## 1 Introduction  
Wastewater containing organic pollutants poses a significant risk to the entire water body, human health, and aquatic life. Although various wastewater treatment methods such as osmosis, ozonation, advanced oxidation processes (AOPs), coagulation, filtration, photo-degradation, adsorption, etc., have been studied, adsorption is most preferred because it is easier to operate, cheapest amongst most methods, environmentally friendly, and has a wide range of adsorbent choices [1]. Conversely, the success of the adsorption process is solely based on the choice of the adsorbent and the intended use. Traditionally, various adsorbents such as activated alumina, zeolites [2] silica gel, activated carbon [3], etc., are some of the adsorbent choices used during the removal of organic pollutants. However, some of these adsorbents have several disadvantages such as the removal of deposits, higher commercial costs, lower adsorbent regeneration efficiency, and lower surface area [1; 4]. Tea is one of the most popular beverages worldwide, with approximately 20 billion cups of tea consumed daily [5; 6; 7] resulting in approximately 2 million of tea waste generated annually [8]. Tea leaves contain more iron embedded in the native leaf tissue than other biochar precursors such as wood. The heteroatom-doped porous biochar is produced without further doping or immobilization, which is advantageous for activating it with other materials to generate greater reactive oxygen species such as sulfate radicals and singlet oxygen atoms [9]. Although biochar has promising aspects of being a good adsorbent, it has a lower surface area, limiting its capabilities and efficiency [10]. Therefore, to enhance the properties of biochar as an adsorbent, biochar modification has been evaluated. The modification can be via chemical, physical, or mineral impregnation, or even engineered magnetically [10]. Modifying biochar is necessary to enhance its surface area, effectiveness, and surface activities and incorporate it with other beneficial materials [11]. [PERSON] and colleagues noted that using modified metal/biochar composites can also improve the reaction rate [12], whereas other modifications have effects such as reduction, complexation, and enhanced sorption potential [13]. rGO is a rich carbon-containing material and a promising adsorbent. The modification of biochar with rGO will result in an increased surface area and increased carbon content that will aid in the adsorption of organic pollutants, whereas DES is a non-toxic, economically friendly adsorbent. DES has excellent properties and is easily manipulated into designer adsorbents. Hence, the introduction of DES-CTAB and DES-glycerol will aid in the incorporation of desired functional groups. Several studies have been conducted that prove that the modification of biochar with other materials is beneficial and greatly improves biochar's adsorption capabilities. [PERSON] et al., 2021 studied activated porous biochar adsorbent made from tea and plane tree leaves biomass for the removal of promipexole dihydrochloride from aqueous solutions [14]. [PERSON] et al. (2019) researched the removal of dye from wastewater using acid-modified tea leaves (AMTL) as an adsorbent [15]. [PERSON] et al. (2018) used activated carbon made from spent tea leaves for the removal of pharmaceutical waste from contaminated aqueous solutions [16]. [PERSON] et al., 2013 studied the removal of phenol compounds from contaminated water using activated tea leaves as an adsorbent [17]. These studies are evident enough to prove that biochar modification can greatly improve biochar's overall characteristics and properties. However, the methods of modification in previous studies were not in line with green chemistry guidelines. These studies used harsh, toxic, and large quantities of chemicals to synthesize materials such as GO and rGO [18; 19]. Furthermore, it is important to note that the current study used methods and chemicals that comply with green chemistry principles.