The Study Of Transfer And Dispersion Behavior Of Nano-TiO₂ In Aquatic System

The rapid development of nanotechnology promotes the wide use of nano-materials. Some nano-materials may release into the nature environment inevitably which would affect the environment and the ecosystem. Nano-TiO2 has been used widely in the field of cosmetics, environmental management and coating for its excellent optical absorption and photocatalytic characteristics. Series of biological effect will occur when nano-TiO2 released into the aquatic system. Suspension, deposition and transfer behavior for nano-TiO2 was investigated by changing pH values and adding electrolytes and surfactants into suspension liquid. The potential energy equation of nano-TiO2 particles in aquatic system were simulated by the DLVO theory. And the relative test results were verifed using the potential energy curve. The main results of this study were described as following.Nano-titanium dioxide is an N-type semiconductor and it complys with the Lambert-Beer law. So, the spectrophotometry was used to measure the concentration of nano-TiO2 in water and the maximum absorption wavelength was 325nm which is obtained from the UV-Vis scanning spectrometer. A linear relationship was obtained between the concentration and absorbance when the concentration of nano-TiO2 suspension was ranged from 5mg·L-1 to 40mg·L-1.The isoelectric point (IEP) of the P25 nano-TiO2 was about 6.7. The particle surface was positively charged when the pH value was lower than IEP, the particle surfaces was negatively charged when the pH value was higher than IEP on the contrary. The more the pH value deviated from the IEP, the more stable of nano-TiO2 in the aquatic system, and the transfer ability would be stronger.The characteristic adsorption ion of A1C13, CaCl2, NaCl and Na2SO4 after ionization on the surface of nano-TiO2 particles were Al3+, Ca2+, Cl-and SO42-, respectively. The adsorption of cations neutralized the negative charge on the nano-TiO2 particles surface which led to the aggregation and deposition of nano-TiO2 particles quickly. The adsorption of anions improved the stability of nano-TiO2 particles in water by increasing electrostatic repulsion between TiO2 particles. The stability of nano-TiO2 was also affected by the concentration of the electrolyte. If the the concentration of electrolyte was too high, the stability of nano-TiO2 would decrease because of the sharp compression of the double electrode layer.The stability and the transfer ability of nano-TiO2 could be improved by the adsorption of surfactant cations and surfactant anions produced by the ionization of ionic surfactants SDBS and CTAC. The stabilizing effect and improvement for transfer ability of Tween-80 on nano-TiO2 relied on the steric hindrance effect formed by the adsorption of Tween-80 on nano-TiO2 surface. Multilayer adsorption would happen if the surfactant concentration were above a certain concentration. In this case, the surfactant interconnected, and the particle would be instability and deposited quickly. At the same time, the transfer ability of nano-TiO2 would be very weak in aquatic system.The total potential energy curve of nano-TiO2 particles was simulated using the DLVO theory. The results showed that the change of environmental factors could affect the interaction of TiO2 nanoparticles in water and thereby affect the environmental behavior of nano-TiO2 further. The simulative potential energy curve was consistent with the results of the study.