Optimization of preparation of microporous activated carbon with high surface area from Spartina alterniflora and its p-nitroaniline adsorption characteristics

Spartina alterniflora activated carbon (SAAC) was prepared by chemical activation with potassium hydroxide. The effects of four preparation variables: carbonization temperature, KOH:char impregnation ratio, activation temperature, and activation time on the iodine and p-nitroaniline adsorption onto the SAAC samples were investigated. Taguchi experimental design method was applied to optimize the preparation of SAACs. Optimized parameters were carbonization temperature of 450 °C, impregnation ratio of 3:1, activation temperature of 800 °C, and activation time of 90 min, respectively. The surface characteristics of the SAACs were examined by pore structure analysis and scanning electron microscopy (SEM). Pore structure analysis showed that micropores constitute 86.75% of the porosity of the SAAC prepared at optimized conditions (SAAC-1) with a large pore volume of 1.374 cm3/g, and the BET surface area is up to 2825 m2/g. The adsorption equilibrium, kinetics and mechanism of p-nitroaniline onto SAAC-1 were carried out to investigate its adsorption ability. The results showed that the maximum adsorption capacity for p-nitroaniline was approximately 719 mg/g. The pseudo-second-order model was found to explain the adsorption kinetics most effectively. The intraparticle diffusion played an important role in the adsorption and primarily controlled the adsorption rate. The negative change in free energy, negative change in entropy, and negative change in enthalpy indicated that the adsorption was a spontaneous and exothermic process, which was primarily driven by enthalpy change. The findings indicated that the microporous S. alterniflora activated carbon with high surface area is a potential high effective absorbent for p-nitroaniline removal from aqueous solutions.