Preparation Of Carbon Nanotubes Composites For Adsorption Of Gallium

In this paper,titanium dioxide/carbon nanotube composites and gallotannin/carbon nanotubes composites were successfully prepared,and the feasibility of the materials was verified by a series of characterization and experiments.The adsorption behavior and adsorption mechanism of gallium?III?were investigated.The research contents and results were as follows:The mesoporous titania/carbon nanotube composites was synthesized by using carbon nanotubes as a matrix and titanium dioxide as an adsorption source,which combined by Ti-O-C bond using one-pot method.To improve the photocatalytic performance of titania/carbon composite,it is necessary to simultaneously increaseits crystallinity and surface area.Therefore,the composite material was transformed from mesocrystalline to porous single crystal by annealing to enhance the adsorption capacity of gallium.The results showed that the composite materials?300-CNT-TiO₂,400-CNT-TiO₂ and 600-CNT-TiO₂?with different annealing temperatures had a certain adsorption effect on gallium in weak acid and weak base solutions,among which pH 3 was the optimal adsorption acidity.The maximum adsorption capacities of 300-CNT-TiO₂,400-CNT-TiO₂ and 600-CNT-TiO₂ at pH 3 were 118.85,136.63and 30.36 mg·g^-1,respectively.Apparently,the adsorption capacity of gallium adsorbent 400-CNT-TiO₂ was the largest.The nonlinear fitting of gallium ion adsorption with time conforms to pseudo-second-order-kinetics.Thermodynamic parameters indicate that adsorption is an endothermic spontaneous process.XRD and raman spectra showed that the crystallinity was enhanced after annealing and it was typical anatase.BET analysis showed that the composite material was type IV adsorption isotherm and mesoporous.FT-IR and XPS analysis confirmed that the adsorption mechanism was the ion exchange between-OH and Ga?III?.400-CNT-TiO₂ showed good selectivity to gallium under the coexistence of Al and Ge mixed ions.At the same time,the material had excellent cyclic regeneration performance.In order to further shorten the preparation period,simplify the preparation process and improve the adsorption capacity of gallium,gallotannin/carbon nanotubes?CNT-GT?composite were synthesized by ultra-fast and simple microwave hydrothermal method.Carboxylated carbon nanotubes?CNT-COOH?and gallotannin were coupled by the coupling agent dicyclohexyl carbon diimine?DCC?to form ester bonds.A series of characterization methods such as FT-IR,Raman,TEM,functional group titration,thermogravimetric,specific surface area analysis proved that composite compound successfully.The CNT-GT obviously enhanced Ga?III?adsorption capability(170.8 mg·g^-1)as compared with the unmodified carboxylic carbon nanotubes?CNT-COOH?and non-microwave synthesized composite?N-CNT-GT?.The adsorbent CNT-GT not only had better selectivity,but also had good cycling performance,which could be confirmed by adsorption-desorption experiments.In a word,the method described in this paper should be a quick and simple way to prepare highly efficient adsorbents,which has definite significance for the application of the environment.