Fabrication of Ag3PO4/N-doped TiO2 nanotubes heterojunction photocatalysts for visible-light-driven photocatalysis

Abstract

As an environmentally friendly and energy-efficient technology, photocatalysis holds considerable potential for eliminating organic pollutants. In this study, novel visible-light-driven Ag₃PO₄-decorated nitrogen-doped TiO₂ nanotubes (Ag₃PO₄/N-TNTs) photocatalysts with advanced properties of heterostructures were successfully synthesized and used to degrade methylene blue (MB) dye. The fabrication of Ag₃PO₄/N-TNTs photocatalysts involved a two-step electrochemical anodization to obtain TiO₂ nanotubes (TNTs) and the wet impregnation of the amorphous tubular structure in NH₃ solution, followed by calcination in air to obtain crystallized nitrogen-doped TiO₂ nanotubes (N-TNTs). Finally, the decoration of the N-TNTs with Ag₃PO₄ nanoparticles was conducted to enhance visible-light reactivity. Various heterojunction photocatalysts were obtained by changing the concentration of NH₃ (0.5-2.5 M) and the dosage of Ag₃PO₄ (0.25-1.5 wt%) in the composites. Results of ultraviolet-visible (UV-Vis) absorption, photocurrent transient, and electrochemical impedance spectroscopy measurement revealed that Ag₃PO₄/N-TNTs possessed a significant response in the visible-light range and good photoelectronic properties. The superior photocatalytic activity of the Ag₃PO₄/N-TNTs catalyst was achieved under the optimal conditions of N-doping using 2-M NH₃ and Ag₃PO₄ deposition at a dosage of 0.75 wt%. Based on the degradation efficiency (DE) of MB, the optimal Ag₃PO₄/N-TNTs exhibited rate constants of 4.5 and 2 times higher than those of the pristine TNTs and N-TNTs, respectively. The high stability of Ag₃PO₄/N-TNTs was confirmed through four cycles of reutilization, with a small decay of only 5.3% in the DE of MB dye for each run of photocatalysis. The scavenger tests of generated reactive oxygen species revealed that ·OH and ·O₂^- were the primary contributors to photocatalytic performance. The synthesized Ag₃PO₄/N-TNTs heterostructure photocatalysts were proven to possess efficient separation of photogenerated charge carriers, high reactivity, and stability in the visible-light region.

Keywords: Ag(3)PO(4); Heterojunction; Methylene blue; N-Doping; Photocatalyst; TiO(2) nanotubes.