氯改性活性炭吸附单质铅(Pb^0)的机理

The mechanism of elemental lead(Pb^0) adsorption on chlorine-embedded activated carbon

利用量子化学中密度泛函方法系统研究氯改性活性炭吸附单质铅(Pb^0)的机理,明确了氯改性对活性炭吸附Pb^0的影响,计算得到吸附过程中各个吸附构型的吸附能、重要键长、对应的Mayor键级和铅的Mulliken原子电荷.几何优化选用B3LYP方法结合def2-SVP基组,单点能任务选用PWPB95双杂化泛函结合def2-TZVP基组进行计算.结果表明:对于扶手椅型(armchair)活性炭,氯改性将使活性炭对Pb^0的吸附能降低74.034kJ/mol;对于锯齿型(zigzag)活性炭,氯改性基本不会改变活性炭对Pb^0的吸附能力,因此氯改性总体上会减弱活性炭对Pb^0的吸附作用,但是吸附类型依然为强烈的化学吸附.分别应用电子密度分布和Mayor键级进一步验证纯活性炭和氯改性活性炭对Pb^0吸附类型,结果与吸附能分析一致.Mayor键级分析表明氯原子通过改变周围碳原子活性影响Pb^0的吸附,而不是与Pb^0直接作用.Mulliken原子电荷分析表明铅的原子电荷正相关于活性炭对其的吸附能,铅的原子电荷越大,对应的吸附构型的吸附能越高.此外笔者发现Pb^0的引入对氯改性活性炭继续吸附Pb^0有抑制作用.

The investigation on adsorption mechanism of chlorine-modified activated carbon on elemental lead(Pb^0) was conducted by density functional method using quantum chemistry method. In this study, we explored the effect of chlorine modification on adsorption of Pb^0 by activated carbon surface, and the adsorption energy, key bond length, corresponding Mayor bond order and Mulliken atomic charge of Pb^0 were acquired. Full-parameter geometrical optimization and single point energy were calculated at B3 LYP/def2-SVP and PWPB95/def2-TZVP level. Results showed that the chlorine modification decreased the adsorption energy of Pb^0 on activated carbon by 74.034 kJ/mol for armchair char but it had little influence on Pb^0 adsorption for zigzag char. Therefore, the chlorine modification would overall suppress the adsorption of Pb^0 on activated carbon, but the adsorption type still belongs to chemical adsorption. The result agreed with the conclusion in regards to Pb^0 adsorption energy on pure activated carbon and chlorine modified activated carbon using electronic density analysis and Mayor bond order analysis respectively. In addition, Mayor bond order analysis suggested chlorine atom would affect the Pb^0 adsorption via affecting carbon atoms, while rather than interacting with Pb^0 directly. Furthermore, the atomic charge of Pb^0 is correlated positively with the adsorption energy on activated carbon, and the higher atomic charge of Pb^0, the larger adsorption energy of the corresponding adsorption configuration. Additionally, we found that the introduction of Pb^0 could block the adsorption of another Pb^0 on chlorine-modified carbon.