Effects of Ca2+ and fulvic acids on atrazine degradation by nano-TiO2: Performances and mechanisms

Abstract

In this study, the adsorption and UV photocatalytic degradation of atrazine using nano-TiO2 particles were studied systematically, and the colloidal stability of nano-TiO2 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 Ca2+ and/or fulvic acids (FA) at pH = 7.0. Results showed that the adsorption rate of atrazine onto nano-TiO2 particles decreased with the increase of Ca2+ and/or FA concentrations, which could be explained well by the colloidal stability of nanoparticles. When the solution contained Ca2+ or Ca2+-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 Ca2+ and/or FA concentration accelerated the aggregation of nano-TiO2 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-TiO2 particles displayed that the fastest sedimentation was happened in the CaCl2 and FA coexistent system and followed by CaCl2 alone, and the results well demonstrated the photodegradation efficiency trends of atrazine by nano-TiO2 particles under the different sedimentation conditions.