Mussabek Gauhar, Baktygerey Saule, Taurbayev Yerzhan, Yermukhamed Dana, Zhylkybayeva Nazym, Diyuk Vitaliy E, Zaderko Alexander, Afonin Sergii, Mariychuk Ruslan, Kaňuchová Mária, Lisnyak Vladyslav V
Nanotechnological Laboratory of Open Type, Al-Farabi Kazakh National University, 71, Al-Farabi Avenue, 050040 Almaty, Kazakhstan.
Institute of Information and Computational Technologies, 125, Shevchenko Street, 050012 Almaty, Kazakhstan.
ACS Omega. 2024 Sep 5;9(37):38618-38628. doi: 10.1021/acsomega.4c04179. eCollection 2024 Sep 17.
A novel method for the concurrent introduction of fluorine and bromine into the surface of nanoporous activated carbon (NAC) is evaluated. According to the method, the preheated NAC was treated with 1,2-dibromotetrafluoroethane at elevated temperatures (400-800 °C). Potentiometric and elemental analysis, nitrogen adsorption-desorption, scanning electron microscopy-energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), and F solid-state NMR were used to study the NAC microstructure and changes in surface chemistry. The specific modification temperature was found to have a decisive influence on the resulting halogen content of the NAC surface. About 1.5 mmol g of bromine and only 0.5 mmol g of fluorine are chemisorbed on the NAC surface when dual-doped at 400 °C. The fluorination efficiency increases dramatically to 1.84-2.22 mmol g when the process temperature is increased to 500-700 °C. Under the same conditions, the bromination efficiency unexpectedly decreases to 0.66-1.32 mmol g. Since halogen-containing groups undergo significant thermal decomposition around 800 °C, the overall halogenation efficiency decreases, accordingly. Both the volume and surface area of the micropores decrease moderately when halogen-containing groups are introduced into the carbon surface layer. Fluorine and bromine are unevenly distributed in the porous structure of the dual-doped NACs, and the outer surface is more halogen-rich than the inner surface of the micropores. XPS and F solid-state NMR revealed the selective formation of CF groups in the NAC surface layer independent of the temperature. In contrast, the percentage of semi-ionic fluorine in the form of CF groups directly bonded to the π-electron system of the carbon matrix increases significantly with temperature.
评估了一种将氟和溴同时引入纳米多孔活性炭（NAC）表面的新方法。根据该方法，将预热的NAC在高温（400 - 800°C）下用1,2 - 二溴四氟乙烷处理。采用电位滴定和元素分析、氮气吸附 - 脱附、扫描电子显微镜 - 能量色散X射线光谱、X射线光电子能谱（XPS）和F固体核磁共振来研究NAC的微观结构和表面化学变化。发现特定的改性温度对NAC表面最终的卤素含量具有决定性影响。在400°C进行双掺杂时，约1.5 mmol/g的溴和仅0.5 mmol/g的氟化学吸附在NAC表面。当工艺温度升至500 - 700°C时，氟化效率急剧增加至1.84 - 2.22 mmol/g。在相同条件下，溴化效率意外地降至0.66 - 1.32 mmol/g。由于含卤素基团在800°C左右会发生显著的热分解，因此整体卤化效率相应降低。当将含卤素基团引入碳表面层时，微孔的体积和表面积会适度减小。氟和溴在双掺杂NACs的多孔结构中分布不均匀，外表面比微孔内表面的卤素含量更高。XPS和F固体核磁共振表明，在NAC表面层中选择性地形成了CF基团，且与温度无关。相比之下，以CF基团形式直接键合到碳基体π电子体系的半离子氟的百分比随温度显著增加。
