Trichloroethene Hydrodechlorination in Water by Highly Disordered Monometallic Nanoiron

Abstract

The small size and high surface-to-volume ratio makes nanoiron attractive for in situ remediation of groundwater contaminants that are susceptible to reductive transformation, e.g. trichloroethylene (TCE). Nanoiron synthesized from borohydride reduction of dissolved iron is the most widely studied. Its reactivity with chlorinated organics such as trichloroethylene (TCE) is unique compared to other nanoiron and to iron filings that are typically used for in situ groundwater remediation, e.g. (1) higher surface-area normalized TCE dechlorination reaction rate constants, (2) the formation of saturated reaction products, and (3) higher reaction rates in the presence of H2. The objectives of this study were to confirm the ability of monometallic Fe(B) to activate and use H2 for TCE hydrodechlorination and to determine how the nanoiron chemical composition and the degree of crystallinity influence nanoiron reactivity with TCE. Fresh (Fe(B)), partially oxidized (Fe(B)ox), and annealed (Fe(B)cr) nanoiron samples made from borohydride reduction of dissolved Fe(II) in a water/methanol solution were characterized by HRTEM, XRD, XPS, and N2-BET. The TCE dechlorination rate and products and the dissolved iron and boron released during reaction with TCE were measured. Fe(B) and Fe(B)ox were poorly ordered and could activate and use H2 to reduce TCE to ethane. Fe(B)cr was crystalline and could not activate and use H2 and reduced TCE to acetylene. The poorly ordered structure rather than the presence of boron (up to 5 wt %) provided the ability of Fe(B) and Fe(B)ox to activate and use H2 for TCE dechlorination. Fe(B) and Fe(B)ox underwent oxidative dissolution during TCE dechlorination, and the Fe0 in the particles was fully accessible. Particle dissolution suggests that normalizing the observed reaction rate constants with the measured specific surface area for comparison with other types of Fe0 may be inappropriate.

“Green” Atom Transfer Radical Polymerization: From Process Design to Preparation of Well-Defined Environmentally Friendly Polymeric Materials

“…It has been shown that various active metallic nanoparticles can react with chlorinated liquids and reduce them to significantly less toxic compounds. [451][452][453][454] Iron nanoparticles are very useful, but to be effective in groundwater treatment they need to be dispersable in water at a broad pH range and in the presence of various electrolytes, transportable through a watersaturated porous matrix (soil), and to have an affinity for the water-DNAPL interface. The particles should also be stable toward oxidation.…”

Numerical prediction of diffusion and electric field-induced iron nanoparticle transport

“…With the development of advanced nanotechnologies since late nineties, due to their size and reactivity that allowed an easy injection,zero valent iron nanoparticles (nZVI) were considered a promising step forward in soil and groundwater clean-up, particularly targeting organochlorines [4][5][6][7][8]. The nZVI transport in porous media was studied in column tests with sand [9][10][11][12][13][14][15][16], glass beads [17][18][19] and model soils [20,21].…”

Improvements in nanoscale zero-valent iron production by milling through the addition of alumina

“…In this respect, better reactivity has been reported to highly disordered Fe compared with crystalline nZVI obtained by H reduction of iron oxides (Liu et al 2005a ) or by vacuum annealed Fe (Liu et al 2005b ), although in the latter case the reactivity against some pollutants seems to be unaffected by crystallization during annealing (Dickinson and Scott 2011 ). In the case of M48h-Al O (Fig.…”

“…The specific surface area (SSA) was analysed by BET gas adsorption drying the ethanol suspension with a maximum degassing temperature of 100 °C (ASAP 2020, Micromeritics). The Fe (0) content was determined in triplicate by the hydrogen production method (Liu et al 2005a ) where iron reacts with sulphuric acid added to the slurry and the volume of produced hydrogen was measured. The morphology of the milled particles was studied by Scanning Electron Microscopy (SEM) (Gemini, Zeiss).…”

“…Since the oxide layer and SSA values do not account for the high Cr(VI) removal capacity of M48h-Al O , this high efficiency must be more related to two other factors: the first would be an enhanced density of reactive sites in the surface (Lapuerta et al 2006 ), the second would be the internal structure of the nanoparticles (Liu et al 2005a ). In the first point, it has been suggested that the new surfaces created by the fracture of the former particles and the presence of a great amount of irregularities offer a large number of reaction sites, which causes an increase of reactivity (Köber et al 2014 ;Li et al 2009 ).…”