本文關(guān)鍵詞：PbO2形穩(wěn)陽極的制備及其電催化氧化降解有機(jī)污染物的作用機(jī)制　出處：《西安建筑科技大學(xué)》2017年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： PbO2陽極材料 電催化氧化 難降解有機(jī)廢水 離子液體 羥基自由基

【摘要】：電化學(xué)氧化技術(shù)被證實(shí)是去除廢水中難降解有機(jī)污染物的有效方法,顯示出良好的應(yīng)用前景和發(fā)展?jié)摿?成為當(dāng)前工業(yè)廢水處理領(lǐng)域的研究熱點(diǎn)。發(fā)展電氧化技術(shù)的首要關(guān)鍵是高性能、低成本電極材料的開發(fā)。鈦基PbO_2形穩(wěn)陽極由于具有良好的導(dǎo)電和耐蝕性、較高的析氧過電位、較低的成本以及強(qiáng)氧化能力,成為被廣泛研究和應(yīng)用的陽極材料對象。為進(jìn)一步改善PbO_2電極的電催化活性與穩(wěn)定性,本論文提出將微量咪唑基離子液體(ILs)添加至電沉積溶液中,利用ILs特有的電化學(xué)性質(zhì)與吸附性,對鈦基PbO_2電極進(jìn)行修飾改性制備,系統(tǒng)考察了ILs分子結(jié)構(gòu)、添加濃度、沉積溫度、電流密度等工藝條件對PbO_2電極涂層晶體結(jié)構(gòu)、形貌及性能的影響特性;通過對PbO_2電沉積過程的原位電化學(xué)分析,以及ILs改性前后PbO_2涂層的微觀晶體和電子結(jié)構(gòu)的表征,分別從電極材料的制備及結(jié)構(gòu)角度闡釋ILs對PbO_2電極的改性機(jī)理,從而為應(yīng)用于難降解有機(jī)廢水處理領(lǐng)域的高性能陽極材料的制備提供借鑒。同時,對PbO_2電極氧化降解有機(jī)物過程中的羥基自由基(·OH)檢測方法、產(chǎn)生規(guī)律及影響因素進(jìn)行了系統(tǒng)研究,確立了降解過程中·OH生成量與有機(jī)物降解效率、歷程的內(nèi)在聯(lián)系,為電氧化生物難降解有機(jī)污染物作用機(jī)制的闡釋提供了事實(shí)依據(jù)。論文研究豐富了環(huán)境電化學(xué)的內(nèi)容,為電化學(xué)法處理有機(jī)污染物提供了理論基礎(chǔ)和技術(shù)支持,主要研究工作和結(jié)論如下:(1)將1-乙基-3-甲基-咪唑四氟硼酸鹽([Emim]BF4)添加到Pb(NO3)2混合電積溶液中,通過陽極氧化電沉積法可以制備得到結(jié)晶良好、晶粒大小均勻、表面致密平整的鈦基β-PbO_2形穩(wěn)陽極材料�？疾飓@得主要制備工藝的優(yōu)化條件為:[Emim]BF4添加濃度為50 mg/L、溫度50℃、電流密度10 mA/cm2。PbO_2電極的電催化活性與其晶體結(jié)構(gòu)密切相關(guān),β-PbO_2比α-PbO_2具有更高的有機(jī)物降解活性;β-PbO_2的結(jié)晶度越高,活性越好;沿(110)晶面擇優(yōu)取向的β-PbO_2相比無擇優(yōu)取向或其他晶面擇優(yōu)取向的β-PbO_2顯示出更高的電催化活性。(2)相比采用Fˉ和十二烷基磺酸鈉(SDS)對PbO_2電極進(jìn)行修飾改性的一般制備方法,由ILs輔助制備的PbO_2電極涂層結(jié)晶度更高、結(jié)晶取向亦發(fā)生明顯改變,在10 mA/cm2下恒流電解180 min時,苯酚模擬廢水的COD去除率相比一般方法制備的PbO_2電極提高了近20%。電極的電流效率在電解初期為38%,比后者高出15%左右。ILs輔助制備得到的PbO_2電極穩(wěn)定性與一般方法制備的電極相比亦明顯提高,加速壽命增加了近2倍。這些試驗(yàn)結(jié)果說明,利用ILs可以影響PbO_2電沉積過程,獲得性能顯著改善的鈦基PbO_2涂層電極。(3)PbO_2電結(jié)晶按照三維生長和連續(xù)成核方式進(jìn)行,ILs的加入沒有改變其電結(jié)晶方式,但增加了陽極極化,對PbO_2形核和核生長均產(chǎn)生抑制作用,且以抑制核生長為主,最終導(dǎo)致晶核密度增加,得到致密的PbO_2涂層。此外,ILs輔助電沉積制備得到的鈦基PbO_2涂層相比未改性電極表面致密規(guī)整、結(jié)晶度和晶格氧含量更高、表面氧空位含量明顯降低。由此提出ILs對PbO_2電極修飾改性的機(jī)理在于使其晶體中氧空位含量明顯減少,從而降低了氧化物電極表面高活性·OH向活性較差的晶格氧(Olat)衍變的發(fā)生幾率。(4)研究對比了水楊酸(SA)和4-羥基苯甲酸(4-HBA)這兩種不同·OH捕獲劑的捕獲效率差異,結(jié)果表明,電化學(xué)體系中SA的主要羥基化產(chǎn)物為2,5-DHBA,而產(chǎn)物2,3-DHBA和兒茶酚的含量非常小,可忽略不計。SA和4-HBA兩種·OH捕獲劑都具備羥基化產(chǎn)物單一、穩(wěn)定的特點(diǎn)。SA和4-HBA與·OH的電化學(xué)氧化反應(yīng)均符合一級反應(yīng)動力學(xué),反應(yīng)速率常數(shù)k分別為2.1833×10-4 s-1和1.3500×10-4 s-1。要達(dá)到相同的·OH捕獲量,4-HBA需3倍于SA的初始用量、約2.3倍于SA的捕捉時間。因此,SA比4-HBA具有更高的靈敏度和更強(qiáng)的?OH捕捉能力,進(jìn)而建立了以SA為·OH捕捉劑,以高效液相色譜為檢測手段的穩(wěn)定可靠的·OH檢測方法。(5)電極材料的電催化活性主要由其產(chǎn)生·OH的能力所決定。電解液中支持電解質(zhì)對體系中·OH生成量的影響不明顯,主要通過其在陽極氧化生成的氧化劑參與有機(jī)物的降解,以NaCl為支持電解質(zhì)時降解效率最高,其次是Na_2SO_4,最后為NaNO3;隨電解液pH值的增加,苯酚廢水的COD去除速率不斷提高,且·OH的生成量在堿性條件下亦顯著增加;升高電解溫度時,苯酚廢水的COD去除率反而下降;增大電流密度會相應(yīng)明顯提高COD去除率;隨著脈沖頻率與占空比的增加,苯酚廢水COD去除率均呈現(xiàn)先升高后下降的規(guī)律,在脈沖頻率為500Hz、占空比為50%時達(dá)到最高。