Hydrothermal Synthesis Of One-dimensional Clay/Carbon Nanocomposites And Its Adsorption Properties

The hydrothermal treatment and acid treatment on the minerals palygorskite, sepioliteand halloysite were investigated. Then we prepared clay/carbon nanocomposites byusing the clay as template, cellulose as carbon precursor through hydrothermal method.The adsorption behaviors of methylene blue (MB) and phenol onto preparedproducts were studied. The main conclusions are listed as follows:(1) The effect of hydrothermal treatment (60-250℃) on the structural character ofpalygorskite was investigated. The results illustrate that the length of palygorskite fibersbecomes shorter, but there is no obvious change of the diameter. The BET specificsurface area of palygorskite gets the largest after hydrothermal treatment at110℃. Asfurther increase of temperature (200-250℃), the specific surface area (BET) graduallyreduces. The adsorption behavior of methylene blue onto hydrothermally treatedpalygorskite was studied to evaluate the modification effect. When the adsorptiontemperature is298K, the adsorption time is4h, the adsorption rate is200r/min, theratio of solid to liquid is1g to2500mL and the pH value is7.5, the adsorption capacityof methylene blue (MB) on the hydrothermal treated palygorskite shows the same trendas the BET value.(2) Two kinds of sepiolite were modified by hydrothermal carbonization. Firstly, theminerals were dissolved in hydrochloric acid solution to remove the impurity. Thehydrothermal treatment on the structural character of the sepiolite was investaged beforepreparing the composite. Then we prepared sepiolite/carbon through hydrothermalcarbonization. The result shows the HCl can remove the impurity in sepiolite. And thehydrothermal treatment has no obvious effect on the structural character on sepiolite.Owing to the different composition of the two kinds of sepiolite, the amount of sepiolite,the aspect ratio and the active sites are all different. The carbon particles loading on thesurface of sepiolite vary so much. The two kind composite materials were applied toremove phenol from the wastewater. When the adsorption temperature is298K, theadsorption time is12h, the adsorption rate is200r/min, the ratio of solid to liquid is1gto100mL and the pH value is7.5, the phenol removal onto the two kinds of sepioliteare3%and5%, the phenol removal of the two kinds sepiolite are61%and46%,respectively. And the phenol removal onto acid treated sepiolite/carbon composites are69%and48%, which means hydrothermal modification and acid treat joint action to improve the adsorption capacity of phenol. It can be attributed to the hydrothermalmodification improves the organophilic of sepiolite and impurities can be removed byacid treatment, so that the active sites of sepiolite exposed for loading carbon.(3) Halloysite/carbon nanocomposite was prepared using halloysite as template andcellulose as carbon precursor by optimizating the hydrothermal parameters. The resultshows the best reaction conditions of time, the amount of catalyst and the mass ratio ofthe halloysite to cellulose are24h,0.5wt%and0.5, respectively. Then we removed thetemplate by dissolving the composite in HF solution to achieve carbon nanotubes. Andthe composite and carbon nanotubes were dissolved in the ZnCl2solution to activate thesamples. The composite, nanotubes and activated samples were all used to adsorbphenol. When the adsorption temperature is298K, the adsorption time is12h, theadsorption rate is200r/min, the ratio of solid to liquid is1g to100mL and the pHvalue is7.5, the phenol removal onto composite is50%, which is higher than that ofnatural halloysite (2%). In addition, the removal rate of material activated by ZnCl2solution o over90%, closing to the adsorption capacity of the activated carbon forphenol. The result shows: the BET value of the hydrothermally modified halloysitereduced slightly, it is44m2/g. But there is a carbon layer with20-30nm loading on thesurface of halloysite, which improved the organophilic of halloysite, so the adsorptioncapacity improved significantly. After ZnCl2activation, the BET value changes to1150m2/g, which is larger than the BET value of the activated carbon (910m2/g).Correspondingly, the adsorption capacity closes to the activated carbon. The adsorptionmechanism of phenol onto the resultant samples conforms to Freundlich isothermaladsorption equation.