title: Field Deployable Chemical Redox Probe for Quantitative Characterization of Carboxymethylcellulose Modified Nano Zerovalent Iron.
abstract: Nano zerovalent iron synthesized with carboxymethylcelluose (CMC-nZVI) is among the leading formulations of nZVI currently used for in situ groundwater remediation. The main advantage of CMC-nZVI is that it forms stable suspensions, which are relatively mobile in porous media. Rapid contaminant reduction by CMC-nZVI is well documented, but the fate of the CMC-nZVI (including "aging" and "reductant demand") is not well characterized. Improved understanding of CMC-nZVI fate requires methods with greater specificity for Fe(0), less vulnerability to sampling/recovery artifacts, and more practical application in the field. These criteria can be met with a simple and specific colorimetric approach using indigo-5,5'-disulfonate (I2S) as a chemical redox probe (CRP). The measured stoichiometric ratio for reaction between I2S and nZVI is 1.45 ± 0.03, suggesting complete oxidation of nZVI to Fe(III) species. However, near pH 7, reduction of I2S is diagnostic for Fe(0), because aqueous Fe(II) reduces I2S much more slowly than Fe(0). At that pH, adding Fe(II) increased I2S reduction rates by Fe(0), consistent with depassivation of nZVI, but did not affect the stoichiometry. Using the I2S assay to quantify changes in the Fe(0) content of CMC-nZVI, the rate of Fe(0) oxidation by water was found to be orders of magnitude faster than previously reported values for other types of nZVI.
authors.affiliation: Institute of Environmental Health, Oregon Health and Science University , 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States.
authors.forename: Dimin
authors.initials: D
authors.lastname: Fan
authors.affiliation: School of Environmental and Materials Engineering, Shanghai Second Polytechnic University (SSPU) , Shanghai 201209, People's Republic of China.
authors.forename: Shengwen
authors.initials: S
authors.lastname: Chen
authors.affiliation: Institute of Environmental Health, Oregon Health and Science University , 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States.
authors.forename: Richard L
authors.initials: RL
authors.lastname: Johnson
authors.affiliation: Institute of Environmental Health, Oregon Health and Science University , 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States.
authors.forename: Paul G
authors.initials: PG
authors.lastname: Tratnyek
mesh_terms: D002266:Carboxymethylcellulose Sodium / Q000737:chemistry*; D004583:Electrons; D060587:Groundwater / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D015335:Molecular Probes / Q000737:chemistry; D053758:Nanoparticles / Q000737:chemistry*; D010084:Oxidation-Reduction; D016062:Porosity; D014867:Water / Q000737:chemistry
chemical_list: D015335:Molecular Probes; D014867:Water; D007501:Iron; D002266:Carboxymethylcellulose Sodium