Removal of tetracycline by NaOH-activated carbon produced from macadamia nut shells: Kinetic and equilibrium studies

A NaOH-activated carbon was prepared from macadamia nut shell using the impregnation ratio of 3:1 (NaOH:char) (wt:wt). The obtained material (ACM) was characterized by several techniques and methodologies such as, N2 adsorption–desorption isotherms, SEM, FT-IR, Boehm titration, and pHpzc. The results demonstrated that the ACM is composed mainly of micropores (78.2%), presenting BET surface area of 1524 m2 g−1. Through the SEM and FT-IR analysis it could be observed that significant changes occurred on the material surface after the activation procedure. According to Boehm titration, the ACM has on its surface a majority of basic groups which is in agreement with the obtained pHpzc value of 8.74. The ACM was applied for tetracycline (TC) removal in order to assess its potential as an adsorbent. Thus, adsorption studies were carried out and several kinetic and isotherm models were employed. The isotherm model which best fitted to experimental data was Temkin, while the best fitted kinetic model was Elovich. ACM showed maximum monolayer adsorption capacity (Qm) of 455.33 mg g−1. The intraparticle diffusion and film diffusion mechanisms were studied by the equations of Weber & Morris and Boyd, respectively. According to the results, the limiting step of the adsorption of TC onto ACM is influenced by intraparticle diffusion and by film diffusion.