Nanostructured aerogels for adsorptive removal of pharmaceutical pollutants from wastewater: A review on synthesis and application

The pharmaceuticals including antibiotics, analgesics, antidepressants, and hormones, etc. are produced in large quantities and subsequently discharged into the environment. Such toxicants are found in aquatic systems and can seriously ruin the water quality subsequently affecting human health and other components in the ecosystem. Aerogels are light weight porous materials that are potentially alternative of powdered nanomaterials for wastewater treatment. The aerogel-based adsorbents have found excellent properties including low density, highly stable, reusable, and easy to separate from solution. This review summaries the synthesis, and tailoring strategies of various types of aerogels for drug adsorption. The adsorption mechanisms and parameters affecting the adsorption of pharmaceuticals onto aerogels have been discussed. Freeze-drying (FD) is the most investigated method compared to supercritical drying because of its low energy consumption and consequent benefits to the environment. The aerogels based on a single material demonstrated a lower adsorption rate than the customized multifunctional hybrid aerogels. The adsorption efficiency of aerogels can be increased by chemical modifications including amination, carboxylation, and sulfonating. This review also explored the mechanistic insight of different drug adsorption onto various aerogels. Hydrogen bonding, electrostatic interaction, π-π stacking, and hydrophobic interactions, etc. are primary forces involved in the drug molecules' adsorption onto aerogels. The literature demonstrated that aerogel materials can be reused for several adsorption-desorption cycles. Furthermore, the sustainability footprint approach was utilized to assess the sustainability of nano-structured aerogels in comparison to alternative materials used for water purification.