-
氨氮是城市生活污水和工业废水中常见的污染物,主要以游离氨(NH3)或铵离子(NH4+)的形式存在于水体中[1]。氨氮的过度排放是造成水体富营养化重要原因[2]。我国已将氨氮列入规划减排项目,故监测水中的氨氮具有重要意义。目前,氨氮的监测方法主要有纳氏试剂分光光度法、滴定法、离子色谱法、离子选择性电极等。但上述方法存在易受环境干扰、仪器价格昂贵和操作复杂等缺点[3]。而电化学方法因其仪器设备简单、耗费低、快速且灵敏度高等优点能有效克服这些缺陷[4]。
由于氨氮具有过高的氧化电位(1.6 V),难以进行直接电化学检测[5]。故在实际应用中,常用于水中氨氮检测的选择电极有氨气敏电极和铵离子选择电极。氨气敏电极利用强碱使水中
${\rm{NH}}_4^{+} $ 转化为NH3扩散至电极内充液中,再利用pH电极间接指示NH3水解导致OH−的变化,从而建立氨氮浓度与pH之间的函数关系。铵离子选择电极则利用选择性透过膜测定${\rm{NH}}_4^{+} $ 引起的电位变化,采用能斯特方程建立[${\rm{NH}}_4^{+} $ ]与电位间的函数关系。然而,离子选择性电极存在机械性能弱、内充液泄漏和易受环境干扰等问题[5]。氨气敏电极测定时易受到水中杂质的干扰,铵离子选择电极容易受到水中钾离子和有机成分的干扰,在实际应用中误差较大[6]。ZHOU等[7]比较了电极法、纳氏试剂分光光度法和水杨酸法测定氨氮的精确度差异,发现电极法在含盐量高的水中测定误差明显增加。直接电化学法可实现氨氮的直接氧化,无需电子介体,可简化电极制备,极大地提高氨氮的检测精度。ZHANG等[1]制备了一种纳米修饰石墨空心球修饰电极,具有优异的吸附和催化氨的能力,实现了氨氮的灵敏快速检测。BDD电极采用硼掺杂金刚石作为电极修饰材料,具有宽电化学窗口、极低背景电流、高化学稳定性和低吸附特性等优良性能,故其在毛细管电泳检测、生物传感器、痕量物质检测及COD检测应用方面相较于常规电极有明显优势[8]。AGNIESZKA等[9]采用BDD电极在浓度为1 mol·L−1的NaClO4电解质中实现了氨氮的直接电化学氧化,在1.6 V处发现了明显的氨氮氧化峰。基于此,本研究筛选了3种市售BDD电极进行性能测试,分析了氨氮在BDD电极上的电化学行为,探究扫描方式、线性范围、检测限、稳定性和抗干扰性等电极参数,以期建立一种直接电化学氨氮检测方法。
运用BDD电极优化废水中氨氮的直接电化学检测方法
Direct electrochemical detection of ammonia in wastewater using boron-doped diamond (BDD) electrode
-
摘要: 针对高氨氮条件下离子选择电极稳定性差的问题,筛选了3种市售硼掺杂金刚石(BDD)电极,以探究直接电化学检测氨氮的可行性。采用极化曲线法测试了3种BDD电极的析氧、析氢和析氯电位,以获得最佳电势窗口。采用循环伏安法研究了氨氮在3种BDD电极上的氧化还原行为,在1.6 V处发现了明显的氨氮氧化峰,可为氨氮直接检测提供定性依据。通过控制变量法优化了方波伏安法(SWV)和差分脉冲伏安法两种扫描方式的测试参数。结果表明,SWV响应电流更高。最佳测试参数为:方波频率10 Hz,阶跃电位2 mV,脉冲幅度50 mV。在最佳条件下,当氨氮浓度为1~18 mmol·L−1时,发现两段线性范围,最低检测限为0.283 mmol·L−1。本研究所建立的测试方法响应时间短、线性范围宽、稳定性强,并成功应用于垃圾渗滤液中氨氮的测定。Abstract: To address the challenges of poor stability of ion-selective electrode under high ammonium condition, three commercial boron-doped diamond (BDD) electrodes were used for the direct electrochemical detection of ammonia-nitrogen to evaluate the feasibility. The best potential window among three BDD electrodes was obtained through measuring the oxygen, hydrogen, and chlorine evolution potentials by the polarization curve method. A clear ammonia-nitrogen oxidation peak was detected at 1.6 V, which could be used as the qualitative basis for direct measurement of ammonia-nitrogen. The parameters of square wave voltammetry (SWV) and differential pulse voltammetry were optimized by the variable control method. The results showed that SWV had a larger response current than DPV and that the optimal parameters of SWV are square wave frequency at 10 Hz, step potential of 2 mV, and pulse amplitude of 50 mV. Two linear ranges were found with the ammonia-nitrogen in the range of 1~18 mmol·L-1 under the optimized conditions, and the minimum detection limit was 0.283 mmol-1. The advantages of this method included short response time, wide linear range and strong stability. Also, this method has been successfully applied to determine the ammonia-nitrogen in landfill leachate.
