Dual-Function Al2O3-TiO2 Ceramic Monoliths: Synergistic Adsorption and Photocatalytic Degradation of Ciprofloxacin Enabled by Nitric Acid Surface Activation

Abstract

The development of multifunctional ceramic materials capable of combining adsorption and photocatalytic activity represents an efficient strategy for the removal of persistent pharmaceutical contaminants from aqueous media. In this work, Al2O3-TiO2 monoliths were synthesized by the ionic encapsulation method and subsequently activated with concentrated nitric acid (HNO3) to enhance surface reactivity. The structural evolution and physicochemical properties of monoliths were analyzed by XRD, FTIR, SEM-EDS, BET, and ζ-potential measurements. XRD results revealed the formation of α-Al2O3 and a mixture of anatase and rutile TiO2 as the dominant crystalline phases after sintering at 1600 °C, while at 800 °C the material consisted of transitional alumina’s and anatase TiO2. FTIR spectra confirmed the presence of Al-O, Ti-O, and oxygen functional groups, which increased upon acid activation. SEM micrographs exhibited a dense polycrystalline morphology with uniform grain distribution, while EDS analysis confirmed the homogeneous dispersion of Al, Ti, and O elements. The activated monoliths displayed a ζ-potential of −23 mV at pH 5, indicating a strong electrostatic affinity toward cationic ciprofloxacin species. Adsorption experiments showed ciprofloxacin removal capacities of 13.03 mg g−1 for Al2O3-TiO2 and 91.2 mg g−1 for acid-activated Al2O3-TiO2, following a mixed adsorption mechanism that combines physical and chemical adsorption, according to Langmuir and Freundlich isotherms (R2 > 0.94). Under a black light bulb, the activated monolith achieved a k1 of 2 × 10−4 min−1 during ciprofloxacin photodegradation, fourfold higher than the untreated monolith (5 × 10−5 min−1) and tenfold higher than photolysis (2 × 10−5 min−1). These findings demonstrate that acid activation enhances adsorption and photocatalytic efficiency of Al2O3-TiO2 monoliths, which is a cost-effective and reusable efficient material for ciprofloxacin removal in real water treatment scenarios.