Development of surface modification method for functinalization of activated carbon

本工作的目的是以物理吸附物种为探针分子，阐明改性活性炭的表面特征，并在此基础上构建有效的活性碳表面改性方法。吸附CO在123K的红外吸收峰可分解为两个峰(2137 cm~(-1))和2155 cm~(-1)~(-1)，它们分别归属于石墨片和表面极性中心上的吸附物种。红外光谱和X射线光电子能谱分析表明，电场的来源为表面氧化物基团。室温下吸附的苯的红外光谱也表明，在低覆盖度时，苯的吸附中心是石墨片，但在高覆盖度时，极性中心也与苯分子发生电性相互作用。通过氧化处理，在活性碳表面引入了表面氧化物基团(酸酐和内酯)，这些基团作为CO(或苯)弱相互作用的吸附中心。在室温下，吡啶吸附在活性碳上的红外光谱表明，表面存在少量弱Lewis酸性中心。H_2O_2处理增加了催化剂的表面酸中心。另一方面，通过HNO_3处理引入了表面NO_2基团。部分官能团暴露在活性碳表面，起到有效的吸附作用，为选择性地讨论活性碳上的真实吸附位置提供了可能。结果表明，这些分析结果对优化碳表面的处理条件是有用的。

The purpose in the present work is to clarify the surface characteristics of modefied activated carbons using physisorbed species as probe molecule and to construct methodology of effective surface modification for activated carbons on the basis of the analyses.Carbon monoxide and two monocyclic aromatic molecules adsorbed on activated carbons were selected as probe molecule, and the IR spectra were analyzed. The IR band of adsorbed CO at 123K can be deconvoluted into two peaks (2137cm^<-1> and 2155cm^<-1>), and they are assigned to adspecies on graphite sheets and on surface polar sites, respectively. The source of electric field was suggested to be surface oxide groups from IR and XPS analyses. IR spectra of benzene adsorbed at room temperature also revealed that the adsorption site for benzene is graphite sheet at low coverage, but polar site also interacts at high coverage with benzene molecule, electrically. Surface oxide groups (anhydride acids and lactones) were introduced onto the activated carbon surface by oxidation treatment, and the sites act as adsorption site for CO (or benzene) with weak interaction. The amount of sites can be discussed using the analyses in this study.IR spectra of pyridine adsorbed on the activated carbons at room temperature showed the presence of small amount of weak Lewis acidic sites on the surfaces. The surface acid sites were increased by H_2O_2 treatment. On the other hand, a surface -NO_2 group was introduced by HNO_3 treatment. A part of functional groups was exposed on the activated carbon surface, and acts as effective adsorption site.The analyses developed in the study make possible to discuss real adsorption sites on the activated carbons selectively. It is found that the analyses are useful to optimize treatment conditions of the carbon surfaces.