静电纺丝法制备的CdS/ZnS/ZnO三元异质结纳米纤维无助催化剂下的光催化产氢性能

CdS/ZnS/ZnO ternary heterostructure nanofibers fabricated by electrospinning for excellent photocatalytic hydrogen evolution without co-catalyst

近年来,由三种半导体组成的三元异质结由于其在促进光生电子和空穴的分离和转移方面的优势而备受关注.在本研究中,我们首先通过静电纺丝技术制备了Zn O纳米纤维,然后对其进行原位硫化,Zn O纳米纤维的表层被硫化成Zn S,得到Zn S/Zn O二元异质结纳米纤维,最后采用连续离子层吸附反应法在Zn S/Zn O纳米纤维上沉积Cd S量子点,得到Cd S/Zn S/Zn O(CZZ)三元异质结纳米纤维.我们对硫化过程中使用的硫化剂(硫脲)的浓度和离子层吸附沉积Cd S的次数进行调节,以优化CZZ三元异质结纳米纤维的产氢性能,经优化后的CZZ三元异质结纳米纤维在没有助催化剂的情况下产氢速率达到51.45 mmol h^–1 g^–1(420 nm处的表观量子效率达到26.88%),是相同情况下氧化锌纳米纤维的93.54倍,Zn S/Zn O二元异质结纳米纤维的2.28倍.加入贵金属Pt作助催化剂后,其产氢速率进一步提高至118.62 mmol h^–1 g^–1.为了突出一维纳米纤维对光催化产氢性能的贡献,我们采用超声辅助水热法制备得到了二维的Zn O纳米页,然后采用同样的方法和工艺对其进行硫化,得到二维的Zn S/Zn O二元异质结纳米页,最后采用同样的方法和工艺进行Cd S量子点的沉积,最终得到二维的Cd S/Zn S/Zn O三元异质结纳米页在没有助催化剂的情况下产氢速率只有9.98 mmol h^–1 g^–1,加入贵金属Pt作助催化剂后其产氢速率仅提高至27.25 mmol h^–1 g^–1.这些结果表明,与二维CZZ纳米页相比,一维CZZ纳米纤维具有更高的产氢性能.其原因可归结为:二维纳米片可以看作是由很多一维纳米纤维沿着轴线方向密集排列堆积而成的,因此与二维纳米片相比,一维纳米纤维的几何尺寸大大减小,光生电子和空穴迁移到表面的距离显著缩短,这样可以有效地抑制光生电子和空穴的复合,从而提高了光催化产氢速率.我们对一维CZZ三元异质结纳米纤维的光催化产氢机理进行了研究,发现在模拟太阳光(320–780 nm)照射下,三种半导体(Zn O,Zn S和Cd S)都能被激发产生电子和空穴.Zn S的导带位置比Zn O和Cd S的导带位置负,因此Zn S导带上的光生电子将向Zn O和Cd S的导带迁移,然后被氢离子捕获生成氢气.同时,Zn O价带上产生的光生空穴被转移到Zn S的价带上,然后与牺牲剂反应被消耗掉.对于Zn S与Cd S之间的界面,Cd S价带上的光生空穴可以跃迁到Zn S的两个杂质能级(VZn和IS)中,这样有效避免了Cd S的光腐蚀,使CZZ三元异质结呈现出很好的光催化稳定性.该工作对构建三元异质结促进光生载流子的分离和迁移具有借鉴意义.

In recent years,ternary heterostructures(HSs)composed of three semiconductors have attracted significant attention because of the effective separation and transfer of photogenerated electrons and holes in these materials.In this work,new ternary Cd S/Zn S/Zn O(CZZ)HSs with one-dimensional(1D)nanofiber morphology have been successfully fabricated for the first time by a series of processes:electrospinning Zn O nanofibers,sulfurizing Zn O in situ to form Zn S/Zn O binary HSs,and depositing Cd S quantum dots in situ on the Zn S/Zn O HSs.Benefiting from the efficient separation and transfer of photoinduced charge carriers,the optimized CZZ ternary HSs exhibit a hydrogen evolution rate of 51.45 mmol h^-1 g^-1(quantum efficiency:26.88%at 420 nm)without any co-catalyst,which is 93.54 and 2.28 times higher than those exhibited by pristine Zn O and Zn S/Zn O binary HSs,respectively,under the same conditions.Furthermore,the rate of hydrogen evolution over the 1D CZZ nanofibers is significantly higher than that over 2D CZZ nanosheets(27.25 mmol h^-1 g^-1,in the presence of a Pt co-catalyst)prepared by the same sulfurization and deposition procedures.This can be ascribed to the significantly smaller geometric sizes of 1D nanofibers compared to those of 2D nanosheets,resulting in effectively suppressed recombination of photogenerated charge carriers and promotion of photocatalytic H2 evolution performance.