羧基甲壳素对Pb(Ⅱ)的吸附性能及机理研究

Adsorption performance and mechanism of Pb(Ⅱ) onto carboxylated chitin

为了提高甲壳素对Pb^(2+)吸附性能,采用2,2,6,6-四甲基哌啶-1-氧基(TEMPO)/次氯酸钠(NaClO)/溴化钠(NaBr)氧化体系对甲壳素羧基化改性.采用FTIR、Solid^(13)C-NMR、XRD和SEM-EDX等对羧基甲壳素结构和形貌进行表征,考察了不同NaClO用量制备的羧基甲壳素、溶液pH值、Pb(Ⅱ)初始浓度、吸附时间和离子强度对吸附量的影响,利用XPS探究其吸附机理.结果表明,氧化改性不改变甲壳素的晶型,羧基出现在甲壳素晶体表面;NaClO用量和溶液pH值对吸附量影响显著,pH值为4.0～6.0,NaClO用量为30mL制备的羧基甲壳素吸附效果好,60min达到平衡,室温下饱和吸附量达233.64mg/g;吸附动力学符合准二阶动力学方程,吸附等温线符合Freundlich等温吸附模型,吸附机理包括静电作用、络合配位和离子交换.

Chitin was modified into carboxylated chitin by 2, 2, 6, 6-tetramethylpiperidine-1-oxyl radical（TEMPO） with hypochlorite（NaClO） and sodium bromide（Na Br） for enhancing adsorption performance of Pb（Ⅱ） from aqueous solution. Carboxylated chitin prepared was characterized by FTIR, solid ^13C-NMR, XRD and SEM-EDX. Batch experiments with various parameters of the carboxylated chitins modified with different volume of NaClO, pH value of solution, initial concentration of Pb（Ⅱ）, contact time and ionic strength on the adsorption performance of Pb（Ⅱ） were investigated. The surface characteristics of carboxylated chitin before and after Pb（Ⅱ） adsorption were examined using XPS. The results showed oxidation modification did not change the crystal structure and crystallinity of chitin and the carboxyl groups were introduced onto the surface of chitins. The volume of NaClO and pH had significant influence on the adsorption capacity. When the p H value of solution was in the range of 4～6, the adsorption capacity of carboxylated chitin prepared with 30 mL NaClO reached a high level and the maximum adsorption was 233.64 mg/g at room temperature. The adsorption process reached equilibrium within 60 min and could well be described by pseudo-second-order kinetic and the Frendlich isotherm models. The Pb（Ⅱ） removal mechanism on carboxylated chitin included electrostatic interaction, chelation and ion exchange.