六方相三氧化钨的制备及光催化性能研究

【作者】 尹翔；

【导师】 李洁；

【作者基本信息】 中南大学 ， 物理化学， 2011， 硕士

【摘要】 三氧化钨是一种重要的半导体材料,在有机污染物的降解、光解水等方面有着广阔的应用前景,而实现三氧化钨优良的性能依赖于特殊的结构与形貌。因此,研究不同因素对三氧化钨结构、形貌以及光催化性能的影响具有重要的意义。本文利用水热法,研究了一价阳离子草酸盐为添加剂对三氧化钨结构与形貌的影响。研究发现,当阳离子为Li+、Na+时,易生成棒状六方相三氧化钨；当阳离子为K+、NH4+时形成六方相三氧化钨纳米线,并聚集成带有孔道的网状结构；当添加剂阳离子为Ru+、Cs+时,得到片状六方相三氧化钨；当添加剂阳离子为H+时,得到片状单斜相三氧化钨。结果表明,随着碱金属阳离子半径的增大,纳米三氧化钨的形貌由一维纳米线向二维纳米片转变；随着碱金属阳离子电负性增加,三氧化钨晶体生长越完全,并引起三氧化钨从六方相到单斜相的转变。以光催化降解亚甲基蓝溶液为模型,首先考察了晶型对光催化性能的影响,研究发现六方相三氧化钨光降解效率在30.0%以上,大于单斜相三氧化钨的光降解效率(21.4%)。本文进一步考察了不同形貌对六方相三氧化钨催化性能的影响,结果表明：当添加剂为K2C204时,由于三氧化钨聚集成网状结构,比表面积为93.73 m2/g,光降解效率最大,达到74.5%；同时发现,纳米棒的光降解效率在44.5%左右,大于纳米片的光降解效率(32.0%左右)。以乙二胺四乙酸二钠和左旋酒石酸钠为添加剂,分别制备了形貌较为少见的针状以及碟状的三氧化钨。以酒石酸为添加剂,考察了分子手性对光催化性能的影响。通过光吸收性能分析,左旋酒石酸为添加剂制备的三氧化钨光降解效率大于右旋酒石酸。此外,研究了水热温度与水热时间对制备六方相三氧化钨的影响,得到结论：三氧化钨晶体的生长随着水热温度的升高而更加完全,晶粒尺寸变大,其对亚甲基蓝溶液光降解效率降低；同样,时间的延长有助于三氧化钨晶体的进一步生长,但其对亚甲基蓝溶液光降解效率有所下降。更多还原

【Abstract】 WO3 is a kind of important semiconductor material with excellent performance and has a wide variety of applications in degradation of organic pollutions, photodecomposition of water and other aspects. However, the performance improvement of WO3 depends on its special structure and morphology. Therefore, it’s very important to study the effects of different factors on the crystal structure, morphology and photocatalytic activity of WO3.Hydrothermal method was used in this paper to investigate the influence on the structures and morphologies of WO3 when using the alkali metal cation oxalate as additives. The results show that nanorods structure hexagonal WO3(h-WO3)were synthesized when the monovalent cations are Li+ and Na+;while K+ and NH4+ induce the formation of h-WO3 nanowires which gathered into mesh structure with porous; besides, nanoplate structures h-W03 were obtained when using Ru+, Cs+ oxalate as additives; however, the addition of H2C2O4 leads to the formation of monoclinic WO3 nanoplates. It is found that the morphology of WO3 changed from 1D nanowires structures to 2D nanoplates structures with the increase of alkali metal cation radius. With the increase of the electronegativity of alkali metal cations, the WO3 crystals grew more completely and induced the crystal structure of WO3 transformed from hexagonal to monoclinic. In addition, we prepared unusual morphologies of needles and acetabuliform structures WO3 by adding EDTA-2Na and L(+)-sodium tartaric as additives respectively.In this paper, the photocatalytic degradation of methylene blue(MB) solution was used as model to investigate the photocatalytic properties of as-prepared WO3. We firstly investigated the influence of crystal structure on the photocatalytic properties of WO3, the results indicate that hexagonal WO3 exhibited higher photocatalytic activity than monoclinic WO3. The degradation rate of MB after 2h UV irradiation is over 30.0% with the h-WO3 as catalyst. While the degradation rate of MB is only 21.4% with monoclinic WO3 as catalyst. Further more, the effect of different morphologies on the photocatalytic properties of h-WO3 was also discussed. It was found that the WO3 prepared with K2C2O4 as additive shows the highest photocatalytic activity due to the network nanowires structure with high specific surface area of 93.73 m/g. Meanwhile, the results indicate that the degradation rate of MB with nanowires WO3 as catalyst is about 44.5%, higher than 32.0% when using the nanoplates WO3 as catalyst.In addition, the influence of molecule chirality on photocatalytic performance of products was also investigated by addition of tartaric acid. The results show that WO3 prepared with L(+)-tartaric acid as additive shows better photodegradation activity than that of WO3 synthesized by adding D(+)-tartaric acid.Finally, the impact of hydrothermal temperature and reaction time on the preparation of hexagonal WO3 was studied and reached the following conclusions:the WO3 crystal grew more perfect and bigger with increasing hydrothermal temperature, while showed lower photodegradation efficiency of MB. Meanwhile, longer reaction time contributed to the further growth of WO3 crystal, but weakened the performance of photocatalytic degradation of MB.更多还原