Terzyk Artur P
Physicochemistry of Carbon Materials Research Group, Department of Chemistry, N. Copernicus University, Gagarin Street 7, 87-100, Toruń, Poland.
J Colloid Interface Sci. 2003 Dec 15;268(2):301-29. doi: 10.1016/s0021-9797(03)00690-8.
The presented study describes the temperature as well as pH dependence of phenol adsorption (and adsorption kinetics) on four carbons with different chemical compositions of the surface layer but almost identical porosity. In the first part, it is shown, applying the most sophisticated method of carbon porosity characterization (i.e., the method of Do and co-workers-ND method), that the porosity does not change much after the chemical modification of carbons. Then it is shown that the ND method leads to the same results as the DFT (density functional theory) does. Next, the TPD results for D43/1 carbons (initial, modified with HNO(3), fuming H(2)SO(4), and with NH(3)) are described. The TPD results for carbon modified with fuming sulphuric acid has not been reported yet by others. The deconvolution of peaks is performed. The obtained results, together with those already published, lead to the chemical structures of surface functionalities for all studied carbons. The thermogravimetric analysis of phenol adsorption shows that the amount of chemically bonded molecules is small. Then it is shown that the adsorption at the acidic pH (1.5) level is lower for all studied carbons than that at the neutral one. The description of the isotherms applying adsorbability, quasi-Freundlich and DA models, together with enthalpy measurements, lead to the mechanism of phenol adsorption at both pH values. The mechanism is, furthermore, confirmed by some empirical correlations. The analysis of the average hysteresis on adsorption-desorption isotherms as well as the comparison of phenol adsorption in oxic and anoxic conditions leads to the mechanism of irreversible phenol adsorption. It is suggested that the irreversibility is caused by two effects: the creation of strong complexes between phenol and surface carbonyl and lactones as well as by the polymerization. The last effect is due to the ability of carbon to adsorb the oxygen from solution and form superoxo ions. Finally, the kinetics is considered. The analytical solution of Fick's law of diffusion for adsorption in cylindrical particles is applied, the diffusion coefficients are calculated. It is shown that phenol diffusion is mixed between a surface process and a pore one. The obtained energy of diffusion is correlated with the values of the physicochemical parameters of studied carbons. As a final point, it is concluded that the mechanism of phenol adsorption is not only determined by so called "pi-pi interactions" and "donor-acceptor complex formation" but also by (strongly depending on temperature) the "solvent effect" balancing the influence of the two mentioned factors on this mechanism.
本研究描述了苯酚在四种表面层化学组成不同但孔隙率几乎相同的碳材料上的吸附（以及吸附动力学）对温度和pH的依赖性。在第一部分中，运用最复杂的碳孔隙率表征方法（即Do及其同事的方法——非局域密度泛函方法）表明，碳材料经化学改性后孔隙率变化不大。接着表明，非局域密度泛函方法与密度泛函理论（DFT）得出的结果相同。接下来描述了D43/1碳材料（初始的、用HNO₃、发烟H₂SO₄和NH₃改性的）的程序升温脱附（TPD）结果。用发烟硫酸改性的碳材料的TPD结果尚未见他人报道。对峰进行了去卷积处理。所得结果 ，连同已发表的结果，得出了所有研究碳材料表面官能团的化学结构。苯酚吸附的热重分析表明，化学键合分子的量很少。然后表明，所有研究碳材料在酸性pH（1.5）水平下的吸附低于中性pH水平下的吸附。应用吸附性、准弗伦德利希和DA模型对等温线进行描述，并结合焓测量，得出了在两个pH值下苯酚吸附的机理。此外，该机理通过一些经验关联得到了证实。对吸附 - 脱附等温线上的平均滞后现象进行分析以及对有氧和无氧条件下苯酚吸附进行比较，得出了不可逆苯酚吸附的机理。认为不可逆性是由两种效应引起的：苯酚与表面羰基和内酯之间形成强络合物以及聚合作用。后一种效应是由于碳能够从溶液中吸附氧并形成超氧离子。最后，考虑了动力学。应用圆柱颗粒中吸附的菲克扩散定律的解析解，计算了扩散系数。结果表明，苯酚扩散是表面过程和孔内过程的混合。所得扩散能与所研究碳材料的物理化学参数值相关。最后得出结论，苯酚吸附的机理不仅由所谓的“π - π相互作用”和“供体 - 受体络合物形成”决定，还（强烈依赖于温度）由平衡上述两个因素对该机理影响的“溶剂效应”决定。
