Green and sustainable synthesis of amorphous CuWO4@TiO2 core-shell nano-adsorbent for the efficient removal of emerging contaminants: Adsorption of ciprofloxacin antibiotic and textile dye from aqueous solution

The increasing concentrations of various antibiotics and textile dyes in aquatic environments present significant risks to both aquatic and human health. To address this issue, a CuWO 4 @TiO 2 core-shell nano-adsorbent was synthesized by a green and sustainable hydrothermal process and applied to efficiently remove ciprofloxacin (CIP) antibiotic and methylene blue (MB) dye molecules from wastewater. A variety of characterization instruments were utilized to identify the physicochemical structure of the synthesized nano-adsorbent. Comprehensive characterizations using XRD, FTIR, FE-SEM, TEM, XPS, and BET studies have provided concrete evidence of the development of a TiO 2 -coated CuWO 4 core-shell-structured adsorbent. Characterizations such as XRD and FTIR have shown the existence of amorphous CuWO 4 and TiO 2 phases with chemical bonding at the interface between CuWO 4 and TiO 2 . FE-SEM and TEM images have clearly demonstrated the morphological difference in which TiO 2 forms an even shell over the CuWO 4 core. XPS results indicate that the outer shell of TiO 2 is enriched in Ti, thus showing that the coating was complete. The Box-Behnken design (BBD) optimized methodology was utilized to optimize the operational variables such as dosages of nano-adsorbent, dosages of CIP, solution pH, and treatment time. The findings showed nearly complete CIP (99.0 ± 0.3%) adsorption at a CIP concentration of 10 mg/L, a dosage of adsorbent of 340 mg/L, and a treatment time of 40 minutes at neutral pH (7.0). The same optimized dosages were also tested for MB dye adsorption, and complete dye adsorption (100 % of MB) was achieved at only five (5) minutes of treatment. The adsorption was found to follow pseudo-second order, which is indicative of chemisorption as the rate-controlling step. The isotherm modeling results showed that the Langmuir equation fitted best with R 2 values of > 0.99, exhibiting maximum monolayer adsorption capacities (q m ) of 113.4 ± 6.4 mg/g for CIP at 30°C, after which the capacities decreased with an increase in temperature, indicating exothermic adsorption. The thermodynamic evaluation confirmed that the process was spontaneous (ΔG 0 = -4.56 to -4.06 kJ/mol), exothermic (ΔH 0 = -12.18 kJ/mol) and accompanied by reduced interfacial randomness (ΔS° = -25.15 J/mol·K). This supports the view that electrostatic attraction, hydrogen bonding, surface complexation, and π-π stacking facilitate the adsorption of CIP and MB via chemisorption. Its reusability over five cycles confirmed its structural integrity and practical applicability. It demonstrates highly efficient and reusable broad-spectrum efficacy in removing mixed emerging contaminants, showing potential for scalable application in treating wastewater from the pharmaceutical and textile industries.