Reduction of azo dyes with zero-valent iron

Sangkil Nam, Paul G. Tratnyek

Research output: Contribution to journalArticlepeer-review

414 Scopus citations


The reduction of azo dyes by zero-valent iron metal (Fe0) at pH 7.0 in 10 mM HEPES buffer was studied in aqueous, anaerobic batch systems. Orange II was reduced by cleavage of the azo linkage, as evidenced by the production of sulfanilic acid (a substituted aniline). Adsorption of the dyes on iron particles was less than 4% of the initial concentration, and >90% mass balance was achieved by summing aqueous concentrations of dye and product amine. All of the 9 azo dyes tested were reduced with first-order kinetics. The kinetics of decolorization at the λ(max) of each dye were rapid: a typical k(obs) was 0.35 ± 0.01 min-1 for Orange II at 130 rpm on an orbital shaker, corresponding to a surface area normalized rate constant (k(SA)) of 0.21 ± 0.01 L m-2 min-1. The rate of reduction of Crocein Orange G varied with initial dye concentration in a way that suggests saturation of surface sites on the Fe0, and varied with the square-root of mixing rate (rpm) in a manner indicative of mass transfer limited kinetics. Correlation analysis using k(obs) for all of the azo dyes, estimates of their diffusion coefficients, and calculated energies of their lowest unoccupied molecular orbitals (E(LUMO)), gave no strong trends that could be used to derive structure-activity relationships. Using an authentic sample of wastewater from a dye manufacturing operation and construction-grade granular Fe0, rapid decolorization was achieved that was consistent with reduction of azo dyes. (C) 2000 Elsevier Science Ltd.

Original languageEnglish (US)
Pages (from-to)1837-1845
Number of pages9
JournalWater Research
Issue number6
StatePublished - Apr 1 2000


  • Correlation analysis
  • Decolorization
  • Iron metal
  • Kinetics
  • Mass transport

ASJC Scopus subject areas

  • Ecological Modeling
  • Water Science and Technology
  • Waste Management and Disposal
  • Pollution


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