【作者】 张宇；

【导师】 余睽；

【作者基本信息】 四川大学 ， 化学工艺， 2023， 硕士

【摘要】 量子点（quantum dots）具有优越的光学、电学及催化性能,在光催化与光能转化、生物应用与检测、光学器件等领域有极好的应用前景。在量子点的合成反应中,有时会伴随着副产物幻数团簇（magic-size clusters）的出现。幻数团簇具有固定的原子组成和数目,尺寸分布窄,结构相对稳定。反应体系中幻数团簇的形成会导致量子点产率、纯度都比较低。对量子点和幻数团簇形成过程进行研究,可以调控二者的形成路径,并以此获取纯度高、性能好的量子点,促进量子点的应用研究。目前对于幻数团簇和量子点的研究大多都是在有机相中进行,对于水相幻数团簇的研究较少,仅有关于CdSe和CdS幻数团簇的少量报道。由于水溶液中Te^2-离子稳定性差,水相CdTe幻数团簇的合成及其形成路径的研究还具有较大挑战性。基于以上问题及挑战,本文介绍了水相CdTe幻数团簇合成方法,并对其可能的形成路径进行了深入讨论,主要内容有:（一）以CdCl₂作为镉源,以NaBH₄还原Na₂TeO₃作为碲源,L-半胱氨酸作为配体,室温下反应得到样品,再把样品分散在伯胺（如丁胺）中制备得到了CdTe幻数团簇。研究发现反应初期存在一个在紫外-可见吸收光谱上没有明显特征吸收的阶段,该阶段命名为反应诱导期阶段。该阶段的样品分散于伯胺后,得到的样品吸收光谱上出现幻数团簇的特征吸收峰。这一结果表明水相反应体系中形成了无特征光学吸收的CdTe前驱化合物,在伯胺作用下前驱化合物通过分子内原子重排的方式转化为CdTe幻数团簇。在没有伯胺存在条件下,诱导期样品在室温下继续反应一定时间后会逐渐生成量子点。本部分工作还对合成过程中部分参数如配体与阳离子的比例,反应体系浓度,溶液p H、伯胺结构及用量等因素进行了研究,并依据实验结果对反应体系的实验条件进行优化。基质辅助激光解吸飞行时间质谱检测结果表明CdTe诱导期样品与CdTe幻数团簇得到相同的含有Cd-Te化学键的组分信号,这一结果进一步支持水相反应体系中CdTe前驱化合物的形成以及其在小分子伯胺存在条件下向CdTe幻数团簇的转化。（二）讨论不同配体对水相合成CdTe幻数团簇的影响。分别探索了以3-巯基丙酸、高半胱氨酸、组氨酸为配体来制备CdTe幻数团簇,研究了配体对幻数团簇形成的影响。使用上述三种化合物作为配体时,样品中均没有观察到量子点的形成,而将得到的反应样品分散到伯胺后在吸收光谱上课观察到CdTe幻数团簇的特征吸收峰。此外,当使用组氨酸作为配体时,通过调节分散体系中伯胺的浓度可以调控得到的幻数团簇结构及光学性质。当分散体系中伯胺量较多时,最终会形成具有特征吸收单峰的CdTe幻数团簇;当分散体系中伯胺量较少时,可得到具有特征吸收双峰的CdTe幻数团簇。这是以非巯基化合物作为配体在水相反应体系中合成幻数团簇的首次报道。（三）研究了在以L-半胱氨酸为配体的水相CdTe幻数团簇的合成体系中,量子点与幻数团簇之间可能的形成路径。发现在较高温度下,幻数团簇消失,同时量子点的特征吸收峰迅速红移。认为高温会使前驱化分解为量子点生长提供原料。通过XRD发现得到的小尺寸量子点是类闪锌矿结构。更多还原

【Abstract】 Quantum dots（QDs）have excellent optical,electrical and catalytic properties.They show great potential applications in the areas such as photocatalysis,light energy conversion,biology,detection,and electroluminescence.In the synthesis of QDs,magic-size clusters（MSCs）are often produced as by-product,resulting in low production yield and purity of QDs.The investigations about the formation process of QDs and MSCs is of help to regulate their growth pathways and obtain QDs with high purity and good performance.At present,most of the researches on MSCs and QDs are carried out in organic phase,while the studies about the synthesis of MSCs in aqueous solutions remain limited.There are only a few reports about CdSe and CdS MSCs,while there is no research on the CdTe magic-size clusters and their formation pathways.On this thesis,the synthesis method of aqueous phase CdTe magic-size cluster is introduced,and its possible formation path is discussed to some extent.There are three main contents in this thesis as follows:（1）In this thesis,with CdCl₂ as the cadmium source,Na₂TeO₃ reduced by Na BH₄ as the telluride source,and L-cysteine（Cys）as the ligand,CdTe magic-size clusters was synthesized at room temperature in the presence of butylamine（BTA）.The aqueous reaction mixture obtained in the initial stage is quite featureless in absorption,but exhibit a sharp absorption peak at about 371 nm after mixing with BTA.We proposed that the transparent CdTe precursor compounds（PCs）form in the aqueous reaction mixture,and transform to CdTe MSCs（denoted as MSC-371 according to their primary absorption peak position）in the presence of BTA.With a longer reaction period of the aqueous reaction mixture,QDs formed gradually and their absorption peak keeps red shifting over the reaction period.The QDs seemed to be dissociated and transform to CdTe MSCs in the presence of BTA.The effects of the ratio of ligand to cation,the concentration of reactant,p H value and the type of primary amine on the synthesis were studied.At the same time,MSC-371 and counterpart PC have almost the same main fragment peak measured by matrix-assisted laser desorption/ionization-time of flight mass spectrometry,which supports the existence of PCs in the early stage of the reaction.（2）The effect of ligands on the formation of CdTe MSCs in aqueous phase is discussed.The experiments are carried out with 3-mercaptopropionic acid（MPA）,homocysteine（Hcy）and histidine（His）as ligands.With MPA as the ligand,the aqueous reaction mixture keeps absorption featureless,which has CdTe MSCs formed upon dispersing with BTA.Meanwhile with Hcy as the ligand,d MSC-371 formed by dispersing with BTA.At the same time,with His as the ligand,MSC-371 and d MSC-371 could be obtained by dispersed into different amounts of butylamine solutions.This is the first report to synthesize MSCs by using His as the ligand in aqueous phase which is non-thiol ligand.（3）The possible relationship between MSCs and QDs in aqueous CdTe synthesis system with Cys as ligand was studied.At higher temperature,it was found that MSCs could not be found under the addition of BTA,while QDs grow qucikly.It means that the higher temperature would lead PCs fragment to monomer then provide their to QDs as raw material.Through XRD characterization of QDs,it is found that the QDs obtained in this system is similar to the structure of sphalerite.更多还原