VO_(2)(M)nanostructures of various shapes were synthesized by a hydrothermal-calcination method.First,VO_(2)(D)nanoparticles were synthesized by the surfactant-free hydrothermal reduction of ammonium metavanadate by o...VO_(2)(M)nanostructures of various shapes were synthesized by a hydrothermal-calcination method.First,VO_(2)(D)nanoparticles were synthesized by the surfactant-free hydrothermal reduction of ammonium metavanadate by oxalic acid at 160-220°C.Then,the produced VO_(2)(D)was further calcined at 250-600°C to obtain the VO_(2)(M)nanoparticles.To understand the hydrothermal reduction processes,both in situ powder X-ray diffraction(PXRD)and ex situ characterization were carried out.The results indicate a sequential process starting from the reduction of ammonium metavanadate and nucleation of the vanadium precursor,followed by the formation of intermediate VO_(2)(B)nanosheets or nanorods,and finally phase transformation from VO_(2)(B)to VO_(2)(D)with a variety of morphologies.A crystal growth mechanism based on self-assembly and Ostwald ripening was proposed to explain the formation process of these unique nanostructures.The as-prepared VO_(2)(M)nanoaggregates exhibited a lower thermochromic phase transition temperature(41.0℃)and a narrower thermal hysteresis width(6.6℃)than those nanopowders prepared by other methods.展开更多
基金the financial support from the National Natural Science Foundation of China(51325203)the Ministry of Science and Technology of China(2014AA032802)+1 种基金the Science and Technology Commission of Shanghai Municipality(15XD1501700 and 13521102100)the Materials Genome Institute of Shanghai University(14DZ2261200).
文摘VO_(2)(M)nanostructures of various shapes were synthesized by a hydrothermal-calcination method.First,VO_(2)(D)nanoparticles were synthesized by the surfactant-free hydrothermal reduction of ammonium metavanadate by oxalic acid at 160-220°C.Then,the produced VO_(2)(D)was further calcined at 250-600°C to obtain the VO_(2)(M)nanoparticles.To understand the hydrothermal reduction processes,both in situ powder X-ray diffraction(PXRD)and ex situ characterization were carried out.The results indicate a sequential process starting from the reduction of ammonium metavanadate and nucleation of the vanadium precursor,followed by the formation of intermediate VO_(2)(B)nanosheets or nanorods,and finally phase transformation from VO_(2)(B)to VO_(2)(D)with a variety of morphologies.A crystal growth mechanism based on self-assembly and Ostwald ripening was proposed to explain the formation process of these unique nanostructures.The as-prepared VO_(2)(M)nanoaggregates exhibited a lower thermochromic phase transition temperature(41.0℃)and a narrower thermal hysteresis width(6.6℃)than those nanopowders prepared by other methods.
