Conventional approaches for recycling metal waste are energy-intensive and some also generate environmentally harmful byproducts such as ammonia and methane during aluminum recycling. To address this challenge, researchers demonstrated an eco-friendly technique to convert aluminum and magnesium waste into high-value, multifunctional aerogels. This upcycling method could be applied to all types of metal waste such as metal chips and electronic waste.
The approach does not produce any hazardous waste, consumes less energy, and is more environmentally friendly than conventional recycling methods for metal waste. The metal-based aerogels created using the fabrication technique have high thermal and mechanical stability, making them candidates for heat and sound insulation in harsh environments with high-temperature or high mechanical impact.
The team developed a simple fabrication process to create metal-based aerogels. Metal waste is first ground into powder and mixed with chemical cross-linkers. The mixture is heated in the oven, frozen, and then freeze-dried to create the aerogel. The process may vary slightly, depending on the metal waste involved. On average, it takes about one to three days to transform powdered metal waste into aerogels, compared to three to seven days using conventional methods of producing aerogels.
Aerogels are highly absorbent, extremely light, and have excellent thermal and sound insulation capabilities. The properties of aerogels can be altered by coating them with chemicals; for example, they can become water-repellent or fire-resistant.
Aluminum aerogel is 30 times lighter and insulates heat 21 times better than conventional concrete. When optical fibers are added during the mixing stage, translucent aluminum aerogels can be created that, as building materials, can improve natural lighting, reduce energy consumption for lighting, and illuminate dark or windowless areas. Translucent concrete can also be used to construct sidewalks and speed bumps that light up at night to improve safety for pedestrians and road traffic.
When coated with a chemical called methyltriethoxysilane (MTEOS), aluminum aerogels can repel water and become a self-cleaning construction material that allows dirt or debris to be easily washed away when it comes into contact with water. Metal-based aerogels are also suitable as fire-retardant boards, thermal insulation materials in buildings and piping systems, for absorption of airborne contaminants for indoor environments, and oil spill cleaning.
Aluminum aerogels also could be used as microcarriers for cell cultivation. Microcarriers are micro-sized beads on which cells anchor and grow. To be used as microcarriers, aluminum aerogels are ground into powder and added to the mixture of cells and growth media (including nutrients, antibiotics, and growth supplements). The cells are cultivated at 37 °C in an incubator for 12 days. The microcarriers are then removed and the cells are harvested for various uses.
In the next phase of research, the team is looking at developing metal-based aerogels for applications that require extremely high temperature tolerance such as for military applications.