Estimating dehalogenation reactivity of nanoscale zero-valent iron by simple colorimetric assay by way of 4-chlorophenol reduction

Abstract

A number of different nanoscale zero-valent iron (nZVI) materials have been prepared and compared depending on the desired properties for the particular application, but different physicochemical properties of this prepared nZVI make it difficult to universally compare and standardize them to the same scale. In this study, we aimed to demonstrate a simple microplate-based colorimetric assay using 4-chlorophenol as an indicator with respect to the remediation of real treatment targets, such as trichloroethylene (TCE), 1,1,1-trichloroethane (TCA), and atrazine. Effect of nickel contents on 4-chlorophenol reduction was successfully investigated by the miniaturized colorimetric assay. In the same manner, the effect of nickel contents on dehalogenation of TCE, TCA, and atrazine was investigated and the pseudo-first-order kinetic constants were compared with the results for 4-chlorophenol. The similar pattern could be observed between 4-chlorophenol reduction obtained by colorimetric assay and TCE, TCA, atrazine reduction obtained by a traditional chromatographic method. The reaction kinetics does not match perfectly, but the degree of reaction can be estimated. Therefore, the colorimetric assay can be a useful and simple screening tool to determine nZVI reactivity toward halogenated organics before it is applied to a particular remediation site.

Developing the Ascorbic Acid Test: A Candidate Standard Tool for Characterizing the Intrinsic Reactivity of Metallic Iron for Water Remediation

“…However, this method was not published in a peer-reviewed journal until 2005 [38]. Nearly 18 years passed and several other independent methods have been presented [39,40,68], but are still not universally tested and accepted [21,35,78]. It is very disappointing that the Fe 0 research community has been working for 30 years without characterizing the Fe 0 materials that are at the center of their systems.…”

“…Regarding granular Fe 0 (micro-scale) as an environmental reducing agent has created a circular reasoning that dragged the research community into an unprecedented confusion [9,17,18,20]. In particular, to enhance the efficiency of Fe 0 to remove selected contaminants from the polluted waters, bimetallic materials (e.g., Fe 0 /Cd 0 , Fe 0 /Ni 0 , Fe 0 /Pd 0 , Fe 0 /Pt 0 ) and nano-scale materials (nano-Fe 0 and nano-bimetallics) have been developed [4,10,21,22]. However, the discussion of the reactivity is still based on the value of E 0 = −0.44 V for the electrode reaction Fe II /Fe 0 [18,21,22].…”

“…In particular, to enhance the efficiency of Fe 0 to remove selected contaminants from the polluted waters, bimetallic materials (e.g., Fe 0 /Cd 0 , Fe 0 /Ni 0 , Fe 0 /Pd 0 , Fe 0 /Pt 0 ) and nano-scale materials (nano-Fe 0 and nano-bimetallics) have been developed [4,10,21,22]. However, the discussion of the reactivity is still based on the value of E 0 = −0.44 V for the electrode reaction Fe II /Fe 0 [18,21,22]. One problem has been that the terms "efficiency" and "reactivity" have been often randomly interchanged [18,[23][24][25].…”

“…Enhanced remediation efficiency by varying the Fe 0 dosage is justified by variability of the surface area available for Fe 0 dissolution which is thought to be coupled to contaminant reductive transformations [11,21,22,26,27]. The higher efficiency of nano-Fe 0 relative to granular Fe 0 is based roughly on the same principle i.e., larger available surface area, despite difference in intrinsic reactivity [22,[28][29][30].…”

“…The characterization of the actual contribution of Fe 0 to the process of contaminant removal using Fe 0 /H 2 O systems is complicated by the complex interactions between relevant contaminants, operating conditions (e.g., initial concentration, stirring intensity), water chemistry (e.g., availability of co-solutes, contamination level, pH value), and transport phenomena (e.g., advection, diffusion) in the bulk solution and in the vicinity of Fe 0 [21,[33][34][35]. Despite the wide application of Fe 0 (e.g., bimetals, Fe 0 , nano-Fe 0 ) for the treatment of a variety of pollutants, the evaluation of Fe 0 reactivity has not been standardized [21,[34][35][36][37][38][39][40]. Of the few characterization tools presented for the Fe 0 intrinsic reactivity, only two are truly contaminant independent as they quantify the kinetics of Fe 0 dissolution (Equation ( 1)) by monitoring either dissolved Fe [34,41,42] or generated H 2 [38,43].…”