| Ordered mesoporous carbon (OMC) has received considerable attention in environmental pollution control due to its highly ordered and well-controlled mesoporous structures. Its unique pore structure provides advantages for the transfer and adsorption of contanminnts, especially for bulky organic compounds. Considering the low adsorption capacity of activated carbon (AC) for aquesous dyes, humic acid, and pharmaceutical antibiotics, ordered mesoporous carbons with varied structures were prepared and their structures were characterized in this thesis. The influence of pore structure on the adsorption behavior was studied using direct yellow 12, humic acids, pharmaceutical antibiotics, tannic acid, and phenol as the probe molecules. The results are summarized as follows:1) The adsorption of direct yellow 12 over both CMK-3 and AC could be well described by the Langmuir isotherm model. The maximum adsorption amounts of CMK-3 and AC for direct yellow 12 at 25℃ were found to be 303.0 mg/g and 161.3 mg/g, respectively, indicative of a substantially higher adsorption capacity of CMK-3 compared to that of AC. The adsorption of direct yellow 12 over CMK-3 and AC obeys the pseudo-second-order kinetics and the adsorption rate decreases with initial concentration. Given at similar equilibrium adsorption amounts (43,106, and 180 mg/g), the adsorption rates over CMK-3 were one order of magnitude higher than that over AC. The present results clearly verify the importance of mesopores in the adsorption of aqueous direct yellow 12.2) Batch experiments were conducte to evaluate adsorption mechanism of two humic acids from coal and soil, respectively, on the synthesized carbon CMK-3. For comparison, a commercial microporous AC with a broad pore size distribution and nonporous graphite were included as additional adsorbents; moreover, phenol was adopted as a small probe adsorbate. The adsorption of the two humic acids was substantially lower on the AC than on CMK-3, because of the size-exclusion effect. In contrast, CMK-3 and AC with a parallel specific surface area showed comparable adsorption for phenol when the size-exclusion effect was not in operation. Additionally, we verified by size-exclusion chromatography studies that CMK-3 exhibited greater adsorption for the larger humic acid fraction than the AC. Within the examined pH range, adsorption of the two humic acids on the three carbonaceous adsorbents decreased with increasing pH, but much stronger effects were observed on soil humic acid than on coal humic acid, resulting from the enhanced hydrophobic effect in adsorption because of the greater sensitivity of pH-mediated hydrophobicity of soil humic acid.3) Three porous carbons, CMK-3, C41, and C-LTA, were synthesized using mesoporous silicas SBA-15 and MCM-41, and block copolymer F127 as their templates, respectively. In contrast with CMK-3, C-LTA has closed pores similar to the template of CMK-3. In addition, C41 has irregular pore structure consisting of carbon nanorods due to structure collapse upon template removal. The adsorption of phenol, sulfamethoxazole, and tylosin on the synthesized carbons was investigated. For comparison, a commercial microporous AC and nonporous graphite were chosen as reference adsorbents. The results of small angle X-ray diffraction, transmission electron microscopy, and N2 adsorption demonstrate that the ordered pores of CMK-3 and C-LTA are p6mm hexagonally arranged, while C41 has disordered pore structure. Moreover, the probable pore sizes of CMK-3 and C-LTA are 3.97 and 4.92 nm, respectively. The adsorption of phenol and sulfamethoxazole over the tested adsorbents was correlative with the specific surface area of the adsorbents, irrespective of their pore structures. However, the adsorption of tylosin over these carbonaceous adsorbents was greatly affected by their pore structures. CMK-3, with open-shaped mesopores, showed the highest adsorption for tylosin among the five adsorbents. The adsorption of tylosin over C41 was higher than that over C-LTA, probably resulting from a weaker size-exclusion effect of C41 with flexible porous character compared with rigid mesoporous C-LTA. In parallel, tylosin adsorption over C-LTA was still higher than microporous AC. The adsorption process of phenol and tylosin over the four porous carbons were well fitted with the pseudo-second-order kinetics. Minor difference in the adsorption rates of phenol over CMK-3, C-LTA, C41, and AC was observed. On the contrary, tylosin adsorption rates over the four adsorbents vary greatly, following an order of CMK-3>>C-LTA>C41>>AC, indicating that pore shape of porous carbon as well as pore size is an important factor controlling the diffusion of bulky tylosin.4) CMK-3 was activated by CO2 and a porous carbon with higher micropore and mesopore volumes was obtained. The adsorption of phenol and tannic acid over CMK-3, the CO2-treated CMK-3, and AC was investigated. The adsorption isotherms showed that the adsorption of phenol and tannic acid was enhanced upon CMK-3 activation by CO2. N2 adsorption results indicated that the increased micropores and mesopores by CO2 activation were suitable for tannic acid adsorption, while a great part of micropores for AC could not be occupied by tannic acid because of the size-exclusion effect. The adsorption process of phenol and tannic acid over the three carbons are both controlled by external mass transfer and diffusion in pores. Additionally, the adsorption rate of tannic acid was found to be more rapid over CO2-treated CMK-3 than over original CMK-3. |
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