Adsorption And Degradation For Chloro-organic Pollutants Via Molecular Recognition With Magnetic Nanomaterials

Organic pollutants are widely distributed in air, water, soil and even in human body due to their world-wide transferability and bioaccumulation, which have severe adverse effects on human health and environment. The traditional analytical techniques of organic pollutants include gas chromatography-mass spectrometry ?GC-MS?, capillary electrophoresis, high performance liquid chromatography ?HPLC?, electrochemical methods, gas chromatography ?GC?, fluorescence spectroscopy and so on. These methods generally require expensive equipment, complicated sample extraction, purification or derivatization, making it not suitable for large-scale samples testing. Alternatively, magnetic separation is a simple and rapid method to extract targeted molecules. Superparamagnetic Fe₃O₄ has the advantages of good redispersability and biocompatibility, tunable magnetic properties, fast binding capacity. However, the water solubility of organic pollutants is quite small, which makes the extraction difficult. Modification of the magnetic particles with corresponding functional monomers could make the enrichment and degradation of the organic pollutants possible.In this paper, Fe₃O₄ magnetic nanoparticles modifying with specific functional monomerswere prepared and used to enrich and degrade organic pollutants. The main contents can be summarized as follows:1. The effective recognition and enrichment of polychlorinated biphenyls ?PCBs? in the environment are currently challenging issues due to human health concerns. The magnetic core-shell Fe₃O₄@I composites were fabricated using Fe₃O₄ nanoparticles and 3-iodopropyltriethoxysilane ??-silane? by a sol-gel process for PCBs recognition and enrichment based on halogen bonding interaction, where I atoms were linked covalently to Fe₃O₄ nanoparticles to generate the bindingsites. The properties of the synthesized composites were characterized by X-ray powder diffraction ?XRD?, transmission electron microscopy ?TEM?, fourier transform infrared ?FT-IR? spectra and alternating gradient magnetometer ?AGM?. The adsorption capacity of Fe₃O₄@I to PCBs in aqueous solutions was evaluated according to various parameters, such as the content of ?-silane, the loading of adsorbent, different functional monomers or analytes and so on. The grafted I atoms on Fe₃O₄ particles contributed to an enhancement of the binding amount for PCBs enrichment, which may be due to the non-covalent halogen bonding interaction between the absorptive layer and PCBs. The results of this work provide an alternative material for PCBs enrichment.2. The effective recognition and enrichment of trace polychlorinated biphenyls ?PCBs? in the environment are currently challenging issues due to human health concerns. A surface absorptive layer coated superparamagnetic for PCBs enrichment were prepared. This protocol involved the synthesis of particles through a solvothermal reaction and the covering of a silica layer bonded ?-cyclodextrin ??-CD? over Fe₃O₄ via a sol-gel process to construct core-shell Fe₃O₄@?-CD composites. The bindingsites to target molecules were generated based on the P-CD cavities anchored covalently with the Fe₃O₄ nanoparticles. ?-CD was linked to Fe₃O₄ nanoparticles by silane, enhancing the stability of Fe₃O₄ nanoparticles in water. Meanwhile, superparamagnetic Fe₃O₄ core could be rapidly separated from matrix to simplify time-consuming washing extraction. The adsorption capacity of Fe₃O₄@?-CD composites to PCB28 and PCB52 in aqueous solutions was investigated. To estimate the theoretical binding site number of Fe₃O₄@?-CD, the obtained binding data were replotted according to Scatchard equation. The host-guest interaction between ?-CD and PCBs were further examined with density functional theory ?DFT? calculations. It provides theoretical evidence of ?-CD as host molecule has a higher binding amount towards PCB-28than PCB-52on the basis of their optimized geometries and calculated complexation energies.The nanomaterial reported herein is an ideal candidate for various applications, including the recognition and removal of environmentally deleterious substances.3. A magnetic nanoscale Fe₃O₄@?-cyclodextrin ??-CD? composite was fabricated via Fe ions and ?-CD in one step and characterized as a heterogeneous Fenton-like catalyst that may be used for the degradation of 4-chlorophenol ?4-CP?. The catalytic capacity of Fe₃O₄@?-CD was evaluated on the basis of various parameters, including pH, H2O2 concentration and catalyst loading, with regards to the pseudo-first-order kinetics of 4-CP degradation. In addition, iron leaching, the effect of radical scavengers and reusability of the Fe₃O₄@?-CD nanocomposite were also studied. The results showed that Fe₃O₄@?-CD exhibited a higher catalytic ability than that Fe₃O₄ toward H2O2 decomposition for 4-CP degradation, observed rate constants ?kobs? were 0.0373 min-1 for Fe₃O₄@?-CD, and 0.0162 min-1 forFe₃O₄, which may be ascribed to the construction of a ternary complex ?Fe2+-?-CD-pollutant? that allowed the produced hydroxyl radicals ?OH? to directly attack the contaminant and simultaneously enhanced the solubility of the organic pollutant. Fe₃O₄@?-CD also exhibited an enhancement effect for chlorobenzene ?CB? degradation with the kobs of 0.0392 min-1, which was significantly higher than that Fe₃O₄ for CB degradation ?kobs= 0.0099 min-1?, which may be due to a synergistic effect in the Fe₃O₄@?-CD composite.Furthermore, Fe₃O₄@?-CD has an excellent catalytic activity, stable mechanical strength and adequate reusability. A possible reaction pathway of 4-CP degradation dominated by OH was proposed according to analyses of the degradation intermediates and chloride ions.The findings of this study provide a novel material used in the Fenton-like process for the degradation of contaminants.