Determining the Electron Storage Capacities of Black Carbon and Humic Acid Through Chemical Redox Titration
| Author(s) | Xian, Minghan | |
| Date Accessioned | 2019-11-21T15:19:47Z | |
| Date Available | 2019-11-21T15:19:47Z | |
| Publication Date | 2017-05 | |
| Abstract | Carbonaceous constituents in soil and sediment play critical roles in biotic and abiotic geochemical redox reactions. In particular, black carbon and humic substances supplying and receiving electrons are of key interest to researchers for their role in facilitating redox transformation of contaminants either directly (i.e., abiotically) or through microbial activity in soil and sediments. Black carbon (BC) is a category of solid carbonaceous materials formed by pyrolyzing biomass in an oxygen-deficient environment. As a commercially available black carbon that aims to promote soil fertility and microbial activity, it has been hypothesized that redox-active functional groups, such as quinone, are presented in the carbon matrix, and that they can exchange electrons with external bulk reactants. In this work, titanium(III) citrate, a colored, one electron transfer reducing agent, was evaluated as a titrant reducing a commercial black carbon and a standard humic acid. Through a series of batch reduction experiments and continuous monitoring of the UV-Vis absorbance at 400 nm, the measured electron storage capacity (ESC) of the black carbon was 4.3(±0.1) mmol electron/gram at pH 6.4, 4.1(±0.1) mmol electron/gram at pH 5, and 4.2(±0.4) mmol electron/gram BC at pH 7.5. In addition, to standardize titanium(III) citrate and to demonstrate that it has the capability to fully reduce quinone functional groups (the redox active component in black carbon and humic acid), 99% purity 1,4-benzoquinone was used to quantitatively titrate titanium(III) citrate stock solution to standardize the exact concentration of titanium(III) used prior to the ESC experiment. We show that the reduction of anthraquinone-2,6-disulfonate (AQDS) and benzoquinone (BQ) are kinetically facile processes; therefore, the slow kinetic of black carbon reduction is ascribed to slow intra-particle diffusion in black carbon particles. The ESC of humic acid was also estimated using similar titration applied on black carbon. Leonardite humic acid (LHA), one of the most studied standardized humic acid forms, was titrated using a similar approach. By observing the net change of absorbance at 250 nm upon mixing known amounts of titanium(III) citrate and LHA in solution, the electron transfer from titanium(III) citrate to humic acid can be studied. The ESC of Leonardite humic acid was determined to be 4.7(±0.4) mmol/g LHA at pH 6.4, 3.1(±0.3) mmol/g LHA at pH 5 and 4.1(±0.4) mmol/g LHA at pH 8. An approach of redox reduction of black carbon are hereby proposed, and upon acquirement of additional research progress, a protocol of black carbon titration can be developed and enables researchers to determine the electron storage capacity of black carbon synthesized using various materials and approaches in an efficient and affordable manner. | en_US |
| Advisor | Pei C. Chiu, Ph.D | |
| Program | Chemical Engineering | |
| URL | http://udspace.udel.edu/handle/19716/24746 | |
| Publisher | University of Delaware | en_US |
| Keywords | Chemical engineering, Black carbon, Humic acid, Electron storage capapcity | en_US |
| Title | Determining the Electron Storage Capacities of Black Carbon and Humic Acid Through Chemical Redox Titration | en_US |
| Type | Thesis | en_US |