Study Of Humic Acids Low/High Molecules On Reducing Capacity And Distribution Of Redox Active Functional Groups

Humic substances (HS) are redox-active organic compounds and play an important role in biogeochemical cycle, which are ubiquitous in terrestrial and aquatic environments. HS can be chemical and microbial reduced and then reduced HS have a higher reducing capacity than native to influence the fate of organic matter and redox elements such as iron. Reducing capacities of HS depend on their distribution of redox functional groups and redox potentials, and molecular structure of HS, including molecular weights, particle size and degree of aromatic condensation, have contribution to redox functional groups. Understanding of redox properties can help us offer a potential method to predict the transformation of redox active organic matter or inorganic matters.This study focuses on one of the components of humic substances-humic acid (HA). The quantity of reducing capacities by chemical and microbial methods, combined spectroscopic techniques to analysis molecular structure change during the reduction and detection characterization of RFG. Therefore, develop the relationship of molecular structure and reducing capacities, electron shuttle to understand the application of humic substances as electron shuttle in environment. The main study results as follows:Low molecular weights fraction (LMWF) of HA have a significant contribution to reducing capacity. Quinone moieties are main RFG for LMWF which is responsible for high reducing capacity of LMWF. There is quinonoid π-π* to benzenoid π-π* transition during the reduction of LMWF. Standard humic acids PPHA have increased in E465 and E465*E665 with the concentration increased, indicating that aromatic contents increased, particle size decreased with the concentration increased 0.5 mg/ml.Measurements of Eh values by using Eh-pH meter showed that native and reduced HA had Eh range of+245--620 mV, respectively, and that all of the HA studied had comparable Eh, suggesting that the measured Eh represent a combination of different redox potentials of various redox functional groups. Native PPHA have a uniform redox potentials range. Redox functional groups of reduced PPHA are used to reduced when redox potentials more than 0.Sinopharm Chemical Reagent Co.Ltd (TJHA) has a high reducing capacity than intentional commercial Aldrich humic acids (AHA). A highly significant inverse relationship between HA concentration and E465, a log arithmic function relationship between HA concentration and E465/E665.AHA has a high aromatic degree than TJHA, and TJHA have a smaller partical size than AHA. The fluorescence spectroscopy analysis of HA observed that relative fluorescence intensities decreased for reduced HA samples, which indicated that π-π* bonds ruptured during reduction. TJHA have more fluorophores proving that TJHA have a high reducing capacity.The redox potential of sludge HA increased after reduction. The reducing capacity-Eh0 diagram indicates that redox potentials of functional groups in sludge HA range from-314 mV to+430 mV. Semiquinone radicals, with a higher redox potential formed during the reduction process of sludge.