Abstract:

Significance Activated carbon fiber (ACF) is the third-generation novel carbon-based adsorbent material, featuring high specific surface area, abundant micropores, and rich functional groups, and widely used in the field of volatile gas adsorption. However, because the oxygen-containing functional groups on the surface of ACF can combine with water molecules through hydrogen bonds in high humidity environments resulting in water molecules adsorbed in ACF, which greatly reduce the adsorption capacity of ACF for volatile gases. This critical limitation severely restricts the practical application of ACF in volatile gas adsorption in high-humidity environments. Therefore, precise regulation of ACF hydrophobicity by surface modification has emerged as a core research direction to enhance its practical value. To date, superhydrophobic functionalized ACF have been developed for volatile gas adsorption, but their modification mechanisms can directly modulate the adsorption performance. In order to comprehensively clarify the intrinsic correlation between ACF hydrophobic modification technologies and volatile gas adsorption properties, as well as to identify the current research status and development bottlenecks, this review conducts a systematic investigation on the hydrophobic modification of ACF and their applications in volatile gas adsorption.

Progress In response to the demand for efficient volatile gas removal under high-humidity conditions, ACF integrating a large specific surface area and excellent adsorption performance has become a research hotspot in the adsorption field. The adsorption performance of ACF is synergistically determined by physical adsorption (dominated by Van Der Waals forces) and chemical adsorption (dominated by chemical bonding), which directly or indirectly influences its volatile gas adsorption efficacy. In order to further enhance the volatile gas adsorption performance of ACF, precise regulation of its specific surface area, as well as the composition and distribution of surface functional groups, is essential to achieve the synergistic optimization of physical and chemical adsorption. Research findings indicate that the physical structure and chemical properties of ACF are key factors governing their hydrophobicity and volatile gas adsorption performance, and the corresponding research progress has been initially summarized and discussed.

Conclusion and Prospect Hydrophobic ACF exhibit tremendous application potential in volatile gas purification and adsorption separation by virtue of their excellent hydrophobicity and superior adsorption performance. This review systematically summarizes the research progress on hydrophobic modification methods of ACF and their effects on volatile gas adsorption performance, and analyzes the physical and chemical adsorption mechanisms of different hydrophobic modification strategies on volatile gas adsorption. The results demonstrate that ACF hydrophobic modification is primarily achieved through two pathways. One is the selective reduction of hydrophilic surface functional groups to minimize hydrogen bonding sites with water molecules, and the other the introduction of low-surface-energy functional groups to decrease the surface free energy of ACF. The modified hydrophobic ACF can effectively inhibit the competitive adsorption between water molecules and volatile gases at the active sites under high-humidity conditions, thereby significantly improving the selective adsorption performance for volatile gases. Furthermore, precise regulation of modification process parameters enables targeted tuning of the specific surface area, pore structure parameters, and surface chemical properties of ACF, which in turn meets the adsorption requirements for different types of volatile gases and realizes the directional optimization of adsorption performance. Future research should focus on three key aspects, i.e., screening environmentally friendly, low-cost, and functionally synergistic hydrophobic modifiers to balance hydrophobicity and adsorption activity, developing high-efficiency and low-energy-consumption modification processes to address the limitations of traditional methods, and deepening the microscopic mechanism underlying the relationship between hydrophobicity and adsorption performance through advanced characterization techniques and density functional theory calculations. The ultimate goal is to develop hydrophobic ACF adsorbents with high adsorption capacity, excellent selectivity, and long-cycle stability, so as to meet the rigorous requirements for volatile gas adsorption in practical industrial applications.

Key words: activated carbon fiber, hydrophobic modification, volatile gas, adsorption performance, physical adsorption, chemical adsorption, porous carbon material