| With the population explosions, agricultural activities, industrialization and other geological and environmental changes, the quality of our water resources is unfortunately deteriorating continuously. Thousands of organic, inorganic, and biological pollutants which affect healthy of people directly or indirectly have been reported as water contaminants. Water pollution, caused by pollutants such as organic dyes, heavy metal ions from industrial sources, has become a serious concern in recent years. Therefore, the removal of poisonous and harmful pollutants has great significance in the water environment. Magnetic nanomaterials have entered into our sight because of the large specific surface area, improving adsorption capacity and easy separation under an external magnetic field. The have great potential applications in many field of scientific research. Therefore, the development of cost-effective magnetic nanomaterials for the toxic pollutants in the wastewater treatment is extremely important in today’s environmental protection industry. In this paper, we have prepared several magnetic nano-materials, and we also systematically explored their adsorption and degradation behavior of several typical toxic pollutants in the water. This study used different materials and different methods to remove toxic contaminants in the water. By examining the various influencing factors on the toxic pcontaminants removal by magnetic nano-materials, the optimal experimental conditions were selected to achieve the purpose of efficient removal harmful pollutants. The main results are summarized as follows:(1) Based on the fact that BiFeO3magnetic nanoparticles (BFO MNPs) have peroxidase-like properties, they can improve the ability of catalytic oxidation of hydrogen peroxide. We established a Fenton-like method of catalytic degradation of dye wastewater. BFO MNPs were successfully prepared with a sol-gel method. Results of XRD suggested the as-prepared BFO MNPs were identified as pure phase BiFeO3with a crystalline structure. No characteristic peaks of impurities were found, indicating high purity of the product. The BFO MNPs were used as a catalyst to removal of an aze dye methyl orange (MO) in the presence of H2O2. Some important reaction parameters were investigated to obtain the optimum conditions. Under the optimal experimental conditions of1.0g/L of BFO MNPs,0.2mol/L of hydrogen peroxide,1min of ultrasonic time,30℃of solution temperature, and24h of reaction time, the removal efficiency of MO was about90%.(2) Fe3O4/Grass magnetic nanoparticles were successfully synthesized based on one-pot hydrothermal method which used ferric chloride and grass, inexpensive and nontoxic reagents, as our raw materials. The as-prepared Fe3O4/Grass were characterized by FT-IR, XRD, TEM, SEM, EDX, and VSM, and they also were used to remove organic pollutants from aqueous solution, namely, using methylene blue (MB) as a model target, because the nanocomposites have enhanced oxidation of hydrogen peroxide. The sythesis method of Fe3O4/Grass nanocomposites is simple, green, and efficient. The experimental results showed that the target compound could be removed efficiently from solution over a wide pH range from2to10in the presence of Fe3O4/Grass as peroxidase-like catalyst and H2O2as oxidant. The effects of Fe3O4/Grass magnetic nanocomposites concentration, H2O2concentration, the value of pH, temperature in the reaction process were investigated in detail. Without adjusting the pH value, when Fe3O4/Grass magnetic nanocomposites concentration is1.0g/L, and H2O2concentration is0.4mol/L, MB could be removed completely after180min of reaction at303K. Finally, the recycling experiment of Fe3O4/Grass magnetic nanocomposites was studied. The results demonstrated that the removal efficiency of MB was still94%after the first three recycle run while the removal efficiency decreased to73%when the recycle number increased to five. Furthermore, the Fe3O4/Grass catalysts showed temperature tolerance, and they could be readily separated from solution by applying an external magnetic field. This showed that the Fe3O4/Grass magnetic nanocomposites may become a promising catalyst in environmental wastewater treatment.(3) A facile hydrothermal process to synthesize nitrogen-doped magnetic carbon nanomaterials (MCNMs) were reported in this paper. The MCNMs were carried out by one-pot reaction of1,6-hexanediamine, FeCl3·6H2O and eggshell membrane (ESM) in ultrapure water at200℃for6h, which employed1,6-hexanediamine and ESM together as the reductants and functionalization reagents simultaneously and ESM provided carbon sources and the hexanediamine was the main nitrogen dopant. Structure and morphology of the prepared nanomaterials were carefully characterized. All chemicals used were low cost compounds and environmental benign. It has abundant amine on their surface, when tested as adsorbent for chromium removal, the nanomaterials showed excellent adsorption properties. Moreover, the adsorption of Cr(Ⅵ) were found to follow pseudo-second-order kinetic model and the Langmuir model. With maximum capacities of350mg/g, these low cost nanomaterials are attractive adsorbent for removal of Cr(Ⅵ) from aqueous solution. The adsorption mechanism for Cr(Ⅵ) onto MCNMs was elucidated by XPS and XRD. The nanomaterials can be easily manipulated in magnetic field for desired separation, leading to the removal of Cr(Ⅵ) from polluted water. In addition, the results obtained by XPS and XRD, performed on the as-prepared MCNMs before and after Cr(Ⅵ) adsorption, suggested that some of adsorbed Cr(Ⅵ) were reduced to Cr(Ⅲ) during the removal process, demonstrating that the MCNMs could detoxify Cr(Ⅵ). The resulting Cr(Ⅲ) was either released back into the solution at lower pH in the form of water-soluble Cr(Ⅲ) species or precipitated on the surface of the MCNMs in the form of Cr(OH)3and Cr2O3. These results indicate that MCNMs can be used as the efficient, green adsorbent to removal of Cr(Ⅵ) in water. |
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