Biomimetic Light-Driven Aerogel Passive Pump for Volatile Organic Pollutant Removal

Abstract

Inspired by the solar-light-driven oxygen transportation in aquatic plants, a biomimetic sustainable light-driven aerogel pump with a surface layer containing black manganese oxide (MnO₂ ) as an optical absorber is developed. The flow intensity of the pumped air is controlled by the pore structure of nanofilbrillated cellulose, urea-modified chitosan, or polymethylsilsesquioxane (PMSQ) aerogels. The MnO₂ -induced photothermal conversion drives both the passive gas flow and the catalytic degradation of volatile organic pollutants. All investigated aerogels demonstrate superior pumping compared to benchmarked Knudsen pump systems, but the inorganic PMSQ aerogels provide the highest flexibility in terms of the input power and photothermal degradation activity. Aerogel light-driven multifunctional gas pumps offer a broad future application potential for gas-sensing devices, air-quality mapping, and air quality control systems.

Keywords: VOCs degradation; aerogel; manganese oxide; passive pump; thermal transpiration.

Figure 1

Aerogel membranes implemented with surface‐active absorber layer. Photos of A) polymethylsilsesquioxane (PMSQ) based bilayer aerogels. B) SEM and C) HRTEM image of MnO₂ nanoflakes with the selected area electron diffraction (SAED) pattern of MnO₂ embedded in PMSQ. TEM of MnO₂ nanoflakes embedded in D) nanofibrillated cellulose (NFC), E) urea‐modified chitosan (UMCh), and F) PMSQ aerogels. 3D volume rendering based on X‐ray tomography of the top absorber layer cutout of the low‐density aerogel matrix (red) with shown/separated MnO₂ nanoflakes (grey, 10 wt%) embedded in G) NFC (178.75 × 178.75 × 157.63 µm³, stacks of 1100 cross sections), H) UMCh (211.25 × 1625.00 × 28.11 µm³, stacks of 1000 cross sections), and I) PMSQ aerogel matrix (363.68 × 351.00 × 61.10 µm³, stacks of 2160 cross sections).

Figure 2

Effect of pore size and structure on pumping performances. Thermal transpiration across A) cellulose nanofibrillar (NFC), B) urea‐modified chitosan (UMCh), and C) polymethylsilsesquioxane (PMSQ) nanoparticulate aerogel structures. White represents the neat aerogel structure; brown represents the aerogel matrix with embedded MnO₂. The blue and red arrows depict the air molecules’ movement. D) Contour plots of K _n as a function of pore diameter and temperature at 1 bar of air pressure. The test conditions for the NFC, UMCh, and PMSQ membranes are indicated by symbols. E) Pumping performance indicated by the mass and volumetric flow rates and temperature difference per unit sample thickness (∆T/t) after irradiation at 20 cm (97 mW cm²) and 5 cm (222 mW cm², PMSQ only). F) Flow rate versus power input and comparison with state of the art (Tables S2 and S3, Supporting Information). The performance of reported Knudsen pumps (KP) made from porous materials and lithographic microchannels are highlighted using full and open black triangles, respectively.

Figure 3

Pollutant degradation performance of the dual‐functional aerogel membranes. A) Adsorption capacity and B) degradation efficiency of toluene and steady‐state temperature on the irradiated surface (T _HOT). C) X‐ray diffraction (XRD) patterns of NFC, UMCh, and PMSQ samples with 10 and 50 wt% of MnO₂. D) Thermogravimetric analysis (TG and derivative TG) of pristine aerogel materials. XPS spectra of the absorber layer (50 wt% MnO₂): E) Mn2p_3/2 electron energy overlay of neat MnO₂ and MnO₂ embedded in aerogels, and a list of full width at half maximum. F) FTIR spectra of pure PMSQ, UMCh, and NFC aerogels (more details in Figure S17, Supporting Information).

Figure 4

Toluene degradation performance of MnO₂‐PMSQ membrane. A) Toluene concentration evolution as a function of the irradiation time. B) Comparison of the state‐of‐the‐art for VOC degradation efficiency versus irradiation intensity (Table S5, Supporting Information). C) Solar‐driven thermal transpiration with simultaneous photothermal catalytic VOC degradation (left panel) with scanning electron microscopy (SEM) and energy dispersive X‐ray analysis (EDX) images of MnO₂‐PMSQ and PMSQ aerogel interface (right upper panel), and representation of photothermal conversion on MnO₂ nanoflakes (right lower panel).