Effects of Ca(2+) and fulvic acids on atrazine degradation by nano-TiO(2): Performances and mechanisms

In this study, the adsorption and UV photocatalytic degradation of atrazine using nano-TiO(2) particles were studied systematically, and the colloidal stability of nano-TiO(2) particles in solution was also investigated to reveal the removal mechanism. Experiments which contained the first 6.0 hours darkness and 4.0 hours UV illumination later were conducted at different concentrations of Ca(2+) and/or fulvic acids (FA) at pH = 7.0. Results showed that the adsorption rate of atrazine onto nano-TiO(2) particles decreased with the increase of Ca(2+) and/or FA concentrations, which could be explained well by the colloidal stability of nanoparticles. When the solution contained Ca(2+) or Ca(2+)-FA, the nanoparticles were aggregated together leading to the decrease of the contact surface area. Besides, there existed competitive adsorption between FA and atrazine on the particle surface. During photocatalytic degradation, the increase of Ca(2+) and/or FA concentration accelerated the aggregation of nano-TiO(2) particles and that reduced the degradation efficiency of atrazine. The particle sizes by SEM were in accordance with the aggregation degree of nanoparticles in the solutions. Sedimentation experiments of nano-TiO(2) particles displayed that the fastest sedimentation was happened in the CaCl(2) and FA coexistent system and followed by CaCl(2) alone, and the results well demonstrated the photodegradation efficiency trends of atrazine by nano-TiO(2) particles under the different sedimentation conditions.