Controlled Synthesis,Characterization And Performance Research Of Transition-metal Phosphides Nanostructures

Transition-metal phosphides are attacting increasing scientific interest in materials science due to their superior properties,including magnetism,electrochemistry and energy storage,especially applications in catalytic reaction.Among them,phosphides of nickel or cobalt were widely synthesized and investigated.To date,many methods have been developed for the synthesis of phosphides of nickel or cobalt mirco/nanostructures,and simultaneously their properties were explored.However,highly toxic,expensive reaction reagents or higher temperature are often needed in the above methods.Therefore,our work is how to search a nontoxic reaction reagents with low cost and high activity for controlled preparations of phosphides of nickel or cobalt mirco-/nano-materials.Recently,the low-temperature phosphidation method is paid much attention due to its simplity,high efficiency,low-cost,environmental-friendness and easy morphology-control.In this disseratation,some phosphides of nickel or cobalt with controllable morphologies or phases have been successfully synthesized through the hydrothermal orphosphidation route,respectively.At the same time,their catalytic or electrochemical properties were investigated.Main contents are summarized as follows:1.A two-step solution process was designed for the preparation of grass-like Co₂P superstructures.Firstly,cobalt microspheres?0.5-15mm?were solvothermally fabricated through the reaction between CoSO₄·7H₂O,NaOH and N₂H₄·H₂O in glycol at 100°C for 10 h.Then,freshly-prepared Co microspheres reacted with white phosphorus via a hydrothermal route at 180°C for16 h to produce grass-like Co₂P superstructures.Experiments showed that the as-prepared grass-like Co₂P superstructures presented outstanding catalytic activity in the reduction of some aromatic nitro compounds such as 4-nitrophenol,2-nitrophenol and 4-nitroaniline in excess NaBH₄ solution.Simultaneously,several organic dyes including Rhodamine B,Pyronine B and Safranine T could be also rapidly reduced in excess NaBH₄ solution,which provides a new choice for the room-temperature decoloration of the dyes.2.A facile precursor phosphidation route was designed for morphology-controlled synthesis of Ni₂P nanostructures,employing NiCl₂ and NaH₂PO₂ as the initial reactants in the presences of polyvinylpyrrolidone?PVP?and hexamethylenetetramine?HMT?.Experiments showed that under the same hydrothermal conditions NiHPO₃·H₂O nanorods and Ni nanospheres were separately obtained via only changing the original amount of HMT.The as-obtained NiHPO₃·H₂O nanorods and Ni nanospheres could be used as the precursors in low-temperature phosphidation reaction under N₂ atmosphere.Under the same phosphidation conditions Ni₂P nanorods and nanospheres were formed,respectively.The electrochemical performance and the catalytic property of Ni₂P nanorods and nanospheres were investigated.It was found that the as-obtained Ni₂P nanostructures displayed marked shape-dependent property: Ni₂P nanorods presented better electrochemical performance,such as higher specific capacitance and more stable cycle feature,and stronger catalytic activity for the reduction of 4-nitrophenol?4-NP?to 4-aminophenol?4-AP?in excess NaBH₄ solution than Ni₂P nanospheres.3.A mild hydrothermal route was developed for the synthesis of spherical nickel phosphide nanostructures with controllable phase and morphology,using nickel chloride,sodium hypophosphite and white phosphorus?WP?as starting reactants in the absence of any surfactant.The reaction was carried out at 170°C.Experiments showed that the phases of the as-prepared nickel phosphide nanostructures were highly dependent on the reaction conditions including the amount of sodium hypophosphite,WP and the reaction time.Experiments discovered that Ni₂P and Ni₁₂P₅ nanospheres have good catalytic properties for the reduction of 4-nitrophenol in excess NaBH4 solution.Some other aromatic nitro compounds such as 2-nitrophenol and 4-nitroaniline were also discussed.The results demonstrated pure Ni₂P phase has a better catalytic reduction 4-nitrophenol than pure Ni₁₂P₅ phase.4.Nickel phosphide nanostructures with different phases have been successfully synthesized by a precursor phosphidation route employing nickel and NaH₂PO₂ as the initial reactants.Ni₂P and Ni₅P₄ were separately obtained by selecting different calcination temperature,time and the mass ratios of Ni²⁺/ H₂PO₂^-.Experiments showed that the mass ratio of Ni²⁺/H₂PO₂^-has a great influence on the phase of the final product.Ni₅P₄ phase can be obtained at the low mass ratio,and Ni₂P phase is formed at the high mass ratio.In addition,it is discovered that Ni₅P₄ nanospheres have better catalytic properties for the reduction of 4-nitrophenol in excess NaBH4 solution than Ni₂P nanospheres,indicating that the phase of the final product can strongly affect the catalytic performance.