Effects of fulvic acids and electrolytes on colloidal stability and photocatalysis of nano-TiO2 for atrazine removal

The colloidal stability and photocatalysis of nano-TiO2 particles were investigated in the presence of fulvic acids (FA) and electrolytes (NaNO3, Na2SO4, Na3PO4) at different pH. Results showed that increasing FA concentration, the absolute value of zeta potential of nano-TiO2 increased and particle size decreased at all pH which promoted the colloidal stability of nano-TiO2. Particle size of nano-TiO2 was larger with the coexistence of FA and electrolytes than with FA only as the concentration of electrolytes was greater than or equal to 0.01 mol/L. The largest particle size occurred in the presence of Na3PO4, followed by Na2SO4 and NaNO3. Particle size of nano-TiO2 decreased with higher pH and stability further increased in the presence of FA and/or electrolytes. Nano-TiO2 stabilization was enhanced by increasing FA concentration when the solution pH was 7.0. However, the removal efficiency of atrazine by nano-TiO2 decreased with the increase in FA concentration. Adding electrolytes (0.01 mol/L), atrazine removal by nano-TiO2 further decreased, albeit slightly. The inhibitory effect of electrolytes on nano-TiO2 removal of atrazine was highest for Na3PO4, followed by Na2SO4, and NaNO3, which were consistent with the results of colloidal stability of nano-TiO2. These findings help to better understand the mechanisms and correlation between colloidal stability and photocatalysis of nano-TiO2 in the presence of FA and electrolytes.