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工矿、印刷等行业的快速发展,大量含铅污染物被排放到水环境中,水质铅污染物检测及治理正成环境与材料领域的研究热点。传统的重金属检测技术主要包含质谱分析法[1]、原子吸收光谱测试法[2]、荧光分析法[3]和色谱分析法[4]等,但这些方法存在设备大、价格昂贵、操作复杂以及便携性差等局限性,限制了其在水环境中的实时监测应用。基于电化学方法的碳基传感器技术因具有便于携带、操作简单、灵敏度高、价格低廉等优势,在水质实时测定分析与治理方面具有极大优势[5]。作为一种新型介观碳材料,有序介孔碳因具有大的比表面积、有序的介孔结构、良好的导电性能,可望成为潜在的新型电极传感器材料。
最近,越来越多的研究[6-7]证实,通过氮磷等杂原子掺杂能在生物炭结构上形成更多的富电子边缘和空位缺陷等活性位和更高的极化度,进而增强材料对极性有机污染物和重金属的吸附固定;同时,改性掺杂的氮磷原子具有更高的电负性和更强的给电子能力,掺杂改性置入多孔碳材料的碳晶格中后,不仅能增强多孔碳材料的电子传递能力,并可以诱导与氮磷相邻的C原子或氧原子产生较大的自旋和电荷密度,作为氧化还原反应的活性位点,增强碳材料的氧化还原性能,从而提高其对检测物的循环伏安响应能力[8-9],如高杨等[10]研究表明,氮掺杂能明显增加石墨烯表面的活性点位,提升石墨烯的自由载流子密度和导电性能,从而增强其对硝酸根的检测性能。但也有研究表明,N/P共掺杂后多孔碳材料的氧化还原活性不仅没有提高,甚至降低[11-12],这可能是由于掺杂改性新生成的氮磷基团破坏或阻塞了多孔碳材料的微孔与介孔孔道,降低了氧化还原反应的有效活性位点和被检测物质在孔道中传递性能所致[13]。为此,本研究探索在氮磷双掺杂的同时,控制多孔碳材料的微中孔结构,规则的孔径结构与发达的孔隙率,使得氮磷等官能活性位点可以分散在不同长度的孔中并且增大了界面运输面积、提高电子转移速率,从而提升其电化学性能,保证制备的氮磷双掺杂多孔碳材料对水中痕量重金属铅的响应度与测定精确性。
在本研究中,以间苯二酚、甲醛和F127为碳源和模板剂制备出富含微孔的介孔碳,并使用生活中常见的磷氮双成份磷酸二氢铵为改性剂,在氮气气氛下,通过一步碳化实现碳材料的双重掺杂。在碳化改性过程中,磷酸二氢铵的分解可引起磷酸化反应,可有效减少碳材料中原有碳氧官能团的分解;同时,磷酸二氢铵中的氮和磷元素,在高温碳化的过程中与碳材料原有碳氧官能团结合,在碳骨架上生成大量活性氮磷结构,这将大大改善碳基材料在水性电解质中的润湿性;而且,磷酸二氢铵在高温下分解释放的氨气对多孔碳进行再次活化,可在制备碳材料上生成丰富的微孔结构。氮磷双掺杂、中孔结构的保持和微孔结构的增加,将增加氮磷掺杂介孔碳的有效活性点位,从而提升其对水中铅离子的识别敏感程度,实现对水中痕量铅离子的电化学检测。
氮磷双改性酚醛树脂基有序介孔碳电极对水中痕量铅的测定
Determination of trace lead in water by nitrogen and phosphorus double modified phenolic resin-based ordered mesoporous carbon electrode
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摘要: 以常见的磷氮双成份磷酸二氢铵为改性剂,间苯二酚/甲醛和F127为碳源和模板剂,成功制备了对痕量铅具有高灵敏度的氮磷双改性介孔碳OMC-MAP改性玻碳电极。通过N2吸附脱附等温线、FT-IR、XPS和阳极溶出伏安法对OMC-MAP的物化性质及其改性玻碳电极电化学性能进行了表征和分析。结果表明:OMC-MAP具有较高的孔容(0.835 mL·g−1)、比表面积(579 m2·g−1)和丰富的氨基、羧基、羰基等氮氧官能团,以及P—C、P—O—C等含磷官能团,介孔主要分布在5~10 nm区域,峰值在7.45 nm;OMC-MAP良好的介孔结构及其分散在微介孔表面的氮、磷、氧活性官能团为其改性玻碳电极传感器提供了良好的电子传递通道和高识别铅离子的活性位点。在醋酸-醋酸钠支持电解质底液下,OMC-MAP介孔碳改性玻碳电极传感器对溶液铅显示极优的电催化还原活性,当pH=3.8、富集电位为−1.2 V和富集时间为240 s时,循环伏安溶出电流的响应值达到最大。在该条件下,OMC-MAP改性玻碳电极在1~10 000 µg·L−1宽范围内对铅离子均表现出极优的响应性,R2>0.98,灵敏度高、检测范围广,说明OMC-MAP是一种潜在痕量铅的电极材料。Abstract: N/P co-doped OMC-MAP modified glassy carbon electrode with high sensitivity for lead ions was prepared when common ammonium dihydrogen phosphate, formaldehyde/resorcinol and F127 were taken as modifier, carbon source and template agent of OMC-MAP, respectively. N2 adsorption-desorption isotherm, FT-IR, XPS and anodic stripping voltammetry were used to characterize the physicochemical properties of OMC-MAP and electrochemical performance of modified glassy carbon electrode. The results showed that OMC-MAP had high pore volume (0.835 mL·g−1) and large specific surface area (579 m2·g−1), which contained amino nitrogen, carboxyl, carbonyl and other nitroxide functional groups, as well as P—C, P—O—C and other phosphorus functional groups. The mesopores were mainly distributed in the region of 5~10 nm, with a peak at 7.45 nm. The great mesoporous structure of OMC-MAP and the active functional groups of nitrogen, phosphorus and oxygen dispersed on the surface of the micro-mesopores provided a good electron transfer channel and active sites for high lead ions identification. Under the condition of acetic acid-sodium acetate supporting electrolyte solution, modified glassy carbon electrode sensor of OMC-MAP showed excellent electrocatalytic reduction activity on lead solution. When pH was 3.8, enrichment potential was −1.2 V and enrichment time was 240 s, the cyclic voltammetric stripping current response value reached the maximum. Under this condition, the OMC-MAP modified glassy carbon electrode showed excellent responsiveness and regularity to lead ions within a wide range of 1~10 000 µg·L−1. The linear correlation of R2 was higher than 0.98, with high sensitivity and wide detection range. This indicated that OMC-MAP modified glassy carbon electrode was a potential electrode material for trace lead ions detection.
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