活性炭表面含氧基团对苯酚吸附平衡及动力学的影响

Effect of surface oxygen groups of activated carbon on phenol adsorption:equilibrium and kinetics

煤基活性炭分别用烧失处理和HNO3氧化处理后得到不同表面性质的活性炭,采用X射线光电子能谱(XPS)、N2吸附、酸碱滴定及零电荷点(pHPZC)对活性炭表面性质及孔结构进行表征,研究了活性炭表面性质对苯酚吸附平衡和吸附动力学影响。经HNO3氧化后,活性炭表面含氧基团显著增加,烧失处理后,表面含氧基团尤其是羧基显著减少。苯酚最大平衡吸附量随活性炭表面含氧基团的增多而减少,吸附速率常数与碳表面含氧基团的量呈正相关,而吸附活化能与活性炭在一定吸附条件下表面所带电荷多少相关。随着活性炭表面含氧基团增多,吸附活化熵增大(负值减小),苯酚在活性炭表面排列的有序性减小。静态吸附与动态吸附实验结果都表明:在含氧基团较少而碱性更强的活性炭上,发生化学吸附的程度更大。

Three activated carbons （ACs） with different surface chemical property were prepared by partial bum-off under insufficient air or oxidation using HNO3 respectively from an initial coal-base AC. These ACs were characterized by X-ray photoelectron spectrometry （XPS）, N2 adsorption isothermal, acid-base titration and point of zero charge（ pHPZC ）. When oxidized by HNO3 , the AC had a significantly increase of surface oxygen content , on the other hand when by partial burn-off treatment, amount of carboxylic group significantly decreased with a slightly decrease of surface oxygen content. The adsorption capacity for phenol enhanced with the decrease of surface oxygen amount. However, the adsorption rate was increased with tile increase of surface oxygen. The results of adsorption experiments showed that the activation energies（ Ea ）of adsorption may be a function as surface charges amount under certain adsorption conditions. Activation entropies of adsorption（ △S≠）which were calculated using transition state theory increase with the increase of surface oxygen-containing groups. And the arranging order of phenol molecules is lower on the AC which have more oxygen-containing groups. Both of themtodynamic and kinetic experiment results indicated that chemical adsorption was occurred to a greater degree on the surface of AC-H which has lower surface oxygen content and more basic adsorption sites.