Potential of used Camellia sinensis leaves as precursor for activated carbon preparation by chemical activation with H3PO4; optimization using response surface methodology

In this study, an attempt was made to produce a low cost activated carbon (AC) from a cheap precursor material, used tea leaves (UTLs) by chemical activation with H3PO4. The operating variables of the preparation process were optimized by central composite design (CCD), a subset of response surface methodology (RSM). The conditions optimized were activation temperature, chemical impregnation ratio (IR) and activation time with % age yield, iodine (I2) and methylene blue (MB) number as the targeted responses. The optimization was carried out to maximize yield, I2 and MB number values. The optimal preparation conditions were determined as: activation temperature of 600 °C, IR of 1.30 and activation time of 130 min, under which a carbon yield 33.55%, I2 and MB uptake of 1051 mg g−1 and 321 mg g−1 respectively, could be achieved. The surface properties of optimized AC were characterized by various physio-chemical techniques including scanning electron microscope imaging (SEM), FTIR analysis, surface area and X-rays diffraction analysis, Boehm's titration, point of zero charge (pHPZC) and proximate-ultimate analysis. The results showed that the surface of AC was highly porous with many channels and cracks and has acidic nature, have large amount of acidic functional groups and low ash content.