IL-assisted synthesis of defect-rich polyaniline/NH2-MIL-125 nanohybrids with strengthened interfacial contact for ultra-fast photocatalytic degradation of acetaldehyde under high humidity

Abstract

A novel strategy and design for ionic liquid (IL) assisted in-situ grafting of polyaniline (PANI) oligomers in NH2-MIL-125 was proposed to synthesize the defect-rich IL-PANI/NMIL(Ti) nanohybrids with an intimate interface for the superior photodegradation of CH3CHO. PANI was dissolved into small oligomers with the aid of IL [EMIM]BF4 and was composited to NH2-MIL-125 by a strong interfacial connection through Ti-N bonds (XPS) with high dispersion and large surface area (BET = 1125 m2/g). Characterizations results showed that smart grafting of PANI-oligomers generated abundant defects (3.4-times, ESR) and intensified Lewis acid sites (1.2-times, CO-DRIFT) in IL-PANI/NMIL(Ti) compared to NH2-MIL-125. It promoted adsorptive interactions for aldehyde VOCs capturing, which in-turn increased the adsorption rate (ka) of CH3CHO. Smart grafting also improved the light absorption of IL-PANI/NMIL(Ti) from 500 to 800 nm, reduced band gap (1.7 eV), increased photo-current density (2.2-folds of pure MOF), enhanced O2− and OH radicals generation and improved e−/h+ mobility. As a result, IL-PANI/NMIL(Ti) showed 11.4 and 4.2 times higher ka (0.262 min−1) of CH3CHO photodegradation kinetics than PANI and NH2-MIL-125, respectively, at 75% relative humidity (RH). The ka of CH3CHO degradation was steadily increased with increasing humidity (<80 RH%), indicating that H2O from humid air was beneficial for CH3CHO degradation. Furthermore, IL-PANI/NMIL(Ti) exhibited the excellent recycling stability compared to NH2-MIL-125, as only a 5% decrease in photocatalytic activity was observed after five cycling runs. Considering the excellent photostability and ultrafast photodegradation of CH3CHO, the current study opens up new perspectives in fabricating MOFs for a wide-range of practical applications.