and Magnetite in Aqueous Environment

Nano-sized iron colloids are formed as acid mine drainage is exposed to surface environments and is introduced into surrounding water bodies. These iron nanomaterials invoke aesthetic contamination as well as adverse effects on aqueous ecosystems. In order to control them, the characteristics of their behaviour should be understood first, but the cumulative research outputs up to now are much less than the expected. Using zero-valent iron (ZVI) and magnetite, this study aims to investigate the behaviour of iron nanomaterials according to the change in the composition and pH of background electrolyte and the concentration of natural organic matter (NOM). The size and surface zeta potential of iron nanomaterials were measured using dynamic light scattering. Characteristic behaviour, such as aggregation and dispersion was compared each other based on the DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory. Whereas iron nanomaterials showed a strong tendency of aggregation at the pH near point of zero charge (PZC) due to electrostatic attraction between particles, their dispersions became dominant at the pH which was higher or lower than PZC. In addition, the behaviour of iron nanomaterials was likely to be more significantly influenced by cations than anions in the electrolyte solutions. Particularly, it was observed that divalent cation influenced more effectively than monovalent cation in electrostatic attraction and repulsion between particles. It was also confirmed that the NOM enhanced the dispersion nanomaterials with increasing the negative charge of nanomaterials by coating on their surface. Under identical conditions, ZVI aggregated more easily than magnetite, and which would be attributed to the lower stability and larger reactivity of ZVI.

Selenate removal by zero-valent iron in oxic condition: the role of Fe(II) and selenate removal mechanism.

In this study, batch experiments were conducted to investigate the effect of the concentration of ferrous [Fe(II)] ions on selenate [Se(VI)] removal using zero-valent iron (ZVI). The mechanism of removal was investigated using spectroscopic and image analyses of the ZVI-Fe(II)-Se(VI) system. The test to remove 50 mg/L of Se(VI) by 1 g/L of ZVI resulted in about 60% removal of Se(VI) in the case with absence of Fe(II), but other tests with the addition of 50 and 100 mg/L of the Fe(II) had increased the removal efficiencies about 93 and 100% of the Se(VI), respectively. In other batch tests with the absence of ZVI, there were little changes on the Se(VI) removal by the varied concentration of the Fe(II). From these results, we found that Fe(II) ion plays an accelerator for the reduction of Se(VI) by ZVI with the stoichiometric balance of 1.4 (=nFe(2+)/nSe(6+)). Under anoxic conditions, the batch test revealed about 10% removal of the Se(VI), indicating that the presence of dissolved oxygen increased the kinetics of Se(VI) removal due to the Fe(II)-containing oxides on the ZVI, as analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) spectra also showed that the reductive process of Se(VI) to Se(0)/Se(-II) occurred in the presence of the both ZVI and Fe(II). The final product of iron corrosion was lepidocrocite (γ-FeOOH), which acts as an electron transfer barrier from Fe(0) core to Se(VI). Therefore, the addition of Fe(II) enhanced the reactivity of ZVI through the formation of iron oxides (magnetite) favoring electron transfer during the removal of Se(VI), which was through the exhaustion of the Fe(0) core reacted with Se(VI).

Common oxidants activate the reactivity of zero-valent iron (ZVI) and hence remarkably enhance nitrate reduction from water

The surface passivation and the subsequent reduction of ZVI reactivity seriously restricted the application of zero-valent-iron (ZVI) for water remediation. This study comprehensively investigated the critical role of common oxidants, such as O2, H2O2, KMnO4 and CrO42− in activating the reactivity of ZVI surface and hence in facilitating nitrate reduction from the aqueous solution at non-acidic pH. Nitrate reduction by ZVI was negligible in the absence of O2 at pH>5. To the contrary, obvious reduction of nitrate was observed in the presence of O2, although with a clear trend of decreasing nitrate reduction with pH increase. KMnO4, H2O2, and CrO42− were observed to strongly enhance the reactivity of ZVI. Dosing KMnO4 and H2O2 achieved 94% and 97% of nitrate reduction at pH 5.0, and 74% and 98% at pH 7.0. Five cycles of nitrate removal by the combined system of ZVI/oxidant/zeolite demonstrated the overcoming of the impedance of passivation layer, strongly facilitating the ultimate removal of nitrogen species from the aqueous solution.

