Shen Yu-Jen, Lee Yuh-Lang
Department of Chemical Engineering, National Cheng Kung University, Tainan 70101, Taiwan.
Nanotechnology. 2008 Jan 30;19(4):045602. doi: 10.1088/0957-4484/19/04/045602. Epub 2008 Jan 4.
Colloidal cadmium sulfide (CdS) quantum dots (QDs) were prepared and surface modified by mercaptosuccinic acid (MSA) to render a surface with carboxylic acid groups (MSA-CdS). The MSA-CdS QDs were then assembled onto bare TiO(2) mesoporous films using the carboxylic groups/TiO(2) interaction. The TiO(2) film was also surface modified by 3-mercaptopropyl trimethoxysilane (MPTMS) or 3-aminopropyl-methyl diethoxysilane (APMDS) to prepare, respectively, a thiol (-SH) or amino (-NH(2)) terminated surface for binding with the CdS QDs. The experimental results showed that the MPTMS-modified film has the highest adsorption rate and adsorption amount to the CdS QDs, attributable to the strong thiol/CdS interaction. In contrast, the adsorption rate and incorporated amount of the QDs on the bare TiO(2) film are much lower than for the silane-modified films. The incident photon-to-current conversion efficiency (IPCE) obtained for the CdS-sensitized TiO(2) electrode was about 20% (at 400 nm) for the bare TiO(2), 13% for the MPTMS-TiO(2), and 6% for APMDS-TiO(2). The current-voltage measurement under dark conditions reveals a higher dark current on the MPTMS- and APMDS-modified electrodes, indicating a lower coverage ratio of CdS on these TiO(2) films. This result is attributed to the fast adsorption rate of CdS QDs on the bottleneck of a mesopore which inhibits the transport of the QDs deep into the inner region of a pore. For the bare TiO(2) film, the lower incorporated amount of CdS but higher energy conversion efficiency indicates the formation of a better-covered CdS QDs monolayer. The moderate adsorption rate of MSA-CdS QDs using the carboxylic acid/TiO(2) interaction is responsible for the efficient assembly of QDs onto the mesoporous TiO(2) films.
制备了硫化镉（CdS）胶体量子点（QDs），并用巯基琥珀酸（MSA）对其进行表面修饰，以得到具有羧酸基团的表面（MSA-CdS）。然后利用羧基与TiO₂的相互作用，将MSA-CdS量子点组装到裸露的TiO₂介孔薄膜上。TiO₂薄膜还用3-巯基丙基三甲氧基硅烷（MPTMS）或3-氨丙基甲基二乙氧基硅烷（APMDS）进行表面修饰，分别制备用于与CdS量子点结合的巯基（-SH）或氨基（-NH₂）封端的表面。实验结果表明，MPTMS修饰的薄膜对CdS量子点的吸附速率和吸附量最高，这归因于巯基与CdS之间的强相互作用。相比之下，量子点在裸露TiO₂薄膜上的吸附速率和掺入量远低于硅烷修饰的薄膜。对于CdS敏化的TiO₂电极，裸露TiO₂的入射光子-电流转换效率（IPCE）在400 nm处约为20%，MPTMS-TiO₂为13%，APMDS-TiO₂为6%。暗条件下的电流-电压测量显示，MPTMS和APMDS修饰电极上的暗电流较高，表明这些TiO₂薄膜上CdS的覆盖率较低。该结果归因于CdS量子点在介孔瓶颈处的快速吸附速率，这抑制了量子点向孔内部区域的深入传输。对于裸露的TiO₂薄膜，CdS掺入量较低但能量转换效率较高，表明形成了覆盖较好的CdS量子点单层。利用羧酸与TiO₂的相互作用，MSA-CdS量子点的适度吸附速率有助于量子点在介孔TiO₂薄膜上的有效组装。
