Controlled Synthesis,Characterization And Performance Of Transition-metal Phosphides Micro/Nano Materials

Over the past decades,nanostructural transition-metal phosphides?TMPs?always attracted considerable attention due to their wide applications in fields,including the hydrogen evolution reaction,the magnetocaloric behavior,the removal of heavy metal ions,and Li-ion batteries,etc.More importantly,TMPswithhighlyactivehydrodesulfurization?HDS?and hydrodenitrogenation?HDN?have become a new selection as promising candidates for next-generation catalysts.So far,TMPs have been prepared through a variety of synthetic paths and their possible applications were explored.At present,the methods to prepare TMPs nanomaterials include:the hydrothermal/solvothermal route,the high energy ball milling and organometallic precursor decomposition.In recent years,the low temperature phosphidation technology of the precursor has attracted increasing research interest due to its advantages including easy shape-control,low energy consumption,safe and easy to operate.In this dissertation,we employ the low-temperature phosphidation technology of the precursors to successfully prepare phosphides of cobalt and nickel micro-nanomaterials with controlled morphology and phase.The main contents are summarized as follows:1. A simple precursor phosphidation route was developed for the preparation of Co P nanocrystals.Firstly,smooth precursor nanoflakes were obtained by a hydrothermal-vapor route.Then,the flake-like precursor was calcinated at 400°C for 2 h in air to produce porous Co₃O₄ nanoflakes.Finally,porous Co₃O₄ nanoflakes were converted to Co P nanoflakes in the presence of Na H₂PO₂ in N₂ atmosphere at 300°C for 2 h.It was found that the as-obtained porous Co P nanoflakes exhibited excellent catalytic activity for the reduction of some organic small molecules including aromatic nitro compounds and dyes in excess Na BH₄ aqueous solution.This provides widely potential applications in many fields,including a new selection of catalyst for the catalytic reduction of aromatic nitro compounds in aqueous solution,and an alternative route for the room-temperature decoloration of the dyes in the absence of outer light sources.2.Magnetic Ni@Ni₅P₄ core-shell microstructures were successfully synthesized by a simple low-temperature phosphidation route of Ni nanospheres,employing Na H₂PO₂·H₂O as the phosphorus ion source.The phosphidation reaction was carried out in N₂ atmosphere at 300°C for 2 h.Experiments showed that the initial Ni/Na H₂PO₂ molar ratio affected the phase of the as-produced nickel phosphide:Ni₂P phase was obtained when the Ni/Na H₂PO₂ molar ratio was 1:2.77;and Ni₅P₄ phase was produced when the molar ratio was changed to 1:5.54.Simultaneously,the magnetic properties of the products gradually decreased with the conversion from Ni nanospheres,to Ni@Ni₂P and to Ni@Ni₅P₄.It was found that initial Ni nanospheres,Ni@Ni₂P core-shell microstructures and Ni@Ni₅P₄ core-shell microstructures presented outstanding catalytic activities for the reduction of 4-nitrophenol?4-NP?to 4-aminophenol?4-AP?in excess Na BH₄ solution,but Ni@Ni₅P₄core-shell microstructures owned the best catalytic activity.3.A solvothermal-high temperature carbonation-low temperature phosphidation route was designed for the synthesis of Ni₅P₄@C nanocomposites.Firstly,Ni nanospheres were prepared by a simple solvothermal method.Secondly,Ni nanospheres and n-hexane were treated at high temperature to obtain Ni@C nanocomposites.Finally,Ni@C nanocomposites reacted with Na₂HPO₂ to form Ni₅P₄@C nanocomposites.Research displayed that the as-obtained Ni₅P₄@C nanocomposites presented good electrochemical performances.At the current density of 1 A g^-1,the initial specific capacitance of Ni₅P₄@C was 522 F g^-1,which is higher than310 F g^-1 of Ni₅P₄ obtained through the direct phosphidation of nickel nanospheres under the same conditions.The above fact implies that the presence of carbon in the composites markedly improves the electrochemical property.Furthermore,the as-obtained Ni₅P₄@C nanocomposites also possessed good rate performance and cycle stability.After 3000 cycles the specific capacitance of Ni₅P₄@C still remained 86.5%.