Fabrication Of Carbon Nanocomposites Derived From Layered Double Hydroxides Precursors And Their Application In Water Treatment

Carbon nanocomposites have potentially been used in many fields, such as catalysts, magnetic materials, lithium ion batteries, chemical sensors, and adsorbents due to their excellent physicochemical properties. How to design and synthesis novel carbon nanocomposites with controlled composition, morphology, as well as high performances becomes the main topic in material science. This dissertation describes a study on the preparation of CNTs/M/Al2O3(M=Co, Ni), CNTs/Mg(Al)O, and hexagonal C/Mg(Al)O nanocomposite through solid-state pyrolysis of layered double hydroxides with organic anions in the interlayer. With changing the composition of precursor and the calcination parameter, we have realized controllable preparation of functional carbon nanocomposites with different composition, size, and morphology. As an example of the potential applications of the resulting functional carbon nanocomposites, they were directly used as adsorbents for the removal of organic dyes and heavy ions in waste-water treatment. The adsorption mechanism has been studied systematically. The main results of this dissertation are as follows:1. Synthesis of CNTs/M/Al2O3(M=Co, Ni) and their application in water treatment. Uniform CNTs/M/Al2O3(M=Co, Ni) nanocomposites have been synthesized by one-step solid-state pyrolysis of CoAl LDHs and NiAl LDHs precursor containing salicylate anions. The influences of the calcination conditions including temperature and time on the composition, particle size, and morphology of resulting products have been studied. Study of the mechanism indicate that the astonishing upward growth of CNTs indicates the presence of a liquid or liquid-like phase, and the Cn intermediates derived from the decomposition salicylate anions self-assemble into CNTs on the surface of the product. The FT-IR and XPS results show that the external surfaces of CNTs are extensively functionalized with C-OH and COO-M (M=Al and Co) groups and exhibit very high performance in the removal of both organic dyes CR, EB and toxic heavy metal ions Pb2+, Cd2+.2. Synthesis of CNTs/Mg(Al)O nanocomposites and their application in water treatment. The influence of the calcination temperature on the composition, particle size, and morphology of CoFe alloy nanoparticles and CoFe/MgO nanocomposites has been studied. The result indicate that CoFe alloy nanoparticles are highly dispersed in the MgO matrix, exhibiting very high thermal stability. Encouraged by the high catalytic activity of CoFe alloy nanoparticles, uniform CNTs/Mg(Al)O have been synthesized by one-step solid-state pyrolysis of CoFeMgAl LDHs precursor containing terephthalate anions. As an example of the potential applications of the resulting CNTs/Mg(Al)O nanocomposites, they were used as adsorbents in waste-water treatment and exhibit very high performance in the removal of organic dyes, such as CR, MO, and Orange II. Especially for CR, the Qmax is as high as1260mg/g. Further mechanism study indicate that the Mg(Al)O mixed metal oxides recover the original layered structures of LDH during the adsorption process, and improve the adsorption ability of CNTs/Mg(Al)O nanocomposites by combination with the excellent adsorption performance of CNTs and Mg(Al)O nanoparticles.3. Synthesis of hexagonal C/Mg(Al)O nanocomposite and their application in water treatment. A series of uniform hexagonal C/Mg(Al)O nanocomposite have been successfully prepared by solid-state pyrolysis of a simple organic-inorganic MgAl LDHs precursor containing salicylate anions, which exhibit hexagonal platelet morphology. The influence of calcination temperature on the crystalline, particle size and specific surface areas of the resulting hexagonal C/Mg(Al)O nanocomposite have been studied. The results revealed that the as-prepared the Mg(Al)O nanoparticles with particle size in the range of4-6nm are highly dispersed in hexagonal carbon matrix, exhibiting high thermal stability and high specific surface areas. Encouraged by this porous structure and unique memory effect of LDHs materials, the as-obtained hexagonal C/Mg(Al)O nanocomposites were used as adsorbents in waste-water treatment and exhibit very high performance in the removal of both organic dyes CR (Qmax=6529mg/g), Orange II (Qmax=3977mg/g) and toxic heavy metal ions Pb2+(Qmax=123mg/g). Further mechanism study indicate that the small Mg(Al)O nanoparticles recover the original layered structures of LDHs during the adsorption, resulting the fabrication of an hierarchical structure of LDHs nanosheets on carbon matrix, which can provide more active sites for adsorption of pollutants. The adsorption ability of hexagonal C/Mg(Al)O nanocomposites are highly improved by combination the excellent adsorption performance of carbon matrix and Mg(Al)O nanoparticles. Furthermore, the C/Mg(Al)O nanocomposite can be separated from the solution by simple natural settlement due to its large size.