Young Aidan G, Green David P, McQuillan A James
Department of Chemistry, University of Otago, P.O. Box 56, Dunedin, New Zealand.
Langmuir. 2006 Dec 19;22(26):11106-12. doi: 10.1021/la061999s.
Probing the surface chemistry of thiol ligand binding to cadmium chalcogenide nanocrystals is important to clarify factors involved in quantum dot stability and surface functionalization. Deposited CdS nanocrystal films have been used in this work as model quantum dot surfaces for ligand adsorption studies. The adsorption of mercaptoacetic acid, mercaptopropionic acid, and mercaptoethanol, from aqueous solution to CdS thin films, has been studied by in situ infrared spectroscopy. The absence of a S-H stretch absorption for the adsorbed species shows that adsorption occurs via the deprotonated thiol group, and the spectrum of the adsorbed carboxylic acid species closely resembles those of the solution ligands. Adsorption of mercaptoacetic acid and of mercaptopropionic acid resulted in pKa(COOH) decreases of 1.5 and 0.5, respectively. Significant changes in the spectrum of mercaptoethanol upon adsorption have been observed, but the present uncertainty in mercaptoethanol spectral interpretation does not provide structural inferences. Adsorption isotherms determined from the spectral data indicate strong thiol adsorption to CdS. The adsorption isotherms have been fitted to both Langmuir and Freundlich equations, with the latter providing a better fit. This may be attributed to a change in the probability of adsorption to vacant surface sites due to the increased CdS surface negative charge as the surface coverage increases.
探究硫醇配体与硫族镉化物纳米晶体结合的表面化学对于阐明量子点稳定性和表面功能化所涉及的因素至关重要。在这项工作中，已沉积的硫化镉纳米晶体薄膜被用作配体吸附研究的模型量子点表面。通过原位红外光谱研究了巯基乙酸、巯基丙酸和巯基乙醇从水溶液到硫化镉薄膜的吸附情况。吸附物种不存在S-H伸缩吸收表明吸附是通过去质子化的硫醇基团发生的，并且吸附的羧酸物种的光谱与溶液配体的光谱非常相似。巯基乙酸和巯基丙酸的吸附分别导致pKa(COOH)降低1.5和0.5。吸附后观察到巯基乙醇光谱有显著变化，但目前巯基乙醇光谱解释的不确定性无法提供结构推断。由光谱数据确定的吸附等温线表明硫醇对硫化镉有强烈吸附。吸附等温线已根据朗缪尔方程和弗伦德利希方程进行拟合，后者拟合效果更好。这可能归因于随着表面覆盖率增加，硫化镉表面负电荷增加，导致吸附到空表面位点的概率发生变化。
