杨彩迪(1995—),女,山西运城人,博士研究生,主要研究方向为土壤物理。E-mail:
设置五种有机物料(水稻秸秆、玉米秸秆、小麦秸秆、稻壳和竹子)制备的生物质炭改良酸性土壤的田间试验,以不施生物质炭为对照(CK),运用电化学阻抗谱法研究不同生物质炭对酸性土壤电化学特性的影响。结果表明,不同处理的等效电路拓扑结构一致,但电路元器件参数存在差异;Nyquist图表现为高频区圆弧和低频区斜线的形式,各曲线与横坐标的截距对应等效电路中土壤多孔层电阻
Climate change and the continuous impact of high-intensity human activities are intensifying soil acidification and has caused serious harm to the ecological environment and agricultural production. In recent years, studies on acid soils have focused on the effects and related mechanisms of soil conditioners on physicochemical properties and crop production, but the combined application of electrochemistry theory and other interdisciplinary principles have been given less attention. Electrochemical impedance spectroscopy(EIS)is an electrochemical measurement method using small-amplitude sinusoidal potential(or current)as a disturbance signal. Its application in the soil field has attracted much attention. In this study, EIS was combined with soil physical and chemical properties to analyze the electrochemical mechanism of biochar in improving acid soils.
A field study was conducted to amend acid soil by applying biochars produced from five biomass materials (rice straw, maize straw, wheat straw, rice husk, and bamboo). The EIS was used to study the influence of different biochars on the electrochemical characteristics of acid soil.
Results showed that the equivalent circuit topology structure was the same in different biochar-amended treatments, but the circuit component parameters were different. The equivalent circuit model was the charge transfer resistor
The decrease of
由于气候条件的变化和高强度人类活动的持续影响,我国南方普遍分布的酸性土壤出现了土壤酸化问题,对生态环境和农业生产造成了严重危害[
电化学阻抗谱(electrochemical impedance spectroscopy,EIS)是一种以小振幅正弦波电位(或电流)为扰动信号的电化学测量方法。在测试过程中,给被测系统施加一个频率不同的小振幅的交流信号,测量系统的阻抗或阻抗的相位角Φ随频率变化。然后通过构建等效电路,确定等效电路中的各元器件参数。进而通过这些元器件的物理化学意义,分析电化学系统的结构、电极过程动力学、双电层和扩散等,广泛用于研究材料性能和腐蚀机理等领域[
土壤电化学研究体系的形成从更微观的角度揭示了土壤化学现象的本质,阐明了土壤氧化还原过程和酸性红壤修复原理[
将水稻秸秆(RSB)、玉米秸秆(MSB)、小麦秸秆(WSB)、稻壳(RHB)和竹子(BCB)五种有机物料制备的生物质炭按1%的添加量均匀施入酸性农田土壤进行改良,以不施生物质炭为对照(CK),进行水稻-油菜-玉米三季作物轮作后,采集土壤样品,风干后过2 mm筛备用。生物质炭和土壤pH分别按照土水比1:20和1:2.5采用pH计(Metler Toledo)测定;电导率分别按照土水比1:20和1:5采用电导率仪(DDB-350)测定;水溶性盐含量分别按照土水比1:20和1:5采用残渣烘干-质量法测定;土壤有机质采用重铬酸钾氧化-外加热法测定;土壤CEC采用乙酸铵交换法测定;土壤孔隙度采用容重法测定,以上测定方法参考《土壤农化分析》[
生物质炭及其改良土壤的理化性质
Physicochemical properties of biochars and biochar-amended soils
处理 |
生物质炭Biochars | 土壤Soil | ||||||||
pH | 电导率 |
水溶性盐总量 |
pH | 有机质 |
CEC/(cmol·kg–1) | 电导率 |
水溶性盐总量 |
孔隙度 |
||
