Hydrothermal Synthesis,Phase Evolution And Properties Of VO₂ Nanomaterials

VO2 has multiple polymorphs,such as VO,(R),VO2(M),VO2(B),VO2(A),VO2(D)and VO2(P),et al.Being having a reversible semiconductor-metal transition,VO2(M)has a wide application in the fields like energy saving,energy storage and photoelectric devices.The controllable synthesis of metastable phases,such as VO2(D)and VO2(P),is one of the research hotspots in nanomaterials science in recent years because of their easy transformation to VO2(M).Deep understanding of the formation mechanism of VO2 polymorphs and clarification of phase evolution process between them is essential for the controllable synthesis of VO2 nanomaterials with specific crystal structures and excellent properties.The project of this thesis is to realize the infrared modulation of vanadium dioxides nanomaterials;to develop controllable synthesis technique of VO2 polymorphs with low cost;particularly to investigate hydrothermal synthesis technique,growth mechanism and phase evolution process of VO2 as well as infrared performance of VO2(M).Star-shaped VO2(D)nanoparticles(NPs)were synthesized by a low temperature hydrothermal method.The influence of annealing treatments on the morphology’and size of VO2(M)NPs was studied.It was found the phase transition temperature of VO2(M)NPs can be modulated because of the interfaces effect.VO2(M)NPs/Ag nanowires self-heating composite film device was fabricated,and it was found the infrared properties of the device can be regulated dynamically by input voltage.VO2(M/D)continuous films were hydrothennally synthesized at low temperature by TiO2 seed-assistant growth,and the oriented growth mechanism as well as phase evolution process of VO2 film was studied.The thennochromic performances of the annealed VO2(M)/TiO2 composite films were investigated,and it was found the optical performances of the films are comparable with that obtained by physical methods.The composite films can be used to fabricate multi-function film devices.Metastable VO2(D)and VO2(P)NPs were synthesized by hydrothermal method,and VO2 polymorphs(VO2(B),VO2(D)and VO2(P))have been realized by controlling the experimental conditions(the content of AOT and formic acid,hydrothermal reaction temperature and time).A new phase evolution process was observed for the first time during the formation process of VO-2(P)NPs:(NH4)2V6O16·1.5H2O→NH4V4O10～VO2(B)→VO2(B+D)→VO2(D)→VO2(D+P)→VO2(P),and the formation mechanism of VO2(D)and VO2(P)was confirmed.VO2(M)NPs were obtained by a low-temperature annealing treatment of VO2(P)NPs and it was found the VO2(M)composite films show an excellent infrared performance.Ammonium vanadium bronze(NH4)0.6V2O5 nanosheets were synthesized by hydrothermal method,and it was found the initial discharge capacity(290 mAh/g)of(NH4)0.6V2O5 nanosheets as a cathode material in Li-ion batteries was more than three times higher than the reported value(89.8 mAh/g)of brick-like(NH4)0.6O5 with micrometer level thickness.