Statistical modeling and enhanced performance of a hybrid catalytic photomicroelectrolysis (CPMC) system for tetracycline removal: a Box-Behnken design approach.

Tetracycline (TC), a widely used and persistent antibiotic in veterinary and human medicine, is considered a major aquatic environmental contaminant. This study aimed to synthesize and evaluate a novel TiO2-functionalized layered double hydroxides (LDH@TiO₂) as a catalyst in a catalytic photomicroelectrolysis system (CPMC) for the efficient removal of TC from aqueous solutions. The study was conducted in three phases: 1- Nanoparticle fabrication using a simple and low-cost co-precipitation method and investigation of its structural, morphological and surface properties using FESEM, EDX, Mapping, XRD, FTIR BET analyses, 2- Optimization of process parameters affecting TC removal including initial pH (3-11), contact time (5-60 min), initial concentration (10-100 mg/L) and carbon to iron ratio (C/Fe: 1/1, 2/1, 1/2) using Box-Behnken design (BBD) approach in design expert software and modeling of the TC removal process in the microelectrolysis (MC) system, 3- Comparison of the performance of the MC system in the presence of catalyst (CMC) and UV light (CPMC). The results showed that the synthesized nanocatalyst has a uniform structure with an average particle size of approximately 50 nm and a homogeneous elemental distribution. Optimization via BBD identified optimal conditions as: pH: 3.5, contact time 55 min, initial TC concentration 22 mg/L, and C/Fe ratio 1:2, yielding 97% removal efficiency in the MC system. When integrated with 0.05 g/100 mL LDH@TiO₂ under UV irradiation (CPMC), removal efficiency increased to 98% at 100 mg/L TC concentration. The presence of LDH@TiO₂ significantly increased the TC removal efficiency in the catalytic microelectrolysis process. The CPMC system achieved 98% TC removal efficiency at 100 mg/L concentration within 55 min, representing a 36, 13, and 5% improvement over MC (62%), LDH alone (85%), and CMC (93%) systems, respectively. The quadratic model demonstrated excellent fit (R² = 0.942, adjusted R² = 0.918, p < 0.001). The results of this study showed that the synergy between LDH@TiO₂ photocatalysis and redox processes at the iron-carbon microelectrolysis scale can be effectively, economically, and sustainably applied to remove resistant antibiotics such as tetracycline in pharmaceutical wastewater.