Formulation and optimization of a novel TiO₂/calcium alginate floating photocatalyst

For the first time, TiO₂ immobilized in alginate polymer was modified to turn it into a buoyant photocatalyst for achieving both higher radiance utilization efficiency and easier post-treatment separation. In this work, the low-density TiO₂ alginate-based photocatalyst was synthesized by ionotropic gelation using a gas-forming agent (CaCO₃, NaHCO₃) in an acid medium (CH₃COOH). The TiO₂, CaCO_3, and CH₃COOH concentrations affect buoyancy, and the best response (100% of floating beads) after 24 h was determined using a central composite rotatable design combined with the response surface methodology. It was found that the optimal TiO₂/CaAlg formulation were the following concentrations: 1.1 wt% TiO₂, 2.3 wt% CaCO_3, and 6.4 vt% CH₃COOH. The resulting floating beads were uniform (size: 3.4 ± 0.4 mm, density: 0.9215 g/cm³), with a rough surface and porous internal structure, as observed in the characterizations using SEM/EDX, TGA, XRD, and FT-IR. The photocatalytic activity under UV irradiation (125 W, 254 nm) was evaluated for tartrazine dye removal, achieving up to 89% discoloration upon the first use with TOC removal capacity even after seven use cycles. This easily recoverable floating photocatalyst may be applied to improve the photocatalytic treatment of industrial wastewater, making most efficient use of photoactivation with no mechanical stirring.