Bi2WO6/ZnO:一种在可见光下具有优良光催化性能的花状新型复合材料

摘要

The photocatalytic ability of ZnO is improved through the addition of flower-like Bi2WO6to prepare a Bi2WO6/ZnO composite with visible light activity. The composite is characterized by X-ray diffrac-tion, transmission electron microscopy, scanning electron microscopy with UV-vis diffuse reflec-tance spectroscopy, X-ray photoelectron spectroscopy and N2adsorption-desorption isotherms. After modification, the band gap energy of Bi2WO6/ZnO is reduced from 3.2 eV for ZnO to 2.6 eV. Under visible light irradiation, the Bi2WO6/ZnO composite shows an excellent photocatalytic activity for degrading methylene blue (MB) and tetracycline. The photo-degradation efficiencies of (0.3:1) Bi2WO6/ZnO for MB and tetracycline are approximately 246 and 4500 times higher than those of bare ZnO, respectively, and correspondingly, the photo-degradation rates for the two pollutants are approximately 120 and 200 times higher than those with bare ZnO, respectively. Moreover, the photocatalyst of (0.3:1) Bi2WO6/ZnO exhibits a higher transient photocurrent density of approxi-mately 4.5 μA compared with those of bare Bi2WO6and ZnO nanoparticles. The successful recom-bination of Bi2WO6and ZnO enhances the photocatalytic activity and reduces the band gap energy of ZnO, which can be attributed to the effective separation of electron-hole pairs. Active species trap-ping experiments display that [O2]-is the major species involved during photocatalysis rather than ·OH and h+. This study provides insight into designing a meaningful visible-light-driven photocata-lyst for environmental remediation.%印染废水具有水量大、色度高、难生化降解、有毒有害物质多等特点; 另外抗生素废水的大量排放对水生和陆地生态系统带来了危害. 光催化可有效降解有机物, 因而被广泛研究和应用, 其多以半导体作为光催化剂. ZnO因价廉、无毒、来源广、光催化活性高而广受关注. 但是, 由于其带隙较宽, 只能被紫外光激发, 对太阳光的利用率低, 且易发生光腐蚀, 光稳定性较差, 从而大大降低了光催化活性, 不利于其应用. 将ZnO与其他半导体复合是改善其光催化活性的最有效方法之一. 铋基光催化剂一直是光催化领域的研究热点, 作为无机半导体纳米晶之一, Bi2WO6具有无毒性、适当的带隙和优异的光催化性能, 因而得到广泛关注. 本文将Bi2WO6复合到ZnO上以降低ZnO带隙能, 提高其对太阳能的转换, 降低电子-空穴的复合几率, 促进电荷转移的有效分离, 从而提高ZnO的光催化性能.本文采用两步水热法合成了一种异质结的花状Bi2WO6/ZnO复合材料. 通过降解亚甲基蓝(MB)和四环素, 研究了其光催化性能. 结果表明, 该Bi2WO6/ZnO复合材料对MB和四环素具有优异的光催化活性, 对它们的光降解效率分别是纯ZnO的246和4500倍, 相应地, 对这两种污染物的光降解率分别是纯ZnO的120和200倍. 活性因子捕获实验结果显示, 超氧自由基在光催化降解过程中起主要作用, 其次是羟基自由基和光生空穴.采用X射线衍射、透射电镜、扫描电镜、紫外-可见漫反射、N2吸附脱附、X射线光电子能谱、荧光光谱、光电流等方法对材料的形态结构、孔结构、化学组成、带隙能、光吸收性质、载流子复合效率等进行了分析. 复合后Bi2WO6/ZnO的形貌为微米尺寸纳米结构的花状绒球, 直径约为4 μm, 带隙能量从3.2 eV降为2.6 eV. Bi2WO6/ZnO为介孔结构, 复合后比表面积为原来的4.98倍. 所制备的Bi2WO6/ZnO光催化剂比纯Bi2WO6和ZnO颗粒具有更高的瞬态光电流密度(约为4.5 μA).综上, Bi2WO6和ZnO成功复合形成了异质结, 降低了ZnO的禁带宽度, 促进了电子和空穴的有效分离, 从而提高了其光催化活性.