From Waste to Value: Banana-Peel-Derived Adsorbents for Efficient Removal of Polar Compounds from Used Palm Oil  
[PERSON]  
1 Department of Chemistry, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand;  
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2 Center of Excellence for Innovation and Technology for Detection and Advanced Materials, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand;  
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2 Center of Excellence for Innovation and Technology for Detection and Advanced Materials, Faculty of Science, Naresuan University, Phitsanulok 65000, Thailand;
broad applications across various fields, such as water purification, oil spill remediation, and as supports for catalytic reactions [3; 4; 5; 6]. The fabrication of porous adsorbents from banana peel waste involves several essential stages, including the pre-treatment of raw banana peels, calcination, chemical activation, and post-treatment procedures. These steps are carefully designed to enhance the adsorption properties of the material by substantially increasing its surface area and facilitating the formation of a well-defined porous structure. Conventional chemical activation techniques commonly employ potent chemical agents, such as sodium hydroxide (NaOH), potassium hydroxide (KOH), phosphoric acid (H\({}_{3}\)PO\({}_{4}\)), and sulfuric acid (H\({}_{2}\)SO\({}_{4}\)) [7; 8]. Despite their effectiveness, these methods present considerable challenges, including safety hazards during handling, high production costs, and environmental issues due to the generation of hazardous waste. To overcome these challenges, acetic acid has been investigated as a sustainable chemical activation agent due to its widespread use in both household and industrial applications, offering a safe and cost-effective approach for the production of porous adsorbents. In the future, banana chip industries could use commercially available acetic acid to produce porous adsorbents on their own. This method offers a practical and eco-friendly solution for both small- and medium-sized enterprises (SMEs) and larger industries. The production of banana chips in small- and medium-sized businesses often generates substantial quantities of used palm oil during the frying process, posing a common operational challenge. The recycling of used palm oil has the potential to lower costs, as it contains numerous polar molecules. Effective removal of these molecules through adsorption could address this issue. This process is important because the quality of used cooking oil is determined by key indicators of degradation, such as the free fatty acid content, the peroxide value, and the concentration of polar compounds. Free fatty acids (FFAs) serve as critical indicators of oil hydrolysis and are widely monitored to assess oil quality. According to the Ministry of Public Health in Thailand, fresh oils with FFA levels exceeding 2% are generally deemed unsuitable for consumption. For used oils, it is advised that they be discarded once the FFA content reaches a threshold of 5% [9]. Peroxide values (PVs), which reflect the degree of lipid oxidation, are essential indicators for evaluating oil quality. For oils designated for food-grade applications, PVs must remain below 10 meq O\({}_{2}\)/kg to ensure compliance with safety and quality standards [10]. Polar compounds, including polymerized triglycerides, free fatty acids, and secondary oxidation products, are also regulated to preserve oil quality and safety. Specifically, the polar compound content in used cooking oil is typically restricted to a maximum of 25% for continued use in food frying [11]. Exceeding this limit renders the oil unsuitable for consumption and poses significant health risks. In the adsorption process, activated carbon and other carbon-based materials are extensively utilized as adsorbents to mitigate degradation markers, owing to their high surface area, significant porosity, and robust capacity for adsorbing polar molecules [12; 13; 14; 15; 16; 17; 18; 19]. [PERSON] et al.