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生物质在部分或完全缺氧的条件下通过高温热解产生的富碳、具有高度芳香环分子结构和多孔性副产物称之为生物炭[1]。生物炭可以通过微生物作用、氧化还原、表面沉淀、离子交换以及表面络合作用等一系列物理化学和生物作用影响土壤理化特性及重金属的形态、生物毒性、迁移和转化过程,以期实现土壤修复的目标[2-4]。采用生物炭来实施的重金属污染场地修复技术具有经济性、稳定性、环境友好等优势[5],因此,可以将生物炭用作为重要的土壤重金属修复改良剂。
水可提取的有机质(water extracted organic matter,WEOM)作为生物炭中最具活性的组分,对土壤中重金属的环境地球化学行为的影响同样不容忽视。WEOM中含有众多的荧光的有机质,诸如类蛋白物质、类富里酸和类腐殖酸等[6-10],这些荧光物质能够与土壤中的重金属发生络合作用,从而影响土壤重金属的环境化学行为。而荧光光谱方法是研究荧光有机质组分与相对含量的重要手段。荧光光谱结合荧光猝灭滴定已经广泛的用于研究这些水溶性的荧光有机物与重金属的络合作用[11-12],结合荧光猝灭络合模型能够计算出荧光组分与重金属的络合常数,以及参与络合过程中荧光物质的比例,如修正的Stern-Volmer模型[13]、非线性Ryan-Weber模型[14]。一些有机质的荧光信息经常被强的荧光基团掩盖而无法识别,而导数荧光也能够很好地用于识别有机质光谱中被掩盖的荧光组分,从而获得更多的光谱信息[7, 15]。同时,二维相关光谱方法也已经广泛用于研究WEOM与重金属络合的异质性[16-17]。
然而,不同的热解温度影响了生物炭中WEOM的含量、组分及结构特性,这些荧光组分对土壤重金属的环境化学行为起着非常重要的作用,尤其是低温热解时会产生的生物炭具有较高的WEOM含量,这些WEOM中的有机组分能够与重金属发生络合作用[18]。因此,为了进一步研究不同热解温度下生物炭中的WEOM对重金属的影响,本研究针对300℃和600℃热解下生成的生物炭提取的WEOM与重金属Cu(Ⅱ)的络合特性进行研究,采用导数荧光和二维相关光谱分析结合荧光猝灭滴定方法研究高温和低温热解条件下,生物炭WEOM中荧光组分变化及其与Cu(Ⅱ)的络合参数,解释两种温度下生物炭WEOM对Cu(Ⅱ)环境化学行为的影响,为土壤改良与重金属修复提供理论指导。
热解温度对棉杆生物炭中水可提取有机物与Cu(Ⅱ)络合特性的影响
Effect of pyrolysis temperature on the binding properties of Cu(Ⅱ) with WEOM extracted from cotton stem biochar
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摘要: 本文以棉杆生物炭中水可提取的有机物(water extracted organic matter,WEOM)为研究对象,采用二阶导数荧光和二维相关光谱分析方法研究低温(300 ℃)和高温(600 ℃)热解温度下生物炭WEOM的荧光组分变化及其与Cu(Ⅱ)离子的络合特性。研究结果表明,低温和高温热解生物炭WEOM的含量分别为20172.3 mg·kg−1和5.9 mg·kg−1;低温热解生物炭WEOM以类腐殖酸为主,而高温热解生物炭WEOM以类富里酸为主。二维相关光谱(2D-COS)分析结果显示,低温热解生物炭WEOM中类腐殖酸(409 nm)能够优先与Cu(Ⅱ)离子发生络合作用,而高温热解生物炭WEOM中类富里酸组分(372 nm)优先与Cu(Ⅱ)离子结合。300℃热解生物炭WEOM-Cu(Ⅱ)的lgK值在4.85—5.30之间,类富里酸物质表现出较高的lgK值。600℃热解棉杆生物炭WEOM与Cu(Ⅱ)的lgK值在4.23—5.19之间,随着波长的增加,lgK值呈现逐级增大的趋势,且具有较高的荧光配位比,研究结果能够为生物炭用于土壤改良和修复提供指导依据。Abstract: In this study, water extracted organic matter (WEOM) were extracted from cotton stem biochar at 300 ºC and 600 ºC pyrolysis temperatures, whose fluorescent components and binding properties with Cu(Ⅱ) were investigated by using second derivative fluorescence and two-dimensional correlation spectroscopy (2D-COS). The results showed that the content of WEOM for biochar was 20172.3 mg·kg−1 and 5.9 mg·kg−1 at low and high pyrolysis, respectively. Biochar-derived WEOM was dominated by humic-like substances at low temperature pyrolysis and fulvic-like substances at high temperature pyrolysis, respectively. The result of 2D-COS indicated that humic-like substances at 409 nm combined preferentially with Cu(Ⅱ) at low temperature pyrolysis and fulvic-like substances at 372 nm preferentially complexed with Cr(Ⅲ) at high temperature pyrolysis. The lgK values were in the range of 4.85—5.30 for biochar-derived WEOM-Cu(Ⅱ) at 300 ºC, in which fulvic-like obtained a relatively high lg K value. The lgK values ranged from 4.23 to 5.19 for biochar-derived WEOM-Cu(Ⅱ) at 600 ºC, and lgK value increased with an increase of wavelength. Meanwhile, the fraction in the initial fluorescence (f) was higher for biochar-derived WEOM-Cu(Ⅱ) at 600 ºC than these at 300 ºC. The results of WEOM-Cu(Ⅱ) can provide guidance for the application of biochar in soil improvement and remediation.
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Key words:
- biochar /
- WEOM /
- two-dimensional correlation spectroscopy /
- Cu(Ⅱ) /
- fluorescence quenching
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表 1 不同温度热解WEOM中各组分与Cu(Ⅱ)离子的络合参数
Table 1. Binding parameters of biochar-derived WEOM components with Cu(Ⅱ)
生物炭
Biochar荧光峰
Peak对数稳定常数
lgK荧光配位比
f/%决定系数
R2300℃ 270c FM FM FM 309abc FM FM FM 367ab 5.30 26.15 0.80* 409abc 4.85 57.81 0.93* 431b 5.08 43.41 0.88* 500ac 5.25 44.97 0.91* 600℃ 272c FM FM FM 290c FM FM FM 303abc FM FM FM 327b FM FM FM 338ac 4.23 38.18 0.98* 372abc 4.82 71.00 0.95* 418c 4.94 74.56 0.94* 460bc 5.02 79.13 0.94* 500abc 5.19 77.76 0.91* a, b, c分别为同步荧光光谱、二维相关光谱和二阶导数光谱识别的荧光峰; * p= 0.01 level (2-tailed). FM, not modeled. -
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