【作者】 时鹏辉；

【导师】 李登新；

【作者基本信息】 东华大学 ， 环境工程， 2013， 博士

【摘要】 基于硫酸根自由基(SO4-·)的高级氧化技术是近些年发展起来的、具有发展潜力的、降解难降解有机污染物的新技术。和羟基自由基(·OH)相比较,SO4-·具有更高的氧化还原电位、对pH值的要求范围广、反应不会产生大量的铁泥需要处理、对有机物的矿化程度高、操作简便、与环境兼容、SO4-·的产生方式多、失活因素少等优点。其中,均相催化氧化技术虽然操作简便、反应迅速,但存在催化剂不易回收再利用造成的成本高、Co2+对自然环境可能造成潜在的二次污染和生物毒性等问题。而非均相催化氧化技术将催化剂钴固定在载体上,从而解决了以上问题。本研究主要对非均相Co3O4/GO/PMS催化氧化体系降解典型偶氮染料酸性橙Ⅱ进行研究,选择氧化石墨烯(GO)作为C0304的载体制得Co3O4/GO纳米复合物作为非均相复合催化剂,催化活化单过氧硫酸氢钾(PMS)产生硫酸根自由基,同时考察超声辅助的影响因素及作用,探讨无机盐离子对非均相Co3O4/GO/PMS催化氧化体系降解酸性橙Ⅱ的影响,并对催化剂Co3O4和载体GO之间存在的协同作用机理进行研究,主要进行了以下几个方面的研究：(1)制备了高效非均相催化剂C0304/GO。以天然鳞片石墨为原料,利用Hummers法制备了氧化石墨,又以氧化石墨为前躯体,在正已醇体系中采用溶剂热法一步合成Co3O4/GO纳米复合物催化剂。采用SPM、XRD、FT-IR、Raman、 XPS、SEM、EDS、TEM、TAG等手段对制得的GO及Co3O4/GO纳米复合物进行测试表明,制得氧化石墨烯厚度集中在0.9-1.1nm之间,层间距为0.845nm,表面较光滑且边缘处有氧化石墨烯特有的褶皱,片层上还有大量的羧基、羟基、环氧基等含氧官能团；而Co3O4/GO纳米复合物中有Co3O4的存在,但XRD衍射峰较小,同时由于GO片层上形成了大量的Co3O4而使氧化石墨烯的层状结构消失,且Co3O4的平均粒径约为13.75nm,复合物中存在N1s峰,N可能来源于反应前躯体硝酸钴,N的进入将增强Co和GO的结合能,同时N的引入有助于其与钴离子配位从而有利于Co3O4的形成,Co3O4颗粒均匀的分散在GO片层上,同时EDS证实了复合物是由C、O、Co三种元素组成,TGA显示复合物中Co3O4的质量含量大约在58%左右。(2)制得的催化剂复合物Co3O4/GO具有很高的催化活性。将制得的Co3O4/GO纳米复合物作为非均相催化剂应用到Co3O4/GO/PMS体系降解酸性橙Ⅱ废水,Co3O4/GO复合物表现出了很高的催化活性。溶液的pH值、温度等对反应影响很大且催化剂和氧化剂的投加量均存在一个最佳值。考虑到反应效率及经济实用性等方面的因素,最终确定的最佳反应条件为：原始酸性橙Ⅱ浓度为0.2mM,用磷酸盐缓冲液调节pH值为中性,催化剂投加量为0.1g/L,氧化剂投加量为2mM,反应温度为室温。此条件下,完全降解酸性橙Ⅱ仅需6min,且反应3h时COD的去除率可达79.9%,表现出很高的矿化程度。将催化剂循环使用5次后,催化剂仍然表现出较高的催化活性表明催化剂的稳定性很好。另外,研究还表明,GO、Co3O4及Co3O4/GO均有一定的吸附作用,但吸附作用很不明显且存在一个动态平衡,同时实验显示复合物Co3O4/GO的催化活性明显比GO和Co3O4都要大,表明Co3O4和载体GO之间存在协同作用。考察了无机盐离子对反应体系的影响,结果表明,PMS可以与H2PO4-反应而生成H2PO5-,生成的H2PO5-还有可能与Co2+配位生成H2PO5--Co2+络合物,形成新的活性中心,从而加速酸性橙Ⅱ的降解速率；当HCO3-的浓度低于10mM时,增大酸性橙Ⅱ的降解速率,但当HCO3-的浓度大于20mM时,将抑制酸性橙Ⅱ的降解反应；硫酸根自由基能够氧化Cl-生成活性比SO4-·低很多的Cl·,从而Cl-会明显的抑制酸性橙Ⅱ的降解反应；而SO4-·与NO3-反应生成活性较低的NO3·自由基,因此NO3-对酸性橙Ⅱ的降解速率几乎没有影响。(3)超声辅助能对非均相Co3O4/GO/PMS催化氧化体系起到促进作用。考虑到超声波、微波会对反应体系产生一定的辅助作用,本文对超声辅助下的Co3O4/GO/PMS催化氧化体系降解酸性橙Ⅱ进行了研究。结果表明,超声空化作用能有效的增大降解速率,同时曝气的引入,为溶液提供了更多的空化泡的同时还增大了溶液的湍动,从而增大了空化作用的几率,使得相同条件下能产生更多的自由基,从而对降解效率有很大的促进作用。当酸性橙Ⅱ的原始浓度为1mM时,超声辅助下的最佳条件是：催化剂投加量为0.05g/L、氧化剂投加量为10mM、pH值为7、超声功率为180W、室温。在此条件下,完全降解1mM的酸性橙Ⅱ只需12min。(4)催化剂中Co-OH复合物的形成是存在协同作用的关键。研究发现,在非均相Co3O4/GO/PMS催化氧化降解酸性橙Ⅱ的反应体系中,Co3O4/GO的催化活性比纯GO和纯Co3O4均明显增大,说明催化剂复合物中的GO和C0304之间存在一定的协同作用。本文对协同作用的机理进行了研究,结果表明,催化剂的催化活性还和催化剂中Co304的载量有关。当催化剂的载量为50%时,催化剂的催化活性最高。同时,Co-OH复合物在协同作用的产生反应中起到了至关重要的作用。而Co-OH复合物是由钴离子和其周围的氧化石墨烯片层上自带的羟基结合或和所吸附水离解出的羟基结合形成的。Co-OH复合物的形成为非均相催化PMS产生硫酸根自由基起到了很好的促进作用。然而,尽管Co304和GO表现出了很好的协同作用,但并不是催化剂中C0304的含量越多越好,过高浓度的C0304会覆盖在氧化石墨烯片层表面而阻碍Co-OH复合物的形成,从而使得催化剂的催化活性降低。更多还原

【Abstract】 Advanced oxidation technologies based on thegeneration of sulfate radicals (SO4-·) have emerged over the past years as a promising technique to degrade completely most organic pollutants. Compared with·OH (1.7eV), SO4-· has a higher oxidation potential (2.5eV to3.1eV) and it has emerged over the past years as a promising technique to degrade completely most organic pollutants over a wide pH range and no more vast iron cement need to dispose, has high degree of mineralization and simple to handle. Furthermore, SO4-· has a longer half-life, friendly to the environment, more