Synthesis,Characterization And Activation Of Porous Boron Nitride And Their Applications In Environment And Energy Fields

Activated porous boron nitride exhibits unique physical and chemical properties including non-toxicity,low density,oxidation resistance,superb corrosion,chemical stability,high specific surface area and large pore volume,which make activated porous boron nitride a promising candidate for applications in the new energy and environmental remediation fields.In this dissertation,the porous boron nitride was successfully synthesized via chemical blowing of the precursor at high temperature,the reaction mechanisms of chemical blowing and chemical activation were thoroughly analyzed;the free-standing membranes were made of the activated porous boron nitride for water cleaning for the first time;the synthetic process of the NaOH-embedded three-dimensional porous boron nitride via a molten-salt route with the assistant of NaCl was studied.Based on the mention above,their abilities of hydrogen storage and environmental remediation were evaluated.The results of the dissertation were summarized as follow:?1?The porous boron nitride was successfully synthesized by using H3BO3 and C₃N₆H₆ as the starting reactants via chemical blowing at high temperature under a flow of N₂,which exhibited a high specific surface area of 1687 m²/g and large pore volume of 0.99m³/g.The effects of molar ratio of the starting reactions and processing temperature on textural parameters of the porous boron nitride were studied.The reaction mechanism of chemical blowing was thoroughly analyzed.The hydrogen adsorption capacity was up to5.6 wt%at room temperature and 3 MPa.Additionally,the adsorption performance and mechanism of the porous boron nitride for methyl orange in the solution were studied.The effects of the experimental parameters,including contact time,adsorption temperature and pH value,etc.on methyl orange removal were systematically investigated.?2?The activated porous boron nitride was prepared via chemical activation in stiu,which exhibited a high surface area of 2078 m²/g and large pore volume of 1.66 m³/g.The effects of chemically activated process on the porous structure and physical and chemical properties were analyzed.The chemical activation mechanism was deeply studied.The activated porous boron nitride exhibited an excellent adsorption performance for various metal ions and organic pollutants in the solution,as well as volatile organic compounds in air.The adsorption capacities of the activated porous boron nitride for Cr³⁺,tetracycline and benzene were 352,300 and 762.5 mg/g,respectively.?3?Using the porous boron nitride fibers and mixture acid as the precursor and activating agent,respectively,the activated porous boron nitride fibers were synthesized by chemical activation.After chemical activation,the adsorption capacity of the activated porous boron nitride fibers for methylene blue increased from 243.2 to 392.2 mg/g.The effect of the chemical activation on the component,the microstructure and surface physicochemical properties was deeply studied.The activated porous boron nitride fibers also exhibited excellent regeneration,the removal efficiency of about 94%was still retained even after 15 adsorption/regeneration runs.In addition,the effects of adsorption experimental parameters such as contact time,the characteristic of the adsorbents,pH value and temperature,etc.were systematically analyzed.?4?The free-standing activated porous boron nitride-based filtration membrane,which combined the high adsorption capacity of the activated porous boron nitride and the ultrafiltration technique,was successfully fabricated in a vacuum filtration process.The effect of the activated porous boron nitride content in the composite membrane on the tensile strength,surface physicochemical properties and filtration capacity was disclosed.The composite membrane not only possessed mechanically strong enough for filtration adsorption even under a fast flux,but also exhibited excellent filtration adsorption ability,which was 20 times higher than that of the activated carbon column.Additionally,the effects of adsorption experimental parameters such as pH value,the characteristic of the adsorbents and adsorption temperature,etc.on removal capacity were studied.?5?The three-dimensional porous boron nitride was successfully synthesized by the molten-salt route,exhibiting a specific surface area of 363.5 m²/g and large pore volume of1.07 m³/g.The as-prepared three-dimensional porous boron nitride was impregnated into NaOH aqueous solution to obtain NaOH-embedded three-dimensional porous boron nitride.The effects of fabrication process parameters such as solution concentration,experimental temperature and impregnated time on their removal ability for formaldehyde were studied.The catalytic reaction and regeneration mechanisms of the NaOH-embedded three-dimensional porous boron nitride for formaldehyde were deeply disclosed.Batch of experiments confirmed that it exhibited excellent removal ability for formaldehyde?380mg/g?at room temperature.In addition,NaOH-embedded three-dimensional porous boron nitride could easily be regenerated,the removal efficiency of 90.5%remained even after 15cycles.