| Fluoride is an essential trace element for human beings. However, the excessive intake of drinking water with excess fluoride can cause severe health problems. In many villages and remote areas of China, because of the economic backwardness, people are suffering from the high fluoride drinking water. In order to solve this problem, a high-efficient and low-cost technology must be adopted to remove the excess fluoride from drinking water. However, most of the reported adsorbents still have some drawbacks, the capacity is not high, the pH range it can be applied in is not wide and the collection of adsorbent is difficult. Therefore, a novel magnetic adsorbent of iron-aluminum oxide nanoparticles anchored on graphene oxide (IAO/GO) was prepared in this study. The performance of IAO/GO on fluoride removal and adsorption mechanism was also analyzed. The main contents and results are as follows:(1) IAO/GO was synthesized by simple one-step method of alkaline co-precipitation for fluoride removal from aqueous solution. Through the one-step method, this study simplified the operation processes to realize the magnetic composite of binary iron-aluminum mixed oxide and graphene oxide (GO) and changed the core-shell structure of traditional magnetic material. By combining the advantages of GO and IAO, IAO/GO exhibited a high adsorption capacity, good acid-alkali stability, super paramagnetism and fine selectivity for fluoride. In this present study, the effects of composition ratio of raw materials and calcination temperature on adsorption capacity were investigated when synthesizing IAO/GO. The optimum composition ratio of raw materials was Fe3+:Fe2+:Al3+=1.5:1:4.5, and the ratio of total mass of FeCl3·6H2O, FeCl2·4H2O, AlCl3·6H2O to GO was 10:1. The optimum calcination temperature was 200℃.(2) The physicochemical properties of IAO/GO were characterized by N2 adsorption/desorption, XRD, TEM, XPS, FT-IR, and AGM. The results showed that: GO and IAO/GO were successfully synthesized, and IAO was distributed homogeneously onto the GO layers with an amorphous structure. The combination of IAO and GO could reduce the aggregation of IAO and improve the specific surface area, the specific surface area of IAO/GO was 349 m2/g,15% larger than that of IAO (303 m2/g). The saturation magnetization value of IAO/GO was 7.5 emu/g. With magnetic property, IAO/GO could easily be collected from aqueous solution by an external magnetic field.(3) Several main factors, such as dosage, initial solution pH, contact time, initial fluoride concentration, and co-existing anions, were investigated through batch static adsorption tests. Kinetic data revealed that the adsorption process followed a pseudo-second-order model. Fluoride sorption onto the adsorbents fitted well with the Langmuir model. The maximum sorption capacity calculated from the Langmuir model was 64.72 mg/g for IAO/GO. The pHPZC of IAO/GO was 6.2. Effective fluoride removal occurred in a wide pH range from 4 to 10, and the optimum pH was 4.22. IAO/GO showed a good selectivity for fluoride when anions existed except for HPO42-.(4) According to the characterization results and adsorption studies, electrostatic attraction, anion exchange, and inner-sphere complexation are the most likely mechanisms for fluoride sorption.Overall, based on the above-mentioned merits, the IAO/GO prepared in this study could be applied widely for fluoride removal in the natural water environments. |
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