Bio-beads with immobilized anaerobic bacteria, zero-valent iron, and active carbon for the removal of trichloroethane from groundwater.

Chlorinated hydrocarbons are the most common organic pollutants in groundwater systems worldwide. In this study, we developed bio-beads with immobilized anaerobic bacteria, zero-valent iron (ZVI), and activated carbon (AC) powder and evaluated their efficacy in removing 1,1,1-trichloroethane (TCA) from groundwater. Bio-beads were produced by polyvinyl alcohol, alginate, and AC powder. We found that the concentration of AC powder used significantly affected the mechanical properties of immobilized bio-beads and that 1.0 % (w/v) was the optimal concentration. The bio-beads effectively degraded TCA (160 mg L(-1)) in the anaerobic medium and could be reused up to six times. The TCA degradation rate of bio-beads was 1.5 and 2.3 times greater, respectively, than ZVI + AC treatment or microbes + AC treatment. Measuring FeS produced by microbial reactions indicated that TCA removal occurred via FeS-catalyzed dechlorination. Analysis of clonal libraries derived from bio-beads demonstrated that the dominant species in the community were Betaproteobacteria and Gammaproteobacteria, which may contribute to the long-term stability of ZVI reactivity during TCA dechlorination. This study shows that the combined use of immobilized anaerobic bacteria, ZVI, and AC in bio-beads is effective and practical for TCA dechlorination and suggests they may be applicable towards developing a groundwater treatment system for the removal of TCA.

Reactive Transport Modeling of ZVI Column Experiments for Nickel Remediation

AbstractMIN3P, a multicomponent reactive transport model for variably saturated porous media, is used to simulate the outputs of column tests carried out using zero valent iron (ZVI) for nickel contaminated groundwater remediation. The objective of this study is to investigate the main chemical reactions involved in contaminant removal and the main causes of the reactivity decline of ZVI over time. According to the results of the model the major causes of ZVI reactivity loss is identified in the mineral precipitation of α‐FeOOH on iron surface that probably caused ZVI passivation and led to a decline of the electron transfer rate. An existing empirical relationship between mineral precipitation and the reactivity loss of ZVI, included in the model, reproduced the changes in nickel removal observed during different laboratory column tests.

Effects of geochemical constituents on the zero‐valent iron reductive removal of nitrobenzene in groundwater

AbstractNitrobenzene (NB) was chosen as the model contaminant, and batches lab scale experiments were conducted to investigate the effects of geochemical compositions on reductive removal of nitrobenzene by zero‐valent iron (ZVI) in groundwater. Experimental results showed that the kinetics of nitrobenzene reduction by ZVI was a pseudo‐first order with an observed rate constant, kobs, of 3.67 × 10−4/s; the calculated half‐life of nitrobenzene was 1.89 × 103/s. The geochemical constituents of groundwater have significant influences on ZVI reactivity and nitrobenzene reduction. The presence of high concentration of nitrate, carbonate, sulphate and hardness had detrimental effects on reduction of nitrobenzene and formation of aniline; chloride had a slight positive effect on the nitrobenzene reduction and the formation of aniline. Bicarbonate enhanced the ZVI reactivity initially at lower concentration and inhibited the nitrobenzene reduction at high concentration. Therefore, the performance and reactivity of ZVI were found to be strongly affected by the geochemical constituents of groundwater.

