When thick oil from tanker or pipeline accidents infiltrates the ocean, the clean-up process often generates more waste than oil removed. Traditional synthetic tools, such as polypropylene pads and oil dispersants, consist of toxic chemicals that decompose slowly. To offer a more eco-friendly solution, scientists are looking to natural materials like coconut shells, which can absorb oil without causing additional contamination. This Bio-based material is safe and decomposes naturally without harming the environment.

One category of bio-based materials under investigation for oil spill clean-up consists of long chains known as repeating molecules polymers. Researchers have combined various bio-based polymers to create what are called hybrid materials Composite Materials. These composites include a unique type of highly porous solids primarily made of air—Air Gel. Depending on the material composition, iPhone-sized aerogels can weigh less than small paper clips and are highly porous, allowing them to absorb significant amounts of oil, functioning like an overactive sponge!

Previously, scientists utilized chitosan (CS) derived from crustacean shells to construct bio-based aerogels with sodium alginate (SA) from brown seaweed. However, both CS and SA are water-attracting compounds, Hydrophilicity, causing them to dissolve in water. This makes it challenging to apply them for oil spill clean-ups in bodies of water, as they dissolve before capturing much oil. Additionally, CS-SA aerogels tend to be relatively weak and flexible, raising concerns about their reusability.

To address these issues, researchers at the National University of Singapore developed a new CS-SA aerogel. This enhanced aerogel not only repels water but is also lightweight, durable, and reusable through multiple oil absorption cycles.

To create the aerogels, researchers initially dissolved CS and SA in a solution and sent sound waves through it. The sound waves intertwine polymer chains, releasing and reassembling them into smaller chains of Nanofiber. To counteract the hydrophilic nature of CS and SA, researchers introduced water-repelling agents—Hydrophobicity chemicals such as Methyltrimethoxysilane or MTMS.

The mixture was then poured into a mold and placed in liquid nitrogen. This facilitated the formation of ice crystals within the solution, pushing the nanofibers towards the edges where they bonded to create honeycomb-like microstructures. The researchers then froze the mixture and directly sublimated it into steam to eliminate the water.

After producing the aerogels, researchers assessed their porosity and strength. They employed a high-powered microscope to examine the internal structure of the aerogels and determine how the nanofibers influenced porosity. They discovered that aerogels containing nanofibers are more porous than those without. An increase in nanofiber concentration from 0.5% to 2% resulted in aerogels that are up to 9.5 times stronger, albeit with lower porosity, increasing density by 2.5 times. The team settled on a 1% nanofiber concentration as the optimal formula to balance strength and porosity.

The researchers also evaluated the strength of each aerogel by stretching them and measuring how much deformation they could withstand without losing their shape—a concept referred to as Top yield strength and the force they could handle before failure—Ultimate strength. With increasing amounts of MTM, the aerogels became stronger, boosting yield strength by up to 300% and ultimate strength by 200%. They also tested the recovery of the aerogels after compression, showing that they could regain up to 96% of their original shape and exhibited 32% resilience to compression, with minimal bending or structural deformation.

Finally, researchers examined how effectively the aerogels repelled water and absorbed oils. When placed on the aerogel’s surface, water droplets retained a nearly spherical shape instead of spreading out. The droplets were observed moving across the surface and rolling off without leaving any residue, confirming the hydrophobic nature of the aerogel. To test oil absorption, researchers submerged the aerogels in an oil-water mixture, where the aerogels absorbed more than 90% of the oil volume and weighed 30-90 times their initial mass.

Researchers concluded that their new aerogels could be a powerful and sustainable alternative to synthetic materials for oil spill clean-up. They emphasized that designing materials at multiple scales—ranging from molecules to small fibers—can enhance their strength and performance. They proposed that further advancements could allow these aerogels to support reusable and eco-friendly solutions for oil spill remediation, particularly in sensitive coastal areas.

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