Study On The Preparation And Adhibition On Nitrobenzene Wastewater Treatment With Modified Ti/SnO₂-Sb Electrode And Graphite Electrode

Nitrobenzene, as a kind of highly toxic substances, is too hard tobiodegrade and play inhibited and toxic roles against the biochemical reactions.The wastewater included nitrobenzene comes from a variety of sources withbroad pollution. There are some solutions mainly involving biological, physicaland chemical methods. In recent years, advanced oxidation technology with apriority that it produces highly oxidizing hydroxyl radicals is regarded as aneffective technical approach on degrading organic pollution in the waste water.This technology for water treatment has become a hot research topic.The anode plays an oxidation role in the electrochemical oxidation system,and therefore the speed of electro-catalytic oxidation is determined by thecharacteristics of the anode. The different electrode materials cause the differentremoval efficiency of organic matter. The anode materials of electrochemicaloxidation that are appropriate for degrading wastewater are generally sufficientfor some conditions such as good conductivity, less energy loss, good stability,acid and alkali resistance, and standing a certain temperature and mechanicalstrength, higher electro-catalytic activity, etc. However, there is a lack of goodelectrode materials to satisfy the needs of the electrochemical oxidation.Consequently, the researches for the electrochemical oxidation technology havefocused on the development of high effective inexpensive electrode material. Inthis dissertation, the preparation of SnO₂anode has been investigated. In orderto increase the overall efficiency of electro-catalytic oxidation system, thedegradation of nitrobenzene has been also discussed.Titanium-based Sb-doped tin dioxide electrode was prepared by thermaldecomposition brush coating and doped by metal nitrate ions during the wholepreparation to respectively gain some electrodes as follows: Ti/SnO₂-Sb,Ti/SnO₂-Sb-Cu, Ti/SnO₂-Sb-Ni, Ti/SnO₂-Sb-La, Ti/SnO₂-Sb-Nd, Ti/SnO₂-Sb-Ce,Ti/SnO₂-Sb-Zn, Ti/SnO₂-Sb-Bi. The electrode surface morphology and crystal of SnO₂were characterized by scanning electron microscopy （SEM） and X-raydiffraction （XRD）. The life span and stability of the electrodes were examinedby strengthening the electrode life test, and its deactivation mechanism wascarried on a preliminary analysis. The modified electrodes were used in thewastewater simulated by electric degradation of nitrobenzene. The purpose is tostudy on the influence of the electro catalytic performance by the metal-dopedtin dioxide electrode, measure the cell voltage in every stage during theelectrolytic period, research the effect of modified electrode on energyconsumption, and analyze the effects of doped different metal on electrodedegradation rate by nitrobenzene degradation kinetics equation and the currentefficiency of COD. The initial discussion is on determining the concentration ofOH·by using the salicylic acid captured hydroxyl radicals by liquidchromatography, and meanwhile the production of hydrogen peroxide isdetermined by spectrophotometer method. Then the degradation mechanism ofnitrobenzene was discussed through UV-Vis ultraviolet spectrum and massspectrum.Experimental results show that the modified stannic oxide electrodeimproved surface morphology, and the coating of electrode surface covered moresmoothly and uniformly. The grain of crystal was so fine that the surface area ofthe electrode was increased. Meanwhile, the XRD pattern showed that themodified tin dioxide electrode did not transform into other crystals and justchanged the diffraction peak intensity of tin dioxide, which is showed that themetal formed solid solution crystals as it came into the tin dioxide lattice.Accelerated life test showed the life of the modified Ti/SnO₂-Sb electrode hadrisen obviously. Nitrobenzene wastewater electrolysis experiment proved thatmetal doping significantly improved the electro-catalytic degradation.Nitrobenzene degradation corresponds to the first order kinetic equation.Hydroxyl radicals and hydrogen peroxide concentration indicates that the higherconcentration of free radicals was, the faster degradation rate of nitrobenzenewould be. Since it reacted for60min, the OH·concentration of the blank electrode fell by one-fifth by contrast to the one mixed with Cu. Other peak oforganic materials did not appear in the absorption in Nitrobenzene degradationof ultraviolet absorption spectra, whereas aniline was just found in the massspectrum of5-10min degradation in FIG presence. This result indicates thatnitrobenzene oxidation, first, is reduced to the aniline on the cathodic reactionand then degraded on the anodic. The catalytic oxidation reaction was promptafter revivification. The absorption of other substances was not observed in thesubsequent mass spectrum.It was investigated that the electro catalytic oxidation affects on the currentintensity, initial solution pH, and initial concentration with modified SnO₂electrode in the electro catalytic oxidation of nitrobenzene experiments.Experimental results show that the higher current was, the higher removal ratewould be. In a certain range of the current intensity, the current efficiency hadincreased significantly once the electrode was modified. The acidic initial pHwas in favor of nitrobenzene degradation. The higher of the initial concentrationwas, the lower of the organic removal rate would be. In a certain concentrationrange, with increase of the initial concentration, the current efficiency alsoincreased. The modified SnO₂electrode enlarged the adaptability of the initialconcentration range.The influences of different doping levels of metals Cu, Ni on the modifiedSnO₂electrodes were investigated. The surface morphology and crystal structureof the electrodes were