Preparation of metal sulfide mixtures in montmorillonite by solid-solid reactions

Novel hybrids composed of mixed metal sulfides (manganese sulfide and zinc sulfide (MnS/ZnS) or cadmium sulfide (MnS/CdS), as well as zinc sulfide and cadmium sulfide (ZnS/CdS)) with montmorillonite were synthesized by solid-solid reactions between the ion exchanged montmorillonite and sodium sulfide. The products were characterized by powder X-ray diffraction, transmission electron microscopy, as well as Raman, UV-visible and photoluminescence spectroscopies. The Raman spectra indicated the presence of manganese sulfide, zinc sulfide, and/or cadmium sulfide in the products. The absorption onsets observed at 318-366. nm for MnS/ZnS@montmorillonite, at 330-521. nm for MnS/CdS@montmorillonite, and at 360-480. nm for ZnS/CdS@montmorillonite indicated the formation of two metal sulfides in the interlayer spaces. In comparison with those of bulk MnS (340. nm), ZnS (360. nm) and CdS (525. nm), the absorption onsets owing to both metal sulfides were blue shifted probably due to quantum confinement effect, suggesting that the products are composed of nanometer sized sulfide particles. The photoluminescence bands owing to manganese sulfide (416 and 435. nm), zinc sulfide (413 and 440. nm), and cadmium sulfide (451 and 469. nm) were also seen. The emission intensity of MnS/ZnS@montmorillonite was stronger than that of MnS/CdS@montmorillonite, probably due to the higher band gap energy of MnS/ZnS system that resulted in the increase of recombination of excitons.