Encapsulating site-directly carbonized CDs in MOF(Cr) as adsorption-photothermal sites for boosting toluene Ad/de-sorption process via photo-assisted strategy

Abstract

Metal-organic frameworks (MOFs) require high energy for the desorption of volatile organic compounds (VOCs) due to their strong adsorption affinity. For this purpose, a photo-assisted desorption is proposed for MOF regeneration. Herein, carbon dots (CDs) with efficient light absorption and thermal conductivity are encapsulated in MOFs using the “site-directly carbonization” approach, forming ship-in-a-bottle o-CDs-M101. These CDs can act as “VOCs affinity sites” and “photothermal spots” in MOFs, simultaneously maintaining toluene adsorption capacity, while enhancing desorption efficiency under humid conditions. Consequently, the designed o-CDs-M101 (2558 m²/g) achieves a 40 % increase in toluene uptake compared to the original MIL-101(Cr), reaching up to 3.6 mmol/g under 400 ppm and RH = 60 %. During the desorption process, CDs rapidly generate heat/electrons under light radiation to attack the adsorbed VOCs and make them quickly and thoroughly desorb. Owing to this attribute, it shows 3.4 and 3.8 times faster desorption rate and higher concentration ratio under photo-assisted conditions at 110 °C compared to thermal conditions. Interestingly, these adsorbed H₂O further dramatically accelerate toluene desorption from MOFs, up to 2.5 times faster compared to water-free conditions. This approach is also broadly applicable to HKUST-1 and MIL-100(Fe), achieving similar high efficiency in toluene photo-assisted desorption. The findings demonstrate that the introduction of photothermal sites offers a promising approach to MOF regeneration with high efficiency and low energy consumption.