Synthesis and characterization of nano zinc oxide/zinc chloride–activated carbon composite based on date palm fronds: adsorption of methylene blue

Zinc chloride–activated carbon (AC) and nano zinc oxide/activated carbon composite (NZAC) as solid adsorbents were synthesized from date palm fronds (DPF) as a green material of activated carbon, while zinc oxide nanoparticles (NZ) were prepared in the presence of polyethylene glycol as capping agent. All the prepared solid adsorbents were investigated by several characterization techniques such as thermogravimetric analysis (TGA), nitrogen adsorption/desorption isotherm, Fourier transform infrared spectroscopy (FTIR), pH of point of zero charges (pH PZC ), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The NZAC sample had the highest total pore volume (0.960 cm 3 /g), specific surface area (2085.47 m 2 /g), and with pH PZC of 7.8. Adsorption of methylene blue was tested by Langmuir, Freundlich, and Temkin adsorption isotherms. NZAC had the highest Langmuir adsorption capacity (456.62 mg/g) at 40 °C with a dimensionless separation factor ( R L ) of 0.030. MB adsorption matched well with pseudo-second-order and Elovich kinetic models. The entropy, free energy, and heat changes for MB adsorption onto NZAC were found to be 0.0243 (kJ/mol. K), − 3.5589 (kJ/mol), and 3.561 (kJ/mol), respectively. Thermodynamic analysis demonstrated that the adsorption process of MB is favorable, spontaneous, physisorption, and endothermic. Desorption studies showed that HCl (0.01 mol/L) achieved the higher desorption percent (87%) compared with the other eluents.