Preparation of polydopamine-coated TiO₂ composites for photocatalytic removal of gaseous ammonia under 405 nm violet-blue light

Although photocatalytic reactions using the ultraviolet (UV) range (particularly UV B (280–320 nm) wavelengths) is well-established, the photocatalytic effect of longer wavelengths (especially that of UVA (≥380 nm) and visible light (≥400 nm)) have only recently been studied and utilized for environmental applications. In this work, we coated polydopamine (PDA) and TiO₂ on a support and investigated the synergistic effects of the corresponding composites for the photocatalytic removal of gaseous ammonia under 405 nm violet-blue light. The PDA layer with TiO₂ was covalently attached on a ceramic ball using the drop-casting method. The roughness and functional groups of the TiO₂-PDA coated ball surfaces were verified using an infrared imaging microscope and field emission scanning electron microscope (FE-SEM). The photocatalytic activity of the obtained hybrid TiO₂-PDA coated ball for the removal of ammonia was investigated using a UV C and 405 nm LED lamp at 24 °C. The results showed that both the TiO₂ (control sample) and TiO₂-PDA coated balls successfully removed ammonia under similar experimental conditions with the 254 nm UV C lamp. Notably, the TiO₂-PDA coated ball exhibited an enhanced ammonia removal efficiency of 72% under 405 nm LED light irradiation. Thus, the TiO₂-PDA coated ball is a promising indoor air cleaning technique under LED light irradiation.