Montmorillonite-loaded copper sulfide for the removal of tetracycline hydrochloride from aqueous solutions

Copper sulfide (CuS) is a common catalytic degradation material, but its adsorption performance for tetracycline hydrochloride (TCH) remains insufficiently studied. In this work, a modified CuS material was developed for the adsorption of TCH in water. Montmorillonite (MMT) was employed as a carrier to enhance the dispersion of CuS, resulting in the synthesis of montmorillonite-loaded CuS (CuS@MMT). Comprehensive characterization revealed that the composite material exhibited a block like morphology with nanoflower clusters anchored on the supports, demonstrating good crystallinity and a structure comprising hexagonal CuS and montmorillonite phases. The (001) diffraction peak of the composite shifted compared to the standard MMT reference, indicating an expanded interlayer spacing of montmorillonite and successful intercalation of CuS into the interlayers, which effectively dispersed CuS particles. During the purification process, the leaching concentration of Cu ions was measured at 1.6 mg·L-1, demonstrating minimal secondary contamination. Adsorption kinetics followed the pseudo-second-order kinetic model, suggesting chemisorption as the rate-limiting step. Isothermal adsorption data aligned with the Langmuir model, confirming monolayer adsorption. A response surface methodology (RSM) based on the DM matrix was employed for mathematical modeling and optimization, yielding optimal adsorption conditions: adsorbent dosage of 0.08 g, initial TCH concentration of 20 mg·L-1, and pH 6.5, achieving a 100% removal efficiency. Recyclability tests showed that the material maintained an adsorption capacity of 25 mg·g-1 after five cycles. Among coexisting anions, CO32- exerted the most significant inhibitory effect on TCH adsorption, while Cl- and SO42- showed minor impacts. Remarkably, the material exhibited high adsorption capacities exceeding 151 mg·g-1 for TCH in real water matrices, including tap water, Xuanwu Lake water, and Yangtze River water, highlighting its practical applicability in natural aqueous environments.