Direct CO2 capture from simulated and ambient air over silica-rich MIL-101(Cr)

Abstract

Metal–organic frameworks (MOFs) are efficient adsorbents, but their application for low-concentration direct CO₂ capture is mostly limited to amine-incorporating MOFs. Herein, the textural properties of the MOF [MIL-101(Cr)] are tuned by in situ incorporation of silica-rich rice husk ash (RHA) in MIL-101(Cr) to achieve enhanced CO₂ capture from simulated and indoor ambient air over RHA-MIL-101(Cr). With an optimised loading of RHA, RHA-MIL-101(Cr) exhibited over 2.4 times higher CO₂ capture (1.06 mmol g⁻¹) as compared to the pristine MIL-101(Cr) (0.45 mmol g⁻¹), owing to 48% enhanced micropore volume and 16% high ultra-micropore volume upon RHA incorporation in MIL-101(Cr). Notably, both powdered and structured forms of the high-performing RHA-MIL-101(Cr) showed better cyclic stability with no significant loss in CO₂ capture under simulated (400 ppm CO₂ in He) and indoor ambient air (≥400 ppm CO₂ in air) conditions at room temperature. The enhanced CO₂ capture performance (high capacity and kinetics) of the studied silica-rich RHA-MIL-101(Cr) adsorbents as compared to MIL-101(Cr) demonstrated the suitability of these adsorbents for direct air capture (DAC) application.