**12. Case studies of green adsorbents**

The utilization of waste tea residue, a green biosorbent, for the removal of heavy metals from water, was investigated in a study by Wang et al. [39]. It was discovered that the discarded tea residue had significant potential for adsorbing elements like lead (Pb), cadmium (Cd), and copper (Cu). The performance of the biosorbent was on par with or even better than that of traditional adsorbents. The study showed the potential of using waste products as environmentally friendly adsorbents for heavy metal removal.

Chitosan-Based Adsorbent for Dye Removal: Chitosan, a green adsorbent derived from crustacean shells, was modified and used to remove dye pollution in a study by Zhang et al. [40]. For a variety of colors, the modified chitosan shows outstanding adsorption capacity and great removal efficiency. Chitosan may be used as an environmentally acceptable adsorbent for color removal in wastewater treatment, according to the study.

A Plant-Based Adsorbent for the Removal of Pharmaceuticals *Azadirachta indica* leaves, a waste plant product, was employed as a green adsorbent in a study by Verma and Dash [41] to remove pharmaceuticals from water. Ibuprofen, paracetamol, and naproxen were only a few of the pharmaceuticals that the plant-based adsorbent effectively absorbed. The study showed that using plant-based materials as green adsorbents for drug removal is feasible.

Ahmad et al.'s [42] study looked into the usage of biochar made from agricultural waste for the removal of organic contaminants, especially bisphenol A (BPA). The BPA levels in the water were significantly reduced by the biochar's strong BPA adsorption ability. The study demonstrated the potential of using biochar as an environmentally friendly adsorbent for the elimination of organic contaminants.
