负载零价铁膨胀石墨的合成及对水中NO_3^-去除的效果与机制

Nitrate Removal by Expanded Graphite Loaded with Zero-valent Iron:Performance and Mechanism

以网络状孔型结构发达的膨胀石墨(EG)为载体,采用化学沉积法制备了负载零价铁(ZVI)的膨胀石墨(EG-ZVI).利用扫描电子显微镜(SEM)、X射线衍射(XRD)仪及X射线光电子能谱仪(XPS)等对负载及反应前后的EG-ZVI进行表征,探究了EG-ZVI对硝酸根(NO_3^-)的去除效果并对其反应产物及机理进行了分析.结果表明,亚微米级零价铁已负载到EG石墨表面,且分布均匀;与EG相比,EG-ZVI对NO_3^-的去除能力显著提升,其去除率是EG的2.3倍.得益于铁碳原电池效应,EG-ZVI对pH依赖性比零价铁低,即使在pH=9的条件下,NO_3^-去除率依然能达到65%以上,是单独用零价铁处理时的1.83倍;EG-ZVI去除NO_3^-是吸附和还原过程共同作用的结果,符合三级动力学模型,其还原过程由负载在EG表面的零价铁发生腐蚀提供电子,从而还原NO_3^-产生以NH_4^+-N为主的含氮化合物;EG-ZVI对NO_3^-具有较强的还原吸附作用,并能解决零价铁在反应过程中生成惰性层或金属氢氧化物导致去除效率低的缺陷,使其在含NO_3^-废水的处理中具有较高的应用潜力.

Zero-valent iron （ZVI） loaded onto expanded graphite （EG） as a composite material（EG-ZVI） was prepared through chemical deposition method to remove nitrate. The EG/ZVI was characterized by X-ray diffraction（XRD）, scanning electron microscopy （SEM） and X-ray photoelectron spectroscopy （XPS）. It is observed that the EG was successfully loaded with sub-micron scale zero-valent iron. Batch experiments with variable theoretical ZVI mass loading, pH values and temperature were conducted to evaluate the removal performance of EG-ZVI. The results showed that the removal rate of nitrate was 2.3 times higher than that for EG. Furthermore, the removal of nitrate by EG-ZVI shows little dependence on solution pH. Even at pH = 9, the nitrate removal efficiency could attain 65% after reaction for 90 min. Galvanic cell effect and high specific surface area are the main reasons for the enhanced removal of nitrate by EG-ZVI with chemical reduction and physical adsorption. And third-order kinetic model is well fitted. XPS were used to analyze the mechanisms of nitrate removal, which indicated that ZVI loaded on the surface was oxidized, and the removed nitrate was reduced to NH4-N and NO2-N. In addition, EG-ZVI could overcome the shortcomings of ZVI which formed undesirable precipitation of ferrous hydroxide on the surface during reaction frequently. High removal capability, excellent stability and broad applicability make EG-ZVI ideal candidates for nitrate removal in practical application.