Performance of apricot stone to remove dyes from aqueous solutions – Equilibrium, kinetics, isotherms modeling and thermodynamic studies

Abstract

This study investigates the potential use of activated carbon prepared from Apricot stone with H3PO4 activation as an adsorbent and its ability to removal dyes from aqueous solutions. The quantitative kinetics and equilibrium adsorption parameters for activated carbon ASAC were studied by UV visible absorption spectroscopy. ASAC with a specific surface area (88.04 m2/g) respectively are characterized by the Brunauer-Emmett-Teller (BET) method and the point of zero charge pHpzc.The infrared spectra of (ASM) were recorded with Fourier transform Bomen-Michelson type spectrometer by mixing (AS) sample (∼2% wt.) with KBr of spectroscopic in a range of 4000–400 cm−1. The adsorptive properties of the adsorbent with dyes are conducted at variable process parameters such as initial pH, adsorbent dosage, initial dye ion concentration, contact time and temperature were investigated in their respective range and their optimum conditions were ascertained using batch mode operation to find the optimal conditions for a maximum adsorption. The equilibrium adsorption data for dyes onto ASAC is analyzed by the Langmuir, Freundlich, Elovich, and Temkin models. The results indicate that the Langmuir model provides the best correlation. Kinetic parameters; rate constants, equilibrium adsorption capacities and determination coefficients, for each kinetic and isotherm model were calculated and discussed. The pseudo-second order model fit the kinetic data better than the pseudo-first order model and the intraparticle diffusion and film diffusion mechanisms jointly influenced the adsorption process but the latter was the rate-controlling step.The adsorption isotherms at different temperatures have been used for the determination of thermodynamic parameters such as Free Energy (ΔGo), Enthalpy (ΔHo), Entropy (ΔSo) and Activation Energy (Ea) of adsorption. The negative ΔGo and positive ΔHo values indicate that the overall adsorption is spontaneous and endothermic in nature.