Reduction of Hexavalent Chromium by Green Tea Polyphenols and Green Tea Nano Zero-Valent Iron (GT-nZVI)

Abstract

This study reports on the direct reduction of hexavalent chromium [Cr(VI)] by green tea polyphenols, including a green tea solution and pure epigallocatechin gallate (EGCG) solution. A linear trend was observed between the amount of reduced Cr(VI) and the amount of added polyphenols. The green tea solution showed a continued decrease in the observed stoichiometry with increasing pH, from a maximum of 1.4 mol per gallic acid equivalent (GAE) of green tea at pH 2.5, to 0.2 mol/GAE at pH 8.8. The EGCG solution exhibited different behavior, with a maximum stoichiometry of 2 at pH 7 and minimum of 1.6 at pH 4.4 and 8.9. When green tea was used to first react with Fe and form GT-nZVI, the amount of Cr(VI) reduced by a certain volume of GT-nZVI was double compared to green tea, and 6 times as high considering that GT-nZVI only contains 33 % green tea.

Sustainable Synthesis of Nanoscale Zerovalent Iron Particles for Environmental Remediation

“…studied the synthesis of nZVI particles from green tea and pure epigallocatechin gallate (EGCG) solution and used them for the reduction of Cr IV . The nZVI prepared from green tea (GT‐nZVI) was able to reduce twice the amount of Cr VI than direct reduction of Cr VI with green tea . Kozma et al.…”

“…studied the synthesis of nZVI from green tea and EGCG solution and used it for the reduction of Cr IV . nZVI prepared from green tea (GT‐nZVI) could reduce twice the amount of Cr VI than direct reduction with green tea alone . In another study, the comparative Cr VI remediation performance for contaminated soil was investigated by using green tea extract‐synthesized nZVI and calcium polysulfide (CPS).…”

“…The functionality of nZVI and CPS was evaluated by using columns packed with contaminated soil, and the eluents were analyzed by colorimetric and micro‐X‐ray absorption near edge structure (XANES) analysis. The CPS for Cr VI removal increased the mobilization of Mn and As, and also increased the acidity for a short period . Chromium reduction has also been carried out by using green nZVI derived from willow leaves, Citrus limetta peel, Nephrolepis auriculate extract, green tea extracts, Eriobotrya japonica , Eucalyptus leaves, Rosa damascene , Thymus vulgaris and Urtica dioica , S. jambos Alston, Oolong tea and A. moluccana Willd extract and S. jambos Alston leaves …”

Cr (VI) Removal from Aqueous Solution Using Starch and Sodium Carboxymethyl Cellulose-Coated Fe and Fe /Ni Nanoparticles

“…To investigate the reduction mechanism, Zhu [27] used the Langmuir-Hinshelwood first-order kinetic model to evaluate the reaction kinetics: (7) …where K represents the reaction rate constant of a solid surface and b is a constant associated with adsorption heat and temperature. When the reaction substrate concentration is very low, bC«1 and formula (7) can be written as: (8) When k obs is equal to Kb in Equation 8, the reaction can be simplified as a first-order reaction model being integrated into Equation 9:…”

“…In the last two decades, nanoscale zero-valent iron (nZVI) has been widely used to tackle polluted water [7,8]. Due to the larger reactive surface area and faster reaction rate, nZVI is considered more efficient than iron.…”