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几种钒氧化物纳米材料的合成、表征及其在颜料催化降解中的应用
Synthesis, Characterization of Several Vanadium Oxides Nanomaterials and Their Application in Catalytic Degradation of Dyes
【作者】 韩德(Hayder Abdulhasan Abbood);
【导师】 黄开勋;
【作者基本信息】 华中科技大学 , 无机化学, 2013, 博士
【摘要】 纺织工业废水含有各种复杂的很难降解的染料类污染物,而这些污染物未经处理释放到我们的环境,就会导致水的严重污染。因此,合成高效的处理纺织工业染料废水的催化剂是一种挑战,而且具有重要的科学意义和应用前景。近几十年来,半导体光催化剂被广泛地研究,并被用于各种领域,诸如水处理、空气净化及分解水制氢等。但在光催化剂中,主要是一些宽禁带的半导体材料,而这些宽禁带的半导体如二氧化钛纳米材料只有在紫外光的照射下才有活性。因此,合成一种能有效利用如太阳能这样用之不竭的或者低廉的可见光的光催化剂是很有必要的。五氧化二钒半导体常常用于太阳能电池中,其禁带宽度为2.05eV,其电子比二氧化钛更容易被激发。然而,钒氧化物纳米材料用于污染光催化降解的研究较少。本文利用水热法合成了的具有几种形貌特征的钒氧化物纳米材料,并研究了其光催化特性或电化学特征。主要结果如下:1.通过水热法,用NH4VO3作为前体,以羧甲基纤维素钠(CMC)为软模板,在160下反应6小时,合成出具有竹席形中心的类交叉结构氧化钒铵纳米带阵列,用XRD、FE-SEM、TEM、SA-ED、HRTEM及FT-IR对合成出的产物进行了表征,并研究了CMC浓度、pH值以及温度对产物形貌的的影响。结果表明pH值对合成产物的形成起了至关重要的作用。基于随时间变化实验的结果,提出竹席形中心的类交叉结构NH4V4O10纳米带阵列的生长过程。进一步,本文通过在400下将类交叉结构氧化钒铵纳米带阵列煅烧40分钟,得到混合价态的氧化钒产物。在此基础上,研究了其在可见光的照射下催化氧化降解水溶液中罗丹明B的效果,并与其他阴离子染料进行了对比。此外,还探讨了温度对催化剂光催化的影响和重复使用效果,结果表明其在pH6.8,75下保持3小时30分钟,煅烧后的产物对罗丹明B的催化降解率达到了约95%,在同等条件下其效果明显优于二氧化钛纳米材料(P25),并且具有较好的重复使用率,这说明煅烧过的竹席形中心的类交叉结构氧化钒铵纳米带阵列是一种较为理想的可见光照射下降解罗丹明B的催化剂。2.利用水热反应合成出单晶MnV2O6·V2O5类交叉结构纳米带阵列,并用XRD、TEM及HRTEM对其进行了表征。并研究了各种反应条件(如pH,V5+/Mn2+比,CMC浓度及反应时间等)对产物形貌的影响,利用漫反射光谱分析计算了其禁带宽度。在此基础上,评价了其煅烧产物在可见光照射下对甲基蓝的光催化降解活性和重复使用效果。结果表明,由于Mn的掺杂,煅烧后的产物对甲基蓝的降解活性明显提高,而且具有较好重复使用率,这说明MnV2O6·V2O5类交叉结构纳米带阵列的煅烧产物是一个比较优越的可见光驱动的光催化剂。3.以草酸钒作为前体,苄醇为辅助剂,采用简单的一步水热法合成出了VO2(B)中空类纳米球材料,研究了草酸钒浓度、苄醇的存在和浓度以及过氧化氢的加入对产物形貌的影响,所合成产物用XRD, FE-SEM, TEM, HR-TEM及FT-IR等手段进行了表征。通过时间影响实验的结果,提出了VO2(B)中空类纳米球的晶体成长过程。对Ostwald成熟机理在球形颗粒的成长及中空类纳米球颗粒形成中的作用进行了讨论。此外,采用循环伏安法对在不同反应时间下合成出的VO2(B)中空类纳米球的电化学性质进行了评价。
【Abstract】 Textile industry effluents contain a variety of complex and hard to degrade pollutantssuch as dyes that may cause significant water pollution when they are released to ourenvironment. Therefore, to synthesize a highly effective catalyst for treating textile dyewastewater is still a challenge and has important scientific significance and applicationprospects.Semiconductor photocatalysts have been extensively studied in recent decades, andhave been applied in numerous areas, such as water treatment, air purification,decomposition of water into hydrogen, etc. However, most of photocatalysts work underultraviolet light. Thereinto, nano-TiO2has been extensively studied as an effectivephotocatalyst, but it is not a good candidate under visible light irradiation. Therefore, it isstill a challenge to synthesize a highly effective catalyst for treating textile dye wastewaterunder visible light. Vanadium oxides semiconductor materials have received significantattention recently because of their distinctive structural versatility and novel applicationsin catalysis, high-energy lithium batteries, electric field-effect transistors, chemicalsensors/actuators and electrochemical devices. Nevertheless, a few studies about usingvanadium oxides in photocatalytic degradation of organic pollutants have been reported.In this thesis, several kinds of vanadium oxide nanomaterials were synthesized viahydrothermal method, and their photocatalytic or electrochemical properties were