| In recent years, there have been increasing environmental and toxicological interests about heavy metals and refractory pollutants such as phenolic compounds due to their widespread occurrence, poor degradable nature and relative frequency in the aquatic environment. Among all the techniques for wastewater treatment, adsorption, as one the most straightforward, convenient and effective methods, and enzymatic oxidation, with its efficient and low-cost degradation of refractory organic pollutants, has received great attention. Mesoporus materials, with their large surface area and pore volume, have been proved to be very promising adsorbents, and their uniform mesopores are very suitable for the immobilization of enzymes. Moreover, the good adsorption performance of mesoporous materials is favorable for the transfer and diffusion of the substrates, thus could enhance the catalytic efficiency of the immobilized enzyme.In this thesis, a group of mesoporous carbon-based adsorbents and immobilized enzymes based on mesoporous carbons were constructed. With their high effiency, easy operation and good reusability, these composites could be applied in the adsorption and degradation of some heavy metals and refractory organic pollutants. The adsorption and removal characteristics of the composites were discussed, and the removal mechanisms were investigated. Moreover, the effects of p H, coexisting ions, temperature and time on the removal of the pollutants were studied; therefore the optimum conditions for the application of those mesoporous-based materials were achieved. More importantly, the potential for the application of these materials in the complicated wastewater treatment were also investigated.Magnetic Fe/Ni nanoparticles doped bimodal mesoporous carbon(MBMC) exhibited greater potential in adsorption compared with conventional porous adsorbents and the unimodal mesoporous carbons. Therefore, MBMC was prepared for highly effective adsorption of cationic dye methylene blue(MB) and anionic dye methyl orange(MO). Structure characterization demonstrated that Fe/Ni nanoparticles were embedded into the interior of the mesoprous carbon, and MBMC maintained ordered and bimodal mesopores. The effects of several parameters such as contact time, p H, temperature, ionic strength and dye molecular structure on the adsorption were investigated. Alkaline p H was better for MB adsorption, while acidic p H was more favorable for MO uptake. The adsorption capacity was slightly enhanced when existing ion concentrations increased. Adsorption on MBMC was affected by the molecular structures of different dyes, and both primary and secondary pores of MBMC were involved in dye adsorption. The adsorption kinetics fitted well with pseudo-second-order model and exhibited 3-stage intraparticle diffusion mode. Equilibrium data were best described by Langmuir model, and the estimated maximum adsorption capacity for MB and MO was 959.5 mg/g and 849.3 mg/g, respectively. Thermodynamic studies indicated that the adsorption process was spontaneous and endothermic. Moreover, the adsorbent could be regenerated using ethanol, and the regenerated adsorbent after seven cycles could retain over 80% of the adsorption capacity for the fresh adsorbent. The results suggested that MBMC could be considered as very effective and promising materials for both anionic and cationic dyes removal from wastewater.A novel adsorbent was prepared by chelating magnetic mesoporous carbon with polyacrylic acid(PAA) to improve the performance of Cd(II) adsorption. Structure characterization demonstrated that the composites were successfully modified with carboxyl groups and preserved ordered mesostructure after modification. The high saturation magnetization(9.2 emu/g) of the modified composites indicated easy and fast separation from water under a moderate magnetic field. Batch experiments with variable p H, contact time and ionic strength were conducted to evaluate the adsorption performance. The modification accelerated the cadmium adsorption rate. The adsorption kinetics of the two materials followed pseudo-second-order model and exhibited 3-stage intraparticle diffusion mode. Equilibrium data were best described by Langmuir model, and the estimated maximum adsorption capacity for the modified adsorbent increased to 406.6 mg/g, which was 140.8% higher than the pristine materials. Moreover, the Cd(II) loaded adsorbent could be regenerated using 0.1 M ethylenediaminetetraacetic acid solution, and the regenerated adsorbent after five cycles could retain 85.2% of the adsorption capacity for the fresh adsorbent. The results suggested that PAA modified adsorbents could be considered to be very effective and promising materials for Cd(II) removal from wastewater.Compared with the pure water, landfill leachates consist of high concentration of complex organic and inorganic materials, thus the appropriate and effective disposal of landfill leachate is a great challenge. N-doped mesoporous carbons were synthesized in the highly efficient removal of Zn(II) in the intermediate and stabilized leachate from some sites. Structure characterization results indicated that the ordered mesoporous carbon nitide have been prepared, and NH2 and pyridine of the N-doped mesoporous carbons were responsible for the Zn(II) adsorption. The physiochemical characteristics of the leachates on Zn(II) adsorption were investigated, and the results showed that larger adsorption capacity of Zn(II) could be achevied with higher p H values, and the varieties and concentrations of the organic matters and coexisting ions could also pose effects on the adsorption. The adsorption kinetics in the two leachates followed pseudo-second-order model and the diffusion mode could be divided into external mass transfer and intraparticle diffusion. Equilibrium data were best described by Langmuir model, and the estimated maximum adsorption capacity in the pure water, intermediate, mixed and stabilized leachate was 138.8 mg/g, 168.5 mg/g, 193.6 mg/g and 294.3 mg/g, respectively. Moreover, the adsorbent could be regenerated using EDTA. The results indicated that the adsorbent could be considered as very promising candidate for complex wastewater disposal.A novel magnetically separable laccase immobilized system was constructed by adsorbing laccase into bimodal carbon-based mesoporous magnetic composites(CMMC). A large adsorption capacity(491.7 mg/g), excellent activity recovery(91.0%) and broader p H and temperature profiles than free laccase have been exhibited by the immobilized laccase. Thermal stability was enhanced to a great extent and operational stability was increased to a certain extent. The shift of kinetic parameters indicated affinity change between enzyme and substrate. Application of the immobilized system in phenol and p-chlorophenol removal was investigated in a batch system. Adsorption effects of the support were responsible for the quick removal rate in the first hour, and up to 78% and 84% of phenol and p-chlorophenol were removed in the end of the reaction, respectively, indicating that the magnetic bimodal mesoporous carbon is a promising carrier for both immobilization of laccase and further application in phenol removal.The application of the mesoporous carbon-based adsorbents and biocatalysis in the removal of aqueous heavy metals and refractory organic pollutants has been investigated in this dissertation. The research was aimed at providing mechanism and technology support for the fast, effective and economic wastewater treatment, and investingating the application of mesoporous carbon-based materisl in the environmental area. |
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