The effect of steam on the physicochemical properties of activated carbons based on Ziziphus jujube stones for reactive dye removal

Activated carbons (JSAC45 and JSAC55) were fabricated via both processes of pyrolysis and gasification using steam with burn-off of 45 and 55%. These materials derived from Ziziphus jujube were characterized by the adsorption–desorption of N₂, thermogravimetric analyzer coupled with mass spectrophotometer (TGA/MS), electron microscope (SEM), Fourier transform infrared spectroscope (FTIR), Boehm titration, and pH_PZC. The specific surface area (S_BET) of activated carbons was 953 m²/g for both materials with the predominance of basic character (\({\mathrm{pH}}_{\mathrm{PZC}}\cong 10)\). Then, the prepared carbons were used to adsorb BEZAKTIV Red S-Max (RS). The effect of initial RS concentration (10–100 mg/L), contact time (0–1440 min), pH (2–10), and temperature (25–45 °C) on adsorption capacity of JSAC45 and JSAC55 were examined; and it was revealed that RS dye was well adsorbed at pH = 10. The equilibrium adsorption data suggested that the Langmuir model fitted well the RS dye adsorption, and the pseudo-second-order model best fitted the adsorption kinetic data. The maximum of adsorption capacity of RS onto JSAC55 was 113.3 mg/g. Thermodynamics studies of JSAC45 and JSAC55 indicated that the adsorption process was endothermic, spontaneous, and feasible. The activated carbons were reused after applying the thermal regeneration process. The Ziziphus jujube adsorbents could adsorb industrial wastewater (IW) with an elimination rate of about 40% for both adsorbents. These results confirm that the Ziziphus jujube stones may be considered as an inexpensive and promising precursor for commercial activated carbons production.