Designed Synthesis And Property Study Of Molybdenum Basedoxides And Composites Nanomaterials

Molybdenum oxide and molybdenum-based composites micro-/nano-materials have potential applications in photochromism,lithium ion battery,catalysis and smart windows,due to their outstanding optical and electrical properties and high stability.Therefore,synthesis and study of molybdenum oxide and molybdenum-based composites have attracted increasing interests these years.The optical and electrical properties of nanomaterials depend on their structure,morphology,constituent and other factors.On the basis of these dependent factors,efforts were devoted to design and synthesis of molybdenum-based micro-/nano-structures with excellent optical and electrical properties in this thesis,by controlling different parameters in preparation systems.The property improvement of molybdenum-based materials has important significance in expanding their application fields.In this thesis,a series of molybdenum-based materials,including h-MoO3 microrods,α-MoO3 nanobelts,hollow Mo/W oxide microspheres,W-MoO3 microspheres,Ti-MoO3 nanoparticles and MoO2 nanoparticles were synthesized using organic molecule induction,parameter-controlled synthesis,metal dope and reduction method.The formation mechanisms of molybdenum oxide and molybdenum-based were proposed.And their photochromic,dye adsorption and electrochemical properties were studied.First,h-MoO3 microrods in different size were synthesized by a low temperature aqueous synthesis method using PVP as an inducer.The size of h-MoO3 microrods can be adjusted by controlling the reaction temperature,reaction time,amount of acid and amount of PVP.It is found that h-MoO3 microrods with uniform size can be obtained in 60 min in the presence of PVP induced at 50-60℃.Whether prolonging reaction time,or increasing reaction temperature,amount of acid and PVP will accelerate the reaction,inducing the secondary nucleation,and resulting in h-MoO3 rods in heterogeneous sizes and morphologies.Based on the optimized synthetic condition,h-MoO3 microrods with uniform size and morphology were synthesized.The photochromic properties of h-MoO3 microrods in different sizes were studied.The results showed that the smaller the size,the better the photochromism.Second,molybdenum oxides in different crystalline phases(α-MoO3 nanobelts、α-MoO3·H2O nanobelts and h-MoO3 microrods)were synthesized in aqueous solution at 98℃.The influence of different Mo:H+ molar ratio,kinds of acid and different cational additives were examined.(1)The stable phase of α-MoO3 nanobelts with[001]and[100]preferential growth directions can be obtained from transformation of metastable phase h-MoO3 microrods and homogeneous nucleation.α-MoO3·H2O nanobelts were also obtained by homogeneous nucleation with controlled Mo:H+ molar ratio.Fomatiom mechanisms of each molybdenum oxides were studied.(2)Changing the species of acid can affect the reaction rate.Using HCl as acid,h-MoO3 microrods will transform to α-MoO3 nanobelts in 9 h.Using HNO3 or H2SO4 as acid,the reaction rate significantly slowed,demonstating NO3-and SO42-have an inhibited effect in the reaction.(3)Cationic additives may also affect the formation and size of a-MoO3 nanobelts.From the experimental phenomena,NH4+ inhibitted the transformation from h-MoO3 microrods to α-MoO3 nanobelts.Introduction of Na+ resulted in α-MoO3 nanobelts with smaller size,while K+ had little effects on the size of α-MoO3 nanobelts.The photochromic property of different phase MoO3 materials showed that the photochromic property of stable phase α-MoO3 nanobelts transformed from metastable phase h-MoO3 microrods was best,followed by homogeneous nucleation of α-MoO3 nanobelts,and the photochromic of α-MoO3·H2O was worst.Third,Mo/W oxide nanocomposites with hollow hierarchical structure were synthesized under acid environment at 90℃ with PEG 20K as morphology control agent.The morphologies of the samples were adjusted by Mo/W ratio,reaction temperature,reaction time,the amount of PEG 20K,kinds of surfactants and amount of acid.Formation mechanism of Mo/W oxide hollow hierarchical structure showed that:WO3 nucleus formed at first,then WO3 combined with PEG molecular to form soft template,which induced the deposition of MoO3,resulting hollow Mo/W oxide microspheres.The study of photochromic and dye adsorption performance of different Mo/W oxide samples showed that:at 90℃,controlling the Mo:W moler ratio as 9:1,amount of PEG 20K as 3%,reaction time as 3 h,the obtained Mo/W oxide microspheres with hollow hierarchical structure exhibitted the best photochromic and dye adsorption properties.Research also found that PEG 20K,a reductant that can provide electronic can improve the photochromic property of Mo/W oxide and speed up the photochromic rate under visible light.Fourth,WO3-MoO3 and TiO2-MoO3 composite nanomaterials were successfully synthesized through a seeding method at 60℃.The impact of W and Ti on Mo-based materials was studied.By controlling amount of sodium tungstate,titanium sulfate,amount of acid,reaction time,reaction temperature and kind of surfactants,WO3-MoO3 microspheres and TiO2-MoO3 nanoparticles were obtain.The samples were characterized by XRD,SEM,FT-IR,UV-vis and EDS to study the crystal structure,surface property and optical property.The photochromism of differnent samples were investigated.It was found that the phtochromic performance of WO3-MoO3 microspheres and TiO2-MoO3 nanopartics were better than that of pure MoO3.Research also found that,adding surfactants with a lone electron pair(chitosan,PEG 20K and PEG 6K)was beneficial to the photochromism of samples.Fifth,MoO2 nanoparticles were prepared on the basis of h-MoO3 microrods by adding hydrazine hydrate as reducing agent through a simple aqueous method.The compositon and morphology of the samples can be regulated by controlling the amount of hydrazine hydrate,kinds of surfactants and amount of NaOH.Expermiment showed that MoO2 obtained with different amount of hydrazine hydrate,like 5 mol·dm-3,7.5 mol·dm-3 and 10 mol·dm-3,showed corresponding specific capacitance as 162.2 F·g-1,91.1 F·g-1 and 122.1 F·g-1。And MoS2 nanoparticles were prepared on the basis of M0O2 nanoparticles by adding Na2S·9H2O,the electrocatalytic activity in the hydrogen evolution reaction(HER)of different samples were studied.It was found that the reaction time has a little influence on the performance of the samples and increasing amount of hydrazine hydrate will reduce their catalytic properties.But the interval time of hydrazine hydrate and Na2S·9H2O had a greater influence on the catalytic properties.The shorter the interval time,the better the catalytic properties,among them,the overpotential of the sample with interval time of 15 min can reach-0.319 V.In summary,a series of MoO3 and Mo-based composites were designed and synthesized by a simple,economic and environmentally friendly aqueous method.The structurer,morphology and constituent of Mo-based materials can be controlled by in this thesis.The photochromic and electrical properties were studied.The results showed that the photochromic performance of the synthesized Mo-based materials have a significant improvement compared to previous literature,while MoO2 and MoS2 nanoparticles showed good performance in electrochemistry.