比較發(fā)現(xiàn),采用脈沖電源時單位COD處理能耗相比直流電源可降低44%,具有明顯節(jié)能效果。電解液性質(zhì)和操作條件對·OH生成量的影響與其對苯酚廢水COD去除率的影響規(guī)律基本一致,表明電氧化體系參數(shù)通過影響產(chǎn)生及進(jìn)入到電解體系中的·OH量而影響電氧化效率,·OH的生成量與PbO_2電極對苯酚的電化學(xué)氧化降解效率密切相關(guān)。(6)PbO_2電極上苯酚模擬有機(jī)廢水的COD去除符合一級反應(yīng)動力學(xué)規(guī)律,加入·OH淬滅劑叔丁醇后COD去除率急劇下降,氧化反應(yīng)速率常數(shù)降低了45%,充分證明了苯酚的電化學(xué)氧化降解遵循·OH反應(yīng)機(jī)理。根據(jù)苯酚電氧化過程中間產(chǎn)物分布情況,推測苯酚在·OH的進(jìn)攻下生成對苯醌、間(鄰)苯二酚及馬來酸等中間產(chǎn)物,隨著電氧化反應(yīng)的進(jìn)行,中間產(chǎn)物亦被氧化去除而逐漸減少,最終實(shí)現(xiàn)有機(jī)物的完全降解。在含苯酚水溶液的循環(huán)伏安曲線中出現(xiàn)苯酚的氧化峰,說明苯酚的降解過程中存在直接電氧化作用。由此推斷,PbO_2電極對苯酚有機(jī)污染物的電化學(xué)氧化降解作用機(jī)制是直接氧化(電子轉(zhuǎn)移)與間接氧化(·OH氧化)共同作用的結(jié)果,其中·OH的間接氧化作用起絕對主導(dǎo)作用。(7)應(yīng)用電催化氧化技術(shù)處理初始COD值為1009 mg/L的實(shí)際焦化廢水時,升高溫度、增大電流密度、增加支持電解質(zhì)Na_2SO_4添加濃度等均有利于COD的去除。綜合考慮處理效果和成本,較適宜的電流密度范圍是20~30 mA/cm2;較適宜的Na_2SO_4用量是0.25 mol/L。脈沖電解相比直流電解能夠降低能耗約35%。在40 mA/cm2,30℃、0.25 mol/LNa_2SO_4的操作條件下降解3 h時后,焦化廢水的COD去除率達(dá)到90%以上,出水COD值可以達(dá)到國家一級排放標(biāo)準(zhǔn)值,此時單位COD處理能耗為178 kWh/kg。
[Abstract]:Electrochemical oxidation technology has been proved to be an effective way to remove refractory organic pollutants in wastewater. It shows good application prospects and development potential and has become a research hotspot in the field of industrial wastewater treatment. The key to the development of Electrooxidation is the development of high performance and low cost electrode materials. Titanium based PbO_2 stabilized anode has been widely studied and applied as anode material because of its good conductivity and corrosion resistance, high oxygen evolution overpotential, low cost and strong oxidation capacity. To further improve the electrocatalytic activity and stability of PbO_2 electrode, this paper will trace imidazolium ionic liquids (ILs) added to the electrodeposition solution, the electrochemical properties and adsorption of ILs specific and modified preparation of titanium based PbO_2 electrode, the effect of characteristics of ILs molecular structure, concentration the temperature, current density, deposition conditions of PbO_2 electrode coating crystal structure, morphology and properties of PbO_2; by in situ electrochemical deposition analysis, and ILs characterization of PbO_2 coating micro crystal and electronic structure of ILs before and after modification mechanism explanation respectively from the preparation of the electrode material and structure angle on the PbO_2 electrode, thus high performance anode material is used in treatment of refractory organic wastewater in the field of preparation of reference. At the same time, the hydroxyl radical PbO_2 electrode oxidation degradation of organic