Chiang Yu-Chun, Chin Wei-Ting
Department of Mechanical Engineering, Yuan Ze University, Taoyuan 320, Taiwan.
Fuel Cell Center, College of Engineering, Yuan Ze University, Taoyuan 320, Taiwan.
Nanomaterials (Basel). 2022 Apr 28;12(9):1492. doi: 10.3390/nano12091492.
In this study, polyacrylonitrile (PAN)-based activated nanofiber composites, which were embedded inside zeolitic imidazolate framework-8 (ZIF-8) crystals or ZIF-8-derived carbons (ZDC-850), were fabricated using an electrospinning process, to serve as CO2 adsorbents. The adsorbents were characterized using various techniques. The degree of crystallinity of ZDC-850 totally changed compared to that of ZIF-8. For nanofiber composites, the timing of the ligand decomposition of ZIF-8 significantly affected the material properties. The Zn metals in the ZIF-8/PAN or ZDC-850/PAN could be embedded and protected by the PAN fibers from excess volatilization in the following treatments: ZIF-8 had significant pore volumes in the range of 0.9−1.3 nm, but ZDC-850 and ZIF-8/PAN exhibited a distinct peak at approximately 0.5 nm. The CO2 adsorption capacities at 25 °C and 1 atm followed the order: ZIF-8/PAN (4.20 mmol/g) > ZDC-850 (3.50 mmol/g) > ZDC-850/PAN (3.38 mmol/g) > PAN (2.91 mmol/g) > ZIF-8 (0.88 mmol/g). The slope in the log−linear plot of isosteric heat of adsorption was highly associated with CO2 adsorption performance. Under 1 atm at 25 °C, for Zn metal active sites inside the pores, the pores at approximately 0.5 nm and in C-N (amines) groups could promote CO2 adsorption. At low CO2 pressures, for a good CO2 adsorbent, the carbon content in the adsorbent should be higher than a threshold value. Under this condition, the percentage of ultra-micropore and micropore volumes, as well as the functional groups, such as the quaternary or protonated N (amines), N=C (imines or pyridine-type N), C-OH, and -COOH groups, should be considered as significant factors for CO2 adsorption.
在本研究中，采用静电纺丝工艺制备了嵌入沸石咪唑酯骨架-8（ZIF-8）晶体或ZIF-8衍生碳（ZDC-850）内部的聚丙烯腈（PAN）基活性纳米纤维复合材料，用作二氧化碳吸附剂。使用各种技术对吸附剂进行了表征。与ZIF-8相比，ZDC-850的结晶度发生了完全变化。对于纳米纤维复合材料，ZIF-8配体分解的时机对材料性能有显著影响。ZIF-8/PAN或ZDC-850/PAN中的锌金属可以被PAN纤维嵌入并保护，以防止在后续处理中过度挥发：ZIF-8在0.9−1.3 nm范围内有显著的孔体积，但ZDC-850和ZIF-8/PAN在约0.5 nm处出现明显峰值。25℃和1 atm下的二氧化碳吸附容量顺序为：ZIF-8/PAN（4.20 mmol/g）>ZDC-850（3.50 mmol/g）>ZDC-850/PAN（3.38 mmol/g）>PAN（2.91 mmol/g）>ZIF-8（0.88 mmol/g）。吸附等量热的对数线性图中的斜率与二氧化碳吸附性能高度相关。在25℃、1 atm下，对于孔内的锌金属活性位点，约0.5 nm的孔和C-N（胺）基团可促进二氧化碳吸附。在低二氧化碳压力下，对于良好的二氧化碳吸附剂，吸附剂中的碳含量应高于阈值。在此条件下，超微孔和微孔体积的百分比以及季铵化或质子化的N（胺）、N=C（亚胺或吡啶型N）、C-OH和-COOH等官能团应被视为二氧化碳吸附的重要因素。
