Fabrication of AgPO/N-doped TiO nanotubes heterojunction photocatalysts for visible-light-driven photocatalysis.

As an environmentally friendly and energy-efficient technology, photocatalysis holds considerable potential for eliminating organic pollutants. In this study, novel visible-light-driven AgPO-decorated nitrogen-doped TiO nanotubes (AgPO/N-TNTs) photocatalysts with advanced properties of heterostructures were successfully synthesized and used to degrade methylene blue (MB) dye. The fabrication of AgPO/N-TNTs photocatalysts involved a two-step electrochemical anodization to obtain TiO nanotubes (TNTs) and the wet impregnation of the amorphous tubular structure in NH solution, followed by calcination in air to obtain crystallized nitrogen-doped TiO nanotubes (N-TNTs). Finally, the decoration of the N-TNTs with AgPO nanoparticles was conducted to enhance visible-light reactivity. Various heterojunction photocatalysts were obtained by changing the concentration of NH (0.5-2.5 M) and the dosage of AgPO (0.25-1.5 wt%) in the composites. Results of ultraviolet-visible (UV-Vis) absorption, photocurrent transient, and electrochemical impedance spectroscopy measurement revealed that AgPO/N-TNTs possessed a significant response in the visible-light range and good photoelectronic properties. The superior photocatalytic activity of the AgPO/N-TNTs catalyst was achieved under the optimal conditions of N-doping using 2-M NH and AgPO deposition at a dosage of 0.75 wt%. Based on the degradation efficiency (DE) of MB, the optimal AgPO/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 AgPO/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 ·O were the primary contributors to photocatalytic performance. The synthesized AgPO/N-TNTs heterostructure photocatalysts were proven to possess efficient separation of photogenerated charge carriers, high reactivity, and stability in the visible-light region.