Coupling of polyhydroxybutyrate (PHB) and zero valent iron (ZVI) for enhanced treatment of chlorinated ethanes in permeable reactive barriers (PRBs)

In this work, the use of polyhydroxybutyrate (PHB) as a feasible carbon source in a permeable reactive barrier (PRB) was investigated as a strategy for enhancing the performance of zero valent iron ZVI towards chlorinated ethanes, increasing iron reactivity and longevity and enhancing biological reductive processes. Results concerning PHB fermentability under the conditions created by the ZVI reactive zone are presented. Column experiments were performed to verify whether PHB can be anaerobically fermented with the production of volatile fatty acids (VFAs) and H2, which in turn can be used as electron donors for downstream biological reductive dechlorination. Acetate and butyrate were detected in the effluent of the Fe/PHB-column at concentrations as high as 2500 and 700mg/L, respectively, confirming that microbially induced PHB hydrolysis and fermentation was readily established without the need for an external inoculum. The formation of high VFA concentrations significantly lowered the pH of the Fe/PHB-column liquid phase with respect to that observed in the presence of only ZVI. The combined effect of the acidic conditions and the dissolved VFA significantly enhanced ZVI reactivity and longevity, likely due to the prevention of passivation of the iron surface by Fe(II) and Fe(III) (hydro)oxide precipitation. As a consequence, TeCA, used as a target parent contaminant, and its byproduct degradation rates were significantly increased, as was the durability of the reactive material.

Reduction of As(V) to As(III) by commercial ZVI or As(0) with acid-treated ZVI

Zero-valent iron (ZVI) consists of an elemental iron core surrounded by a shell of corrosion products, especially magnetite. ZVI is used for in situ removal or immobilization of a variety of contaminants but the mechanisms for removal of arsenic remain controversial and the mobility of arsenic after reaction with ZVI is uncertain. These issues were addressed by separately studying reactions of As(V) with magnetite, commercial ZVI, and acid-treated ZVI. Strictly anoxic conditions were used. Adsorption of As(V) on magnetite was fast with pH dependence similar to previous reports using oxic conditions. As(V) was not reduced by magnetite and Fe(II) although the reaction is thermodynamically spontaneous. As(V) reactions with ZVI were also fast and no lag phase was observed which was contrary to previous reports. Commercial ZVI reduced As(V) to As(III) only when As(V) was adsorbed, i.e., for pH < 7. As(III) was not released to solution. Acid-treated ZVI reduced As(V) to As(0), shown using wet chemical analyses and XANES/EXAFS. Comparisons were drawn between reactivity of acid-treated ZVI and nano-ZVI; if true then acid-treated ZVI could provide similar reactive benefits at lower cost.

Comparison of Reactivity of Nanoscaled Zero‐Valent Iron Formed on Clay Surfaces

Clay minerals were used as template‐supporting matrices to synthesize nanoscaled zero‐valent iron (ZVI). The size and distribution of the synthesized ZVI particles were related to clay structure, origin of negative charges, and surface charge density. The average particle size ranged from 0.5 nm (perpendicular to the clay layers) for the ZVI intercalated in smectite interlayers, to 1 to 2 nm for the ZVI residing on kaolinite and pyrophyllite surfaces, and ∼5 nm for the ZVI formed on illite and smectite external surfaces. The reactivity of the ZVI was evaluated based on the rate and extent of reduction of nitrobenzene to aniline. The results revealed that the reactivity of ZVI decreased with increasing particle size, and the ZVI intercalated in smectite clay manifested the highest reactivity. The reaction efficiency of the ZVI associated with smectite clay was estimated to be as high as 90% based on the equivalency of electron transfer from ZVI to nitrobenzene. The great reactivity and high efficiency of smectite‐intercalated ZVI, along with many other advantageous properties of smectite (e.g., a layer structure that protects ZVI from aggregation and oxidation), warrants its potential utilization in the development of in situ remediation and treatment technologies for inorganic and organic contaminants.

