The phase and morphological features of materials are often tunable by adjusting the reaction parameters of solvothermal synthesis but this versatility also poses a challenge for preparing materials with a desired pha...The phase and morphological features of materials are often tunable by adjusting the reaction parameters of solvothermal synthesis but this versatility also poses a challenge for preparing materials with a desired phase and morphology if the behaviors of phase and morphological evolution during the solvothermal synthesis are not known.In this work,the formation and growth of VO_(2) nanomaterials in the solvothermal systems via the reduction of V_(2)O_(5) by ethylene glycol(EG)were investigated by in situ powder X-ray diffraction(PXRD).The results show that both fast and slow heating produce the same VO_(2)(B)final product but the phase evolution during the synthesis is very sensitive to the heating rate.Fast heating(10℃ min^(−1))involves an unknown intermediate while V_(3)O_(7)·H_(2)O is the intermediate phase at slow heating(2℃ min−1).The formation mechanism was employed to design the synthesis of VO_(2)(B)nanorods and the phase transformation paths were verified by large-scale batch synthesis.Furthermore,ex situ PXRD and SEM were employed to follow the structure and morphology evolution during growth.This research indicates that in situ PXRD,as a powerful tool to monitor the whole reaction process and to collect information such as phase evolution and the fate of the transient intermediates,can be used to direct the controlled synthesis of materials.展开更多
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financial support from the National Natural Science Foundation of China(51172265 and 51325203)the Ministry of Science and Technology of China(2014AA032802)+4 种基金the Science and Technology Commission of Shanghai Municipality(13521102100)the Education Commission of Shanghai Municipal(14ZZ099)the Guangdong Provincial Department of Science and Technology(2011A091104001)the Materials Genome Institute of Shanghai University(14DZ2261200)the China Postdoctoral Science and Foundation(2014M561528).
文摘The phase and morphological features of materials are often tunable by adjusting the reaction parameters of solvothermal synthesis but this versatility also poses a challenge for preparing materials with a desired phase and morphology if the behaviors of phase and morphological evolution during the solvothermal synthesis are not known.In this work,the formation and growth of VO_(2) nanomaterials in the solvothermal systems via the reduction of V_(2)O_(5) by ethylene glycol(EG)were investigated by in situ powder X-ray diffraction(PXRD).The results show that both fast and slow heating produce the same VO_(2)(B)final product but the phase evolution during the synthesis is very sensitive to the heating rate.Fast heating(10℃ min^(−1))involves an unknown intermediate while V_(3)O_(7)·H_(2)O is the intermediate phase at slow heating(2℃ min−1).The formation mechanism was employed to design the synthesis of VO_(2)(B)nanorods and the phase transformation paths were verified by large-scale batch synthesis.Furthermore,ex situ PXRD and SEM were employed to follow the structure and morphology evolution during growth.This research indicates that in situ PXRD,as a powerful tool to monitor the whole reaction process and to collect information such as phase evolution and the fate of the transient intermediates,can be used to direct the controlled synthesis of materials.
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.
