纳米片聚结Co_3O_4微球催化甲苯燃烧（英文）

采用乙二胺辅助的水热法制备了纳米片聚结的Co3O4微球.利用多种分析技术表征了其物化性质,并评价了其对甲苯燃烧的催化活性.结果表明,由添加1.0 ml乙二胺经140°C水热处理12 h后制得的Co3O4样品呈纳米片聚结的微球状表面形貌.Co3O4微球样品的比表面积约为66 m2g-1.与体相Co3O4样品相比,Co3O4微球样品具有较高的氧吸附物种浓度和较好的低温还原性.当空速为20000 ml g-1h-1时,在Co3O4微球样品上甲苯转化率达到50%和90%时的反应温度分别为230和254°C.这与该样品具有较大的比表面积、较高的氧吸附物种浓度和较好的低温还原性相关.

Preparation of ultrafine WC-10Co composite powders by reduction and carbonization

A solid state synthesis of ultrafine/nanocrystalline WC-10Co composite powders was reported from WO3 , Co3O4 and carbon powders after reduction and carburization at relatively low temperatures in a short time under pure H2 atmosphere. The effects of ball milling time and reaction temperature on the preparation of ultrafine/nanocrystalline WC-Co composite powders were studied using X-ray diffraction and scanning electron microscope (SEM). The results show that fine mixed oxide powders (WO3 , Co3O4 and carbon powders) can be obtained by long time ball milling. Increasing the reaction temperature can decrease the formation of Co3W3C and graphite phases and increase the WC crystallite size. Long-time ball milling and high reaction temperature are favorable to obtain fine and pure composite powders consisting of nanocrystalline WC from WO3 , Co3O4 and carbon powders.

Synthesis and Characterization of Cobalt-Carbon Core-Shell Microspheres in Supercritical Carbon Dioxide System

The synthesis of cobalt-carbon core-shell microspheres in supercritical carbon dioxide system was investi- gated. Cobalt-carbon core-shell microspheres with diameter of about 1μm were prepared at 350 ℃ for 12 h in a closed vessel containing an appropriate amount of bis（cyclopentadienyl）cobalt powder and dry ice. Characterization by a variety of techniques, including X-ray powder diffraction, X-ray photoelectron spectroscopy, TransmissiOn electron microscope, Fourier transform infrared spectrum and Raman spectroscopy analysis reveals that each cobalt-carbon core-shell microsphere is made up of an amorphous cobalt core with diameter less than 1 μm and an amorphous carbon shell with thickness of about 200 nm. The possible growth mechanism of cobalt-carbon core-shell microspheres is discussed, based on the pyrolysis of bis（cyclopentadienyl）cobalt in supercritical carbon dioxide and the deposition of carbon or carbon clusters with odd electrons on the surface of magnetic cobalt cores due to magnetic attraction. Magnetic measurements show 141.41 emu/g of saturation magnetization of a typical sample, which is lower than the 168 emu/g of the corresponding metal cobalt bulk material. This is attributed to the considerable mass of the carbon shell and amorphous nature of the magnetic core. Control of magnetism in the cobalt-carbon core-shell microspheres was achieved by annealing treatments.

Oxygen vacancies boosting ultra-stability of mesoporous ZnO-CoO@N-doped carbon microspheres for asymmetric supercapacitors

Long-term cycling stability of pseudocapacitive materials is pursued for high-energy supercapacitors.Herein,the mesoporous zinc-cobalt oxide heterostructure@nitrogendoped carbon(ZnO-CoO@NC)microspheres with abundant oxygen vacancies are self-assembled through a hydrothermal method combined with an annealing post-treatment.The multifunctional polyvinyl pyrrolidone(PVP)is used as a structure-directing agent,the precursor of NC and the initiator of abundant oxygen vacancies in zinc-cobalt oxide microspheres.XPS demonstrates the generation of surface oxygen vacancies resulted from the reduction effect of conductive NC,and further confirms the weaker interaction between the metal ions and oxygen atoms.As a result,the electrode based on ZnO-CoO@NC in 2 mol L^-1 KOH shows enhanced capacitive performance with an excellent cycle stability of 92%retention of the initial capacitance after 40,000 charge-discharge cycles at 2 A g^-1,keeping the morphology unchanged.The assembled asymmetric supercapacitor,graphene//ZnO-CoO@NC,also performs good cyclic stability with 94%capacitance retention after 10,000 cycles at 2 A g^-1.The remarkable electrochemical performance of the self-assembled ZnO-CoO@NC composite is attributed to the mesoporous architecture,abundant oxygen vacancies,conductive ZnO scaffold for CoO crystals forming heterostructure of ZnO-CoO and the high conductive NC layer covering outside of the multi-metal oxide nanoparticles.Hence,the ZnO-CoO@NC holds great promise for high-performance energy storage applications.