Catalytic hydrodechlorination of 1,2-dichloroethane using copper nanoparticles under reduction conditions of sodium borohydride

1,2-Dichloroethane (1,2-DCA) is a raw material used for the manufacture of vinyl chloride monomer (VCM) and therefore has very often been detected in the groundwater nearby the VCM manufacturing plant. Zero-valent iron (ZVI) is capable of degrading a wide array of highly chlorinated contaminants; however, the reactivity of ZVI towards 1,2-DCA is very low. In this study, zero-valent copper nanoparticles have been synthesized for effective dechlorination of 1,2-DCA under reduction conditions of sodium borohydride. Copper nanoparticles consisted of mainly metallic copper (Cu(0)) with small amounts of cuprous oxide (Cu(2)O). They have surface areas of about 19.0 m(2) g(-1) and an average diameter of 15 nm. Batch experiments were conducted to test the effectiveness of copper nanoparticles for 1,2-DCA degradation using sodium borohydride as electron donors where the ORP was measured as -1100 mV. More than 80% of 1,2-DCA (30 mg L(-1)) was rapidly degraded within 2 h in the presence of both copper nanoparticles (2.5 g L(-1)) and borohydride (25 mM). No reduction of 1,2-DCA was observed when the system contained either copper nanoparticles alone or borohydride alone. The degradation intermediates included ethane and ethylene accounting for 79% and ∼1.5% of the 1,2-DCA lost, respectively. Potential environmental applications can be achieved by immobilizing copper nanoparticles onto the surface of reducing metals to form a reactive bimetallic structure.

Degradation of PCE, TCE and 1,1,1-TCA by nanosized FePd bimetallic particles under various experimental conditions

The degradation of chlorinated organic compounds, such as PCE (tetrachloroethene), TCE (trichloroethene) and 1,1,1-TCA (1,1,1 -trichloroethane), was conducted using nanosized FePd bimetallic particles. In order to enhance the reactivity of ZVI (zero valent iron) nanoparticles, surface modification of ZVI nanoparticles was performed using Pd and CMC (carboxymethyl cellulose). The surface modification was found to form CMC-stabilized FePd bimetallic nanoparticles (CMC-FePd). The average TCE removal efficiency by the CMC-FePd was significantly increased by ∼85% compared to employing conventional ZVI nanoparticles (∼15%). This increase in the TCE removal efficiency was most likely due to the increased amount of atomic hydrogen produced by the formation of CMC-FePd. For PCE and 1,1,1-TCA, the removal efficiencies by CMC-FePd were approximately 80% and 56%, respectively. For all three chlorinated organic compounds, the amount of Cl − ions in the aqueous phase during the degradation increased with increasing reaction time. This result suggests that the main degradation mechanism of the chlorinated compounds by CMC-FePd was reductive dechlorination.

Degradation of diclofenac in water by homogeneous and heterogeneous sonolysis

The study is about the degradation of a widely used anti-inflammatory drug-diclofenac (DCF) by high frequency ultrasound to select the operating conditions and to improve the process efficiency by the addition of iron species. The initial concentration, pH and frequency of operation that rendered maximum degradation of the drug were 30 μM, 3.0 and 861 kHz, respectively. The efficacy (EF) of each additive was expressed by a “yield factor” defined as the change in DCF concentration in 1-h sonication per unit mass of Fe in the reactor. Estimated values of EF were 41.54, 1.65 and 0.02 μM mg −1, respectively for non-reactive iron superoxide nanoparticles (NPI), reactive divalent iron (DVI) and reactive zero-valent iron (ZVI). The remarkably high yield in presence of NPI was attributed to the synergy of nanotechnology and ultrasound; i.e. combined effects of massive surface area, excess cavitation nuclei, enhanced mass transfer and continuous cleaning of the metal surface. Total mineralization after 90 min sonication of DCF in the presence of 8.9 mM ZVI, 0.01 mM DVI and 0.001 mM NPI were 22%, 43% and 30%, respectively. Although DVI provided a larger degree of mineralization, the efficiency of NPI was still higher owing to its 10-fold lower effective dose.