Ultrasonic spray pyrolysis synthesis of TiO 2 /Al 2 O 3 microspheres with enhanced removal efficiency towards toxic industrial dyes.

Developing low-cost and highly effective adsorbent materials to decolorate wastewater is still challenging in the industry. In this study, TiO 2 -modified Al 2 O 3 microspheres with different TiO 2 contents were produced by spray pyrolysis, which is rapid and easy to scale up. Results reveal that the modification of γ-Al 2 O 3 with TiO 2 reduced the crystallite size of Al 2 O 3 and generated more active sites in the composite sample. The as-synthesized Al 2 O 3 -TiO 2 microspheres were applied to remove anionic methyl orange (MO) and cationic rhodamine B (RB) dyes in an aqueous solution using batch and continuous flow column sorption processes. Results show that the Al 2 O 3 microspheres modified with 15 wt% of TiO 2 exhibited the maximum adsorbing capacity of ∼41.15 mg g -1 and ∼32.28 mg g -1 for MO and RB, respectively, exceeding the bare γ-Al 2 O 3 and TiO 2 . The impact of environmental complexities on the material's reactivity for the organic pollutants was further delineated by adjusting the pH and adding coexisting ions. At pH ∼5.5, the TiO 2 /Al 2 O 3 microspheres showed higher sorption selectivity towards MO. In the continuous flow column removal, the TiO 2 /Al 2 O 3 microspheres achieved sorption capacities of ∼31 mg g -1 and ∼19 mg g -1 until the breakthrough point for MO and RB, respectively. The findings reveal that TiO 2 -modified Al 2 O 3 microspheres were rapidly prepared by spray pyrolysis, and they effectively treated organic dyes in water in batch and continuous flow removal processes.