Sustainable waste management and recycling of Zn-Al layered double hydroxide after adsorption of levofloxacin as a safe anti-inflammatory nanomaterial

Abstract

Inorganic nano-layered double hydroxide (LDH) materials are used in the catalytic field, and have demonstrated great applicability in the pharmacological fields. In the current study, we report Zn-Al LDH as an adsorbent for levofloxacin (levo). The physical and chemical properties of the prepared material before and after adsorption were monitored using X-ray diffraction, Fourier-transform infrared (FT-IR) spectroscopic analysis, energy dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) surface area measurements, high-resolution transmission electron microscopy (HRTEM), and field emission scanning electron microscopy (FESEM). Density functional theory (DFT) calculations for levo and its protonated species were studied at the B3LYP/6-311G (d,p) level of theory. The removal percentage of levo was 73.5%. The adsorption isotherm was investigated using nine different models at pH 9, where the obtained correlation coefficients (R ²) using the Redlich-Peterson and Toth models were 0.977. The thermodynamic parameters ΔS°, ΔG° and ΔH° were estimated and discussed in detail. Also, to support the adsorption research field, the applicability of the formed waste after the adsorption of levo onto Zn-Al LDH was investigated for medical purposes. The toxicity of levo in both normal and nanocomposite form was studied. Neither toxicological symptoms nor harmless effects were exhibited throughout the in vivo study. The oral anti-inflammatory activity, tested using 6% formalin to produce edema in the footpad, was manifested as a significant increase of 37% in the anti-inflammatory effect of the Zn-Al LDH/levo nanocomposite compared to levo in its normal form.

Fig. 1. EDX spectrum of the prepared Zn–Al LDH in which the inset shows the elemental composition percentage.

Fig. 2. XRD patterns of the (a) Zn–Al LDH, (b) Zn–Al LDH/levo and (c) levo.

Fig. 3. FTIR spectra of levo, Zn–Al LDH/levo and the Zn–Al LDH.

Fig. 4. FESEM images of the (a) Zn–Al LDH, (c and d) Zn–Al LDH/levo and (b) HRTEM of the Zn–Al LDH.

Fig. 5. Adsorption–desorption isotherms of N₂ for the Zn–Al LDH at 77 K, where the inset figures show (A) the pore width distribution and (B) the particle size distribution.

Fig. 6. The optimized structure of protonated levo (H₃L²⁺), the vector of the dipole moment, and the natural charges on the active centers of the ligand using the B3LYP/6-311G(d,p) functional.

Fig. 7. MEP surface of L⁻ and zwitterionic H(N3)L^± calculated using B3LYP/6-311G(d,p).

Scheme 1. The acid-base equilibria of levo at different pH values.

Fig. 8. (a) Potentiometric titration curve of an aqueous solution of levo, (b) point zero charge of the Zn–Al LDH, (c) the removal percentage of levo (15 ppm) by Zn–Al LDH (0.125 g/50 mL) at different solution pH values and (d) species distribution curves of levo at different pH values (d) species distribution curve of levo at different pH.

Fig. 9. Effect of the adsorbent dose on the adsorption of levo [15 ppm, 50 mL, and pH = 9].

Scheme 2. Suggested mechanisms for the adsorption process.

Fig. 10. Experimental adsorption isotherm data of levo on the Zn–Al LDH fitted using (a) two-parameter isotherm models and (b) three and four-parameter non-linear isotherm models.

Fig. 11. The effect of temperature on the levo removal efficiency using Zn–Al LDH.

Fig. 12. Plot of the Gibbs free energy change (ΔG°) versus temperature T (K).

Fig. 13. Paw thickness (anti-inflammatory activity) of levo, Zn–Al LDH/levo, Zn–Al LDH, diclofenac sodium (standard group), and non-treated (control group) at (A) pre-inflammation, (B) zero time and (C and D) post inflammation induction at 1 and 2 h, respectively.

Fig. 14. Paw thickness (anti-inflammatory activity) of the levo, Zn–Al LDH/levo, Zn–Al LDH, diclofenac sodium (standard group), and non-treated (control group) groups at 3 and 4 h.

Fig. 15. Histopathological investigation of the paws of rats carried out 4 h post-inflammation induction in the different groups. The black arrows refer to the signs of inflammation (congestion, redness), thrombus formation, edema, and the appearance of inflammatory cells like mast cells and eosinophils in control non-treated, Zn–Al LDH, which were very mild in the standard group. There was the absence of inflammation signs in the levofloxacin and levofloxacin nanocomposite groups samples.