Adsorption And Oxidative Transformation Of Phenolic Acids By Fe(III)-Montmorillonite

Abstract

Phenolic acids participate in various soil processes and are of great concern due to their allelopathic activity. The interactions of phenolic acids (ferulic, p-coumaric, syringic, and vanillic) with montmorillonite enriched with Fe(III) was investigated. Adsorption of the phenolic acids on Fe(III)-montmorillonite was accompanied by their oxidative transformation and formation of Fe(II). Oxidative transformation of phenolic acids was affected by their molecular structure. The order of maximal transformation at the initial acid concentration of 20 mg/L on the surface of Fe(III)-montmorillonite was ferulic (94%), syringic (60%), p-coumaric (35%), and vanillic (25%). Benzoic acid which was used as a reference aromatic compound exhibited only 5% transformation. Removal of the phenolic acids from solution increased with decreasing pH. LC-MS analysis demonstrated the presence of dimers, trimers, and tetramers of ferulic acid on the surface of Fe(III)-montmorillonite. Oxidation and transformation of ferulic acid were more intense on the surface of Fe(III)-montmorillonite as compared to Fe(III) in solution due to stronger complexation on the clay surface. The results of the current study demonstrate the importance of Fe(III)-clay surfaces for the abiotic formation of humic materials and for the transformation of aromatic (phenolic) pollutants.

Interactions of aromatic acids with montmorillonite: Ca2+- and Fe3+-saturated clays versus Fe3+–Ca2+-clay system

“…Previously we demonstrated that adsorption of aromatic acids on Fe 3+ -montmorillonite was accompanied by their oxidative transformation, which was dependent on their molecular structure. The following order of transformation intensity was observed: ferulicN syringic N p-coumaric N vanillic N benzoic (Polubesova et al, 2010). The strongest interactions of the studied acids with Fe 3+ -clay were observed at pH b4 (Fig.…”

“…Interactions of adsorbed organic molecules with Fe 3+ may result in electron transfer from the organic molecules to the metal cations, and a reduction of metal ions to lower valence (Sparks, 2003). Previously we demonstrated oxidation of phenolic acids on the surface of Fe 3+ -montmorillonite, accompanied by reduction of Fe 3+ to Fe 2+ (Polubesova et al, 2010). In contrast, divalent Ca 2+ ions do not form strong coordination complexes with organic molecules and are effective only to the extent that a bridge linkage can form.…”

Fe3+-saturated montmorillonite effectively deactivates bacteria in wastewater

“…It is highly likely that the latter two bacterial deactivation mechanisms are at play when wastewater is exposed to Fe 3+ -saturated montmorillonite. Recent research has shown mineral surface-catalyzed Fe 3+ reduction by organic phenolic compounds exposed to Fe 3+ -saturated montmorillonite, forming radical cations of aromatic molecules and Fe 2+ cations (Gu et al, 2008;Liyanapatirana et al, 2009;Polubesova et al, 2010;Qin et al, 2014). Hence, the surface-catalyzed redox reaction and formation of radical cations could possibly induce oxidative stress on bacterial cells, resulting in disrupted bacterial cell membrane and subsequent bacterial deactivation.…”

What happens when pharmaceuticals meet colloids

“…Colloids are strong sorbents for organic matter (e.g., dyestuffs) in aqueous solution (Gürses et al 2006;Hu et al 2006;Liu and Zhang 2007;Errais et al 2011). In addition to the natural clays, modified clays were used to enhance adsorption efficiency (Danis et al 1998;Zadaka et al 2007;Polubesova et al 2010;Gil et al 2011). A number of experimental and mathematical models have been developed to describe colloid-facilitated remediation and assess the environmental risks of these pollutants (Flury and Qiu 2008).…”