-
表 1 3种市售BDD电极的基本信息
Table 1. Basic information of three commercially available BDD electrodes
电极编号 厂家 基体材料 规格/mm 表面积/cm2 硼掺杂水平/(mg·L−1) 单价/元 BDD 1 湖南新峰 单晶硅 30×20×0.625 12.00 750 1 500 BDD 2 湖南新峰 多晶硅 45×35×3 31.50 750 1 000 BDD 3 瑞士Neocoat 多晶硅 50×25×3 25.00 700 8 000 表 2 对氨氮实际样品(垃圾渗滤液)检测结果
Table 2. D etermination of a mmonia- nitrogen concentrations in real samples (landfill leachate)
加标量/
(mmol·L−1)检测值/
(mmol·L−1)回收率/% RSD/% 0 8.38 — — 10 18.17±0.24 97.90±2.4 1.3 15 23.37±0.87 99.93±5.8 3.7 -
[1] ZHANG H, WANG Y, ZHANG B, et al. Construction of ultrasensitive ammonia sensor using ultrafine Ir decorated hollow graphene nanospheres[J]. Electrochimica Acta, 2019, 304: 109-117. doi: 10.1016/j.electacta.2018.11.215 [2] 王芳君, 桑倩倩, 邓颖, 等. 磁性铁基改性生物炭去除水中氨氮[J]. 环境科学, 2021, 42(4): 1913-1922. [3] 王晨, 姜姗, 海燕, 等. 氨氮监测分析方法研究进展[J]. 资源节约与环保, 2015, 11(10): 50-55. doi: 10.3969/j.issn.1673-2251.2015.10.052 [4] DILIMON V S, NARAYANAN N S V, SAMPATH S. Electrochemical reduction of oxygen on gold and boron-doped diamond electrodes in ambient temperature, molten acetamide-urea-ammonium nitrate eutectic melt[J]. Electrochimica Acta, 2010, 55(20): 5930-5937. doi: 10.1016/j.electacta.2010.05.047 [5] MICHELS N L, KAPA A, ABD-EL-LATIF A A, et al. Enhanced ammonia oxidation on BDD induced by inhibition of oxygen evolution reaction[J]. Electrochemistry Communications, 2010, 12(9): 1199-1202. doi: 10.1016/j.elecom.2010.06.018 [6] LI D, XU X, LI Z, et al. Detection methods of ammonia nitrogen in water: A review[J]. TrAC Trends in Analytical Chemistry, 2020, 127: 115890. doi: 10.1016/j.trac.2020.115890 [7] ZHOU L, BOYD C E. Comparison of Nessler, phenate, salicylate and ion selective electrode procedures for determination of total ammonia nitrogen in aquaculture[J]. Aquaculture, 2016, 450: 187-193. doi: 10.1016/j.aquaculture.2015.07.022 [8] 高成耀, 常明, 李晓伟, 等. 硼掺杂金刚石电极及其电分析应用[J]. 化学进展, 2011, 23(5): 951-962. [9] AGNIESZKA K K, LISA J, ÁNGELA A, et al. Direct and mediated electrochemical oxidation of ammonia on boron-doped diamond electrode[J]. Electrochemistry Communications, 2010, 12(12): 1714-1717. doi: 10.1016/j.elecom.2010.10.004 [10] GABRIELE P, ALESSANDRA A, EUGENIO G, et al. Electrodeposition of cobalt thin films and nanowires from ethylene glycol-based solution[J]. Electrochemistry Communications, 2019, 103: 31-36. doi: 10.1016/j.elecom.2019.04.012 [11] ZHAO Y, YUAN F, QUAN X, et al. An electrochemical sensor for selective determination of sulfamethoxazole in surface water using a molecularly imprinted polymer modified BDD electrode[J]. Analytical Methods, 2015, 7(6): 2693-2698. doi: 10.1039/C4AY03055A [12] EISELE A P P, VALEZI C F, SARTORI E R O. Exploiting the high oxidation potential of carisoprodol on a boron-doped diamond electrode: an improved method for its simultaneous determination with acetaminophen and caffeine[J]. The Analyst, 2017, 142(18): 45-51. [13] MATSUSHIMA J T, SILVA W M, AZEVEDO A F, et al. The influence of boron content on electroanalytical detection of nitrate using BDD electrodes[J]. Applied Surface Science, 2009, 256(3): 757-762. doi: 10.1016/j.apsusc.2009.08.055 [14] 高成耀, 佟建华, 边超, 等. 掺硼金刚石薄膜电极分析检测痕量镉、铅、铜、汞[J]. 新型炭材料, 2017, 32(3): 277-283. [15] 张克东, 豆俊峰, 丁爱中, 等. 基于方波溶出伏安法的电化学传感器检测水体中痕量铅[J]. 环境工程学报, 2013, 7(8): 2973-2978. [16] 沈丽丽, 青华. 水中氯离子对氨氮测定的影响及消除[J]. 干旱环境监测, 2009, 23(1): 59-60. doi: 10.3969/j.issn.1007-1504.2009.01.014 [17] DEMUTHKAYA L N, KALINICHENKO I E. Interaction of aliphatic polyamines with Nessler reagent[J]. Journal of Analytical Chemistry, 2006, 61(11): 1063-1066. doi: 10.1134/S1061934806110037 [18] KEYIKOGLU R, KARATAS O, REZANIA H, et al. A review on treatment of membrane concentrates generated from landfill leachate treatment processes[J]. Separation and Purification Technology, 2021, 259: 118182. doi: 10.1016/j.seppur.2020.118182