Preparation of TiN-WN composite particles for selective adsorption of methylene blue dyes in water

This study synthesizes TiN-WN composite nanoparticles with a broad Ti molar ratio, i.e., f_Ti ranging from 0.18 to 0.94, by a facile urea-assisted nitridation route at 800 °C in flowing nitrogen atmosphere. The particles comprise mainly mixtures of TiN and WN nanocrystallites when f_Ti ≤ 0.80. The composites show a selective adsorption against methylene blue (MB) dyes in water; to which, the adsorption under dark situations reaches as much as 90% within 90 min duration when using an initial MB concentration of 10^?5 M. In comparison, the composites show virtually negligible adsorption to methyl orange dye. This selective adsorption stems partly from the electrostatic interaction since surface of the composite particles bears a negative net charge for the cationic MB molecules. In addition, the composite particles also render a moderate photocatalytic degradation to the MB molecules under visible light illuminations.