The Preparation And Modification Of Novel Micro-/Nanostructured Materials For Adsorption Of Micropollutants From Aqueous Solution

Micropollutants (ppm-ppb level) in drinking water are a serious threat to human health. The direct relationship between the high risk of cancer in specific regions and the drinking water pollution was firstly confirmed by Chinese Center for Disease Control and Prevention (CDC) in June,2013. Micropollutants in drinking water contain inorganic and organic micropollutants. Because of the persistence and amplification impact of the toxic effect caused by micropollutants, the address of the safety issues of drinking water is highly desired. Currently, the main methods for the removal of micropollutants include adsorption, flocculation, and photodegradation, etc. Among them, adsorption is one of the most prospective approaches due to its attractive advantages such as simple operation. Conventional adsorbents (e.g., active carbon and zeolite) can remove part of the pollutants in water; however, the amount of adsorbents should be significantly increased to enable the micropolluted water to be purified as clean as national standard of drinking water, and thereby increase the cost of the water treatment. The reason for this is that the adsorption sites of conventional adsorbents are less, as well as adsorption capacity is low, resulting in low removal efficiency. Nanoadsorbents not only possess relatively large specific surface area, but also have many active functional groups on the surface which can physically and chemically interact with micropollutants, leading to the removal of micropollutants by adsorption. So, nanoadsorbents can promisingly find applications for the removal of micropollutants in drinking water. However, it remains an issue that nanoscale adsorbents aggregate easily. In this condition, numerous active functional groups on the surface can hardly take part in the adsorption. As we know, micro-/nanostructured materials are one of the ordered assembly architecture of nanomaterials in which both advantages of nanoadsorbents can be maintained and the aggregation can be reduced effectively. This enables it an important direction in nanomaterials research field. Therefore, this thesis performed a series of investigations on the preparation of micro-/nanostructured hierarchical adsorbents and their adsorptions properties for the removal of micropollutants in drinking water. They are summarized as follows:1) A snowflake-like Zn4(CO3)(OH)6·H2O micro-/nanostructured hierarchical nanomaterial was prepared via a hydrothermal method. By following the next steps including annealing to form porous ZnO, coating SiO2on the surface of ZnO, and hydrothermally growth of Fe3O4/ Clayer, a final product of magnetic ZnO@SiO2@Fe3O4/C micro-/nanostructure was achieved. The adsorption properties towards Pb(II), As(V), and methylene blue (MB) were investigated. The results show that the adsorption towards the selected micropollutants fit well with the Langmuir adsorption model. The maximum adsorption capacities towards Pb(II), As(V), and MB are81.9,23.8and131.6mg g-1, respectively. In addition, the influence of adsorption performance by pH value was also studied. It is found that the removal efficiencies towards Pb(II) and MB decrease slightly when the pH value is larger than8; while the pH value shows great impact for the removal of As(V).2) Flower-shaped MnO2with a micro-/nanostructure was synthesized, and then it was modified with chitosan (CS) nanoparticles to form a MnO2/CS nanoadsorbent. The results on the adsorption performance show that the adsorption behavior belongs to Langmuir model, and the maximum adsorption capacity is102.5mg g-1. The kinetic adsorption results exhibit that the removal efficiency reachs93%in3min towards10ppm of Pb(II) in a neutral solution.3) On the basis of activated carbon fiber (ACF) cloth which was employed as a template, a hierarchical ACF/MnO2micro-/nanostructured adsorbent was obtained through a hydrothermal growth of MnO2nanowires on the surface. Methyl orange (MO) was employed as organic pollutant here. The adsorption results show that the kinetic adsorption fits with the Pseudo-second-order model, while the adsorption matches with the Freundlich model by the fitting of adsorption isothermal. In the pH range of1to7, the removal efficiency is close to100%, while it still about95%when the pH value is10, indicating that the presented adsorbents can be potentially applied in a large pH value range. Moreover, the recyclable measurements show that the adsorbents can remain about90% after5times of recycling adsorption.