分子量不同的奥德里奇腐植酸的官能团及其反应活性

Functional Groups and Reactivity of Size-fractionated Aldrich Humic Acid

研究了奥德里奇公司提供的腐植酸和钴60的络合能力与腐植酸分子大小的关系以及腐植酸的结构对两者络合作用的影响。在腐植酸浓度较低时,钴60与分子量大于100000 Da[HA(100【)]的腐植酸相互作用,随着腐植酸浓度的增加,钴60倾向于与分子量在30000~100000 Da[HA(30~100)]之间的腐植酸相互作用。本研究用FTIR(傅里叶变换红外光谱),13C核磁共振光谱和酸碱滴定曲线表征分离出来的HA(100【)和HA(30~100)。实验发现,HA(10【)具有脂肪支链结构,-COOH较小,且具有较大的质子交换能力,该腐植酸成分在络合过程中共价键作用较小,离子交换作用起主要作用。此外,支链卷曲造成的空间位阻作用能影响两者的络合作用。HA(30~100)结构中以芳香-COOH和-OH为主,因此与钴60相互作用是以形成共价键为主,本研究用XPS测定了钴和腐植酸间的结合能,其结果证实了前面的假设。

The complexation affinity of the Aldrich Chemicals humic acid with 60 Co was examined with respect to molecular size of humic acid. Correlations between the affinity and the structures of humic acid were studied. At low humic acid concentration range, 60 Co was interacted with the humic acid of size fraction over 100000 Da [HA(100<)]. With increasing humic acid concentration, the 60 Co was preferentially interacted with the 30000~100000 Da of humic acid [HA(30~100)]. Fractionated HA(100<) and HA(30~100) were characterized from their FTIR(Fourier Transform Infra-Red), 13 C NMR spectral analyses and acid–base titration curves. The HA(10<) having aliphatic branched structure, smaller amount of COOH group and large proton exchangeable capacity, seem to show low covalent bonding nature and highion exchangeability in the complexation. In addition, steric hindrance may affect on the complexation, by winding up like random coils from the branched structure. The HA(30~100) is dominated with the aromatic COOH group and OH group and it may preferentially coordinate to 60 Co by covalent binding. These presumptions were supported by XPS analysis, in which the binding energy of cobalt-humates was discussed.