Electron And Energy Transfer Among Small Molecular Compounds,Electrochemically Active Bacteria And Nanomaterials:Mechanism Elucidation And Application

Due to global energy crisis and pollution control, renewable and clean energy are the best choice for the human beings in the future. So the electric energy from electrochemically active bacteria (EAB) and hydrogen production from visible-light promoted photocatalytic systems are studied in this thesis. EAB are environmentally ubiquitous and critically involved in broad fields from biogeochemistry, environment remediation to bioenergy generation. A lot of researches have been done on extracellular electron transfer (EET) mechanism of EAB. Until now, there are three possible routes for the EAB transferring extracellular electron to the solid electron acceptor:(a) Direct contact electron transfer,(b) extracellular electron shuttles, and (c) electrically conductive pili. The studies on EET mechanism give us a direction to detect and quantify the EET ability of EAB and also give us a clear way to enhance the role of EAB in the environmental application.1. Previous studies show that rapid and sensitive methods for detection and quantification of extracellular electron transfer ability of EAB are still to be established. Herein we report a rapid, in situ and high sensitive fluorescence method to detect EAB and quantify their extracellular electron transfer ability by using riboflavin as a probe, which fluoresce when oxidized but not under reduced state. This method was successfully used to quantify the average extracellular electron transfer ability of Shewanella MR-1(1.32±0.04fA) and Geobacter sulfurreducens DL-1(9.08±0.23 fA). Our approach may also be used for rapid identification of some genes related to the extracellular electron transfer of Shewanella through quantifying average extracellular electron transfer ability of the wild strain and its mutants.2. Carbon materials are widely used as electrodes for these bioelectrochemical systems (BES). However, a thick biofilm tends to grow on the electrode surface during continuous operation, resulting in constrained transport of electrons and nutrients at the cell-electrode interface. In this work, we tackled this problem by adopting a WO3-nanorods modified carbon electrode (C-WO3nanorods), which completely suppressed the biofilm growth of Shewanella Oneidensis MR-1. Moreover, the C-WO3nanorods exhibited high electric conductivity and strong response to riboflavin. These two factors together make it possible for the C-WO3nanorods to maintain a sustained, efficient process of electron transfer from the MR-1planktonic cells. As a consequence, the microbial fuel cells with C-WO3nanorods anode showed more stable performance than the pure carbon paper and W03-nanoparticles systems in prolonged operation. This work suggests that WO3nanorods have the potential to be used as a robust and biofouling-resistant electrode material for practical bioelectrochemical applications.3. Modification of electrode surface with carboxylic acid terminated alkanethiol self-assembled monolayers (SAMs) has been recently reported to be an effective strategy to improve the extracellular electron transfer (EET) of electrochemically active bacteria (EAB) on electrode surface, but the underlying mechanism of such an enhanced EET remains unclear. In this work, mercapto-acetic acid and mercapto-ethylamine modified gold electrodes (Au-COOH, Au-NH2) were used as anodes in microbial electrolysis cells (MECs) inoculated with Geobacter sulfurreducens DL-1, and their electrochemical performance as well as the bacteria-electrode interactions were investigated. Results showed that the Fe (CN)63-/4-redox reaction occurred on the Au-NH2with a higher rate and a lower resistance than the Au or the Au-COOH. With G. sulfurreducens as the inoculum, both the MECs with Au-COOH and Au-NH2anodes exhibited a higher current density than that with a bare Au anode. The biofilm formed on Au-COOH was denser than that on Au, while the biofilm on Au-NH2had a larger thickness, suggesting a critical role of direct EET in this system. This work suggests that functional groups such as-COOH and-NH2could promote electrode performance by accelerating the direct EET of EAB on electrode surface.4. The desire for photocatalytic splitting of water into hydrogen to provide clean energy has driven intensive search for efficient photocatalytic system. Here, we report a low-cost, easy-prepared and environment-friendly hydrogen-producing system that can directly utilize visible light. This system contained xanthene dyes and inorganic Ni (Ⅱ) or Co (Ⅱ) salts in aqueous solution and was added with2-mercaptoethanol (ME) as a surfactant to improve the hydrogen-producing efficiency and stability. The results of hydrogen production test, transmission electron microscope (TEM) and hydrogen evolution reaction (HER) analysis show that the in-situ formed Ni or Co based nanoparticles were the catalytic center for hydrogen production. DLS analysis revealed that the H2production was enhanced by ME through stabling Ni or Co based nanoparticles as heterogeneous catalysts.