The Activation For Preparing Of One-dimensional Clay/Carbon Nanocomposites And Its Adsorption Properties

The clay/carbon composites were prepared via acid activation,hydrothermal and one-step carbonization-activation process which using sepiolite and halloysite as template, cellulose and chitosan as carbon source, respectively. The effects of activation conditions on the morphology and structure of clay/carbon composites were investigated. The main activation mechanism during preparation process was also studied. Meanwhile, the adsorption capacity for phenol, methylene blue and NO onto clay/carbon composites was studied. The main conclusions were described as follows:(1) The sepiolite/carbon composites are prepared by 220℃-autoclave hydrothermal carbonization of cellulose using 1.2-mol/L-hydrochloric-acid-activated sepiolite fibers.The deposited amorphous carbon nanoparticles (30-150 nm) nonuniformly and partially covering the sepiolite surface have surface functional groups (-CH2, -CH3, C=C and C=O), which enhance the organophilicity. Compared to a mixture of pristine sepiolite and hydrothermal carbon prepared without sepiolite, the carbon-coated sepiolite exhibits lower specific surface area but greater organic adsorption, due to the lower pore size and particle size of the hydrothermal carbon coating compared to the hydrothermal carbon prepared without sepiolite. The acid pre-activation decreases the sepiolite crystallinity and increases the deposited carbon content from 24.67 to 31.63 vol.%,while increasing the specific surface area from 26.53 to 33.98 m~2/g, increasing the fraction of phenol removed from 47.1% to 57.1%, and increasing the monolayer phenol adsorption capacity from 4.1 to 5.26 mg/g. Compared to the acid activated but uncoated sepiolite, the carbon coating decreases the density from 2.227 to 1.696 g/cm3 and decreases the specific surface area from 118 to 34 m~2/g, but increases the fraction of phenol removed from 6.1% to 57.1%.(2) The halloysite/carbon composites with higher specific surface area and micro-mesoporous structure were synthesised using halloysite as template, chitosan as carbon source and potassium carbonate as activating agent via one-step carbonization-activation. The halloysite/carbon composites remained tubular morphology,a carbon layer with thickness of 20-40 nm and organic groups (C=O, N-H,C-N and C-H) wrapped the halloysite nanotubes. During activation pocess,carbothermal reduction of K2CO3 leading to the consumption of carbon in the char and the potassium vapour etching the carbon layer, thereby increasing the specific surface area of halloysite/carbon. The specific surface area of halloysite/carbon was up to the maximum value 1509 m~2/g under the activation temperature of 800 ℃, activation time of 90 min and impregnation ratio of 2:1. The adsorption of methylene blue onto halloysite/carbon composites well conformed to Langmuir adsorption isotherm model and pseudo-second order model under 25 ℃,the maximum adsorption capacity was 694.4 mg/g which value is enhanced by 8-fold in comparison with that of pristine halloysite. The calculated thermodynamics parameters during 25-45 ℃ indicated that the adsorption of methylene blue onto halloysite/carbon is an endothermic, spontaneous and physical process. Also, the NO adsorption capacity onto halloysite/carbon (4.83 mg/g) has been significantly improved which was enhanced by 22-fold in comparison with that of pristine halloysite.