Rapid Quantification of Soil Organic Carbon via Photocatalytic Kinetics

Abstract

Sequestering carbon as total organic carbon (TOC) in soil is seen as one way to mitigate climate change by reducing atmospheric carbon dioxide. The primary goal of this research is to develop a protocol to rapidly measure TOC in soils via photocatalytic reaction kinetics. The developed protocol will be integrated into MANTECH’s existing PeCOD analyzer to carry out rapid and informative soil TOC analysis. The measurement of soil organic carbon (OC) fractions is currently carried out using techniques such as Walkley-Black method, dry combustion, heated persulfate, mid-infrared spectroscopy, etc. However, these analytical methods are either time consuming, technically demanding, costly, or employ toxic chemicals, which limits their applicability for large-scale and long-term soil carbon accounting. In this study, organic matter was extracted from several soil samples (of varying organic matter content) using low-frequency sonication and optimized aqueous media. Optimal parameters for the extraction were distinguishing particle size ranges of 50um-100um and 100-250um prior to sample preparation, ultrasonicating for 15 minutes at 80% amplitude, and mixing a ratio of 1.5 g of soil in 100 mL of DI water. Extractants were tested in the PeCOD, wherein the photocatalytic oxidation of OC generates electrical current proportional to the rate and extent of reaction. The COD values were correlated to %TOC values for the samples, to find a relationship of COD = 27.293 %TOC for the soil samples that were collected specific to the region. The kinetics data from the photocatalytic reaction gave slight indication of unique curve characteristics but were not distinguishable enough to confidently allow for differentiation of type of OC in these samples. The technology may be used to indicate the levels of TOC in soil, and potentially gauge its stability with respect to types of OC, in a fast and environmentally conscious manner. More research needs to be explored within this realm to further develop the precision of the TOC and carbon differentiation measurements.