Stabilization of the Thermodynamically Favored Polymorph of Cadmium Chalcogenide Nanoparticles CdX (X = S, Se, Te) in the Polar Mesopores of SBA-15 Silica

A versatile synthetic approach to cadmium chalcogenide nanoparticles in the mesopores of SBA-15 silica as a host
matrix was developed. The use of cadmium organochalcogenolates of the type Cd(XPh)2·TMEDA (X = S, Se, Te)
allowed the preparation of nanoparticles of all three cadmium chalcogenides following the same experimental protocol.
Particles of CdS, CdSe, and CdTe with a particle size of 7 nm were prepared from this class of single-source
precursors. The incorporation of the precursor molecules into the pores was achieved by melt infiltration at a
temperature of 140 °C. Subsequent pyrolysis of the precursors in the mesopores yielded the semiconductor particles.
Owing to the high polarity of the silanol-covered pore walls, which lower the surface energy of the particles to a
large extent, the dimorphic cadmium chalcogenides are obtained in their thermodynamically favored modifications;
e.g., CdS particles crystallize in the wurtzite type, CdTe particles are obtained in the zinc blende structure, and
CdSe (where no unambiguous preference exists) crystallizes as a “mixture” of both structures with a rather random
stacking sequence.

本研究开发了一种以介孔SBA-15二氧化硅为载体基质的镉硫族化合物纳米颗粒通用合成方法。采用通式为Cd(XPh)₂·TMEDA（X=S、Se、Te）的有机硫族镉配合物，可通过同一实验方案制备全部三种镉硫族化合物纳米颗粒。通过该类单源前驱体，可制备粒径为7 nm的硫化镉（CdS）、硒化镉（CdSe）及碲化镉（CdTe）纳米颗粒。将前驱体分子引入孔道的过程可通过140 ℃下的熔融浸渍法实现；随后在介孔孔道内对前驱体进行热解，即可得到半导体纳米颗粒。由于孔道内壁覆盖的硅羟基具有高极性，可大幅降低颗粒的表面能，因此双晶型镉硫族化合物均可生成热力学稳定的晶型：例如，硫化镉纳米颗粒以纤锌矿（wurtzite）型结构结晶，碲化镉纳米颗粒为闪锌矿（zinc blende）结构，而硒化镉则无明确的晶型偏好，以两种结构的“混合态”形式结晶，堆垛序列相当随机。