【作者】 王韶华；

【导师】 周少奇；

【作者基本信息】 华南理工大学 ， 环境工程， 2010， 博士

【摘要】 作为一种先进的高级氧化技术,纳米二氧化钛因具有高的光催化活性、良好的化学稳定性、廉价无毒等优点,被广泛应用于污水处理、空气净化等领域,成为环境、化学、材料科学等领域的研究热点。但二氧化钛禁带宽度大(3.2 eV),只能利用太阳光中的紫外线部分(仅占太阳能3-4%),而且存在分离回收难的问题,因而实际应用受到限制。通过多种改性方法提高催化剂的活性,丰富分离手段,提高催化剂的太阳光利用率是这一技术大规模应用的重要环节。本文通过对纳米二氧化钛掺杂改性、负载技术及光催化降解水中染料污染物的研究,探索最佳制备工艺和光催化降解条件,以期进一步充实光催化技术的研究。采用浸渍法和溶胶-凝胶法,首先制备了负载有MnxZn1-xFe2O4软磁粒子的活性炭,然后以钛酸四丁酯为钛源,将TiO2负载到具有磁性的多孔活性炭表面,在氮气气氛下程序升温处理得到可磁分离的TiO2/MnxZn1-xFe2O4/AC磁性光催化剂(TFAC)。研究结果表明:在对甲基橙(MO)的光催化降解中,TiO2/MnxZn1-xFe2O4/AC磁性光催化剂的最佳质量比为8∶1∶4,最适宜煅烧温度为450℃、煅烧时间为2 h。TFAC磁性光催化剂具有比P25和纯TiO2高的光催化活性,且具有良好的软磁性能,在外加磁场的作用下很容易从体系中分离出来,撤掉外加磁场后又很容易再次分散,催化剂经五次循环使用MO去除率仍接近90%。经过XRD、FT-IR、SEM、BET等表征手段分析,活性炭负载TiO2后,TiO2晶相结构为高催化活性的锐钛矿型,活性炭的负载可以有效抑制TiO2晶粒的尺寸,减少颗粒团聚;同时活性炭和TiO2相互作用,接触面形成了新的Ti-O-C键,具有很强的协同效应,均有利于提高磁性光催化剂的光催化活性。研究了TiO2/MnxZn1-xFe2O4/AC的吸附和光催化性能,考察了染料初始浓度、溶液pH值、H2O2浓度等因素对光催化降解MO的影响。结果表明,染料初始浓度与其脱色速率成反比;pH值在等电点附近,脱色效果最差,酸性或碱性条件有利于甲基橙的脱色;适量的H2O2能够提高MO的脱色效率,其最佳浓度为2 mmol/L;不同共存离子对脱色效率影响不同。根据降解过程中TOC、SO42–和NH4+等无机离子生成量、UV-Vis光谱及HPLC的变化分析了MO的脱色降解过程。随着反应的进行,脱色率不断提高,但是TOC的去除相对缓慢一些,HPLC研究表明中间产物较少。根据溶液中总S和总N的理论值与实际检测值推断MO的降解过程中磺酸基和N的转化过程。脱磺酸基和脱色反应均为初始反应,大部分N是以N2形式释放出去。运用Langmuir和Freundlich等温吸附模型对甲基橙和苯酚在TiO2/MnxZn1-xFe2O4/AC表面的吸附规律进行模拟,然后分别计算并对比各参数值,结果表明TiO2/MnxZn1-xFe2O4/AC对MO具有更高的吸附能力。甲基橙的光催化降解反应符合L-H准一级动力学模型。以钛酸四丁酯为原料,次磷酸为磷源,碳纳米管为载体,采用水热法制备了复合光催化剂P/TiO2/MWCNTs。研究表明:水热法制备的复合光催化剂比纯TiO2的晶粒小,比表面积有所增加,P-TiO2颗粒均匀地包覆在MWCNTs表面上。微量的P掺杂后,P以+5价氧化态(P5+)存在,它可以取代部分锐钛相二氧化钛晶格中的Ti4+。而P5+能够接受电子从而成为光生电子捕获中心,这样磷掺杂就降低了光生载流子的复合几率,从而增加了量子效率。同时,MWCNTs负载后,MWCNTs和P-TiO2之间产生协同作用,MWCNTs可作为电子接受体,易接受TiO2导带上的光生电子,有效地抑制TiO2光生电子和空穴的复合。复合光催化剂的荧光强度明显降低,也表明MWCNTs负载后光生电子和空穴复合几率下降。复合光催化剂吸收边发生红移,在可见光和紫外光下都表现出较高的光催化活性。其中,光催化活性最好的是MWCNTs和P-TiO2质量比为5%的样品CPT005。因此,掺杂适量的P和MWCNTs,可以显著地提高TiO2的光催化活性,拓宽光响应范围。采用溶胶-凝胶法制备P/TiO2/MWCNTs进行了对比研究。采用水热法,以十六烷基三甲基溴化铵(CTAB)为模板,尿素为沉淀剂,制备了结构新颖的半导体光催化剂Bi2O3中空微球。利用XRD、FT-IR、SEM等方法进行表征,研究了对水中亚甲基蓝的可见光催化降解。研究表明:Bi2O3中空微球是通过碱式碳酸铋的热分解得到的,水热反应的温度为260℃、反应时间为24 h、Bi3+/CO(NH2)2的最佳摩尔比为1∶4.5。Bi2O3对低浓度的亚甲基蓝溶液具有良好的可见光催化活性,酸性环境下有利于亚甲基蓝的光催化降解;适量添加氧化剂H2O2能有效提高Bi2O3的可见光催化活性。更多还原

【Abstract】 Nano-TiO2 as an advanced oxidation technology has become a research hotspot in environmental, chemistry and material field, because of its high photocatalytic activity, chemical stability, low cost, and nontoxicity in wastewater treatment, air purification, etc. However, the practical application of TiO2 is hampered by the fact that it absorbs only the very small ultraviolet part (3-4%) of solar light due to its wide band-gap of 3.2 eV, and moreover there exists problems of separation and recycles. Through a variety of modification methods to improve the photocatalytic activity, enrich the separation means and increase the utilization of sunlight is the important step to make this technology large-scale application. Our long term in this dissertation is to initiate the research of doping modification, support technology and the photodegradation of dye pollutants in water, and explore the optimal preparation techniques