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随着工业和农业的快速发展,水环境问题中的硝酸盐污染日益严重,引起了世界各国的广泛重视。硝酸盐污染物的主要来源有垃圾渗滤液、牲畜粪便、生活和工业废水等[1]。水体中的硝酸盐含量高会破坏生态环境,造成水体富营养化,影响水生生物生存[2]。用于饮用的地表水或地下水中含有过高浓度的硝酸盐会严重危害人类的健康,导致婴儿出现蓝婴综合征(高铁血红蛋白血症)、肝损伤等,世界卫生组织的国际癌症研究机构将摄入硝酸盐归类为可能对人类致癌的一类物质,特别是在促进内源性亚硝化的条件下摄入硝酸盐,硝酸盐会在体内形成N-亚硝基化合物,增大了人类患胃癌等疾病的风险[3]。因此,世界卫生组织设定饮用水中硝酸盐的最大浓度为50 mg·L−1
${\rm{NO}}_3^- $ [4]。中国最新生活饮用水卫生标准(GB 5749—2006)设定硝酸盐氮浓度为10 mg·L−1,地下水源限制时标准可放宽至20 mg·L−1。由于水中硝酸盐污染的严重性和危害性,人们研究出各种方法致力于去除水中的硝酸盐,主要分为生物法[5]、物理分离法[6]、催化加氢法[7]、化学还原法[8]、电催化还原法[9]。其中生物法是利用微生物在生物反应器中的反硝化作用还原硝酸盐,释放出分子态氮或一氧化二氮。该方法由于微生物培养周期较长、反应器占地面积较大、出水可能存在细菌污染,其应用存在一定的限制性[10]。离子交换法和反渗透法等物理方法操作简单,但只是将硝酸盐从污水中分离出来,并没有将污染物从根本上去除。催化加氢法需要持续投加反应所需的氢气,而氢气的易燃易爆性质使工艺存在很大危险性。电催化还原法即电催化反硝化法,是在通电的条件下,硝酸盐离子在阴极上被还原生成氮气等产物的一种脱氮方法。具有不产生污泥,占地面积小,处理效率高,安全环保、操作易控等优点[11]。1980年代,人们就已经开始将硝酸盐电化学还原法用于水处理,HORÁNYI等[12]采用金属铂作为电极材料,探究了硝酸盐氮在碱性条件下的还原反应。近年来,水中硝酸盐的电催化还原研究受到广泛关注,被认为是很有前景的处理方法。在硝酸盐的电催化还原过程中,主要在阴极上进行硝酸盐吸附和电子传递等关键步骤。电极材料、支持电解质和施加电流等对反应的动力学和产物选择性都有影响,因此,开发一种性质稳定、电催化还原活性高的电极具有重要意义。
目前,许多研究人员已将Zn[13]、Fe[14]、Cu[15]、Pt[16]、Ti[17]、碳纸[18]等材料应用于硝酸盐还原电极的制备。由于不同材料间可能存在协同效应,关于双金属、三元金属或合金电极上的硝酸盐电还原也有广泛的研究[19]。Jonoush等[20]采用Ni、Ni-Fe0和Ni-Fe0@Fe3O4电极对硝酸盐氮的去除效果以及硝酸盐氮还原反应动力学进行探究,结果表明,Ni-Fe0@Fe3O4电极的电催化还原性能最好,在电解电流密度为5 mA·cm−2、pH=6.2的条件下,对50 mg·L−1的硝酸盐溶液进行电解,240 min后硝酸盐去除率达到90.19%。Zhou等[21]以3D Pd-Cu(OH)2/CF电极为阴极,对50 mg·L−1的硝酸盐溶液进行电解,能够在45 min内将
${\rm{NO}}_3^- $ 转化为${\rm{NH}}_4^+ $ ,转化率为98.8%,并且在60 min内${\rm{NH}}_4^+ $ 最终被彻底氧化为氮气,反应体系的总氮去除率为98.7%。泡沫镍是一种导电导热性良好、疏松多孔、比表面积大、成本较低的电极材料[22],本研究提出了Ni foam/Cu电极的制备方法,将其作为阴极分析电催化还原硝酸盐氮反应的影响因素,采用动力学模型对硝酸盐氮还原过程进行探究。并对Ni foam/Cu电极的电催化活性和运行稳定性进行评价。
Ni foam/Cu电极电催化还原硝酸盐氮
Electrocatalytic reduction of nitrate nitrogen by Ni foam/Cu electrode
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摘要: 采用恒流电沉积法制备了泡沫镍/铜(Ni foam/Cu)电极。以Ni foam/Cu电极为阴极、Ti/RuO2-Ir2O3电极为阳极构建电解体系,对水中硝酸盐氮进行电催化还原处理。并研究了电解质对总氮和氨氮去除率的影响和电极的稳定性。在一定范围内,增大电解质NaCl的浓度可以提高总氮和氨氮去除率。当NaCl浓度为0.5 g·L−1时,在电解电流密度为8 mA·cm−2的条件下对100 mg·L−1
${\rm{ NO}}_3^-$ −N溶液进行6次重复电解实验,2.5 h后硝酸盐氮去除率均可以达到94.5%以上。当NaCl浓度为1.25 g·L−1时,在电解电流密度为8 mA·cm−2的条件下对100 mg·L−1${\rm{NO}}_3^-$ −N溶液电解2.5 h,出水中氨氮浓度只有2.90 mg·L−1,总氮去除率达到79.47%。实验结果表明,Ni foam/Cu阴极具有较高的电催化还原活性和良好的稳定性。Abstract: The Ni foam/Cu electrode was prepared by galvanostatic electrodeposition method. The Ni foam/Cu and the Ti/RuO2-Ir2O3 electrode were used as the cathode and anode respectively to construct an electrolysis system to perform electrocatalytic reduction of nitrate nitrogen in water. The effect of the electrolyte on the removal rate of total nitrogen and ammonia nitrogen and the stability of the electrode were also investigated. In a certain range, the removal rate of total nitrogen and ammonia nitrogen can be improved by increasing the electrolyte NaCl concentration. When the concentration of electrolyte NaCl increased to 0.5 g·L−1, six repeated electrolysis experiments were performed in 100 mg·L−1${\rm{NO}}_3^- $ -N solution for 2.5 h under the condition of 8 mA·cm−2, and the removal rate of nitrate nitrogen could reach more than 94.5%. When the concentration of electrolyte NaCl increased to 1.25 g·L−1, the concentration of ammonia nitrogen was only 2.90 mg·L−1 after 2.5 h of electrolysis under the condition of 8 mA·cm−2, and the total nitrogen removal rate reached 79.47%. The experimental results show that the Ni foam/Cu cathode has high electrocatalytic reduction activity and good stability.-
Key words:
- nitrate nitrogen /
- electrocatalytic reduction /
- Ni foam/Cu
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