Enhanced photocatalytic decolorization of methyl orange dye and its mineralization pathway by immobilized TiO2/polyaniline

An immobilized TiO 2 /polyaniline (TiO 2 /PANI) bilayer photocatalyst was fabricated to decolorize methyl orange (MO) dye in aqueous solution. The synergistic decolorization of MO occurred via photocatalysis by TiO 2 top layer and adsorption by PANI sub-layer. The fabrication of the photocatalyst was pertaining to the loading of TiO 2 (0.32–2.24 mg cm −2 ) and PANI (0.32–1.92 mg cm −2 ). Increasing the loading would increase the thickness of the layer whereas an increment in the adsorption rate constant would essentially increase the synergistic photocatalytic–adsorption in the decolorization of MO. The TiO 2 and PANI layer loading was optimized at 1.27 and 0.63 mg cm −2 , respectively. The optimized TiO 2 /PANI photocatalyst removed MO dye by four and three times more effectively than the TiO 2 and PANI single layer, respectively. The aeration, which supplied the dissolved oxygen, was optimized at 40 mL min −1 of flow rate. The photocatalytic degradation mechanism of MO was initiated by the demethylation followed by the aromatic ring opening and ended with a complete oxidation of the aliphatic chain to become CO 2 and H 2 O. The TOC and IC analyses confirmed the mineralization of MO. Graphical abstract