A new green floating photocatalyst with Brazilian bentonite into TiO2/alginate beads for dye removal

The floating alginate beads were obtained by cross-linking of sodium alginate solution containing TiO2, organobentonite (NaOB) and CaCO3; with Ca2+ in acidified solution (CH3COOH). Adsorption and discoloration/ degradation activities of the floating TiO2-NaOB/CaAlg beads were evaluated using tartrazine (TZ) and methylene blue (MB) dye solutions. The particles were characterized by scanning electron microscopy (SEM/EDS), thermogravimetric (TGA), infrared spectroscopy (FT-IR) and surface area (BET/BJH) analysis. The addition of 1 wt% NaOB improved the thermal stability and favored the adsorption process, consequently, enhanced the photocatalytic activity. Adsorptive removal of 23.5% and 59.0% were observed for TZ and MB dyes, respectively. The pseudo-second-order kinetic and Langmuir isotherm models adjusted better to the experimental data. When applying UVLED irradiation, the removal achieved 95% and 99%; and the total organic carbon reduction achieved 34.4% and 53.6% for TZ and MB solutions, respectively. The L-H pseudo-first order adequately predicted the photocatalytic data. The floating adsorbent-photocatalyst presented good stability, keeping up to 80% discoloration capacity even after seven reuse cycles. Besides the simple methodology of obtaining floating particles, the system makes efficient use of UV photoactivation, since it allows the TiO2 availability at the interface water/air. The easy separation from the treated solution and its recyclability make it a promising photocatalyst.