compounds in the process (OH) production rules and influence factors of detection method and system research, established the relationships in the degradation process of OH generation and degradation efficiency, process of organic matter, provide the basis for the electro oxidation of bio refractory organic pollutants the mechanism of interpretation. This study enriches the content of environmental electrochemistry, provides a theoretical basis and technical support for the electrochemical treatment of organic pollutants, the main research work and conclusions are as follows: (1) 1- ethyl -3- methyl imidazole tetrafluoroborate ([Emim]BF4) added to Pb (NO3) 2 mixed electrolyte, by anodic oxidation and electro deposition can be prepared with good crystallinity and uniform grain size, surface smooth titanium based anode material -PbO_2 beta shape stability. The optimization conditions of the main preparation process are as follows: the concentration of [Emim]BF4 is 50 mg/L, the temperature is 50, and the current density is 10 mA/cm2. PbO_2 is closely related to the electrocatalytic activity of the electrode and its crystal structure, beta -PbO_2 has organic matter degradation activity higher than alpha beta -PbO_2 -PbO_2; the crystallization degree is higher, the better the activity; (110) the preferential orientation of the beta -PbO_2 compared with no preferred orientation or other preferential orientation of the beta -PbO_2 show power higher catalytic activity. (2) compared with F - and twelve sodium dodecyl sulfate (SDS) on PbO_2 electrode preparation method modified by ILs, assisted preparation of PbO_2 electrode coating crystallinity and higher crystallinity also changed, electrolytic 180 min under 10 mA/cm2 constant current, the phenol wastewater the removal rate of COD compared with PbO_2 electrode preparation method generally has increased by nearly 20%. The current efficiency of the electrode is 38% at the initial stage of electrolysis, which is about 15% higher than that of the latter. The stability of the PbO_2 electrode prepared by ILs is also significantly higher than that of the electrode prepared by the general method, and the accelerated life of the electrode has increased by nearly 2 times. These results show that ILs can affect the PbO_2 electrodeposition process and obtain a titanium based PbO_2 coating electrode with remarkable improvement in performance. (3) PbO_2 crystal according to three-dimensional growth and continuous nucleation, the addition of ILs did not change the electric crystal, but increased the anodic polarization of PbO_2 nucleation and nucleus growth inhibition were produced, and the inhibition of nuclear