In situ observation
of molybdenum disulfide (MoS2) sheet
exposed to water was performed using atomic force microscopy (AFM)
to obtain a better understanding for the preparation and application
of two-dimensional molybdenum disulfide. It was found that the MoS2 sheet underwent chemical reactions in water, leading to the
partial etching of the surface layer and the formation of needlelike
protrusions on the surfaces. X-ray photoelectron spectroscopy (XPS)
and atomic absorption spectroscopy (AAS) analyses showed that this
behavior might arise from the oxidation of MoS2 into Mo(VI)
and SO4
2–. The oxidative product Mo(VI)
was present in the form of either MoO3·H2O crystals on the MoS2 surface or molybdate ions in aqueous
solution, whereas SO4
2– was present in
the solution, resulting in the etching of the surface layer and the
formation of needlelike protrusions. These findings might be significant
in terms of applications of two-dimensional MoS2 and the
concentration of molybdenite.
A three-dimensional
porous MoS2/chitosan (MoS2/CS) aerogel with
excellent mechanical strength and stability was
constructed in this work through anchoring MoS2 to the
surface of the CS aerogel. It is found that the MoS2/CS
aerogel can effectively recover gold from thiosulfate solution via
direct in situ reduction of Au(I) to Au0 under sunlight,
thus realizing the one-step recovery of gold, which greatly benefits
the development of thiosulfate leaching for gold extraction. Furthermore,
according to the results of photocurrent, ultraviolet–visible
absorption, and atomic absorption spectrophotometry, it has been found
that the reduction of the MoS2/CS aerogel to Au(I) is mainly
consisted of photoreduction and chemical reduction, where photoreduction
plays a dominant role, primarily because of the narrow band gap and
higher conduction band edge of the MoS2/CS aerogel as well
as the strong reducibility of photogenerated electrons.
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