Low cost adsorbents derived from vegetables and fruits: Synthesis, properties, and applications in removal of heavy metals from water

Vegetable and fruit-derived adsorbents are quite popular in adsorptive removal of heavy metal ions from aqueous media because of their greenness, abundance, low-cost, easy synthesis, renewability, and excellent efficiency. They are used both in the original or modified forms. The physicochemical properties that impact the adsorption behaviour of vegetable and fruit-derived adsorbents include surface area, porosity, functional groups, modification or functionalization, chemical and thermal strength, and others. Such adsorbents can be synthesized by a variety of routes that involve physical, chemical or both treatments. Among several factors, solution pH, initial metal concentration, amount of adsorbent, temperature, and contact time are critical for the performance evaluation of such adsorbents for removal of heavy metals. The potential adsorption mechanisms indicated in several studies include physical adsorption, chemisorption, electrostatic interactions, hydrogen bonding, π-π interactions, and precipitation among others. Many of such adsorbents can be easily regenerated and employed for several cycles without compromising their adsorption performance. In this review, we critically discuss physicochemical properties, synthesis, applications in removal of metals, affecting parameters, adsorption mechanisms, and regeneration potential of vegetable and fruit-derived adsorbents. In the end, a brief account of advantages, limitations and challenges is provided. In summary, this review presents valuable insights, challenges, and prospects for enhancing the efficiency of vegetable and fruit-derived adsorbents. It will be beneficial for researchers focused on developing new adsorbents for removing heavy metals from aqueous media.