Synthesis Of Porous Boron Nitride Nanosheets And Their Application Of Gas Adsorption

Boron nitride(BN) has attracted enormous attention due to its outstanding physical and chemical properties. Porous BN materials show important potential applications in addressing global energy and environmental problems, especially in the areas of energy storage, water cleaning and dye adsorption. In this thesis, porous BN nanosheets have been prepared by a facile, one-step, template-free reaction using boric acid and urea as precursors. In order to control the morphology of BN nanosheets, we conducted a series of experiments by varying different parameters such as reactant ratio, temperature time, and gas flow rates. As a result, the best synthetic conditions for porous BN nanosheets were determined.The morphological structures, chemical composition and crystallography of the as-prepared materials were characterized in detail by using the advanced techniques such as field emission scanning electron microscope, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscope and Raman spectrum etc. The XRD and TEM analysis confirms the expanded(0002) peak with interlayer spacing 0.365 nm which correspond to the standard d-spacing of graphitic BN and reveals special dislocation structures in the BN nanosheets. The XPS analysis proved that the as-synthesized material is composed of boron and nitrogen elements with a ratio of 0.97:1(B:N). The E2 g vibrational peak of Raman spectrum well matched with the standard peak; the shifting of E2 g vibrational mode towards higher frequency compared to the bulk h-BN indicates a weaker interaction between the interlayers in BN porous nanosheets, whereas the obvious broadening of E2 g peak reflects a clear size shrinking of the ordered BN phase.In order to find the specific surface area, BET analysis were performed which indicates that the surface area of the as-prepared sample has a value of 735 m2/g with utrahigh pore volume of about 1.24 cm3/g which is the largest pore volume among the BN porous materials. High SSA and pore volume enabled the BN nanosheets to exhibit excellent gas adsorption property. It has been demonstrated that these microporous materials(with pore width 0.93 nm) displayed relatively high and reversible H2 sorption capacity 1.50 wt% at 1 atm and 77 K. Stronger interactions with the heteropolar B-N bonds and partial chemisorption contribute to H2 uptake. Oxgen doping can increase adsorption energies of H2 on BN. The BN nanosheets reversibly adsorbed 11.92 wt% carbon dioxide at 1 atm and 273 K. Mesopores in in the material provide passways for carbon dioxide molecules to immigrate, and thus decrease the diffusion resistance, resulting in larger effective micropore surface area.