Study On The Structure Activity Relationship And The Catalysis Mechanism Of Dissolved Redox Mediators During The Azo Dyes Biodegradation Processes

Azo dye wastewater is difficult to be treated by traditional biotreatmeni technology because of its refractory and lower efficiency of traditional biotreatment. so the high effective technology of this wastewater is becoming hot domains and focus in environmental fields. The reduction rate of pollutants could be enhanced one to several orders of magnitude and indirectly promote the degradation of dye with addition of redox mediators. But continuous dosing of redox mediators implies continuous expenses related to procurement of the chemical. as well as continuous discharge of this biologically recalcitrant compound. And there are no catalytic mechanism and qualitative/quantitative structure-activity theory about non-dissolved redox mediators, and the research should be thorough.Therefore. the experiments are carried out to study catalytic mechanism and structure-activity characteristics of non-dissolved redox mediators during the azo dyes decolorization processes.In this study. four similar chemical structure redox mediators (1.4.5.8-tetrachloroanthraquinone. Anthraquinone.1.5-dichloroanthraquinone. 1.8-dichloroanthraquinone) were seclected to expolre the ralationship of the accelerating effects and those characteristics of cyclic voltammetry (CV). chemical structure and ORP during the decolorization and acid red B was as model compounds.The results showed four redox mediators could accelerate decolorization of acid red B and the order of its acceleration was 1.5-dichloroanthraquinone> 1.8-dichloroanthraquinone> anthraquinone> 1.4.5,8-tetrachloroanthraquinone under the same reaction conditions. The effect factors of 1.5-dichloroanthraquinone on the acid red B decolorization was studied and the optimum factors was 35℃and pH of 7.5; The dye concentration was not the limiting factor of decolorization reaction when the concentration of acid red B was lower than 500mg·L-1; and 1.5-dichloroanthraquinone also accelerated the decolorization of other eight azo dyes.At the same time, the accelerating mechanism of the redox meditors was also conducted from three aspects of electrochemistry (cyclic voltammetry). biochemistry (oxidation reduction potential (ORP). electron transport inhibitors) and Structural Chemistry (effect of substituents, density functional B3LYP method). The results showed the following conclusions:①The change of ORP had similar descending trend in the acid red B decolorization for the added quinone mediator system and non-added quinone mediator system. But the ORP decresed rate quickly and stable potential lower slightly for the added quinone mediator system. The stabilized ORP values of 1.4.5.8-tetrachloroanthraquinone. Anthraquinone.1.8-Dichloroanthraquinone and 1.5-Dichloroanthraquinone were about-350mY.-370mV.-385m V and-390m Y. respectively And there are positive correlation betwwen the reduced stabilized ORP and catalysis of quinone mediator:②Four electron transport inhibitors of CuCl2. NaN3. dicoumarol and rotenone was selected to study the role of redox mediator during the decolorization processes. The results of experiments showed that the added quinone mediator could offset or reduce the inhibitory effect of rotenone and indicated that quinone mediator may play NAD(P)H role in the electron transport chain. And in the absence of inhibitor, quinone mediator may collaborate with NAD(P)H to transfer electron for azoreductase:③The electrochemical characteristics of quinone mediators in the cyclic voltammograms indicated that selected redox mediator might conduct semi-reversible reaction and that the redox potential (E(?)) of quinone mediator related to catalysis. And the relationship between the EO'of quinone mediator and the decolorization rate constant K was K= 0.4311 E01+124.77; the ratio of anode peak current and cathode peak current was about 1 which reflected the degree of reversibility. And the degree of reversibility had a positive correlation with the catalysis of quinone mediator:④The relationship between the effect of chlorine substituents in the quinone mediator and the redox activity was qualitative analized by the effect of substituents and quantum chemical calculations-DFT B3LYP method, and assessed how the molecular structure and stability of redox mediator would impact the ability of a quinone molecule to catalyze a biogeochemical process (e.g., decolorization of azo dyes). There are two relative effects electron withdrawing effect and conjugative effect of chlorine substituents by calculated ring target charge density(p) on the anthracycline. Its number and location joint decided the different dominant effect on the anthracene ring. And consequently impact on redox activity of quinone mediator:It was showed that theρmore, the feasibility of system lose the electron lower and the system redox activity worse.For the acceletrating technology of redox mediator, the accelerated effect, mechnism and structure-acitivity was studied in detail and the results construted the basic of practical application and knowledge values.