纳米TiO_2对沉积物吸附氨氮的影响及其机制探讨

纳米TiO2在生产使用过程中不可避免地大量进入水环境,并影响到其他传统污染物质(如氨氮)的迁移转化.氨氮在沉积物上的吸附和解吸附是水环境中氮素循环的关键过程之一.本研究测定了受纳米TiO2污染沉积物、常规TiO2污染沉积物和未受TiO2污染沉积物的零电荷点,并通过氨氮吸附热力学和吸附动力学实验,研究了纳米TiO2对沉积物吸附氨氮的影响.得出如下结论:(1)研究中的三组沉积物与NH4+-N之间没有静电吸引力;(2)修改后的Freundlich和修改后的Langmuir模型对氨氮吸附的拟合效果都比较好,且后者拟合度更高;(3)纳米TiO2的添加降低了氨氮的吸附—解吸平衡浓度,减小了沉积物向上覆水中释放氨氮的趋势;(4)抛物线扩散模型能较好地拟合三组沉积物吸附氨氮的动力学过程,结果显示纳米TiO2对沉积物吸附氨氮的动力学特征(快慢)没有影响,但增强了沉积物吸附氨氮的强度.

Effects and mechanism of titania nanoparticles on ammonium adsorption on sediments

In the processes of production, a mass of nano-titanium dioxide inevitably enters aquatic environment, and affects the transference and transform of other traditional pollutants, such as ammonia nitrogen. The adsorption and desorption of ammonium on sediments is a key process in the nitrogen cycle of aquatic environment. This study measured the point of zero charge of nano-TiO₂contaminated sediments, conventional TiO₂ contaminated sediments and uncontaminated sediments. Furthermore, the ammonium sorption thermodynamic and sorption kinetic processes were investigated to discover the effects of nano-TiO₂ on the ammonium sorption on sediments. The results indicated that: (1) There was no electrostatic attraction between the three groups of sediments and NH4+-N in this study; (2) The sorption thermodynamic data were fitted well by both modified Freundlich and modified Langmuir models, and the fitting degree of the latter was higher; (3)The adding of nano-TiO₂ to sediments reduced ammonia sorption-desorption equilibrium concentration, then the tendency of sediments releasing ammonia nitrogen in water was weakened; (4) The sorption kinetic processes of the three groups of sediments were well fitted by parabolic diffusion model, and the results showed that nano-TiO₂ could not affect ammonium sorption character(speed), but the sorption strength of ammonium on sediments was improved.