Effect of particle size of titanium dioxide nanoparticle aggregates on the degradation of one azo dye.

INTRODUCTION: Titanium dioxide (TiO(2)) nanoparticle powders have been extensively studied to quickly photodegrade some organic pollutants; however, the effect of the particle size of TiO(2) nanoparticle aggregates on degradation remains unclear because microscale aggregates form once the nanoparticle powders enter into water.
METHODS: The degradation of azo dye by different particle sizes of TiO(2) nanoparticle aggregates controlled by NaCl concentrations was investigated to evaluate the particle size effect. Removal reactions of reactive black 5 (RB5) with TiO(2) nanoparticles followed pseudo-first-order kinetics.
RESULTS: The increase of TiO(2) dosage from 40 to 70 mg/L enhanced the degradation. At doses around 100 mg/L TiO(2), degradation rates decreased which could be the result of poor UV light transmittance at high-particle concentrations. At average particle sizes of TiO(2) nanopowders less than around 500 nm, the degradation rates increased with decreasing particle size. As the average particle size exceeded 500 nm, the degradation rates were not significantly changed.
CONCLUSIONS: For the complete degradation experiments, the mineralization rates of total organic carbon disappearance are generally following the RB5 decolorization kinetic trend. These findings can facilitate the application of TiO(2) nanoparticles to the design of photodegradation treatments for wastewater.