producing methods and little deactivation factors. The homogeneous system has a swift response and simple to handle. However, the oxidation reaction using cobalt and PMS under homogeneous system has profound disadvantages due to cobalt leaching. The leach of cobalt has biological toxicity and is recognized as a priority metal pollutant. Therefore, the activation of PMS by heterogeneous cobalt sources has been given great attention recently. The current paper investigated the removal of the azo dye Orange II from water using Co3O4/GO/PMS catalytic oxidation system. The cobalt oxide catalyst immobilized on graphene oxide (GO) can activate peroxymonosulfate (PMS) for the degradation of Orange II in water. Meanwhile, ultrasound (US) and aeration applied were introduced into the system, and the possible beneficial effects of ultrasound and aeration were assessed. Effects of [PMS],[Co3O4/GO], pH, reaction temperature and various inorganic anions on the degradation of Orange II were investigated. And, the synergistic catalytic mechanism of Co3O4and graphene oxide (GO) nanocomposite in the heterogeneous activation of peroxymonosulfate (PMS) to generate sulfate radicals was studied. The following studies were carried out:(1) Effective heterogeneous catalyst (Co3O4/GO) was prepared.GO was prepared from purified natural graphite with a mean particle size of48μm according to the method reported by Hummers and Offeman. Using graphite oxide as the presoma, Co3O4/GO was been synthesized by a one-pot solvothermal method in1-hexanol solvent. The Co3O4/GO catalyst is characterized by scanning probe microscope (SPM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), Thermogravimetric analysis (TG), and high resolution transmission electron microscopy (HRTEM). Results show that the Co3O4/GO catalysts are large GO sheets decorated homogenously with well-dispersed Co3O4nanoparticles. The thickness of graphene oxide (GO) is about0.9～1.1nm and with the interlayer spacing of0.845nm. The surface of GO was quite smooth and have a lot of oxygen-containing functional groups like carboxyl, hydroxyl, epoxy and so on. While, the existence of Co3O4in Co3O4/GO caused the GO sheets to stack more loosely and the stratified structure disappeared. Scherrer formula show the average particle size of Co3O4on GO is about13.75nm. The XPS spectra of Co3O4/GO exhibit two additional N1s and Co2p peaks, in which N originated from the precursor of cobalt nitrate hexahydrate. N-doping of GO may be afford stronger coupling between Co and GO in Co3O4/GO. N-groups on GO serves as favorable nucleation and anchor sites for Co3O4nanocrystals because of the coordination with Co cations. The EDS of Co3O4/GO clearly show the sample consisted mainly of cobalt, carbon, and oxygen. TGA show the loading of Co3O4in the Co3O4/GO material is about58wt%.