characterized by SEM and XRD. The effects of differentamount of doping electrode of the electro catalytic oxidation stability andactivity were examined by the accelerated life test and nitrobenzeneelectro-catalytic oxidation of simulated wastewater experiments. The resultsshowed that both the angle and the intensity of diffraction peaks of theelectrodes with different doping levels had brought into changes. They weremuch different on the surface morphology. The surface of doped1/2electrodehad more cracks and the one doped twice electrode had more particles.Compared with them, the surface of doped equivalent electrode morphology was better. The coating that was uniform with honeycomb hole was easy to beoxidized. While the investigation of the electrode life also proved dopedequivalent electrodes had the longest life and best stability. It also demonstratedgood catalytic oxidation in nitrobenzene degradation experiments.It was investigated that how to influence the electrodes with differentquantity of doped Cu and Ni on nitrobenzene wastewater degradation byelectrolysis current intensity, pH value and initial concentration. Theexperimental results showed that different electrolysis conditions had greatimpact on the electrodes with different doping quantity. After comprehensivecomparisons, the doped equivalent quantity of the electrode gave the bestperformance, doped twice quantity guaranteed the stable performance, but thecatalytic ability was low. While doped1/2quantity showed a poor stability andlower electro-catalytic ability.The treatment of highly toxic and non-biodegradable organic wastewaterwill be important and difficult points of environmental improvement over alonger period of time. Metal-doped electrodes that were compared withTi/SnO₂-Sb electrode showed a better performance on stability andelectro-catalytic oxidation activity. It suggested that the metal impurity dopedSnO₂was feasible.In the electrochemical oxidation technology, the electrode is always themain part in the electro-catalytic oxidation system. The preparation of the highstability electrode has been the goal of scientific investigator. But in order toremove recalcitrant organic substances in water better, the use of more efficientpower source is also an important mean of improving the efficiency of thedegradation besides preparation of the high-performance electrode. The powersource of catalytic degradation system has been used DC output power. Cathodeand anode is the main portion in electro-catalytic degradation of system. Theanode electrode is the main working and the cathode only plays a supportingrole. If the two electrodes of the electrolysis system were changed to workingelectrode, the anode in the form of double plays a role in the degradation process, the degradation of organic wastewater will be greatly enhanced. So theexperiment which changes DC to AC as power supply, and uses the workingelectrode in the form of dual anode electrode,studies the ability ofhigh-frequency AC power supply electro-catalytic oxidation of nitrobenzene.The experiment proves that the AC power is higher than DC power in thedegradation of nitrobenzene with the same output power. Ti/SnO₂-Sb of blankand Ti/SnO₂-Sb of metal-doped electrodes exhibit good electrocatalyticproperties. The greater the frequency of the AC power output of electrolyticsystem, the higher the nitrobenzene removal. AC power is different from DCpower, the removal rate of nitrobenzene is better than the initial pH value of thealkaline. Impact on nitrobenzene removal of electrode material indicates ACelectrolysis system could expand the scope of application of the alternatingcurrent in the electrode. When the two electrodes are Ti/SnO₂-Sb-Cu, theremoval rate is up to98.8%and the removal efficiency is very significant underthe best conditions of electrolysis for45minutes.In response to the DC power supply as the main power source for theelectrolysis system, the anode electrode is main working one, also the cathodeplays a significant role in the electrolysis system, mainly for the reduction of thecathode, for some oxidation of refractory organic materials, the cathode canreduce the degradation of organic matter remaining after its degradation throughthe anode. Therefore, the study of high-performance anode materials, whilechoosing the right as an auxiliary electrode cathode electro-catalytic oxidationalso has a positive meaning. This paper, based on carbon nanotubes modifyinggraphite electrode as the cathode electrode electrolysis system to explore thepreparation of carbon nanotubes modifying graphite electrode and electrode wasstudied as a cathode removal of organic pollutants. Experimental results showthat in the process of preparing carbon nanotube modified electrode, the coatingwears for embedding method, carbon nanotubes and graphite substrate cancombine more closely, electrode coating method which optimizes carbonnanotubes can make much uniformly dispersed in the electrode surface. Activated carbon nanotubes have a high specific surface area, increase thechemical reactivity. When the initial pH of acidic presents, increasing oxygenevolution potential to improve the utilization efficiency of the oxidant.Increasing the initial concentration of nitrobenzene, carbon nanotubes modifiedgraphite electrodes after nitrobenzene removal is still able to maintain a highlevel.The treatment of highly toxic and non-biodegradable organic wastewaterwill be important and difficult points of environmental improvement over alonger period of time.By the preparation of the anode which has higy-capacity and high-stability,the application of AC power dual anode electrolytic system, or the improvementthe performance of the cathode electrode in an electrolytic DC power system,they are feasible to improve the electro-catalytic oxidation degradation of highlytoxic biodegradable organic waste.