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自1972年Fujishima和Honda首次发现光催化效应[1]以来,光催化作为一种环境友好型技术,在挥发性有机物(VOCs)治理领域得到了快速发展[2]. 光催化治理VOCs具有反应可控、条件温和、无二次污染等优点[3].
Ti、Bi、Zn、Sn、Al等氧化物是常用的半导体光催化材料[4-7],其中TiO2由于廉价易得、无毒无害等优点,应用最为广泛. 但这些金属氧化物带隙较宽,且光生电子空穴复合率高,光催化效率比较低. 以TiO2为例,禁带宽度为3.2 eV,只能利用波长低于380 nm的紫外光,该部分紫外光在太阳光中占比不到5%;此外TiO2稳定性不佳,在使用过程中易发生光腐蚀导致性能下降. 光催化效率和稳定性提升的常用方法有贵金属掺杂[8]、表面形貌控制[9]和复合改性[10]等,但这些方法制备过程复杂、成本高,不利于推广应用. 开发制备过程简单、光催化效率和稳定性好、适宜在可见光下应用的光催化剂具有广阔应用前景.
尖晶石型化合物AB2O4为立方晶或者四方晶系,其中的A—O和B—O键为强离子键,稳定性和耐光腐蚀性好;同时表面有大量电子空穴对,光催化性能优异. 尖晶石型光催化剂是一种理想的便于推广应用的材料. 尖晶石型铋系光催化剂,由于O的2p电子轨道会与Bi 的6s2 价带发生杂化,可进一步缩短带隙、提高可见光响应性能,成为近些年的研究热点,其中以CuBi2O4最为常见[11],但纯相的CuBi2O4化学亲和能较低且光生电子-空穴易复合,光催化性能仍有待提升.
铋系光催化剂的铋源一般为Bi(NO3)3·5H2O,该物质只有在强酸条件下才能避免水解产生碱式盐沉淀,所以常规溶胶凝胶法不适用于铋系光催化剂的制备,常用方法有共沉淀法[12]和水热法[13]. 本文通过一种新颖的酯化溶胶凝胶法制备出了尖晶石型铋系的CuBi2O4和ZnAlBiO4可见光光催化剂,制备过程不额外添加水作为溶剂,避免了Bi(NO3)3·5H2O的水解. 此外,将上述催化剂分别负载在蜂窝陶瓷上,对比两者光催化降解乙醛废气性能,为室内空气净化提供理论指导.
尖晶石CuBi2O4和ZnAlBiO4铋系光催化剂的制备及可见光催化降解乙醛废气
Synthesis of CuBi2O4 and ZnAlBiO4 nanomaterials for enhanced photocatalytic acetaldehyde removal under visible light irradiation
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摘要: 通过一种新颖的酯化溶胶凝胶法制备出了CuBi2O4和ZnAlBiO4铋系光催化剂,对负载上述催化剂的蜂窝陶瓷进行了光催化降解乙醛废气实验. 制备的铋系光催化剂结晶度良好,原子比例和离子化合价均符合尖晶石型化合物特征;粒径均为纳米-亚微米量级,分散性良好;ZnAlBiO4样品表面存在少量固溶体析出,和反尖晶石型结构,有助于提高其表面积和光催化活性. 两种铋系光催化剂禁带宽度均远低于常用TiO2 (P25)的3.1 eV,其中ZnAlBiO4为1.2 eV,CuBi2O4为1.5 eV,两者在420—800 nm波段的可见光响应性能良好. 负载光催化剂的蜂窝陶瓷对乙醛的暗反应初始吸附效率均约为30%,但负载ZnAlBiO4的蜂窝陶瓷样品光催化净化效率可以达到85%,远高于负载CuBi2O4的样品. 两种样品光催化稳定性较高,循环使用6次光催化活性未见明显降低,对乙醛的矿化率均达到了95%以上. 以上结果表明,ZnAlBiO4光催化剂净化VOCs性能优异,具有较高的实用价值.Abstract: The bismuth-based photocatalysts of CuBi2O4 and ZnAlBiO4 were synthesized by a novel sol–gel–esterification method. The photocatalytic performances of acetaldehyde degradation were carried out on the honeycomb ceramics supports. Both of them were the spinel structures and submicron sizes with good crystallinity and dispersion. The band gaps of CuBi2O4 and ZnAlBiO4 photocatalysts were narrower than that of the commercial TiO2 P25, in the order of ZnAlBiO4 (1.2 eV) < CuBi2O4 (1.5 eV) < (3.1 eV). Additionally, the CuBi2O4 and ZnAlBiO4 photocatalysts were provided with available visible light response in the region of 420–800 nm. Furthermore, owing to an anti–spinel type structure and fewer solid solution precipitation on surface, the photocatalytic efficiency of honeycomb ceramics with ZnAlBiO4 could reach 85%, higher than that of CuBi2O4. Combined with the initial adsorption efficiency of 30% in dark, the mineralization rate of acetaldehyde on ZnAlBiO4 was above 95%, with no significant decrease after six cycles. Therefore, the ZnAlBiO4 nanomaterial is considered as a potential photocatalyst to eliminate VOCs.
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表 1 样品中不同原子的百分比含量(%,物质的量)
Table 1. The atomic percentage of samples
样品
SampleCu Zn Al Bi O 原子比例
Atomic ratioCuBi2O4 14.47 — — 28.71 56.82 1∶1.98∶3.93 (Cu∶Bi∶O) ZnAlBiO4 — 14.27 13.36 13.81 58.56 1∶0.94∶0.97∶4.1 (Zn∶Al∶Bi∶O) -
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