| Ordered mesoporous materials (OMMs) are a kind of ones with long-range ordered pores and their pore sizes are between 2-50 nm. After a two-decade development, OMMs with tunable framework compositions, mesostructures, porosities, surface properties and morphologies can be easily synthesized, which have been widely studied in many applied areas such as the environment, energy and delivery of biomolecules. Presently, the most promising OMMs for large-scale production and actual industrial application are focused on silica and carbon based materials. Because of their fascinating properties including huge specific surface areas, uniform and adjustable pore sizes and friendly to environment, ordered mesoporous silica/carbon materials (OMSs/OMCs) show a promising prospect for adsorption and separation, gas storage, catalysis, electrochemistry and many other applications. However, to find a way about making full use of mesopores in nature, targeted synthesis of corresponding OMMs which meets the actual application and establishment of a complete system for promoting potential applied studies to practical application is still a big challenge. Importantly, this process is a necessary road for OMMs to maintain their vitality. Therefore, this thesis pointedly choose special toxin microcystins whose molecular sizes are matched mesopore dimensions as the targets for adsorption application, thus to furthest explore the advantages of OMMs. Microcystins (MCs), produced by cyanobacterica from blue algae, are threatening human health and the environment due to their acute and irreversible liver damage. However, the large molecular toxins are very stable and difficult to remove from water source through traditional technologies. The present researches of MCs focus on toxicology, analysis and their environmental behavior, but the efficient technologies about removal of MCs from polluted water is still not perfect. Especially, there is lack of a better understanding of the possible influences of the properties of MCs on their adsorption and a better design for materials with suitable structure, texture and surface chemistry for adsorption. Moreover, among the application of adsorption and separation, efficient adsorption of carbon dioxide (CO2), which lead to environmental greenhouse effect, is also of urgent.This thesis focuses on design and synthesis of perfect OMMs for application in adsorption and separation and their corresponding adsorption mechanisms, including clear correlations between adsorption performances of MCs and several influencing factors such as pore structure, texture and size of an adsorbent though a comprehensive study; surface functionalized OMMs and their adsorption performances on MCs and CO2; adsorption mechanism analyzed by thermodynamics and kinetics studies; systematic static, dynamic and competitive adsorption behavior of microcystins onto OMMs and evaluation of regeneration to the OMMs as adsorbents.In chapter 2, a detecting method for MCs by high performance liquid chromatography (HPLC) has been established. An octadecyl silica silica gel column (C18) is adopted for isocratic elution. After determination of the detection wavelength and optimization the types, proportion and flow rate of mobile phases, well separated peaks of MCs are observed. The reproducibility, precision and sensitivity of this method are perfect. Furthermore, standard curves related to areas of peaks and concentrations of MCs solutions are established to provide reliable analyses for the following tests in adsorption.In chapter 3, a detailed study of MCs adsorption onto a series of ordered mesoporous silica materials is presented and corresponding adsorption mechanisms are revealed. To the best of our knowledge, we first clarify in detail the effects of adsorbents’ properties on the adsorption performance of large toxin MCs by adopting mesoporous silica materials SBA-15, KIT-6, MCM-41 and MCM-48 with precisely adjusted structural and textural properties. The correlation among the adsorption capacity of MCs and the mesostructure, pore size/pore volume, surface area has been well revealed. Resultantly, excellent candidate SBA-15 have been sorted out for extremely rapid and high-capacity removal of MCs, capable of removing high-concentration MCs within one minute with high capacities of 5.99 mg/g for microcystin-LR (MC-LR) and 12.98 mg/g for MC-RR. Furthermore, using a pristine mesoporous silica SBA-15 as a model, the static thermodynamics and dynamic adsorption behaviors are also worked out to get a comprehensive understanding of the adsorption process of MCs on mesoporous silica materials. Our detailed study can be also treated as a model for providing theoretical guidance to select an appropriate adsorbent for other pollutants.In chapter 4, mesoporous silica materials SBA-15 with various surface properties are employed to explore the adsorption effect on MC-LR. Three grafted organic groups (amino, quaternary ammonium and carboxyl) are successfully modified onto the pore surfaces by post-modification without any damage of its original mesostructure, which is based on a SBA-15 sample with 8.7 nm pore size by hydrothermal temperature at 100 ℃. After comparing the adsorption behavior of MCs onto pristine and functional SBA-15 adsorbents at different pH values, the results display the highest adsorption/removal for MC-LR increase from 50 to 95% around pH 4 on functional SBA-15, which is explained by the enhanced surface electrostatic interaction and hydrophobic bonding. By studying the adsorption performance under a series of pH values, it is also possible to realize regeneration of adsorbents.In chapter 5, an integral and detailed study about static, dynamic and competitive adsorption performances towards MC-LR onto MCS/C materials has been explored. Firstly, different samples such as FDU-14, FDU-15, FDU-16, FDU-18, CMK-3, MCS/C and MCS/C-APS with various mesostructures, pore sizes/volumes, surface areas and surface properties are synthesized precisely. Through systemically static adsorption tests, a definite relationship between properties of adsorbents and adsorption performance is clarified. Sample MCS/C shows the best performance of 526 mg/g for MC-LR due to its unique pore structure and texture. Then, MCS/C is employed for a comprehensive dynamic adsorption behavior study. The column filled with MCS/C performed high adsorption capacity, which is 30 times than that of powder active carbon (AC). Moreover, the MCS/C adsorbent can be easily regenerated and remain unaltered adsorption capacity over three consecutive cycles. Furthermore, the candidate MCS/C is evaluated by competitive adsorption with Rhodamine B (RhB) and phenol to simulate the practical surroundings in waste water. It is found that competitive adsorbates with large molecular size and positive charged impact the adsorption amount of MC-LR, but eventually the total amount of adsorbed/removed pollutants increase.In chapter 6, an efficient route by post-modification is developed for controllable synthesis of surface functional OMCs. A bimodal mesoporous (2.8 and 5.5 nm) carbon MCS/C is chose as based-materials. The amino groups are successfully modified onto the surface of MCS/C by the route of wet oxidation, acylation and then modification of ethylenediamine (EA). The amount of modified amino groups can be adjusted by control the reaction time of wet oxidation and the amount of added EA. The amino content can be achieved to 3.84 mmol/g. After modification, the MCS/C samples are still maintain their ordered mesostructures and high surface areas with 1200 m2/g (a few decrease compared to pristine MCS/C). The isoelectric point (IEP) of MCS/C can be changed to pH 7 - 8. The amino-functional MCS/C materials are very attracting adsorbents for microcystins removal and CO2 capture. |
PDF Full Text Request