Design of Quinonoid-Enriched Humic Materials with Enhanced Redox Properties

Abstract

The primary goal of this work was to develop quinonoid-enriched humic materials with enhanced redox properties that could be used as potentially effective redox mediators and reducing agents for in situ remediation of soil and aquatic environments. Two different strategies were formulated and tested to derive these materials. The first strategy called for the oxidation of phenolic fragments associated with the humic aromatic core. In a second strategy, polycondensation of these phenolic fragments was carried out with hydroquinone and catechol. The oxidized derivatives and copolymers obtained were characterized using elemental and functional group analyses, and capillary zone electrophoresis. The redox properties were evaluated using ESR spectrometry and reducing capacity determinations. The reducing capacities of copolymers ranged between 1 and 4 mmol/g, which were much higher than the parent material and the oxidized derivatives. Hence, preference should be given to the copolycondensation approach. The quinonoid-enriched humics are nontoxic, water soluble, and resistant to biodegradation; thus, they could be applied as soil amendments to reduce highly mobile oxoanions of heavy metals and radionuclides, or as redox mediators to enhance in situ bioremediation. Otherwise, cross-linked copolymers could be created to serve as inexpensive reductants in permeable reactive barriers designed to remove highly oxidized contaminants from polluted groundwaters.