| Chlorinated organic compounds(COCs) are widely used in the industrial production, drinking water disinfection system and the manufacture of wood preservatives, pesticides, pharmaceuticals, lubricants, and in the synthesis of petroleum chemicals etc. Chlorophenols(CPs) is a kind of synthetic biology exogenous substances, carcinogenic, teratogenic and mutagenic. And there is a long residence time and absorbed by organism easily in the environment. Once CPs were released into water, it will cause serious problems due to their toxicity are highly mutagenic and adverse effects on the human.At present, there are three main methods of degrading the CPs: physical, chemical and biological method, among these the core-shell nano zero-valent iron(NZVI) particles are characterized with its strong reducing ability, low cost and as one of the most intensively investigated strategy for removing chlorinated organic contaminants, nitroaromatic compounds, heavy metal ions, nitrate and so on in the environmental remediation of wastewaters. However, NZVI technology is flawed with certain shortcomings which were easy to agglomerate and oxidize. So development of methodologies for the preparation of surface-protected corrosionresistive NZVI particles has been a key demand.Here, in order to obtain the nanoparticles with superior reactivity, enhanced controlled morphology and facile dispersibility, a novel core-shell amino-functionalized silica coated nanoscale zero valent iron(NH2-Si O2@NZVI) was prepared by the combination of liquid phase reducing method and improved st?ber method in a single step.The surface, structure and characteristics of the nanoparticles(NPs) were investigated by Transmission Electron Microscope(TEM), Scanning electron microscopy(SEM), powder X-ray diffraction(XRD), Fourier transform infrared spectrometer(FTIR) and the elemental analysis. From the SEM results, we can see that NZVI particles coated with amino-functionalized silica layer existed as necklace-like aggregation and showed a clearly uniform core/shell structure with a diameter of about 100-120 nm and smooth surface. The XRD, the FTIR and the elemental analysis results show that NZVI particles prepared by the liquid phase reduction method was mainly composed of 色-Fe0, no iron oxide and other miscellaneous present, indicating the success coating of the amino-functionalized silica layer and the NH2-Si O2@NZVI particles prepared effectively improve the oxidation resistance. The dispersibility, oxidation resistance and the removal efficiency of 2,4,6-TCP have also been investigated and as the consequece, coating aminofunctionalized silica layer on the surface of NZVI particles have shown the improvements in the oxidation resistance, reducing capacity, and stability. The removal efficiency of 2,4,6-TCP have reached 79.65% in 48 h.The uniform spherical structure with desirable loading of amino-functionalized NZVI particles could only be prepared under optimized formulation of synthesis conditions, which means the processing conditions of the synthesis have a significant effect on the formation of uniform core/shell structure, good dispersibility and oxidation resistance of NH2-Si O2@NZVI particles and thus have an influence on removal efficiency of 2,4,6-TCP in polluted water. After investigating processing conditions, the experimental results proved that the appropriate dropping rate of Na BH4(1ml/min) and the optimum dosage of TEOS(4ml) and APTMS(0.3ml/ml TOES) would contribute to the well-dispersed nanoparticles with desirable loading of amino groups(0.38%) and a kind of reasonable scale core-shell structure with relatively large surface area(123.3845 m2/g). The average particles size of NH2-Si O2@NZVI were 108 nm, while the diameter of NZVI cores were 66 nm. Due to the amino functionalized silica layers, the nanoparticles possessed a strong adsorption affinity and enhanced reducing ability.In order to obtain the optimal conditions of the degradation process of 2,4,6-TCP by NH2-Si O2@NZVI, the effect of the dosage of nanoparticles, concentration of 2,4,6-TCP, initial p H, co-existing ions(cations Al3+,Mn2+,Cu2+and anions Cl–,PO43–,NO3– etc.) and natural subatances on the degradation activity were investigated. The results showed that when the dosage of nanoparticles were excess, the growth rate of the removal efficiency of 2,4,6-TCP was low and would make waste. And when the nanoparticles were insufficient, the pollutants couldn’t be removed efficiently. The concentration of 2,4,6-TCP have showed the opposite tendency. The influence of p H showed that when the initial p H was neutral(7.09) and acidulous(5.17), the removal efficiency were 79.6 and 83.3% respectively. And when the initial p H is alkaline(9.14 and 10.34), the removal rate of TCP is a little reduced because of the silica shell protection against the iron oxides. So the best application conditions of NH2-Si O2@NZVI was that the dosage was 1g/L, p H was 7.0, and the concentration of 2,4,6-TCP was 0.5m M. Because of the functional silica shell, co-existing ions(cations Al3+,Mn2+,Cu2+and anions Cl–,PO43–,NO3– etc.) and natural subatances(HA龓TA) were inhibited to contact and affect the reducing reaction and thus improved the reducing performance of NH2-Si O2@NZVI.The change of the surface morphology, elemental composition and the change of valence have been discussed before and after the reaction of the degredation of 2,4,6-TCP by NH2-Si O2@NZVI. The TEM and SEM images showed that a lot of acicular crystals lay on the serface of nanoparticles which means the silica shell didn’t influence the reducing reation of NZVI. Most of the shells still coated on the NZVI and some dissolved, after the reaction, Fe0 oxidized into acicular crystal formed α-Fe2O3 and Fe OOH. Amono modified silica shells not only hadn’t inhibit the reducing reaction of the n Fe0, but also kept iron oxide from depositing on the surface of n Fe0 which may reduce the reducing reactivity. As the consequence, nanoparticles NH2-Si O2@NZVI with large specific surface area, good dispersity will exhibited strong adsorption affinity and adsorbed 2,4,6-TCP to the “active site” of the nanoparticle surface at first with more amine-containing ligands. At the same time, 2,4,6-TCP migrated rapidly and attached to the “active site” of nanoparticle by hydrogen bonding with the amino groups on the surface or adsorbed to the pores of mesoporous structure at first and then come into contact with the active NZVI cores on the inside of pores for further dechlorination. Besides, some ferrous ions and ferric ions were also dissolved out and diffused through the silicon pores to contact and reduce 2,4,6-TCP adsorbed on the surface directly. |
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