Adsorptions of Astrazon Dye onto Granular Carbon-Silica Aerogels Synthesized from Recycle Palm-Date Pits: Kinetics, Thermodynamic and Isotherm Studies

Abstract

In this work, an environmental friendly management process was achieved to solve solid and liquid hazardous contaminants in our environment. In this case, a granular carbon (gAC) sorbent impregnated with SiO₂ aerogels as composite (gAC/SiO₂) was synthesized from the rceycling of palm-date pits solid waste products to remediate wastewater solution contaminated with Astrazon pink FG cationic dye. The Astrazon dye adsorption onto the gAC/SiO₂ was investigated by compared to gAC sorbent alone using a batch system with respect to initial dye concentration, pH, contact time, solution temperature and adsorbents dosage. It was found the amount of adsorbed dye was strongly depended on pH with low significant important of temperatures levels range from 298 to 318 K. The prepared gAC/SiO₂ aerogels composite exhibits high efficiency for Astrazon dye adsorption by approximately 1.5 times than that of gAC alone. The equilibrium adsorption states could be achieved in 6 h when using gAC/SiO₂ comparable to 12 h by gAC for the different initial dye concentrations. The adsorption kinetics were  found to best described by the pseudo-second order model (PSOM) and pseudo-first order (PFOM)  kinetic models respectively, when using gAC and gAC/SiO₂ sorbents, and poorest-fit with Elvoich equation as confirmed by nonlinear chi-square error test and determination coefficient values. The equilibrium isotherm study indicated that dye adsorption data were analyzed and fitted well by the nonlinear expressions of both Langmuir and Langmuir-Freundlich models compared to Freundlich, Temkin and Redlich–Petersonmodels. The maximum monolayer Astrazon dye adsorption was estimated to be 185.59 and 256.02 µmol/g by gAC and gAC/SiO₂ adsorbents. The positive values of the enthalpy (ΔH°) and negative Gibbs free energy (ΔG°) changes indicate an endothermic as well as feasible and spontaneous nature of the adsorption process respectively.