基于密度泛函理论的活性炭孔径分布改进算法

Modified approach of determining pore size distribution of activated carbon by using density functional theory

为提高非定域密度泛函理论(NLDFT)预测活性炭孔径分布(PSD)的精度,考虑了活性炭孔壁面晶体粗糙度对结果的影响。在传统NLDFT基础上,结合吸附壁面碳原子的密度分布,推导出改进NLDFT,预测了氩在光滑及具粗糙碳晶体表面的吸附平衡,并根据87.3 K、氩在活性炭上的吸附平衡数据,在由两种NLDFT确定了不同孔径的理论等温线核后,由寻优函数确定活性炭在0.35~12 nm区间的PSD。结果表明,以改进的NLDFT预测活性炭的PSD时,确定的活性炭孔径呈连续分布,预测平衡数据的相对误差小于10%;传统NLDFT确定的孔径在1 nm处出现断点,最大的预测相对误差范围达45%。改进NLDFT能较准确预测氩在具有粗糙晶体碳表面活性炭的PSD。

In observation of accurately determining the pore size distribution（PSD） of activated carbons by employing the non-local density functional theory（NLDFT）, the effect of surface roughness resulted from the distribution of carbon atoms on the accuracy was evaluated in terms of comparison of the adsorption equilibrium of argon. The classical NLDFT, which was developed based on the approximation to the smooth distribution of the density near the surface, was modified by taking into account the influence from the uneven distribution of the carbon atoms on the surface. The accuracies of the results from the modified model were firstly evaluated by the adsorption data of argon on adsorbent surfaces which respectively have even and uneven distribution of carbon atoms. Experimental data of argon adsorption on the activated carbon at 87.3 K was then taken as a reference, and comparisons were accordingly made between the adsorption isotherms calculated by the classical and modified NLDFT. The PSD, which covers the range of 0.35—12 nm, was finally determined by employing optimization function. Results show that the modified model can bring about the continuous distribution of PSD, and the relative error between the results determined by calculation via the PSD and those from experiment can be less than 10%. However, the calculation from the classical model has an interrupt at a pore width about 1nm, and the resulted maximum relative error amounts to 45%. It suggests that the modified model can more accurately calculate the PSD of the activated carbon having uneven distribution of carbon atoms around the surface.