CDFT的两种改进算法表征活性炭孔径分布的比较

Comparison of Two Improved Algorithms for Determining Pore Size Distribution of Activated Carbon Based on CDFT

为了提高经典密度泛函理论CDFT(classical density functional theory)在预测活性炭孔径分布时的准确性,比较了两种基于活性炭孔壁表面粗糙度影响的CDFT改进算法。结合狭缝孔壁上相同的碳原子密度分布,分别利用平滑密度近似(SDA)和基本测量理论(FMT)求解二元流体混合态的过剩自由能展开项,并预测氩气在非石墨化炭黑BP280上的吸附平衡。根据87.3 K下活性炭吸附氩气等温线,确定不同孔径的理论等温线核后,利用优化函数计算活性炭孔径在0.35~12 nm的分布。结果表明,MNLDFT算法预测孔径分布具有连续分布性,活性炭的比表面积为1252.63 m^(2)/g;QSDFT算法测定的PSD(pore size distribution)在1 nm处具有断点,测定的活性炭比表面积为1431.64 m^(2)/g,这一结果与通过BET方法确定的比表面积1445 m^(2)/g接近。运用QSDFT来表征活性炭孔径分布更合理。

In order to improve the accuracy of classical density functional theory(CDFT) while predicting pore size distribution(PSD) of activated carbon, two CDFT algorithms based on the assumption on the influence of surface roughness of activated carbon pore walls were compared in this paper. The same density distribution of carbon atoms on the walls of the slit pores were supposed, the excess free energy of the mixed state of the binary fluid and the adsorption equilibrium of argon on non-graphitized carbon black BP280 were then determined by smooth density approximation(SDA) and fundamental measure theory(FMT), which is respectively denoted as MNLDFT and QSDFT. The theoretical isotherm kernels of different pore sizes were calculated based on the isotherms of argon at 87.3 K by combining two improved algorithms, the optimization function was employed to determine the PSD of activated carbon within the range of 0.35-12 nm. Results show that the PSD predicted by MNLDFT is in a continuous distribution with a specific surface area about 1252.63 m^(2)/g, and the PSD determined by QSDFT has a breakpoint at 1 nm with a specific surface area about 1431.64 m^(2)/g, which is close to 1445 m^(2)/g determined by the BET approach. It suggests that it is more reasonable to use QSDFT to calculate the PSD of the activated carbon.