Selected pharmaceuticals removal using algae derived porous carbon: experimental, modeling and DFT theoretical insights

Abstract

Porous carbon from Laminaria digitata algae activated using NaOH (PCLD@NaOH) was prepared by a chemical activation approach and has been tested for the adsorption of ketoprofen and aspirin molecules. The prepared PCLD@NaOH was characterized using XPS, FTIR, Raman, N₂-physisorption, SEM, acidic/basic character (Boehm), and pH_PZC. The batch adsorption of ketoprofen and aspirin was investigated under different parameters. The adsorption kinetics on PCLD@NaOH were well described by the Avrami-fractional kinetic model and the equilibrium data by Liu isotherm model. The adsorption capacity of aspirin (970.88 mg g^-1 at 25 °C) was higher than ketoprofen (443.45 mg g^-1 at 25 °C). The thermodynamic values indicate that the adsorption of ketoprofen and aspirin is exothermic and spontaneous. These results were in good agreement with DFT calculation that shows that the aspirin molecule presents high reactivity, electrophilicity, and softness compared to the ketoprofen molecule. Finally, the response surface methodology was used to optimize the removal efficiency of ketoprofen and aspirin.

Fig. 1. (a) XPS survey scans; (b) high-resolution fitted XPS C 1s; (c) high-resolution fitted XPS O 1s, (d) high-resolution fitted XPS N 1s.

Fig. 2. (a) FTIR spectra; (b) Raman spectra; (c) adsorption–desorption isotherm; (d) SEM image of PCLD@NaOH.

Fig. 3. (a) Effect of adsorbent mass; (b) effect of pH solution (c) point of zero charges pH_PZC.

Fig. 4. Nonlinear kinetic model: pseudo-first-order (PFO), pseudo-second-order (PSO), intraparticle diffusion (IPD), and Avrami fractional model of (a) aspirin (b) ketoprofen.

Fig. 5. Nonlinear isotherm models: Langmuir, Freundlich, and Liu of (a) ketoprofen (b) aspirin.

Fig. 6. (a) Linear dependence of ln K_c on 1/T based on the adsorption thermodynamics; (b) regeneration and recyclability of PCLD@NaOH over five cycles of use.

Fig. 7. FTIR analysis before and after adsorption of aspirin and ketoprofen onto PCLD@NaOH.

Fig. 8. Schematic representation of the proposed mechanism.

Fig. 9. Optimized geometry of ketoprofen, the electrostatic surface potential (ESP), highest occupied orbital (HOMO), and lowest molecular orbital (LUMO) structure computed using DFT method.

Fig. 10. Optimized geometry of aspirin, the electrostatic surface potential (ESP), highest occupied orbital (HOMO), and lowest molecular orbital (LUMO) structure computed using DFT method.

Fig. 11. RSM presentations for ketoprofen adsorption on different possible plans (a) adsorbent dose – pH (b) pH – concentration (c) concentration – temperature and (d) adsorbent dose – temperature.

Fig. 12. RSM presentations for aspirin adsorption on different possible plans (a) adsorbent dose – pH (b) pH – concentration (c) concentration – temperature and (d) adsorbent dose – temperature.