In Situ Growth of Gamma-Cyclodextrin-Based Metal Organic Frameworks on Poly(ethylene terephthalate) Fibers

Metal organic frameworks (MOFs) are highly porous materials with large surface areas of 1000–10,000 m²/ g, which are much higher than those of zeolites and activated carbons. However, when MOFs are used alone in toxic gas removal systems, they are difficult to handle because they are very fragile and often break down into nanosized particles, which have low stability and tend to form agglomerates. Thus, MOFs are often used in composites, where they are embedded in a polymeric matrix, or attached to a matrix surface. A common limitation of MOF fibrous composites is the low binding strength of the MOFs to the substrate. When MOF crystals are coated on a substrate surface, they are often only weakly adhered to the surface and easily fall off. In addition, when MOFs are incorporated into a polymeric matrix, their cavities can be blocked, resulting in a decrease in the surface area and porosity.<br/>The growth of self-supported MOFs onto the surfaces of substrates may solve this problem. Specifically, fibrous substrates can provide mechanical support and reduce MOF aggregation, leading to good performance for gas adsorption. Moreover, MOF growth on fibrous substrates enables more than one type of MOF to be incorporated to simultaneously provide multiple functions.<br/>Cyclodextrin-based MOFs (CD-MOFs) are synthesized from the enzymatic degradation of starch and have received much attention toward the green synthesis of MOFs. CD-MOFs have truncated cone-shaped crystals with an external hydrophilic surface owing to the hydroxyl groups and internal hydrophobic cavity covered by glycosidic oxygens and C–H units. The presence of –OCCO– binding groups only in the CD primary and secondary faces is advantageous for fabricating biocompatible and non-toxic MOFs. CD-MOFs are versatile because of the free primary hydroxyl groups present in CD that bind with reactive functional groups for the reversible formation of carbonic acid. These features have led to their applications into gas capture, adsorption, and removal of air pollutants &lt;!--![endif]----&gt;<br/>In this study, an effective strategy was introduced for <i>in situ </i>growth of cyclodextrin-based metal organic frameworks (CD-MOFs) through the vapor diffusion method combined with O₂ plasma treatment. A structure of self-supported γ-CD-MOF on poly(ethylene terephthalate) (PET) fibers was developed, and the effect of the <i>in situ </i>growth time on its properties was evaluated. The growth rate of γ-CD-MOFs on PET fibers (CD-MOFs–PET) was determined over 136 h, and 24 h growth of CD-MOFs-PET showed the highest surface area and CD-MOFs growth without deformation for air-filter applications. The CD-MOF crystals grown on PET fibers had an average side length of 818 nm. The specific surface area of the CD-MOFs-PET grown with 24 h growth time was 142.88 m²/g, which was almost 235 times higher than that of the pristine showed a high efficiency of SO₂ gas adsorption performance up to 95% removal using a real-time gas monitoring system. The reusability of CD-MOFs-PET recovered most of its adsorption ability (85–95%) after vacuum oven drying. This study intends to provide an informative discussion of the applicability of textile-based CD-MOFs and the development of reusable filters for the removal of SO₂.