Raw material | Physical activation | Chemical activation | Highlighted results |
Palm tree branches | 700˚C for 1 hour under steam | At 500˚C for 2 hours Activating agent: Phosphoric acid and K2CO3 | SEM: The highest development of pores could be observed as the concentration of phosphoric acid was increased [44] . pH: The highest percentage removal of Cr (VI) ions was observed at pH 2. |
Olive wastes | 573 K for 3 hours under steam | 1073 K for 1 hour Activation agent: Phosphoric acid and potassium hydroxide | BET: 1375 m2/g and 466 m2/g for the activated carbon impregnated with KOH and phosphoric acid, respectively [45] . Activated carbon impregnated with KOH has the highest micropore volume (0.52 m3/g), mesopore volume (0.3 cm3/g) if compared to phosphoric acid. Adsorption of indigo carmine supported Freundlich model, and pseudo-second order kinetic equation. |
Oak sawdust | 500˚C for 5 minutes | 500˚C for 35 minutes Phosphoric acid | Carbon yield (29.4%), moisture content (4.6%) and ash content (6.6%) for the activated carbon impregnated with phosphoric acid were reported [46] . The Langmuir adsorption of phenol (99 mg/g) and nicotinic acid (99 mg/g) for the activated carbon impregnated with phosphoric acid was highlighted. |
Rice straw | 400˚C for 4 hours | Tube furnace at various temperature (650˚C, 750˚C and 850˚C) KOH | The highest carbon content could be observed for the activated carbon prepared at 850˚C (80.46%) if compared to 650˚C (66.18 %) and 750˚C (70.92%). The highest surface area (1048 m2/g), total pore volume (0.64 cm3/g), micropore volume (0.0436 cm3/g) and mesopore (0.568 cm3/g) could be seen in activated carbon produced at 850˚C [47] . |
Prawn shell | 800˚C for 3 hours | 800˚C for 1 hour KOH | Activated carbon impregnated with KOH showed the highest surface area (3160 m2/g) and pore volume (2.38 cm3/g). XRD: Data supported activated carbon impregnated with KOH has disorder carbon structure and crystallite layer if compared to carbonized sample [48] . The obtained activated carbon can remove Cu2+, Cr6+ and Cd2+ ions. |
Jackfruit peel waste |
| Phosphoric acid | Adsorption capacity of methylene blue was increased with contact time (6, 24 hours), adsorbent dosage (0.5 to 1.5 g) and initial concentration (1 to 2 mg/L) [49] . |
Elaeagnus stone | 600˚C for 6 hours | ZnCl2 | BET surface area and micropore volume strongly depended on the concentration of zinc chloride such as 20% (1121 m2/g, 0.22 cm3/g), 30% (1588 m2/g, 0.08 cm3/g) and 40% (1404 m2/g, 0.01 cm3/g) [50] . Removal of rhodamine B, methylene blue, malachite green fitted with Langmuir isotherm and pseudo second order kinetic model. |