and degradation conditions, by which we look forward to building up the research of photocatalytic technology.TFAC as a magnetically separable photocatalyst has been successfully prepared by dip-coating technique and sol-gel method. Firstly, soft magnetic ferrite of MnxZn1-xFe2O4 was adsorbed onto AC (FAC). Afterward, anatase titania was deposited onto the FAC using n-Ti(OBu)4 as titania precursor followed by calcining in N2 atmosphere. The results showed that TFAC catalysts calcined at 450°C for 2 h exhibited the highest activity for degradation of methyl orange (MO) and the best mass proportions of TiO2/MnxZn1-xFe2O4/AC was 8∶1∶4. These photocatalysts exhibited enhanced photocatalytic activity compared to Degussa P25 and pure TiO2. The composite photocatalysts could be easily separated from the bulk solution by a magnetic field and also could be easily redispersed into aqueous solution after removing the external magnetic field. Furthermore, the photocatalysts could maintain high photocatalytic activity after five cycles, and the degradation rate of MO was still close to 90%. The prepared composites were characterized by XRD、FT-IR、SEM、BET etc. The crystal phase of TiO2 was anatase after deposited onto AC, the AC could inhibit the grain size and decrease aggregation of TiO2. Meanwhile, there was a synergetic effect between AC and TiO2 and formed a new Ti-O-C bond. The interaction of AC and TiO2 could enhance the photoactivity of TFAC.The adsorption and photocatalytic properties of TiO2/MnxZn1-xFe2O4/AC were studied. The influence of operational variables, such as initial MO concentration, pH values, hydrogen peroxide concentration on UV photodegradation of MO was investigated. The results showed that the decolorization of MO was inversely proportional to the initial MO concentration. The worst decolorization of MO was obtianed at the pH value near the isoelectric point, acidic or alkaline conditions were beneficial to the decolorization of MO. In order to promote the efficiency of MO decolorization, there was an optimal concentration of H2O2, which was 2mmol/L. The effect of different co-existing ions on the adsorption and decolorization of MO was distinct. The decolorization and degradation of MO was analyzed according to the the TOC decrease, inorganic ion production from the dye degradation, such as SO42– and NH4+, change of UV-Vis spectra and HPLC. With the reaction proceeded, decolorization rate was increased ,but TOC removal was slower. The characteristic absorption peak of MO disappeared completely and there was not any new peak appeared. The HPLC study indicated that there were small amounts of intermediates. The transformation of -SO3– and -N=N- in the degradation of MO was inferred from differences between the theoretical value and the detected values of SO42– and the total N. The release and decolorization was the initial step, with the nitrogen of azo group transformed predominantly to N2. The Langmuir and Freundlich isotherm adsorption