Novel TiO₂@Mg/Fe-LDH for photocatalysis and adsorption of selenium species from wastewater: RSM & ANN/ML modeling

Selenocyanate (SeCN⁻) contamination in wastewater poses environmental hazards due to its toxicity and persistence. Its removal remains challenging with a single-treatment approach due to its stability in aqueous environments. This study investigated a combined approach of photocatalytic degradation and adsorption for effective SeCN⁻ removal. A TiO₂@Mg/Fe-LDH calcined at 250°C composite was developed to harness the photocatalytic activity of TiO₂ under UV light, which facilitated the breakdown of SeCN⁻ into oxidized forms, SeO₃^2- and SeO₄^2-, which were subsequently adsorbed onto Mg/Fe-LDH. The characterization confirmed successful TiO₂ integration, enhanced thermal stability, and strong interfacial interactions. The photocatalytic degradation (PCD) study was optimized using RSM, examining the effects of the TiO₂:LDH (w/w) ratio, composite dose, and selenocyanate concentration. The fitted model showed strong statistical performance (R² = 0.9627, adjusted R² = 0.9420, predicted R² = 0.8642). The removal efficiency increased with the increase in TiO₂:LDH ratio, composite dose, and the decrease in SeCN⁻ concentration. The maximum removal efficiency of 78.5 % was achieved at a 1:1.5 ratio, 2 g/L dose, and 2.5 mg/L selenocyanate concentration. Additionally, the ANN model improved prediction accuracy. The fitted ANN model demonstrated superior performance (R² = 0.979) with lower RMSE and strong correlation. The kinetic study showed that the pseudo-second-order model provided a better fit (R² = 0.9916) than the pseudo-first-order model (R² = 0.8942). This dual-function approach highlights the TiO₂@Mg/Fe-LDH-250⁰C composite as a promising material for advanced wastewater treatment.