Yi Zhang,Zhenyun Lan,Ni Jian,Zhuanghe Ren,Jianjiang Hu,Mingxia Gao,Hongge Pan,Yunhao Lu,Yongfeng Liu
In this work, we demonstrate a first attempt at understanding the catalytic mechanism of nanosized Co in reducing the dehydrogenation temperature of the Li–B–N–H hydrogen storage system by experimental observation and theoretical calculation. A nanosized Co@C composite (Co particles <10 nm) is successfully synthesized by casting a furfuryl alcohol-filled, Co-based metal–organic framework, MOF-74(Co), at 700 °C. Adding small quantities of the prepared nanosized Co@C composite significantly reduces the dehydrogenation temperature of the LiBH4–2LiNH2 system. The 5 wt% Co@C-containing sample releases approximately 10.0 wt% hydrogen at 130–230 °C with a peak temperature of 210 °C, which is reduced by 125 °C from that of the pristine sample. During hydrogen desorption, nanosized Co remains in the metallic state and only works as a catalyst to reduce the kinetic barriers of hydrogen release from the LiBH4–2LiNH2 system. Ab initio calculations reveal that the presence of a Co catalyst induces a redistribution of charge, which not only weakens the chemical H–B bonding but also enhances the electrostatic interactions between Hδ+ in the NH2 groups and Hδ− in the BH4 groups, consequently reducing the energy barriers for the formation of H2 molecules. This explains the low-temperature dehydrogenation behaviour of the Co-catalysed Li–B–N–H systems.
Composite powder of tungsten carbide with nano-cobalt coatings was successful manufactured via a novel sol-gel process, and coarse grained WC-4 wt% Co cemented carbide was produced from the cobalt-coated WC powder. Phase composition and microstructure evaluation were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results revealed that the WC particles were completely encased in the CoC 2 O 4 layers by the sol-gel process. Core-shell structured WC-4 wt% Co composite powder was subsequently prepared by reducing the WC-CoC 2 O 4 precursor powder in hydrogen atmosphere. The morphology and crystal structure of the cobalt-coating were found to depend on the reduction temperature. Chemical analyses revealed that the WC-Co composite powders were non-contaminated and composition-controllable. WC-4 wt% Co cemented carbide fabricated from the cobalt-coated WC composite powder showed a refined and uniform microstructure, and therefore improved mechanical properties , compared to the cemented carbide made by ball-milled WC-Co powder. The transverse rupture strength was 2249 MPa in the cemented carbide from the cobalt-coated WC powder, compared to 1871 MPa of the carbide made by the ball-milling powder.
This study firstly reported the regulation of PMS activation pathway via the novel catalyst (CQDs/Co@CN) that contained carbon quantum dots (CQDs) and confined nano Co dual active sites. CQDs/Co@CN showed superior catalytic activity for PMS activation due to the synergistic effect of CQDs and confined nano Co, and sulfamethoxazole degradation rate reached 0.661 min −1 , which was even higher than that obtained by single atom catalyst. The reactive species in the system of CQDs/Co@CN/PMS could be easily regulated by the visible light. In the absence of visible light, PMS was mainly activated to produce Co(IV) = O, while it was activated to simultaneously produce radicals and Co(IV) = O in the presence of visible light. Moreover, the yields of Co(IV) = O increased by about 10 %. Experimental results and DFT calculation demonstrated that CQDs played crucial role in the regulation of reactive species. This study could provide a way to modulate the reactive species by visible light.
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