Adsorption of Levofloxacin onto Chitosan- and Layered Double Hydroxide-Functionalized Montmorillonite

Key operational parameters, including solution pH, contact time, temperature, and initial LVX concentration, were then optimized. Both adsorbents showed maximum adsorption at pH 3 in a 30 mg L^–1 LVX solution after 60 min, with removal efficiencies of 77.7% and 99.1% for 0.01 g of LDH/MMT and CTS/MMT, respectively. Temperature variation data showed that LVX adsorption efficiency for LDH/MMT remained largely unaffected, ∼78.0% for a 0.01 g dosage, ∼90.0% for 0.05 g, and ∼87.0% for 0.1 g throughout the temperature range 15–35 °C. In contrast, CTS/MMT consistently achieved near-complete LVX removal (∼100.0%) across all tested temperatures regardless of dosage.

For 0.01 g of adsorbent dosage, CTS/MMT adsorbed >99.0% LVX within 60 min, whereas adsorption onto LDH/MMT achieved equilibrium within 10 min with 77.1% removal efficiency. The Langmuir model fitted the CTS/MMT adsorption data well, with a maximum adsorption capacity of 107.53 mg g^–1, whereas the Freundlich model better described the adsorption behavior of LDH/MMT. For CTS/MMT, at pH < 5.59, surface adsorption through electrostatic attraction between cationic LVX and the negatively charged composite surface, coupled with cation exchange into the MMT interlayer, may be the principal adsorption phenomenon.

On the other hand, heterogeneous intercalation of cationic LVX molecules into the MMT interlayer was the principal mechanism for LVX adsorption onto LDH/MMT.