Influence of TiO2 morphology on the photocatalytic efficiency of direct Z-scheme g-C3N4/TiO2 photocatalysts for isoniazid degradation

Direct Z-scheme graphitic carbon nitride (g-C3N4)/TiO2 (nanoparticle and nanotube) photocatalysts with different g-C3N4 loadings were prepared using a facile wetness impregnation method. TiO2 nanotubes were synthesized using a hydrothermal method. The influence of the TiO2 morphology on the photocatalytic efficiency of the direct Z-scheme g-C3N4/TiO2 photocatalysts was studied through the photodegradation of isoniazid. The firm connection between g-C3N4 and TiO2 was investigated using powder X-ray powder diffraction, field emission-scanning electron microscopy, transmission electron microscopy, X-ray photoelectron and Fourier-transform infrared spectroscopy. Subsequently, both the direct Z-scheme photocatalysts were used for the decomposition of isoniazid. Our results revealed that the Z-scheme g-C3N4/TiO2 nanotube (3%-CN/TNT) photocatalyst exhibited enhanced (90.8%, 4 h) photocatalytic activity, and the g-C3N4/TiO2 nanoparticles (5%-CN/TNP) had a higher activity (79.5%, 4 h) than the photocatalysts with other g-C3N4 loadings, TiO2 nanotubes (73.3%, 4 h), TiO2 nanoparticles (56.3%, 4 h), and g-C3N4 (13.5%, 4 h). Presumably the enhancement of photocatalytic activity was due to effective separation of the charge carriers between g-C3N4 and TiO2 through the Z-scheme mechanism. The separation of the charge carriers was confirmed using photoluminescence and photocurrent measurements. A direct Z-scheme charge transfer process was confirmed through free radicals (h(+), (OH)-O-center dot, and O-2(center dot-)) scavenging and hydroxyl ((OH)-O-center dot) radical determination studies. The enhanced (OH)-O-center dot radical generation using 3%-CN/TNT photocatalyst could also lead to enhanced photocatalytic performance than the other photocatalysts. We proposed a mechanism for the enhanced photocatalytic activity and the probable degradation pathway for isoniazid. Further confirmation of the isoniazid degradation was performed using kinetic studies and chemical oxygen demand analysis. Our results suggested that the TiO2 morphology significantly influenced the photocatalytic efficiency of the direct Z-scheme photocatalysts under our reaction conditions. (C) 2015 Elsevier B.V. All rights reserved.