| With synchronistical functions of degradation efficiency, wide application and especially environmental compatibility, electrochemical degradation(ECD) technique has been recognized as an effective approach for the purification of the sality organic wastewater. However, lack of the mechanism for the coupling of the electrode materials and the discrepant organic compounds together with a comprehensive kinetic model during organic matters(OMs) electro-catalytic elimination are restricting the in-depth development and popularization of this technique. The present situation described above hightlights the significance and urgency for a thorough research toward the process. In consideration of the indispensable association of anodes and particle electrodes with OMs’ removal efficiency, the rule current acted on the interface of anode-organics and particle electrode-organics are investigated. Furthermore, on the basis of the intrinsic kinetics and Faraday’s laws for electrolysis reaction, the phase-reaction kinetics modelling was proposed. The electro-catalytic oxidation of simulate phenol, methyl orange wastewater and landfill leachate by using a packed-bed electrode reactor were performed, and breakthrough the electrolysis experiment, the established mathematical models were used for the prediction of the constantly changed OMs’ concentration. The achievement are as follows:(1) The Ir O2-Ta2O5/Ti and β-Pb O2/Ti anodes were fabricated with brush-thermal decomposition and galvanostatic electrodeposition process. SEM, XRD and XPS techniques were employed to investigate the surface morphology and crystal structure of the electrodes. The results show that Ir and Pb combining with oxygen atoms are valence in +4, and the formed active oxides distributed on the outermost layers of electrodes, which promised the excellent electro-catalytic performance. Their oxygen evolution potential(vs. SCE) analyzed through polarization curves conducted in simulate phenol, methyl orange wastewater and landfill leachate electrolytes are 1.08 V and 1.79 V, respectively. EIS plots obtained with the mentioned three electrolytes at potential of 1.85 V discovered that the Nyquist equivalent circuit for OMs anodic oxidation could be described as R(CW(R(QR))) model. Associating the proposed equivalent circuit with the utilization of the inputted current, anodic oxidation coefficient was introduced for the characterization of effective current participated in OMs anodic degradation. On the other hand, quantitative assessment of the electro-oxidation capacity of anodes toward a specific wastewater would be realized.(2) Semiconductor metal oxides loaded AC fillers Ti O2/AC, Mn O2/AC and Sn O2-Sb/AC, Sn O2-Sb-Mn/AC were prepared with sol-gel, redox and thermal decomposition methods, respectively. The optimal loading capacity of the four particles characterized by BET specific surface area test, BJH pore size distribution calculation and CV curves obtained in K3Fe(CN)6/K4Fe(CN)6 electrolyte were 4.4%, 4.9%, 1.9% and 6.8%. Additionally, the results of XRD, SEM, EDS and TEM reveal that the synthesis titanium dioxide is typed in rutile and anatase crystal with lattice size 10.64 nm, and a continuous uniform film arise on the AC surface. On Mn O2/AC surface, the lattice size of manganese dioxide is 11.34 nm, and structured in tetragonal and rhombohedral lattice termed as α-Mn O2 and δ-Mn O2, agglomerating as spherical particles on AC pore structures. The tin and antimony molar ratio is 8.33:1 on Sn O2-Sb/AC surface. However, the binary oxides are poor in crystallinity with the lattice size of 14.68 nm. While, after the intervention of Mn, the crystallinity for Sn O2-Sb-Mn species improved greatly, this will benefit the electro-catalytic activity and extend the life of the electrode particles during the OMs electro-oxidation. Packed-bed electrode reactor exhibits an expanded anodic area for the packing of the particle electrode, which permit a fast OMs elimination with the limited power depletion. The constructed packed-bed electrode reactor with semiconductor metal oxide coated AC particle electrode promise a high degradation efficiency and long period operation for phenol wastewater purification, on the other hand, there is no accumulation of quinone. And this would be ascribed to the improved degradation ability of MOx/AC particle electrode. The Nyquist equivalent circuit for OMs electro-oxidation in a packed-bed electrode reactor could also be discribed as the model of R(CW(R(QR))), parameter called current ratio for OMs decomposition on particle electrode β is promoted to characterize the effective current for OMs oxidation on particle electrode surface.(3) Through the comparison of the effective current density on anode and particle electrode surface with the instant limiting current density a comprehensive kinetic mechanism used for OMs electro-catalytic oxidation was proposed. The fundmental of this theory is the relationship between the effective charge and the OMs mass transfer speed. According to this theory, control steps at different OMs degradat ion process are definited, therefore a multifarious dynamic characteristics would turn out. The mathematical relationship of the OMs COD concentration related with electrode material, operating conditions, physical and chemical properties of the wastewater and shape of the reactor are builded, which also provide the modelling approach for the calculation of current efficiency and energy consumption. Experiments of organic wastewater electro-oxidation were carried out, the obtained dates displayed high correlation with the theoretical ones.(4) A new concept of “capacitance behavior” during OMs electro-oxidation reactions is proposed, furthermore, the specific capacitance of Ir O2-Ta2O5/Ti and β-Pb O2/Ti in various aqueous solution are characterized. Their kinetic reasons are explored detailedly. The results show that the active Ir O2-Ta2O5/Ti electrode incurs an order of magnitude larger specific capacitance than the non-active β-Pb O2/Ti electrode. The Cs of Ir O2-Ta2O5/Ti electrode in electrolyte phenol, methyl orange and landfill leachate at 5.0 m V/s scaning rate ranged within 28.0~32.5 m F/cm2, the discharge current density could reach 15.0~18.0 m A/cm2. However, β-Pb O2/Ti electrode arised only 9.0~12.0 m F/cm2 specific capacitance under the same test conditions and the discharge current density is 1.0~3.0 m A/cm2. The smaller electrode resistances and charge transfer resistance of Ir O2-Ta2O5/Ti electrode than β-Pb O2/Ti electrode would give a reasonable explanation for this phenomenon. On the other hand, specific capacitance for a single electrode would be changed in different OMs contained electrolytes. The reason would be attributed to different Faraday pseudocapacitance ignited by the electro-oxidation reactions of OMs. The greatest specific capacitance is detected in methyl orange solution, landfill leachate take second place and the phenol electrolyte performed the worest. Packed-bed electrode reactor holds greater specific capacitance than flat-bed electrode reactor, and the charge storage capacity of the prepared particle electrodes could be ranked as Mn O2/AC>Sn O2-Sb-Mn/AC>Sn O2-Sb/AC>Ti O2/AC>AC. The largest Cs in phenol electrolyte at discharge 5.0 m A/cm2 current density is 48.28 m F/cm2. The biggest discharge current density is 20.0 m A/cm2 with duration of 0.6 s. Conclusion could draw that the discharge current will take extra OMs decomposition after the power cuts. The capacitance behavior characterization and specific capacitance calculatio n are the prerequisite for a pulse power supply electrolysis model.(5) A multi-current electrolysis strategy operated through step by step power supply method is proposed. The principle of this new strategy is to maintain the effective time for OMs electrolysis equal to the duration of reaction control stage. Thus, the electro-catalytic reactions would undergo a rather effective process. The current efficiency is close to 100%, and a rapid, energy saving electrolytic model is come true. Different modulated current electrolysis modellings that dominated by anode and particle electrode are explored. The experiments dates displayed high correlation with the theoretical ones. |
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