studied.The main results are as follows:1. The ammonium vanadium oxide cross-like nanobelt arrays with bamboo matcenter were synthesized via hydrothermal method using NH4VO3as precursors inpresence of sodium carboxymethyl cellulose (CMC), the soft template, at160C for6h.The synthesized-products were characterized by XRD, FE-SEM, TEM, SA-ED, HRTEM,and FT-IR. The effects of CMC concentration, pH value and temperature on the productmorphology were investigated. It showed that pH value plays a crucial role in theformation of cross-like nanobelt arrays. Based on the results of time dependentexperiments, the growth process of the cross-like NH4V4O10nanobelt arrays is proposed.Furthermore, the mixed valance state vanadium oxide nanobelt arrays were obtained bycalcination of the cross-like NH4V4O10nanobelt arrays at400°C for40min and its capability of catalytic degradation of rhodamine B with oxygen in aqueous under UV/vislight irradiation was studied and compared with anionic dyes. Besides, the influence oftemperature on the photocatalytic degradation was also investigated. The result showedthat the degradation efficiency of rhodamine B catalyzed by the calcinated product wasabout95%at pH6.8and75C for3h and30min, suggesting it is a candidate of efficientcatalysts for the photocatalytic degradation of rhodamine B under visible light irradiation.2. Single-crystalline MnV2O6·V2O5cross-like nanobelt arrays were successfullysynthesized by hydrothermal reaction. The products were characterized by XRD, TEMand HR-TEM. The effects of the reaction conditions such as pH, V5+/Mn2+ratio,carboxymethyl cellulose concentration and reaction time on the morphology of theproducts were studied. The band gap of the as-prepared products was calculated viadiffuse reflectance spectral analysis and their activity of photocatalytic oxidation wasevaluated by photodegradation of methylene blue under visible-light irradiation. Theresults showed that the degradation efficiency of methylene blue catalyzed by thecalcinated products is remarkably enhanced due to Mn doping, suggesting thatMnV2O6·V2O5cross-like nanobelt arrays are a good candidate for visible-light-drivenphotocatalysts.3. VO2(B) hollow like-nanosphere material was synthesized via a facile one-stephydrothermal process using vanadium oxalate as precursors in the presence ofwater-benzyl alcohol. Effects of vanadium oxalate concentration, existence of benzylalcohol and its concentration, and addition of hydrogen peroxide on the morphologies ofas-prepared products were investigated. The as-synthesized products were characterizedby XRD, FE-SEM, TEM, HR-TEM and FT-IR. Based on the results of time dependentexperiments, the growth process of VO2(B) hollow like-nanosphere were proposed. Theinside-out Ostwald ripening is responsible for the growth of spherical particles and theformation of hollow like-nanosphere. In addition, the electrochemical properties of VO2(B) like-nanosphere at various reaction times were compared by using cyclicvoltammogram.
【Key words】 Vanadium Oxide; Nanomaterials; Hydrothermal Synthesis; Characterization; Photocatalytic Degradation; Dye; Cyclic Voltammogram;