# Fine Activated Carbon from Rubber Fruit Shell Prepared by Using ZnCl\({}_{2}\) and KOH Activation
## 1 Introduction  
Nowadays, activated carbon is used in many industrial applications, including gas storage/adsorption [1, 2], wastewater treatment [3, 4, 5], catalyst support [6], air purification [7], and supercapacitors [8, 9]. In recent years, biomass has attracted significant attention for the preparation of activated carbon [10], due to its renewable nature, low price, minimal environmental impact, and abundant supply [11]. Many different biomass materials have been proposed, including coconut shell [12], cashew shells [13], rice hunks [14, 15], durian skin [16], sugarcane trash and corn crops [17, 18, 19], potato starch [20], and banana skin [21] However, these materials typically have low carbon content, high volume-to-weight ratio, and high ash content [22]. Accordingly, studies on developing alternative, low-cost carbon sources continue to attract significant attention from researchers.  
According to the Republic of Indonesia Ministry of Agriculture [23], Indonesia has an estimated 3.671.387 ha of rubber plantations. On average, a rubber plantation produces around 1000 kg/ha/yr of rubber seed or fruit [24]; equivalent to roughly 3.6 million tons of rubber fruit shells (RFSs) per year. While rubber seeds can be used to produce rubber seed oil [25], the majority of the shells are left as plantation waste, and hence pose a major environmental concern. Accordingly, in this study, we explore the feasibility of using RFS as a precursor material for the preparation of fine activated carbon (FAC).  
The preparation of activated carbon generally involves two steps, namely pyrolysis (or precursor carbonization) and activation [25]. The activation step may be performed using either physical or chemical methods [25]. Chemical methods use many different activators, including alkali (e.g., KOH and NaOH), acidic (e.g., H\({}_{3}\)PO\({}_{4}\) and H\({}_{2}\)SO\({}_{4}\)), and chemical compound salt (e.g., AlCl\({}_{3}\) and ZnCl\({}_{2}\)) [26]. Among these agents, KOH and ZnCl\({}_{2}\) are two of the most commonly used agents, since their chemical activation can produce the highest surface area and yield values [26, 27]. Generally speaking, the activation performance of chemical agents is strongly dependent on the temperature at which the activation process is performed. For example, the optimal temperatures for KOH and ZnCl\({}_{2}\) are around800 \({}^{\circ}\)C [28; 29; 30; 31] and 500 \({}^{\circ}\)C [32; 33; 34], respectively. However, while KOH and ZnCl\({}_{2}\) are commonly used in the preparation of activated carbon nowadays, the literature contains little information on their use in preparing FAC with RFS as a precursor.  
Accordingly, in the present study, we prepare activated carbon using RFS as raw material and KOH and ZnCl\({}_{2}\) as activating agents. In performing the activation process, the temperature is set at 800 \({}^{\circ}\)C for the KOH agent and 500 \({}^{\circ}\)C for ZnCl\({}_{2}\). For both activating agents, the activation process is performed using three different impregnation ratios, namely 1:3, 1:4, and 1:5. Following the activation experiments, the properties of the various RFSACs (i.e., the element composition, specific surface area, pore size distribution, and structure) are systematically explored to determine the optimal activation agent and processing conditions for large-scale preparation of FAC utilizing RFS as a low-cost, green carbon source.