Nanosized Zerovalent Iron Particles Research Articles

Multiple roles of extracellular polymeric substance in nitrobenzene reduction by nano-sized zero-valent iron in water and their mechanism

ABSTRACT Extracellular polymeric substance (EPS) is secreted by many organisms and makes up a significant constituent of natural organic matter in the environment. However, nothing is known about EPS’s role in the reduction of pollutants by nano-sized zero-valent iron (NZVI). This research showed that the degradation kinetics of nitrobenzene (NB) by NZVI with EPS (0.0272 ± 0.006 min−1) were 2.27 times lower than that without EPS (0.0618 ± 0.006 min−1) in the first cycle, mainly due to competition for reactive sites on the NZVI surface and the complexation of EPS with Fe(II) and Fe(III). In the second and third cycle, the degradation kinetics of NB by NZVI alone decreased obviously, while those in the presence of EPS were preserved or accelerated. Comparative studies with a quinine model compound indicated that EPS did not function as the electron shuttle to transmit electrons effectively. X-ray photoelectron spectroscopy, scanning electron microscopy and X-ray diffraction results suggested that EPS could prevent the oxidation of NZVI and even expose more effective sites on the NZVI surface, thus leading to the preservation or enhancement of NZVI reactivity in the second and third NB degradation cycles. Moreover, we found that EPS also provided colloidal stability to NZVI particles, either by steric mechanisms or electrostatic repulsion. These results indicate that EPS can play an important role in the prolongation of NZVI reactivity during standing application.

Mechanisms of electro-assisted persulfate/nano-Fe0 oxidation process: Roles of redox mediation by dissolved Fe

Mechanisms involved in an electrochemically assisted oxidation process using persulfate and nanosized zero-valent iron (NZVI) were elucidated. Initially, Fe0 acted as a source of Fe2+ to activate the persulfate, then Fe2+/Fe3+ redox mediation between cathode and persulfate played a decisive role in persulfate activation at a current density low enough not to inhibit Fe0 corrosion. An excessive current density which resulted in a low cathodic potential limited Fe0 corrosion and therefore limited the supply of dissolved Fe to activate the persulfate. Direct oxidation of phenol at the anode therefore became more important under the excessive current density than oxidation by sulfate radicals. At a low current density, Fe0 in the NZVI particles was completely transformed into iron (oxyhydr)oxides such as ferrihydrite, lepidocrocite, and magnetite. Fe0 was transformed into Fe2+ little when the current density was high. Increasing the current density increased the energy cost by increasing the amount of electrical energy dissipated in side reactions that decreased sulfate radical formation. The results indicated that a low current density can generally be used to give a high reaction rate and a high energy efficiency and that a high current density can be used when the NZVI particles need to be preserved.

Synthesis, characterization and application of nanoscale zero-valent iron in the degradation of the azo dye Disperse Red 1

In this work, a multivariate response surface methodology (RSM), was applied to analyze the effects of the synthesis variables that affect the reactivity of nanosized zero valent iron particles (NZVI), obtained by chemical reduction with sodium borohidride on the decoloration of azo dye Disperse Red 1 (DR1). Statistical analysis and data interpretation revealed that the generated model showed significant regression and fitting. The conditions that generated NZVI with higher reactivity correspond to [Fe 2+]:[BH4−] molar ratio=1:3, higher rates of reducing agent addition and lower pH (2–3). NZVI particles synthesized under the optimal conditions were characterized via XRD, BET surface area and electron microscopy. The results showed that the nanostructured material had composition, morphology and crystallinity typical of zero-valent iron, with BET surface area of ​​45m2g−1 and an average particle size of 60nm. NZVI yielded high color removal in fairly short time (around 98% in 10min). Latter combination with H2O2 allowed high mineralization.

Degradation kinetics of Endosulfan isomers by micron- and nano-sized zero valent iron particles (MZVI and NZVI)

Degradation kinetics of Endosulfan isomers by micron- and nano-sized zero valent iron particles (MZVI and NZVI)

Treatment of Landfill Leachate by Fenton Process with Nano sized Zero Valent Iron particles

Leachate treatment from municipal landfills has been always a major anxiety in waste management due to its high level of various contaminations. In this paper the effect of Nanosized Zero Valent Iron particles (NZVI) in Fenton process for the treatment of high COD strength landfill leachate was scrutinized. The results corroborated this procedure was fast and efficient. In fact, about 87% of initial COD (38 g/L) was reduced in an hour. The various operation conditions such as pH, initial H2O2 concentration, H2O2/Fe molar ratio and temperature in a batch reactor were investigated. The optimum condition was obtained at pH value of 2, temperature of 40°C and H2O2 to Fe molar ratio equal to 39 by using only 0.07 M of NZVI. In such conditions, 0.08 M H2O2 for the removal of 1 g/L of COD was needed. Furthermore, hydrogen peroxide consumption after Fenton process was evaluated and it was found that it had a direct relationship with COD removal efficiency.