Electrocatalytic method to quantify the redox reactivity of agricultural byproducts

Abstract

Redox reaction is one of the determining fate pathways for biofertilizer, bio-stimulant, and other biomass-derived soil amendments. Versatile electrochemical method is in demand to screen redox reactivity of solid samples with minimal pretreatments to maintain the material integrity. This study employed reductive (anthraquinone-2,6-disulfonate) and oxidative (quercetin) mediators to visualize the electron donating and accepting functional groups in sugarcane mill mud, a potential bio-stimulant originating from raw sugar production. Mill mud was redox inert under the electrochemical conditions employed, and mediator was required to transfer electrons to and from the working electrodes. Peak areas of cyclic voltammograms were plotted as a function of sample weight, and the slope was used to compare samples. Higher redox reactivity was observed for aromatic, heat-treated (≈90 °C) mill mud samples, and those characteristics decreased by aging. Developed catalytic electrochemistry could be used to (1) screen organic carbon samples for plant growth stimulation in anoxic and sub-oxic soils and (2) monitor the life cycles of biomass feedstocks and value-added products for environmental fate pathways including redox transformation and photolysis.