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

• Metal sulfides were prepared in montmorillonite by solid–solid reactions.
• The products showed blue shift of the onsets due to quantum size effect.
• PL intensities of the products were increased after storage for 17 months.

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.

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