Advances in lemon peel‐based adsorbents for wastewater treatment applications

Water pollution threatens the environment and human health. Treatment methods must be sustainable and affordable. Lemon peel‐based adsorbents offer a practical option for wastewater treatment. This review assesses their preparation, performance, mechanisms, and application. The adsorbents were classified into lemon peel biosorbents, activated carbon, biochar, and composites. Adsorbent modification was found to improve performance. Chemically modified lemon peel adsorbents achieved high maximum adsorption capacities, particularly for lead(II), among the heavy metals reviewed, with performance influenced by pH, adsorbent dosage, temperature, initial pollutant concentration, and contact time. Most systems followed Langmuir isotherms and pseudo‐second‐order kinetics. These patterns point to chemisorption dominated by ion exchange, electrostatic attraction, and hydrogen bonding. Thermodynamic analysis showed negative Gibbs free energy values, indicating spontaneous processes. Regeneration tests showed that appreciable adsorption capacity was retained after repeated cycles. Competitive adsorption showed strong selectivity with little interference from common ions. Mechanistic studies showed multiple adsorption pathways, including surface complexation, which binds metals to oxygen‐containing groups; π–π stacking, which secures aromatic pollutants; and electrostatic forces, which attract charged species. Lemon peel‐based adsorbents provide low‐cost and environmentally friendly alternatives for wastewater treatment. They convert agricultural waste into useful treatment materials. Such conversion supports waste valorization and circular economy principles while addressing global water quality challenges.