We took Co_(0.2)Ni_(0.8)-MOF-74 with bimetallic synergistic effect as the basic material,and selected rare earth ions Ho,Gd,and Er with ion radii close to Co and Ni as the research objects for doping.The influence of ...We took Co_(0.2)Ni_(0.8)-MOF-74 with bimetallic synergistic effect as the basic material,and selected rare earth ions Ho,Gd,and Er with ion radii close to Co and Ni as the research objects for doping.The influence of rare earth ion doping amount and doping type on the eNRR performance of the catalyst was explored.The experimental results show that the ammonia yield rate and Faraday efficiency doped with Co_(0.2)Ni_(0.8)-MOF-0.5Ho are the highest,reaching 1.28×10^(-10)mol·s^(-1)·cm^(-2)/39.8%,which is higher than the1.12×10^(-10)mol·s^(-1)·cm^(-2)/32.2%of Co_(0.2)Ni_(0.8)-MOF-74,and is about 14.3%/23.7%higher than that without doping,respectively.And the stability of Co_(0.2)Ni_(0.8)-MOF-0.5 Ho is good(after 80 hours of continuous testing,the current density did not significantly decrease).This is mainly due to doping,which gives Co_(0.2)Ni_(0.8)-MOF-74 a larger specific surface area and catalytic active sites.The catalyst doped at the same time has more metal cation centers,which increases the electron density of the metal centers and enhances the corresponding eNRR performance.展开更多
Recrystallized silicon carbide（ RSi C）,a high purity Si C material sintered by the process of evaporation-condensation without any additives,is one of the most important structural materials in the fields of high te...Recrystallized silicon carbide（ RSi C）,a high purity Si C material sintered by the process of evaporation-condensation without any additives,is one of the most important structural materials in the fields of high temperatures. However,its low density and porous structure caused by the sintering mechanism in the absence of shrinkage,restrict its wide applications in engineering.This paper reviews the research progress and related technologies on the preparation of high-density RSi C and its composites. RSi C with relative high density up to 2. 75g·cm- 3can be obtained by a combination of pretreatment to Si C raw materials such as reshaping,modification and particle size distribution,and appropriate forming method. Post treatments such as cyclic pyrolysis and impregnation- recrystallization,and slurry impregnation- recrystallization are needed for the further density increase of RSi C（ 2. 99 g·cm- 3）. In addition,high performance RSi C- Mo Si2 and RSi C- Al composites obtained by melt infiltration are also reviewed.展开更多
The present study focuses on the adsorption of a polyelectrolyte, the component of which is a polymer of maleic anhydride sodium salt, on the surface of nanometric zinc oxide particles and the colloidal stability of a...The present study focuses on the adsorption of a polyelectrolyte, the component of which is a polymer of maleic anhydride sodium salt, on the surface of nanometric zinc oxide particles and the colloidal stability of aqueous dispersions. FTIR spectroscopic data provided evidence in support of hydrogen bonding and chemical interaction in the case of the polyelectrolyte-ZnO system. The adsorption iso-therms showed the influences of polyelectrolyte concentra-tion, pH and ionic strength on the adsorption. With the in-crease of pH the saturated adsorbed amount decreased, while the thickness of adsorption layer increased. The saturated adsorbed amount increased with increasing salt concentra-tion, and decreased with further increasing salt concentra-tion. It should be noted that in the presence of a CaCl2 solu-tion the adsorbed amount and the adsorption layer thickness were greater than those in the NaCl solution of the same concentration. The change of the absorbance of zinc oxide dispersions showed that the absorbance decreased slowly at high pH. There was a maximum point for the absorbance of the zinc oxide dispersions in the presence of various polye-lectrolyte concentrations. The change of dispersion stability resulted from the change of macromolecular chains confor-mation at the interface.展开更多
基金Funded by the Central Government Guides Local Funds for Scientific and Technological Development(No.2023ZYQ004)the Hunan Provincial Natural Science Foundation of China(No.2021JJ50036)the Hunan Provincial Key Research and Development Plan(No.2023GK2083)。
文摘We took Co_(0.2)Ni_(0.8)-MOF-74 with bimetallic synergistic effect as the basic material,and selected rare earth ions Ho,Gd,and Er with ion radii close to Co and Ni as the research objects for doping.The influence of rare earth ion doping amount and doping type on the eNRR performance of the catalyst was explored.The experimental results show that the ammonia yield rate and Faraday efficiency doped with Co_(0.2)Ni_(0.8)-MOF-0.5Ho are the highest,reaching 1.28×10^(-10)mol·s^(-1)·cm^(-2)/39.8%,which is higher than the1.12×10^(-10)mol·s^(-1)·cm^(-2)/32.2%of Co_(0.2)Ni_(0.8)-MOF-74,and is about 14.3%/23.7%higher than that without doping,respectively.And the stability of Co_(0.2)Ni_(0.8)-MOF-0.5 Ho is good(after 80 hours of continuous testing,the current density did not significantly decrease).This is mainly due to doping,which gives Co_(0.2)Ni_(0.8)-MOF-74 a larger specific surface area and catalytic active sites.The catalyst doped at the same time has more metal cation centers,which increases the electron density of the metal centers and enhances the corresponding eNRR performance.
基金the financial support from the National Science Foundation of China ( Grant Nos. 51302076, 51372078 )the China Postdoctoral Science Foundation ( Grant No. 2013M531783)
文摘Recrystallized silicon carbide（ RSi C）,a high purity Si C material sintered by the process of evaporation-condensation without any additives,is one of the most important structural materials in the fields of high temperatures. However,its low density and porous structure caused by the sintering mechanism in the absence of shrinkage,restrict its wide applications in engineering.This paper reviews the research progress and related technologies on the preparation of high-density RSi C and its composites. RSi C with relative high density up to 2. 75g·cm- 3can be obtained by a combination of pretreatment to Si C raw materials such as reshaping,modification and particle size distribution,and appropriate forming method. Post treatments such as cyclic pyrolysis and impregnation- recrystallization,and slurry impregnation- recrystallization are needed for the further density increase of RSi C（ 2. 99 g·cm- 3）. In addition,high performance RSi C- Mo Si2 and RSi C- Al composites obtained by melt infiltration are also reviewed.
文摘The present study focuses on the adsorption of a polyelectrolyte, the component of which is a polymer of maleic anhydride sodium salt, on the surface of nanometric zinc oxide particles and the colloidal stability of aqueous dispersions. FTIR spectroscopic data provided evidence in support of hydrogen bonding and chemical interaction in the case of the polyelectrolyte-ZnO system. The adsorption iso-therms showed the influences of polyelectrolyte concentra-tion, pH and ionic strength on the adsorption. With the in-crease of pH the saturated adsorbed amount decreased, while the thickness of adsorption layer increased. The saturated adsorbed amount increased with increasing salt concentra-tion, and decreased with further increasing salt concentra-tion. It should be noted that in the presence of a CaCl2 solu-tion the adsorbed amount and the adsorption layer thickness were greater than those in the NaCl solution of the same concentration. The change of the absorbance of zinc oxide dispersions showed that the absorbance decreased slowly at high pH. There was a maximum point for the absorbance of the zinc oxide dispersions in the presence of various polye-lectrolyte concentrations. The change of dispersion stability resulted from the change of macromolecular chains confor-mation at the interface.
