Fe3O4/BC复合材料的制备及其吸附除磷性能

为解决磁性吸附剂Fe₃O₄不稳定、易在水中团聚以及吸附效率较低的问题，以BC（生物炭）为载体，采用化学共沉淀法制备了Fe₃O₄/BC（生物炭负载的纳米四氧化三铁）复合材料，并将其应用于水体中PO₄3--P的吸附去除；探究了Fe₃O₄/BC对水中PO₄3--P的吸附-解析性能，考察了纳米Fe₃O₄负载比例、吸附体系pH和初始ρ（PO₄3--P）等因素对Fe₃O₄/BC吸附PO₄3--P效率的影响，并考察了吸附机制.结果表明:所制备的Fe₃O₄纳米颗粒呈球形，均匀散布在生物炭表面；Fe₃O₄/BC复合材料能高效吸附水中的PO₄3--P，在pH=3、温度为25℃、ρ（PO₄3--P）为50 mg/L、Fe₃O₄/BC投加量为400 mg（二者质量比为1:1），吸附3 h达到平衡后，Fe₃O₄/BC吸附PO₄3--P效率达到92.14%. Fe₃O₄/BC复合材料吸附PO₄3--P的机制包括配位体交换和静电吸引，吸附过程较好地符合准二级动力学模型和Langmuir等温吸附方程. Fe₃O₄/BC具有良好的解析性能，用c（NaOH）为2.0 mol/L的溶液对吸附PO₄3--P饱和后的Fe₃O₄/BC进行解析，解析效率达到80%.研究显示，Fe₃O₄/BC重复利用性好，在第4次利用后还能保持75%以上的吸附效率. 

Preparation of Fe3O4/BC Composite and Its Application for Phosphate Adsorptive Removal

Phosphate is one of the key factors that responsible for eutrophication of surface waters, and adsorption technique is competitive to remove phosphate from aqueous solutions due to its high efficient and low cost. As is known, magnetic adsorbent such as magnetite (Fe₃O₄) can be easily recovered from aqueous solution by magnetic force, which avoids adsorbate release from adsorbent surface. However, magnetite is unstable and easy to aggregate in aqueous solutions, resulting in low removal efficiency. In the present study, a nano-composite (Fe₃O₄/BC) was synthesized by co-precipitation method, which was to load nano-Fe₃O₄ ontothe surface of black carbon (BC). Subsequently, Fe₃O₄/BC was applied to remove phosphate from wastewater. Fe₃O₄/BC was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and Zeta potential. Furthermore, removal efficiency and desorption efficiency of phosphate by Fe₃O₄/BC was investigated.Results showed that the removal efficiency of phosphate by Fe₃O₄/BC was higher than that of Fe₃O₄. The maximum removal efficiency reached 92.14% under the following conditions: pH 3, initial phosphate concentration 50 mg/L, 400 mg Fe₃O₄/BC (t mass ratio Fe₃O₄:BC=1:1) and reaction temperature of 25 ℃. BC as supporter improved the dispensability of Fe₃O₄. The removal mechanism can be explained by ligand exchange and electrostatic attraction. Fe₃O₄/BC was observed good adsorption capacity and could be separated fast and easily from aqueous solution by a permanent magnet. Kinetics studies showed that the adsorption process followed the pseudo-second-order kinetic model. Meanwhile, isotherm data showed that phosphate removal by Fe₃O₄/BC could be well described using Langmuir model. The desorption efficiency of phosphate from Fe₃O₄/BC reached 80% in NaOH solution (2 mol/L). Moreover, the removal efficiency of the recycled Fe₃O₄/BC reached 75% even during the fourth cycle. Fe₃O₄/BC could effectively remove phosphate from aqueous solutions, which was consistent with green chemistry principle and was a promising phosphate adsorbent in future application.