Abstract:
Halloysite nanoclay was utilized to retain aqueous oxytetracycline (OTC) which is extensively used in the veterinary
industry. The micro-structure and functionality of the nanoclay were characterized through spectroscopic
techniques before and after adsorption. The OTC removal experiments were performed at different pH
conditions (pH 3.0–9.0), ionic strengths (0.001, 0.01, 0.1M NaNO3) and contact time (up to 32 h) at an initial
25 mg/L OTC concentration with 1.0 g/L halloysite. Oxytetracycline adsorption was pH dependent, and the best
pH was observed in the range of pH 3.5–5.5 at a 0.001M ionic strength. At pH 3.5, the maximum OTC adsorption
amount was 21 mg/g which translated to 68% removal of the initial OTC loading. Positively charged inner
lumen and negatively charged outer lumen of the tubular halloysite structure led to form inner-sphere complexes
with the anionic and cationic forms of OTC, respectively. A rapid adsorption of OTC was observed in the kinetic
study where 62% OTC was adsorbed in 90 min.. Pseudo-second order equation obeyed by the kinetic data
indicated that the adsorption was governed by chemisorption, whereas Hill isotherm equation was the most
fitted with a maximum adsorption capacity of 52.4 mg/g indicating a cooperative adsorption phenomenon.
