Selective
oxidation of cyclohexane to KA oil (cyclohexanol and
cyclohexanone) is one of the most important industrial procedure.
In this study, we reported a remarkably enhanced cyclohexane oxidation
under visible-light irradiation by a novel MoS2@Cu/Cu2O@C composite photocatalyst with multilevel hierarchy, which
was prepared by immersing (NH4)2MoS4 guest into Cu-metal–organic framework (MOF) polyhedra host
and subsequently pyrolyzing the Cu-MOF–guest polyhedra to encapsulate
MoS2 into Cu/Cu2O@C. Importantly, the composite
photocatalyst showed much better photocatalytic cyclohexane oxidation
performance than that of the simple mechanical mixture of MoS2 and Cu/Cu2O@C. The distinct photocatalytic performance
of MoS2@Cu/Cu2O@C composite can be ascribed
to its heterojunction band reconstruction and unique multilevel architecture
to facilitate the separation of photoinduced electrons and holes and
generation reactive species during photoirradiation. The Cu nanoparticles
in the MoS2@Cu/Cu2O@C composite also effectively
capture electrons and prevent electron–hole recombination due
to the surface plasmon resonance (SPR). The photogenerated holes (h+) and ·OH radical were supposed to be predominant components
of the valence band (VB) and oxidize cyclohexane (C6H12) to produce cyclohexyl radical (C6H11·), which can be further oxidized to cyclohexanol and cyclohexanone.
According to the above results, a possible photocatalytic mechanism
was proposed.
The sulfide catalyst is a subject of great interest in developing a MgH2 system as a potential hydrogen storage medium. In this work, FeS2 micro-spheres were successfully prepared by the surfactant-assisted solvothermal method, and later were ball milled with MgH2 to fabricate the MgH2-16.7 wt% FeS2 composite. FeS2 addition could dramatically improve both the hydrogenation and dehydrogenation kinetics, and lower the dehydrogenation temperature of MgH2 as well. The MgH2-16.7 wt% FeS2 composite could absorb 3.71 wt% H2 at 423 K, which is 3.59 times as high as that of the as-milled pure MgH2. The composite started to release hydrogen at 569 K, and it could release 1.24 wt% H2 at 573 K within 1400 s. However, pure MgH2 could only release 0.18 wt% H2 under the identical conditions. Furthermore, the activation energy of hydrogen desorption was reduced to 68.94 kJ mol-1. FeS2 addition also altered the rate-controlling steps and facilitated the H diffusion of MgH2 in the hydrogen absorption process. The synergistic catalytic effects of the in situ formed Fe active species and MgS may contribute to the enhanced hydrogen storage properties of MgH2.
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