Preparation Of Modified Clay Nano-adsorbents And Their Application In Removing Micro-pollution From Water

Water is one of the basic conditions to the survival of all life on the earth. However, with the development of economy, industry and human being’s daily life make the water pollution worse and worse. China’s national control section water quality monitoring data show that 31.1% of river basins,38.7% of the lake water quality of drinking water under III class water quality standard. Slightly polluted source water contains kinds of pollutants, divided into organic pollutants and inorganic pollutants. And people found out that heavy metals (As, F and so on), which belong to inorganic pollutants, are harmful to humans health, and are difficult to removed by conventional water treatment methods. Therefore, it is urgent that the study of micro-pollution removal methods and techniques in the water.We know that the main methods for water pollution are adsorption, ion exchange, membrane separation technology and biological technology and so on. But adsorption becomes the first choice because of its low cost, high efficiency and easy operation. However, the adsorbents we’ve already have are useful for high concentration water pollution of industry, so many researchers try to figure out the problem for low concentration pollution in the drinking water.Natural nano clay materials have nano structure, huge specific surface area and abundant pore structure. And the materials have a lot of advantages, which are wide resources, nice adsorption performance. But after years’ aging, the active sites gradually lost, and the materials are hard to recycle. Recent years, people prepared kinds of magnetic clay-based adsorbents for easy recycle. We considered both advantages and disadvantages of materials in adsorption, tried to modify the materials and their structures, meant to get theory and technology about adsorption, aimed at reliable scientific basis for drinking water purification.This task is based on one the national key basic research projects "Integration and demonstration of nano technology in high efficiency and low cost water purification" (fu ndamental research of using nano technology to get rid of micropollutants from drinking water). The main task in this research is to develop amodification technology of natural clay nano materials which was removed from inorganic micro pollutants in drinking wat er. Cr, As and F are chosen as the target micro pollutant because of its broad impact a nd strong toxicity. HNTand SEP are chosen to be the natural clay nano material because of its large specific surface area and abundant porous structure. With a special structure design and chemical treatment, magnetic nano material, which has high adsorption and high capacity, arecombined. Nano-composite, which has high selectivity, high adsorption c apacity and easy in magnetic recycle, are being selected. By analyzing the characters lik e morphology, combination of phase, and porous structure, studying the inner connection between the structure parameters and preparation conditions of nano clay materials. By u sing single factor experiment, found out the impact of modification in nano clay material s adsorbing micro pollutants in drinking water. The mechanism of adsorption has also b een studied.The main contents divide into three parts:A) Modifying halloysite adsorbent with alkali and the performance of removing fluorineThis study investigates the activaction of Halloysite (aluminosilicate) with alkali, and explains the characterization of structure. After treatment, the structure of the clay changed. Hollaysite turned to zeolite, and the products have different morphologies,which are nanotubes, nano flower-shape hierarchical structures and nanosheets. Based on the morphologies, we studied the adsorption application and some others. The as-prepared nanocomposites were characterized by the XRD, FTIR, SEM, TEM, HR-TEM, NMR, N2 adsorption-desorption and so on. And these nanocomposites were used as adsorbents for F- removal. Through single factor study, the influence of the initial concentration of F-, contact time, and PH value on adsorption properties were investigated. And the adsorption mechanisms were studied. The main contents are as follows:(a)After alkali treatment, pure hollaysite turned to many different nanosubstances with different morphologies. We obtained the same crystalline zeolite under the condition 2wt%NaOH hydrothermal treatment, and we got two kinds morphologies:nanotubes (100℃) and nano flower-shape hierarchical structures(120℃).And we obtained flake zeolite under hydrothermal treatment with 2wt%NaOH、5wt%NaOH and the temperature ranged from 100℃ to 150℃.