Sulfate-Anchored Hierarchical Meso-Macroporous N-doped TiO2: A Novel Photocatalyst for Visible Light H-2 Evolution

Abstract

Visible light-active hierarchical meso-macroporous S,N-modified TiO2 has been synthesized through a precipitation and deposition method and characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, BET surface area, X-ray photo electron spectroscopy, and photoluminescence studies. The finding demonstrates that N exists in the form of N-Ti-O in the crystal lattice of TiO2; however, sulfate (S6+) is bidentately coordinated on the surface of TiO2. The existence of sulfate maintains the morphology as well as enhances the surface area, decreases the crystallite size, shifts the optical absorption toward the red end, acts as co-catalyst, and facilitates the photogenerated charge carriers. Moreover, the presence of a hierarchical meso-macroporous frame enhances visible light-harvesting properties as well as favors easy channelization of electrons, which effectively reduces the charge recombination. The photocatalytic activity has been evaluated through H-2 evolution. The observed enhancement in activity for 4SNTP-400 has been explained on the basis of a synergistic combination of anionic-cationic species, hierarchical meso-macroporous frames with high surface area, and high crystallization of anatase phase with small crystallite size and low PL intensity, which makes the system more potential toward visible light activity.