Controllable Growth Of Transition Metal Oxides/Sulfides And Their Applications

Three dimensional hierarchical mesoporous nanostructures?3DHNs?are in high demand to be used in applications relating to catalysis and energy storage.As3DHNSs has shown great promise to be used in photocatalysis for removing contamination,and has also shown potential as electrode in lithium ion batteries?LIBs?.Latest research has shown that controllable growth of novel metal oxides/sulfides with versatile morphology can be of great importance to enhance the physiochemical properties.There have been many studies reporting various methods to control morphology by fine-tuning.During this research work,we achieved fine tuning of the morphology firstly,by using different synthesis approaches?top down and bottom up?at room temperature.Secondly,by annealing metal organic frameworks?MOF?with sulfur powder in argon atmosphere.Lastly,by chemical modification and introduction of defects by soaking precursors in reducing agents?NaBH₄?.The focus of this dissertation is to study and analyze the shortcomings of commercially used electrodes and photocatalysts,and suggest ways to improve their efficiency.The main results are as follows:In this work,wet chemical method was employed to synthesize ZnO 3DHNs at room temperature.Potassium hydroxide?KOH?was used as etchant and citric acid?CA?was added as capping agent.In previously reported works,effect of etching or capping agents are explained separately.The possible formation mechanism based on capping–etching competitive interactions has also been proposed.The as synthesized ZnO 3DHNs with different morphologies by selective concentration of KOH and CA was analyzed as a photocatalyst for degrading carbon-based contaminants.It is considered that its decent photocatalytic functioning can be because of its morphology.In addition,unique nitrogen-doped porous carbon networks encapsulating Co₉S₈nanoparticles?Co₉S₈@NMCN nanocomposites?were synthesized by facile synthesis of metal organic framework?MOF?ZIF-67 and then annealing it with sulfur powder in argon?Ar?atmosphere.When tested as anode material for LIBs,Co₉S₈@NMCN nanocomposites showed a reversible specific capacity of 988 mAhg^-1.This worthy electrochemical performance can be credited to porous nature,large specific surface area(76.9 m²g^-1)and continuous network of nitrogen-doped carbon layer.The modified Co₃O₄ crystalline core-amorphous shell nanoparticles decorating ultrathin nanosheets of hierarchical Co₃O₄ nanostructures?Co₃O₄ C@A NPs-NSs HNs?were synthesized by solvothermal method and then reducing in the presence of NaBH₄.The as synthesized 3DHN when studied as an electrode?anode?material in LIBs,showed promising reversible capacity of 1053.1 mAhg^-1 even after 50 cycles.The improved electrochemical performance was accredited to this unique nature of these mesoporous hierarchical structures.Lastly,tuning oxygen vacancies in Co₃O₄ nanostructures can significantly alter the intrinsic electrical conductivity as well as surface electronic states,without the addition of any extra conductive agents.Oxygen vacancies were introduced in as prepared Co₃O₄ nanostructures by soaking them in different concentration of sodium borohydride?NaBH₄?.The optimal sample?soaked in 1 mole of NaBH₄?possesses a reversible capacity of 888.8 mAhg^-1 even after 80 cycles.The decent results of this anode can conveniently be assigned to the collective effects of novel hierarchical morphology,crystal structure of the active materials,and the improvement of intrinsic conductivity and inner surface induced by the oxygen vacancies.In the nutshell,we synthesized 3DHNs by fine-tuning the morphology.Different synthesis approaches and methods were employed to achieve novel hierarchical morphology of ZnO,Co₉S₈ and Co₃O₄.The synthesized nanostructures were used for photocatalysis and as anode material for LIBs.The combined effect of compliant morphology,larger surface area,pore size and enhanced conductivity of these nanostructures is the driving force for their good electrochemical properties.