| Because of the low efficiency of extracellular electron transfer, microscopic green algaes are unable to exert their advantages of environmental adaptive ability and rapid metabolic rate. These make them difficult to construct the high efficiency pollutants degradation and electricity generation systems. Therefore, the synthesis of redox mediators (RMs) which matching the mechanism of algal extracellular electron transfer and construction of algal fuel cell will be able to improve the abilities of pollutants degradation and electricity generation simultaneously.In this paper, the RMs based on the oxidation respiratory chain of a strain of Chlorella vulgaris with the ability of extracellular enzyme degradation of azo dyes was synthesized. Through the regulation of metabolic type of Chlorella vulgaris, the algal fuel cell (AFC) was constructed in order to enhance the degradation of azo dyes. The operating mechanism of the systems and the transformation rules of azo dyes in the device were analyzed, and the theoretical basis of the performance and degradation efficiency of the AFC was obtained. The selective regulation of biological electrochemical system was realized. The main research contents and results are as follows:Firstly, a series of riboflavin-based RMs were synthesized through the esterification and amino aldehyde condensation. The electrochemical properties and structures of these compounds were analyzed. The results showed that the modification outside the structure of isoalloxazine had little effects on the activity center of RMs. These RMs have almost the same redox potential (-0.43V). The electrode reaction kinetics analysis showed that the reaction rate constants of all the RMs were more than 0.1cm×s-1. In these systems, all the electrode reactions are redox reversible.Secondly, Chlorella vulgaris growth regularity and degradation mechanism of azo dyes were studied. The degradation efficiency and michaelis equation calculation proved that the decolorization of azo dyes is mainly controlled by extracellular enzymes. The strengthening degradation system of azo dyes was constructed based on the above-mentioned RMs and Chlorella vulgaris with the extracellular degrading enzymes. The degradation of azo dyes in this system was in accordance with the first order reaction kinetics model. This approach allows the degradation rate of three azo dyes methyl orange, orange ? and reactive brilliant red X-3B are raised approximately 1 times and the degradation efficiencies improve about 20%. Compared with riboflavin, a traditional catalyst, the degradation rate are raised approximately 20%and the degradation efficiencies improve about 5%. Through the analysis of the degradation products, the enhanced degradation system and the original system have the same degradation mechanism.That is the reduction of the azo bond.Thirdly, the conversion of metabolism types of Chlorella vulgaris was controlled only by illumination. By using a pleiotropic RM and a cupric hexacyanoferrate modified cathode, a two-phase three-stage charge transfer chain was formed. Through this pathway, the one microorganism self-sustained system got a long-term power output up to 0.4773W/m2 at 0.423V without any material exchange with external, the indirect photoelectric conversion efficiency was 1.36%, which was 50 times higher than that obtained from the original system. The system was stable operated for more than 240 days. It was proved that the RM can not only act on the key enzyme active site, but can also promote the electron transfer efficiency of the anode surface.Fourthly, by removing the sulfur or adding hydrophobic groups, two lipid soluble self-immobilized hydrophilic RMs with the similar electrochemical activity were synthesized. These had realized the synchronous degradation of azo dyes and generate electricity by using MFCs with long life. When the azo dyes were used as carbon source, the open circuit voltage (OCV) of the system modified by riboflavinyl-salicylate-1-tetracarboxylate ester could reach 0.72V, the maximum power density (PD) was 0.2620W/m2, and the coulombic efficiency (CE) was 4.12%. When sodium acetate was used as carbon source, the OCV could reach 0.76V, the maximum PD was 0.6728W/m2, and the CE was 11.2%. When the azo dyes were used as carbon source, the OCV of the system modified by riboflavinyl-salicylaldehyde 4-aminosalicylie-1-tetracarboxylate ester could reach 0.76V, the maximum PD was 0.3559W/m2, and the CE was 6.22%. When sodium acetate was used as carbon source, the OCV could reach 0.81V, the maximum PD was 0.8470W/m2, and the CE was 14.1%. The degradation of Orange II and its metabolites by above two methods are all in line with the rule of extracellular enzymatic degradation. The effects of hydrophilic property on the electrochemical activity of the RMs were the same as that of the homogeneous or heterogeneous phase. The schiff-base structure can greatly increase the electrode life in the case of little impact on the hydrophilicity while the electron transfer efficiency was improved. By cyclic voltammetry analysis, the electrochemical properties of the system are controlled by the addition of external RMs. As the primary electron acceptor of node, the effect of internal current on CE has been greatly reduced by RMs. |
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