(2) The Co3O4/GO exhibits good heterogeneous activity in the degradation of Orange II used in advanced oxidation technology based on sulfate radicals.The heterogeneous Co3O4/GO/PMS system exhibited high activity in Orange II oxidation. Several operational parameters, such as catalyst amount, oxidant amount, pH, temperature, and oxidation rate, affected the degradation of Orange II. In the optimum addition,100%decomposition could be achieved within6min with0.2mM Orange Ⅱ,0.1g/L catalyst, and2mM PMS. Meanwhile, inductively coupled plasma analysis revealed that the leach of cobalt ions was low. The catalyst also exhibited stable performance after several rounds of regeneration. The adsorption of Orange Ⅱ onto Co3O4, GO and Co3O4/GO were studied and the adsorption/desorption was found to be a reversible process. Moreover, although Co3O4or GO alone has little catalytic activity, their hybrid (Co3O4/GO) exhibits an unexpected high catalytic activity in degradation of Orange Ⅱ in water by Co3O4/GO/PMS system, suggesting synergistic coupling between Co3O4and GO is indispensable to the high catalytic activity of the hybrid.H2PO4-can activate PMS and generate H2PO5-, H2PO5-and Co2+can complex to H2PO5--Co2+, which is new active centre., so the effects of H2PO4-had positive effect on the degradation of Orange Ⅱ. Low concentration HCO3-(<10mM) had positive effect and high concentration HCO3-(>20mM) had negative effect. Cl-had negative effect and NO3-had little effect.(3) The heterogeneous catalytic system coupled with Ultrasound (US) and aeration demonstrates an enhancement in terms of Orange Ⅱ degradation.The US and aeration applied were introduced into the heterogeneous Co3O4/GO/PMS system, and the possible beneficial effects were assessed. Ultrasonic cavitation can increase degradation rate efficient, and aeration can Increase the solution of the turbulent, so US and aeration can enhance the Orange Ⅱ degradation. The optimal operation condition for degradation of1mM Orange Ⅱ solution over60min is considered to be the dosage of0.05g/L Co3O4/GO and10mM PMS, ultrasonic power of180W, pH7and25℃. Under the optimal condition,100%degradation of Orange Ⅱ could be obtained within only12min.(4) The formation of Co-OH complexes is crucial for synergistic catalysis.In the degradation of Orange Ⅱ by heterogeneous Co3O4/GO/PMS system, although Co3O4or GO alone exhibit little catalytic activity, their hybrid (Co3O4/GO) exhibits an unexpectedly high catalytic activity, there exist synergistic effect between Co3O4and GO. In this study, the synergistic catalytic mechanism of Co3O4and GO nanocomposite in the heterogeneous activation of PMS to generate sulfate radicals was studied. The results show that a proportional relation exists between C03O4and the catalyst. The highest catalytic activity is observed when the Co3O4loading was about50%in the catalyst. Co-OH complexes form on the surface of the GO sheet through the direct interaction of Co species with nearby hydroxyl groups or through the dissociation of H2O with Co2+. The formation is proposed to facilitate the heterogeneous activation of PMS. However, a high Co3O4loading on the GO surface prevents the formation of Co-OH complexes, which is important in the catalytic reaction.更多还原