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摘要: 基于前驅體合成與氨氣氮化兩步法，通過對前驅體合成關鍵參數B源/N源比、分散劑種類、前驅體干燥方式進行調控，實現了大比表面積、少層氮化硼納米片材料的制備。其優化條件為以硼酸為硼源，尿素為氮源，硼酸與尿素摩爾比為1∶30，甲醇和去離子水作為分散劑，利用真空冷凍干燥方式合成前驅體。將前驅體在氨氣氣氛下900 ℃保溫3 h合成了氮化硼納米片。利用X射線衍射測試、X射線光電子能譜測試、拉曼光譜測試、熱重分析測試等對合成產物進行了物相和結構表征，利用掃描電子顯微鏡、原子力顯微鏡、透射電子顯微鏡、氮氣吸脫附曲線等對合成產物進行了形貌及比表面積表征。結果表明：合成的氮化硼為六方氮化硼納米片（h-BNNSs），純度高，形貌類石墨烯，層數為2～4層，厚度平均為1 nm，比表面積為871.8 m2·g?1，單次產物質量平均可達240 mg，合成產物平均產率可達96.7%。該方法簡單易操作，實現了大比表面積少層氮化硼的制備，有助于氮化硼在各應用領域的研究，如氮化硼/石墨烯復合材料、納米電子器件、污染物的吸附、儲氫等。Abstract: Hexagonal boron nitride nanosheets (h-BNNSs) are two-dimensional nanomaterials whose structure, similar to graphene, is called white graphene. They have excellent physical and chemical properties. Few-layered and monolayer h-BNNSs have more extensive applications compared to block BNs due to their wider band gap and stronger insulation. However, the existing preparation methods have the disadvantages of uncontrollable product size, low yield, high cost, and pollution. Researchers are striving to develop an efficient and cheap method, and some have tried to prepared h-BNNSs through evaporation and recrystallization. However, it is difficult to control morphology in this method and prepared products are usually thick with uneven size distribution. Meanwhile, vacuum freeze-drying has been widely used in functional porous ceramics due its simple operation, controllability, and environmental friendliness. In this study, based on the two-step process of precursor synthesis and ammonia nitriding, few-layered h-BNNSs with large surface areas were successfully synthesized on a large scale by controlling key factors of precursor synthesis, such as ratio of atoms B to N in the raw material, dispersant, and drying method. The optimum preparation was using boric acid and urea with a molar ratio of 1∶30 as the source of B and N, and using methanol/deionized water as dispersant to obtain the precursors by vacuum freeze drying. Precursors were then transformed from ammonia vapor to nitride for 3 h at 900 ℃. The product was characterized by X-Ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, thermogravimetric analysis, and differential thermal analysis for phase and molecular structure, and scanning electron microscope, atomic force microscope, transmission electron microscope, and N2 adsorption-desorption isotherms for microstructure and specific surface area. Results indicate that the products are h-BNNSs with high purity, two to four atomic layers, 1 nm thickness, and with a high specific surface area of 871.8 m2·g?1, similar to the microstructure of graphene. Single product mass averages 240 mg and average yield is steadily 96.7%. This method is economical, simple, and easy to operate. It could achieve macro-synthesis of few-layered h-BNNSs with a large area, conducive to research on boron nitride in various field applications, such as boron nitride/graphene composite materials, nano-electronic devices, pollutant adsorption, hydrogen storage, etc.
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Key words:
- hexagonal boron nitride /
- nanosheets /
- freeze drying /
- few-layers /
- precursor
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圖 1 不同條件下制備所得h-BNNSs試樣的掃描電鏡圖. (a) 1#; (b) 2#; (c, d) 3#; (e, f, g) 4#; (h) 5#; (i) 6#
Figure 1. Scanning electron microscope images of h-BNNSs prepared under different experimental conditions: (a) 1#; (b) 2#; (c, d) 3#; (e, f, g) 4#; (h) 5#; (i) 6#
圖 3 h-BNNSs的物相表征. (a) X射線衍射圖譜；(b) 熱重–差熱分析曲線；(c) 拉曼光譜；(d) X射線光電子能譜；(e) N1s元素特征譜；(f) B1s元素特征譜
Figure 3. Phase characterization of h-BNNSs: (a) XRD pattern; (b) TG-DTA patterns; (c) Raman spectrum; (d) XPS spectra; XPS spectra: core-level B1s (e) and core-level N1s (f) of h-BNNSs
圖 4 h-BNNSs的微觀形貌表征.（a，b）透射電鏡圖；（c）高分辨率透射電鏡圖；（d）選區電子衍射圖；(e) 原子力顯微鏡圖；(f) 單片納米片的基本尺寸和厚度表征
Figure 4. Morphologies of h-BNNSs: (a, b) TEM images; (c) HRTEM image; (d) SAED image; (e) AFM image; (f) height profiles showing typical size and thickness of a single nanosheet
圖 5 h-BNNSs的N2吸附脫附等溫線(插圖為產物在石英舟中普通光學圖)(a)和孔徑分布圖(b)
Figure 5. Nitrogen adsorption–desorption isotherm, inserted image showing ordinary optical image of the reaction product in a fused-silicon boat (a) and corresponding pore size distributions of h-BNNSs (b)
表 1 少層h-BNNSs制備因素調控
Table 1. Experimental conditions of few-layer h-BNNSs
試樣編號 硼酸/尿素摩爾比 分散劑種類 前驅體制備干燥方法 1# 1∶10 乙醇水溶液 45 ℃水浴式蒸發結晶 2# 1∶20 乙醇水溶液 45 ℃水浴式蒸發結晶 3# 1∶30 乙醇水溶液 45 ℃水浴式蒸發結晶 4# 1∶30 甲醇水溶液 45 ℃水浴式蒸發結晶 5# 1∶30 甲醇水溶液 45 ℃鼓風干燥箱蒸發結晶 6# 1∶30 甲醇水溶液 冷凍干燥式蒸發結晶 
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