Effect of a typical antibiotic (tetracycline) on the aggregation of TiO2 nanoparticles in an aquatic environment.

The effect of tetracycline (TC) on the behavior of TiO 2 nanoparticles (NPs) in solution is investigated. The results illustrate that TC molecules do not exhibit an obvious effect on the aggregation of TiO 2 NPs under circumneutral conditions (pH of approximately 5.5). However, the TC molecules exhibit a remarkable effect on the behavior of TiO 2 NPs when the environmental factors (such as pH, ionic strength, and humic acid; HA) are adjusted. In the pH range from 3.0 to 10.0, the zeta potentials of NPs become more positively charged after TC adsorption. The point of zero charge of the TiO 2 NPs increases from 6.5 to 7.5. The stability of the TiO 2 NPs is improved after TC adsorption in different salt solutions. The critical coagulation concentration (CCC) increases from 10.57 mmol/L to 17.21 mmol/L, 4.95 mmol/L to 9.73 mmol/L, and 0.23–1.67 mmol/L in the presence of NaCl, CaCl 2 , and Na 2 SO 4 (where Cl − and SO 4 2− are the counter-ions), respectively. Under different HA concentrations, the C HAPZC (the HA concentration that causes the zeta potential of NPs to be zero) increases from 0.5 mg/L to 1.3 mg/L after TC adsorption. The sizes of the TiO 2 NP aggregates are larger than those without TC adsorption. All of these results are due to an increase in the surface charge of the TiO 2 NPs after TC adsorption. The adsorption of H + during TC adsorption causes protonation of the dimethylamine group on the TC molecules. [ABSTRACT FROM AUTHOR]