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Oil contamination from various human activities (such as oil spills from production, transportation, shipping, and storage) and natural events (e.g., natural seepage) has caused significant environmental, ecological, and economic impacts. Enhancing the adsorption efficiency of adsorbent materials for high-viscosity oil remains a significant challenge for researchers.

A research team from the University of Alberta has developed a highly robust, compressible, anisotropic, and fire-retardant aerogel adsorbent composed of polyimide (PI), hydroxyapatite nanowires (HAPnws), and reduced graphene oxide (rGO). This innovative material leverages reduced flow tortuosity through its anisotropic structures and solar-assisted viscosity reduction via photothermal materials. The findings are in the journal Research.

"It is challenging for most conventional porous adsorbent materials to efficiently adsorb viscous oils," said Hongbo Zeng, who led the research. "This is because randomly distributed pores exert high resistance to oil flow, particularly for highly viscous oils, preventing the oil from penetrating the internal space of the adsorbent materials. This results in low adsorption capacity and slow adsorption rates."

Inspired by the aligned channels in wood, which facilitate rapid water transport, the authors believe that fabricating porous materials with aligned channels using directional freeze-casting can significantly enhance the adsorption efficiency for viscous oils. In addition, incorporating photothermal materials to reduce oil viscosity through photothermal effects is a promising strategy to improve the adsorption performance of porous adsorbents for viscous oils.

The anisotropic PI/HAP/rGO aerogel developed in this work features vertically aligned channels, enabling superior adsorption efficiency (with an adsorption coefficient Ks 0.37 Kg m^-1 s ^-1/2 for engine oil with a viscosity of 144.36 mPa·s) for oils of varying viscosities compared to aerogels with uniform pores, thanks to the significantly reduced flow tortuosity.

Meanwhile, the photothermal properties of rGO enhance the adsorption speed of PI/HAP/rGO under sunlight, even for ultra-high-viscosity crude oil. In addition, PI/HAP/rGO exhibits excellent fire resistance, allowing reusability via both adsorption-compression and adsorption-combustion cycles.

This study provides valuable insights into the design of porous adsorbents for highly viscous oils, with the PI/HAP/rGO aerogel showing great potential for the rapid cleaning and recovery of viscous oil spills.