Multifunctional Fe3O4@Ag@TiO2-xNx core-shell composite particles for dye adsorption and visible-light photocatalysis

This study prepares Fe3O4@Ag@TiO2 (FAT) particles via a solvothermal route, then thermally treats the particles over a temperature range from 300 to 500 ? in flowing nitrogen atmosphere to form Fe3O4@Ag@TiO2-xNx (x = 0.056 to 0.15) (FATN) core-shell composite particles. The FATN particles comprise an outermost TiO2-xNx shell of about 20-50 nm in thickness, a Brunauer-Emmett-Teller surface area of 103.2-152.5 m(2)/g, and a Barrett-Joyner-Halenda pore size of 12.9-30.2 nm. The particles show dye adsorption and visible-light photocatalysis against a model methylene-blue (MB) dye in water. For the FATN particles being treated at 400 ?, they show a dark adsorption of 54.8% and an additional visible-light photodegradation of 25.1% when using a dyed wastewater with an initial MB concentration of 5 x 10(-6) M. This compares favorably to those being treated at other nitridation temperatures. The 500 C-treated FATN particles yet exhibit a dark adsorption of 99.1% against the MB solution. Use of an external magnet can facilely recycle the composite particles. The recycled particles remain greater than 72% of their initial MB removal capability after use of five times. The intermediate Ag nanolayer can release Ag ions to the surrounding water medium through the mesoporous shell channel. The time-dependent Ag release appears to follow the Voigt-Maxwell model and reaches 0.764 ppm after 48 h, suggesting a long-time releasing efficacy.

Automated summary

This study synthesized core-shell composite particles (FATN) with excellent adsorption and visible-light photocatalysis properties. The particles showed high adsorption and degradation efficiency against a dye solution at specific treatment temperatures, and could be easily recycled using an external magnet.