Research On Electrode Process For Phenol Degradation With Rare Earths Doped Ti Base SnO₂ Electrodes

The wastewater becomes one of the urgent issues to be resolved currently. The water pollution is diverse and complexity, therefore it puts forward a rigorous test to the traditional methods for the removal of resist biodegradable organic pollutants. Nowadays simple treatment process is hard to satisfy the social need, due to more and more refractory organic pollutants emergence. Advanced electrochemical oxidation process (AEOP), as one of advanced oxidation process (AOP), can efficiently decompose of organic pollutants and make it transform to CO₂ and H2O completely, owing to the oxidative hydroxide radical (?OH) being produced during electrochemical process. AEOP attracts extensive attention and shows a good application foreground, because of its small-bulk set, no second pollution, and easy combining with other treatment methods.Pt, Ti/RuO₂, Ti/SnO₂ and Ce, Dy, Eu, Gd, Nd doped Ti/SnO₂ electrodes were introduced to degrade of phenol and electrochemical process was studied using Pt and Ti/RuO₂ electrodes as contrastive electrodes in the experiment. Electronic Spin Resonance (ESR) was used to detect the electrolysis process of Ti/RuO₂ electrode using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as capture agent, which showed that ?OH was produced in this process. Taking benzoic acid as ?OH capture agent, fluorescence spectroscopy were used to study ?OH producing capacity on Pt, Ti/RuO₂, Ti/SnO₂ electrodes. The results indicated that ?OH producing capacity is strong for Ti/SnO₂ electrodes, and ?OH producing capacity is poor for Pt electrode but indistinct for Ti/RuO₂ electrode. Taking terephthalic acid as ?OH capture agent, fluorescence spectroscopy were used to study ?OH producing capacity on the researched electrodes. The result exhibited that rare earths doping enhances ?OH producing capacity of Ti/SnO₂ electrode, ?OH, and the sequence of ?OH producing capacity for rare earths doped Ti/SnO₂ electrodes is Ti/SnO₂-Ce 2-Eu 2-Gd 2-Dy 2-Nd. In phenol solution, cyclic voltammetry(CV) was applied to analyze directly electrocatalytic oxidation on Pt, Ti/RuO₂, Ti/SnO₂ electrodes. The results showed that phenol was electrocatalytic oxidized irreversibly and the sequence of phenol oxidation peak current on the three electrodes is Pt 2 2. Pt, Ti/RuO₂, Ti/SnO₂ electrodes were tested using constant current polarization in H2SO4 solution. From Tafel curves, it indicated that the sequence of oxygen evolution potential of the electrodes is Ti/RuO₂ 2, which is consistent with phenol degradation capacity for the three electrodes. Electrochemical impedance spectroscopy (EIS) was tested in phenol solution, which exhibited that phenol adsorption process existed on Pt and Ti/RuO₂ electrodes, but it had no adsorption process on Ti/SnO₂ electrode. Cyclic voltmmetry was carried out in [Fe(CN)6]4-/[Fe(CN)6]3- solution with different scan rates. which indicated that E 0'of Ti/SnO₂ shifts negatively to 4 mV compared with Pt and Ti/RuO₂ electrodes as well as ? Ep is 0.061 V, further smaller than Pt and Ti/RuO₂ electrodes,showing that catalytic activity of Ti/SnO₂ electrode is strong on the redox system.Voltammetry and polarization curve were introduced to investigate Ce, Dy, Eu, Gd and Nd with different mass content doped Ti/SnO₂ electrode. Results showed that phenol directly electrocatalytic oxidation peak is absent for Ce doped Ti/SnO₂ electrode, but the highest phenol oxidation current is present for Dy, Eu, Gd and Nd doped Ti/SnO₂ electrode with content of 50:1, 200:1, 50:1, 50:1, respectively. When Ce, Dy, Eu, Gd and Nd doped Ti/SnO₂ electrode with content of 50:1, 200:1, 50:1, 50:1 and 200:1,respectively, the electrodes had the highest oxygen evolution potential. Compared with different rare earths doped with Ti/SnO₂ electrodes, it indicates that the capacity of phenol direct electrocatalytic oxidation on the electrodes is the same as the sequence of oxygen evolution potential of the electrodes: Ti/SnO₂-Ce 2-Eu 2-Gd 2-Dy 2-Nd, which is the same as ?OH producing capacity and the effect of degradation of phenol on the electrodes. EIS was used to test rare earths doped Ti/SnO₂ electrodes under various potentials in phenol solution, which represented that double-layer capacitance of rare earths doped Ti/SnO₂ electrodes were influenced by potential change, most remarkably for Ti/SnO₂-Ce electrode, but relatively stable for Ti/SnO₂-Nd electrode. CV tests on rare earths doped electrodes with different scan rate in [Fe(CN)6]4-/[Fe(CN)6]3- solution exhibited that Ti/SnO₂-Nd electrode had better catalytic capacity.The deactivation of the electrodes was studied by electrochemical technique, such as CV, constant current polarization and EIS, assistant by Scenning Electron Microscope (SEM) and X-Ray Diffraction (XRD), et.al, exhibiting that the electrodes deactivated mainly due to large molecule polymer accumulating and electro-insulated TiO₂ producing on the electrode surface. A electrodeposition layer-by-layer was introduced to prepare Ti/SnO₂ electrode in order to enhance service life of the electrodes. It exhibited that the electrode surface prepared by the method was more compact after characterized by SEM and Atomic Force Microscope (AFM). Degradation performance test indicated that the electrode annealed at 550℃has the best catalytic-oxidation capacity, and the accelerated service life tests showed that the service life was enhanced for the electrode.The dissertation discusses the electrochemical process of organic degradation by the electrode. It has important significance on establishing electrocatalytic capacity evaluation system, investigation in mechanism of electrocatalytic oxidation of organic pollutants and preparing high catalytic efficient electrode for electrocatalytic oxidation of organic pollutants.