Synthesis Of Metal Oxide And Sulfide And Their Photocatalytic Properties

Nowadays,semiconductor photocatalytic technology is an attractive process to alleviate the global energy crisis.Photocatalyst is crucial to the photocatalystic reaction.In the research field of photocatalyst,searching for new and high efficiency photocatalyst is highly desirable,especially novel visible light responding semiconductor photocatalysts.In recent years,compared with the traditional noble metal catalysts,oxide catalysts have aroused more and more attentions due to their unique advantages such as facile preparation process,stable performance during the catalytic reaction and less agglomerationin the reaction.Bimetallic multi-stage metal oxides generally have fluent porosity and large specific surface area therefore they hold great application potentials in the field of photocatalysis and electrochemistry.Metal sulfide has the proper bandgap and excellent photocatalytic performance,which has become a hotspot in recent field of photocatalysis.However,the presence of photogenerated electrons and holes is easy to complex,and the quantum efficiency is low,the specific surface area is small,and the inherent defects such as light corrosion are likely to occur,which limit its practical application.The photocatalytic performance of metal sulfide can be effectively improved by changing the morphology of photocatalyst,composite semiconductor and other methods.Based on the above background,bimetal transition oxide and metal sulfide as well as the compound were investigated as the objects of this thesis in order to prepare the bimetal oxide with controllable morphology and amorphous-layer relative high performance,metal sulfide with yolk-shell structure as well as high catalytic activity and stability,and metal sulfide with novel visible light photocatalyst derived from metal-organic-framework precursor.In the meantime,the effect of novel functional construction strategy with multilevel structure,together with the synergistic effect between multilevel structure and active ingredients on improving the comprehensive properties of catalytic materials and electrode materials,were explored.The detailed research contents in this paper are shown as follows.(1)Iron chloride and ammonium molybdate were used as the raw materials to prepare Fe2(MoO4)3 with three distinct morphologies by adjusting the pH value of the initial solution via the simple template-free hydrothermal method and low temperature calcination.The three dimensional(3D)Fe2(MoO4)3 microsphere with amorphous layer(FMO-A),possessed excellent photocatalytic performance and lithium storage performance.FMO-A microsphere with diameter of 3-5 ?m was formed through self-assembly of the irregular nanosheet.Different hydrothermal reaction times can affect the proces of microsphere nucleation and crystal growth according to the Oswald Law of Curing.It was indicated in this thesis that iron molybdate possessed good visible light photocatalytic degradation property.FMO-A had the highest degradation rate,which could completely degrade Rhodamine B target pollutant within 100 min,with the maintained visible light degradation rate of 94.26%after 4 cycles.This may be attributed to the fact that 3D structure has larger specific surface area to provide more active sites,while crystal defects induced by amorphous layer can absorb more visible light,thus enhancing the photocatalytic efficiency.Meanwhile,it was found that the principal product of FMO-A exhibited the best electrochemical performances for lithium ion batteries in terms of high capacity,good cyclability and high-rate capability.It delivered a stable high capacity of 1138.2 mAh g-1 during 250 cycles at 0.1 C.When the current density increased from 0.1 C to 1 C,2 C,5 C,reversible capacities of 761.1 mAh-g-1 694.4 mAh·g-1?544.4 mAh-g-1 could be still retained.These good electrochemical performances have been mainly attributed to the synergetic effect of three-dimensional multi-level layered structure,amorphous layer coating,and bimetal synergistic effect,which can be used to increase the electrical conductivity,structural stability,shorten the diffusion way of ions and charge and buffer the volume change during cycles.(2)Cd-Fe Prussian blue analogue(Cd-Fe-PBA)was also used as the precursor to synthesize the unique C d S microcubes with yolk-shell structure constituted by nano particdes using microwave-assisted hydrothermal method.The morphological features that changed with synthetic reaction time were studied in this thesis with the focus on the formation mechanism of yolk-shell structure change-under the anion exchange and Kirkendall effect.The yolk-shell CdS microcubes possessed the following advantages:3D open structure,small-sized primary nano particles,high specific surface area and excellent structural stability.These contributed to light absorption and utilization in light catalysis,and could inhibit the recombination of photoinduced electrons and electron holes.The CdS microcubes displayed excellent ability of photocatalytic hydrogen production by water decomposition based on the above advantages.The production rate of photocatalytic hydrogen by water decomposition was 3051.4?mol-h-1g-1(the apparent quantum yield at 420 nm was 4.9%),which was 2.43 times of photocatalytic efficiency as large as that of CdS nano particle.Furthermore,the CdS microcubes with yolk-shell structure maintained high catalytic activity after 6 cycles of photocatalytic hydrogen production by water decomposition.It could be seen from transmission electron microscope images that CdS maintained the yolk-shell cubic structure after cycling,demonstrating the high structural stability of CdS microcubes.It is indicated that MOF derived yolk-shell material has great application prospect in photocatalytic field.(3)2-aminotetrephthalic acid and zirconium tetrachloride were served as the raw materials,while N,N-dimethylformamide as the solvent to synthesize the amino group(-NH2)containing Zr-metal organic framework-UiO-66-NH2 using the one-step solvothermal method,which had high stability.Subsequently,a series of visible light composite photocatalysts(Cd0.2Zn0.8S@UiO-66-NH2 with various UiO-66-NH2 contents)were prepared using solvothermal method.The photocatalytic properties of the obtained nanomaterials were evaluated through photocatalytic hydrogen production by water decomposition and methanol production by carbondioxide reduction under visible light radiation.The experimental results had verified that the visible light photocatalyst of Cd0.2Zn0.8S@UiO-66-NH2 had superior photocatalytic activity compared to Cd0.2Zn0.8S alone,either in photocatalytic hydrogen production by water decomposition or methanol production by carbon dioxide reduction.These results had revealed that the composite quantity of UiO-66-NH2 had great influence on photocatalytic activity,and the visible light photocatalyst of Cd0.2Zn0.8S@UiO-66-NH2 had the highest photocatalytic activity when the UiO-66-NH2 content was 20 wt%.The rate of photocatalytic hydrogen production by water decomposition of the visible light photocatalyst was 5846.5?mol·h-1g-1 while the production rate of methanol by carbon dioxide reduction was 6.8 ?mol·h-1g-1.The significantly enhanced photocatalytic activity may be attributed to the isolation and transfer of effective charges on the interface between Cd0.2Zn0.8S and UiO-66-NH2,as well as the large specific surface area of the composite photocatalyst,which can provide more active sites.Besides,the visible light composite photocatalyst Cd0.2Zn0.8S@UiO-66-NH2 maintained high photocatalytic activity after 4 cycles,suggesting its strong photocatalytic stability.