On the BET Surface Area of Nanocellulose Determined Using Volumetric, Gravimetric and Chromatographic Adsorption Methods
On the BET Surface Area of Nanocellulose Determined Using Volumetric, Gravimetric and Chromatographic Adsorption Methods
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DOI：
10.3389/fceng.2021.738995
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发表时间：
2021-09
期刊：
影响因子：
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通讯作者：
A. Kondor;Alba Santmarti;A. Mautner;Daryl R. Williams;A. Bismarck;Koon-Yang Lee
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作者：
A. Kondor;Alba Santmarti;A. Mautner;Daryl R. Williams;A. Bismarck;Koon-Yang Lee
在−196°C下的体积N2吸附通常被接受为用于估计纳米纤维素的Brunauer-Emmet-Teller（BET）表面积的“黄金标准”。然而，不清楚在这样的低温和低压下获得的纳米纤维素的BET表面积是否在绝对意义上是有意义的，因为纳米纤维素在环境温度和压力下使用。在这项工作中，使用高度结晶的细菌纤维素（BC）作为模型纳米纤维素的纳米纤维素的BET表面积进行了系统的评估，以实现对纳米纤维素的BET方法的局限性的全面理解。将在−196°C下使用体积N2吸附获得的BET表面积与从基于使用动态蒸气吸附（DVS）的正辛烷吸附和通过反相气相色谱（iGC）测定的正辛烷吸附的重量实验获得的BET表面积进行比较，两者都在25°C下。发现由体积N2吸附数据计算的BET表面积比使用DVS和iGC吸附方法获得的25°C下正辛烷吸附的BET表面积低25%。这些结果支持了纳米纤维素的BET表面积是分子尺度（N2对正辛烷，分子横截面为0.162 nm 2对0.646 nm 2）和温度（−196°C对25°C）依赖性的假设。这项研究还证明了根据既定标准选择适当BET压力范围的重要性，并表明室温测量与许多纳米纤维素应用更相关。
Volumetric N2 adsorption at −196°C is generally accepted as “gold standard” for estimating the Brunauer-Emmet-Teller (BET) surface area of nanocellulose. It is unclear however, whether the BET surface area of nanocellulose obtained at such low temperatures and pressures is meaningful at an absolute sense, as nanocellulose is used at ambient temperature and pressure. In this work, a systematic evaluation of the BET surface area of nanocellulose using highly crystalline bacterial cellulose (BC) as model nanocellulose was undertaken to achieve a comprehensive understanding of the limitations of BET method for nanocellulose. BET surface area obtained using volumetric N2 adsorption at −196°C was compared with the BET surface area acquired from gravimetric experiments based on n-octane adsorption using dynamic vapour sorption (DVS) and n-octane adsorption determined by inverse gas chromatography (iGC), both at 25°C. It was found that the BET surface area calculated from volumetric N2 adsorption data was 25% lower than that of n-octane adsorption at 25°C obtained using DVS and iGC adsorption methods. These results supported the hypothesis that the BET surface area of nanocellulose is both a molecular scale (N2 vs n-octane, molecular cross section of 0.162 nm2 vs 0.646 nm2) and temperature (−196°C vs 25°C) dependent property. This study also demonstrates the importance of selecting appropriate BET pressure range based on established criteria and would suggest that room temperature measurement is more relevant for many nanocellulose applications.