growth, resulting in increase of nucleus density, obtain dense PbO_2 coating. In addition, the PbO_2 coating prepared by ILs assisted electrodeposition process is more regular than that of the modified electrode, and the crystalline and lattice oxygen content is higher, and the surface oxygen vacancy content is significantly reduced. It is suggested that the mechanism of modification of PbO_2 electrode by ILs is to decrease the content of oxygen vacancies in the crystals, thereby reducing the probability of evolution of lattice oxygen (Olat) on the surface of oxide electrodes with high activity and OH. (4) the difference of capture efficiency between two different OH capture agents of salicylic acid (SA) and 4- hydroxybenzoic acid (4-HBA) was studied and compared. The results showed that the main hydroxylated product of SA was 2,5-DHBA, while the content of 2,3-DHBA and catechol was negligible. Both SA and 4-HBA two OH capture agents have the characteristics of single and stable hydroxylation products. The electrochemical oxidation of SA and 4-HBA and. OH conforms to the first order reaction kinetics. The reaction rate constant k is 2.1833 x 10-4 S-1 and 1.3500 x 10-4 s-1, respectively. To achieve the same amount of OH capture, 4-HBA needs to be 3 times the initial amount of SA and about 2.3 times the capture time of SA. Therefore, SA has higher sensitivity and stronger OH capture ability than 4-HBA. Therefore, a stable and reliable OH detection method based on SA OH capture agent and high performance liquid chromatography is established. (5) the electrocatalytic activity of the electrode material is mainly determined by its ability to produce OH. The electrolyte support effect of electrolyte on the system content of OH is not obvious, mainly through its oxidative degradation agent by anodic oxidation in organic matter, with NaCl as the supporting electrolyte degradation efficiency is the highest, followed by Na_2SO_4, the last is NaNO3; with the increase of the pH value of the electrolyte, phenol removal rate constant COD to improve the production of OH, and also increased significantly under alkaline conditions; higher electrolysis temperature, phenol removal rate of COD decreased; the increase of current density will significantly improve the removal rate of COD; with the pulse frequency and duty ratio increases, the removal rate of COD phenol wastewater were increased and then decreased. In, 500Hz pulse frequency and duty ratio of 50% reached the highest. It is found that pulse electricity is used in comparison
【學(xué)位授予單位】：西安建筑科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：X703
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本文編號：1338317