Goethite nanoparticle aggregation: effects of buffers, metal ions, and 4-chloronitrobenzene reduction
Goethite nanoparticle aggregation: effects of buffers, metal ions, and 4-chloronitrobenzene reduction
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DOI：
10.1039/c3en00063j
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发表时间：
2014-09
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影响因子：
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通讯作者：
Amanda M. Stemig;T. Do;V. Yuwono;W. Arnold;R. L. Penn
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作者：
Amanda M. Stemig;T. Do;V. Yuwono;W. Arnold;R. L. Penn
铁矿物系统可有效转化自然和工程系统中的高度氧化污染物。污染物降解的速率可能会受到可用矿物表面积的影响。本研究采用动态光散射和低温透射电子显微镜监测针铁矿纳米粒子与4-氯硝基苯（4-ClNB）反应前后聚集状态的变化。监测缓冲液特性、缓冲液浓度和吸附金属特性对针铁矿纳米颗粒悬浮液特性和反应性的影响。结果表明，用于在反应过程中保持pH几乎恒定的缓冲液在间歇反应器中不是良性添加剂。事实上，所用缓冲液的特性和浓度强烈影响表面缔合亚铁离子降解4-ClNB的速率。增加缓冲液浓度导致更紧凑的针铁矿纳米颗粒聚集体，并观察到较慢的4-ClNB降解。此外，降解速率随着缓冲液特性的变化而显著变化，当从4-（2-羟乙基）-1-哌嗪乙磺酸（HEPES）转换为三（2-羟乙基）胺（TEA）时，反应速率变化了一个数量级。最后，在选择的三种金属离子（Ca（II）、Fe（II）和Co（II））中，两种过渡金属的添加和吸附导致平均纳米颗粒聚集体尺寸急剧减小。此外，吸附的Fe（II）的氧化，通过O2或4-ClNB还原，产生zeta电位降低，并增加聚集体的大小。这项工作表明，反应参数的微小变化通过纳米颗粒聚集状态的变化对污染物降解速率有很大的影响。
Iron mineral systems are effective at transforming highly oxidized contaminants in natural and engineered systems. The rate at which the contaminant degrades may be influenced by the amount of available mineral surface area. This study used dynamic light scattering and cryogenic transmission electron microscopy to monitor changes in the aggregation state of goethite nanoparticles before and after reaction with 4-chloronitrobenzene (4-ClNB). The effects of buffer identity, buffer concentration, and adsorbing metal identity on the goethite nanoparticle suspension characteristics and reactivity were monitored. Results demonstrate that buffers, which serve to hold pH nearly constant over the course of a reaction, are not benign additives in batch reactors. In fact, the identity and concentration of the buffer used strongly influences the rate of 4-ClNB degradation by surface-associated ferrous ion. Increasing buffer concentration resulted in more compact goethite nanoparticle aggregates, and slower 4-ClNB degradation was observed. In addition, the rate of degradation changed dramatically with changing buffer identity, with rates of reaction changing by an order of magnitude when switching from 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) to tris(2-hydroxyethyl)amine (TEA). Finally, of the three metal ions selected (Ca(II), Fe(II), and Co(II)), the addition and adsorption of the two transition metals resulted in a dramatic decrease in the average nanoparticle aggregate size. Furthermore, oxidation of the adsorbed Fe(II), via O2 or 4-ClNB reduction, yielded decreases in zeta potential and increases in aggregate size. This work demonstrates that small changes in reaction parameters have a large effect on the rate of contaminant degradation through changes in nanoparticle aggregation state.