Adsorptive Removal Of Phosphate Ions From Aqueous Solution Using Zirconia-Functionalized Carbonaceous Materials

Excessive phosphorus discharging into fresh waters may cause the eutrophication of water bodies, which has been an increasing problem to ecosystems and human beings during the last decades. Phosphate removal has become one of the hot research topics recently. ZrO2 is found to be an efficient adsorbent for phosphate adsorption, which has high resistance against attacks by acid, alkalis, oxidants and reductants and also remarkable selectivity to phosphoric ions. The carbonaceous materials has high performance with excellent chemical and physical stability, which possess various oxygen containing functional groups after surface modifications. These abundant surface oxygen-containing functional groups favor organic Zr to be anchored to the surface of adsorbents via covalent binding. Accordingly, ZrO2 moieties with high dispersion as well as high ZrO2 content normalized adsorption capacity can be obtained. The theme of this thesis is about zirconization of carbonaceous materials which have different distribution for surface oxygen-containing functional groups and adsorption behavior of phosphate by such adsorbents. We prepared three zirconia-functionalized carbonaceous materials by post-grafting or hydrothermal method. These adsorbents were characterized by X-ray diffraction(XRD), transmission electron microscope(TEM), infrared Fourier transform spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), zeta potential measurements and N2 adsorption/desorption. Hence, the static and dynamic adsorption tests were conducted in details. The conclusions are summarized as follows.(1) GO-Zr adsorbent was prepared by the post-grafting method and its adsorption behavior for the removal of phosphate in water was investigated. Characterization results show that nanosized ZrO2 particles are successfully introduced to GO surface. Accordingly, enhanced phosphate adsorption is shown on the GO-Zr adsorbent than on GO. The ZrO2 content-normalized adsorption amount was calculated to be 160 mg·g-1·ZrO2-1, much higher than the adsorption amount of ZrO2 prepared under the same conditions. Phosphate adsorption to the adsorbent is favored under acid conditions. For column tests, both Thomas and Yoon-Nelson models fit the data well. Moreover, the GO-Zr adsorbent exhibits high stability in eleven consecutive adsorption-desorption cycles.(2) The ACF-Zr adsorbent was successfully prepared using the post-grafting method and its static and dynamic adsorptions for phosphate uptake were investigated in details. The adsorbent patterns were fitted better by Freundlich adsorption isotherm than Langmuir isotherm. And kinetics was well described by the pseudo-second-order model. Phosphate adsorption on ACF-Zr increased with decreasing the pH value. Little influence of the ion strength was observed in the batch experiment. The ZrO2 content-normalized adsorption amount was higher than mesoporous ZrO2 and commercial ZrO2 reported by others.Yoon and Nelson model, Thomas model, Clark model, and Adams-Bohart model were applied to evaluate the dynamic performance at different inlet concentrations and flow rates in column system. The Yoon and Nelson model and the Thomas model made a more suitable descriptions than the Clark model. The initial region of the breakthrough curves were well predicted by Adams-Bohart model. The results provide useful theoretical basis for the design of actual wastewater treatment process.(3) The uptake of phosphate by GO-Zr and ACF-Zr were mainly through electrostatic forces and ion-exchange. And the adsorption process is governed by an inner-sphere complex adsorption mechanism. Hence, the adsorption of phosphate onto the two sorbents was only slightly influenced by the increase of the background ionic strength. However, their adsorption behavior strongly depended on the solution pH.(4) The MWNT-Zr adsorbents with different ZrO2 loading were successfully prepared using hydrothermal method. It was found that the particle size of ZrO2 moiety strongly dependent on ZrO2 loading. The adsorption capacity increased with the ZrO2 loading, but the ZrO2 content-normalized adsorption amount decreased with the ZrO2 loading. This is because that the lower ZrO2 loading, the smaller particle size of ZrO2 moiety, which made more activated sites exposed. Finally, the adsorption capacity increased.