model was used to simulate the adsorption kinetics of MO and phenol on TiO2/MnxZn1-xFe2O4/AC. Then their model parameters were calculated and compared to study the differences of their adsoption properties. The results show that TiO2/MnxZn1-xFe2O4/AC has excellent adsorption property, and has a higher adsorption capacity to MO than phenol. The photocatalytic degradation of MO follows L-H kinetic model.The composite photocatalyst of P/TiO2/MWCNTs was prepared by hydrothermal method using n-Ti(OBu)4 as starting material, hypophosphorous acid (H3PO2) as phosphorous precursor and MWCNTs as supporter. The results showed that P-TiO2 particle size was smaller than pure TiO2 and the specific surface area was also increased. The P-TiO2 particles were uniformly coated onto the surface of MWCNTs. After trace amount of P doping into TiO2, doped phosphorus was present as the pentavalent-oxidation state, which could replace a part of Ti4+ in the crystal lattice of anatase. Because P5+ can accept photoelectron as the electron trap center, its doping reduces the recombination rate of photogenerated charge carriers and increases the photon efficiency. At the same time, there was a synergetic effect between MWCNTs and P-TiO2. MWCNTs were eminent electronic acceptors that could orderly export excited electron (e–) from conduction band of TiO2 and fleetly reduce electronic accumulation on TiO2 nanoparticles. So the recombination of electron/hole (e–/h+) pairs could be effectively decreased. The fluorescence intensity of composite catalysts reduced obviously, indicating the reduction of the recombination of electron/hole (e–/h+) pairs. The composite catalysts not only extended the adsorption edge to visible light region, but also exhibited high photoactivity under visible light and UV irradiation. Among them, the CPT005 with a mass ratio of CNTs to P-TiO2 of 5% had the best photoactivity. Therefore, adding a suitable amount of phosphorus and MWCNTs could greatly improve the photocatalytic activity of TiO2 and expand the light response scope. The composite photocatalysts were also prepared by sol-gel method for contrast study. a mass ratio of CNTs to P-TiO2 in the nanocomposite catalyst was considered at 5:100A novel structure of semiconductor Bi2O3 hollow microsphere was prepared by hydrothermal method with cetyltrimenthylammonium bromide (CTAB) as a template and urea as precipitant, and characterized by XRD、FT-IR and SEM technologies. Photocatalytic degradation of methylene blue under visible light was carried out using Bi2O3 as the photocatalyst. It was found that Bi2O3 hollow microsphere was obtained through theral decomposition of bismuth subcarbonate at 260°C for 24 h and the best mol proportions of Bi3+/CO(NH2)2 was 1∶4.5. Bi2O3 exhibited good photoactivity under visible light for degradation of low concentration methylene blue solution. The photoactivity of Bi2O3 could be enhanced under acidic environment or by adding centain amounts of oxidant H2O2.更多还原