*2.2. Synthesis of Activated Carbon*

Eucalyptus leaves were collected from the surrounding of NIT Warangal, India. Eucalyptus leaves were pre-treated with DI water and dried, oil was extracted from the eucalyptus leaves using steam distillation. After extracting oil, the left over bio-waste (eucalyptus residue) was dried at 80 ◦C for 8 h. The dried biomass was crushed in fine powder by using a mortar and pestle and sieved with a mesh size of 60 to 80. The resultant eucalyptus leaves powder (ELP) was carbonized in tubular furnace under an inert atmosphere (nitrogen) with an inlet flow rate of 75 mL min−<sup>1</sup> . The furnace consist of PID temperature controller with long tube of length 160 cm and the diameter of 40 mm. Inside the tubular furnace a quartz boat is used to hold the sample. The ELP was carbonized at 300 ◦C for 1 h. @ 5 ◦C min−<sup>1</sup> . Next, the samples were mixed with ZnCl<sup>2</sup> in the proportion of 1:4 (ZnCl2: sample). The obtained mixture was agitated to create a homogenous slurry and dried for 12 h and at 100 ◦C. The resultant products were then carbonized to 400–800 ◦C for 1 h. @ 5 ◦C min−<sup>1</sup> under an inert atmosphere. The product was dried at 80 ◦C for 10 h. After the process was completed, the material was cooled and taken from the tubular furnace. The carbonized material was then rinsed with 1 M HCl till the pH reached 7 and then filtered and dried for 12 h at 100 ◦C. The resultant product of this post-treatment was activated carbon, abbreviated as AC. The AC was labelled as AC-x, where x (*x* = 400 to 800 ◦C) represents the carbonization temperature and stored AC-x materials in sample bottles.
