Selective and efficient removal of volatile organic compounds by channel-type gamma-cyclodextrin assembly through inclusion complexation
Cyclodextrins (CD), produced from enzymatic degradation of starch, are a form of biorenewable cyclic oligosaccharide which has an outstanding capability to form inclusion complexes with a variety of molecules including pollutants due to their toroid-shaped molecular structure. In this study, by a simple reprecipitation method, we obtained "channel-type" packing from γ-CD where CD molecules are stacked on top of each other to form long cylindrical channels. The γ-CD "channel-type" crystals have shown very effective removal of organic volatile compounds (VOCs; aniline and toluene) from the surroundings, whereas cage-type γ-CD could not entrap VOCs from the same environment. Encapsulation capability of channel-type γ-CD is at a ∼2:1 and ∼1:1 molar ratio for aniline/CD and toluene/CD, respectively. Thus, channel-type γ-CD crystals have shown higher removal efficiency for aniline compared to toluene. Channel-type γ-CD is also able to remove aniline selectively from surroundings. Additionally, computational modeling studies suggested that single γ-CD cavity can host two molecules of aniline or toluene for the complexation, yet, aniline is more insistent to make a complex with the γ-CD cavity when compared to toluene. We show that channel-type γ-CD can remove VOCs molecules (aniline and toluene) as efficiently as activated carbon. Hence, being a starch-based biorenewable cyclic oligosaccharide in the form of white powder, the use of "channel-type" γ-CD crystals could be a competitive alternative to activated carbon as an adsorbent for the VOC removal/filtering.