(b)We used zeolites as absorbents to removed F-.At the same absorption condition, we finally achieved that maximum immobilization capacity of flower-shape hierarchical structures reached to 161.78 mg/g, that of flake zeolite reached to 122.02 mg/g,and that of nanotube zeolite reached to 95.97 mg/g, so we chose flower-shape hierarchical structure zeolite as the best absorbent to remove F-.After series experiment, we knew the optimal condition:the pH value is about 2,concentration of absorbent is 10mg/50mL.The absorption equilibrium time is about 30 min. Kinetics of the F- removal was found to follow a pseudo-second-order rate equation. The Fruedlish adsorption isotherm was applicable to fit the removal process.B) Synthesis of magnetic halloysite-based nanocomposites and their application in the removal of chromium(Ⅵ)In order to remove the Cr(Ⅵ) efficiently and recycle the adsorbent, we tried to modify the adsorbent with magnetic oxides. In this paper, based on the hot issue of Cr(Ⅵ) polluted water treatment, two kinds of halloysite-based nanocomposites were synthesized, including HNT@C, Fe3O4/HNT@C. The as-prepared nanocomposites were characterized by the FTIR, TEM, N2 adsorption-desorption, XRD, XPS and so on. And these nanocomposites were used as adsorbents for Cr(Ⅵ) removal. Through single factor study, the influence of the initial concentration of Cr(Ⅵ), and pH value on adsorption properties were investigated. And the adsorption mechanisms were studied. The main contents are as follows:(a) A new kind of carbonization halloysite (HNT@C) adsorbent was prepared with a one-step hydrothermal carbonization process by using halloysite and glucose. The FT-IR spectrum of the HNT@C nanocomposite showed the existence of a large number active functional groups, such as -COOH, C=O, C-OH and C=C. Then the HNT@C nanocomposite was used as adsorbent for Cr(Ⅵ) removal from its aqueous solution. The results showed that the new HNT@C nanocomposite exhibited selective and high efficient adsorption ability for Cr(Ⅵ) with maximum adsorption capacity of 136.98 mg/g. Kinetics of the Cr(Ⅵ) removal were found to follow a pseudo-second-order rate equation. The Langmuir adsorption isotherm was applicable to fit the removal process. In addition, the results obtained by X-ray photoelectron spectroscopic analysis (XPS) suggestted that some of Cr(Ⅵ) anions were reduced to Cr(Ⅲ), demonstrating that HNT@C could detoxify Cr(Ⅵ). According to the previous research, a probable mechanism for the removal of Cr(Ⅵ) was proposed to be the synergistic effect of surface complexation, redox reaction, and cation exchange. The results demonstrate that this nanocomposite is an exceptionally promising candidate as a low-cost, effective and environmetally friendly adsorbent for the removal of Cr(Ⅵ) ions from water.(b) Fe3O4/HNT@C was prepared via solvothermal reaction by using HNT@C and FeCl3 as reactant. The Fe3O4/HNT@C nanocomposite possessed high reduction and immobilization capability for Cr(Ⅵ), and the maximum immobilization capacity reached to 132.82 mg/g. The saturation magnetization of Fe3O4/HNT@C was found to be 24.5 emu/g, the adsorbents could be separated in a short time by using the external magnetic field. The uptake of Cr(Ⅵ) onto the surface of Fe3O4/HNT@C was mainly governed by reduction and adsorption process. After adsorption, most of Cr(Ⅵ) were reduced to Cr(Ⅲ), and immobilized on the surface of adsorbent. These results indicated that Fe3O4/HNT@C can be applied in the immobilization of Cr(Ⅵ) from contaminated water and soil.C) Synthesis of magnetic sepiolite-based nanocomposites and their application in the removal of As (Ⅲ)In this thesis, based on the issue of As (Ⅲ) polluted water treatment, two kinds of iron oxides@sepiolite nanocomposites were synthesized using environmental friendly, low cost natural sepiolite clay by a variety of chemical methods for surface activation and assembly, including y-Fe2O3/SEP@C and Fe2O3/SEP. The iron oxides@sepiolite nanocomposites were characterized by XRD, SEM, TEM and FT-IR and so on. In the removal of As (Ⅲ), we study the effect of the initial concentration, initial pH, adsorbent dosage, the coexisting anion and adsorption time and so on, and further explore the adsorption mechanism. The main contents of this paper are as follows:(a) Intermediate product Fe3O4/SEP@C turned toy-Fe2O3/SEP@C under 250 ℃ calcinations, and Fe2O3/SEP@C turned to Fe2O3/SEP(Mixed y-Fe2O3 and a-Fe2O3) with amorphous carbon lost under 500 ℃ calcinations. Modified SEP has abundant porous structure, its pore diameters are much bigger than the pore diameters of SEP, but the exist of iron oxide makes the specific surface area and pore volume smaller. And the saturation magnetizations of Fe2O3/SEP and y-Fe2O3/SEP@C are 29.53 emu/g and 31.95 emu/g.(b) The maximum adsorption capacities of Fe2O3/SEP and y-Fe2O3/SEP@C are 38.62 mg/g and 30.88 mg/g. Fe2O3/SEP is suitable for adsorption in neutral As(Ⅲ) ion solution, and its adsorption ability are greatly influenced by the coexistence of anion. When the environment is alkaline, the adsorption performance of y-Fe2O3/SEP@C gets smothered. And when F- and PO4-exist in the water, it impacts the adsorption for separation of As (Ⅲ).(c) The adsorption processes of two kinds of modified SEP follow the Langmuir adsorption isotherm model and the quasi-second-order kinetic model. On the one hand, adhere to the sepiolite fiber surface gamma Fe2O3, Fe2O3 nanoparticles changed the adsorbent’s surface electrical, provided more active sites, promote the adsorbent adsorption of As (Ⅲ). On the other hand, coordination complexation reaction of iron oxide and arsenous acid anion helps the adsorbent for selective adsorption of As (Ⅲ).