利用水熱法製備Cobalt-Silicate和Nickel-Silicate孔洞複合性材料作為吸附劑和催化觸媒

Abstract

In this thesis, we mainly focused on providing a simple method to synthesize high surface-area porous cobalt-silicate and nickel-silicate. In practical applications, these metal-silicate composites demonstrate high performances to be used as adsorbents of toxic ions (of Hg2+, HAsO42-) and as catalysts towards O3, NH3 and N2O-decompositions. Because we can mass-produce the mesoporous silica of high surface-area, it was directly used to combine with metal hydroxides. In neutral or alkaline solution, mesoporous silica can dissolve and reconstruct to exfoliate the layered metal hydroxides during hydrothermal treatment, and then sheet-like structure was formed. This clay structure is similar to the metal phyllosilicate minerals in nature. In order to find an optimal synthesis conditions, many experimental factors (the ratio of metal/silica, the pH value and aging time of metal hydroxide, the hydrothermal reaction time, silica sources, alkali sources, etc.) have been studied. The resulted materials are highly reproducible and this synthetic concept can be extended to use other cheap sources. For example, sodium silicate can also be used as the silica source to prepare porous cobalt-silicate with 454 m2/g and nickel-silicate with 551 m2/g, respectively. These good results reveal that this synthesis method possesses advantages of convenience and low-cost. In nature, most of gramineae plants contain inorganic silica to enhance the structural strength. The bio-silicate isolated from rice husk can be used as an alternative silica source to prepare metal-silicates. During hydrothermal reaction, silica in rice husk dissolves and then combines with metal hydroxide under an alkaline environment. In addition to silica, rice husk also contains lignin, cellulose and other organic matters. The desired substance can be extracted in sequence by changing water amount and the pH value of the solution. Lignin can be further carbonized to form porous carbon with high surface-area, cellulose can be used as raw material of the bio-ethanol, and the silica-extracted rice husk is easier to burn off to release heat for electricity generation. These applications are fit the green chemistry concepts of reusing agricultural wastes.