Study On Soft-template Assisted Synthesis Of Boron Nitride,Mechanism And Adsorption Properties

Boron nitride is a new functional material which has an excellent performance,important research significance and broad application prospects with high thermal conductively,oxidation resistance,acid and alkali corrosion resistance,chemical stability,good insulation,and many other advantages.Hereon,the preparation methods and adsorption properties were studied,andthe mechanism of synthesis was studied with density functional theory.First at all,the precursor ammonia borane?AB?was synthesized with ammonium fluoroborate?NH₄BF₄?as nitrogen source,sodium borohydride?NaBH₄?as boron source and 1,4-dioxane as solvent.Then,the ammonia borane with different amount of octadecylamine?0.1 g,0.2 g,0.5 g?were dissolved in 1,4-dioxane.Next,we transferred the mixed solutionto the autoclave and solvent thermal for 12 h at 160?and drying treatment for 5 h at 80?to obtain hybrid.Eventually,boron nitride was made by calcination treatment of the hybrid which was put in the high temperature tube furnace under different temperature in ammonia atmosphere.The samples were analyzed by scanning electron microscope?SEM?,transmission electron microscope?TEM?,X-ray diffraction?XRD?.And then,the BN sampleswere studied by adsorption study with methylene blue as adsorbate.The results were fitted the isotherm and kinetics,and the results fitted the Freundlich model and Pseudo-second-order kinetics.Thermodynamic parameters such as?G^?,?S^?and?H^?were calculated.It was seen that the proposed adsorbent has high tendency and adsorption capacity for MB adsorption in a feasible,spontaneous and endothermic way.The adsorption propertiesis best at 60?.The results ofadsorptionof copper irons also follow Pseudo-second-order kinetics.In the simulation part,we used the simulation software which based on density function DMol3 package in Materials Studio to create models and optimizethe synthesized route of boron nitride which assisted by soft template.The results showed that the atom N of octadecylamine could interact with the atom H of AB and polymeric aminoborane?PAB?and the atom B of polyiminoborane?PIB?,which made the N-H bond in AB and in PAB and B-H bond in PIB became longer than before,so that the bond energy reduce and the dehydrogenation became easy to achieve BN at a lower temperature.Based on the optimization of the crystal lattice layer structure of boron nitride?002?surface and octadecylamine template molecule,and the energy of adsorption was negative.The negative value of E_ads proved that octadecylamine template molecule and boron nitride?002?crystal surface can form stable structure.Finally,we successfully explained the synthesis mechanism of octadecylamine directed synthesis of BN inthe thermodynamicswith the Gibbs free energy of nucleation theory.