注:CEC,阳离子交换量;CK,对照,不添加生物质炭;RSB,水稻秸秆生物质炭;MSB,玉米秸秆生物质炭;WSB,小麦秸秆生物质炭;RHB,稻壳生物质炭;BCB,竹炭。下同。Note:CEC,cation exchange capacity;CK,control,without biochar;RSB,rice straw biochar;MSB:maize straw biochar;WSB,wheat straw biochar;RHB,rice husk biochar;BCB,bamboo charcoal. The same below. | ||||||||||
CK | - | - | - | 4.73 | 17.43 | 8.98 | 46.70 | 2.92 | 55.9 | |
RSB | 10.52 | 380 | 23.0 | 5.30 | 27.57 | 9.35 | 54.85 | 3.82 | 56.6 | |
MSB | 10.65 | 375 | 11.8 | 5.25 | 30.66 | 9.19 | 64.05 | 6.15 | 56.6 | |
WSB | 10.54 | 338 | 15.3 | 5.07 | 33.35 | 9.32 | 54.05 | 5.47 | 57.0 | |
RHB | 7.75 | 1601 | 60.5 | 5.35 | 31.04 | 10.95 | 73.25 | 6.90 | 59.6 | |
BCB | 9.48 | 1915 | 12.5 | 5.10 | 24.72 | 9.72 | 58.00 | 8.23 | 58.1 |
按照容重1.35 g·cm–3、质量含水率200 g·kg–1,制备体积60 cm3(Φ61.8 mm×20 mm)的试样,每个试样需干土64.8 g,蒸馏水16.2 mL。将所需土样平铺于不吸水的托盘,用喷雾设备喷洒定量蒸馏水,充分搅拌后密封置于保湿缸内24 h,使土水分布均匀。根据《土工试验方法标准》制备环刀试样[
采用直径为58 mm的铜片作为工作电极和辅助电极,并用定制模具固定试样,保证试样与电极接触良好。使用武汉科思特有限公司的CS350型电化学工作站进行试样的电化学阻抗谱测试,直流电位为0.05 V,交流幅值为10 mV,测试频率为10–2~105 Hz,滤波器带宽为10~100 pF,最小高频段量程为2 mA,每个样品扫描时间为15 min。通过Nyquist图和Bode图,分析阻抗图谱,运用Z-view软件拟合出等效电路图[
EIS是研究化学反应机理的重要工具,用以测量电化学体系中线性电路网络频率响应特性,该方法可测定不同频域内Nyquist图和Bode图。Nyquist图由阻抗实部Z'和阻抗虚部Z″组成,称为Randles模型,但在实际测量中得到的Randles模型均会出现偏离,因此称为准Randles模型。Bode图是以lgf(f为频率)为横坐标,lg|Z|为纵坐标所组成的曲线图,用以清晰地表征阻抗谱数据[
土壤是由土壤颗粒、孔隙水和气体组成的三相共存介质,其导电路径可分为3种:沿土体颗粒传导、沿孔隙溶液传导、沿土水相连而成的界面路径传导(即沿固液界面传导),导电路径如
土壤导电路径
Conductive path of soil
理想状态下,土壤的电化学体系中存在两个平行过程。一是电极电位发生变化时,电极-溶液界面双电层电容的充电和放电过程(
理想状态下土壤等效电路模型
Equivalent circuit model of soil under ideal condition
由于电极表面不均匀,实际上电极与溶液之间形成的双电层电容的频响特性与“理想电容”不一致,存在“弥散效应”。因此用常相位角元件CPE来代替双电层电容
实际土壤等效电路模型
Actual soil equivalent circuit model
经过电化学阻抗谱测试,不同生物质炭改良酸性土壤的Nyquist图和Bode图如
不同生物质炭改良酸性土壤的Nyquist图及Bode图
Nyquist diagram and Bode diagram of acid soil modified by different biochars
(1)从Nyquist图(
(2)从Bode图(
由
酸性土壤阻抗谱拟合结果
Results of impedance spectrum fitting of acid soil
根据电化学阻抗谱测试得到的Nyquist图,结合等效电路,运用Z-view软件进行阻抗谱拟合,等效电路图中各元器件的拟合参数结果如
等效电路各元器件拟合参数值
The fitting parameter values of each component of the equivalent circuit
处理 |
CPE | ||||||
CPE-T | |||||||
CK | 17.35 | 1.78×10–10 | 4.32 | 1.55×10–5 | 0.43 | 34.63 | 5.09×1016 |
RSB | 17.83 | 3.93×10–11 | 22.85 | 5.10×10–6 | 0.42 | 108.82 | 3.24×1020 |
MSB | 16.34 | 4.36×10–11 | 15.80 | 9.27×10–6 | 0.37 | 72.65 | 2.94×1020 |
WSB | 17.32 | 8.22×10–11 | 8.42 | 1.19×10–5 | 0.39 | 58.93 | 1.00×1020 |
RHB | 16.43 | 5.40×10–11 | 12.32 | 5.13×10–6 | 0.42 | 170.00 | 4.55×1020 |
BCB | 16.75 | 4.31×10–11 | 16.87 | 5.69×10–6 | 0.42 | 87.90 | 1.00×1020 |
CPE-T和
生物质炭改良后的酸性土壤经电化学测试,Nyquist图呈现准Randles模型,表现为高频区圆弧和低频区斜线的形式,各曲线最低点与横坐标的截距对应等效电路中土壤多孔层电阻
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