Adsorption film with sub-milli-interface morphologies via direct ink writing for indoor formaldehyde removal

In-situ thermally regenerated flexible adsorption films are superior for long-term purification of indoor low concentration volatile organic compounds (VOCs). To further improve the adsorption kinetics of the films, the surface morphology of adsorption films was suggested in hierarchical channel structure. However, such structure is far from practical applications because of its complicated fabrication method and limited flexibility. In this study, we proposed a convenient and fast method named direct ink writing (DIW) based 3D printing to fabricate flexible adsorption films. Inks were prepared to have appropriate rheological properties and good printability. Three types of adsorption film (flat, straight finned, and trough-like finned) were constructed on flexible polyimide circuit substrates by DIW. We utilized the printed adsorption films for indoor level (1 ppm) formaldehyde removal. The trough-like finned film achieved the best performance among the three printed films, showing a 275% longer penetration time and 252% larger effective adsorption capacity than the flat film. By conducting a 7-cycle adsorption-desorption experiment (more than 12 h), we verified that the films' adsorption performance could effectively recover via in-situ heating. This work could dance around the complicated coating process, increase the structural flexibility and reduce the adsorbent interfacial modification cost.