Thermal air oxidation changes surface and adsorptive properties of black carbon (char/biochar).
Thermal air oxidation changes surface and adsorptive properties of black carbon (char/biochar).
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DOI：
10.1016/j.scitotenv.2017.11.008
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发表时间：
2018-03
期刊：
影响因子：
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通讯作者：
F. Xiao;A. Bedane;J. Zhao;Michael Mann;J. Pignatello
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文献类型：
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作者：
F. Xiao;A. Bedane;J. Zhao;Michael Mann;J. Pignatello
在这项研究中，我们系统地研究了热空气氧化对在300-700 °C的碳化温度（HTTs）下制备的生物质衍生黑碳（BC）的性质的影响。发现通过在碳化步骤中包括空气产生的BC具有低表面积和欠发达的孔结构。热解后热空气氧化（PPAO）后，观察到BC的实质性变化。在相对高的HTT（600和700 °C）下在缺氧下制备的良好抗氧化的BC样品显示，在PPAO之后，包括两种三嗪除草剂和一种天然雌激素的中性有机物质的N2 BET表面积（SA）（高达700倍）、孔隙率（< 60 μ m）（高达95倍）和吸附性（高达120倍）显著增加。在较低HTT（300或400 °C）下制备的部分碳化BC在PPAO后显示出这些性能的适度增加，但对应于各种含氧官能团的傅里叶变换红外光谱带的强度大幅增加。另一方面，即使在PPAO处理后，良好的抗氧化BC样品也缺乏表面氧官能度。测试有机化合物在BC上的吸附在其小于300 m2/g时通常倾向于BET SA，但BET SA在其大于300 m2/g时对吸附的预测性较差。总的来说，我们的结果表明，分子氧和BC之间的热反应1）对于低HTT BC样品比对于高HTT BC样品更有效地增加表面氧官能度; 2）特别是对于高HTT BC样品增加SA和孔隙率（< 60 μ m）;和3）产生新的吸附位点和/或减轻有机分子对微孔的空间限制，从而增强BC的吸附性。这些结果将被证明不仅有助于了解环境BC的命运，而且有助于设计改善BC工程形式的实际性能的策略（即，生物炭）。
In this study, we systematically investigated the effects of thermal air oxidation on the properties of biomass-derived black carbon (BC) made at carbonization temperatures (HTTs) of 300–700 °C. BC produced by including air in the carbonization step was found to have a low surface area and underdeveloped pore structure. Substantial changes of BC were observed after post-pyrolysis thermal air oxidation (PPAO). Well-carbonized BC samples made anoxically at relatively high HTTs (600 and 700 °C) showed, after PPAO, significant increases in N2BET surface area (SA) (up to 700 times), porosity (< 60 Å) (up to 95 times), and adsorptivity (up to 120 times) of neutral organic species including two triazine herbicides and one natural estrogen. Partially carbonized BC made at a lower HTT (300 or 400 °C) showed moderate increases in these properties after PPAO, but a large increase in the intensity of Fourier transform infrared spectroscopy bands corresponding to various oxygen-containing functional groups. Well-carbonized BC samples, on the other hand, were deficient in surface oxygen functionality even after the PPAO treatment. Adsorption of the test organic compounds on BC generally trended with BET SA when it was less than 300 m2/g, but BET SA was poorly predictive of adsorption when it was greater than 300 m2/g. Overall, our results suggest that thermal reactions between molecular oxygen and BC 1) increase surface oxygen functionality more effectively for low-HTT than for high-HTT BC samples; 2) increase SA and porosity (< 60 Å) especially for high-HTT BC samples; and 3) create new adsorption sites and/or relieve steric restriction of organic molecules to micropores, thereby enhancing the adsorptivity of BC. These results will prove useful not only for understanding the fate of environmental BC but also in devising strategies for improving the practical performance of the engineered form of BC (i.e., biochar).