Remarkable improvement of visible light photocatalysis with PANI modified core–shell mesoporous TiO2 microspheres

PANI modified core–shell mesoporous TiO2 (PANI/M-TiO2) with efficient photocatalytic capability under visible light irradiation was fabricated by hydrothermal method and chemisorption approach. The nitrogen adsorption–desorption characterization indicated that the specific surface area of mesoporous M-TiO2 was 2.8 times as great as that of P25, which resulted in the increased uptake of PANI molecule on the surface of M-TiO2. Environmental scanning electron microscopy and transmission electron microscopy images demonstrated that the PANI/M-TiO2 possessed a unique core–shell structure, which allowed multiple reflection or scattering of light in the photocatalyst and led to the increase of optical path length subsequently. Both the increased uptake of PANI molecules and optical path length in photocatalyst contributed to enhance the visible light absorption. The UV–vis diffuse reflectance spectra confirmed that the optical absorption for PANI/M-TiO2 was more intensive than that for PANI modified TiO2 nanoparticle (PANI/NP-TiO2) in the visible light region. The intensive visible light absorption and effective charge separation owing to the heterojunction built between TiO2 and PANI lead to remarkable improvement of visible light photocatalysis. The pseudo-first-order kinetic constant of photocatalytic degradation of rhodamine B and 4-chlorophenol under visible light irradiation with 6% PANI/M-TiO2 was 5.04 and 2.03 times as great as that with PANI/NP-TiO2 respectively, showing the advantage of the unique core–shell mesoporous structure in the PANI/M-TiO2 for efficient photocatalysis.