Methylene blue dye adsorption onto activated carbon developed from Calicotome villosa via H3PO4 activation

Powdered activated carbon (AC) was prepared from biomass resource ( Calicotome villosa ) by H 3 PO 4 activation. The optimal activation conditions were determined according to iodine number and the yield of prepared AC. The best activation conditions were obtained by using 100 mL of H 3 PO 4 (50%wt) solution to activate 20 g of raw material, and by applying a pyrolysis temperature of 500 °C for 1 h. The highest iodine number 997 mg/g was obtained for the previous AC with an activation yield equal to 45%. The prepared AC was characterized by Fourier transform infrared spectroscopy (FTIR); X-ray diffraction (XRD); Brunauer, Emmett, and Teller (BET) surface area; scanning electron microscope (SEM); and the point-of-zero charge (pH PZC ) method. AC showed high BET surface area (1051 m 2 /g) and pH PZC equals 2.50, indicating the suitability for cationic pollutants removal from aqueous solutions such as methylene blue (MB). The effect of AC dosage (25–150 mg), contact time (5–150 min), initial MB concentration (100–300 mg/L), and temperature (298–330 K) on MB adsorption was investigated in batch mode. Adsorption kinetics is described well by the pseudo-second order model with correlation coefficient R 2 = 0.9969, while the experimental adsorption isotherm data are better fitted by the Freundlich isotherm with adsorption intensity 1/n = 0.2109 which indicates the favorability of the adsorption. It was also found that the adsorption process is spontaneous and endothermic. The results showed that Calicotome villosa wood is a promising biomass precursor to develop an efficient activated carbon. Graphical abstract