Preparation Of Clay/Carbon Nanocomposites Via One-step Activation And Its Adsorption Properties

Clay/carbon nanocomposites were prepared by one step activation method. The clay minerals were used as templates which were widespread in nature. The studies aimed at the effect of reaction conditions on the structures and properties of caly/carbon composites. Also the selective adsorption studies of dyes were also investigated. The main conclusions were described as follow.(1) The halloysite/carbon nanocomposites have been prepared via one-step activation using chitosan as carbon precursor and ZnCl2 as activating agent. The obtained composite was characterized by Fourier transform-infrared (FTIR) spectroscopy, Transmission electron microscope (TEM), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) analysis. The halloysite/carbon nanocomposite was used as an adsorbent for adsorption of benzoylformic acid from aqueous solution. The equilibrium adsorption dataof benzoylformic acid well conformed to Langmuir isotherm models and the calculated maximum adsorption capacity (qm) was 95 mg/g which is 10 folds of the qm of unmodified halloysite, indicating that the coating of carbon carbonized from chitosan greatly improve the adsorption properties. The effects of molecular size and conjugated bond mainly affects the adsorption process which is confirmed by FT-IR and BET analysis. The adsorption thermodynamics and kinetics for benzoylformic acid were investigated. The kinetic study illustrated that the adsorption of benzoylformic acid onto halloysite/carbon nanocomposites was fast because the adsorption equilibrium reached within 30 minutes. And the adsorption processes followed a pseudo-second order model (R2>0.99). The calculated thermodynamics parameters showed that the adsorption of benzoylformic acid onto halloysite/carbon nanocomposites was an exothermic, spontaneous and entropy process during 298 K to 318 K.(2) Halloysite/carbon adsorbents were prepared by one-step ZnCl2 activation as activation agents, which have a micro-mesoporous structure with abundant functional groups. The fabricated halloysite/carbon exhibited a specific high surface area of 1969 m2/g. The adsorption of single and mixed dyes onto halloysite/carbon nanocomposites was investigated in this study. The halloysite/carbon showed selective adsorption for cationic dyes.the adsorption capacity for malachite green and methylene blue reached 420 mg/g and 408 mg/g, respectively. In the cases of the mixture of cationic and anionic dyes, halloysite/carbon also showed highly selective adsorption for cationic dye which is due to the electrostatic attraction between halloysite/carbon and cationic dyes. Molecular size is also important for selective adsorption. The adsorbent had a better adsorption efficiency to dyes when the molecular size of dyes is smaller or equal to the pore size of adsorbent.(3) Clay/carbon nanocomposites were prepared by one-step ZnCl2 activation method using different biomass as carbon resources and different clays as templates at 500 ? for 1 h. The impregnation of ZnCl2 and cellulose was 2:1. The BET surface area showed that all the samples were above 800 m2/g. Montmorillonite/carbon, whose carbon resource is chitosan, had the highest adsorption capacity (39mg/g) for K2Cr2O7. It is much higher than that of ordinary montmorillonite (4mg/g). It's probably due to the electrostatic attraction between the ions of the montmorillonite and Cr6+ in water. The activated carbon with specific BET surface area coated on the surface of montmorillonite can provided more active sites for adsorption.